Module 2 Lecture 4

Question 1

What are the three key processes of urine formation? please LABEL the DIAGRAM

Answer 1

Glomerular filtration, tubular reabsorption and tubular secretion

Question 2

What is involved in glomerular filtration?

Answer 2

filters the blood
–> produces a cell-and protein-free
filtrate

Question 3

What is involved in tubular absorption?

Answer 3

Selectively moves substances from the filtrate back into the blood to reclaim what the body needs –> anything that is not reabsorbed becomes urine

Question 4

What is involved in tubular secretion?

Answer 4

selectively adds
substances from the blood into the
filtrate –> anything that is secreted
becomes urine

Question 5

What are some key processes of urine formation?

Answer 5

• the kidney filters about 180 L of blood each day, less than 1% of body weight but consume 20-25% of all oxygen at rest

Question 6

How is filtrate and urine different?

Answer 6

filtrate is plasma without proteins, while urine contains excess solutes, ions and metabolic waste

Question 7

Glomerular function in detail (pls label)

Answer 7

Hydrostatic pressure forces fluids & solutes

through a membrane, “simple mechanical filters”

Question 8

What are the 3 layers of the filtration membrane?

Answer 8

• Capillary endothelium
• Basement membrane
• Podocyte foot processes

Question 9

What is the outward pressures in the glomerular filtration

Answer 9

Outward pressures
• Hydrostatic pressure in glomerular capillaries (glomerular
blood pressure forces fluid out of capillary)
• Osmotic oncotic/protein pressure in Bowman’s capsule
space (this is zero as proteins don’t really enter capsule)

Question 10

What is the inward pressures in the glomerular filtration

Answer 10

Hydrostatic pressure in Bowman’s capsule space (filtrate
in capsule draws fluid into capillary)
• Osmotic oncotic/protein pressure in glomerular capillaries
(proteins in blood draw fluid into capillary)

Question 11

What does net filtration pressure favour?

Answer 11

net filtration pressure favours and outward pressure and therefore fluid is forced out of capillary

Question 12

What is glomerular filtration rate measured in?

Answer 12

Glomerular filtration rate (GFR) is the volume of filtrate formed
each minute by the kidneys

Question 13

What is GFR directly proportional to?

Answer 13

Net filtration pressure

• Filtration membrane permeability and total SA for filtration

Question 14

What is step 2 (tubular r re-absorption)

Answer 14

Reabsorption selectively
reclaims tubule contents &
returns it to blood

Question 15

What occurs in tubular re-absorption

Answer 15

• Reabsorption of almost all
substances is coupled to
active sodium reabsorption
– Basolateral membrane:
Na+/K+ ATPase pump
– Apical membrane: secondary
active transport/cotransport
carriers or facilitated diffusion
– Water reabsorption:
aquaporins act as water
channels (regulated by ADH in
collecting duct)

Question 16

What occurs in tubular secretion?

Answer 16

Secretion selectively moves
substances from blood into
filtrate – waste products that
‘escaped’ filtration
E.g. H+, excess K+, creatinine, urea,
uric acid, certain drugs & metabolites
bound to plasma proteins
- Urine eventually excretes both filtered
(& not reabsorbed) & secreted
substances

Question 17

OVERALL tubular re absorption and secretion? (LABEL)

Answer 17

Each tubule segment is
responsible for reabsorbing
and/or secreting different
solutes
• Some are regulated by hormone
action
• Maintains an osmotic gradient in
the medullary interstitial space