The Kidney Flashcards
what happens in the glomerulus?
it’s the part of the kidney where the plasma is filtered, the ultrafiltrate from this part moves on to the nephron.
what is allowed to pass through the glomerulus and what isn’t?
water and small molecules can pass through.
blood cells and proteins cannot pass through,
how many litres of filtrate are produced a day?
180
how many times is the plasma filtered a day?
it’s filtered 65 times a day.
what moves through the afferent arteriole?
what moves through the efferent arteriole?
the plasma moves in through the afferent arteriole.
the unfiltered plasma moves out through the efferent arteriole.
where does the ultra-filtrate go?
through bowman’s capsule to the nephron
what’s the filtration barrier made up of?
the first barrier is the endothelial cells.
the basement membrane is the middle barrier and this is the main barrier.
the epithelial cells are the third barrier, these aren’t a good barrier as they are mainly for support.
describe the endothelial cells.
they are flat, have large nuclei, have circular fenestrations and are in contact with each other?
what are circular fenestrations? what do these allow to flow through?
they are the quite large gaps between the cells.
these allow water and ions to pass through.
what do the endothelial cells filter?
blood cells and platelets
how do you know if the endothelial barrier has failed?
because blood cells and platelets will be detected in urine.
describe the basement membrane
it is continuous, it contains glycoproteins, collegen, laminin, fibronectin and is negatively charged
what is filtration through the basement membrane based on?
filtration is based on the molecular shape, size and charge.
describe the epithelial cells.
what is another name for the epithelial cells?
they have trabeculae, pedicle, they interdigitate to show slit pores.
podocytes
what are pedicles and what do they do?
they are finger like projections coming off the trabeculae, these interdigitate to form slit pores which allows gaps for things to pass into bowmann’s capsule.
what are the epithelial cells involved in?
they are involved in maintanence and phagocytosis
what determines filtration?
the molecular size, shape and charge.
what does it mean if something has a filtration/plasma ratio of 1?
that it freely filtrates.
what happens to the filtration/plasma ratio of a negatively charged molecule? why is this? does this apply to all molecules?
if negatively large they have a lower F/P ratio as they are less likely to be filtered due to the basement membrane having neg charged proteins, meaning they will be repelled.
this doesn’t apply to all molecules, it only applies to molecules with a large molecular weight.
what are the forces governing filtration?
the filtration co-efficient Kf
starlings forces
what is the filtration co-efficient? does this change?
it is a measure of the permeability of the filtration barrier.
it can change but it is basically constant
what does GFRα =
(Pcap + IIbc) - (Pbc +IIcap)
P= hydrostatic pressure
II= oncotic pressure
why is IIbc essentially 0?
because there’s very little protein in bow’s cap.
why is IIcap so important?
lots of protein in plasma, makes this very important.
why does Pbc oppose filtration?
because it’s pushing the filtrate back.
why is there a small drop in capillary pressure across the legnth of the glomerular capillary?
because there’s fluid leaving.
what is the pressure in the capillary at the start and end of the glomerular capillary?
60 mmHg.
what is the pressure in bowmann’s capsule?
20 mmHg.
what is oncotic pressure (II)?
the osmotic gradient set up by proteins
what is hydrostatic pressure?
the pressure exerted by any fluid in a confined space.
what is the IIbc across the glomerular capillary?
0 mmHg
what is the IIcap across the glomerular capillary?
goes from ~25 mmHg to ~30 mmHg at the end
what is the average Net filtration pressure across the glomerili?
10 mmHg
why does the IIcap increase across the length of the glomerilus capillary?
because as going along, fluid is lost however the proteins stay, resulting in an increase in protein concentration which increases oncotic pressure.
what is GFRα proportional to?
glomerular filtration rate
what is GFRα expected to be in humans?
125ml/min
why are glomerili capillary beds different to the other capillary beds in the body?
because in other capillary beds halfway through the capillary direction reverses, this meaning starlings forces reverse.
GFR=
Kf (Pcap+IIbc) - (Pbc+IIcap)
how can we measure the GFR in humans?
using a clearance technique
what is a single nephrons GFR?
50 nl/min
what happens to GFR if a kidney is removed?
GFR is halved.
why is autoregulation critical?
it is critical in maintaining filtration
what is the autoregulatory range? what is it maintaining filtration at?
~85 - ~200 mmHg
maintaning at ~125 ml/min
what happens if pressure is altered within the autoregulatory range?
filtration and renal blood flow are maintained
if arterial pressure drops what would happen if there was no autoregulation?
the hydrostatic pressure in the capillary would drop and the glomerular filtration would drop.
this could lead to the kidneys stopping filtering
would be very very bad.
if resistance in the afferent arteriole is decreased what happens to:
renal blood flow
Pcap
GFR?
renal blood flow increased
Pcap increases
GFR increases
if resistance in the afferent arteriole is increased what happens to:
renal blood flow
Pcap
GFR?
Renal blood flow decreases
Pcap decreases
GFR decreases
ultimately what happens if change resistance in afferent arteriole?
glomerular filtration rate is changed
what does the kidney do if there’s an increase in arterial BP?
it increases the resistance in the afferent arteriole as this then reduced RBF and Pcap which leads to a decrease in GFR (these were all increased by increase in arteriole BP)
what does the kidney do if there’s a decrease in arteriole BP?
decreases afferent arteriole resistance, as this then increases RBF and Pcap = increases GFR
what is the myogenic theory
this is that there are stretch receptors in the afferent arteriole smooth muscle.
meaning when arterial BP increases there is an increase in RBF. This stretches the afferent arteriole and activates the receptors.
these receptors then constrict the arteriole which increases arteriole resistance and decreases RBF.
what is the tubuloglomerular feedback theory?
this is where the macula densa cells in the distal tubule of the nephron detect an increase in the rate of fluid flow throught the nephron. these cells relsea vasoactive chemicals which diffuse and act on the afferent arteriole, this causing constriction and reducing GFR.
what’s it important to remember about the mechanisms for maintaining GFR?
they are continuous processes! they are always changing, not on and off mechanisms.
why is it important to have an acid-base balance in the body?
because a small change in pH leads to a large change in body function
pH =
-log10[H+]
what does the pH scale being a log scale mean?
one unit change in pH leads to a x10 change in [H+]
what does the pH scale being recipricol mean?
so if pH increases then [H+] decreases and visa versa
what’s the normal pH for intersticial, intracellular and plasma?
7.35 - 7.45
what’s the normal physiological pHs?
6.8-8.0
what’s the normal [H+] in the plasma?
45-35 nmoles/litre
what’s the typical venous and arterial pHs?
venous 7.35 arterial 7.45
what is the average pH of the intracellular and extracellular compartents?
7.40
what does it mean if the intra and extracellular compartments have a pH lower than 7.35? what does it mean if higher than 7.45?
lower 7.35 = acidosis
higher 7.45 = alkalosis
what profound physiological effects can fluctuations in [H+] have?
- excitabilty of muscle or nerve altered
- enzyme activities altered
- potassium levels altered.
why are potassium levels altered due to [H+]?
because extracellular H+ is taken in for a K+ out, this changes the nernst potential and alters the excitability.
what's the pH of: Gastric secretions CSF Pancreatic secretions Final urine
GS: 0.7
CSF: 7.3
PS: 8.1
FU: 5.4
what is metaolism a large source of? why is this?
source of a large amount of acid, this is due to breakdown of food to produce ATP:
15 moles/day CO2
40 nmoles/day net H+ (e.g sulphuric acid)
how do different diets effect H+ levels?
people with more protein release more H+ compared to those with a carbohydrate rich diet
how else does diet effect [H+]?
20mmol/day H+ is injested
also lose about 10mmol/day of base [OH-]
what is the net excess of H+ per day?
approximately 70mmoles
varies with what eat etc.
what systems are inovled in acid base regulation? how long doe these take?
are all of these systems involved in acid/base extrusion
- blood and tissue buffers - seconds
- respiration - minutes
- renal - hours/ days
no renal is the only mechanism for extrusion.buffers and respiration just minimise the changes.
what are buffers present in?
blood - plasma and red blood cells
extracellular fluid
intracellular fluid
urine
give examples of some buffers
haemoglobin
HCO3
inorganic phosphate
weak acids/ bases on proteins
what kind of buffer is HCO3? what system does it use?
it is a primary ECF buffer, it uses an equilibrium system and is dynamic.
what is the equation for HCO3?
CO2 + H2O - - H2CO3 - - H+ + HCO3
what happen to the HCO3 equation if CO2 is increased?
equilibrium shift to the right, resulting in an increase in H+ resulting in acidosis.
what happens to the HCO3 equation if H+ is increased?
equilibrium shift to the left resulting CO2
