Urinary System Flashcards
what is the primary function of the urinary system
production of urine
how is urine produced by the urinary system
thru regulating the extracellular fluid environment in the body
what is the extracellular fluid in the body
interstitial fluid and plasma
specifically, how can the extracellular fluid environment in the body be regulated (i.e. what components/characteristics of the plasma can be controlled)
- ionic composition
- volume and blood pressure
- osmolarity
- pH
- metabolic waste products
- foreign substances
how is plasma volume regulated
by controlling rate of water excretion in the urine
plasma volume and pressure have direct effects on
total blood volume and total blood pressure
regulation of plasma osmolarity refers to
regulation of solute concentration thru rate of water excretion
regulation of plasma pH refers to
controlling bicarbonate and hydrogen ions in conjunction with lungs
what does metabolic waste refer to
uric acid, food additives, drugs, toxins
what are the secondary functions of the urinary system
- secretion of erythropoietin and renin
- activation of vitamin D3
- gluconeogenesis
secretion of erythropoietin and renin can be considered what type of system function
hormonal
what is erythropoietin important for
stimulation of red blood cells in marrow
what is renin needed for
angiotensin production
what is angiotensin
hormone that regulates salt and water balance, which regulates blood pressure
what is vitamin D3 important for
regulating blood calcium and phosphate levels
what is gluconeogenesis
production of glucose from glycerol and amino acids
draw out a diagram on a kidney including the arteries stemming from the renal artery: interlobular, arcuate, interlobar, segmental
….
what is the hilus
- indentation area of kidney
- variety of different vessels will enter/exit in this area
why are renal arteries important
they receive 20% of cardiac output at rest and directs this into the kidney itself
draw out a flow chart of renal artery branching
renal → segmental → interlobar → arcuate → interlobular → afferent arterioles → glomerular capillary bed
what stems (leaves) from the glomerular capillary bed; draw a flowchart
glomerular capillary bed → efferent arteriole → peritubular capillaries and vasa recta
where are peritubular capillaries found
cortex (outer layer of kidney)
where is the vasa recta found
medulla (inner part of kidney)
what is the relationship between vasa recta and peritubular capillaries
vasa recta are peritubular capillaries around the loop of Henle in the juxtamedullary nephrons only
how do kidneys regulate the composition of plasma
thru exchanging water and solutes between plasma and fluid in renal tubules
where do the substances removed from plasma go
urine excretion
what are the exchange processes occurring within the nepron
- glomerular filtration
- reabsorption
- secretion
what is glomerular filtration
bulk flow of protein-free plasma from glomerulus to Bowman’s capsule
describe the pathway of blood flow during basic renal exchange processes (incl. excretion) in a summary diagram; use arrows to indicate exchange movement direction
….
what is reabsorption
- selective transport of molecules from renal tubules to interstitial fluid
- molecules are first selectively transported to interstitial fluid outside of peritubular capillaries
- reabsorbed molecules enter peritubular capillaries thru diffusion
- molecules returned to general circulation
describe secretion
selective transport of molecules from plasma of peritubular capillaries back to renal tubules
define excretion
elimination of materials from body in the form of urine
what barriers must glomerular filtrate cross to enter the Bowman’s capsule
- capillary endothelial layer
- surrounding epithelial layer
- basement membrane (sandwiched between the 2 layers mentioned above)
what cells is the surrounding epithelial layer (in reference to glomerular filtration) made of
podocytes
the wall of the Bowman’s capsule and renal tubule are considered _______ layers of endothelial cells
continuous
what is the role of the basement membrane; how?
- to act as a primary filtration barrier
- as fluid passes out of glomerular capillaries, it moves thru gaps in podocytes
what are foot processes
- adhesive finger-like projections
- interlink like a puzzle but have gaps (filtration slits)
what is another name for filtration slits
slit pores
what is the pathway for filtrate flow in glomerular filtration
fluid passes out of glomerular capillaries → in gaps of podocytes (i.e. filtration slits)
how is movement in glomerular filtration regulated
slit diaphragm (intracellular contact points)
what force(s) drive glomerular filtration
- glomerular capillary hydrostatic pressure (P gc)
- bowman’s capsule hydrostatic pressure (P bc)
- glomerular osmotic pressure (π gc)
- bowman’s capsule osmotic pressure (π bc)
the sum of the starling forces in renal corpuscle make
glomerular filtration pressure
what can we compare glomerular filtration pressure in the urinary system to
net filtration pressure in the circulatory system
describe P gc
- blood pressure in glomerular capillaries
the variable P refers to
hydrostatic pressures
π refers to
osmotic pressures
why is the hydrostatic pressure in glomerular capillaries higher than hydrostatic pressure in most capillaries
- due to the high resistance in efferent arteriole
- consider water flowing thru a hose and a clamp was put on it
- water would then flow backwards which increases pressure upstream the clamp
- therefore when there is high resistance in efferent arteriole, the pressure is lower there but increases pressure on other side (in glomerular capillaries)
what is the hydrostatic pressure of the glomerular capillaries equal to
60 mmHg
what is the hydrostatic pressure of the glomerular capillaries equal to
15 mmHg
why is the hydrostatic pressure of the bowman’s capsule higher than the hydrostatic pressure in interstitial fluid surrounding most capillary beds
- due to large volume of fluid filtering in to bowman’s capsule
- similar to when pouring liquid down a funnel and doing it too fast in which the fluid backs up causing back pressure
why does π gc happen
presence of proteins that tend to draw fluid back into glomerulus
what does osmotic pressure of glomerular capillaries equal to
29 mm Hg (which is higher than osmotic pressure in most capillaries - 25 mmHg)
what does osmotic pressure of bowman’s capsule equal to
~0 mmHg (negligible)
since proteins cannot move between plasma and bowman’s capsule, what type of force generates
osmotic force (proteins stay in plasma)
proteins in the interstitial fluid around the glomerulus pull the fluid out of the capillaries into the capsule, but very little protein leaves. what does this mean for the concentration of proteins inside the bowman’s capsule
remains very small (leading to that ~0 mmHg amt.)
