Which structures form the filtration membrane in the nephron?
a) afferent arteriole and the glomerular capsule
b) efferent arteriole and the glomerular capsule
c) afferent arteriole and the efferent arteriole
d) glomerulus and the glomerular capsule
The Correct Answer and Explanation is :
The correct answer is d) glomerulus and the glomerular capsule.
Explanation:
The filtration membrane in the nephron is a crucial structure involved in the filtration of blood to form urine. It is located between the blood in the glomerulus (a network of capillaries) and the interior of the glomerular capsule (also called Bowman’s capsule). The filtration membrane consists of three key components that regulate which substances are filtered from the blood and into the nephron for further processing:
- Fenestrated Endothelium of the Glomerular Capillaries:
The glomerulus is made up of fenestrated (porous) capillaries that allow water and small solutes, such as ions, glucose, and urea, to pass through. However, the fenestrations prevent large molecules like proteins and blood cells from being filtered into the glomerular capsule. - Basement Membrane:
This layer lies between the endothelial cells and the podocytes (cells of the glomerular capsule). It acts as a selective barrier that further restricts the passage of larger proteins and molecules. It is composed of a matrix of collagen and glycoproteins, which helps in preventing the passage of large proteins like albumin into the urine. - Podocytes of the Glomerular Capsule:
The glomerular capsule (Bowman’s capsule) has specialized epithelial cells called podocytes that have foot-like extensions (pedicels). These pedicels wrap around the glomerular capillaries, leaving small gaps called filtration slits. These slits allow only smaller molecules (such as water, electrolytes, and waste products) to pass through while blocking larger molecules.
These three components (glomerular capillaries, basement membrane, and podocytes) together form the filtration membrane, which is critical in selectively filtering the blood. Blood is filtered through this membrane as it flows from the afferent arteriole into the glomerulus, and the filtered fluid (called filtrate) enters the glomerular capsule to continue through the nephron for further processing and eventual excretion as urine.
In contrast, the afferent and efferent arterioles (mentioned in options a, b, and c) are responsible for regulating blood flow into and out of the glomerulus but do not directly contribute to the filtration membrane.