What is the structure and function of the human Kidney?
Describe the structure and function of Kidney?
In this articles we will discuss about the Kidney:-(1) Description & Location, (2) Structure, (3) Histology, (4) Function.
(1) General Description and location of the Kidney
(2) External Structure of the kidney
(3) Internal Structure of the kidney
(4) Histology of the Kidney
(5) Structure of Nephrons
(6) Parts of Nephrons
(7) Bowman’s & Glomerular Capsule
(8) Renal Blood supply
(9) Function of the Kidney
Description & location of the Kidney:-
The kidneys of man are the chief organ of excretion. There are two dark-red, bean-shaped, metanephric kidneys attached to the dorsal wall of the peritoneal cavity outside the coelom They are asymmetrical in position i.e., the right kidney is present a little behind the left one (due to the presence of liver towards the right side). Each kidney is about 11 cms in length, 6 cms wide and 4 cms thick and enclosed in a capsule of connective tissue. It weighs nearly 150 gms in adult male and 135 gms in adult female. The outer surface is convex and the inner surface is concave bearing a depression called hilus from which the ureter arises. The ureters are narrow tubes which proceed back and open into the urinary bladder. Blood containing excretory matter is brought to the kidneys by means of a pair of renal arteries and purified blood is drained away by a pair of renal veins. At its anterior end, each kidney bears a small triangular endocrine gland called adrenal gland.
Excretion may be defined as the separation and elimination of the nitrogenous metabolic waste from the body.
The waste eliminated are called excretory products. The chief excretory organ in man is a pair of kidney. They are metanephros. The kidney are dark red and Beam shaped.
Adult man each kidney weight about 140 gm and measures about 10-13cm length 6cm breath and 3.cm in thickness.
There are a pair of kidneys at the back of abdominal cavity one and each side of the vertebral column in the lumar region.
The right kidney is placed slightly lower then the left due to the presence of liver which occupies considerable space on the right side.
External structure of Kidney:-
Each kidney is covered by thin fibrous connection tissue covering called renal capsule. Which protect it from infection and injuries around the renal capsule there is a layer of fat called adipose capsule the outer boarder kidney of capsule is convex while the inner shape is concave which faces the invertible column. These inner surface has deep natch called hilus of slender muscular tube called ureter leaves the hilus curve and run backwards to join the urinary bladder.
The renal artery and renal vein passed in and out of the kidney at the hilus it’s anterodorsal boarder is covered by the adrenal glands. Which is an endocrine gland.
Internal structure of Kidney:-
A vertical section of human kidney shows two distinct regions an outer cortex and an inner medulla.
The medulla is devided into 15-16core shape pyramid like bodies called renal pyramids which contains papillae.
Internal Structure of Kidney.
To study the anatomy and histology of the kidney the outer capsule is removed and a longitudinal section is taken. In section, the kidney is differentiated into an cortex and an inner medulla. The medulla is made of several conical lobes called pyramids which contains papilla. The cortex extend inward between the pyramids as renal columns of Bertini. The pyramids open into small channels known as calyces (Sing, calyx) which collectively open into the pelvis or renal sinus of ureter. The calyces can be divided into major and minor calcyes. The minor calyces open into the major calyx.The kidney is made up of a mass of microscopic tubules fabout one million in number per kidney) called uriniferous tubules or nephrons . These tubules are the structural and functional units of the kidney.
The average number of these calyces is 10.The calyces can be devided into measures calyces and minor calyces.
The kidney is the made up a mass of microscope tubules called nephrons.
Histology of the Kidney:-
The kidney is composed of large number of coiled uriniferous tubules, bound together by connective tissue, blood vessels, lymphatic vessels and nerves. The uriniferous tubules are joined with the collecting tubules which carry urine to the terminal duct of Bellini. It opens into minor calyx at the apex of renal papilla. Each renal papilla has 10 to 40 minute openings of ducts of Bellini.
