3. INTRODUCTION:
• The two kidneys are the chief excretory organs of the body.
• These kidneys are made up of numerous functional
microscopic units called ‘NEPHRON’.
• Nephron is the basic structural and functional unit of kidney
which helps in formation of urine.
• They perform excretory and homeostatic (acid-water balance)
functions.
• There are near about 1 million nephrons present in each
human kidney.
• The word nephron is delivered from the gr. word-’NEPHROS’
meaning ‘KIDNEY’
4. Fig.1: Section of the human kidney showing basic
structure of nephron.
5. TYPES OF NEPHRON
NEPHRON
Cortical Nephron Juxtamedullary Nephron
Cortical Nephron:
• These are the nephrons present with in the cortex.
• These nephrons are also short and is about 80% of the total
nephrons present in each kidney.
• Small in size and are fully functional under normal condition.
6. Juxtamedullary Nephron:
• These nephrons extends into the medulla.
• These nephrons are about 20% of total nephrons present in each
kidney.
• These are larger in size and works only in conditions of stress.
(Fig.2:
schematic representation
of cortical nephron and
Juxtamedullary nephron.)
7. Anatomical divisions of NEPHRON
NEPHRON
Renal Corpuscles Renal Tubules
-Glomerulus. -Proximal Convoluted Tubule(PCT).
-Bowman’s capsule. -Loop of Henle/Medullary loop.
-Distal Convoluted Tubule(DCT).
Renal Corpuscle:
• Found in the cortex of the kidney.
• It measures about 200 microns in diameter.
• The corpuscle consist of 2 parts:Glomerulus and Bowman’s capsule.
8. GLOMERULUS:
• It is the capillary tuft that invaginates Bowman’s capsule.
• The afferent arteriole breaks up into about 50 capillary loops and
forms the glomerular tuft.
• Blood enters to the glomerulus through afferent arteriole and
exits glomerulus through efferent arteriole.
• Afferent vessel is short and wide where as Efferent vessel is
narrow and long.
BOWMAN’S CAPSULE:
• It is the dilated blind end of the nephron,invaginated by the
glomerular tuft.
• Bowman’s capsule is a cup-like sac at the beginning of the tubular
component of nephron named after Sir William Bowman.
A. Outer perietal layer : made up of epithelial cells.
B. Middle layer : made up of fibrils and selectively permeable.
C. Inner visceral layer : consist of podocytes which contains finger-
like podocel.it contains filtration slits.
10. Renal Tubules:
• The renal tubule is a long and convoluted structure that emerges
from the Bowman’s capsule.
• Renal tubules are metabolically active, being responsible for
absorption or excretion of a wide range of substances.
• These are the tube like structure that that collectively form
collecting duct.
• These can be divided into 3 parts.
A. Proximal Convoluted Tubule : Due to it’s proximity to bowman’s
capsule . It is named so . It stays in the renal cortex.
B.Loop of Henle : It forms a loop(with descending and ascending)that
goes through the renal medulla.
C.Distal Convoluted Tubule : This part also restricted to the renal
cortex.
12. PROXIMAL CONVOLUTED TUBULE(PCT):
• The blood brought by the renal artery is filtered by the glomerulus
and then passed to the PCT.
• Maximum reabsorption takes place in PCT of nephron.
• PCT is the region of renal tubule where reabsorption of essential
substances like glucose , proteins , aminoacids , a major portion of
electrolytes and water takes place.
• PCT is made up of simple cuboidal epithelium tissues . It selectively
secretes ions such as hydrogen,ammonia and pottassium into the
filtrate and absorbs HCO3 from it.
• PCT are very metabolically active and contains large no. of enzymes.
• These cells reabsorb about two-third of water of glomerular filtrate
and all the glucose and a part of sodium chloride and phosphates.
13. LOOP OF HENLE(MEDULLARY LOOP):
• It is a u-shaped loop , dipping for a variable length into the medulla
and has a descending and an ascending limb.
• Both the descending and ascending limbs show different
permeability.
• Descending limb is permeable to water but impermeable to an
electrolyte , while ascending limb is permeable to electrolytes but
impermeable to water.
• Since the electrolytes gets reabsorbed at the ascending loop of
Henle , the filtrategets diluted as it moves towards the ascending
limb.
DISTAL CONVOLUTED TUBULE(DCT):
• The DCT , which is the last part of the nephron , connects and
empties it’s contents into collecting ducts that line the medullary
pyramids.
• It is lined by cubical epithelium which contains a large no. of
microvilli.
14. • The reabsorption activity of the DCT and collecting duct is under the
influence of ADH , VASSOPRESSIN.
• Distal tubular cells are able to reabsorb small quantities of water
and electrolytes due to a small no. of microvilli in addition to
determining urinary acid-base balance.
• DCT secretes ions such as hydrogen , potassium and NH3 to the
filtrate while reabsorbing HCO3 from filtrate.
• Conditional reabsorption of sodium ions and water takes place in
DCT . Thus it maintains pH and Na-k level in blood cells.
COLLECTING DUCT:
• It is also called as duct of bellini.
• The renal collecting duct system comprises series of tubules and
ducts that connect the nephrons to the ureter.
• The collecting duct accounts for 4-5% of the kidney’s reabsorption
of water.
• Also secretes H+ and K+ ions to maintain the electrolyte balance .
16. MECHANISM OF FORMATION OF URINE:
• About 1300 ml. of blood enters the kidneys every minute.
• Normal Urinary Output 1-1.5 L/Day.
Entering of blood to glomerulus through efferent arteriole.
Pure blood go to Glomerular filtration.
efferent arteriole (received by Bowman’s capsule)
Proximal Convoluted Tubule
(Reabsorbs water , glucose , sodium and chloride ions)
Descending and ascending limb(loop of Henle)
(Absorption of water and sodium ions)
Distal convoluted Tubule wastes pass to
(Reabsorbs chlorides and water) collecting duct
17. FUNCTION OF NEPHRON:
• Mainly nephron function to formation of urine that includes 3
steps: Glomerular Filtration, Selective Reabsorption, Tubular
Secretion from blood.
• Nephron absorbs and reabsorbs many useful substances from
the blood and remove solid wastes and other excess water
from the blood.
• Nephron also regulates the amount of mineral salts and pH of
blood in the body.
