Week 8 - Kidney filtration, absorption and secretion

Question 1

What % of cardiac output do the kidneys receive?

Answer 1

20-25%

Question 2

What % of glomerular filtrate is reabsorbed?

Answer 2

99%

1% enters bladder to be excreted as urine

Question 3

What are the two distinct areas of the kidney?

Answer 3

cortex and medulla

Question 4

What are the features of the cortex?

Answer 4

extensive blood supply

medullary rays

cortical labyrinth

Question 5

What are medullary rays?

Answer 5

aggregation of stright tubles and collecting ducts

Question 6

What are renal columns?

Answer 6

between renal pyramids, extension of cortex

Question 7

What is the capillary network of the medulla called?

Answer 7

vasa recta

Question 8

What is the renal interstitium?

Answer 8

the connective tissue surrounding the nephrons, ducts and blood vessels

it comprises fibroblasts and collagen fibres

Question 9

What artery supplies blood to the kidney?

Answer 9

renal artery

(branch of abdominal aorta below SMA)

Question 10

Where do the kidneys lie in relation to the peritoneum?

Answer 10

retroperitoneum

Question 11

At what vertebral level do the kidneys lie?

Answer 11

T12-L3

Question 12

At the hilum of the kidney, which structure is most anterior?

a) renal artery
b) renal vein
c) renal pelvis

Answer 12

renal vein

hilum - entrance to space in kidney

vein is most anterior followed by artery and pelvis

Question 13

What are two types of nephron?

Answer 13

juxtamedullary

cortical

Question 14

What is the difference between the juxtamedullary and cortical nephrons?

Answer 14

juxtamedullary - loop of henle is longer and dips down into the inner medulla

constitute 15 - 25% of all nephrons

Question 15

What is the renal corpuscle?

Answer 15

glomerulus and Bowman’s capsule

Question 16

What structures comprise the glomerular filtration barrier?

Answer 16

fenestrated endothelium, glomerular basement membrane, visceral epithelial podocytes

fenestrated - ‘holey’

Question 17

What is the inner visceral layer of Bowman’s capsule?

Answer 17

consists of cells called podocytes that have pedicels that wrap around glomerular capillaries

Question 18

How are podocytes specialised?

A) positively charged

B) fenestrated

C) interdigitation of foot processes

D) possess a glycocalyx

Answer 18

C)

podocytes are the epithelial cells of Bowman’s capsule

they have projections from their cell body called ‘foot processes that interdigitate with each other and the spaces between are called slit pores

plasma passes through the slit pores

Question 19

Describe the structure of Bowman’s capsule

Answer 19

parietal layer of simple squamous cells

Bowman’s space into which filtrate enters after passing through filtration slits in the podocytes

the visceral layer containing podocytes sitting on the glomerular basement membrane

Question 20

What feature of glomerular capillary endothelium makes it adapted for glomerular filtration?

Answer 20

they are fenstruated which allows small molecules to pass through them

fenstruated - ‘holey’

Question 21

Where do the renal arteries branch from the abdominal aorta?

A) superior to the coeliac trunk

B) superior to the middle suprarenal arteries

C) inferior to the superior mesenteric artery

D) At the level of L3

E) inferior to the gonadal arteries

Answer 21

C) - renal vessels branch at about L1-L2, below SMA

Coeliac trunk branches at T12, SMA at L1 and the gonadal arteries at L2

Question 22

Which vessels branch off renal arcuate arteries?

A) afferent arterioles

B) efferent arterioles

C) interlobular arteries

D) segmental arteries

E) interlobar arteries

Answer 22

C) also known as cortical radial arteries

The renal arteries branch of the abdominal aorta at the level of L1-L2 below the SMA and separate into 5 segmental arteries close to the hilum. Interlobar arteries ascend between renal pyramids to the level of the base of renal pyramids. They turn 90 degrees and become arcuate arteries that pass in parallel with the base of the pyramids. These give off the interlobular arteries that run downwards to nephrons and give off afferent arterioles.

Venous drainage is the same in the opposite direction

Question 23

What is the total body fluid for an average 70kg person?

Answer 23

42L

approx 60%

Question 24

Where is extracellular fluid distributed in the human body?

Answer 24

plasma, interstitial fluid, transcellular fluid

interstitial fluid - found in the interstitial spaces

Question 25

What is hydrostatic pressure?

