What is Biology?

Happy New Year 2011

Bygones are bygones! New Year has finally arrived. Time to express gratitude, clear off all the blemishes and complains, motivate the week, congratulate the winners and play pranks on friends. A new start ought to be marked with love and care.

I wish you Health...

So you may enjoy each day in comfort.

I wish you the Love of friends and family...

And Peace within your heart.

I wish you the Beauty of nature...

That you may enjoy the work of God.

I wish you Wisdom to choose priorities...

For those things that really matter in life.

I wish you Generosity so you may share...

All good things that come to you.

I wish you Happiness and Joy...

And Blessings for the New Year.

I wish you the best of everything...

That you so well deserve.

HAPPY NEW YEAR!

New Year's Resolution Tips

Chances are, at some time in your life, you've made a New Year's Resolution -- and then broken it. This year, stop the cycle of resolving to make change, but then not following through. If your resolution is to take better care of yourself and get your inflammatory bowel disease (IBD) under control, you'll have a much better year if your resolution sticks. Here are some tips to help get you started.

Be realistic

The surest way to fall short of your goal is to make your goal unattainable. For instance, resolving to never eat your favourite food again because it bothers your IBD could be a bad choice. Strive for a goal that is attainable, such as avoiding it more often than you do now.

 

Plan ahead

Don't make your resolution on New Year's Eve. If you wait until the last minute, it will be based on your mindset that particular day. Instead, it should be planned well before December 31 arrives.

Outline your plan

Decide how you will deal with the temptation to skip that exercise class or have one more cigarette. This could include calling on a friend for help, practicing positive thinking and self-talk, or reminding yourself how your bad habit affects your IBD.

Make a "pro" and "con" list

It may help to see a list of items on paper to keep your motivation strong. Develop this list over time, and ask others to contribute to it. Keep your list with you and refer to it when you need help keeping your resolve.

Talk about it

Don't keep your resolution a secret. Tell friends and family members who will be there to support your resolve to change yourself for the better or improve your health. The best case scenario is to find yourself a buddy who shares your New Year's resolution and motivate each other.

Reward yourself

This doesn't mean that you can eat an entire box of chocolates if your resolution is to diet. Instead, celebrate your success by treating yourself to something that you enjoy that does not contradict your resolution. If you've been sticking to your promise to eat better, for example, perhaps your reward could be going to a movie with a friend.

Track your progress

Keep track of each small success you make toward reaching your larger goal. Short-term goals are easier to keep, and small accomplishments will help keep you motivated. Instead of focusing on losing 30 pounds, say, focus on losing that first 5. Keeping a food diary or a symptom journal may help you stay on track.

Don't beat yourself up

Obsessing over the occasional slip won't help you achieve your goal. Do the best you can each day, and take each day one at a time.

Stick to it

Experts say it takes about 21 days for a new activity, such as exercising, to become a habit, and 6 months for it to become part of your personality. Your new healthful habits will become second-nature in no time.

Keep trying

If your resolution has totally run out of steam by mid-February, don't despair. Start over again! There's no reason you can't make a "New Year's resolution" any time of year.

Fast Facts About New Year's Resolutions

63% of people say they are keeping their resolutions after two months

67% of people make three or more resolutions

Top four resolutions:

Increase exercise

Be more conscientious about work or school

Develop better eating habits

Stop smoking, drinking, or using drugs (including caffeine)

People make more resolutions to start a new habit than to break an old one.

 

Adios.....

Tips for Time Management

Perhaps you have a heavy workload and want to find ways to become more effective so you can get more done in less time.

Maybe you feel overwhelmed or “stressed out” and want to find ways to do less and enjoy more. Or maybe you simply want to feel more focused and in control of your time, instead of feeling like you rush madly from one activity to the next until you fall into bed exhausted every night.

Benjamin Franklin said, “Do you love life? Then do not squander time, for that's the stuff that life is made of.”

Time management is a set of principles, practices, skills, tools, and systems working together to help you get more value out of your time with the aim of improving the quality of your life.

The important point is that time management is not necessarily about getting lots of stuff done, because much more important than that is making sure that you are working on the right things, the things that truly need to be done.

Smart time managers know that there is much more to do than anyone could possibly accomplish. So instead of trying to do it all, smart time managers are very picky about how they spend their time.

They choose to focus and spend their time doing a few vital projects that will really make a difference, rather than spending all their time doing many trivial things that don't really matter all that much.

If you become a good time manager, you’ll not only get a lot more done in less time, but you’ll feel more relaxed, focused and in control of your life.

You’ll be able to use your time in a much more balanced and effective way, and you’ll be able to make time for the people and activities that you love. When you get to the end of a busy day, you’ll feel a strong sense of accomplishment from everything that you actually got done.

Improving your time management skills can even help you get better results by doing less work, because you're focusing on the things that really matter rather than all the low-priority busywork that just keeps you busy.

If you don’t learn how to manage your time well, you’ll be far less productive than you could be and you’ll get a lot less done. You’ll also feel much more stressed and overwhelmed, and you’ll struggle to find time to spend with the people you care about and to do the things you enjoy.

In the end, time management comes down to choices. Good choices lead to better results, while poor choices lead to wasted time and energy.

The good news is that time management skills can be learned and mastered by anyone. All it takes is practice and dedication.

Like any other skill, you can learn time management the easy way or you can learn it the hard way.

The hard way usually involves years of trial and error and lots of false starts trying to figure out what works and what doesn't.

If you'd like to save yourself some time, money and effort, I recommend you try the easy way: learn from someone who has already done it.

Makes sense, right?

15 Time Management Tips

In the meantime, here are 15 practical time management tips to help you get started...

1. Write things down

A common time management mistake is to try to use your memory to keep track of too many details leading to information overload. Using a to-do list to write things down is a great way to take control of your projects and tasks and keep yourself organised.

2. Prioritise your list

Prioritising your to-do list helps you focus and spend more of your time on the things that really matter to you. Rate your tasks into categories using the ABCD prioritisation system described in the time management course.

3. Plan your week

Spend some time at the beginning of each week to plan your schedule. Taking the extra time to do this will help increase your productivity and balance your important long-term projects with your more urgent tasks. All you need is fifteen to thirty minutes each week for your planning session.

4. Carry a notebook

You never know when you are going to have a great idea or brilliant insight. Carry a small notebook with you wherever you go so you can capture your thoughts. If you wait too long to write them down you could forget. Another option is to use a digital recorder.

5. Learn to say no

Many people become overloaded with too much work because they overcommit; they say yes when they really should be saying no. Learn to say no to low priority requests and you will free up time to spend on things that are more important.

6. Think before acting

How many times have you said yes to something you later regretted? Before committing to a new task, stop to think about it before you give your answer. This will prevent you from taking on too much work.

