LESSON OBJECTIVES
At the end of the lesson, you should be able to;
1. Explain homeostasis
2. Describe the structure and functions of Kidney and liver
3. Name some Kidney and liver diseases and explain their symptoms and effects
4. Identify the treatment of the mentioned kidney and liver diseases.

LESSON CONTENT

Homeostasis is the process by which a fairly constant internal environment is maintained in an organism. The internal environment of an organism is made up of the body fluid such as blood, lymph and tissue fluid. For efficient functions of body cells and healthy growth, a living organism must be able to adjust to any change in the physical and chemical conditions of its body fluids. These conditions include temperature, pH, osmotic pressure, concentrations of dissolved substances and mineral ions.

Mechanism of Homeostasis

Homeostatic processes are control mechanisms which are used to detect and adjust to changes in the internal environment of the organism. These mechanisms usually include:

Homeostasis is a property of a human biological system where the self-regulating process tends to maintain the balance for the survival. The regulation takes place in a defined internal environment.

Sensory detectors which recognize a change in a given condition and stimulate the relevant body parts.

Effectors organs or glands which react and restore the normal state.

Structures of Homeostasis

Osmoregulation (homeostasis) in unicellular organisms is ensured by the use of contractile vacuole. The main organs involved in homeostasis in multicellular organisms include; kidney, liver, skin, ductless glands (hormones) and the brain which has the overall control of the homeostatic process in the body.

The mammalian kidney is a bean-shaped, reddish-brown organ located in the posterior end of the abdomen. The right kidney is slightly lower in the body than the left. Cutting a kidney longitudinally, two distinct regions are observed; an outer cortex and an inner medulla. Several narrow tubules called urinary tubules (nephrons) pass through the two regions stated above. The tubules open at the tips of triangular-shaped masses of tissues called pyramids. The pyramids open into a funnel-shaped cavity called the pelvis. The kidney has many tiny capillaries which are branches of the renal artery and the renal vein. The pelvis continues as the ureter, a long narrow tube connecting the kidney to the urinary bladder.

Functions of the kidney

The kidney serves as the chief osmoregulator and excretory organ in the body of mammals.

It removes toxic wastes and harmful substances.

2. It produces heat during cold.

3. It excretes nitrogenous wastes like urea.

4. It regulates the water level in the body.

5. It assists to regulate the pH of the body.

6. It maintains salt or ion-balance in the body.

The first three are excretory functions while the last three are osmoregulatory functions of the kidney

Kidney as an osmoregulator

The kidney is an osmoregulator by maintaining the water, salt and pH balance of the blood and this occurs in the distal tubules and collecting ducts of urinary tubules.

The normal pH of the blood is 7.4. When the pH becomes acidic, the hydrogen ions are excreted and when it becomes alkaline, the hydrogen carbonate ions are excreted.

Water balance:

When the body is dehydrated (little water in the body) which results from drinking a small quantity of water or losing water through sweat on a hot day, the osmotic pressure of the blood increased. The osmoreceptors in the hypothalamus detect the changes and stimulate the pituitary gland to secrete more antidiuretic hormone (ADH) which makes the walls of the urinary tubules more permeable so that more water is reabsorbed into the blood; therefore less water is lost from the body as concentrated urine.

When the body is hydrated (too much water in the body) which results from drinking a large quantity of water or on cold days when we sweat less, the osmotic pressure of the blood is lowered and less ADH is secreted and the wall of the kidney becomes less permeable and more water is lost from the body as dilute urine.

Control of blood sodium ions and pH levels:

When the concentration of sodium ion in the blood is higher than normal, the excess is excreted. If it is lower, then more sodium ions are reabsorbed. This process is regulated by inhibiting or stimulating the secretion of the hormone aldosterone.

Kidney (renal) diseases, effects and remedy

Renal diseases

1. Nephritis: This is the inflammation of the blood vessels (glomeruli) in Bowman’s capsule of nephron caused by bacteria (streptococci). The blood vessels become porous and useful materials from the blood are leaked into the glomerular filtrate. Inflamed blood vessels can also be blocked as a result of the accumulation of dead cells which can lead to kidney failure.

2. Diuresis: This is a condition in which large quantities of dilute urine are produced because the cells of the kidney tubules are not reabsorbing water from the glomerular filtrate. Diuresis is common in patients suffering from diabetes insipidus.

Regulation of Internal Environment 2

This lesson includes:

Lesson Content

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Regulation of Internal Environment 3

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