Structure of Nephrons:-
Nephrons is the structural and functional unit of kidney.
Each kidney posses about 1million Nephrons. Each nephron is made up to 2main parts :
(a) Malpighian corpuscles
(b) Renal tubules
(a) Malpighian capsules:-
These are most visible in the cortex. Each malpighian corpuscles is consists of following parts :
(i) Bowman’s capsule
It is blind expanded end of renal tubules. It’s cup shaped double wall cavity.
It is branch of capillaries blood vessels held together by little connective tissue.
The different attical enter into the up shaped cavity of the bowman capsule and remits to emerge as different atrial.
(b) Renal Tubule.
Each renal tubule is about 3.0 cms long and 20-60 microns wide and consists of the following regions :
(i) Proximal Convoluted Tubule (PCT):
It joins the Bowman’s capsule by a short narrow neck. It is about 14 mm long and 60 um wide. The inner space is about 15-25 μm wide. It is a much coiled structure. It is lined with cuboidal epithelial cells with free villi, forming brush border. Each microvillus is about 1 mm long. The absorptive surface increases due to the presence of these villi. These cells absorb about two thirds of water of glomerular filtrate, all glucose and a part of sodium chloride and phosphates.
The terminal part of PCT is slightly spiral (spiral tubule) and runs towards medulla.
(ii) Descending Limb:
The descending limb enters into the medulla. The distal portion of descending limb is narrow and is more permeable to H₂O than solutes.
(iii) Loop of Henle:
It is a ‘U’-shaped loop, present between descending and ascending limbs. It is narrower, thin-walled and is present in the medulla.
(iv) Ascending Limb:
It is narrow, thin walled tube. It is wider at its distal region and joins with distal convoluted tubule.
(V)Distal Convoluted Tubule (DCT).
This portion is present in the cortex. It has an average length of 4.6 to 5.2 mm and diameter of about 20 to 50 m. It is lined with cubical epithelial cells without any brush border.
The part of the distal convoluted tubule joins with the broad collecting tubules by junctional tubules. It contains juxtaglomerular apparatus.
(Vi) Collecting Tubule or Straight Tubule:
The distal convoluted tubules join the collecting or straight tubule. It is about 20 mm long. Several collecting tubules of different nephrons join to form duct of Bellini.
Renal blood supply:-
(1) Renal Artery:
It starts from the dorsal aorta and enters into the kidney at hilus. It branches into smaller vessels to form arterioles. Each arteriole breaks into glomerular capillary. There are about 50 capillaries in each glomerulus. These capillaries rejoin to form efferent arterioles, which carry blood from the Bowman’s capsule. The diameter of afferent renal arteriole is larger than the efferent renal arteriole. It causes rise in the blood pressure in the glomerulus. The efferent renal arteriole comes out and breaks up in capillaries around the renal tubules to form vasa recta.
(2) Renal vein:
The blood from vasa recta is drained through the renal vein. Peculiarities of Renal Circulation
1. Almost all blood pass through the kidney.
2. It resembles portal system as the blood passes through a double capillary network i.e. first through glomerular capillaries and then through peritubular capillaries.
3. Renal blood pressure is comparatively high.
4. Rate of blood supply to the kidney is comparatively high (i.e. 1200-1300 ml of blood/ minute).
Function of Kidney:-
1. It excretes different waste products. These waste products are normally nitrogenous or sulphur containing end products of protein metabolism.
2. It maintains osmoregulation. It regulates hydrogen ion concentration of the body fluids and electrolytes.
3. It helps to maintain the water balance of the body.
4. It helps to maintain the optimum concentration of several constituents of the blood by selective reabsorption.
5. It eliminates some drugs and several poisonous substances from the body.
6. It manufactures certain substances like ammonia, hippuric acid and inorganic phosphate.
7. It maintains osmotic pressure of blood and tissues.
8. It helps to maintain blood pressure.
9. It regulates erythropoiesis.
10. It takes major role in the preparation of vitamin D.