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?
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/
The large hydrostatic pressure in the capillary
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)