7. Continuously improve yourself

Make time in your schedule to learn new things and develop your natural talents and abilities. For example, you could take a class, attend a training program, or read a book. Continuously improving your knowledge and skills increases your marketability, can help boost your career, and is the most reliable path to financial independence.

8. Think about what you are giving up to do your regular activities

It is a good idea to evaluate regularly how you are spending your time. In some cases, the best thing you can do is to stop doing an activity that is no longer serving you so you can spend the time doing something more valuable. Consider what you are giving up in order to maintain your current activities.

9. Use a time management system

Using a time management system can help you keep track of everything that you need to do, organize and prioritise your work, and develop sound plans to complete it. An integrated system is like glue that holds all the best time management practices together.

10. Identify bad habits

Make a list of bad habits that are stealing your time, sabotaging your goals, and blocking your success. After you do, work on them one at a time and systematically eliminate them from your life. Remember that the easiest way to eliminate a bad habit, it to replace it with a better habit.

11. Don’t do other people’s work

Are you in the habit of doing other people’s work because or a ‘hero’ mentality? Doing this takes up time that you may not have. Instead, focus on your own projects and goals, learn to delegate effectively, and teach others how to do their own work.

12. Keep a goal journal

Schedule time to set and evaluate your goals. Start a journal and write down your progress for each goal. Go through your goal journal each week to make sure you are on the right track.

Keeping a journal on your computer has never been easier!

13. Don’t be a perfectionist

Some tasks don’t require your best effort. Sending a short email to a colleague, for example, shouldn’t take any more than a few minutes. Learn to distinguish between tasks that deserve to be done excellently and tasks that just need to be done.

14. Beware of “filler” tasks

When you have a to-do list filled with important tasks, be careful not to get distracted by “filler” tasks. Things such as organising your bookcase or filing papers can wait until you tackle the items that have the highest priority.

15. Avoid “efficiency traps”

Being efficient doesn’t necessarily mean that you are being productive. Avoid taking on tasks that you can do with efficiency that don’t need to be done at all. Just because you are busy and getting things done doesn’t mean you are actually accomplishing anything significant.

Memorising facts in Biology

• Mnemonics can be used wherever possible. don't give it up totally.
• Sometimes writing the first letters of names & amp; reading them in a nonsensical & amp; funny way can help.
• Write down the points, after reading the answers; draw pictures like parts of the plant, body parts, nerves etc. to connect to the point.,
• Write the number of points you have to learn for an answer & amp; arrange them in a sequence easy for you to remember.
• When learning objective type answers you can request a family member to ask the qns. This may look funny but mothers are a wonderful support in this.
• Divide your portions & amp; learn thoroughly before going to the next one
• Don't accumulate too much of study material.
• Prepare a time table & amp; follow it sincerely.
• Keep your goal in mind & amp; work towards it.

Nothing is impossible when you work hard.
Like what you are doing at present.
Best of luck.

Understand what you are learning and have confidence.

Good relationship with your teachers

A good relationship between students and teachers makes the classroom a more inviting place. When you like your teacher, it's easier to pay attention to his explanations and improve your grades. When you consider your teacher a friend, you'll certainly have more respect for him. When your teachers consider you to be a friend and not only a student, they'll feel freer in class and that will probably affect the classroom in a very positive way. Now here are some tips to develop a friendly relationship with your teachers:

Ask questions. If you have any questions about that subject, ask them. Teachers like to teach and asking questions is the first way of interacting with them. Show them that you're interested in their subject. That will make them notice you. But never ask questions that you already know the answer to. If your teachers realise that you are not asking real questions, they might think that you're not actually trying to learn, but only trying to make an impression.

No need for compliments. Don't say things like "You look lovely today, Mrs. Lim" or "Did you lose weight, Mr. Smith?" Your teacher will probably think you're being false and only trying to get some advantage, and that's not what you want. Instead, you could do some innocent jokes (jokes that won't offend your teacher). The moment they start doing some of the same jokes (but towards you), then you'll know that your relationship is becoming friendly.

 

When you see one of your teachers in the hall, greet him and ask if he's going to that concert or if he's seen that movie. That way you'll show that you consider him a friend, and that's why you talk about common subjects. Some teachers don't like to have a friendly relationship with a student, but most of them want to have those simple talks with their students. And after a while, they will start to talk with you about non-school subjects in the class. That will make more students in your class get involved in those talks, and everyone will start to consider that teacher to be a friend.

The rest is totally up to you; it is very easy to develop a friendly relationship with any of your teachers. If you want to be friends with your teachers, just treat them as friends, but don't forget that no matter how good of friends you are, they will still be your teachers and deserve your respect.

Tata.....

Don't give up

Careers in Bio



Pursuing a career in biology can be immensely rewarding and exciting. Studying biology teaches us to ask questions, make observations, evaluate evidence, and solve problems. Biologists learn how living things work, how they interact with one another, and how they evolve. They may study cells under a microscope, insects in a rainforest, viruses that affect human beings, plants in a greenhouse, or lions in the African grasslands. Their work increases our understanding about the natural world in which we live and helps us address issues of personal well being and worldwide concern, such as environmental depletion, threats to human health, and maintaining viable and abundant food supplies.

What do biologists do?

There are several career paths you can follow as a biologist, including these:

Research: Research biologists study the natural world, using the latest scientific tools and techniques in both laboratory settings and the outdoors, to understand how living systems work. Many work in exotic locations around the world, and what they discover increases our understanding of biology and may be put to practical use to find solutions to specific problems.

Health care: Biologists may develop public health campaigns to defeat illnesses such as tuberculosis, AIDS, cancer, and heart disease. Others work to prevent the spread of rare, deadly diseases, such as the now infamous Ebola virus. Veterinarians tend to sick and injured animals, and doctors, dentists, nurses, and other health care professionals maintain the general health and well being of their patients.

Environmental management and conservation: Biologists in management and conservation careers are interested in solving environmental problems and preserving the natural world for future generations. Park rangers protect state and national parks, help preserve their natural resources, and educate the general public. Zoo biologists carry out endangered species recovery programs. In addition, management and conservation biologists often work with members of a community such as landowners and special interest groups to develop and implement management plans.

Education: Life science educators enjoy working with people and encouraging them to learn new things, whether in a classroom, a research lab, the field, or a museum.

Colleges and universities: Professors and lecturers teach introductory and advanced biology courses. They may also mentor students with projects and direct research programs.

Secondary school: Teaching younger students requires a general knowledge of science and skill at working with different kinds of learners. Secondary school teachers often specialise in biology and teach other courses of personal interest.

Science museums, zoos, aquariums, parks, and nature centres: Educators in these settings may design exhibits and educational programs, in addition to teaching special classes or leading tours and nature hikes.

