HOMEOSTASIS

Homeostasis is defined as the maintenance of a fairly constant environment in an organism. All living things must be able to maintain a steady internal environment. Body fluid such as blood, lymph and tissue fluids make up the internal environment of the organism. A living organism must be able to adjust to any change in the physical and chemical conditions which are body temperature, pH, osmotic pressure, concentration of dissolved substance in the body, substance such as carbon dioxide, oxygen, urea, food substance like glucose, amino acid and mineral ions such as sodium, potassium, chloride.

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Osmoregulation In Unicellular Organisms

Unicellular organism such as Amoeba and Paramecium possesses contractile vacuole which enable them to carry out osmoregulation. The cell content of these animal is hypertonic to the external medium hence water enter them by osmosis into the cytoplasm and then into the contractile vacuole. In order to prevent the cell from being over turgid and bursting, the contractile vacuole discharge its content from time to time thereby maintaining water balance within the organism.
Parts Involved In Homeostasis In Complex Organisms
• Kidney • Liver • Skin • Hormones • Brain
In this post and the next three or two post, I'll be talking exclusively about the kidney and liver.

The Kidney
The kidney is the two-bean shaped organ located both on the left and right side of a vertebrate. The basic structural and functional unit of the kidney is the Nephron. It has various functions, like osmoregulation, excretion and maintenance of acid-base balance.

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Osmoregulation

Osmoregulation is defined as the process whereby the organism regulate the balance between salt and water in his body fluid. The body does not have room for excess or shortage of water or salt. Hence, there is a need to always maintain the level in the body.

Osmoregulation In Man

The kidney carry out osmoregulation in man when the osmotic concentration of blood is higher than that of the cell content by means of sugar, mineral salt, amino acids and other plasma solute. The kidney extracts the this substance from the blood or body cells and absorbs more water when there is a small quantity in the body cell, thus decreasing the osmotic concentration of the blood and the kidney extracts more water than usual by the action of the Anti-diuretic hormone (ADH). More concentrated urine is produced thus keeping the osmotic concentration in man especially. Less of water is also carried out through sweating by skin and expiration and exhalation by the lungs.

Excretion

The kidney are also involved in the removal of metabolic waste products from the body in form of urine. The process involved occurs in three (3) phases which are • Ultrafiltration • Selective Reabsorption • Hormonal Secretion.

Blood is brought up to the kidney by the renal artery, as it circulates through the capillaries or glomerulus of Bowman's capsule. Water, urea, nitrogenous compounds, mineral salts, sugar, glucose and plasma solute are filtered into the capsule. This process of filtering materials from the glomerulus, into the Bowman's capsule is called Ultrafiltration. The fluid in the capsule or glomerulus filtrates now flows down to the tubule at the proximal convoluted tubule and Henle's loop. Some water, sugar, amino acids and salt which are useful to the body are reabsorbed into the blood capillaries against concentration gradient by active transport. This process of reabsorbing useful material back into the blood is called Selective Reabsorption. The fluid in the tubule then becomes more concentrated as it flows through the distal convoluted tubule where more water is reabsorbed by the actions of Anti-diuretic hormone and urine is finally formed. The urine gradually trickles into renal pelvis and then dispersed by peristalsis through the ureter into the urinary bladder. When the bladder is full, it contracts, discharging the urine out of the body through the urethra.

Maintenance Of Acid-Base Balance

The kidney helps to maintain acid-base balance in the body. When the body fluid becomes acidic, more acid is excreted by the kidney with the urine. Excessive loss of bases is prevented at the Same time by the kidney. If the concentration of a base becomes higher, more salts will be excreted with the urine.

Conditions Affecting The Functions Of Kidney
These conditions are environmental temperature, drugs, habitat and diseases.

• Environmental Temperature : Temperature affects the function of the kidney. In cold days, there is every tendency to urinate more than we do during hot days. On hot days, much water is lost by sweating but on cold days, very little or no water is lost by sweating, hence, more of the excess water, salt and other waste products forms in the body.

• Drugs : Most drugs taken by human being do affect the functions of the kidney, among the essential drug which affects the kidney are diuretics. These are usually taken to get rid of excess water from the body.

• Habitats : Habitat especially aquatic habitat do not have some effects on the functioning of the kidney. In fresh water habitats, animals live in an environment which is hypotonic to their body fluid. As a result, fresh water animals have constant inflow of water into their body. However, they are able to solve this problem of excessive intake of water by excreting salt and other nitrogenous waste through the urine, thereby maintaining a normal salt and water balance in the body.
In marine habitats, the animals lives in an environment which is hypertonic to their body fluid. This animals are able to solve this excessive loss of water by either absorbing urea into the body or drinking plenty of water so that the concentration of the blood is raised.

Thank you for reading through, in my next post, I will be talking about the diseases of kidney, their effects and remedies.
Upvotes and comments are appreciated.

References
The Kidney
Kidneys: Facts, Function & Diseases