Renal Physiology Overview

Questions and Answers

Where does filtration occur?

In the renal corpuscle as fluid moves under pressure across the wall of glomerular capillaries into Bowman's space.

Describe the pathway of fluid through the renal corpuscle.

Perfusion of glomerular capillaries -> filtration of plasma -> formation of urine.

Sympathetic nerves in the renal corpuscle project where?

To the granular and smooth muscle cells.

What are mesangial cells?

Immunoreactive transformed smooth muscle cells that can contract in response to circulating vasoactive substances impeding glomerular blood flow and filtration. Signup and view all the answers

What forms the juxtaglomerular apparatus?

Granular cells, macula densa, and external mesangial cells. Signup and view all the answers

Describe the juxtaglomerular apparatus.

At a site of its transition into the distal tubule, the thick ascending limb of the Loop of Henle makes contact with the afferent arteriole in each nephron. Signup and view all the answers

What are the functions of the cells of JGA?

Granular cells (renin), macula densa (monitor flow rate of filtrate). Signup and view all the answers

What is the glomerular filtration barrier?

The wall of glomerular capillaries. Signup and view all the answers

What does the glomerular filtration barrier do?

Controls passage of substances from plasma into the renal tubule. Signup and view all the answers

What are the layers of the glomerular filtration barrier?

Leaky endothelium (pores/fenestrae), basement membrane (porous matrix of negatively charged glycoproteins), podocytes (specialized epithelial cells with interdigitating pedicels separated by filtration slits). Signup and view all the answers

How are substances in the blood filtered?

Through capillary fenestrae between endothelial cells, the filtrate then passes across the basement membrane and through slit pores between the foot processes and enters the capsular space. Signup and view all the answers

Filterability of substances depends on what?

Molecular weight (radius in angstroms) and molecular charge; large molecular radius and negative charge impedes filtration. Signup and view all the answers

What substances filter easily?

Water, urea, glucose, and inulin. Signup and view all the answers

What substances don't filter?

Albumin and hemoglobin. Signup and view all the answers

What substances filter moderately?

Myoglobin. Signup and view all the answers

Compare the permeability of glomerular capillaries with systemic capillaries.

Glomerular capillary walls are more permeable. Signup and view all the answers

What is filtrate?

Water and dissolved solutes like ions, glucose, amino acids, etc. Signup and view all the answers

What is the filtration coefficient?

Kf, a measure of permeability; 100x greater for the glomerular capillaries than systemic capillaries. Signup and view all the answers

What doesn't pass through the walls of glomerular capillaries?

Blood cells and most plasma proteins. Signup and view all the answers

How are proteins reabsorbed in the proximal tubule?

Endocytosis. Signup and view all the answers

What are Tamm-Horsfall proteins?

Proteins synthesized within the renal tubule and normally detected in urine; unclear function, may prevent calcification and formation of kidney stones. Signup and view all the answers

How much protein should be found in urine?

Only trace amounts. Signup and view all the answers

When can the filtration barrier leak?

When the glomerulus isn't healthy. Signup and view all the answers

What is proteinuria?

Loss of proteins in urine due to the damaged leaky glomerular capillaries. Signup and view all the answers

What can profound proteinuria lead to?

Low plasma protein concentration and a decrease of plasma oncotic pressure; 3g/day. Signup and view all the answers

What happens when there is a decrease in plasma oncotic pressure?

Fluid shifts into interstitial space; swelling. Signup and view all the answers

What does oncotic pressure do?

Helps keep water inside the vessel, depends on protein concentration. Signup and view all the answers

What is a typical feature of nephrotic syndrome?

Swelling/edema due to profound decrease in plasma protein concentration (hypoalbuminemia). Signup and view all the answers

Diseases of the glomerulus cause what?

Breakdown of glomerular capillaries, protein leak and reduction in filtration. Signup and view all the answers

Study Notes

Glomerular Filtration: Key Concepts

Filtration occurs in the renal corpuscle, with fluid moving under pressure from glomerular capillaries into Bowman's space.
Fluid pathway: perfusion of glomerular capillaries leads to plasma filtration and urine formation.

Renal Nerves and Cell Types

Sympathetic nerves in the renal corpuscle project to granular and smooth muscle cells.
Mesangial cells are smooth muscle cells that contract in response to vasoactive substances, impacting blood flow and filtration.

Juxtaglomerular Apparatus (JGA)

JGA is formed by granular cells, macula densa, and external mesangial cells, located where the thick ascending limb of the Loop of Henle meets the afferent arteriole.
Functions of JGA cells: granular cells produce renin, and macula densa monitors filtrate flow rate.

Glomerular Filtration Barrier

The glomerular filtration barrier comprises the leaky endothelium, basement membrane of negatively charged glycoproteins, and specialized podocytes with filtration slits.
This barrier controls what substances can pass from blood into the renal tubule.

Filtration Process

Substances in the blood are filtered through capillary fenestrae, the basement membrane, and podocyte slits before entering the capsular space, leading to the proximal tubule.
Filterability is influenced by molecular weight and charge; larger and negatively charged substances are more obstructed.

Filtered Substances

Easily filtered substances: water, urea, glucose, and inulin.
Substances that do not filter: albumin and hemoglobin.
Myoglobin filters with moderate difficulty.

Comparison to Systemic Capillaries

Glomerular capillaries have a higher permeability compared to systemic capillaries, indicated by the filtration coefficient (Kf), which is 100 times greater for glomerular capillaries.

Urine Composition and Protein Dynamics

Filtrate consists of water and solutes such as ions and glucose, with proteins reabsorbed in the proximal tubule through endocytosis.
Tamm-Horsfall proteins are produced in renal tubules and may prevent kidney stone formation.

Proteinuria and Associated Conditions

Typical urine contains only trace amounts of protein; excessive leakage indicates glomerular health issues.
Proteinuria results from damage to glomerular capillaries, leading to a reduction in plasma protein concentration and lower oncotic pressure.
A decrease in oncotic pressure causes fluid to shift into interstitial spaces, resulting in swelling (edema).

Nephrotic Syndrome

Characterized by significant swelling due to reduced plasma protein levels (hypoalbuminemia).
Glomerular diseases can lead to breakdown of capillaries, protein leakage, and various renal complications.

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Description

This quiz explores key concepts of glomerular filtration, renal nerves, and the juxtaglomerular apparatus. It provides insights into the mechanisms of filtration and the functions of different cell types in the renal system. Test your understanding of how these components contribute to kidney function and urine formation.