New directions in biological careers: There are many careers for biologists who want to combine their scientific training with interests in other fields. Here are some examples:

Biotechnology: Biologists apply scientific principles to develop and enhance products, tools, and technological advances in fields such as agriculture, food science, and medicine.

Forensic science: Forensic biologists work with police departments and other law enforcement agencies using scientific methods to discover and process evidence that can be used to solve crimes.

Business and industry: Biologists work with drug companies and providers of scientific products and services to research and test new products. They also work in sales, marketing, and public relations positions.

Mathematics: Biologists in fields such as bioinformatics and computational biology apply mathematical techniques to solve biological problems, such as modeling ecosystem processes and gene sequencing.

Science writing and communication: Journalists and writers with a science background inform the general public about relevant and emerging biological issues.

Art: All the illustrations in your biology textbook, as well as in newspaper and magazine science articles, were created by talented artists with a thorough understanding of biology.

Human papillomavirus

Vaccinating 13 year old girls with human papillomavirus vaccine (HPV) can help reduce cases of cervical cancer and genital warts. Studies had shown that teenage girls aged less than 15 have a better immunity response compared with older girls or women.

Immunity among teenagers (15 years and below) vaccinated with HPV is very high even after five and a half years. Free HPV vaccination programme carried out by the government for teenage students was an initiative to prevent cervical cancer. HPV is a common virus that is passed on through genital contact, most often during sex and most sexually active people will get HPV at some time in their lives, though most will never even know it and is most common among people in their late teens and early 20s.  Malaysian women were at a high risk of HPV which can led to cervical cancer due to their smoking habits, diet and family history.

According to the World Health Organisation (WHO) 80 percent of women who have reached 50 years would have been affected by HPV and almost 20 percent of them would have reached a chronic stage, resulting in cervical cancer. The government would be spending RM150 million to vaccinate about 300,000 teenagers throughout the country.

A human papillomavirus (HPV) is a member of the papillomavirus family of viruses that is capable of infecting humans. Like all papillomaviruses, HPVs establish productive infections only in the stratified epithelium of the skin or mucous membranes. While the majority of the nearly 200 known types of HPV cause no symptoms in most people, some types can cause warts (verrucae), while others can – in a minority of cases – lead to cancers of the cervix, vulva, vagina, and anus in women or cancers of the anus and penis in men.

More than 30 to 40 types of HPV are typically transmitted through sexual contact and infect the anogenital region. Some sexually transmitted HPV types may cause genital warts. Persistent infection with "high-risk" HPV types—different from the ones that cause skin warts—may progress to precancerous lesions and invasive cancer. HPV infection is a cause of nearly all cases of cervical cancer; however, most infections with these types do not cause disease.

Most HPV infections in young females are temporary and have little long-term significance. 70% of infections are gone in 1 year and 90% in 2 years. However, when the infection persists—in 5% to 10% of infected women—there is high risk of developing precancerous lesions of the cervix, which can progress to invasive cervical cancer. This process usually takes 15–20 years, providing many opportunities for detection and treatment of the pre-cancerous lesion. Progression to invasive cancer can be almost always prevented when standard prevention strategies are applied - however the lesions still cause considerable burden necessitating preventive surgeries which do in many cases involve loss of fertility.

In more developed countries, a cervical Papanicolaou (Pap) test is used to detect abnormal cells which may develop into cancer. During a colposcopic inspection biopsies can be taken and abnormal areas can be removed with a simple procedure, typically with a cauterizing loop or—more common in the developing world—by freezing (cryotherapy).

Pap smears have reduced the incidence and fatalities of cervical cancer in the developed world, but even so there were 11,000 cases and 3,900 deaths in the U.S. in 2008. Cervical cancer has substantial mortality in resource-poor areas; worldwide, there are 490,000 cases and 270,000 deaths.

HPV vaccines (Cervarix and Gardasil), which prevent infection with the HPV types (16 and 18) that cause 70% of cervical cancer, may lead to further decreases.



Highly sensitive person?

Are you?

Now, as an introduction to the trait of high sensitivity, see if some of these statements resonate with you, or relate to someone important in your life...

• You, your partner, or someone important to you have a heightened awareness of subtleties in your environment, whether it's sight, sound, touch, taste, or smell.
• You can become stressed out and upset when overwhelmed and may find it necessary to get away, maybe into a darkened room, to seek solitude, relief and comfort.
• You are very creative.
• You are very conscientious, hard working, and meticulous, but may become uncomfortable and less efficient or productive when being watched or scrutinised.
• You feel compelled to file and organise things and thoughts, also enjoy simplicity and may become overwhelmed or even immobilised by chaos, clutter, or stress.
• You are very uncomfortable when feeling things are getting out of your control.
• You get a sense of comfort and well being when around a lake, river, stream, the ocean, or even a fountain.
• You may experience mood swings, sometimes occurring almost instantly and can also be affected by other people's moods, emotions and problems.
• You have a deep, rich, inner life, are very spiritual, and may also have vivid dreams.
• You are very intuitive and you feel that you can usually sense if someone isn't telling the truth or if something else is wrong.
• You get concerned and think or worry about many things, and have also been told "you take things too personally."
• You have had the experience of "cutting people out" of your life.
• You were considered quiet, introverted, timid, or shy as a child.

Here are a few more to consider... Can be startled easily. Cautious in new situations. May have trouble sleeping. Extra sensitive to pain. Don't like crowds (unless they are kindred spirits). Avoids violent movies and TV shows. Has a deep respect and appreciation of nature, music and art.

Do some, or many, of these statements ring true for you, your partner, or someone important in your life? If so, you or they may be a highly sensitive person.

Tata....

Scientific Names

There are many times where you might need to know or write down the scientific name of a plant or an animal. Scientific names allow us to talk about species with a greater degree of accuracy than if we were to just use the common name. Many plants and animals have a more than one common name and so using the correct scientific terms makes talking about plant and animal species less ambiguous.

The scientific name of a species is made up of a combination of two special terms The first name is the genus of the organism and is capitalised, while the second is the species which is not capitalised. Below I will show you the conventions used when writing down a scientific name correctly.

Genus name

The genus name of a species is always written first and it is also underlined (in written) or italicised (only when using computers). Another point to note is that the first letter of the genus name is always capitalised.

• in the STPM if students write in italic the scientific names, you'll get 0 mark
• students must underline separately; don't underline the whole thing

Species name

The species name of an organism is written second and the specific epithet is always underlined (in written) or italicised (using computers).

Example of a correct scientific names :

Homo sapiens for human

Oryza sativa for paddy

Nephelium lappaceum for rambutan

Once you get to understand the convention then you will find that learning the correct scientific name for a plant or animal is not that hard. By learning the correct scientific names for a plant or animal you will be able to communicate with other scientists around the world unambiguously.

