kidney anatomy and physiology

The two kidneys are bean-shaped reddish-brown organs located on the abdominal wall outside the peritoneal cavity posteriorly, the two kidneys are on either side of the vertebral column at the level of the T12 to L1 vertebrae. The left kidney is slightly higher than the right kidney as a result of the large size of the right liver lobe.

The internal Gross anatomy of kidneys is composed of:

1. Renal hilum and renal sinus
2. Renal medulla
3. Renal pelvis
4. Renal cortex

The 5 Functions of the kidneys

The kidneys perform their most important functions by filtering the plasma and extracting substances from the filtrate at variable rates, depending on the body's needs. eventually, the kidneys "clear" unnecessary substances from the filtrate (and thus from the blood) by excreting them in the urine while adding substances that are required back to the blood. kidneys perform several vital functions in addition to the production of urine. The kidneys have many essential homeostatic functions, including the following:

1. Role in homeostasis

kidneys are the homeostatic control center. The primary function of the kidney is homeostasis. It is achieved by the production of urine. During the production of urine, the kidneys control different activities in the body that is connected with homeostasis, such as:

• Excretion of metabolic waste products and foreign chemicals

  Kidneys excrete the unwanted waste products, which are formed during metabolic activities:

  • Urea (the end product of amino acid metabolism)
  • Uric acid (the end product of nucleic acid metabolism)
  • Creatinine (the end product of metabolism in muscles)
  • Bilirubin (the end product of hemoglobin degradation)
  • Metabolites of various hormones

  The kidneys also eliminate most toxins and other foreign substances that are either produced by the body or ingested, such as pesticides, drugs, heavy metals, and food additives. The kidneys eliminate these substances from the body at a rate that matches their production.

• Regulation of water and electrolyte balances

  The excretion of water and electrolytes must balance the intake precisely for the preservation of homeostasis. If the intake exceeds the excretion, the amount of the substance in the body will increase. If the intake is smaller than the excretion, the amount of this material in the body will decrease. The intake of water and many electrolytes is primarily regulated by the eating and drinking habits of a person, causing the kidneys to change their excretion rates to balance the intake of different substances. The kidneys perform this role by functioning in combination with the cardiovascular, endocrine, and central nervous system components. Kidneys preserve the balance of the water in the body by storing the water when it is reduced and by excreting the water when there is excess in the body. This is an important process for homeostasis. Maintenance of electrolyte balance, particularly sodium, is in relation to water balance. Kidneys retain sodium as the osmolarity of body water decreases and eliminate sodium as osmolarity increases.

• Regulation of acid-base balance

  The kidneys contribute to acid-base regulation, the pH of blood and body fluids should be preserved within a limited range for healthy living. The body is under constant threat to the development of acidosis due to the production of a lot of acids during metabolic activities. However, it is prevented by kidneys, along with the lungs, liver, and body fluid buffers, by excreting acids and by regulating the body fluid buffer stores. Among these organs, the kidneys are the only means of eliminating certain types of acids from the body, such as sulfuric acid and phosphoric acid, generated by the metabolism of proteins.

2. HEMOPOIETIC FUNCTION: Regulation of Erythrocyte Production

The kidneys secrete erythropoietin, which induces the development of red blood cells by hematopoietic stem cells in the bone marrow. Hypoxia is an essential stimulus for the secretion of erythropoietin by the kidneys. Usually, the kidneys account for almost all of the erythropoietin secreted into the circulation. Serious anemia occurs as a result of reduced erythropoietin production in people with extreme kidney failure or who have had their kidneys removed and have been placed on hemodialysis. The kidney also secretes another element called thrombopoietin that stimulates thrombocyte production.

3. ENDOCRINE FUNCTION (Hormonal function)

Kidneys secrete many hormonal substances in addition to erythropoietin and thrombopoietin. Hormones secreted by kidneys:

1. Erythropoietin
2. Thrombopoietin
3. Renin: Renin stimulates the renin-angiotensin-aldosterone system that regulates blood pressure and the balance of sodium and potassium.
4. 1,25-dihydroxycholecalciferol (calcitriol): The kidneys manufacture the active form of vitamin D, 1,25-dihydroxyvitamin D3 (calcitriol) by hydroxylating the vitamin at the "Number 1" position. Calcitriol is essential for normal calcium deposition in the bone and for calcium reabsorption in the gastrointestinal tract. Calcitriol plays a significant function in the regulation of calcium and phosphate (influences calcium balance).
5. Prostaglandins.

4. Regulation of blood pressure (Regulation of Arterial Pressure)

The kidneys play a significant role in the long-term regulation of blood pressure by two means:

1. By regulating the volume of extracellular fluid (excretion of varying quantities of sodium and water)
2. Renin-angiotensin mechanism: The kidneys also contribute to the control of short-term arterial pressure by secreting hormones and vasoactive factors or substances (e.g. renin) that lead to the formation of vasoactive products ( e.g. angiotensin II) that induce vasoconstriction and increase the secretion of aldosterone, all of which help to increase blood pressure.

5. Gluconeogenesis (Glucose Synthesis)

The kidneys synthesize glucose from amino acids and other precursors during prolonged fasting, in a process referred to as gluconeogenesis. The ability of the kidneys to add glucose to the blood during prolonged periods of fasting rivals that of the liver. With chronic kidney disease or acute kidney failure, these homeostatic functions are disrupted and severe abnormalities of body fluid volumes and composition rapidly occur. With complete renal failure, enough potassium, acids, fluids and other substances accumulate in the body to cause death within a few days, unless therapeutic procedures such as hemodialysis are undertaken to restore, at least partially, body fluid and electrolyte balances.