Renal Corpuscle and Glomerulus Overview

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Questions and Answers

What is the primary function of the fenestrated capillaries within the glomerulus?

To prevent the passage of all molecules larger than 10 nm

To secrete hormones that regulate blood pressure

To allow for the passage of small proteins, water and electrolytes (correct)

To actively transport large proteins into Bowman's capsule

Which of the following describes the arrangement of the glomerular basement membrane (GBM) layers from the endothelial cells to the podocytes?

Lamina rara interna, lamina densa, lamina rara externa (correct)

Lamina rara externa, lamina rara interna, lamina densa

Lamina rara externa, lamina densa, lamina rara interna

Lamina densa, lamina rara interna, lamina rara externa

The slit diaphragm, formed by nephrin, primarily functions to:

Actively transport large proteins into the glomerulus

Allow any molecule smaller than 50 nm to pass through

Prevent passage of molecules larger than 7 to 9 nanometers (correct)

Regulate blood flow to the glomerulus

What is the functional significance of the negatively charged heparan sulfate found in the glomerular basement membrane (GBM)?

To allow positively charged molecules to pass more readily. Signup and view all the answers

Which of the following structures is specifically responsible for the primary filtration of blood?

The fenestrated capillaries of the glomerulus Signup and view all the answers

What is the approximate diameter of the pores contained within the fenestrated capillaries in the glomerulus?

50 to 100 nanometers Signup and view all the answers

What is the role of the pedicels in the filtration process?

To form filtration slits with adjacent pedicels Signup and view all the answers

Considering the filtration barriers, a protein with a diameter of 15 nanometers is most likely to be retained where?

Within the fenestrated capillaries Signup and view all the answers

Which of the following best describes the role of mesangial cells within the glomerulus?

Regulate glomerular blood flow and phagocytose trapped macromolecules. Signup and view all the answers

A patient has a condition that results in a significant increase in plasma protein concentration. How would this most likely affect the net filtration pressure (NFP) in the glomerulus?

Decrease NFP, due to increased colloid osmotic pressure. Signup and view all the answers

Which of the following correctly describes the sequence of filtration barriers that substances must pass through within the renal corpuscle, when moving from the blood to the Bowman's capsule?

Fenestrated capillaries → glomerular basement membrane → filtration slits Signup and view all the answers

A patient is diagnosed with diabetic nephropathy. What is the most likely effect of this condition on their glomerular filtration rate (GFR)?

Decreased GFR due to a reduction in the surface area of the glomerulus. Signup and view all the answers

If a patient has a kidney stone obstructing the flow of filtrate from Bowman's capsule into the renal tubules, what direct effect will this have on glomerular filtration?

Increases capsular hydrostatic pressure, decreasing GFR. Signup and view all the answers

Which of the following substances would be least likely to pass through the glomerular filtration barrier under normal physiological conditions due to their size and charge?

Albumin proteins Signup and view all the answers

If the glomerular hydrostatic pressure (GHP) is significantly decreased due to a sudden drop in blood pressure, how will the net filtration pressure (NFP) and the glomerular filtration rate (GFR) be affected?

NFP will decrease, and GFR will decrease. Signup and view all the answers

What is the primary function of juxtaglomerular (JG) cells in the nephron?

To produce renin in response to changes in blood pressure and sodium level. Signup and view all the answers

What does a filtration coefficient (KF) value, represent in the kidneys?

The product of the surface area of the glomerular capillaries and the permeability of the glomerular membrane Signup and view all the answers

Which of the following values represents a normal, average glomerular filtration rate (GFR) in an adult?

125 mL/min Signup and view all the answers

Study Notes

Renal Corpuscle

The renal corpuscle is comprised of two structures: the glomerulus and Bowman's capsule.
The glomerulus is a tuft of capillaries that filters blood.
Bowman's capsule encases the glomerulus and collects the filtered fluid.

Glomerulus

The glomerulus is fed by the afferent arteriole and drained by the efferent arteriole.
The capillaries within the glomerulus are fenestrated capillaries, meaning they have pores in the endothelial cells.
These pores are approximately 50 to 100 nanometers in diameter.
Formed elements (red blood cells, white blood cells, and platelets) are too large to pass through the fenestration pores.
The glomerular filtration membrane consists of the endothelial lining of the fenestrated capillaries and the glomerular basement membrane.
The fenestrated capillaries allow small proteins, water, electrolytes, nutrients, and waste products to pass through.

Glomerular Basement Membrane

The glomerular basement membrane (GBM) is a specialized structure located between the endothelial cells and the podocytes.
The GBM consists of three layers:
- Lamina densa: Contains Type IV collagen and laminins, providing structural support.
- Lamina rara interna: Consists of negatively charged heparan sulfate, located closer to the endothelial cells.
- Lamina rara externa: Also consists of negatively charged heparan sulfate, located closer to the podocytes.
The negative charge of the GBM repels negatively charged molecules like plasma proteins, helping prevent them from entering Bowman's capsule.
Positively charged molecules, like electrolytes, pass through more readily.