Kingdom     : Animalia

Phylum        : Chordata

Class           : Mammalia
Order          : Primates
Family         : Hominidae
Genus         : Homo
Species       : sapiens

Facts about your body

The length from your wrist to your elbow is the same as the length of your foot.

Your heart beats 101,000 times a day. During your lifetime it will beat about 3 billion times and pump about 400 million litres (800 million pints) of blood.

It is impossible to lick your elbow. Well, for almost everyone… but a few can.

Your mouth produces 1 litre (1.8 pints) of saliva a day.

The human head contains 22 bones. More on the head and brains

On average, you breathe 23,000 times a day.

Breathing generates about 0.6g of CO2 every minute.

On average, people can hold their breath for about one minute. The world record is 21 minutes 29 seconds, by David Merlini.

On average, you speak almost 5,000 words a day – although almost 80% of speaking is self-talk (talking to yourself).

Over the last 150 years the average height of people in industrialised nations increased by 10 cm (4 in).

In the 19th century, American men were the tallest in the world, averaging 1,71 metres (5’6″). Today, the average height for American men is 1,763 m (5 feet 9-and-half inches), compared to 1,815 m (5’10″) for Swedes, and 1,843 m (5’11″) for the Dutch, the tallest Caucasians.

The tallest nation in the world is the Watusis of Burundi: 1.98 m (6 feet 6 inches) tall.

If the amount of water in your body is reduced by just 1%, you’ll feel thirsty.

It is impossible to sneeze and keep one’s eyes open at the same time.

55% of people yawn within 5 minutes of seeing someone else yawn.

A person can live without food for about a month, but only about a week without water.

You’ll drink about 75,000 litres (20,000 gallons) of water in your lifetime.

After a certain period of growth, hair becomes dormant. That means that it is attached to the hair follicle until replaced by new hair.

Hair on the head grows for between two and six years before being replaced. In the case of baldness, the dormant hair was not replaced with new hair.

Men loose about 40 hairs a day. Women loose about 70 hairs a day.

In the Middle Ages the length from the tip of the middle finger to the elbow was called an ell.

A person remains conscious for eight seconds after being decapitated.

The first successful human sex change took place in 1950 when Danish doctor Christian Hamburger operated on New Yorker George Jorgensen, who became Christine Jorgensen.

The muscle that lets your eye blink is the fastest muscle in your body. It allows you to blink 5 times a second.

On average, you blink 15 000 times a day. Women blink twice as much as men.

A typical athlete’s heart churns out 25 to 30 litres (up to 8 gallons) of blood per minute.

Unless food is mixed with saliva you cannot taste it.

The liver is the largest of the body’s internal organs. The skin is the body’s largest organ.

On average a hiccup lasts 5 minutes.

Fingernails grow nearly 4 times faster than toenails.

Your middle fingernail grows the fastest.

Your finger nails grow at 1 nanometre per second (0.000 000 001 m/s). Your hair grows at 4 nanometres per second (0.000 000 004 m/s).

It takes about 3 months for the transplanted hair to start growing again.

About 13% of people are left-handed. Up from 11% in the past.

In 1900, a person could expect to live to be 47. Today, the average life expectancy for men and women in developed countries is longer than 70 years.

A newborn baby’s head accounts for one-quarter of its weight.

King Henry I, who ruled in the England in the 12th century, standardised the yard as the distance from the thumb of his outstretched arm to his nose.

The bones in your body are not white – they range in colour from beige to light brown. The bones you see in museums are white because they have been boiled and cleaned.

Our eyes are always the same size from birth.

Every person has a unique tongue print.

If all your DNA is stretched out, it would reach to the moon 6,000 times.

Approximately two-thirds of a person’s body weight is water. Blood is 92% water. The brain is 75% water and muscles are 75% water.

The coloured part of the eye is called the iris. Behind the iris is the soft, rubbery lens which focuses the light on to a layer, called the retina, in the back of the eye. The retina contains about 125 million rods and 7 million cones. The rods pick up shades of grey and help us see in dim light. The cones work best in bright light to pick up colors.

We actually do not see with our eyes – we see with our brains. The eyes basically are the cameras of the brain.

Hormones involved in Menstrual Cycle

Can be divided into 2 groups :
 i) hormones that control the changes in the ovaries - FSH and LH
 ii) hormones that control the changes in the uterus - oestrogen and progesterone

FSH
secreted by - anterior pituitary gland
stimulates the development in the ovary

LH
secreted by - anterior pituitary gland
stimulates ovulation, the development of corpus luteum
promotes the secretion of progesterone

Oestrogen
secreted by - follicle cells of the ovary
stimulates further growth of the follicles
promotes the repair of endometrium from 12th day of the menstrual cycle, it has positive feedback action on the secretion of FSH and LH

Progesterone
secreted by - corpus luteum
stimulates the endometrium to become thick, folded & highly vascular (enriched with blood vessels) for the implantation of an embryo
inhibits the secretion of FSH & LH to prevent the development of Graafian follicles &  ovulation

                      

Global warming

Exam Fever

Signs and symptoms
1. Room is in a complete mess. Books and papers are laid everywhere because the study table is too small to contain the pile of paper that you were just referring to earlier on.

2. Increased in appetite, leading to munching habits, and too much snacking results in weight gain.

3. In some individuals, the reverse occurs. Loss of appetite is seen, together with loss of weight.

4. Some persons even have loss of hair!

5. Some people have headaches, gastritis, or diarrhoea due to the overwhelming stress. Ah well, the diarrhoea could be due to too much coffee.

6. Because of not leaving the house as often as you usually would, you tend to bathe less, sweat more, and have more body odour.

7. The television is your companion when you get too bored of studying.

8. Sometimes Facebook is also an entertaining outlet to check out on others to see if they are studying or playing Facebook games just like you are now.

9. Some people watch Youtube while studying because multi-tasking improves memory power, or so you think.

10. A few people have the tendency to do spring cleaning of the entire house instead of studying, just to make themselves feel useful.

Diagnosis

Purely clinical. Radiographs not required. CT scan of the brain might help.

Treatment

Not required. It is a self-limiting disease

Structure & Function of Blood and Lymph

The components of blood

Blood is the main medium of transport within the body and consists of a liquid phase called plasma in which are floating cells and formed elements.

About 55% of the blood volume consists of a straw coloured liquid called plasma, the other 45% being made up of cells. The cells are either erythrocytes (red cells) or leucocytes (white cells). In addition there are

also platelets (thrombocytes) present which are fragments of cytoplasm.

