Eureka Physiology Flashcards
Function of nephron?
Regulates plasma composition via processes if filtration, reabsorption and secretion
What is glomerular filtration?
1st stage of urine production
-Hydrostatic pressure with glomerular capillaries forces plasma components through capillary wall into Bowmans space
(large components remain in capillary)
What is the term for what happens in glomerular filtration?
Ultrafiltration
What is albuminuria?
Albumin in urine
-Indicates pathological process affecting GF
What is GFR?
Rate @ which fluid is filtered by glomerulus from blood into Bowman’s space
How is GFR estimated?
By measuring clearance of substance which satisfies this criteria:
- Steady blood conc
- Freely filtered (passed unhindered across GF membrane)
- Neither absorbed nor secreted by cells of renal tubule
What substances meet criteria for GFR?
Inulin (too tricky to measure and administer though)
THEREFORE
-Creatinine clearance is used
Con with using creatinine clearance for GFR?
Some is secreted by renal tubules so the value is always overestimated by 10-20%
Factors affecting GFR?
- Differences in hydrostatic pressure & oncotic pressure between tubule & capillaries (starling’s forces)
- Renal blood flow and perfusion pressure
Where is fluid secreted along a capillary?
Arterial end
Where is fluid reabsorbed along a capillary?
Venous end
What happens to hydrostatic pressure as fluid travels along capillary towards venous end?
Decreases
Regulation GF?
- Myogenic mechanism autoregulation occurs when SM in wall of blood vessels responds to pressure changes within vessel wall
- Tubuloglomerular feedback mechanism: tubular flow rate affects tone of renal blood vessels
Flow diagram of myogenic mechanism when BP is increased?
Increased BP
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Increased renal perfusion pressure & increased blood flow
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Stimulates stretch receptors in smooth muscle fibres within wall of afferent arterioles: causing them to constrict
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Results in resistance to flow in glomerulus increased
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As a result, blood flow & GFR remain constant despite increase in perfusion pressure
Function of glomerulus?
Filtration of blood to form filtrate
Function of PCT?
Reabsorption of 65% of Na+ & water and most glucose, AAs, HCO3-, PO3-
Loop of Henle function?
Concentration of urine via countercurrent exchnage mechanism
Function of DCT?
- Reabsorption of Na+/Ca2+
- Reabsorption and secretion of K+/H+
Function of CDs?
ADH: Mediated water reabsorption
Aldosterone: Mediated Na+ reabsorption
Secretion of K+/H+
Acid-base balance
K+ secretion
What is the energy bank of tubular transport?
Na+ gradient
What/ where do Na+K+ATPase pumps do their wee thing?
- On basolateral sides of cells of PCT
- Create Na+ gradient by pumping Na+ out of cells into Interstitial fluid, K+ into cells
Where does tubular reabsorption mostly occur?
PCT
What is tubular secretion?
Movement of substances from blood in peritubular capillaries into tubular lumen
What is tubular reabsorption?
Movement of solutes out of luminal filtrate into tubular cells then into interstitium and into peritubular capillaries
Function of PCT?
2/3rds of filtered Na+/H20 are reabsorbed into blood here as well as almost all glucose, AAs and some Phosphates and bicarbonates
Function of Loop of Henle?
Concentrates urine achieved by counter current exchange mechanism
What is descending loop permeable to?
Permeable to H20
Impermeable to Na+
Water moves freely out of this limb and into interstitium whereas Na+ remains within this tubule
What is ascending loop permeable to?
Permeable to: Na+
Impermeable to: Water
Fluid in the PCT is…?
Isosmotic with interstitium
Fluid entering descending loop of henle is…?
Isosmotic with interstitium
What happens in thick section of ascending loop of henle?
Impermeable to water
Water is unable to follow Na+ to equilibrate osmolality of filtrate with that of iterstitium
Therefore osmolality of interstitium is equal to osmolality of fluid in descending limb of loop & interstitium differing with the osmolality of interstitium being greater than that of filtrate
(I don’t know what I mean her either TBC)
Because the descending limb is permebale to water…
Water leaves filtrate and moves into interstitium to equilibrate osmolality of interstitium with that of descending limb
What does the counter current exchange mechanism allow?
Osmotic gradient to increase the deeper the tubule lies in medulla
Fluid leaving loop of henle is?
Hypotonic
Why is fluid leaving loop of henle hypotonic?
Action of Na+/K+-2cl- cotransporter in ascending limb & it’s water impermeability
What is water excretion altered by in ascending limb?
Action of ADH
What is vasa recta permeable to?
Solutes and water
What is osmolality of cap blood at bend of vessel?
= to interstitium osmolality
What does distal convoluted tubule do?
Regulates balance of Na+/K+ as well as Ca2+ within body
What type of reabsorption occurs within DCT?
Hormone mediated of Na+/Cl-
What induces reabsorption of Na+/H20 IN CDs?
Aldosterone and ADH
ADH deficiency/resistance =?
Diabetes insipidus
Hence
The frequent weeing and xsive thirst
Where is urea formed?
Liver
Where does urea concentrate urine?
Loop of Henle
Why are all invasive procedures involving the kidney, such as biopsy, so risky?
-Kidneys are so highly vascularised
Damage to renal blood vessels can cause catastrophic bleeding
How does a long loop of Henle help a desert animal survive?
They must produce v concentrated urine
- Long loop of Henle allows more water to be reabsorbed by kidney tubule = concentrated urine
Why are females more prone to urinary tract infections?
Female urethra is shorter
- Bacteria have shorter distance to travel to the bladder
- Also closer to anus and therefore faecal bacteria
What are the fluid compartments of the body?
2 major compartments
- Intracellular space
- Extracellular space
ECF divided into
- Intravascular space (plasma)
- Interstitium (including lymph)
- Transcellular space (pericardial and peritoneal fluid)
How is Na+ involved in control of body fluid volume?
-Sodium is main determinant of plasma osmolality
(Osmol/Kg)
-As water follows sodium along an osmotic gradient, from low to high osmolality, when Na+ is reabsorbed by kidneys , water is too.
-This is how control of plasma sodium is closely linked to control of Blood volume and pressure
Why must XS acid be excreted?
Metabolism constantly creates acid as by-product
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If left uncontrolled this alters structure and function of macromolecules and disturbs cellular metabolism
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pH also alters degree of ionisation of weak acids and bases which can affect generation of ATP in electron transfer chain
How are the K+ concentration and acid-base balance of blood related?
They are interconnected
- Acidaemia is usually assoc with hypokalaemia
-Alkalaemia assoc with hyperkalaemia
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Overall effect is reduction in acid secretion and metabolic acidaemia, normalising K+ concentration can correct this
Why might a patient with chronic respiratory condition develop a raised haemoglobin?
May have chronic hypoxia
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May develop secondary polycythaemia
This is because hypoxia stimulates release of erythropoietin, which in turn increases RBC production
Functional units of kidneys?
Nephrons
How is kidney part of endocrine system?
-Important endocrine roles in regulation of BP, RBC formation, and activity of vitamin D
Does a foetus pass urine in the womb?
- Yes foetus begins to make urine from 8 weeks
- Excreted via the urinary tract into amniotic fluid
Why would a kidney be found in the pelvis?
Kidneys normally ascend in embryonic development from pelvis to superior abdomen
- The ascent can sometimes be interrupted
Why might the kidney have more than one renal artery?
- Due to the way the vasculature develops
- Relatively common for blood vessels to persist in development as the kidney ascends it receives transient blood vessels originating at aorta from progressively higher levels
What cells produce erythropoeitin?
Renal peritubular fibroblasts
