Section 3

Question 2

What is the glomerulus and what is its function?

Answer 2

The glomerulus is a network of capillaries located at the beginning of a nephron. It filters blood across its walls through the glomerular membrane, yielding filtrate into Bowman’s capsule.

Question 3

How does the glomerulus receive its blood supply and where do the glomerular capillaries exit?

Answer 3

The glomerulus receives its blood supply from an afferent arteriole and the glomerular capillaries exit into efferent arterioles.

Question 4

What are the three layers that make up the glomerular membrane?

Answer 4

1. OUTSIDE: The glomerular capillary wall
2. The basement membrane
3. The inner layer of Bowman’s capsule

Question 5

What is glomerular filtration rate (GFR)?

Answer 5

Glomerular filtration rate (GFR) is the rate at which blood is filtered through all of the glomeruli, serving as a measure of overall renal function.

Question 6

What is the composition and function of the glomerular capillary wall?

Answer 6

The glomerular capillary wall consists of a single layer of endothelial cells with large pores that make it 100 times more permeable to fluids and solutes than regular capillaries. While large plasma proteins cannot pass through, smaller ones like albumin can.

Question 7

Describe the composition and function of the basement membrane in glomerular filtration.

Answer 7

The basement membrane contains no cells and is composed of collagen to provide structural strength, and glycoproteins to discourage the filtration of small plasma proteins. The negatively charged glycoproteins repel proteins that do get through the capillary walls, allowing only about 1% of filtered albumin to pass into Bowman’s capsule.

Question 8

What is the composition and function of the inner layer of Bowman’s capsule?

Answer 8

The inner layer of Bowman’s capsule is composed of podocytes, which are cells that wrap around the capillaries of the glomerulus. These podocytes form narrow filtration slits between them that allow fluid to pass into Bowman’s capsule.

Question 9

What is glomerular capillary blood pressure, and how does it differ from regular capillary blood pressure?

Answer 9

Glomerular capillary blood pressure is the pressure exerted by the blood in the glomerular capillaries, which averages around 55 mmHg. Unlike regular capillaries with a blood pressure of about 18 mmHg, glomerular capillary pressure is higher due to the larger diameter of the afferent arteriole compared to the efferent arteriole, preventing pressure decrease along the capillaries and favoring filtration.

Question 10

What is plasma-colloid oncotic pressure, and how does it affect glomerular filtration?

Answer 10

Plasma-colloid oncotic pressure is the pressure exerted by large proteins in the plasma that resist the movement of water into Bowman’s capsule. It is about 30 mmHg and opposes filtration.

Question 11

What is Bowman’s capsule hydrostatic pressure, and how does it influence glomerular filtration?

Answer 11

Bowman’s capsule hydrostatic pressure is the pressure of the fluid in Bowman’s capsule, which opposes the movement of water out of the glomerular capillaries. It is approximately 15 mmHg.

Question 12

How is net filtration pressure calculated, and what does it represent?

Answer 12

Net filtration pressure equals the glomerular capillary blood pressure minus the sum of the plasma-colloid oncotic and Bowman’s capsule hydrostatic pressures. It represents the driving force for glomerular filtration and is typically around 10 mmHg.

Question 13

What is glomerular filtration rate (GFR)?

Answer 13

Glomerular filtration rate (GFR) is the rate at which fluid is filtered through the glomeruli of the kidneys into Bowman’s capsule per unit of time.

Question 14

What factors influence glomerular filtration rate (GFR)?

Answer 14

Glomerular filtration rate (GFR) is dependent not only on filtration pressure but also on the glomerular surface area available and the permeability of the membrane, collectively referred to as the filtration coefficient (Kf).

Question 15

How is glomerular filtration rate (GFR) mathematically expressed?

Answer 15

filtration coefficient (Kf) x filtration pressure.

Question 16

What are the average values of glomerular filtration rate (GFR) in males and females?

Answer 16

In the average male, the glomerular filtration rate (GFR) is 125 ml/min, while in females it is 115 ml/min.

Question 17

Describe two pathological conditions that can lead to changes in glomerular filtration rate (GFR).

Answer 17

A kidney stone obstructing the ureter can increase Bowman’s capsule hydrostatic pressure, leading to decreased GFR.

Severe diarrhea can lead to decreased GFR. Dehydration resulting from fluid loss in diarrhea decreases blood pressure and increases plasma-colloid osmotic pressure, ultimately decreasing GFR.

Question 18

What is the equation used to determine net filtration pressure?

Answer 18

Glomerular Capillary Blood Pressure - (Plasma colloid Oncotic Pressure + Bowman’s Capsule Hydrostatic Pressure) = Net Filtration Pressure

Question 19

How are changes in glomerular filtration rate (GFR) related to changes in glomerular capillary blood pressure?

