Urinary: Glomerular Filtration Flashcards Preview

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Flashcards in Urinary: Glomerular Filtration Deck (18)
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1
Q

How does the kidney deal with glucose, amino acids and bicarbonate?

A
  • 100% of the glucose, AA and bicarbonate are reabsorbed
  • 99% of water and Na+, Cl- are reabsorbed
  • only a few wast products are not recovered
2
Q

What are the functions of the kidney?

A
  • regulation of concentrations of substances in the ECF
  • excretion of waste products
  • endocrine: synthesis of renin, prostaglandins
  • metabolism: active form of vit D, catabolism of insulin
3
Q

How many litres of ECF do the kidneys filter each day?

How much urine is produced?

A

Filter 180L/day

1.5L of urine produced per day

4
Q

What is the role of the PCT?

A

ISOSMOTIC REABSORPTION (major site of reab)

  • reabsorbs 67% of Na+ and water
  • 80-90% of K+
  • 90% bicarb
  • all glucose and AA

The reabsorbed material leave by peritubular capillaries

5
Q

What is the role of the loop of henle?

A

Some reabsorption of salts

Major function is to create gradient of increasing osmolarity in the medulla using counter-current multiplication.

6
Q

What is the role of the DCT?

A

Major site of VARIABLE reabsorption of electrolytes and water - fluid leaving LoH is hypotonic.
Removes more Na+ and Cl- and actively secretes H+ –> water may or may not follow.

7
Q

What is renal plasma flow?

A

Not all the blood that goes to the glomerulus is filtered - the plasma is filtered (55% of blood) but the haematocrit isnt (45% of blood).

Therefore renal plasma flow is 0.55 x 1.1L/min (renal blood flow) = 605ml/min of plasma

8
Q

What are the 2 types of nephrons?

A

Cortical Nephrons: (90%)
Short with tangled peritubular capillaries

Juxtamedullary Nephrons: (10%)
Long with golmerulus next to medullary border
Have vasa recta running parallel with LoH but flow in different direction.

9
Q

What percentage of blood is filtered?

A

Only 20%, the other 80% flows through unchanged (however has haematocrit from 20% added meaning an increase in velocity and oncotic pressure)

10
Q

What are the layers of the filtration barrier?

A
  1. Capillary Endothelium - water salts and glucose can pass through, filtrate moves between cells
  2. Basement membrane - acellular layer of collagen and glycoproteins (have a neg charge so repel proteins)
  3. Podocyte layer - forms filtration slits
11
Q

What are the 3 forces creating a net filtration pressure/

A

Favouring filtration:
The large hydrostatic pressure in the capillary

Opposing filtration:
Oncotic pressure in the capillary drawing water in
Hydrostatic pressure in the bowmans capsule

12
Q

What are the autoregulatory mechanisms to maintain the hydrostatic pressure in the capillary?

A
  1. Myogenic response (maintains GFR when BP is within physiological limits)
  2. Tubular Glomerular feedback
13
Q

Outline the myogenic response to maintain GFR

A

Myogenic response maintains GFR when BP is within physiological limits

Increase hydrostatic pressure:

  • Decreasing afferent resistance
  • Increasing efferent resistance

Decrease hydrostatic pressure:
- Increasing afferent resistance

14
Q

Outline the tubular-glomerular feedback to maintain GFR

A

Relies on the distal tubule nestling between the AA and EA. Macula densa cells detect changes to NaCl conc

If NaCl conc increases:

  • GFR needs to decrease
  • macula densa release adEnosine to vasodilate EA

If NaCl conc decreases:

  • GFR needs to increase
  • macula densa release prostAglandins to vasodilate AA
15
Q

Outline the different types of sodium channels in the apical membrane of the nephron

A

PCT: Na-H antiporter and Na-Glucose cotransporter
LoH: Na-K-2Cl symporter
Early DT: Na-Cl symporter
Late DT and CD: ENaC

16
Q

How is glucose reabsorbed in the PCT?

A

The Na-Glucose cotransporter (SGLUT) reabsorbs 1 glucose with 2 sodium. The glucose leaves the basolateral side by facilitated diffusion.

If the transport maximum of the plasma is exceeded then excess glucose is spilled over into the urine - glycosuria resulting in polyuria (water follows)

17
Q

What substances are secreted into the tubular fluid?

A

Protons
Potassium
Organic anions and cations (many drugs are secreted this way)

18
Q

What is the mechanism of organic cation secretion in the PCT?

A

Na-K-ATPase on apical keeps Na low
Therefore Na - H antiporter works to lower H conc
Therefore a H - Cation antiporter secretes cations

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