Blood has several major functions:

1. Transport

2. Defence

3. Formation of lymph and tissue fluid

4. Homeostasis

 

Blood plasma

The composition of plasma e.g. its pH, salt concentration and osmotic pressure are precisely regulated by the kidney. This helps to provide an optimum environment for the cells which are bathed in tissue fluid, itself derived from blood. Plasma contains: Plasma proteins e.g. albumins, globulins and clotting factors, such as fibrinogen. Albumins and fibrinogen are made by the liver and secreted into the blood, while the gamma globulins are made by plasma cells (activated lymphocytes) already present in the blood and lymphatic system. The gamma globulins are antibodies which protect against disease organisms.

Albumins are the most abundant of the plasma proteins and are responsible for much of the osmotic pressure of blood, therefore holding water in the blood, thus maintaining blood pressure and volume. Albumins and some globulins also act as carrier proteins for substances which are insoluble in plasma. For example, the hormone thyroxine is transported from the thyroid gland by attaching onto a specific globulin and cholesterol is carried on lipoproteins (protein plus lipid units). Absorbed digested food products such as glucose, excretory products such as urea, salts such as sodium chloride and many hormones are dissolved and carried in the plasma.

Erythrocytes

Erythrocytes are little more than packets of the red coloured protein, haemoglobin, surrounded by a cell membrane. The nucleus is lost during differentiation in the red bone marrow so that a mature red cell is shaped like a biconcave disc. This disc shape gives it a large surface area in relation to volume, as required for efficient gas exchange. The shape can also be distorted to enable cells to squeeze through capillaries and sinusoids as narrow as 6 micrometres in diameter. Thus the passage of red cells is slowed up allowing more efficiency in gas exchange in the capillaries.  The respiratory pigment, haemoglobin, allows the blood to carry enough oxygen to meet the body’s needs, buffers the blood pH to between 7.2 and 7.6, and carries some waste carbon dioxide. The red cells also contain the enzyme carbonic anhydrase, which is involved with blood carbon dioxide transport in the form of hydrogen carbonate ions.

In order to synthesise haemoglobin when red blood cells are made in the red bone marrow, there must be a supply of iron, vitamin B12 and folic acid. A lack of any of these results in some form of anaemia. Before birth, red cells are also formed in the fetal liver and in the placenta. As red cells age they become fragile and eventually rupture when squeezing through the narrow blood sinusoids of the liver and spleen. Eventually, they are broken down in the liver.

Leucocytes

There 5 structures of leucocytes.. The granulocytes have granules in their cytoplasm and multilobed nuclei (i.e. they are polymorphonuclear), whereas the agranulocytes have no cytoplasmic granules and have either an oval or horseshoe shaped nucleus. The granulocytes and monocytes can all move through the tissues by moeboid action. Lymphocytes cannot, since they do not have enough cytoplasm to form pseudopodia. They move passively with blood and tissue fluid flow.

 

Intercellular fluid or lymph is derived from blood plasma but contains virtually no protein, since the plasma proteins are too large to escape through the capillary walls. Thus they are retained within the blood where they exert an osmotic pressure. Lymph is formed at the arterial end of the capillary bed where it is forced out of the capillaries by a relatively high blood pressure of around 4.8 kilopascals. This carries glucose, salts, other nutrients, oxygen and hormones to the cells. The proteins, retained in the blood plasma, exert an osmotic pressure of around 4.3 kPa which tends to draw some of the water of the lymph back into the blood, thus concentrating the lymph. The effective filtration pressure forming lymph is thus 4.8 - 4.3 = 0.5 kPa.

The lymph then percolates around the cells exchanging oxygen and nutrients for waste products, such as carbon dioxide and urea. The lymph in this situation is known as tissue fluid. Much of the lymph returns to the blood plasma at the venous end of the capillary bed. Here the blood pressure has fallen to around 3.9 kPa, but the osmotic pressure of the plasma proteins remains around 4.3 kPa. Thus the net uptake pressure for drawing lymph back into the capillaries is 4.3 - 3.9 = 0.4 kPa. Since the formation pressure was 0.5 kPa, this means that some of the lymph formed cannot get back into the capillaries at the venous end. This surplus lymph is collected up into open ended vein like vessels called lymphatics. These eventually all join up and empty the lymph into the blood at the left subclavian vein. The lymph vessels contain valves to prevent backflow of lymph which is moved along by the pressure of surrounding muscles and other organs.

Along the lymph vessels, at intervals are small bodies called lymph nodes, through which the lymph drains. Here phagocytes can engulf any bacteria or other debris in the lymph. The lymph nodes also contain and produce lymphocytes, which can be released into the lymph.

Blood group systems

The ABO system concerns the presence or absence of two antigens (actually called agglutinogens since they can agglutinate or clump together the red cells). These agglutinogens are proteins A and B which are situated

on the surface of the red blood cells. The presence or absence of agglutinogens is genetically controlled. Plasma contains specific antigens (called agglutinins) which are also determined genetically. Agglutinin A will cause the clumping together of red cells which contain agglutinogen A. Agglutinin B will clump together red cells which contain agglutinogen B. You do not possess agglutinins against your own red cells but your plasma does contain agglutinins to attack any foreign agglutinogens. Thus, Group A people possess agglutinin B in their plasma and Group B people possess agglutinin A. Thus in blood transfusions it is important to match the bloods correctly so that the recipient’s agglutinins (in their plasma) will not agglutinate the donor’s red cells. If this occurs the clumped red cells block small blood vessels, such as the glomeruli in the kidney, resulting in death. Group AB people have no antibodies and so can, in theory, receive blood of all groups. Thus they are called ‘universal recipients’’. Group O blood can, in theory, be given to all recipients, and thus Group O people are referred to as ‘universal donors’. In transfusion, the agglutinin in the donation is so diluted by entry into the whole blood volume of the recipient, that it does not cause any agglutination problems.

The rhesus system was first discovered in rhesus monkeys but also occurs in humans. People who are rhesus positive possess the rhesus agglutinogen on their red blood cells and make up about 85% of the UK population. 15% of the population have no agglutinogens and are called rhesus negative. Under normal circumstances the plasma does not contain anti rhesus agglutinins (anti D) which only develop if the immune response is invoked by the introduction of rhesus positive cells into a rhesus negative person. This could happen if a rhesus negative person receives a transfusion of rhesus positive blood in error. This is not serious on the first occasion, but if it occurs twice, because the first transfusion sensitised the immune system to the rhesus agglutinogen, a quick serious agglutination reaction occurs.

 

Blood clotting

Excess blood loss is prevented by haemostasis. Damaged blood vessels immediately constrict, decreasing blood flow and loss. Damage to the endothelium of the vessel exposes collagen fibres. Platelets that touch this collagen become large and sticky and rapidly form a plug to cover the exposed area. Clotting then occurs as follows:

1. Damaged tissue cells and platelets release the enzyme thromboplastin.

2. Thromboplastin converts the inactive plasma protein prothrombin into the enzyme thrombin. Ca2+ ions are needed as a cofactor for this reaction.