Answer 19

Changes in GFR are proportional to changes in glomerular capillary blood pressure, as indicated by the equations:

Filtration Coefficient (Kf) x Net Filtration Pressure = Glomerular Filtration Rate (GFR)

Net Filtration Pressure = Glomerular Capillary Blood Pressure - (Plasma colloid Oncotic Pressure + Bowman’s Capsule Hydrostatic Pressure)

Question 20

Why are autoregulatory mechanisms in place for GFR?

Answer 20

to prevent sudden swings in glomerular filtration rate (GFR) as changes in GFR are directly proportional to glomerular capillary blood pressure

Question 21

How do autoregulatory mechanisms primarily regulate glomerular capillary blood pressure?

Answer 21

By controlling the diameter of the afferent arterioles.

Constricting the afferent arterioles decreases glomerular capillary blood pressure, while dilating them increases it.

The two intrarenal mechanisms (myogenic activity and tubuloglomerular feedback) allow for this to happen

Question 22

Describe myogenic activity in the context of renal physiology.

Answer 22

Myogenic activity in renal physiology refers to the response of the afferent arterioles to changes in blood pressure.

When blood pressure increases, the arteriole walls automatically constrict to reduce blood flow to the glomerular capillaries, preventing an increase in glomerular filtration rate (GFR).

Conversely, if blood pressure decreases, the arterioles dilate to increase blood flow and prevent a decrease in GFR.

Question 23

What is the tubuloglomerular feedback (TGF) mechanism?

Answer 23

Tubuloglomerular feedback (TGF) is a regulatory mechanism involving the juxtaglomerular apparatus, where specialized tubular cells called the macula densa sense changes in salt levels of the tubular fluid.

If arterial pressure increases and subsequently increases glomerular filtration rate (GFR), more fluid and salt flow through the distal tubule. The macula densa responds by releasing ATP, which is converted to adenosine, leading to constriction of the afferent arterioles to reduce GFR.

Question 24

What are the components of the juxtaglomerular apparatus?

Answer 24

The juxtaglomerular apparatus consists of a combination of vascular and tubular cells, with specialized tubular cells called the macula densa playing a key role in tubuloglomerular feedback (TGF) mechanism.

Question 25

What would occur to glomerular capillary blood pressure, net filtration pressure, and glomerular filtration rate if there was vasoconstriction in the afferent arteriole?

Answer 25

Vasoconstriction in the afferent arteriole would lead to a decrease in glomerular capillary blood pressure, resulting in a decrease in net filtration pressure and subsequently a decrease in glomerular filtration rate.

Question 26

What would occur if there was vasodilation of the afferent arteriole?

Answer 26

Vasodilation of the afferent arteriole would cause an increase in glomerular capillary blood pressure, leading to an increase in net filtration pressure and subsequently an increase in glomerular filtration rate.

Question 27

How is glomerular filtration rate (GFR) controlled extrinsically?

Answer 27

Glomerular filtration rate (GFR) is controlled extrinsically by the sympathetic nervous system, which innervates the afferent arterioles

Question 28

Describe the effect of increased sympathetic activity on glomerular filtration rate (GFR) during a hemorrhage.

Answer 28

During a hemorrhage, increased sympathetic activity leads to constriction of the afferent arterioles, decreasing glomerular capillary pressure, GFR, and urine production. This mechanism helps correct depleted plasma volumes.

Question 29

What percentage of the total cardiac output do the kidneys receive at rest?

Answer 29

At rest, the kidneys receive approximately 22% of the total cardiac output.

Question 30

How is renal blood flow adjusted to calculate the proportion of cardiac output received by the kidneys?

Answer 30

Renal blood flow is adjusted considering that only 55% of whole blood is filterable plasma, resulting in an estimated renal blood flow of 1140 ml/minute. This proportion is then compared to the total cardiac output, which is around 5000 ml/minute at rest, to calculate that the kidneys receive around 22% of the total cardiac output.

Question 31

What is the functional significance of the kidneys receiving a high proportion of total cardiac output?

Answer 31

The kidneys receive a high proportion of total cardiac output to fulfill their primary purpose of filtering blood, maintaining tight control of volume and electrolyte concentrations, and efficiently eliminating wastes from the body. This ensures effective regulation of the body’s water pools and overall homeostasis.

Question 32

Arrange these in order of the sequence of actions of the body in response to decreased arterial blood pressure (to re-increase arterial blood pressure):

• Increase in conservation of fluid and salt
• Afferent arteriolar vasoconstriction
• decrease in GFR
• generalized arteriolar vasoconstriction
• increase in sympathetic activity
• decrease in glomerural capillary bp
• decrease in urine volume
• detection by aortic arch and carotid sinus baroreceptors

Answer 32

Decrease in arterial bp
1. Detection by aortic arch and carotid sinus baroreceptors
2. Increase in sympathetic activity
3. Generalized arteriolar vasoconstriction
4. Afferent arteriolar vasoconstriction
5. Decrease in glomerular capillary bp
6. Decrease in GFR
7. Decrease in urine volume
8. Increase in conservation of fluid and salt
Increase in arterial bp