what are the types of starling forces that affect glomerular filtration
- favouring
- opposing
glomerular filtration pressure is the difference between
- favouring and opposing filtration pressures
- (Pgc + π bc) - (P bc + π gc)
what are the favouring filtration pressure
P gc and π bc
what are the opposing filtration pressures
P bc and π gc
where the blood is actually coming from is referred to as
upstream (afferent)
where the blood is actually going to is referred to as
downstream (efferent)
P gc and π bc favour filtration because
they promote water and solutes in blood plasma to move thru glomerular filter
P bc and π gc oppose filtration because
creates back-pressure
osmotic pressure refers to
pressure due to solutes in the blood that can’t leave, which makes a pull to draw water back into the capillaries
hydrostatic pressure refers to
pressure of a fluid on (the walls of) a confined space
what is the renal plasma flow rate
625mL/min
what is the glomerular filtration rate
125mL/min (180L/day)
what is glomerular filtration rate used to estimate
kidney function
define renal plasma flow
amount of plasma that flows thru kidneys each minute
define glomerular filtration rate
volume of plasma filtered per unit time
what is the filtration fraction
fraction of renal plasma volume filtered into bowman’s capsule (GFR/renal plasma flow)
what is filtered load
quantity of certain solute that is filtered per unit time (GFR * plasma conc. of X)
what classifies as a freely filterable solute
solute molecules that are small enough to move across glomerular membrane without restriction
small increases in GFR lead to large increases in
volume of fluid filtered and excreted
is GFR regulated or unregulated
regulated
draw out the intrinsic control pathway of GFR for myogenic regulation in afferent arterioles and glomerulus
↑ in mean arterial pressure leads to higher pressure in afferent arteriole and higher glomerular pressure in glomerulus
afferent arteriole: ↑ press. → stretch of arteriolar smooth muscle by stretch receptors → inc. constriction → inc resistance causing lower glomerular capillary pressure
glomerulus: higher pres. from MAP balances out lower pres. from high resistance; higher gc pres → higher glomerular filtration pres. → inc in GFR
draw out the intrinsic control pathway of GFR for tubuloglomerular feedback in afferent arterioles and glomerulus
↑ in mean arterial pressure leads to higher pressure in afferent arteriole and higher glomerular pressure in glomerulus
afferent arteriole ↑ press. → ↑ gc pres. in glomerulus → ↑ glomerular filtration press. → ↑ GFR → ↑ flow in macula densa → ↑ paracrine secretion → ↑ constriction in afferent arteriole → ↑ resistance → dec. in gc pressure in glomerulus (neg feedback by balance)
what is the role of the macula densa in tubuloglomerular feedback
releases paracrine factors in distal tubules which the smooth muscle of afferent arteriole is sensitive to
how do paracrine factors affect afferent arteriole
by constriction and relaxation
what are examples of extrinsic control mechanisms of the GFR
- hemorrhage
- excessive sweating
what systems and receptors are involved in extrinsic control of GFR
- sympathetic nervous system
- baroreceptors
why does GFR rise or fall when MAP varies outside range of 80-180 mmHg
intrinsic mechanisms aren’t able to prevent glomerular capillary pressure changes
draw out the extrinsic control of GFR including where negative feedbacks occur
…
what are the end results of extrinsic control of GFR
- decreased urine output
- lower reductions in blood volume which counteracts further decreases in arterial pressure
why does increased urine output occur at the end of extrinsic GFR control
to conserve water
describe solute and water reabsorption
movement of filtered solutes and water from lumen of tubules back into plasma
what percentage of most substances filtered by glomerulus are reabsorbed by renal tubules
100%
where does solute and water reabsorption occur mostly
proximal and distal convoluted tubules
when a substance is absorbed it must move across what number of barrier(s)
2
what are the barrier(s) that reabsorbed substances must cross
- epithelial cells of renal tubules
- endothelial cells of capillaries
what is the role of the tight junctions in the tubule epithelial cells
serve as connectors for cells lining tubules which makes for movement between the cells high restricted
on the apical membrane of the tubule epithelial cells there us microvilli facing the
lumen of renal tubule
the basolaterial membrane of tubule epithelial cells faces the
interstitial fluid in the peritubular space
when does sodium reabsorption happen
- movement happens into cell thru sodium channels or cotransport
- movement happens into peritubular fluid thru active transport (Na+/K+ pump) across basolateral membrane
- via diffusion thru plasma
water reabsorption is based on
differences in osmolarity
what is the “simple rule” on excretion vs reabsorption of material entering renal tubules
assumed that material which enters lumen of renal tubules is excreted unless it is reabsorbed
the amount of substance excreted equals
amt filtered - amt secreted - amt reabsorbed
excretion rate depends on what factor(s)
- filtered load
- secretion rate
- reabsorption rate
if the amount of solute excreted per minute is less than filtered load, we can say the solute was
reabsorbed
if the amount of solute excreted per minute was greater than filtered load, we can say that the solute was
secreted
