Homeostasis

Homeostasis is the process by which the body maintains a stable internal environment. This includes regulating factors like temperature, pH, osmotic pressure, and concentrations of dissolved substances and mineral ions in body fluids such as blood, lymph, and tissue fluid. These adjustments are essential for efficient cellular function and healthy growth.

Homeostatic processes use control mechanisms to detect and correct changes in the body's internal environment. These mechanisms include:

Regulation by the Kidneys

The kidneys regulate water, salt, and pH balance in the blood, particularly in the distal tubules and collecting ducts of urinary tubules.

For example, when the body loses water through sweating (e.g., during exercise), the hypothalamus detects changes in the blood's osmotic pressure. This triggers the pituitary gland to release more anti-diuretic hormone (ADH), making kidney tubule walls more permeable to water. Water is then reabsorbed into the blood, conserving it and preventing cell damage due to dehydration.

Maintaining Acid-Base Balance

The kidneys maintain the acid-base balance by regulating the excretion of acids and bases:

• When body fluids become too acidic, the kidneys excrete more acids into the urine while conserving bases.
• If the fluids become too basic, the kidneys excrete more bases in the urine to restore balance.

Kidney Complications

Kidney diseases impair the body's ability to remove metabolic waste, leading to conditions such as:

1. Nephritis: Inflammation of blood vessels in the nephron, often caused by bacteria, leading to leakage of essential substances or kidney failure.
2. Kidney Stones: Hard mineral masses formed in the urinary tubules, caused by low water intake and high salt consumption, obstructing urine flow.
3. Diuresis: Excessive production of dilute urine due to the inability of kidney tubules to reabsorb water, common in diabetes insipidus.
4. Dropsy (Oedema): Water retention in the body tissues, leading to swelling of body parts.

Consequences of Kidney Diseases

• High blood pressure
• Excessive urination, resulting in weight loss
• Abdominal pain and bloody urine from kidney stones
• Presence of protein and blood cells in urine (nephritis)

Dialysis

Dialysis is a medical procedure used to remove waste from the blood when kidneys fail. Blood is passed through dialysis tubing, which has small pores that allow substances like salts and urea to pass into a surrounding fluid bath. Larger molecules like proteins remain in the tubing, cleansing the blood effectively.

The Liver

The liver, the largest gland in the body, is dark-red, spongy, and lobed. It overlaps the stomach and connects to the duodenum via the bile duct.

Functions of the Liver

1. Regulating Blood Sugar: Converts excess glucose to glycogen for storage (via insulin) and converts glycogen back to glucose (via glucagon) to maintain a stable blood sugar level.
2. Detoxification: Neutralizes harmful substances like drugs and bacterial by-products, converting them into excretable forms.
3. Lipid Regulation: Converts lipids to glucose or oxidizes them for energy.
4. Protein Manufacture: Produces blood proteins like fibrinogen and prothrombin for blood clotting.
5. Bile Production: Produces bile for fat emulsification, stored in the gall bladder.

Liver Complications

1. Diabetes Mellitus: Failure to convert excess blood glucose to glycogen due to lack of insulin.
2. Hepatitis: Inflammation of the liver caused by infections.
3. Gallstones: Hardened masses in the bile duct blocking bile flow.
4. Liver Cancer: Abnormal growth of liver cells.
5. Jaundice: Yellowing of the skin due to excess bilirubin, often caused by liver damage or bile duct blockage.
6. Cirrhosis: Replacement of liver cells with fibrous tissue, often caused by alcohol abuse or hepatitis.

Effects of Liver Disease

• General weakness
• Jaundice
• High blood pressure
• Fever

Remedies

1. Rest
2. Removing the cause of the disease (e.g., gallstones)
3. Liver transplant in severe cases

The Skin

The skin consists of two main layers:

1. Epidermis: The outer layer composed of:
   • Cornified Layer: Made of dead cells and keratin, providing a tough, waterproof barrier.
   • Granular Layer: Produces new cells that harden to form the cornified layer.
   • Malpighian Layer: Contains melanin for skin color and produces keratin.
2. Dermis: The inner layer containing blood capillaries, hair follicles, sweat glands, sebaceous glands, and nerve endings.

Functions of the Skin

1. Protection from dehydration, microbes, and chemicals.
2. Temperature regulation through sweating and blood flow control.
3. Sensitivity to stimuli like heat, cold, and touch.
4. Excretion of excess water and waste like urea.
5. Production of vitamin D from sunlight.

Temperature Regulation

The skin helps maintain a constant body temperature (37°C in humans) by:

• When Hot:
  • Vasodilation: Blood vessels widen to release heat.
  • Sweating: Evaporation of sweat cools the body.
  • Flattening hairs to reduce insulation.
• When Cold:
  • Vasoconstriction: Blood vessels narrow to retain heat.
  • Shivering to generate heat.
  • Raising hairs to trap air as insulation.

Skin Care

1. Regular cleaning
2. Exposure to fresh air
3. Wearing clean clothes
4. Avoiding harmful chemicals