GFR filtration

Question 1

list a few functions of the kidney

Answer 1

regulation - control substances
excretion
endocrine - secrete renin
metabolic - active form of vit D

Question 2

what do the kidneys filter the most

Answer 2

extracellular fluid

Question 3

what are the different body fluid compartments and how are they divided

what component is directly affected by the kidneys

Answer 3

1/3 intracellular
2/3 extracellular (interstitial and intravascular)

divided by semi permeable membrane

only extracellular fluid is affected by kidney not intracellular

Question 4

what will happen when there is a failure to control electrolytes

Answer 4

disruptance in electrical functions and transport

Question 5

what is the functional meaning of osmolarity and osmolality

Answer 5

total concentration of substance that cannot move through the membrane freely (due to oncotic pressure)

Question 6

give examples of substances that cannot move through the membrane freely

Answer 6

ions and organic molecules

Question 7

how much of the blood passing through the kidney is actually turned into filtrate

Answer 7

80% reabsorbed whilst 20% filtered at one time

Question 8

what are the two typed of kidney, what is the difference and do they function the same

Answer 8

cortical and juxtaglomerular, function same but jg has a longer loop of henle

Question 9

what is auto regulation and what does it apply to

what happens when GFR up or down

Answer 9

auto regulation is the kidneys way of maintaining GFR within normal BP
only occur in cortisol nephrons

afferent constrict when high and dilate when low. GFR remains unchanged

Question 10

what does the filtrate coming out of the glomerulus resemble in terms components

Answer 10

plasma (no RBC, large proteins etc)

Question 11

describe how the kidney filters blood within the glomerulus

Answer 11

• blood enters
• BM has fenestrations which are permeable to small ions and small proteins
• BM negatively charged so repels other - ions (proteins)
• beneath this is bowman capsule
• bowman capsule has visceral and parietal layer of podocytes with heparin in between to catch remaining proteins
• ultra filtrate passes through funnel into PCT

Question 12

what is the biggest substance that can go through the selective membranes

Answer 12

inulin

Question 13

what happens in proteinuria that allows proteins to pass this selective membrane

Answer 13

membrane lost charge allowing negatively charged particles like albumin and other proteins to seep through

Question 14

describe the charges applied in the glomerulus

Answer 14

PGC (capillary hydrostatic pressure) - pushing in
COP (oncotic) - pushing out
PBC (hydrostatic p in bowman capsule) - pushing out due to funnel overfilling
BCOP (bowman capillary oncotic pressure) - usually zero as should be no proteins in bowman

all of these determine NFP which is proportional to GFR

Question 15

what happens to the oncotic protein pressure as ultra filtrate is lost

Answer 15

concentration goes up as it reaches efferent arteriole (important for reabsorption)

Question 16

what are the 2 types of auto regulation

Answer 16

myogenic and tubuloglomerular

Question 17

what is myogenic auto regulation

Answer 17

arterial smooth muscle responds to incr or decr in vascular tension

consists of arterial mechanisms (resistance vessels)

Question 18

describe what happens in myogenic auto regulation (high BP)

Answer 18

mechanoreceptors in afferent arteriole detect pressure , the special Na channels in the smooth muscles cells stretch making them leaky which send Na into arteriole, amount reaches threshold potential and stim Ca release from ER and contracts

efferent article dilate so follow path of least resistance and flow out causing drop in PGC

Question 19

PGC is proportional to how much blood coming in

Answer 19

reminder

Question 20

what happens in tubuloglomerular AR

Answer 20

main action is linking Na and CL concentration at macula densa to determine whether dilation or constriction need to occur

by controlling distal solute delivery it control tubular reabsorption

Question 21

what are the 2 components of TG AR

Answer 21

afferent arteriole resistance and efferent arteriole hormones

Question 22

describe TG feedback if GFR incr

Answer 22

incr NaCl delivery to macula densa and DCT (cl go into blood while na stays in cells)

triggers ATP release which turn to AMP then adenosine

adenosine bind to mesengial cells through A1 which stim ca concentration to incr and inhibits renin in Jg cells via gap junctions

ca move to afferent arteriole via gap junctions and constricts

vasodilation of EA via A2 receptors also found

Question 23

what happens when decr GFR via TG system

Answer 23

less adenosine means less ca which means vessel dilates

arachidonic acid broken down to prostaglandins and nitro oxide to help with dilation in macula densa

Question 24

why is assessing what conditions a patient has in regards to kidneys (and meds) important to know before administering medicines such as ACE inhibitors and NSAIDS

Answer 24

NSAIDS block prostaglandins from working which would decr GFR and impair renal function

when GFR low angiotensin II can help maintain it but ACE inhibitors stop this

Question 25

describe the nerve innervation to the A and E arterioles

Answer 25

both sympathetically innervated but usually low

fight or flight/bleeding can stim renal vessels and vasoconstriction can occur which conserve blood and cause a fall in GFR

parasympathetic release NO for endothelial cells and vasodilation

Question 26

what is the 2nd line of defence for GFR

Answer 26

1st line is myogenic and TG AR

2nd is when TG balance blocks sodium excretion response to any GFR changes by absorbing the same amount of sodium that is being let in

called glomerulotubular balance