Podocytes

Podocytes are specialized epithelial cells that wrap around the capillaries of the glomerulus.
They have foot-like processes called pedicels, which interdigitate with adjacent podocytes, forming filtration slits.
The filtration slits are approximately 25 to 30 nanometers in diameter.
Nephrin is a key protein located in the filtration slits, forming a structure called the slit diaphragm.
The slit diaphragm acts as a final barrier, allowing only molecules smaller than 7 to 9 nanometers to pass through.

Components Filtered Through the Renal Corpuscle

The following substances are readily filtered through the renal corpuscle:
- Water
- Electrolytes (sodium, potassium, calcium, magnesium, chloride, bicarbonate)
- Nutrients (glucose, amino acids, lipids)
- Waste products (urea, creatinine, lactic acid)
The following substances are repelled by the glomerular basement membrane:
- Plasma proteins (albumin, immunoglobulins, fibrinogen)

Filtration Process Recap

Substances must pass through three barriers to be filtered into Bowman's capsule:
- Fenestrated capillaries: Allows substances less than 50 to 100 nanometers in diameter to pass.
- Glomerular basement membrane: Repels negatively charged molecules; positively charged particles pass readily.
- Filtration slits: Allows substances less than 25 to 30 nanometers to pass.
- Slit diaphragm (nephrin): Allows substances less than 7 to 9 nanometers to pass.
The filtered substances then collect in Bowman's space and enter the proximal convoluted tubule.

Mesangial Cells

Mesangial cells are important for glomerular structure.
Mesangial cells phagocytose macromolecules that get stuck in the slit diaphragm.
Mesangial cells have contractile activity that controls blood flow through the glomerular capillaries.
Mesangial cells are connected to JG cells via gap junctions.

Juxtaglomerular (JG) Cells

JG cells are located in the juxtaglomerular apparatus, next to the glomerulus.
JG cells produce renin, which raises blood pressure.
JG cells are pressure receptors (baroreceptors) that sense changes in blood pressure.
JG cells receive signals from mesangial cells via gap junctions.

Glomerular Filtration Rate (GFR)

GFR is the amount of plasma filtered from the glomerulus into Bowman's capsule per minute.
The average GFR is 125 milliliters per minute.
About 1200 milliliters of plasma flow through the glomerulus per minute.
Only 625 milliliters per minute are used in filtration, and the rest passes through.
Only 20% (~125 milliliters per minute) of the 625 milliliters of plasma used in filtration is actually filtered.

Factors Affecting GFR

GFR is determined by net filtration pressure (NFP) and the filtration coefficient (KF).
NFP is the difference between pressures pushing things out and pressures pulling things in.
KF represents the permeability and surface area of the glomerulus.

Pressures Affecting GFR

Pressures forcing out:
- Glomerular hydrostatic pressure (GHP) – the pressure pushing plasma out of the glomerular capillaries into Bowman's space; ~55 mmHg.
- Capsular osmotic pressure (COP) – the pressure pulling things out of the capillaries; assumed to be 0 mmHg under normal conditions.
Pressures pulling in:
- Colloid osmotic pressure (COP) – the pressure exerted by plasma proteins (like albumin) to keep water in the bloodstream; ~30 mmHg.
- Capsular hydrostatic pressure (CHP) – the pressure built up in Bowman's capsule as fluid filters in, pushing fluid back into the glomerular capillaries; ~15 mmHg.
Net Filtration Pressure:
- NFP = GHP + COP - COP - CHP
- NFP ~ 10 mmHg

Clinical Correlations

Glomerular Hydrostatic Pressure:
- Increased systemic blood pressure leads to increased GHP.
- Decreased systemic blood pressure leads to decreased GHP.
Colloid Osmotic Pressure:
- Increased plasma proteins increase COP (e.g., multiple myeloma).
- Decreased plasma proteins decrease COP (e.g., hypoproteinemia).
Capsular Hydrostatic Pressure:
- Kidney stones (renal calculi) larger than 5 millimeters can obstruct flow and increase CHP.
- Hydro nephrosis, caused by renal ptosis, can also increase CHP.

Filtration Coefficient (KF)

KF = surface area of the glomerulus x permeability of the glomerulus
KF impacts GFR: increases to KF increase GFR. decreases to KF decrease GFR
Conditions that affect KF:
- Diabetic nephropathy: Thickening of the glomerulus caused by protein and other deposits, leading to decreased surface area and a lower GFR.
- Glomerulonephritis: Damage to the glomerulus, making the basement membrane more porous, which can increase GFR and cause protein loss in urine.

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Description

This quiz explores the structure and function of the renal corpuscle, focusing on the glomerulus and Bowman's capsule. Discover how these components work together to filter blood and manage essential substances. Test your knowledge on the intricacies of kidney filtration.