3 week 16 Flashcards
input + production = ____ + ____
utilization + output
what are average water inputs vs outputs for a 70kg human?
- inputs: 2.2 L/day (ingested) + 0.3 L/day (cell metabolism) = 2.5 L/day
- outputs: 0.1 L/day (feces) + 0.9 L/day (insensible) + 1.5 L/day (urine) = 2.5 L/day
how much of the body is made up of water?
- 60%
- 50% obese to 70% child
- about 42L for 70kg human
what is…
a) TBW
b) intracellular fluid
c) extracellular fluid
d) plasma
e) interstitial fluid
a) all the water that is contained in the body
b) fluid that is contained within cells
c) fluid that is located outside the cells
d) fluid that is located outside of the cell and found in the blood
e) fluid that is located outside of the cell and found outside of the blood
how much of TBW is ICF vs ECF?
- ICF = 2/3 TBW
- ECF = 1/3 TBW
how does water move between extracellular and intracellular compartments? (2)
1) osmosis (cells)
2) starling forces (capillaries)
osmosis is… (3)
1) always passive
2) unaffected by membrane potentials
3) water moves from low osmolarity to high osmolarity
whats molarity vs osmolarity?
- molarity: concentration of a substance in 1L solution
- osmolarity: concentration of PARTICLES in 1L solution
if a cell with an osmolarity of 300 mOsM were placed in a solution of 150 mM NaCl what would happen?
- 150 mM of NaCl dissociates into 2, = 300 mOsm
- the osmolarity is equal
- therefore no change
what are the 4 starling forces that make water move between extracellular and intracellular compartments?
1) capillary hydrostatic pressure (favours movement OUT of capillary)
2) capillary oncotic pressure (favours movement INTO capillary)
3) tissue hydrostatic pressure (favours movement INTO capillary)
4) tissue oncotic pressure (favours movement OUT of capillary)
what is clearance?
- the rate at which a solute is excreted
- excretion rate / plasma concentration
what are the roles of the…
a) kidneys
b) ureters
c) bladder
d) urethra
a) form urine
b) transport urine from kidneys to bladder
c) stores urine
d) transports urine from bladder to outside of body
T or F: kidneys don’t weigh much and receive relatively little of the cardiac output
- FALSE!
- despite their small fraction of body weight, the kidneys receive about 20% of the cardiac output under normal resting conditions!
what is a nephron?
- self-contained “mini- kidney” that filters blood and forms urine
- located in the many renal pyramids
describe the key features of a nephron (6)
1) RENAL CORPUSCLE [Bowman’s capsule + glomerulus]: where blood is filtered and filtrate has its origin.
2) PROXIMAL TUBULE [proximal convoluted + proximal straight tubule].
3) LOOP OF HENLE [descending limb + thin ascending limb + thick ascending limb].
4) DISTAL CONVOLUTED TUBULE: like proximal tubule but shorter.
5) CONNECTING TUBULE: joins the nephron with the collecting duct, where fluid is emptied.
6) MINOR CALYCES: common passageways ducts drain into.
describe the process of how blood/filtrate is filtered by the nephron
- blood enters glomerular capillaries via afferent arteriole.
- glomerular filtration: protein-free plasma passes through capillaries into Bowman’s capsule
- remaining blood leaves glomerulus via efferent arteriole
- filtrate flows from Bowman’s capsule > proximal tubule > loop of Henle > distal convoluted tubule > connecting tubule > collecting duct > minor calyces.
describe cortical vs juxtamedullary nephrons
- cortical nephrons: short loop of Henle, closer to kidney surface (most common).
- juxtamedullary nephrons: long loops of Henle, deeper into kidney.
note: both function in urine formation, but juxtamedullary nephrons also function in maintaining an osmotic gradient in the renal medulla (helps produce highly concentrated urine + conserve water).
what are the components and functions of the juxtaglomerular apparatus?
two components:
1) macula densa (epithelial cells)
2) granular/juxtaglomerular cells (in walls of afferent arterioles)
functions:
regulation of blood pressure, blood volume, and electrolyte balance
how is blood supplied to the nephron?
- arcuate arteries > interlobular arteries, from which blood is carried to individual nephrons by afferent arterioles > glomerular capillary beds > efferent arterioles
- from efferent arterioles can either have peritubular capillaries (cortical nephrons) or vasa recta (juxtamedullary nephrons)
- peritubular capillaries + vasa recta drain into the interlobular veins > arcuate veins > interlobar veins > renal vein
what are the basic renal exchange processes?
1) filtration: from glomerulus to Bowman’s capsule
2) reabsorption: from tubules to peritubular capillaries
3) secretion: from peritubular capillaries to tubules
4) excretion: from tubules out of body (via bladder)
how do you calculate volume of water excreted? what about amount of solute excreted?
- volume of water excreted = volume filtered – volume reabsorbed
- amount of solute excreted = amount filtered – amount reabsorbed + amount secreted
what kind of capillaries are found in the glomerular membrane?
fenestrated capillaries
which epithelial cells cover the glomerular capillaries?
podocytes
what three barriers does the glomerular filtrate cross to enter Bowman’s capsule?
1) capillary endothelial cell layer
2) surrounding epithelial cell layer
3) basement membrane that is sandwiched between them.
T or F: flow of protein-full fluid occurs in Bowman’s space.
false, protein-FREE
what are the starling forces favouring filtration? opposing?
favouring:
- glomerular capillary hydrostatic pressure (Pgc = 60 mm Hg)
- Bowman’s capsule oncotic pressure (Πbc = 0 mm Hg)
opposing:
- glomerular oncotic pressure (Πgc = 29 mm Hg)
- Bowman’s capsule hydrostatic pressure (Pbc = 15 mm Hg)
how do you calculate net filtration pressure?
- (Pgc + Πbc) – (Pbc + Πgc)
- about 16 mm Hg
what is avg glomerular filtration rate (GFR)?
125 mL/min = 180 L/day
note: capillaries in systemic circulation have filtration rate = 3 L/day which is brought back to blood by lymphatic system
how do you calculate the filtration fraction?
- (glomerular filtration rate / plasma flow rate) x 100
- about 20% which means 20% of plasma coming into nephrons ends up as filtrate, 80% goes back to body
how is the rate of glomerular filtration regulated?
- intrinsic (myogenic regulation, tubuloglomerular feedback)
- extrinsic (sympathetic nervous system)
describe myogenic regulation
- smooth muscle in wall of afferent arteriole contracts in response to stretch/pressure, leads to -glomerular capillary pressure
- stretch/pressure also leads to +glomerular capillary pressure which +GFR
- the decrease and increase in glomerular capillary pressure counteract one another and GFR stays at the normal value
describe tubuloglomerular feedback
- macula densa cells secrete paracrine factors in response to change in flow of fluid
- smooth muscles of arterioles contract or relax in response to these paracrines
- ex: +MAP = +GFR = +macula densa paracrine secretion = constriction = -glomerular capillary pressure
- ex: -MAP = -GFR = +macula densa paracrine secretion = vasodilation = +glomerular capillary pressure
describe the extrinsic regulation of GFR through the example of fluid loss due to hemorrhage or sweating
- fluid loss = -BP = +sympa activity
- kidneys vasoconstrict to +resistance and -GFR
- TPR in body increases, BP increases back to normal level
what is the composition of the initial filtrate?
- same ionic and small molecule composition and osmolarity as plasma
- BUT: mainly protein free
what is the filtered load? how do you calculate it?
- filtered load = quantity filtered/min
- GFR × Plasma concentration of the substance (Px)
