JAUNDICE: SKIN AND EYES

This is a yellow colouration of the skin and eyes.

Cause:

• Presence of excess bile pigments.
• This happens due to blockage of bile duct or destruction of liver.

Symptoms:

Yellow pigmentation of skin and eyes, nausea, vomiting and lack of appetite. Itching of skin.

Treatment

1. Removal of stones from the gall bladder by surgery.
2. Give patient fat-free diet, reduced amount of proteins.
3. Give antihistamines to reduce itching.

Homeostasis

1. Homeostasis is the maintenance of a constant internal environment.
2. The internal environment consists of intercellular or tissue fluid.
3. This fluid is the medium in the space surrounding cells.
4. Tissue fluid is made by ultra-filtration in the capillaries.
5. Dissolved substances in the blood are forced out of the capillaries and into intercellular spaces.
6. Cells obtain their requirements from tissue fluid while waste products from cells diffuse out into the tissue fluid.
7. Some of the fluid gets back into the blood capillaries while excess fluid is drained into the lymph vessels.
8. Cells function efficiently if there is little or no fluctuation in the internal environment.
9. The factors that need to be regulated include temperature, osmotic pressure and pH.
10. The body works as a self-regulating system and can detect changes in its working conditions bringing about corrective responses.
11. This requires a negative feedback mechanism e.g. when body temperature falls below normal, mechanisms are set in place that bring about increase in temperature.
12. And when the increase is above normal, mechanisms that lower the temperature are set in place.
13. This is called a negative feedback and it restores the conditions to normal.

Neuro-Endocrine System and Homeostasis

Homeostatic mechanisms are brought about by an interaction between nervous and endocrine systems.

Nerve endings detect changes in the internal and external environment and relay the information to the brain. The hypothalamus and pituitary are endocrine glands situated in the brain.

The hypothalamus detects changes in the blood. The pituitary secretes a number of hormones involved in homeostasis e.g. anti-duretic hormone (ADH). The discussion below shows the nature of these interactions.

The Skin and Temperature Regulation

1. The optimum human body temperature is 36.8°C.
2. A constant body temperature favours efficient enzyme reaction.
3. Temperatures above optimum denature enzymes, while temperature below the optimum range inactivates enzymes.
4. The skin is involved in regulation of body temperature as follows:
5. The skin has receptors that detect changes in the temperature of the external environment.

When the body temperature is above optimum the following takes place:

Sweat:

1. Sweat glands secrete sweat onto the skin surface.
2. As sweat evaporates it takes latent heat from the body, thus lowering the temperature.

Vasodilation of Arterioles:

1. The arterioles near the surface become wider in diameter.
2. More blood flows near the surface and more heat is lost to the surrounding by convection and radiation.

Relaxation of hair erector muscle:

1. When hair erector muscles relax, the hair lies flat thus allowing heat to escape from the skin surface.

When body temperature is below optimum the following takes place:

Vasoconstriction of Arterioles:

1. The arterioles near the surface of the skin become narrower.
2. Blood supply to the skin is reduced and less heat is lost to the surroundings. Contraction of hair erector muscles.
3. When hair erector muscles contract, the hair is raised.
4. Air is trapped between the hairs forming an insulating layer.
5. Animals in cold areas have a thick layer of subcutaneous fat, which helps to insulate the body.
6. Besides the role of the skin in thermoregulation as discussed above, the rate of metabolism is lowered when temperature is above optimum and increased when temperature is below optimum.
7. The latter increases the temperature to the optimum.
8. When this fails, shivering occurs.
9. Shivering is involuntary contraction of muscles which helps to generate heat thus raising the body temperature.

Homeostatic Control of Body Temperature in Humans

Body size and Heat Loss

1. The amount of heat produced by metabolic reactions in an animal body is proportional to its mass.
2. Large animals produce more heat but they lose less due to small surface area to volume ratio.
3. Small animals produce less heat and lose a lot, due to large surface area to volume ratio.
4. Small animals eat a lot of food in relation .to their size in order to raise their metabolic rate. Behavioural and Physiological Responses to Temperature Changes
5. Animals gain or lose heat to the environment by conduction, radiation and convection.
6. Birds and mammals maintain a constant body temperature regardless of the changes in the environment.
7. They do this mainly by internally installed physiological mechanisms hence they are endotherms, also known as homoiotherms.
8. At the same time behavioural activities like moving to shaded areas when it is too hot assist in regulating their body temperature.
9. Other animals do not maintain a constant body temperature e.g. lizards.
10. They are poikilotherms (ectotherms) as their temperature varies according to that of surroundings.
11. They only regulate body temperature through behavioural means.
12. Lizards bask on the rocks to gain heat and hide under rocks when it is too hot.
13. Some animals have adaptive features e.g. animals in extreme cold climates have fur and a thick layer of subcutaneous fat like polar bear.
14. Those in extremely hot areas have tissue that tolerate high temperatures e.g. camels.
15. Some animals avoid cold conditions by hibernating e.g. the frog while others avoid dry hot conditions by aestivation e.g. kangaroo rat.
16. This involves decreasing their metabolic activities.

Skin and Osmoregulation

1. Osmoregulation is the control of salt and water balance in the body to maintain the appropriate osmotic pressure for proper cell functioning.
2. Sweat glands produce sweat and thus eliminate water and salt from the body.

The Kidney and Osmoregulation

The kidney is the main organ that regulates the salt and water balance in the body. The amount of salt or water reabsorbed into the bloodstream is dependent on the osmotic pressure of the blood.

When the osmotic pressure of the blood rises above normal due to dehydration or excessive consumption of salt, the osmo-receptors in the hypothalamus are stimulated.

These cells relay impulses to the pituitary gland which produces a hormone called anti-diuretic hormone – ADH (vasopressin) which is taken by the blood to the kidneys.

The hormone (ADH) makes the distal convoluted tubule and collecting duct more permeable to water hence more water is reabsorbed into the body by the kidney tubules lowering the osmotic pressure in the blood.

When the osmotic pressure of the blood falls below normal due to intake of a large quantity of water, osmoreceptors in the hypothalamus are less stimulated. Less antidiuretic hormone is produced, and the kidney tubules reabsorb less water hence large quantities of water is lost producing dilute urine (diuressis).

The osmotic pressure of the blood is raised to normal. If little or no ADH is produced, the body may become dehydrated unless large quantities of water are consumed regularly.

Diabetes insipidus is a disease that results from the failure of the pituitary gland to produce ADH and the body gets dehydrated.

1. A hormone called Aldosterone produced by the adrenal cortex regulates the level of sodium ions.
2. When the level of sodium ions in the blood is low, adrenal cortex releases aldosterone into the blood.
3. This stimulates the loop of henle to reabsorb sodium ions into the blood.
4. Chloride ions flow to neutralise the charge on sodium ions.
5. Aldosterone also stimulates the colon to absorb more sodium ions into the blood.
6. If the sodium ion concentration rises above optimum level, adrenal cortex
7. Notes missing – The liver
8. Formation of Red Blood Cells.
9. In the embryo, red blood cells are formed in the liver.
10. Breakdown and elimination of old and dead blood cells.
11. Dead red blood cells are broken down in the liver and the pigments eliminated in bile.

Manufacture of Plasma Proteins.

1. Plasma proteins like albumen, fibrinogen and globulin are manufactured in the liver.
2. Storage of blood, vitamins A, K, BI2 and D and mineral salts such as iron’ and potassium ions.

Detoxification.

Toxic substances ingested e.g. drugs or produced from metabolic reactions in the body are converted to harmless substances in a process called detoxification.