GFR and Renal Blood Flow Overview ch 27

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Questions and Answers

Approximately what percentage of renal plasma flow is typically filtered at the glomerulus?

10%

20% (correct)

30%

What is the primary reason that plasma proteins do not readily pass through the glomerular filtration membrane?

They are physically blocked by the basement membrane.

They are positively charged, so they are repelled by the membrane.

They are too large to pass through the fenestrations and negatively charged. (correct)

They are too small to pass through the fenestrations.

Which component of the glomerular capillary membrane contains pores known as fenestrae?

The Podocytes

The Epithelial cells

The Basement membrane

The Endothelium (correct)

What is the average daily volume of fluid filtered by the glomerular capillaries?

180 liters (A) Signup and view all the answers

What does the term 'filtration fraction' represent?

The ratio of glomerular filtration rate to renal plasma flow. (B) Signup and view all the answers

Which of the following factors does NOT directly influence capillary filtration rate?

The reabsorption rate in the tubules (A) Signup and view all the answers

Besides size, what other characteristic of plasma proteins hinders their passage through the glomerular filtration membrane?

Their negative charge (C) Signup and view all the answers

Which of the following best describes the function of podocytes in the glomerular filtration process

Forms slit pores that affect fluid filtration. (D) Signup and view all the answers

What is the primary function of pressure diuresis and pressure natriuresis?

Regulation of body fluid volumes and arterial pressure. (B) Signup and view all the answers

Where is the macula densa located?

In the initial portion of the distal tubule. (A) Signup and view all the answers

What is the effect of decreased GFR on the flow rate through the loop of Henle?

It decreases the flow rate. (A) Signup and view all the answers

What is the primary effect of the signals secreted by the macula densa?

To relax the afferent arterioles and release renin. (A) Signup and view all the answers

What is the consequence of afferent arteriole relaxation on glomerular hydrostatic pressure and GFR?

It increases glomerular hydrostatic pressure and GFR. (B) Signup and view all the answers

What happens to sodium and chloride reabsorption in the loop of Henle when GFR decreases?

Reabsorption increases. (B) Signup and view all the answers

What is the immediate effect of angiotensin II on the efferent arterioles?

Constriction. (B) Signup and view all the answers

A primary goal of the tubuloglomerular feedback mechanism?

To prevent fluctuation and stabilize sodium chloride delivery to the distal tubule. (A) Signup and view all the answers

What is the direction of secretion of the macula densa?

Toward the afferent and efferent arterioles. (B) Signup and view all the answers

What is the role of the efferent arteriole constriction caused by angiotensin II?

To increase glomerular filtration rate. (A) Signup and view all the answers

What primarily determines the selectivity of the glomerular filtration barrier?

Molecular size and electrical charge. (D) Signup and view all the answers

Why is albumin's filtration almost zero despite its size being smaller than the pore size of the glomerular membrane?

Its negative electrical charge repels it from the membrane. (A) Signup and view all the answers

What could be a cause of increased permeability of the glomerular membrane to plasma proteins?

An abnormal T-cell response and secretion of cytokines. (D) Signup and view all the answers

Which of the following is the correct formula for calculating glomerular filtration rate (GFR)?

GFR = Glomerular Capillary Filtration Coefficient * Net Filtration Pressure (D) Signup and view all the answers

What is considered to be approximately the normal value of Glomerular Capillary Filtration Coefficient?

12.5 ml/min (A) Signup and view all the answers

The increase in pressure in Bowman's capsule would probably cause what change in GFR?

Decrease GFR. (D) Signup and view all the answers

What percentage of total renal blood flow is directed to the renal medulla?

1-2% (D) Signup and view all the answers

What change occurs to plasma protein concentration as blood passes through the glomerular capillaries?

Increases by about 20%. (D) Signup and view all the answers

Which of the following most significantly influences glomerular hydrostatic pressure and is also highly variable and controllable?

Sympathetic nervous system activity. (C) Signup and view all the answers

Strong activation of renal sympathetic nerves results in which of the following?

Constriction of renal arterioles and decreased GFR. (D) Signup and view all the answers

What effect does increasing arterial plasma colloid osmotic pressure have on the glomerular filtration rate?

Decreases GFR. (A) Signup and view all the answers

Which of the following has a primary function of regulation of GFR?

Changes in the hydrostatic pressure. (B) Signup and view all the answers

What effect do norepinephrine, epinephrine, and endothelium have on afferent and efferent arterioles?

Constriction, reducing GFR and renal blood flow. (D) Signup and view all the answers

Where are angiotensin II receptors located in the kidney?

In all blood vessels of the kidneys. (A) Signup and view all the answers

Which of the following would cause an increase in the hydrostatic pressure?

Increased arterial pressure. (A) Signup and view all the answers

How does Angiotensin II affect the glomerular hydrostatic pressure and renal blood flow?

It lowers blood flow and increases pressure. (B) Signup and view all the answers

How does a slight constriction of the efferent arterials affect glomerular filtration?

It increases filtration through an increase in hydrostatic pressure. (B) Signup and view all the answers

Which substances counteract the vasoconstrictor effects of angiotensin II?

Nitric oxide and prostaglandins. (C) Signup and view all the answers

Which scenario would result in reduced GFR due to increased colloid osmotic pressure?