3. Thrombin converts the soluble plasma protein fibrinogen into insoluble fibrin.

4. Fibrin plugs the damaged vessel.

In the hours and days after clotting the fibrin threads contract and cross bond to pull the walls of the damaged vessel closer together and to retract (shrink) the clot. More fibrin may be added as this ruptures more platelets, and so the clot thickens and hardens to become the scab. As the clot retracts, a yellowish fluid called serum is forced out of it. Serum is blood plasma minus the clotting factors. The scab acts as a scaffold on which the tissue can be repaired. Fibrinolysis is the dissolving of the clot once tissue repair is complete. Scabs on the body surface can fall off, but those deep in the body are broken down by enzymes called plasmins which are formed from plasma proteins known as plasminogens.

Perfect Score (Latih tubi Bio SPM)

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Trial STPM Bio 2010

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The Greenhhouse Effect

Many people regard global warming or the greenhouse effect as the most serious environmental threat to our present way of life on earth. Put simply, the greenhouse effect is the natural "trapping in" of heat by some of the gases in the atmosphere. Figure 1 shows the key points of the greenhouse effect.

 
EXAM HINT - Candidates often confuse the greenhouse effect with ozone depletion. Although they have some common causes, their mechanisms and effects are very different.
 

Some of the greenhouse gases, for example, carbon dioxide, occur naturally in the atmosphere, whilst others such as the chlorofluorocarbons (CFCs) are entirely man-made. Regardless of their origin, such gases warm the lower atmosphere by trapping outgoing longwave radiation in a manner similar to that of glass in a greenhouse, hence the term greenhouse effect. It is important to realise that the greenhouse effect is a natural, essential process. Without it, the average temperature on earth would be about -170C and life would be impossible.

However, over the last hundred years human activities have resulted in rising concentrations of all the greenhouse gases. This has led to an increased or "enhanced" greenhouse effect and this in turn seems to have led to an increase in average global temperature.

It is the possible implications of this extra heating effect that are causing so much concern. We simply do not know how much the temperature will continue to rise and what effect any changes will have on local, regional and world climate. Which areas will benefit and which will suffer, and how, is still largely unknown. The temperature will not rise everywhere equally; in fact some areas will probably become cooler (because of this, most of the scientific literature now uses the term "global climate change" rather than global warming). The effects of possible changes will be discussed shortly, but first we need to look at the greenhouse gases in a little more detail.

Why is carbon dioxide so important?

In discussions of the greenhouse effect, attention is almost invariably focused on rising CO2 levels. This is not because it is an unusually powerful greenhouse gas - indeed, gases such as methane are thirty times more powerful weight for weight - but because of its sheer abundance. As a consequence, its effects outweigh those of all the other greenhouse gases combined. Historically, high carbon dioxide concentrations have always coincided with inter-glacial periods and low concentrations with ice ages.



What Can Be Done?

Strategies to reduce the emissions or levels of the greenhouse gases have mainly targeted carbon dioxide. These include:

1. Reducing the consumption of fossil fuels by increasing the fuel efficiency of buildings and vehicles. Improvements to the latter would also reduce N2O  emissions.

2. Switching fuel from coal to oil and gas which release less carbon dioxide upon consumption.

3. Switching from fossil fuels to renewable energy sources such as solar, geothermal, wind, wave, tidal and hydro-electric.

4. Preventing destruction of the tropical rainforests, simultaneously removing a problem and providing a solution.

However, as mentioned earlier, because the other greenhouse gases absorb different infrared wavelengths to carbon dioxide, reductions in this gas alone are unlikely to be sufficient. CFC emissions have already been reduced as a result of the Montreal Protocol in 1989 and subsequent amendments. Alternatives to CFCs are now widely available. Any measures which reduced vehicle use or pollution would simultaneously help to

reduce emissions of carbon dioxide, nitrous oxide and levels of tropospheric ozone. Worldwide however, the trend is in the wrong direction, with one new car joining the roads every second. In Britain fo example, road transport  is responsible for 18% of carbon dioxide emissions,45% of nitrous oxide emissions  and 30% of all hydrocarbon emissions.

Trial Bio SPM 2010

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Trial SBP
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Water Pollution



What is water pollution?

Water pollution is any chemical, physical or biological change in the quality of water that has a harmful effect on any living thing that drinks or uses or lives (in) it. When humans drink polluted water it often has serious effects on their health. Water pollution can also make water unsuited for the desired use.

What are the major water pollutants?

There are several classes of water pollutants. The first are disease-causing agents. These are bacteria, viruses, protozoa and parasitic worms that enter sewage systems and untreated waste.

A second category of water pollutants is oxygen-demanding wastes; wastes that can be decomposed by oxygen-requiring bacteria. When large populations of decomposing bacteria are converting these wastes it can deplete oxygen levels in the water. This causes other organisms in the water, such as fish, to die.

A third class of water pollutants is water-soluble inorganic pollutants, such as acids, salts and toxic metals. Large quantities of these compounds will make water unfit to drink and will cause the death of aquatic life.

Another class of water pollutants are nutrients; they are water-soluble nitrates and phosphates that cause excessive growth of algae and other water plants, which deplete the water's oxygen supply. This kills fish and, when found in drinking water, can kill young children.

Water can also be polluted by a number of organic compounds such as oil, plastics and pesticides, which are harmful to humans and all plants and animals in the water.

A very dangerous category is suspended sediment, because it causes depletion in the water's light absorption and the particles spread dangerous compounds such as pesticides through the water.

Finally, water-soluble radioactive compounds can cause cancer, birth defects and genetic damage and are thus very dangerous water pollutants.

Where does water pollution come from?

Water pollution is usually caused by human activities. Different human sources add to the pollution of water. There are two sorts of sources, point and nonpoint sources. Point sources discharge pollutants at specific locations through pipelines or sewers into the surface water. Nonpoint sources are sources that cannot be traced to a single site of discharge.

Examples of point sources are: factories, sewage treatment plants, underground mines, oil wells, oil tankers and agriculture.

Examples of nonpoint sources are: acid deposition from the air, traffic, pollutants that are spread through rivers and pollutants that enter the water through groundwater.

Nonpoint pollution is hard to control because the perpetrators cannot be traced.

How do we detect water pollution?

Water pollution is detected in laboratories, where small samples of water are analysed for different contaminants. Living organisms such as fish can also be used for the detection of water pollution. Changes in their behaviour or growth show us, that the water they live in is polluted. Specific properties of these organisms can give information on the sort of pollution in their environment. Laboratories also use computer models to determine what dangers there can be in certain waters. They import the data they own on the water into the computer, and the computer then determines if the water has any impurities.

