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  The Mammalian kidney, Biology tutorial

Introduction:

Kidneys are the two reddish brown; bean-shaped organs situated in the dorsal portion of the abdominal cavity on either side of the vertebral column. The kidneys (similar to the liver) encompass quite a few functions comprising homeostasis! It is accountable for the elimination of nitrogenous waste, control of quantity of water, salts (that is, sodium, potassium and chloride ions), acids and osmoregulatory functions. Irrespective of such functions, the kidneys can be damaged through poisons, diseases and physical injuries.

Structure of the Mammalian kidney:

There are two bean-shaped kidneys, one on each side of the abdomen. Each comprises 1 to 2 million nephrones. The kidneys are on the body wall of the lumbar (that is, upper) area of the abdomen and are held through fatty tissue. Above each and every kidney is the adrenal gland. Kidneys are joined to the urinary bladder through the ureters. Blood supply is via the renal artery. The reddish brown kidneys are enclosed by a transparent, tough membrane termed as the capsule. The ureters occur from the depression of the kidneys termed as the hilum. A longitudinal part exhibits the outer cortex, internal medulla and triangular-shaped tissue termed as pyramid, which opens to a broad cavity termed as the pelvis.

Excretion is taken out in the Malpighian body that is found in the cortex and comprises of Bowman's capsule and the glomerulus.  Blood is brought into glomerulus which includes water, urea, mineral salts, nitrogenous waste, sugar and plasma solutes. The diameter of renal artery entering the glomerulus reduces thus rising pressure in the glomerulus. The pressure forces out urea, other nitrogenous material and water; salts are filtered out to capsular as glomerular filtrate apart from the blood cells and proteins, whose diameters are too big to filter throughout. This procedure of filtration under pressure is termed as ultra-filtration.

The filtrate moves via the proximal convoluted tubule where water and glucose are reabsorbed, whereas only water is reabsorbed in the loop of the Henle. The filtrate becomes highly concentrated as salts are reabsorbed through the distal convoluted tubule.

Apart from the function as excretory organs; the kidneys as well perform the function of Osmoregulation. They control the osmotic concentration of the blood plasma and in doing this; maintain the environment around each and every cell fairly constant. This is very significant as fluctuations in osmotic concentration will lead to the serious effects. If the concentration of salts in the blood is more than that of the cells then water is drawn from the latter, leading to shrinkage, which might outcome in irreversible damage. While, if the osmotic concentration of the cells is more, then water is inhibited from the blood leading to abnormal welling of the cells. The concentration of the blood in the osmotic process is determined through the quantities of sodium chloride, sugar, mineral salts, amino acids and some other solutes it might have. If the concentration of such solutes is high, then the kidneys decrease their amount by eliminating some of them. If the concentrations are low, the kidneys would take away more water from the cells thus increasing the concentration of the solutes of their normal levels. The kidneys as well sustain the acid-base balance of the body. They excrete acid to prevent the loss of base.

Functions of the Kidney:

1) Excretion through filtering out waste products like urea, water and salt whose surplus would be poisonous to cells.

2) Manufacture of adrenaline via the agency of the adrenal glands.

3) Osmoregulation is taken out by the kidneys via the re-absorption of glucose, water and salts, based on the body prerequisite for them.

4) Maintaining the pH of the blood fluid constant.

5) Regulation of the composition of the blood that based on the blood solute concentration; that in turn influences the re-absorptive actions of the kidney via hormones.

6) Generation of heat on a cold day by raising its activity.

7) Removal of drugs, toxins and other injurious substances.

Diseases of the Kidney:

1) Kidney Stones:

There are organic matter and crystallized mineral salts in urine. Kidney stones are made when salt ingestion is high or due to low water intake; or when urine is acidic or alkaline. The salts crystallize is formed to store. The dimension of kidney stores differs from very small and similar to grains to big ones which might block the flow of urine. If urine flow is blocked, pressure rising causing severe pain and harm of the kidney tubules.

2) Glomerular Nephritis:

This situation is caused through bacterial (or streptococcal) infection of the kidney, whereby the gromeruli become swollen and the porosity of its membranes rises. If this takes place, proteins and red blood cells leak to the glomerullar filtrate. White blood cells and dead tissue cells combined in the inflamed glomeruli, in several cases, it obstructs the blood flow and even fill the Bowman's capsule, thus prevent the tubules from getting adequate nourishment from the decreased blood supply. In certain extreme cases the glomeruli might become permanently blocked and several tubules damaged. At last, the kidney might become fully damaged leading to kidney failure.

3) Oedema:

As well termed as dropsy, is caused by the accumulation of intercellular fluid in tissues, causing the affected portion of the body to rise in volume. Outward sign of oedema comprise puffy or swollen ankles, swollen face and elbows.

Decreased plasma osmotic pressure in some kidneys might as well cause oedema that is basically related with the excretion of high protein in urine.

4) Diuresis:

This condition comprises the production of huge amount of dilute urine after drinking big quantity of water. This is termed as water diuresis and might last for two to three hours. In diabetes insipidus, the production of anti-diuretic hormone (ADH) becomes decreased or stops resultant in diuresis, rising daily urine production to the abnormal level of 5 to 20 liters. This as well outcomes to drinking of abundance water through such patient.

In diabetes, mellitus excretion of glucose in urine is escorted through excretion of water, due to the osmosis.

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