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Flashcards in Urinary: Glomerular Filtration Deck (18):

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

- 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


What are the functions of the kidney?

- 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


How many litres of ECF do the kidneys filter each day?
How much urine is produced?

Filter 180L/day
1.5L of urine produced per day


What is the role of the PCT?

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


What is the role of the loop of henle?

Some reabsorption of salts

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


What is the role of the DCT?

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.


What is renal plasma flow?

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


What are the 2 types of nephrons?

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.


What percentage of blood is filtered?

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


What are the layers of the filtration barrier?

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


What are the 3 forces creating a net filtration pressure/

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


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

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


Outline the myogenic response to maintain GFR

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


Outline the tubular-glomerular feedback to maintain GFR

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


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

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


How is glucose reabsorbed in the PCT?

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)


What substances are secreted into the tubular fluid?

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


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

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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