Answer 25

pressure exerted by a **liquid** on the sides of a container eg - pressure exerted on fluid on the insides of vessels

Question 26

What is oncotic pressure?

Answer 26

pressure exerted by proteins (albumin) in a blood vessels plasma where plasma proteins are reduced there is a reduction in oncotic pressure

Question 27

How do Starling's forces change from the afferent to efferent end of the glomerular capillaries?

Answer 27

**Increase** in **capillary oncotic pressure** because a large amount of fluid passes out into Bowman's space, which increases hydrostatic pressure in Bowman's space but reduces it in the capillaries Due to fluid loss the capillary plasma proteins become more concentrated There should be no change in oncotic pressure in Bowman's space because normally no protein will pass through the **filtration slits** made by **podocytes**

Question 28

What is the mesangium?

Answer 28

the extracellular matrix that surrounds the mesengial cells and supports capillaries

Question 29

What determines glomerular filtration rate (GFR)?

Answer 29

hydrostatic pressure osmotic pressure properties of the barrier

Question 30

What is glomerular filtration rate (GFR)?

Answer 30

volume of fluid filtered by the glomerular capillaries per unit time

Question 31

What happens to cells when they are placed in a hypotonic solution?

Answer 31

cell increases in size hypotonic - the amount of solute outside the cell is less than inside water moves into the cell to try to balance the osmotic pressure difference and ensure both solutions are equally dilute

Question 32

Which part of the nephron is always impermeable to water?

Answer 32

the thich ascending limb of the loop of Henle is impermeable to both water and solutes except for the Na-K-Cl co-transpoter that acts to remove solutes

Question 33

How will water be distributed in the extracellular and intracellular fluid if a person drinks 60ml of tap water (assuming that all of the fluid is absorbed from the bowel)?

Answer 33

Body Fluid Compartments: Intracellular - 2/3 Extracellular - 1/3 **20ml ECF** **40ml ICF**

Question 34

What parts of the nephron are located in the cortex?

Answer 34

glomeruli, convoluted tubles, cortical collecting ducts

Question 35

Describe the flow of urine from the medullary pyramid to the renal pelvis

Answer 35

medullary pyramid forms a renal papilla that drains urine into a **minor calyx.** These unite to form a **major calyx** and from there urine enters the renal pelvis

Question 36

From which arteries in the kidney do afferent arterioles arise from?

Answer 36

cortical radial (interlobular) arteries

Question 37

What is responsible for most of the colloid osmotic pressure of the plasma?

Answer 37

plasma albumin

Question 38

What three processes are involved in forming urine?

Answer 38

glomerular filtration, tubular reabsorption and tubular secretion

Question 39

What is inulin clearence?

Answer 39

the volume of plasma that inulin is removed from in unit time inulin is the substance used as a gold standard for measuring GFR because it passes through the kidneys without being synthesised or destroyed it is not used in the clinic because it must be infused intravenously and the bladder is usually catheterised **creatinine** is more commonly used

Question 40

Why are measurements of GFR using creatinine sometimes an overestimate (especially during renal disease)?

Answer 40

creatinine is not only filtered but also secreted by the kidney urinary excretion of creatinine is elevated in renal disease

Question 41

What is the effect of GFR is there is an obstruction anywhere along the urinary tract?

Answer 41

GFR decreases ## Footnote increased pressure upstream of the block, increases hydrostatic pressure in Bowmans capsule this pressure opposes filtration net filtration decreases GFR = Kf x net filtration pressure

Question 42

What happens to GFR if a patient is given an intravenous infusion of a large volume of isotonic saline?

Answer 42

GFR increases ## Footnote isotonic saline will decrease the plasma colloid osmostic pressure this increases net filtration

Question 43

What two pressures oppose glomerular hydrostatic pressure?

Answer 43

bowmans capsule hydrostatic pressure plasma oncotic pressure

Question 44

What physiological changes cause ADH secretion?

Question 45

Which part of the nephron in the kidney releases the enzyme renin in response to low blood pressure?

Answer 45

the juxtaglomerular apparatus

Question 46

What part of the loop of Henle is permeable to water but not ions?

Answer 46

**descending limb** ascending limb is impermeable to water but permeable to ions