All about nephron anatomy|The functional unit of kidney

Nephron-the functional unit of kidney

The microscopic structural and functional unit of kidney that actually produces urine in the process called excretion.Each kidney in the human contains about 800,000 to 1,000,000 nephrons.

The kidney cannot regenerate new nephrons. Therefore, with renal injury, disease,or normal aging there is gradual decrease in nephron number.This loss is not life threatening because adaptive changes in the remaining nephrons allow them to excrete the proper amount of wastes,water and electrolytes.

Nephron Anatomy

Nephron is basically consists of two parts:

• Renal corpuscle
• Renal tubule

Renal corpuscle consists of a tuft of capillaries called glomerulus encased in a cup shaped bowman's capsule.

Renal tubules consists of proximal convulated tubule,loop of henle(ascending and descending loop of henle),distal convulated tubule and the collecting duct.

• The glomerulus contains a network of branching capillaries that arises from afferent arterioles and empties into efferent arteriole.The glomerular capillaries have high hydrostatic pressure (about 60mmHg) due to smaller diameter of efferent arteriole than afferent arteriole.

Glomerular Capillary Membrane

The glomerular capillary membrane is similar to that of other capillaries,except that it has three instead of two major layers

• The endothelium of the capillary with minute pores called fenestrations
• A middle basement membrane
• Layer of epithelial cells(podocytes)surrounding the outer surface of capillary basement membrane

Together these layers make up the filtration barrier,which filters several hundred times  as much wastes as the usual capillary membrane.Even with this high rate of filtration, the glomerular capillary membrane normally prevents filtration of plasma proteins.

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• Bowman's capsule is a cup like structure which encloses the glomerulus.
• Proximal convulated tubule-lies in the cortex of kidney and is the proximal part of the renal tubule,next to bowman's capsule.Maximum reabsorption of essential elements like water,glucose,aminoacids and electolytes takes place here.
• From the proximal tubule fluid flows into  loop of henle,which dips in renal medulla.It is U-Shaped and consists of ascending and descending limb.The walls of the descending limb and the lower end of the ascending limb are very thin therefore are called the thin segment of loop of henle.After the ascending limb of the loop returns back to the cortex, its wall become much thicker,and thus called as thick segment of loop of henle.
• Distal convulated tubule is similar in fuction with proximal tubule(reabsorption), and is the distal part of the renal tubule.
• Collecting duct form by many collecting tubules. In each kidney there are about 250 very large collecting ducts,each collects urine from about 4000 nephrons and empties into minor then major calyx and then into renal pelvis.

Types of nephrons

Although each nephron has all the components described earlier, there are some differences,depending on how deep the nephron lies within the kidney mass

• Cortical nephrons-they have glomeruli located in the outer cortex and have short loop of henle.For the cortical nephrons the entire tubular system is surrounded by  an extensive network of peritubular capillaries. 
• Juxtamedullary nephron-they have their glomeruli lie deep in the cortex near the medulla,the vascular structures supply them also differs from those that supply cortical nephrons.