Structure And Function Of The Nephron Notes

Structure and Function of the Nephron

In humans and pigs, each pyramid contains around 100,000 nephrons. Each nephron has a vascular and a tubular component. At the end of the tubular system, there is a double-walled, cup-shaped structure called Bowman’s capsule, which surrounds the vascular component of the nephron, the glomerular capillaries. The space between the two layers of Bowman’s capsule, Bowman’s space, collects the glomerular filtrate. It is then funnelled into the first tubular part of the nephron, the proximal tubule. The tubular part eventually empties into a collecting duct, which is shared by many nephrons. From the end of the collecting ducts, urine is emptied into the renal pelvis.

1. Structure of the glomerulus

The glomerulus consists of many parallel capillaries with interconnections. The glomeruli are confined to the cortex.

In mammals each glomerulus is supplied with blood from an arteriole called the afferent arteriole. Unlike other capillaries, glomerular capillaries do not connect with venules – instead they connect with the efferent arterioles. These branch into the peritubular capillaries surrounding the tubules. The peritubular capillaries empty into venules, which in turn eventually empty into larger veins.

2. Structure of the tubular system

This part of the nephron consists of a fluid-filled tube consisting of a single layer of epithelial cells that rests on a basal lamina. Bowman’s space is the first part of the lumen of the tubular system, while the tubular wall is a continuation of the outer wall of Bowman’s capsule.

The tubular part of the nephron is divided into four segments – the proximal tubule, the loop of Henle, the distal tubule and the collecting duct.

1. The proximal tubule

The proximal tubule drains Bowman’s space and is highly convoluted. It lies entirely in the cortex. It has a distinctive ‘brush border’ of tall, columnar epithelial cells with microvilli lining the luminal surface. The microvilli greatly increase the surface area of the luminal surface, facilitating their reabsorptive function.

Small proteins and peptide hormones are reabsorbed in the proximal tubule by endocytosis. Other substances are secreted or reabsorbed by passive or facilitated diffusion. Movement is via ion channels, co transporters, ATPase pumps and exchangers. 65-80% of the filtrate is reabsorbed in the proximal tubule.

2. The loop of Henle

The loop of Henle forms a hairpin shaped loop, which dips into the medulla. In birds, the loop of Henle is lacking or poorly developed. The loop of Henle is divided into a thin descending, thin ascending and thick ascending...

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