What is heat pollution, what causes it and what are the dangers?

In most manufacturing processes a lot of heat originates that must be released into the environment, because it is waste heat. The cheapest way to do this is to withdraw nearby surface water, pass it through the plant, and return the heated water to the body of surface water. The heat that is released in the water has negative effects on all life in the receiving surface water. This is the kind of pollution that is commonly known as heat pollution or thermal pollution.

The warmer water decreases the solubility of oxygen in the water and it also causes water organisms to breathe faster. Many water organisms will then die from oxygen shortages, or they become more susceptible to diseases.

What is eutrophication, what causes it and what are the dangers?

Eutrophication means natural nutrient enrichment of streams and lakes. The enrichment is often increased by human activities, such as agriculture (manure addition). Over time, lakes then become eutrophic due to an increase in nutrients.

Eutrophication is mainly caused by an increase in nitrate and phosphate levels and has a negative influence on water life. This is because, due to the enrichment, water plants such as algae will grow extensively. As a result the water will absorb less light and certain aerobic bacteria will become more active. These bacteria deplete oxygen levels even further, so that only anaerobic bacteria can be active. This makes life in the water impossible for fish and other organisms.

What is acid rain and how does it develop?

Typical rainwater has a pH of about 5 to 6. This means that it is naturally a neutral, slightly acidic liquid. During precipitation rainwater dissolves gasses such as carbon dioxide and oxygen. The industry now emits great amounts of acidifying gasses, such as sulphuric oxides and carbon monoxide. These gasses also dissolve in rainwater. This causes a change in pH of the precipitation – the pH of rain will fall to a value of or below 4. When a substance has a pH of below 6.5, it is acid. The lower the pH, the more acid the substance is. That is why rain with a lower pH, due to dissolved industrial emissions, is called acid rain.

Why does water sometimes smell like rotten eggs?

When water is enriched with nutrients, eventually anaerobic bacteria, which do not need oxygen to practice their functions, will become highly active. These bacteria produce certain gasses during their activities. One of these gases is hydrogen sulphide. This compounds smells like rotten eggs. When water smells like rotten eggs we can conclude that there is hydrogen present, due to a shortage of oxygen in the specific water.

What causes white deposit on showers and bathroom walls?

Water contains many compounds. A few of these compounds are calcium and carbonate. Carbonate works as a buffer in water and is thus a very important component.

When calcium reacts with carbonate a solid substance is formed, that is called lime. This lime is what causes the white deposit on showers and bathroom walls and is commonly known as lime deposit. It can be removed by using a specially suited cleaning agent.

Feedback control mechanisms

The role and nature of feedback control in homeostasis
It is essential that the physical and chemical processes of the body are controlled. Homeostasis is the maintenance of a stable internal environment by the regulation of these processes within acceptable limits. Organisms receive oxygen, food, water, salts and warmth from the environment and return carbon dioxide and other wastes to it. Due to homeostasis, mammals and birds have a measure of independence from the external environment, whilst still existing in equilibrium with it.

Homeostasis usually involves control by a combination of negative and positive feedback. In negative feedback control, if the physiological value deviates from the mean (norm) the deviation is sensed by receptors which initiate control mechanisms to return the value to the norm. The receptors are then no longer stimulated and the control mechanisms are either reduced (damped) or completely switched off. Control mechanisms may occur either via nerve impulses which are rapid or via hormones which (with the exception of adrenaline) are slow. In positive feedback control, the control mechanism acts to push the deviating value further away from the norm. Once a certain deviation has been reached, the controlling mechanism may be damped or switched off.

Many physiological values and processes vary in a regular fashion over a definite period of time. Most of these are daily (circadian) rhythms, such as temperature control, but some are on different time scales, such as the monthly menstrual cycle. Endogenous rhythms (those which originate from within), appear to follow a spontaneous internal cycle, e.g. core body temperature changes. Exogenous rhythms (those which are affected by external factors), appear to follow regular changes in environmental stimuli, e.g. heart rate and blood pressure changes.

Regulation of blood concentration

The counter current mechanism which operates in the loops of Henlé in the kidneys maintains a high salt concentration around the collecting ducts of the nephrons. This enables water to be reabsorbed osmotically from the collecting ducts, back into the blood, provided that the collecting duct walls are permeable to water. This permeability depends upon the presence or absence of Antidiuretic hormone (ADH) secreted by the posterior pituitary on the target receptors on the collecting duct walls. If ADH is absent, the walls are impermeable to water so no water can be absorbed back to the blood to dilute it, and the urine remains dilute (containing as little as 100 millimoles of NaCl per litre). If ADH is present, the walls become permeable to water and water is reabsorbed back to the blood, thus diluting it and raising the blood volume and pressure. Conversely the urine volume is reduced and its concentration is raised (to around 1200 mllimoles of NaCl per litre).

The presence or absence of ADH is controlled by negative feedback. Receptors in the hypothalamus of the midbrain sense an increase in the sodium concentration and osmotic pressure (osmolarity) of the blood plasma, and transmit nerve impulses down the pituitary stalk to the posterior pituitary body. These impulses cause the release of ADH from the posterior pituitary to the blood (neurosecretion). The ADH attaches to target receptors on the collecting duct walls and makes them permeable to water which can then be reabsorbed back into the blood. As a result, the blood sodium concentration and osmolarity fall, so the receptors in the hypothalamus are no longer stimulated. ADH release is thus damped or switched off and so the collecting duct walls revert to being water impermeable. Thus, the urine becomes more dilute whilst the blood osmolarity starts to rise once more, until the ADH release is switched on again. The control mechanism of ADH is illustrated in Fig 1.

 

Regulation of blood glucose concentration

Blood glucose concentration is regulated by the islets of Langerhans which are tiny patches of endocrine issue embedded in the pancreas. The islets contain two types of secretory cell, the beta cells, which secrete insulin and the alpha cells, which secrete glucagon. Insulin lowers blood glucose levels by:

1. accelerating the facilitated uptake of glucose into cells

2. accelerating the synthesis of the storage polymer glycogen from glucose in the liver and muscles

Glucagon raises blood glucose level by stimulating the conversion of unwanted amino acids and glycerol into lucose. The release of insulin and glucagon is regulated by negative feedback. When the blood glucose level falls below the norm, this is sensed by receptors on the alpha cells of the islets. This stimulates the alpha cells to release glucagon into the blood, which raises the blood glucose level back to the norm and the alpha receptors become switched off. When the blood glucagon level raises above the norm, it is sensed by receptors on the beta cells of the islets. Insulin is released into the blood, which lowers the blood glucose concentration back to the norm and so the beta receptors are switched off.