A severe constriction of the efferent arterials. (C) Signup and view all the answers

What is the primary effect of nitric oxide on vascular resistance in the kidneys?

It decreases vascular resistance. (C) Signup and view all the answers

What is the primary determinant of renal blood flow?

The difference between the hydrostatic pressure of renal artery and renal vein. (A) Signup and view all the answers

What is the role of Arginine in the production of Nitric Oxide?

Arginine is a precursor to Nitric Oxide. (D) Signup and view all the answers

The renal cortex receives what portion of the kidney's blood flow?

The majority of the kidney's blood flow. (C) Signup and view all the answers

Which of the following anatomical section of the kidneys contains most of the glomeruli?

The renal cortex. (C) Signup and view all the answers

What is the term for the kidney's ability to maintain a stable renal blood flow and GFR despite blood pressure changes?

Auto regulation (B) Signup and view all the answers

In the kidneys, is the primary goal of auto regulation to maintain oxygen and nutrient delivery for metabolic waste removal?

No, it is to maintain a relatively constant GFR and water excretion. (C) Signup and view all the answers

According to the information, what is the approximate normal GFR rate per day?

180 liters (C) Signup and view all the answers

What is the approximate normal rate of tubular reabsorption per day according to the information provided?

178.5 liters (C) Signup and view all the answers

Without auto regulation, how would a 25% increase in blood pressure affect the amount of urine output?

Urine output would dramatically increase. (A) Signup and view all the answers

What is the role of cyclic GMP (cGMP) in vasodilation as discussed?

cGMP mediates vasodilation by interacting with phosphodiesterase and reducing intracellular calcium and activating smooth muscle relaxation. (D) Signup and view all the answers

Study Notes

Glomerular Filtration Rate (GFR) and Renal Blood Flow

Approximately 180 liters of fluid are filtered daily from glomerular capillaries into Bowman's capsule.
Most filtered fluid is reabsorbed, leaving ~1 liter for excretion.
GFR and excretion are highly variable, influenced by fluid intake, renal blood flow, and glomerular capillary membranes.
Glomerular capillaries are permeable to water and small solutes but relatively impermeable to proteins and red blood cells.
Filtration fraction (20%) is the ratio of GFR to renal plasma flow.
Filtration rate is linked to capillary filtration coefficient and balance of hydrostatic and colloid osmotic forces.
Filtration barrier consists of endothelium, basement membrane, and epithelial cells (podocytes).

Filtration Barrier Structure and Function

Endothelium has fenestrations (small holes) allowing water and small solutes through.
Basement membrane repels negatively charged proteins, allowing smaller molecules to filter through.
Podocytes have slit pores that filter and prevent larger proteins from entering Bowman's capsule.
Filtration barrier selectivity depends on size and charge of molecules.

Mechanisms Determining GFR

Net filtration pressure is the sum of hydrostatic and colloid osmotic forces.
Glomerular capillary hydrostatic pressure (favors filtration).
Bowman's capsule hydrostatic pressure (opposes filtration).
Colloid osmotic pressure in the capillary (opposes filtration).
GFR is calculated as the filtration coefficient multiplied by the net filtration pressure.
Glomerular filtration coefficient (CF) is a measure of the filterability of the glomerular capillary membranes and is typically 12.5 mL/min.

Factors Affecting GFR

Hydrostatic pressure in Bowman's capsule: Increased pressure reduces GFR.
Colloid osmotic pressure (COP): Increased COP in the glomerular capillaries reduces GFR.
Alterations in afferent and efferent arteriole resistance affect glomerular hydrostatic pressure and hence GFR.
Arteri constrictions influence GFR via opposing effects on hydrostatic pressure and COP .

Regulation of Renal Blood Flow and GFR

Renal blood flow is driven by the pressure gradient between renal artery and vein.
Resistance in interlobular arteries, afferent, and efferent arterioles regulates blood flow.
Sympathetic nervous system, hormones (e.g., norepinephrine, epinephrine, angiotensin II), and local factors (e.g., nitric oxide, prostaglandins) influence resistance.

Renal Blood Flow Distribution

Renal cortex receives most of the blood flow.
Renal medulla blood supply comes from vasa recta.
Vasa recta is a capillary network that descends into the medulla and returns to the cortex.

Autoregulation of GFR

Autoregulation maintains relatively constant GFR despite variations in arterial blood pressure.
Autoregulation is vital to prevent drastic changes in fluid and solute excretion based on fluctuating blood pressure.
Tubuloglomerular feedback mechanism links sodium chloride concentration in the distal tubule with afferent arteriole resistance, ensuring stable sodium chloride delivery to the distal tubule.

Tubuloglomerular Feedback

Macula densa (in distal tubule) senses sodium chloride concentration.
Decreased GFR leads to increased sodium chloride reabsorption in the loop of Henle.
Macula densa then signals afferent arterioles to constrict, decreasing blood flow to the glomerulus and restoring GFR.
Conversely, increased GFR leads to reduced sodium chloride reabsorption and reduced renin release, maintaining GFR

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Description

This quiz explores the concepts of Glomerular Filtration Rate (GFR) and renal blood flow, detailing the filtration process within the kidneys. It covers the anatomy and functions of the filtration barrier, including the roles of endothelial cells, the basement membrane, and podocytes. Understand how various factors influence GFR and the dynamics of renal filtration.