May 29, 2011
CHOLESTEROL is a type of fat that is a normal component of most body tissues, and is required for good health. Yet, high levels can increase the risk of developing diseases (eg heart disease).
High cholesterol levels are asymptomatic, and in many cases, the first sign of any problem is a serious health issue. To help reduce the risk of this occuring, cholesterol levels are measured by a simple blood test. Your healthcare professional can organise this for you, along with other measurements of your cardiovascular health, such as blood pressure testing.
Cholesterol is transported through the blood stream in particles known as lipoproteins. The two most important varieties of lipoproteins to be aware of are low-density lipoproteins (LDL) and high-density lipoproteins (HDL).
High levels of LDL-cholesterol can lead to fatty deposits in the artery walls, referred to as atherosclerosis, or “hardening of the arteries”. Atherosclerosis makes the blood vessels narrower and stiffer, and consequently, increases the risk of heart disease and stroke.
This form of cholesterol is sometimes referred to as “bad” cholesterol.
High-density lipoproteins (HDL-cholesterol) help to reduce the risk of heart disease as they have the ability to help remove excess cholesterol from the arteries and other parts of the body. For this reason, they are sometimes referred to as “good” cholesterol.
The narrowing of the arteries associated with high cholesterol levels can sometimes cause symptoms that include chest pain (angina), or leg pain (intermittent claudication), especially with exercise.
High production of cholesterol by the liver may contribute to the development of gallstones, symptoms of which include episodic abdominal and back pain, especially after consumption of fatty foods.
Cholesterol levels in the blood depend on dietary factors and the amount of cholesterol manufactured by the body. High consumption of saturated fat, trans fat and cholesterol in foods may make your total cholesterol and LDL cholesterol levels rise.
Genetics also play a role in some people with high cholesterol. Your genes will partly determine how much cholesterol you naturally produce. Familial hypercholesterolaemia is more likely to be present in people who experience a heart attack at an early age or who have a family member who had a heart attack at an early age.
Being overweight contributes to increased LDL-cholesterol.
Other blood markers that may be associated with high cholesterol levels and are also risk factors for cardiovascular disease include high levels of a compound called homocysteine and high blood levels of triglycerides (fats).
Free radical damage to cholesterol molecules is believed to increase their ability to damage blood vessels.
Remember that cholesterol is not a disease in itself, but an indicator of the risk of developing heart disease. Your healthcare professional will consider your cholesterol level in the context of other risk factors, such as your family history, blood pressure, level of physical activity, and whether you are diabetic or smoke cigarettes.
Measures you can take to help reduce cholesterol levels include:
● To help maintain healthy cholesterol levels, reduce the quantity of cholesterol and saturated and trans fats in your diet. This involves avoiding animal fats (meat and full-fat dairy products) and sources of hidden fat such as pastries and pies.
● At the same time, increase the amount of fish in your diet (but not deep fried fish), and eat more fruit, vegetables and whole grains.
● A diet high in soluble fibre is highly recommended in order to promote the excretion of cholesterol. Good sources include legumes, oats and psyllium.
● Eating moderate amounts of foods that contain monounsaturated fats may support the management of healthy normal cholesterol levels. Important foods to include in your diet include nuts (especially walnuts), seeds and olive oil.
● Garlic and onion have cholesterol-lowering properties and are valuable additions to your diet.
● Limit your alcohol consumption to one to two standard drinks per day, and avoid binge drinking.
● Quit smoking. Cigarette smoking significantly increases the risk of cardiovascular disease and other health problems, and can exacerbate the negative effects of high cholesterol levels.
● Regular aerobic exercise can be of benefit to those with high cholesterol levels. Aim for at least 30 minutes of brisk walking per day. Always seek the advice of your healthcare professional before commencing an exercise programme.
● If you are overweight, talk to your healthcare professional about ways to address this, as being overweight may contribute to raised LDL and triglyceride levels.
There are also certain natural alternatives you can consider:
● Plant sterols (also known as phytosterols) may help reduce LDL-cholesterol levels and assist in improving the LDL:HDL ratio to healthier levels. They work by lowering cholesterol absorption and reabsorption. Take a daily dose of 2-3 grams of plant sterols, as recommended by the National Heart Foundation of Australia. Choose a formula that also supplies a healthy dose of betacarotene, which may become depleted when taking plant sterols.
● Coenzyme Q10 helps maintain heart and artery health and inhibits the oxidation of LDL–cholesterol.
● Omega-3 fatty acids EPA and DHA from fish oil, may help decrease fat in the blood (triglycerides) in healthy people. Omega-3s also help to maintain the flexibility of the blood vessels, help maintain healthy heart rates, and help maintain healthy blood pressure.
● Antioxidant nutrients such as vitamin C and vitamin E help reduce the oxidation of LDL-cholesterol. Antioxidants are often taken with folic acid and the vitamins B6 and B12. Low intake of these B-group vitamins is a common cause of elevated plasma homocysteine.
● If you’re overweight, achieving a healthy body weight may aid the management of healthy cholesterol levels.
Your cholesterol level is only one aspect of your cardiovascular health profile and should be addressed in conjunction with other risk factors. Talk to your healthcare professional for more information.
