WEEK 4: GLOMERULAR STRUCTURE AND FUNCTION Flashcards

1
Q

What is glomerular filtration?

A

Passing of plasma from glomerulus into Bowman’s capsule

Passive process

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2
Q

Define glomerular filtration rate.

A

Glomerular Filtration Rate (GFR) = rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time or

The volume of filtrate formed each minute by the combined activity of ALL the +/- 2 million glomeruli of the kidney.

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3
Q

What is the Glomerular filtration rate:
*Per minute
*Per day

A

GFR = 125 ml/min
= 180 litres/day

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4
Q

How much % of plasma enters the glomeruli and is filtered and leave via the efferent arteriole?

A

*20% of the plasma is involved in gloeruli filtratiom
*80% leaves is not filtered and leaves via the efferent arteriole.

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5
Q

State the 3 layers of glomerular membrane particles have to pass through during filtration.

A

1.Glomerular fenestrated capillary layer.
2.Basal membrane made of collagen and glycoproteins
3.Inner layer of bowman’s capsule with podocytes

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6
Q

Explain how the kidney is able to maintain no proteins in urine.

A

1.Large proteins are filtered by the fenestrated capillary layer.
2.Some small proteins which might want to cross through are repelled by the by the negatively charged proteins on the basal membrane.
3.Some small proteins which might have made it through are picked up by the proximal tubule by endocytosis, then degraded into amino acids that are returned to the blood.

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7
Q

What does protein in urine mean?
What could be the explanation for this?

A

It is an indication of a kidney disease.

Could be due to disruption of the negative charges within the basement membrane which makes the glomerular membrane more permeable to albumin even though the size of the capillary pores remain constant.

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8
Q

What medical term is used for protein in urine?

A

Proteinuria or albuminuria

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9
Q

Describe the following pressure in glomerular filtration.

1.Glomerular capillary blood pressure
2.What does it depend on?
3.How do the afferent and efferent arterioles brings about the glomerular capillary blood pressure?
4.What is the average estimated value for the glomerular capillary blood pressure?

5.What is the plasma colloid osmotic pressure?
6.Where are the plasma proteins more in this case?
7.Where does the water molecules move?
8.What is the average estimate value for the plasma colloid osmotic pressure?
9.What is the direction of this pressure in reference to the Glomerular capillary blood pressure?

10.What is the Bowman’s capsule hydrostatic pressure?
11.What is the average estimated value for the Bowman’s capsule hydrostatic pressure?

A

1.It is the hydrostatic pressure exerted by the blood in the glomerular capillaries.

2.*Contraction of the heart
*Resistant to blood flow by the afferent and efferent
arterioles

3.The afferent arteriole has a wider lumen so allows more blood to flow in but the efferent arteriole has a narrow lumen, so it offers more resistance.

4.55mmHg

5.It is the pressure caused by the unequal distribution of plasma proteins across the plasma glomerular membrane.

6.The plasma proteins are more in the glomerular capillary and less in the bowman’s capsule.

7.Water molecules will move from the bowman’s capsule into the glomerular capillary.

8.30mmHg

9.It opposes the glomerular capillary blood pressure.

10.It is the pressure exerted by fluid in the bowman’s capsule that tends to push fluid out of the bowman’s capsule, opposing the filtration of fluid from the glomerulus into the bowman’s capsule.

11.15mmHg

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9
Q

Describe the following pressure in glomerular filtration.

1.Glomerular capillary blood pressure
2.What does it depend on?
3.How do the afferent and efferent arterioles brings about the glomerular capillary blood pressure?
4.What is the average estimated value for the glomerular capillary blood pressure?

5.What is the plasma colloid osmotic pressure?
6.Where are the plasma proteins more in this case?
7.Where does the water molecules move?
8.What is the average estimate value for the plasma colloid osmotic pressure?
9.What is the direction of this pressure in reference to the Glomerular capillary blood pressure?

10.What is the Bowman’s capsule hydrostatic pressure?
11.What is the average estimated value for the Bowman’s capsule hydrostatic pressure?

A

1.It is the hydrostatic pressure exerted by the blood in the glomerular capillaries.

2.*Contraction of the heart
*Resistant to blood flow by the afferent and efferent
arterioles

3.The afferent arteriole has a wider lumen so allows more blood to flow in but the efferent arteriole has a narrow lumen, so it offers more resistance.

4.55mmHg

5.It is the pressure caused by the unequal distribution of plasma proteins across the plasma glomerular membrane.

