Kidney: Overview of The Renal Physiology
Kidney: Overview of The Renal Physiology
Kidney: Overview of The Renal Physiology
The kidney is an excretory organ that forms urine and excretes harmful foreign chemical substances such as toxins,
drugs, heavy metals, pesticides, etc.
Other physiological roles of the kidneys include:
1. Role in homeostasis:
a. Maintenance of water balance: water is being conserved when it is decreased in the body and excreted
when it’s in excess in the body
b. Maintenance of electrolyte balance: the kidneys retain sodium if the osmolarity of body water decreases and
eliminate sodium when osmolarity increases.
c. Maintenance of Acid-Base balance
2. Hemopoietic function: kidneys stimulate the production of erythrocytes by secreting erythropoietin.
3. Endocrine function: the kidneys secrete hormonal substances that function in the endocrine system, these inlude:
• Renin
• 1.25-dihydroxycholecalciferol (calcitriol)
• Prostaglandins
• Thrombopoietin
4. Regulation of blood pressure: the kidneys regulate arterial blood pressure by two ways:
• By regulating the volume of extracellular fluid
• Through RAAS mechanism
5. Regulation of blood calcium level
Kidneys regulate blood calcium level by activating 1,25-dihydroxycholecalciferol into Vitamin D.
2. Tubular reabsorption.
As filtered fluid flows through the renal tubules and through the collecting ducts, tubule cells reabsorb about 99% of
the filtered water and many useful solutes.
The water and solutes return to the blood as it flows through the peritubular capillaries and vasa recta.
3. Tubular secretion. As filtered fluid flows through the renal tubules and collecting ducts, the renal tubule and
duct cells secrete other materials, such as wastes, drugs, and excess ions, into the fluid.
Solutes and the fluid that drain into the minor and major calyces and renal pelvis constitute urine and are excreted.
Relation of a nephron’s structure to its three basic functions: glomerular filtration, tubular reabsorption, and
tubular secretion.
By filtering, reabsorbing, and secreting, nephrons help maintain homeostasis of the blood’s volume and composition.
GLOMERULAR FILTRATION
The fluid that enters the capsular space is called the glomerular filtrate. The fraction of blood plasma in the afferent
arterioles of the kidneys that becomes glomerular filtrate is the filtration fraction.
On average, the daily volume of glomerular filtrate in adults is 150 liters in females and 180 liters in males. More than
99% of the glomerular filtrate returns to the bloodstream via tubular reabsorption, so only 1–2 liters (about 1–2 qt) is
excreted as urine.