Posted by rozaini at 5:13 PM
May 12, 2011
One of the most important aspects of the mammalian kidney is its ability to adjust both the volume and osmolarity of urine, depending on the animal′s water and salt balance and the rate of urea production. In situations of high salt intake and low water availability, a mammal can excrete urea and salt with minimal water loss in small volumes of hyperosmotic urine. But if salt is scarce and fluid intake is high, the kidney can get rid of the excess water with little salt loss by producing large volumes of hypoosmotic urine (as dilute as 70 mosm/L, compared to about 300 mosm/L for human blood). This versatility in osmoregulatory function is managed with a combination of nervous and hormonal controls.
One hormone that is important in regulating water balance is antidiuretic hormone (ADH).
ADH is produced in the hypothalamus of the brain and is stored in and released from the posterior pituitary gland, which is positioned just below the hypothalamus. Osmoreceptor cells in the hypothalamus monitor the osmolarity of blood; when it rises above a set point of 300 mosm/L (perhaps due to water loss from sweating or to ingestion of salty food), more ADH is released into the bloodstream and reaches the kidney. The main targets of ADH are the distal tubules and collecting ducts of the kidney, where the hormone increases the permeability of the epithelium to water. This amplifies water reabsorption, which reduces urine volume and helps prevent further increase of blood osmolarity above the set point. By negative feedback, the subsiding osmolarity of the blood reduces the activity of osmoreceptor cells in the hypothalamus, and less ADH is then secreted. But only the gain of additional water in food and drink can bring osmolarity all the way back down to 300 mosm/L.
Conversely, if a large intake of water has reduced blood osmolarity below the set point, very little ADH is released. This decreases the permeability of the distal tubules and collecting ducts, so water reabsorption is reduced, resulting in increased discharge of dilute urine. (Increased urination is called diuresis, and it is because ADH opposes this state that it is called anti diuretic hormone.) Alcohol can disturb water balance by inhibiting the release of ADH, causing excessive urinary water loss and dehydration (which may cause some of the symptoms of a hangover). Normally, blood osmolarity, ADH release, and water reabsorption in the kidney are all linked in a feedback loop that contributes to homeostasis.
A second regulatory mechanism involves a specialised tissue called the juxtaglomerular apparatus (JGA), located near the afferent arteriole that supplies blood to the glomerulus. When blood pressure or blood volume in the afferent arteriole drops (for instance, as a result of reduced salt intake or loss of blood), the enzyme renin initiates chemical reactions that convert a plasma protein called angiotensinogen to a peptide called angiotensin II. Functioning as a hormone, angiotensin II raises blood pressure by constricting arterioles, decreasing blood flow to many capillaries, including those of the kidney. Angiotensin II also stimulates the proximal tubules of the nephrons to reabsorb more NaCl and water. This reduces the amount of salt and water excreted in the urine and consequently raises blood volume and pressure. Another effect of angiotensin II is stimulation of the adrenal glands to release a hormone called aldosterone. This hormone acts on the nephrons′ distal tubules, making them reabsorb more sodium (Na+) and water and increasing blood volume and pressure. In summary, the renin–angiotensin–aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis. A drop in blood pressure and blood volume triggers renin release from the JGA. In turn, the rise in blood pressure and volume resulting from the various actions of angiotensin II and aldosterone reduce the release of renin.
The functions of ADH and the RAAS may seem to be redundant, but this is not the case. Both increase water reabsorption, but they counter different osmoregulatory problems. The release of ADH is a response to an increase in the osmolarity of the blood, as when the body is dehydrated from excessive water loss or inadequate intake of water. However, a situation that causes an excessive loss of both salt and body fluids—an injury, for example, or severe diarrhea—will reduce blood volume without increasing osmolarity. This will not induce a change in ADH release, but the RAAS will respond to the fall in blood volume and pressure by increasing water and Na+ reabsorption. ADH and the RAAS are partners in homeostasis; ADH alone would lower blood Na+ concentration by stimulating water reabsorption in the kidney, but the RAAS helps maintain balance by stimulating Na+ reabsorption.
Still another hormone, a peptide called atrial natriuretic factor (ANF), opposes the RAAS. The walls of the atria of the heart release ANF in response to an increase in blood volume and pressure. ANF inhibits the release of renin from the JGA, inhibits NaCl reabsorption by the collecting ducts, and reduces aldosterone release from the adrenal glands. These actions lower blood volume and pressure. Thus, ADH, the RAAS, and ANF provide an elaborate system of checks and balances that regulate the kidney′s ability to control the osmolarity, salt concentration, volume, and pressure of blood. The precise regulatory role of ANF is an area of active research.
Posted by rozaini at 3:51 PM
May 3, 2011
Blood flow through the kidneys is voluminous. In humans, the kidneys account for less than 1% of body weight, but they receive about 20% of resting cardiac output. Urine exits each kidney through a duct called the ureter, and both ureters drain into a common urinary bladder. During urination, urine is expelled from the urinary bladder through a tube called the urethra, which empties to the outside near the vagina in females or through the penis in males. Sphincter muscles near the junction of the urethra and the bladder, which are under nervous system control, regulate urination.
Posted by rozaini at 7:04 PM