NEPHRON 1. A nephron is a unit of structure and

function of a kidney.

2. A kidney contains about a million nephron.

3. It is about 3 cm long and 20-30 nm in diameter.

4. Nephrons are of two types :

(a)-cortical

(b)-juxtamedullary

Differences between cortical & juxtamedullary nephronsCORTICAL NEPHRONS

Form 80% of total nephrons.

Are small in size. Lie mainly in the

renal cortex. Henle’s loops are

very short and extend only a little into the medulla.

JUSTAMEDULLARY NEPHRONS Form only 20%

of total nephrons.

Are in large in size.

Have bowman’s capsule in the cortex .

Henle’s loops are very long and extend deep into the medulla.

Nephrons - Renal corpuscle

• Bowman’s capsule • Glomerulus

Renal tubule . Proximal convolutes tubule (PCT)

• Loop of Henle

• Distal convoluted tubule (DCT)

Nephron consists of …………………….

1) Renal corpuscle – the head of the nephron (a)The renal corpuscle is composed of Bowman’s capsule and glomeruli (b)Bowman’s capsule is the cover of the corpuscle that surrounds the glomerulus (b)the glomerulus is the network of capillaries found inside the corpuscle2) Renal tubule – the tubular passageway of the nephron (a)The renal tubule consists of Proximal convoluted tubule (PCT) Loop of Henle Distal convoluted tubule (DCT)

Nephron structures and functions Glomerulus

• The glomerulus is surrounded by Bowman's capsule

• It is a network of capillaries that performs the first step of filtering blood.

• operates as a nonspecific filter - removes both useful and non-useful material

• the product of the glomerulus – filtrate

Layers of glomerulus-Endothelial cells• The endothelial cells of the glomerulus contain

numerous pores

• These pores are relatively large, they allow for the free filtration of fluid, plasma solutes and protein

Glomerular basement membrane• The GBM is a fusion of the endothelial cell and podocyte

basal laminas

Podocytes• Podocytes line the other side of the glomerular

basement membrane and form part of the lining of Bowman's space.

• Podocytes form a tight pedicels that control the filtration of proteins from the capillary lumen into Bowman's space.

A The endothelial cells B. Glomerular basement membrane C. Podocytes:

Nephron structures and functions

Bowman’s Capsule

• It is double walled cup-shaped.

• A sac that encloses glomerulus

• transfers filtrate from the glomerulus to the Proximal Convoluted Tubule (PCT)

• The two walls are inner visceral and outer parietal, both are single layered and are supported over basement membrane.

Parietal layer -• A single layer of simple squamous

epithelium. • Does not function in filtration. Bowman's space - • Between the visceral and parietal layers, into which the filtrate enters after passing through the filtration slits.

Visceral layer -• Lies just above the thickened

glomerular basement membrane and is made of podocytes.

Layers of bowman’s capsule-

2. Bowman's capsule – parietal layer3. Bowman's capsule – visceral layer

4. Bowman's space (urinary space)

Proximal Convoluted Tubule (PCT)

Lower part of Bowman’s capsule leads in to PCT.

It lies in the renal cortex.PCT is lined by cuboidal

epithelial having brush borders with long microvilli for increasing absorptive area.

And resting on a basement membrane.

that reabsorbs most of the useful substances of the filtrate: sodium (65%), water (65%), bicarbonate (90%), chloride (50%), glucose (nearly 100%)

Nephron structures and functions The loop of Henle

• U-shaped tube that consists of a descending limb and an ascending limb.

• begins in the cortex, receiving filtrate from the PCT, extends into the medulla, and then returns to the cortex to empty into the distal convoluted tubule(DCT).

• Its primary role is to concentrate the salt in the interstitium, the tissue surrounding the loop

Nephron structures and functions Descending Limb of the Loop of Henle• A part of the counter current multiplier

• fully permeable to water and completely impermeable to solutes (salt particles)

• receives filtrate from the PCT, allows water to be absorbed and passes “salty” filtrate to the next segment.

“Saves water and passes the salt”

Ascending Limb of the loop of Henle• a part of the counter current

multiplier

• impermeable to water and actively transports (reabsorbs) salt (NaCl) to the interstitial fluid of the pyramids in the medulla.

“Saves salt and passes the water.”

• the passing filtrate becomes dilute and the interstitium becomes hyperosmotic

Descending limb has two parts, (a) Thick segment-

• Thick segment constitutes about four-fifth of the descending limb.

• It lies both inside cortex and medulla.

• The cell lining it are cuboidal. (b) Thin segment-

• Thin segment is narrow part of descending limb.

• It lies in medulla and is lined by flat epithelial cell.

(Descending limb-Thick and Thin)

Nephron structures and functions

Distal Convoluted Tubule (DCT)

• It is highly coiled part of nephron

• Lies close to Malphighian body.

• Variably active portion of the nephron

• receives dilute fluid from the ascending limb of the loop of Henle

Nephron structures and functions Collecting Duct

• variably active portion of the Nephron

• Lined by specialized cuboidal epithelial with very few microvilli.

• Collecting duct is not a part of structure of nephron.

• The last segment to save water for the body

Juxtaglomerular apparatus-It is a microscopic structure in the kidney,

which regulates the function of each nephron

The juxtaglomerular apparatus consists of:

(1) the juxtaglomerular cells

(2) the macula densa

(3) the Lacis cells or agranular cells

Function of the JC cells-1-Release of Renin Stimulus : Low blood pressure 2-Release of Aldosterone

hormone

It stimulates the DCT to reabsorb salt.3-Reabsorption of salt (NaCl)

Function of the Macula Densa Cells• It monitors the salt content of the blood.

• If concentration of salt is raised, the macula densa cells inhibit the release of renin from the JC cells.

Function of the extra glomerular mesangial cells• It secretes

erythropoietin

• Erythropoietin is a glycoprotein hormone which controls erythropoiesis or red blood cell production.

Nephrons has the following function- 1-Nephron remove urea and uric acid from the blood 2-Nephron regulate blood pressure. 3-Nephron also remove pigments,drugs,poisons,excess vitamins from the blood. 4-It regulates the amount of mineral salts in the body. 5-Also regulate blood pH.