Structure of The Kidney
The mammalian kidney is a reddish-brown, bean-shaped organ located at the posterior end of the abdomen. The right kidney is slightly lower than the left. On cutting a kidney longitudinally, two distinct regions are observed: an outer cortex and an inner medulla. Narrow tubules called urinary tubules (nephrons) pass through these two regions. The tubules open at the tips of triangular-shaped masses of tissues called pyramids, which in turn open into a funnel-shaped cavity called the pelvis. The kidney has many tiny capillaries, which are branches of the renal artery and renal vein. The pelvis continues as the ureter, a long narrow tube connecting the kidney to the urinary bladder.
Table of Contents
Functions of The Kidney
The kidney serves as the chief osmoregulator and excretory organ in mammals, performing the following functions:
- Removal of toxic wastes and harmful substances.
- Production of heat during cold conditions.
- Excretion of nitrogenous wastes like urea.
- Regulation of water levels in the body.
- Assistance in regulating the body’s pH.
- Maintenance of salt or ion balance in the body.
The first three functions are related to excretion, while the last three are osmoregulatory functions of the kidney.
Kidney As An Osmoregulator
The kidney acts as an osmoregulator by maintaining the water, salt, and pH balance of the blood, primarily in the distal tubules and collecting ducts of the urinary tubules.
- WATER BALANCE:
When the body is dehydrated, the osmotic pressure of the blood increases. Osmoreceptors in the hypothalamus detect these changes and stimulate the pituitary gland to secrete more antidiuretic hormone (ADH). ADH makes the walls of the urinary tubules more permeable, leading to increased water reabsorption into the blood. This results in less water being lost from the body, and concentrated urine is produced.
When the body is hydrated, the osmotic pressure of the blood is lowered, resulting in the secretion of less ADH. Consequently, the walls of the kidney become less permeable, and more water is lost from the body as dilute urine.
- CONTROL OF BLOOD SODIUM IONS AND pH LEVEL:
The concentration of sodium ions in the blood is regulated by excreting the excess or reabsorbing more, which is controlled by the hormone aldosterone.
The blood pH of 7.4 is maintained by excreting hydrogen ions when the pH becomes acidic and excreting hydrogen carbonate ions when it becomes alkaline.
Kidney Diseases, Effects, And Remedies
- Nephritis: Inflammation of the blood vessels (glomeruli) in Bowman’s capsule of the nephron caused by bacteria (streptococci). This inflammation leads to increased permeability of the blood vessels, resulting in the leakage of useful materials from the blood into the glomerular filtrate. Inflamed blood vessels can also become blocked, leading to kidney failure.
- Diuresis: A condition where 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.
- Kidney stones: Stony masses of minerals and organic matter formed in the urinary tubules. Low water intake combined with high salt intake predisposes individuals to this disease, causing the crystallization of mineral salts and obstructing the free flow of urine.
- Dropsy (edema): A disease condition in which the cells of Bowman’s capsule are unable to absorb water from the blood in the urinary tubules. This causes water retention in the blood or tissues, resulting in swelling of certain body parts.
Effects of Kidney Diseases
- Presence of proteins and blood cells in urine (nephritis).
- Swollen face and ankles, constant weakness, and sluggishness (edema).
- Excessive urination leading to weight loss (diuresis).
- Abdominal pain, high blood pressure, and bloody urine (kidney stones).
- General body pains and fever (any renal disease).
- High blood pressure, dizziness, and fatigue.
- Use of drugs such as antibiotics (nephritis) and diuretics (edema).
- Kidney transplant (diuresis, nephritis).
- Dialysis: Utilizing a dialysis machine (artificial kidney) to filter waste out of the patient’s blood (nephritis).
- Reduction in water intake (edema).
- Increasing water intake and avoiding excessive consumption of calcium-rich foods (kidney stones).
- Surgical operation called nephrectomy (kidney stones).