Functions Of The Kidney - Colin Geddes Flashcards
4 functions of kidney?
Remove metabolic waste eg urea and acids
Controlling blood pressure by maintaining ECF volume
Maintain optimal electrolyte concentrations
2nd hydroxylation step of vit D
Make erythropoietin in response to hypoxia
Name the body fluid compartments?
Intravascular space
Interstitial (ECF) space
Intracellular space
What determines the vascular fluid volumes?
Hydrostatic and osmotic
What are the most abundant ions in extracellular fluid? (+ve & -ve)
Sodium, chloride & bicarbonate
What are is most abundant ion in intracellular fluid?
K+
Protein is also abundant in cells
What happens to the volume and conc in each of the 3 body fluid compartments if 1 litre of water is added?
Volume increases in each of the 3 compartments therefore concentration in each decreases
What happens to the volume and concentration of each of the 3 body fluid compartments if 300mmol of sodium is added?
Number of particles in intravascular and interstitial compartments increases but not in the intracellular compartment.
Water then redistributes so all compartments change in size and conc.
Intravascular and interstitial spaces increase in sodium therefore increase in water
Intracellular space does not change in sodium but water moves out to the other spaces so intracellular volume FALLS
What happens to the volume and concentration of each of the 3 body fluid compartments if 300mmol of sodium is added along with 1Litre of water?
This isotonic addition of sodium and water leads to increased volume and increased number of sodiums in the intravascular and interstitial space but no change in volume or conc of intracellular space
What is the extraceullar fluid composition and volume dependent on?
Salt intake - hunger & food availability
Water intake - thirst & water availability
Salt and water loss - gut and sweat
All these are very variable so kidneys are required to maintain homeostasis
How much of the cardiac output do kidneys receive?
Approx 20%
Name the 3 processes in nephron?
Glomerular filtration Tubular reabsorption (selective absorption INTO blood) Tubular secretion (from blood into tubule)
What cells are in glomerus?
Mesangial cells - phagocytes, contractile
Bowmans capsule has parietal simple squamous epithelium and PODOCYTES (visceral layer)
Glomerular endothelial cells
Layers of the glomerular filtration barrier?
SPECIALISED Capillary endothelium
Glomerular Basement membrane - collagen based
PODOCYTE foot processes
Name 3 things that are 100% filtered in the glomerulus
Water, urea, glucose
What percentage of haemoglobin, albumin and RBCs are filtered? (Approx) why?
Hb 3%
Albumin < 0.01%
RBC 0
All too big to be filtered
What’s the normal glomerular filtration rate?
Approx 100ml/min
What aquaporin type is found in the THIN DESCENDING LIMB of loop of Henle?
Aquaporin I
What aquaporin type is found in the proximal convoluted tubule?
Aquaporin I
What aquaporin type is found in the collecting duct?
Aquaporin II on luminal side
Aquaporin III and IV on basolateral membrane
(2,3,4)
Where are aquaporins found in nephron?
PCT, thin descending limb, collecting duct
What’s found on the apical (luminal) membrane of PCT cells?
Microvilli
What’s found on the basolateral (interstitial side) membrane of PCT cells?
Infoldings for ATPase
What connects tubule cells of PCT?
Tight junctions
What are the junctions between thin descending limb cells like? ⚠️⚠️⚠️
Loose junctions
What’s the ENaC? What does it do?
Epithelial sodium channel
Moves sodium alone INTO principle cells from the LUMEN and therefore into interstitium (then blood?)
Give an example of a potassium sparing diuretic?
Amiloride
What is amiloride?
What does it act on?
Potassium sparing diuretic
It is an ENaC blocker (epithelial Na+ channel)
Where is the NaK2Cl symporter found?
Apical (luminal) membrane of DISTAL CONVOLUTED TUBULE cells (macula densa) and THICK ASCENDING LIMB of loop of Henle
What happens to the K+ absorbed into tubule cells by the Na2ClK symporter?
It can be recycled ie passed back out of the cell through a K+ channel (potassium recycling)
Drives paracellular transport of Ca2+ and Mg2+ and provides more K+ for the Na2ClK symporter
Potassium recycling drives _____? How?
PARACELLULAR reabsorption of Mg2+ and Ca2+ by creating a luminal positive voltage
Where is most Na and Cl reabsorbed?
PCT
Where are glucose and amino acids reabsorbed?
NEARLY ALL reabsorbed in PCT
What is usual plasma osmolality?
300mOsm/kg
What is osmolality of PCT?
300mOsm/kg
Isotonic with plasma
What can interstitial osmolality reach by the time you reach the bottom of loop of Henle?
1200 mOsm/kg (max)
Is thin descending limb permeable to water? Salts?
Yes to water
Barely permeable to salts
Describe permeability of thick ascending limb?
Permeable to salts
NOT permeable to water
Describe counter current exchange multiplier?
Na/K ATPase pump in thick ascending limb pumps out sodium creating higher conc in interstitium
Water diffuses out of thin descending limb to match osmolaritys
As water continuously moves out of descending limb the filtrate becomes more and more concentrated
This increases salt movement (via Na2ClK symporter) out of thick ascending limb further increasing interstitial conc but now reducing filtrate conc
How does tubule conc change as filtrate moves down descending limb of loop?
And as it moves up thick ascending limb?
- Increases as water leaves
2. Decreases as salt leaves
Where does ADH come from?
Posterior pituitary
What causes ADH release?
INCREAED serum osmolarity detected by OSMORECEPTORS In hypothalamus
And reduced blood volume detected by BARORECEPTORS in aortic arch and carotid sinus
Effects of ADH?
- Vasoconstriction - which increases arterial pressure
- Increases transcription and expression of aquaporin II channels on the apical surface (luminal) of the collecting duct cells - ^ water reabsorption and more conc urine
- stimulates thirst
How does the vasa recta not wash away the gradient created by the loop of Henle countercurrent exchange multiplier?
Blood flows in opposite direction to tubule fluid
What are the components of the juxta glomerular apparatus?
Macula densa (cells in distal convoluted tubule wall) Juxta glomerular cells (in walls of AFFERENT arterioles)
What does macula densa do?
Detects Na+ conc
What do juxtaglomerular cells do?
Secrete renin
