Homeostasis

Homeostasis Provides a Constant Internal Environment and Independence from

Fluctuating External Conditions
- Features that influence internal environment have a set level → norm
- Any changes from the norm is called deviation
- Negative feedback/caused by deviation from norm/change results in return to norm
- External environment is changing → experienced by body

Homeostatic system even out variations experienced by body
- Liver can store or release glucose
- Blood is kept at a constant, ideal state
- Glucose conc. of 80mg cm-3
- Tissue fluid surrounds working cell with constant ideal conditions
- Optimum glucose for respiration

Negative Feedback Tends to Restore Systems to their Original Level
- Homeostasis is achieved by a negative feedback and involves
      Change in level of an internal factor (change from norm level)
      Detected by receptors / impulse send to hypothalamus
      Activates effectors / stimulates corrective mechanism
      Level of factor returns to norm
 - Factors in blood and tissue fluid must be kept constant :
      Temp and pH
          Change affects rate of enzyme-controlled/biochemical reactions
          Extreme changes denatures proteins
          Humans maintain constant core body temp between 36-37.8°C
          Body temp refers to core body temp → limbs may be cooler than 37°C
      Water potential / avoids osmotic problems → cellular disruption
      Concent. of ions (Na, K, Ca)

Hypothermia

Mechanisms Involved in Heat Production, Conversation, and Heat Loss.
The Role of the Hypothalamus and the Autonomic Nervous System in Temperature Control

Blood flows through receptors in the hypothalamus

Deviation causes the autonomic nervous system to initiate an appropriate response

DEFICIENCY/DROP IN CORE BODY TEMP BY DECREASING HEAT LOSS/INCREASING HEAT PRODUCTION
- Receptors in hypothalamus detect increase in core temp/temp of blood
- Heat conversation centre stimulated
- VASOCONSTRICTION of arterioles
- Arterioles leading to capillaries in the skin narrow
- SHUNT VESSELS DILATE
- Less blood flows to skin surface / less heat is lost by RADIATION
- Hair raising / greater insulation / humans have less dense hair \ no effect
- Shivering / rapid contraction and relaxation of muscles / heat produced by RESPIRATION
- Adrenaline INCREASES METABOLIC RATE of cells //Mammals in cold climates can increase     secretion  of thyroxine / hormone increases metabolic rate on a more permanent basis
- VOLUNTARY CENTRE: put on clothes / seek warmer areas / warm drink

EXCESS/RISE IN CORE BODY TEMP BY INCREASING HEAT LOSS/REDUCING HEAT PRODUCTION
- Receptors in hypothalamus detect increase in core temp/temp of blood
- Heat loss centre stimulated
- VASODILATION of arterioles
- Arterioles leading to capillaries in the skin dilate (expand)
- SHUNT VESSELS CONSTRICT
- More blood flows to skin surface (capillaries) / heat loss by RADIATION
- Heat loss by EVAPORATION of sweat / by using energy
- High(er) rate of sweating leads to a low(er) skin temp
- VOLUNTARY CENTRE: remove clothing / seek cooler area / cold drink

The Role of Temperature Receptors in the Skin
- Hypothalamus detects temp fluctuation inside the body/internal environment
- Skin receptors detect temp changes in external environment
- Information is sent by nerves to voluntary centres of the brain
- Voluntary activities (jogging, moving into a shade) are initiated
- Changes behaviour of human

The Structure and Role of the Skin in Temp Regulation
- Surface area is very large and in direct contact to external environment
- Skin is divided into two layers: outer epidermis and inner dermis
- MALPIGHIAN layer is the boundary between these two layers
- Cells of this layer divide repeatedly by mitosis
- Older cells are pushed towards the surface/EPIDERMIS
- Cytoplasm of old cells becomes full of granules / cells die
- Cells become converted into scales of keratin (waterproof)
- DERMIS is thicker than epidermis and contains
- Nerve endings (temp receptors)
- Blood vessels held together by connective tissue
- Beneath dermis is a region which contains some subcutaneous fat
- Adipose tissue (fat storage tissue) provides vital insulations in humans

Hypothermia
- Body temp falls dangerously below normal
- Heat energy is lost from body more rapidly than it can be produced
- Brain is affected first → person becomes clumsy and mentally sluggish
- As body temp falls, metabolic rate falls as well
- Makes body temp fall even further, causing a POSITIVE FEEDBACK
- Temp is taken further away from the norm

