how does the nephron work?

Question 1

what is the first step in the nephron?

Answer 1

glomerular filtration

• “dumping of filtrate into a waste container”
• does not allow blood cells , protein to pass through larger than 5mm )

Question 2

what is the second step in the nephron?

Answer 2

tubular reabsorption

• reclaiming what the body needs
• reclaims almost everything (all of glucose, amino acid and 99% of water, salt and other components
• most take place in proximal tubule

Question 3

what is the third step of tubular secretion?

Answer 3

tubular secretion

• selectively moving substance from the blood into the filtrate
• most in the pct and dct

Question 4

what is the normal urine look like?

Answer 4

1. clear and pale to deep yellow (urochrome colour)
2. slightly aromatic ( release of ammonia due to the break down of urea)
3. slightly acidic Ph6
4. greater mass than distilled water

Question 5

what is the normal composition of urine ?

Answer 5

95% water 
5% solutes
urea from amino acids 
creratine 
contains Ca Mg Hco3-

has urea> Na> Po43-> SO42-> creatinine> uric acid

Question 6

what are some of the causes of abnormal urine colour?

Answer 6

food 
drugs 
vitamins 
bile pigment 
bacteria

Question 7

what is glomerular filtration?

Answer 7

it is the hydrostatic pressure that forces fluid and solutes through a membrane
it is measured by glomerular filtration rate
only allows molecules smaller than 3mn to pass through

Question 8

what is the corpuscle made up of?

Answer 8

1. fenestrated endothelium of the glomerular capillaries, it is porous and allows all blood components to pass through except blood cells
2. it has basement membrane that forms a physical barrier that blocks all but the smallest protein while still permitting other solutes to pass
3. foot processes of podocytes of glomerular capsule, the slit diaphragm prevent almost all of the macrophages from travelling further

Question 9

what is the reason behind preventing plasma from being filtered?

Answer 9

it is to maintain the colloid osmotic pressure preventing loss of all water into capsular space

Question 10

what are the two pressures affecting filtration?

Answer 10

outward pressure (glomerular hydrostatic pressure)
inward pressure (capsular hydrostatic pressure and blood colloid osmotic pressure)

Question 11

what is the outward pressure that promotes filtration?

Answer 11

glomerular hydrostatic pressure (55mmHg)
- chief force pushing water and solutes out of the blood across the filtration membrane and is caused by the pressure from the afferent and efferent arterioles

Question 12

what are the inward pressure of glomerular filtration?

Answer 12

1. hydrostatic pressure in capsular space (-15mmHg)
   - pressure exerted by filtrate in glomerular capsule
2. colloid osmotic pressure in glomerular capillaries (-30mmHg)
   - pressure exerted by the proteins in the blood that sucks water into the capillary

Question 13

what is the net filtration pressure?

Answer 13

55-30-15 = 10

it is responsible for filtrate formation

Question 14

what happens if the blood pressure decreases?

Answer 14

there will be no filtration and acute renal shut down will happen

Question 15

what to do when there is no filtration?

Answer 15

administer IV fluids and insert renal catheter to monitor the renal output

Question 16

what is glomerular filtration rate?

Answer 16

A glomerular filtration rate (GFR) is a blood test that checks how well your kidneys are working.
A GFR test estimates how much blood passes through these filters each minute.

it is the best overall index of kidney function

Question 17

what is the glomerular filtration rate of a healthy adult?

Answer 17

125ml/min

Question 18

what is he glomerular filtration rate directly proportional to?

Answer 18

1. net filtration pressure , can be changed by changing the diameter of the arterioles
2. total surface area for filtration
3. filtration permeability, very permeable due to the fenestrations

Question 19

what can be used to test the glomerular filtration rate?

Answer 19

inulin as it is filtered freely and is not reabsorbed by the kidney

creatinine is often used as a quick estimate as it does not need to be infused IV

Question 20

what controls the glomerular filtration rate?

Answer 20

1. intrinsic control (renal autoregulation)

2. extrinsic control (nervous and endocrine)

Question 21

what is the intrinsic control of glomerular filtration rate?

Answer 21

it is the tubuloglomerular feedback
- mascula densa cells in dct sense the amount of Nacl in the filtrate
when there is increased blood flow, there is not enough time for reabsorption and there will be more Nacl in the DCt and is detected by macula densa cells
- it will release vasoconstriction and causes afferent arteriole to constrict decreasing blood flow

the mean arteriole pressure is between 80 and 180mmHg

Question 22

what is the hormonal extrinsic control of glomerular filtration rate?

Answer 22

it is the MAIN mechanism to increase bp as without enough pressure, glomerular filtration is not possible
- when BP is low, granular cells of the juxtaglomerular complex releases renin and it leads to an increase in bp

Question 23

what is the mechanism of renin?