6.The plasma proteins are more in the glomerular capillary and less in the bowman’s capsule.

7.Water molecules will move from the bowman’s capsule into the glomerular capillary.

8.30mmHg

9.It opposes the glomerular capillary blood pressure.

10.It is the pressure exerted by fluid in the bowman’s capsule that tends to push fluid out of the bowman’s capsule, opposing the filtration of fluid from the glomerulus into the bowman’s capsule.

11.15mmHg

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9
Q

Describe the following pressure in glomerular filtration.

1.Glomerular capillary blood pressure
2.What does it depend on?
3.How do the afferent and efferent arterioles brings about the glomerular capillary blood pressure?
4.What is the average estimated value for the glomerular capillary blood pressure?

5.What is the plasma colloid osmotic pressure?
6.Where are the plasma proteins more in this case?
7.Where does the water molecules move?
8.What is the average estimate value for the plasma colloid osmotic pressure?
9.What is the direction of this pressure in reference to the Glomerular capillary blood pressure?

10.What is the Bowman’s capsule hydrostatic pressure?
11.What is the average estimated value for the Bowman’s capsule hydrostatic pressure?

A

1.It is the hydrostatic pressure exerted by the blood in the glomerular capillaries.

2.*Contraction of the heart
*Resistant to blood flow by the afferent and efferent
arterioles

3.The afferent arteriole has a wider lumen so allows more blood to flow in but the efferent arteriole has a narrow lumen, so it offers more resistance.

4.55mmHg

5.It is the pressure caused by the unequal distribution of plasma proteins across the plasma glomerular membrane.

6.The plasma proteins are more in the glomerular capillary and less in the bowman’s capsule.

7.Water molecules will move from the bowman’s capsule into the glomerular capillary.

8.30mmHg

9.It opposes the glomerular capillary blood pressure.

10.It is the pressure exerted by fluid in the bowman’s capsule that tends to push fluid out of the bowman’s capsule, opposing the filtration of fluid from the glomerulus into the bowman’s capsule.

11.15mmHg

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10
Q

What is the net filtration estimated value pressure?
How did we get there?

A

10mmHg
55mmHg- (30mmHg-15mmHg) =10mmHg

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11
Q

What is the glomerular filtration rate depended on?
State the formula.

A

*Net filtration pressure
*Filtration coefficient (Kf): How much glomerular filtration surface area is available for penetration and how permeable the glomerular membrane is.

GFR=Kf x net filtration pressure

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12
Q

Describe the two ways in which the Glomerular colloid osmotic pressure and the Bowman’s capsule hydrostatic pressure can be affected.

A

1.A decrease in plasma proteins reduces the Plasma colloid osmotic pressure and result in low glomerular filtration rate.
*When the plasma colloid osmotic pressure is elevated, there is decrease in GFR. This could be in cases of diarrhea.

2.Bowman’s capsule hydrostatic pressure can be elevated in cases of urinary obstruction, such as kidney stone or enlarged prostate. The damming of the fluid behind the obstruction elevates the capsular hydrostatic pressure.

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13
Q

State the determinants of the glomerular filtration rate.

A

GFR = Kf (filtation coefficient) x net filtration pressure

 HPBC (e.g. kidney stone) =  GFR

 COPGC (e.g. diarrhoea) =  GFR

 COPGC (e.g. severely burned patients) =  GFR

 Kf (change in surface area available for filtration) =  GFR
GFR = Kf x net filtration pressure

(where Kf = filtration coefficient = how ‘holey’ the glomerular membrane is)

Glomerular capillary fluid (blood) pressure (HPGC) is the major determinant of GFR

 HPGC =  GFR

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14
Q

Describe the regulation of renal blood flow and glomerular filtration rate.

A

Autoregulation helps to balance unintentional shifts in GFR.

It may be intrinsic or extrinsic.

  1. Intrinsic regulation (inherent/ needs no external input)
    (a) Myogenic mechanism- contraction of afferent arteriolar smooth muscle in response to stretch. Limits blood flow into glomerulus.
    (b) Tubuloglomerular feedback mechanism- macula densa cells release ATP and adenosine (vasoconstriction) and NO (for vasodilation) in response to amount of salt in the filtrate.
  2. Extrinsic regulation (neural & hormonal)
    - For long term regulation
    (a) Sympathetic control to afferent arterioles via baroreceptor reflex
    (b) Renin-Angiotensin-Aldosterone System (RAAS)- renin secreted by granular cells of JGA.