- Death when core body temp is below ≈25°C / by ventricular fibrillation / normal beating of the

   heart is replaced by uncoordinated tremors

- Most at risk are (1) babies and (2) elderly
- (1) High surface area:volume ratio, undeveloped temp regulation mechanisms
- (2) Detoriated thermoregulatory mechanisms
- Deliberate hypothermia is sometimes used in surgical operations on heart
Patient is cooled by
- Circulating blood through a cooling machine
- Placing ice packs in contact with the body
- Reduces metabolic rate / O2 demand by brain + other vital tissues is lowered
Heart can be stopped without any risks of the patient suffering brain damage through lack of O2
Tissues may be permanently damaged if patient is cooled to long

Diabetes
The Factors which Influence Blood Glucose Concentration
Digestion of carbohydrates in diet
Digestion → polysaccharide → glucose
Fluctuation of glucose blood level depend on amount + type of carbohydrate eaten
Breakdown of glycogen
Excess glucose → glycogen → glucose
Storage polysaccharide made from excess glucose by glycogenesis
Glycogen is abundant in liver + muscles
Conversion of non-carbohydrates to glucose by gluconeogenesis
Oxidation of glucose by respiration
Glucose → ATP → energy
Rate of respiration varies for different activities
This affects glucose uptake from blood into cells
Brain is unable to store carbohydrates
Lack of glucose in blood → no respiratory substrate → insufficient energy for brain
Short period of time already causes brain to malfunction
Normal glucose level in blood ≈90mg per 100cm2
After a meal it rarely exceeds 150mg per 100cm2

Role of Hormones in Activating Enzymes Involved in Interconversion of Glucose and Glycogen

The Role of Insulin and Glucagon in Controlling Blood Glucose

The Pancreas
Endocrine role is to produce hormones
Contains islets of Langerhans → sensitive to blood glucose conc
Islet cells contain
α-cells → secrete glucagon and β-cells → secrete insulin
capillaries into which hormones are secreted
delta cells → produce hormone somatostatin → inhibits secretion of glucagon
Insulin mainly affects muscles, liver, adipose tissue
Exocrine role is to produce digestive enzymes
Active trypsin damages pancreas / digests proteins that make up pancreas / amylase leaks into blood from damaged tissues / amylase conc in blood higher

High Blood Glucose Concentration
Detected by β-cells in islet of Langerhans (receptor) → secrete insulin
Increase in insulin secretion (corrective mechanism → effectors bring about a return to norm)
Speeds up rate of glucose uptake by cells from blood
Glucose enters cells by facilitated diffusion via glucose carrier proteins
Cells have vesicles with extra carrier molecules present in their cytoplasm
Insulin binds to receptor in plasma membrane
Chemical signal → vesicles move towards plasma membrane
Vesicle fuses with membrane → increases glucose carrier proteins
Activates enzymes / Converts glucose to glycogen / Promotes fat synthesis

Low Blood Glucose Concentration
Detected by α-cells in islets of Langerhans → secrete glucagon
Increase in glucagon secretion
Hormone activates enzymes in the liver → convert glycogen to glucose
Stimulates formation of glucose form other substances such as amino acids
Glucose passes out of cells into blood, raising blood glucose conc until norm is reached
Diabetes and its Control with Insulin and Manipulation of Carbohydrate Intake
Diabetes mellitus → inability of control of blood glucose level
High levels of blood glucose because
Pancreas becomes diseased → fails to secrete insulin
Target cells lose responsiveness to insulin
Kidney is unable to reabsorb back into blood all the glucose filtered into its tubules
Glucose secreted into urine
Craving for sweet food and persistent thirst
DIAGNOSTIC: glucose tolerance test
Patient swallows glucose solution
Blood glucose level measured at regular intervals

Two Types of Diabetes Mellitus
Type I → insulin dependant/juvenile-onset
Occurs in childhood
Autoimmune reaction → immune system attacks and destroys own cells
Destroys β-cells in islet of Langerhans → unable to produce insulin
TREATMENT: insulin given must match glucose intake and expenditure
Overdose causes hypoglycaemia (to much glucose withdrawn from blood)
Diabetics need to manage their diet and levels of exercise
Need to monitor blood glucose conc
Type II → insulin independent/late-onset
Occurs late in life, more common than type I
Causes by gradual loss in responsiveness of cells to insulin
TREATMENT: regulated diet
Sugar intake must balance with amount of exercises taken
Glycogen levels are lower
Little insulin / no glucose to glycogen
Insulin receptors no longer functional / less glucose taken up by cells
Glycogen is an effective storage molecule
Insoluble → no osmotic effect
Large → cannot diffuse out of cell
Branched → easy to break down / hydrolyse to glucose
Compact → large amount of glucose stored in small space

Insulin Patches
Insulin → peptide chains → digested if swallowed by peptidase → had to be injected
Treat skin area with ultrasound → disrupts underlying fat tissues
Insulin is not soluble in fat
Disrupting tissues allows movement through skin
Apply patch containing insulin to that area