Answer 23

renin converts angiotensin into angiotensin I

ACE convert angiotensin I to angiotensin II

Question 24

what is the function of angiotensin II?

Answer 24

1. it shrinks blood vessels and causes vasoconstriction
2. go to kidney adrenal gland and stimulate aldosterone which increases sodium reabsorption
3. go to pitutary glands and secrete ADH which reabsorbs water from the urine and increase blood volume and BP)

Question 25

what is the extrinsic neural control of the glomerular filtration rate?

Answer 25

when the blood pressure is very low, blood is shunt to vital organs and neural controls may override the autoregulatory mechanism - when blood pressure falls , norepinephrine is released by sympathetic nerve fibers and causes vascular smooth muscles to constrict increasing peripheral resistance bringing blood pressure back up to normal - afferent arterioles also constrict and it decreases GFR and restores blood volume and pressure to normal

Question 26

what is tubular reabsorption?

Answer 26

it is the process if reabsorbing the required substances of the body

Question 27

what are the two different routes for reabsorption?

Answer 27

1. transcellular route | 2. paracellular route

Question 28

what is transcellular route?

Answer 28

1. transport across apical membrane 2. diffusion through the cytosol 3. movement through the membrane into the capillaries active transport, requires ATP

Question 29

what is the paracellular route?

Answer 29

tubular reabsorption through the leaky tight junctions in the PCT passive transport, diffusion

Question 30

what are the things being reabsorbed in the PCT ?

Answer 30

has microvilli to increase the surface area ``` sodium ions (65% is reabsorbed) all nutrients (glucose, aminoacid, vitamins by secondary active transport w NA) Cations (K , Mg, Ca) anions (Cl, HCO3) water urea and lipid soluble solutes small proteins ``` nearly all uric acid and half of urea are reabsorbed in the proximal tubule and later secreted back to the filtrate

Question 31

what is reabsorbed at the descending loop of henle?

Answer 31

water only

Question 32

what is being reabsorbed at the ascending limb of loop of henle?

Answer 32

Na, Cl, K (Secondary active transport) | Ca and Mg

Question 33

what is being reabsorbed in the DCT?

Answer 33

Na (primary active transport) Cl (secondary active transport) Ca (passive)

Question 34

what is being reabsorbed in collecting duct?

Answer 34

Na (primary active transport and requires aldosterone) H, K, HCO3, CL (passive) water (osmosis and requires ADH to insert aquaporins) urea (facilitated diffusion, increased with ADH)

Question 35

what is transport maximum?

Answer 35

maximum amount of substance which can be reabsorbed per unit time every substance that has a transport protein will have a Tmax, it reflects the number of transport protein in the renal tubule available to ferry a particular substance

Question 36

what happens when a transport maximum is reached.

Answer 36

the excess is secreted in urine

Question 37

what us the Tmax of glucose ?

Answer 37

maximum rate is :375mg/min (max reabsorption) body threshold is 180mg/dl if more than that, glycosuria

Question 38

what is tubular secretion? | why is it important?

Answer 38

it is reabsorption in reverse 1, eliminating undesirable substances or end products reabsorbed by the passive process 2. disposing substances that are tightly bounded to plasma proteins 3. getting rid of K+ 4. controls the blood PH

Question 39

where is the main site for secretion?

Answer 39

PCT where H+, K+ Nh4+ , creatine and other organic acids are secreted (blood PH is reduced as H+ is secreted)

Question 40

what is the pathway of K ions ?

Answer 40

it is reabsorbed at PCT and ascending loop of henle but secreted in late DCT and collecting duct by aldosterone

Question 41

what is the pathway of urea?

Answer 41

it is secreted in the ascending loop of henle and secreted in collecting duct

Question 42

what are the total substances secreted by kidney?

Answer 42

``` water 1% sodium 0.5% glucose 0% urea 50% phenol 100% ```

Question 43

what is the function of ADH? secreted by posterior pituitary gland

Answer 43

inhibit diuresis and urine output - makes CD more permeable to water by causing aquaporins - increase urea reabsorption too DIRECTLY cause water reabsorption

Question 44

what is the function of aldosterone ? secreted by adrenal cortex

Answer 44

regulates salt and water balance of the body - increase the retention of sodium and water, decrease urine production - excretion of potassium target collecting duct and principle DCT, directly causes sodium retention

Question 45

what is the function of ANP ?

Answer 45

reduces blood Na, decreasing the blood volume and pressure

Question 46

what is the function of parathyroid hormone ?

Answer 46

increases reabsorption of Ca and acts on DCT