Urinary - Weeks 1 to 5 (inc. Embryology)

Question 1

What pressures contribute to the filtration rate?

Answer 1

Hydrostatic pressure of capillaries and the Bowmans capsule

Oncotic pressure difference between the capillaries and the lumen of the tubule

Question 2

What are the three parts of the filter?

Answer 2

1) capillary endothelium - fenestrated
2) basement membrane
3) podocytes - make sure large proteins etc can’t leave the capillaries, slit diaphragm

Question 3

What does the Glomerulus do?

Answer 3

Filtration
Selective
Allow water, salts and small proteins to pass through
Makes tubule fluid the same tonicity and ion concentration etc as blood plasma, without the larger cells

Question 4

What are the 2 types of nephron?

Answer 4

Cortical - all in the cortex

Juxtamedullary - closer to the medullary boundary, have a longer loop of Henle

Question 5

What is the role of the PCT?

Answer 5

Reabsorption of Water, Na+, Glucose and other solutes
Isosmotic Reabsorption
Reabsorption driven by Na+ uptake

Question 6

What are the Na+ transporters in the PCT?

Answer 6

Na-H anti porter

Na-glucose symporter

Question 7

How does glucose move in the PCT?

Answer 7

Glucose moves with Na+ against its concentration gradient

Then moves from the lumen into the capillaries via facultative diffusion

Normally 100% reabsorbed

There is a threshold and if that goes over, you get glycosuria

Question 8

Calculate the GFR…

Answer 8

Choose something freely filtered, non reabsorbed, non secreted.
Insulin and Creatinine
See how well the kidneys work

Conc. in urine X urine volume / plasma Conc.

Question 9

What is the filtration fraction?

Answer 9

Proportion of substance actually filtered

GFR/RPF

Question 10

What is renal clearance?

Answer 10

Volume of substance completely cleared by kidneys per unit time
Urine Conc. X volume / plasma Conc.

Detect glomerular damage
Follow progress of kidney disease

Question 11

Describe methods of Autoregulation of the GFR

Answer 11

The glomerular filtration rate is kept in normal limits by

1) Myogenic response- vasoconstriction in response to stretch
2) Tubular Glomerular Feedback - macula densa detects Cl- changes. Stimulate the JGA to release vasoconstrictors (adenosine) or dilators (prostaglandins)

Question 12

How do you estimate GFR?

Answer 12

Use Creatinine Clearance

(140 - Age) X Mass (Kg) X Constant over Serum Creatinine

Question 13

Filtered Load definition

Answer 13

The amount of substance filtered per minute
Work out using the normal plasma concentration then times by the glomerular filtration rate (if it is freely filtered) eg glucose, creatinine.

Question 14

What is the transport maximum?

Answer 14

The renal threshold for a substance that can be filtered, when Tm is reached, the substance starts to overflow into the urine

Question 15

What is the main factor in volume control of the ECF?

Answer 15

Na+

Effective Osmole

Question 16

What happens with an imbalance of Na+?

Answer 16

If less excreted, then water retention can lead to increased blood volume, then arterial pressure rises, leads to oedema.

Question 17

How do we describe the changes of volume?

Answer 17

It is isosmotic, so we change ion concentration and water follows, so osmolarity is unchanged

Question 18

Where in the Kidney do the ion and water changes occur?

Answer 18

Mostly in the PCT
Water then has some in the desc. loop of Henle and DCT and collecting duct
Na+ also in asc. limb and DCT and Collecting Duct

Question 19

What are the 2 cell types in the late DCT/CD?

Answer 19

Principle Cells - Reabsorb with ENaC, creates a neg. charge

Type B intercalated cells - Active Cl- reabsorption

Question 20

Describe ADH Structure

Answer 20

Small Peptide

9 Amino Acids long

Question 21

Describe ADH’s action

Answer 21

ADH acts on cells in the DCT and Collecting Duct.

ADH acts on a GPCR on the basolateral membrane, releases cAMP, then PKA, which inserts Aquaporin into the apical membrane.

Increases the permeability to water and urea

Question 22

What are 2 additional effects of ADH (apart from aquaporins)

Answer 22

Vasoconstriction in Glomerulus

Increase Ion reabsorption in the ascending limb of loop of Henle

Question 23

What produces the Corticomedullary gradient?

Answer 23

The Juxtamedullary nephron

Question 24

What 3 Parts of the Nephron create the gradient?

Answer 24

The active NaCl transport in the asc. limb (counter current multiplication)
The Vasa recta (maintain the gradient)
Recycling of Urea (effective osmole)

Question 25

The Urea which leaves the CD does what?

Answer 25

It is recycled back into the ascending loop of Henle.

It increases osmotic pressure so water follows it into the interstitium (cannot follow back into the loop as it is impermiable)

Question 26

Describe counter current multiplication

Answer 26

1) Na+ pumped out of the asc. limb. Increases osmotic pressure of interstitium and lowers the tubules
2) Water follows from the desc. limb. Makes tubule osmotic pressure back to normal
3) Cycle continues, more concentrated fluid is pushed round, creating more and more conc. fluid
4) Bottom most concentrated as it is the first to take Na+ out of the loop to create the 200mol gradient

Question 27

What is the role of the Vasa Recta

Answer 27

Maintaining the Concentration gradient of the Kidney.
It travels in the opposite direction to the tubule and tries to match the interstitial fluid concentration, it picks up Na+ and H20

Question 28

What are 2 problems with ADH secretion?

Answer 28

Diabetes insipidus - not enough ADH produced from the pitruitry gland or kidney is insensitive to it.
Low conc and lots of urine produced
Manage with ADH injections or nasal spray

Syndrome of Inappropriate ADH secretion (SIADH) - excessive release from pitruiry or other leads to dilutional hyponaturaemia, increase in total body fluid
Get nausea and vomiting, headache, confusion
Treat with ADH receptor antagonists