Osmoregulation and Excretion

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Nephron Functional Unit of the Kidney

Cortical

nephron

Juxtamedullary

nephron

Collecting

duct

Nephron types

To

renal

pelvis

Renal

medulla

Renal

cortex

Slide 38

Nephron

Afferent arteriole

from renal artery

Efferent

arteriole from

glomerulus

SEM

Branch of

renal vein

Descending

limb

Ascending

limb

Loop of Henle

Filtrate and blood flow

Vasa

recta

Collecting

duct

Distal

tubule

Peritubular capillaries

Proximal tubule

Bowman’s capsule

Glomerulus

10 µm

Slide 39

Filtration : Glomerulus --> Bowman’s Capsule

Filtration occurs as blood pressure = hydrostatic pressure forces fluid from the blood in the glomerulus to lumen of Bowman’s capsule.

Filtration of small molecules is nonselective.

The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules.

Slide 40

Pathway of the Filtrate

From Bowman’s capsule, the filtrate passes through three regions of the nephron: the proximal tubule --> loop of Henle --> distal tubule…

Fluid from several nephrons flows into a collecting duct ---> renal pelvis ---> ureter.

Cortical nephrons are confined to the renal cortex, while juxtamedullary nephrons have loops of Henle that descend into the renal medulla.

Slide 41

Blood Vessels Associated with the Nephrons

Each nephron is supplied with blood by an afferent arteriole = a branch of the renal artery that divides into the capillaries.

The capillaries converge as they leave the glomerulus, forming an efferent arteriole.

The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules.

Slide 42

Vasa recta are capillaries that serve the loop of Henle.

The vasa recta and the loop of Henle function as a countercurrent system.

The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids.

Slide 43

The nephron is organized for stepwise processing of blood filtrate

Proximal Tubule

Reabsorption of ions, water, and nutrients takes place in the proximal tubule.

Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries.

Some toxic materials are secreted into the filtrate.

The filtrate volume decreases.