Kidney
Table of Contents
Definition
The kidney is the organ of body which helps to produce urine. Ureters transport the urine to urinary bladder. The urinary bladder stores urine until it is voided (emptied). Urine is voided from bladder through urethra .
Structure of Kidney
Kidney is a bean shape, reddish brown and retro peritoneal organ of body.
Length : 10 cm - 12 cm
Breath: 5 cm -7 cm
Thickness : 2 cm -3 cm
Weight : 120 g – 170 g
There is a depression on medial border of kidney called hilum, through which renal artery, renal veins, nerves and ureter pass.
Layers of kidney
- 1. Outer cortex
Cortex is dark and granular in appearance. It contains renal corpuscles and convoluted tubules. At intervals, cortical tissue penetrates medulla in form of columns, which are called renal columns or columns of Bertini.
- 2. Inner medulla
The medulla contains tubular and vascular structures arranged in parallel radial lines. Medullary mass is divided into 8 to 18 medullary or Malpighian pyramid. A broad base of each pyramid is in contact with the cortex and the apex projects into a minor calyx.
- 3. Renal sinus
Renal sinus consists of the following structures:
i. Upper expanded part of ureter called renal pelvis
ii. Subdivisions of the pelvis: 2 or 3 major calyces and about 8 minor calyces.
iii. Branches of nerves, arteries, and tributaries of veins
iv. Loose connective tissues and fat.
Blood vessels in the kidney
In adults, during resting conditions both kidneys receive 1,300 mL of blood per minute or about 26% of the cardiac output.
Renal blood vessels :
- Renal Artery
- Segmental Artery
- Interlobar Artery
- Arcuate Artery
- Interlobular Artery
- Afferent Arteriole
- Glomerular Capillaries
- Efferent Arteriole
- Peritubular Capillaries and Vasa Recta
- Venous System
Functions of Kidney
In Homeostasis
The primary function of kidneys is homeostasis. The formation of urine accomplishes it. During the
formation of urine, kidneys regulate various activities in body, which are concerned with homeostasis such as:
i. Excretion of Waste Products
Kidneys excrete unwanted waste products, which are formed during metabolic activities:
a. Urea (end product of amino acid metabolism)
b. Uric acid (end product of nucleic acids metabolism)
c. Creatinine (end product of metabolism in muscle)
d. Bilirubin (end product of hemoglobin degradation)
e. Products of metabolism of other substances.
Kidneys also excrete harmful foreign chemical substances such as toxins, drugs, heavy metal
pesticides, etc.
ii. Maintenance of Water Balance
Kidneys maintain water balance in body by conserving water when it is decreased and excreting water when it is excess in the body.
iii. Maintenance of Electrolyte Balance
Maintenance of electrolyte balance, especially the sodium is in relation to water balance. Kidneys retain sodium if osmolarity of body water decreases and eliminate sodium when osmolarity increases.
iv. Maintenance of Acid-Base Balance
The pH of blood and body fluids should be maintained within a narrow range for healthy living. It is
achieved by the function of the kidneys.
Hemopoietic function
Kidneys stimulate production of erythrocytes by secreting erythropoietin. Erythropoietin is the important stimulating factor for erythropoiesis. Kidney also secretes another factors called thrombopoietin, which stimulates the production of thrombocytes
Endocrine function
Kidneys secrete many hormonal substances in addition to the erythropoietin and thrombopoietin
Regulation of arterial blood pressure
By two ways
i. By regulating volume of extracellular fluid
ii. Through renin-angiotensin mechanism.
Regulation of blood calcium level
Kidneys play role in regulation of blood calcium level by activating 1,25 dihydroxycholecalciferol into vitamin D.
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