S3) GFR and Glomerulus

Question 1

Label the following blood vessels showing the blood supply and drainage of the kidney:

Answer 1

Question 2

Label the following structures in the lobe of the kidney:

Answer 2

Question 3

Describe the anatomical course of blood supply from the aorta to the peritubular capillaries / vasa recta

Answer 3

Abdominal aorta → renal artery → segmental artery → interlobar artery → arcuate artery → interlobular artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries / vasa recta

Question 4

Describe the anatomical course of blood drainage from the interlobular vein to the inferior vena cava

Answer 4

Interlobular vein → arcuate vein → interlobar vein → segmental vein → renal vein → inferior vena cava

Question 5

Where do the peritubular capillaries drain?

Answer 5

Peritubular capillaries drain into the interlobular veins

Question 6

Where do the vasa recta drain into?

Answer 6

Vasa recta drain into interlobular veins and arcuate veins

Question 7

Compare and contrast the cortical and juxtamedullary nephrons in terms of:

• Location
• Glomerulus size
• Loop of Henle

Answer 7

• Cortical nephron:

I. Found in outer part of cortex

II. Small glomerulus

III. Short LoH slightly in medulla

• Juxtamedullary nephron:

I. Found in inner part of cortex next to medulla

II. Big glomerulus

III. Long LoH in medulla

Question 8

Compare and contrast the cortical and juxtamedullary nephrons in terms of:

• Diameter of afferent arteriole
• Course of efferent arteriole

Answer 8

• Cortical nephron:

I. AA diameter > EA diameter

II. EA forms peritubular capillaries

• Juxtamedullary nephron:

I. AA diameter = EA diameter

II. EA forms vasa recta

Question 9

Compare and contrast the cortical and juxtamedullary nephrons in terms of:

• Sympathetic nerve stimulation
• Concentration of renin
• Ratio

Answer 9

• Cortical nephron:

I. Rich stimulation

II. High [renin]

III. 90% in kidney

• Juxtamedullary nephron:

I. Poor stimulation

II. Low [renin]

III. 10% in kidney

Question 10

What is the value for renal blood flow?

Answer 10

Renal Blood Flow (RBF) is ~1.1L/min

Question 11

How is renal plasma flow calculated?

Answer 11

• Haematocrit is normally ~0.45
• Hence, plasma ~ 0.55

Plasma x RBF = RPF

0.55 x 1.1L /min = 605 mL/min of plasma

Question 12

Where is the glomerulus found?

Answer 12

In the cortex

Question 13

What happens to the blood in the glomerulus?

Answer 13

• 20% of blood from renal artery is filtered at any one time
• 80% blood arriving exits via efferent arteriole (unfiltered)

Question 14

What is the normal total glomerular filtrate per day?

Answer 14

140 – 180 L /day (~125 ml/min)

Question 15

Which two structures compose the renal corpuscle?

Answer 15

• Glomerulus
• Bowman’s capsule

Question 16

State the structure and function of the renal corpuscle

Answer 16

• Structure: filtration barrier produced by capillary endothelium and visceral layer of Bowman’s capsule
• Function: produces ultra filtrate of plasma

Question 17

What sort of epithelium is found in the parietal layer of Bowman’s capsule?

Answer 17

Simple squamous epithelium

Question 18

Filtration is a selective process.

Which substances are filtered and which aren’t?

Answer 18

• Filtered: water, salts and small molecules
• Not filtered: cells and large proteins

Question 19

What is the end product of filtration?

Answer 19

The end product of filtration (ultrafiltrate) is identical to plasma without the large proteins and cells

Question 20

Identify the 3 layers of the filtration barrier

Answer 20

• Capillary endothelium
• Basement membrane
• Podocyte layer (visceral layer)

Question 21

Describe the structure and function of the capillary endothelium

Answer 21

• Structure: permeable
• Function: filtrate (H₂O, salts, glucose) moves between cells

Question 22

Describe the structure and function of the basement membrane

Answer 22

• Structure: acellular gelatinous layer of collagen/glycoproteins
• Function:

I. Permeable to small proteins

II. Glycoproteins (- charge) repel protein movement

Question 23

Describe the structure of the podocyte layer

Answer 23

Contain pseudopodia which interdigitate and form filtration slits

Question 24

Explain the role of permeable selectivity of the filtration barrier to ensure the overall selectivity of filtration

Answer 24

Only particles with the following pass through:

• Small molecular weight
• Effective radius less

Question 25

Explain the effect of the filtration barrier's charge on ensuring the overall selectivity of filtration

Answer 25

- Negative charge of barrier repels proteins (only a few small proteins pass through) - Removing this negative charge increases the filtration of anions *e.g. proteinuria*

Question 26

Identify the three physical forces involved in the filtering of plasma to form ultra filtrate

Answer 26

- **P**_GC – Hydrostatic pressure in the capillary - **P**_BC – Hydrostatic pressure in the Bowman's capsule - **π**_GC – Oncotic pressure difference between the capillary and tubular lumen

Question 27

What conditions are necessary for the net filtration pressure to decrease?

