SS 3 FIRST TERM

REGULATION OF INTERNAL ENVIRONMENT

Homeostasis is the maintenance of a fairly constant internal environment of an organism. Examples of internal conditions maintained by homeostasis are the level of blood glucose, body temperature, blood calcium level, osmotic pressure and concentrations of dissolved substances in the body fluids like carbon dioxide, oxygen, urea, food substances (glucose, amino-acids, etc.) and ions (sodium, potassium, chlorides).  

Thermoregulation is the process by which an organism controls its body temperature. 

Poikilothermic (cold-blooded) organisms do not have internal control of their body temperature, their body temperature is generally similar to or changes with the temperature of the environment. 

Homoeothermic (warm-blooded) animals maintain a constant body temperature in the face of environmental changes. The processes of temperature control are located in the hypothalamus of the brain. 

Osmoregulation is the process by which an organism maintains a balance between the water and salts in its body fluids. 

Homeostasis in unicellular organism is by contractile vacuole while in mammals, the organs involved in homeostasis are kidney, liver, skin, ductless glands and the brain. 

The Kidney 

The kidneys are bean-shaped organs located in the abdominal cavity of mammals. The kidneys remove nitrogenous waste e.g. urea and other ammonium compounds from the blood. The kidneys also control the amount of salt, water and acids in the blood. 

Each of the kidneys contains more than a million tiny units called nephrons that filter blood containing the metabolic wastes from cells. All the blood in the human body is filtered about 60 times a day by the kidneys. The nephrons remove wastes, concentrate them, and form urine that is collected in the bladder.     

Internally, the kidney has three regions—an outer cortex, a medulla in the middle, and the renal pelvis, which is the expanded end of the ureter. The renal cortex contains the nephrons—the functional unit of the kidney. The renal pelvis collects the urine and leads to the ureter on the outside of the kidney. The ureters are urine-bearing tubes that exit the kidney and empty into the urinary bladder. 

The kidney performs three functions of homeostasis in man: osmoregulation, excretion and acid-base balance. 

1. Osmoregulation: when the osmotic concentration of the blood is higher than that of body cells/tissues i.e. the blood is hypertonic compared to the body cells, antidiuretic hormone is secreted into the blood which causes the kidney to reabsorb water from the kidney tubules during excretion process, thus less water is excreted. When the water content of the blood is high, less ADH is secreted making less water reabsorbed and thus more water is excreted. 
2. Excretion: the kidney removes metabolic wastes from the body. It does this by 3 steps: ultrafiltration, selective reabsorption and hormonal secretion.  
3. Maintenance of acid-base balance in the body: the normal pH of the blood is about 7.4 retains bases or bicarbonate ions. When the concentration of base becomes higher, the kidney will excrete more salts. 

Conditions that affect the functioning of the kidney 

1. Environmental temperature 
2. Drugs 
3. Habitats 
4. Diseases such as  

• a. Nephritis: inflammation of the kidney usually caused by bacterial infection (Streptococcus species). This results in an inflamed glomerulus which causes them to be more permeable than normal; protein and red blood cells leak into the glomeruli filtrate and swollen kidney. The symptoms of nephritis include Oedema (swelling of feet and ankle); high blood pressure; amino acids in urine; blood in urine/blood cells in urine; dizziness/back pain/fatigue; general weakness; inflammation of the kidney tubules.  The remedies include washing foods and cooking them properly; drinking boiled water; use of antibiotics and dialysis. 
• b. Kidney stones: Kidney stones are insoluble crystals of dissolved minerals (e.g. calcium phosphate) that form in urine inside the kidneys. Kidney stones may grow large enough before passing to block a ureter. This can cause a build-up of urine above the blockage and severe pain. The symptoms are abdominal pains; decreased frequency of urination; pains during urination; presence of blood in the urine; increased blood pressure.  The remedy to kidney stone is drinking sufficient water; avoid excessive intake of calcium-rich foods; take drugs to dissolve the stones and surgery to remove the stones. 
• c. Diuresis: is increased outflow of urine due to the inability of the nephron to re-absorb water from the glomerular filtrate back to the blood. This is often due to diabetes insipidus where the production of ADH is low. In cases of diabetes mellitus where excretion of glucose is accompanied by excretion of water. Also, some drugs induce diuresis when they are taken to treat oedema.  The symptoms of diuresis include excretion of large amount of urine, thirst and dehydration; loss of electrolytes from the body; loss of appetite; weakness; loss of weight; fatigue; nausea and sometimes death in untreated cases.  The remedy includes avoiding excessive intake of alcohol; treating diabetic patients with insulin and kidney transplant 
• d. Dropsy (oedema): is the accumulation of fluids in the connective tissues due to inefficient ultrafiltration. The symptoms include swollen ankles and joints. The corrective measure is by taking diuretic drugs.

 The Liver 

The liver is a large organ in the body, divided into lobes which is further sub-divided into smaller lobes    

 Functions of the Liver 

1. Regulation of blood sugar 
2. Detoxification 
3. Regulation of blood protein 
4. Production of bile 
5. Production of red blood cells 
6.  Production of heat 
7. Regulation of lipids 
8. Manufacture of essential proteins 
9. Destruction of worn-out red blood cells 
10. Storage of vitamins and iron 
11. Reservoir of blood 

 Diseases of the liver 

1. Infective hepatitis (caused by hepatitis virus): this is an inflammation of the liver.  The effects include loss of appetite, weakness, fever, abdominal discomfort, eyes and skin turns yellow. It can be controlled by washing foods properly before consumption 
2. Gall stones: are solid lumps of cholesterol crystals or pigment material that form in the gallbladder as a result of abnormal formation of bile by the liver. The symptoms of gall stones are severe abdominal pain; as jaundice (yellowing of the skin and eyes) and inflammation of the gallbladder, bile ducts, liver or pancreas. The remedy involve the use of medications and surgery 
3. Cancer of the liver: is caused by dietary deficiencies and cancer cells from elsewhere which affects the liver cells. The symptoms include loss of weight; weakness; anaemia; jaundice; fluid in the abdomen; fever and pains. The disease can be managed by allowing sufficient rest and visiting the medical doctor for chemotherapy. 
4. Cirrhosis of the liver: this is hardening of the liver as a result of excessive consumption of alcohol over a long period. The symptoms include loss of appetite; nausea; weight loss; fatigue; weakness and exhaustion. Liver cirrhosis can be remedied by stopping alcohol intake or performing a liver transplant. 

HORMONES  

Hormones are chemical substances secreted by endocrine or ductless glands in small quantities directly into the blood and are carried to other parts/organ of the body where they stimulate the activity of the target organ or elicit a response. The general effects of hormones are:

1. Homeostasis 
2. Control of growth  
3. Sexual maturity 
4. Changes in cells 
5. Circulation of blood 
6. Co-ordination of organs of the body.

Hormones produced by animals and their effects: