kidney Flashcards
general parts of human urinary system
aorta
vena cava
renal artery
renal vein
kidney
ureter
bladder
urinary sphincter
urethra
human kidney parts
nephron
collection duct
cortex
medulla
fibrous capsule
pelvis
renal pyramids (w apex)
ureter
renal vein
renal artery
parts in diagram of nephron
branch of renal artery
branch of renal vein
afferent/efferent arteriole
glomerulus
Bowmans capsule
PCT
descending and ascending limb of loop of Henle
vasa recta
DCT
collecting duct
barriers between blood and glomerular filtrate
endothelial cells of blood capillary
basement membrane
podocytes (w filtration slits)
describe structure of the blood/nephron barrier
- numerous pores in endothelial cells of capillary walls allow blood to come into close contact
with basement membrane - basement membrane is a selective barrier. water-soluble substances with RMM <69,000 can cross
- podocytes are epithelial cells of the BC with long projections which attach to the basement membrane. filtrations occurs in the slits. allow blood components smaller than 100nm to pass into nephron
presence of proteins in the blood means blood has low WP so some fluid retained by blood
3 functions of the kidney
ultrafiltration
selective reabsorption
secretion
define ultrafiltration
fluid part of the blood is filtered from the glomerulus into the renal tubule
define selective reabsorption in kidney
as fluid flows along tubules, useful substances are reabsorbed back into the blood in amounts required by the body
define secretion in kidney
unwanted substances are actively secreted in to the tubules
what does ultrafiltration require?
positive net filtration pressure
selectively permeable barrier
why does ultrafiltration require positive net filtration pressure?
to force fluid through the barrier
why does ultrafiltration require a selectively permeable barrier?
so rbc,wbc and plasma proteins retained bc remain in capillaries
how to work out net filtration pressure
HP in glomerulus - HP in BC
^^ subtract osmotic pressure in glomerulus
what is the glomerular filtration rate
measure of the volume of blood that can be filtered out by the kidneys every minute
can be used to measure kidney function -> the lower the GFR, the less effective the kidney function
average glomerular filtration rate
125cm3/min
declines with age
describe forces of ultrafiltration
blood enters the afferent arteriole/glomerulus from a branch of the renal artery at high pressure
this pressure forces small molecules into the Bowmans capsule (pressure filtration)
high HP generated by the difference in diameter between afferent and efferent arterioles
HP in BC is lower
oncotic pressure of proteins in blood in glomerulus
features of PCT epithelium
numerous microvilli (brush border)
basal infoldings
numerous mitochondria
good blood supply (close contact to capillaries)
co-transporter proteins and aquaporins
Na+/K+ pumps pump Na+ into blood
why does PCT epithelium have brush border (numerous microvilli)
increased surface area for reabsorption
why does PCT epithelium have basal inholdings
increased surface area for reabsorption into blood
why does PCT epithelium have numerous mitochondria
release ATP for active transport
why does PCT epithelium have good blood supply/ why’s it in close contact to capillaries
maintains steep concentration gradients
close to decrease diffusion distance
why does PCT epithelium have co-trasnporter proteins and aquaporins
transport Na+, glucose and amino acids
water transport
why does PCT epithelium have Na+/K+ pumps
maintains steep concentration gradient for Na+ and drives reabsorption of glucose, amino acids and water
what are the processes involved in selective reabsorption across the PCT membrane
active transport
secondary active transport
osmosis
facilitated diffusion
describe active transport in selective reabsorption across membrane of PCT
Na+/K+ pump actively removes Na+ from the PCT cell cytoplasm, causing it to enter the blood
describe secondary active transport in selective reabsorption across membrane of PCT
Na+ is transported into the PCT cell down its concentration gradient via a co-transporter protein which also carries glucose/amino acids at the same time (against their conc grad)
describe facilitated diffusion in selective reabsorption across membrane of PCT
amino acids and glucose diffuse into the blood
describe osmosis in selective reabsorption across membrane of PCT
water passively follows the salt movement and is reabsorbed by osmosis (via aquaporins)
the cells lining the PCT use end/exocytosis in addition to AT and FD to move molecules across membranes
suggest why
to transport the few proteins that’s have been filtered out into the nephron (<69000 RMM)
endocytosis transports proteins from PCT lumen into cells in its walls
exocytosis transports proteins from cells in PCT wall into the tissue fluid and the blood
how much fluid enters PCT per minute
125cm3
how much fluid enters loop of Henle per minute
45cm3
what percentage of glomerular filtrate is reabsorbed in PCT
over 80%
proportion of glucose, amino acids, vitamins and hormones reabsorbed in PCT
ALL
proportion of Na+ reabsorbed in PCT
85-90% (ACTIVE)
Cl- follows
proportion of water reabsorbed in PCT
65%
proportion of urea that diffuses out of PCT
50% (PASSIVE)
proportion of uric acid and creatinine reabsorbed in PCT
NONE
what is an isotonic solution
solution that has the same solute concentration as a cell
no net movement of water particles
overall concentration on both sides of cell membrane remains constant
what is a hypertonic solution
a solution that has a higher solute concentration than a cell
water particles move out of the cell, causing crenation/plasmolysis as the cell shrivels
what is a hypotonic solution
a solution that has a lower solute concentration than a cell
water particles move into the cell causing the cell to expand and eventually lyse/become turgid
2 hormones which increase water and sodium reabsorption
ADH
aldosterone
how does aldosterone increase water and sodium reabsorption
causes nephron DCT to reabsorb more Na+ and water, which increases blood volume
how does ADH increase water and sodium reabsorption
mediates insertion of aquaporins into nephron collecting duct cells; so more water reabsorbed into blood
increases sodium reabsorption in medulla of the kidney
aldosterone type of hormone
site of release and production
steroid hormone
adrenal cortex
ADH type of hormone
production site
site of release
peptide hormone
hypothalamus
pituitary gland
what moves into blood from DCT
Na+, water and Cl-
(water and Cl- follow the Na+)
what moves into DCT lumen
K+ (opposite direction to Na+), H+, NH4+
describe aldosterone action on DCT
encourages water reabsorption by causing active reabsorption of Na+ so water follows
which part of DCT responds to ADH
second part
behaves like collecting duct
DCT blood pH description
involved in controlling blood pH via secretion of H+ and NH4+ from blood into urine
helps keep blood pH at 7.4
collecting duct role
LoH establishes a WP gradient going down medulla
WP of tissues surrounding CD is lower than the fluid inside of it
if ADH present, CD walls more permeable to water
water removed from the filtrate in CD by osmosis, concentrating the urine
what does the loop of Henle act as
a hairpin countercurrent multiplier
describe loop of Henle structure/ccm
the 2 limbs of the LoH run parallel but the fluid inside them runs in opposite directions
this enables the max concentration to be built up both inside and outside the tubule at the bottom of the loop (v. negative WP so more water can be reabsorbed by CD)
how is the LoH countercurrent multiplier effect Brough about
- bc of close proximity of the descending limb and ascending limb
- descending limb permeable to water but less permeable to ions
- ascending limb impermeable to water
- thin ascending limb highly permeable to Na+ and Cl-
- thick ascending limb has active transport mechanism for pumping Na+/Cl-
step by step counter current mechanism in LoH
- Na+ and Cl- ions diffuse out of thin part of AL. water would follow by osmosis but can’t bc AL impermeable to water
2.as filtrate flows up AL, becomes less concentrated. thick part of AL actively pumps out more of the Na+ and Cl-, decreasing conc of filtrate
3.movement of ions out of AL results in conc of tissue fluid around DL increasing
4.DL is permeable to water and (slightly) to Na+ and Cl-. as filtrate flows through DL, water lost by osmosis and this moves into vasa recta (in close contact w nephron). some Na+ and Cl- diffuse into tubule down their conc grad
5.by the time filtrate has reached bottom of loop, contains much less water and ions than at top. longer loop= gets more conc - as filtrate flows up AL, conc of ions so great it is relatively easy for Na+ and Cl- to be lost so filtrate becomes less conc
ADH vs aldosterone type of hormone
ADH= peptide
aldosterone= steroid
ADH vs aldosterone synthesis and secretion site
ADH synthesised in hypothalamus and secreted from pituitary gland
aldosterone synthesised and secreted by adrenal cortex
ADH vs aldosterone effect
ADH makes DCT and CD more permeable to water
aldosterone makes DCT and CD more permeable to sodium ions
ADH vs aldosterone mechanism
ADH directly increases water reabsorption from tubules using aquaporins
aldosterone increases water reabsorption by creating an osmotic pressure
ADH vs aldosterone effect on blood vessels
ADH increases Bp through vasoconstriction
aldosterone has no effect on blood vessels
2 types on nephrons
cortical
juxtamedullary
fraction of human nephrons that are juxtamedullary
1/3
when do juxtamedullary nephrons perform their function
when water is in short supply
effect of longer loop of Henle
longer loop= steeper WP concentration gradient in medulla
so more water reabsorbed in D
so more concentrated urine of smaller volume
comparison of beaver, rabbit and kangaroo rat nephrons
beaver: cortical only bc aquatic habitat so less likely to become dehydrated (no need to conserve water)
rabbit: cortical and juxtamedullary bc terrestrial habitat so MAY need to avoid dehydration
kangaroo rat: juxtamedullary only bc desert habitat v dry so needs to preserve water
describe changes in rate of flow through nephron
decreases across nephron due to reduction in fluid volume (less fluid to flow means less fluid passes a given point per unit time)
describe rate of flow in PCT
flow rate is highest at beginning of PCT as fluid is entering
flow rate decreases as it flows along PCT as large percentage of fluid is reabsorbed so volume decreases
describe rate of flow in LoH and DCT
flow rate continues to droop as reabsorption of water continues
describe rate of flow in CD
rapid reduction in flow rate as high proportion of water reabsorbed
describe changes in glucose conc through nephron
drops rapidly in PCT bc all glucose reabsorbed (Na+ AT into blood, glucose co-transported with Na+)
describe change in urea conc through nephron
increases in PCT as, despite urea being reabsorbed, lots of water reabsorbed so the volume of water in which urea is dissolved decreases
describe change in Na+ conc through nephron
PCT: conc remains constant, as despite Na+ reabsorption here, this is balanced by reabsorption of water
LOH: DL Na+ increases in con as water lost, in AL Na+ decreases as it is pumped out
DCT: Na+ increases (despite being actively pumped out) as lots of water reabsorbed here
CD: Na+ increases as water removed
describe change in K+ conc through nephron
increases throughout DCT and CD as it is actively moved into the filtrate as sodium is reabsorbed
what is osmoregulation
the control of water and salt content of the body by negative feedback
ensures total volume of blood plasma + concentration remains constant
what is negative feedback
change away from a set point that leads to a reversal of the change to return to the set point
control of water content of the body fluids is achieved by:
- osmoreceptors and thirst centres in hypothalamus
- hormone ADH
- angiotensin system
- aldosterone
what is the angiotensin system
increases thirst
when BP drops, the angiotensin system acts on the adrenal gland (zona glomerulosa) causing release of aldosterone
aldosterone effect
increases active reabsorption of Na+ in DCT and water follows
role of osmoreceptors in stimulating thirst centres
osmoreceptors detect low blood water content and activate thirst centres in the hypothalamus of the brain
increased thirst
more water taken in
stops activation of thirst centres
what does the hypothalamus contain
thermoregulatory and osmoregulatory centres
ADH synthesising neurone role
make ADH in the cell body-> diffuses down axon in the synaptic bulb into vesicles, which are released directly into blood
ADH structure
site of synthesis
where does it move and is stored
polypeptide of 9 amino acids
hormone made in cell body of neurosecretory cells in the hypothalamus
passes down axons to the posterior lobe of the pituitary gland where it can be stored
where are osmoreceptors
hypothalamus
what triggers osmoreceptors
a difference in WP of the blood and WP of the osmoreceptors can cause water to enter or leave the osmoreceptor by osmosis
what happens when WP of blood is low
osmoreceptors lose water, shrink and their volume decreases
this triggers stimulation of neurosecretory cells in the hypothalamus
AP passes along the axon to the nerve endings in the posterior lobe, causing release of ADH which is secreted directly into blood (endocrine gland)
ADH pathway from posterior lobe
travels in blood to kidney
ADH affect on kidney
increases permeability of DCT and CD to water
more water is reabsorbed and therefore th volume of urine produced decreases but the concentration of urine incerases
mechanism of ADH
binds to receptors in cell surface membrane of cells lining CD and DCT
activates G protein, which activates adenyl cyclase which converts ATP to 2nd messenger cAMP
cAMP activates protein kinases A causing vesicles containing aquaporins to move to the cell surface membrane
vesicles fuse w cell surface and insert aquaporins
water can now move freely through membrane down its WP gradient then into tissue fluid and then into the blood
NEGATIVE FEEDBACK
why do CD cells not respond immediately to the stopping of ADH secretion by the posterior pituitary gland
bc it takes some time for the ADH already in the blood to be broken down
however, once ADH stops arriving at the CD cells, it takes only 10-15 minutes for the aquaporins to be removed from the cell surface membrane and taken back to cytoplasm for storage
describe activation of aldosterone
dehydration causes blood pressure to decrease, and this leads to aldosterone release from the adrenal cortex
aldosterone type of hormone
where does it act
steroid hromone
acts on intracellular receptor in cytoplasm and leads to an increase in ion channels in the membrane of the DCT cells
aldosterone effect
induces Na+ reabsorption and K+ secretion
also leads to Cl- reabsorption and water reabsorption by osmosis
salt and water reabsorption increases BP
what is diabetes insipidus
lack of ADH
make lots of dilute urine
factors contributing to/causing kidney failure temporarily/permanently
bacterial infection
external mechanical injury
high BP
diabetes type 1 or 2
polycystic kidney disease
side effects of some medications
kidney stone/blockage preventing kidney drainage
indicators/signs of kidney failure
blood and protein in urine (making it cloudy)
oedema (swelling)
anaemia and tiredness
lower GFR
creatinine in blood
rashes and nausea
retention of urea
why is oedema a symptom of kidney failure
accumulation of salt and water (tissue fluid) in tissues due to blood protein loss in urine also due to high HP
why is anaemia and tiredness a symptom of kidney failure
kidneys stop producing erythropoietin which is a hormone which promotes red blood cell production in the bone marrow
lower GFR due to kidney failure
normally 125cm2/min
cut by half
why is creatinine in blood a symptom of kidney failure
blood can be analysed for waste creatinine
this increases in blood as disease progresses as kidneys fail to remove waste
why are rashes and nausea a symptom of kidney failure
buildup of toxins
why is retention of urea a symptom of kidney failure
cause blood pH to drop and in untreated renal failure can be fatal for this reason
types of treatment for kidney failure
haemodialysis
peritoneal dialysis
kidney transplant
describe haemodialysis
artificial kidney machine
patients blood passes along numerous tubes made of partially permeable dialysis membrane
the tubes are immersed in the dialysis fluid
how is haemodialysis efficiency improved
blood flows in opposite direction to dialysis fluid
COUNTERCURRENT
maintains steep conc gradient
features of haemodialysis: blood vessels used?
efficient dialysis requires a high rate of blood flow through machine (200-300cm3/min)
arteries r the only blood vessel which will deliver blood at the necessary pressure but are deeper and narrower than veins so piercing an artery each time has high risk
therefore, blood can be taken from a vein and fed through a pump, or an artery can be joined to this nearby vein creating an arteriovenous fistula
how often is dialysis fluid replaced and why (haemodialysis)
frequently
ensures steep concentration gradient is maintained for removal of unwanted substances from the blood
temperature of dialysis fluid
warmed to ensure same as body temp so blood temp remains constant
what does haemodialysis fluid contain
glucose
ions (Na+, Cl-)
water
prevents diffusion of these into the dialysis fluid
haemodialysis frequency of treatment
2-3 times a week for several hours
affects lifestyle
any restrictions between haemodilaysis treatment?
monitor and restrict parts of diet e.g. no excess protein, regulate salt and water to regulate BP
why must blood flwo continuously through dialysis machine
so no clots form
describe peritoneal dialysis
dialysis fluid introduced into the abdominal cavity using a catheter
abdominal cavity and all the organs are lined w a peritoneal membrane (covers area of 10m2 and has its own extensive blood supply)
while fluid is in cavity, equilibrium takes place between the fluid and surrounding blood and since fluid is changed regularly, toxic substances are lost from blood
peritoneal dialysis fluid replacement
fluid is left in 24 hours a day and replaced 3-5x a day
freedom w peritoneal dialysis
a person can move around freely and take control of their own dialysis
haemodialysis vs peritoneal dialysis: membrane
H: artificial membrane- cannot do AT/FD so relies on simple diffusion
P: peritoneum: peritoneal wall is made up of living cells so can perform AT and FD
haemodialysis vs peritoneal dialysis: counter current?
H: uses countercurrent flow to maintain steep conc grad
P: doesn’t use countercurrent flow and conc grad is lower/ reaches equilibrium with the blood
haemodialysis vs peritoneal dialysis: fluid change
H: fluid constantly refreshed/changed
P: fluid drained then changed every 4-6 hours
haemodialysis vs peritoneal dialysis: how often
H: only need treatment 3 times a week
P: needs to be carried out every day
disadvantages of kidney transplants
not enough donor organs to go around
risk of rejection and need to take immunosuppressant drugs
kidney must come from a healthy person w a tissue match close to the patient
involves major surgery under anaesthetic so risky
only about 50% of people eligible
advantages of kidney transplants
best life-extending treatment
freedom from repeated and time consuming dialysis
feel physically better almost immediately and diet less limited
improved life quality able to travel whiteout disruption
improve self-image: no longer feeling chronically ill
what can urine testing help to detect
blood in urine: indicates bladder or kidney cancer
urine cytology can detect cancer cells in the urine under a microscope
glucose test using biosensor to diagnose diabetes
detect recreational drug use (gas chromatography)
detect anabolic steroids days/weeks after last dose
pregnancy testing
what are anabolic steroids
drugs which mimic the action of steroid hormones that increase muscle growth by increasing protein synthesis in cells
anabolic steroids effects
athletes can train for longer and ave increased endurance as well as decreased recovery time
side effects of anabolic steroids
liver damage
infertility in men bc sperm production affected
menstrual cycle affected
how is urine used for pregnancy testing
once the embryo has implanted into the uterine lining, the embryo starts secreting a pregnancy hormone called hCG
found in urine as early as 6 days after conception
test for presence of hCG in urine
hCG structure
small glycoprotein
RMM of 36700 so can pass into Bowmans capsule and is therefore found in urine
describe old pregnancy testing using mice
hCG antigens injected
mouse detects foreign antigen
plasma cells produced are fused with myeloma cells (cancer cells) to produce hybridoma cells
this produced a monoclonal antibody which can bind to hCG antigen
describe modern pregnancy test mechanism
urine applied to stick (urine contains hCG) these molecules are carried up the strip in the urine by capillary action
in the 1st region of the stick there are mobile, dye-labelled monoclonal antibodies which recognise and attach to the hCG only
these antibodies are carried to the test window. at the test site, fixed monoclonal antibodies are anchored. these only bind to the hCG-antibody complex, and when they do, the dye/coloured beads make a blue/red line. antibodies which have no hCG attach don’t bind so do not form a blue/red line
2nd window is a control site where 2nd set of fixed antibodies capture labelled antibodies on their own (this is a positive control to prove the test is working as antibodies will attach here whether they have bound to the hCG or not) it proves antibodies have moved to the top of the test strip
explain the role of the Loop of Henle in the production of urine
LOH causes decrease in WP going down medulla
Na+ and Cl- AT out of AL
DL walls permeable to H2O so water removed
WP surrounding CD lower so water removed from CD when ADH present