Answer 27

- P_GC decreases - P_BC increases - π_GC increases

Question 28

What conditions are necessary for the net filtration pressure to increase?

Answer 28

- P_GC ​increases - P_BC decreases - π_GC decreases

Question 29

Which pressure gradient favours filtration?

Answer 29

P_GC – hydrostatic pressure in plasma

Question 30

Which pressure gradient opposes filtration?

Answer 30

- P_BC – hydrostatic pressure in tubule - π_GC – oncotic pressure in glomerulus

Question 31

Identify three processes that drive the autoregulation of the glomerulus

Answer 31

- Myogenic mechanism - Tubuloglomerular feedback - Glomerulotubular balance

Question 32

Why do we need the autoregulation of GFR?

Answer 32

- Keeps RBF and GFR constant - Within the range 80-180 mmHg

Question 33

What would happen if we didn't have autoregulation?

Answer 33

Slight change in BP would cause significant change in GFR: ## Footnote *E.g. 25% increase in BP → 125 mmHg → 225 L/day GFR → 4.6L day urine*

Question 34

What does the myogenic mechanism entail?

Answer 34

- Arterial smooth muscle responds to increases and decreases in vascular wall tension - Occurs rapidly

Question 35

The myogenic mechanism is a property predominantly of the preglomerular resistance vessels. Identify them

Answer 35

- Arcuate arteries - Interlobular arteries - Afferent arteriole

Question 36

Illustrate how the myogenic response is P_GC regulated

Answer 36

- **Increase GFR** (Increase P_GC) I. Dilate AA II. Constrict EA - **Decrease GFR** (Decrease P_GC): I. Dilate EA II. Constrict AA

Question 37

Describe the myogenic autoregulation of the BP

Answer 37

- ↑ BP → afferent arteriole constriction - ↓ BP → afferent arteriole dilatation **GFR is unchanged in both**

Question 38

What does the tubuloglomerular feedback do?

Answer 38

**TG feedback** links control of distal solute delivery to the JGA with renal arteriolar resistance and hence, tubular reabsorption

Question 39

What are the two components of TG feedback?

Answer 39

- Afferent arteriole resistance - Efferent arteriolar feedback (hormonal)

Question 40

Explain how changes in tubular flow rate change the amount of NaCl that reaches the distal tubule

Answer 40

Increased aBP = Increased P_GC = Increased RPF = Increased GFR = Increased [Na⁺] and [Cl⁺] in distal tubule

Question 41

What role do macula densa cells have in autoregulation?

Answer 41

**Macula densa cells** are sensors of DCT luminal [NaCl]

Question 42

The macula densa stimulates the juxtaglomerular apparatus to releases chemicals which regulate arterial tone. Identify them and their effects

Answer 42

- **Adenosine**: reduces GFR (A₁ receptors constrict AA and A₂ receptors dilate EA) - **Prostaglandin**: increases GFR (vasodilates AA)

Question 43

Sympathetic nerve fibres innervate AA and EA. What effect does this have?

Answer 43

- Sympathetic innervation is **low** (no effect on GFR) - **Vasoconstriction** can be stimulated by fight/flight, haemorrhage or ischaemia (reduces GFR)

Question 44

What effect does the parasympathetic nervous system have on the kidney?

Answer 44

PNS releases **nitrous oxide** for endothelial cells and vasodilation

Question 45

Autoregulation by glomerulotubular balance is a second line of defence. What does it do?

Answer 45

**Glomerulotubular balance** blunts Na⁺ excretion response to any GFR changes

Question 46

What type of epithelia is found in the proximal convoluted tubule?

Answer 46

Simple cuboidal epithelia

Question 47

What adaptation do cells in the PCT have to help reabsorption?

Answer 47

- Microvilli - Numerous mitochondria

Question 48

What type of epithelia is found in the descending limb of the Loop of Henle?

Answer 48

Simple squamous epithelia

Question 49

Why are there few mitchondria in the cells of the descending limb of the Loop of Henle?

Answer 49

- Only passive transport occurs - ATP is not needed

Question 50

What type of epithelia is found in the ascending limb of the Loop of Henle?

Answer 50

Simple squamous epithelia

Question 51

Which organelle is abundant in the cells of the ascending limb of the Loop of Henle and why?

Answer 51

- Mitochondria - Active absorption of Na⁺, K⁺, Cl^-

Question 52

What type of epithelia is found in the collecting duct?

Answer 52

- Simple columnar epithelium (no microvilli) - Simple cuboidal epithelium (no microvilli)

Question 53

What structure is formed from the merging of the collecting ducts and what does it do?

Answer 53

**Papillary duct** – acts as a gateway to the minor calyx