 
The insulin-glucagon control mechanism is illustrated in Fig 2.

Regulation of the menstrual cycle

The menstrual cycle depends initially on the secretion of the hormone gonadotrophin release factor (GnRF) by the hypothalamus. Increasing blood levels of GnRF stimulates the release of follicle stimulating hormone (FSH) from the anterior pituitary gland. Increasing blood levels of FSH stimulates the development of primary follicles in the ovary into ovarian (Graafian) follicles, and also stimulates the developing follicles to secrete oestrogens. Oestrogens stimulate the repair and rebuilding of the uterus lining after its shedding during menstruation.

High oestrogen levels in the blood around the time of ovulation have two effects. Firstly, they inhibit the further release of GnRF and hence of FSH by negative feedback. Secondly they cause the anterior pituitary to release increasing amounts of luteinising hormone (LH) - this is a good example of positive feedback.

LH stimulates ovulation, in which the ovarian follicle ruptures to release the secondary oocyte into the ovarian (fallopian) funnel. It also stimulates the remains of the follicle in the ovary to develop into the corpus luteum (yellow body) which then starts to secrete the hormone progesterone as well as oestrogen. Together, oestrogen and progesterone maintain and develop the uterine wall further.

If fertilisation does not occur, the increasing levels of these hormones eventually inhibit the further release of LH by negative feedback. Without the maintaining effect of LH, the corpus luteum degenerates and so the concentrations of oestrogen and progesterone fall and their maintaining action on the uterine wall is lost. Thus, the uterine wall breaks down, resulting in the menstrual flow of cells and blood out through the vagina.

Fig 3 illustrates the changes in hormonal concentrations which occur during the menstrual cycle.

 



Days 8-12

Increasing oestrogen concentrations stimulate LH release by positive feedback.

Days 16-22
Increasing oestrogen and progesterone concentrations inhibit any further release of LH by negative feedback.
 
Regulation of the birth process

1. Throughout pregnancy, high concentrations of progesterone secreted by the placenta inhibit contractions of uterine muscle and thus prevent birth and maintain the pregnancy. Towards the end of pregnancy, from about week 36 in humans, the placenta starts to age. This has two main effects which increase as time passes, resulting in birth at around 40 weeks (humans). The two effects are: 1. The development of foetal anoxia (insufficient oxygen) which causes foetal discomfort resulting in struggling and kicking. This increases the mechanical stimulation on the uterine wall sending nerve impulses to the hypothalamus. When these reach a certain intensity the hypothalamus sends nerve impulses to the posterior pituitary, causing the release of the hormone oxytocin into the blood. This hormone stimulates the contractions of uterine muscle. As the intensity of nervous stimulation increases, so does the output of oxytocin (positive feedback).

2. The ageing placenta produces progressively less progesterone until eventually it no longer inhibits uterine contractions which then commence, initiating the birth process. Secretion of oestrogen from the foetus also occurs at this time which also stimulates uterine contractions (positive feedback). The placenta also secretes substances known as prostaglandins which also stimulate uterine contractions and stimulate oxytocin release from the posterior pituitary (positive feedback). Eventually the amnion ruptures, releasing the ‘waters’ and the foetus is then in direct contact with the uterine wall. This greatly increases mechanical and thus nervous stimulation, resulting in further increases in oxytocin output by positive feedback. The oxytocin also causes dilation of the cervix, so that eventually the uterine contractions push the baby out.

Following the birth of the baby, the high concentration of oxytocin in the blood causes more powerful uterine contractions to expel the bleeding placenta from the damaged uterine wall. The release of oxytocin then falls
back into a lower level by negative feedback, since the mechanical stimulation of the uterine wall is no longer present.

Regulation of body temperature

Precision temperature control is only found in endothermic animals such as mammals and birds, which can maintain their body temperatures within narrow limits by balancing their heat production with their heat loss. The regulation of temperature is due to a thermostat in the hypothalamus which becomes activated if the temperature varies from a set point (370C in humans). The thermostat contains two centres, one promoting heat loss and one promoting heat gain. These centres receive information from temperature receptors (thermoreceptors) in the skin which sense the surface temperature of the body, and in the hypothalamus which senses the core blood temperature.

If the skin or blood temperatures fall below the set point, the heat promoting centre of the hypothalamus is stimulated. This sends impulses through the sympathetic nerves, which stimulate responses leading to an increase in temperature. These responses include:

· Vasoconstriction of arterioles in the skin so that less heat is lost from the blood by radiation and conduction through the skin.

· Contraction of the erector pili muscles to raise the hairs. This traps a thicker layer of air which is a good insulator thus preventing heat loss.

· Release of adrenaline and noradrenaline from the adrenal medulla which stimulates an increase in cell metabolism, thus increasing heat production.

· An increase in striated muscle tone which causes shivering, generating heat.

As the body temperature rises back to the set point, the heat promoting centre is no longer activated. Thus no further impulses are generated and the adjusting mechanisms are damped or switched off by negative feedback. If the skin or blood temperature rises above the set point, the heat losing centre of the hypothalamus is stimulated. This sends impulses, mainly through parasympathetic nerves, which stimulate responses leading to a decrease in temperature. These responses include:

· Vasodilation of arterioles in the skin so that more heat is lost from the blood by radiation and conduction through the skin.

· Relaxation of the erector pili muscles to lower the hairs so that less insulating air is trapped.

· Increasing activity of the sweat glands (actually under sympathetic control) releasing sweat which evaporates, thus cooling the skin by removing latent heat of vaporisation.

As the body temperature falls back to the set point, the heat losing centre is no longer activated. Thus no further impulses are generated and the adjusting mechanisms are damped or switched off by negative feedback.

The norm or set point of body temperature actually fluctuates between set limits (between 36.5 and 37.50C) over a 24 hour period. The temperature is highest at around 1500 hrs and lowest around 0300 hrs and is a result of a similar fluctuation in basal metabolic rate which generates heat as a byproduct. This is an example of a circadian rhythm which is endogenous, although the precise internal reason for it is unknown.

 

During infections, the body temperature may be temporarily controlled by positive feedback. Diseased organisms often produce certain toxins called pyrogens (heat makers) which have the effect of raising the norm of body temperature, and the temperature is raised above the norm by positive feedback. This is of value, since the higher temperature may inhibit the enzymes of the bacteria or viruses, preventing their growth, whilst the enzymes of the host are less affected and can continue to work. Once the bacteria or viruses die and stop producing pyrogens, the control of body temperature reverts to the normal negative feedback.

 

Students usually learn and revise their Biology notes topic by topic - often in the same order that they were taught. However, feedback control mechanisms is a good example of a topic which requires students to be able to integrate in-depth knowledge of several different parts of a syllabus. This is, therefore, a popular topic.