Ch. 26 - Urinary System Flashcards
What are some functions of the kidneys?
- regulate blood ionic composition (Na+, K+ Ca2+, Cl-)
- regulate blood pH, blood volume, BP, blood glucose level
- maintain blood osmolarity
- produce hormones
- excrete wastes and foreign substances
What is a hilum?
region through which ureter leaves
- where BV, lymphatic vessels and nerves enter/exit
What are the 3 layers surrounding each kidney?
renal capsule, adipose capsule, renal fascia
What is the difference between the renal capsule and renal fascia layers?
capsule - transparent membrane that is continuous with ureter; barrier for protection and maintains organ shape
fascia - dense irregular CT that holds kidney against back body wall
What are minor and major calyces?
minor - cuplike structures that collect urine from papillary ducts of papilla
both - empty into renal pelvis which empties into ureter
What are the 3 capillary beds of kidneys?
- glomerular capillaries (where blood is filtered)
- peritubular capillaries in cortex
- vasa recta in medulla
* both 2&3 carry away reabsorbed substances from filtrate
What are the 3 functions of a nephron?
filtration, reabsorption, secretion
What are the 2 major parts of a nephron?
renal corpuscle - filters blood
renal tubule - where filtered fluid passes through
What are parts of the renal corpuscle and what is its function?
glomerulus and Bowman’s capsule
- site of plasma filtration
What are the parts of the renal tubule and what is its function?
- PCT,
- loop of Henle (dips into medulla, descending/ascending limbs)
- DCT
- collecting ducts (where it empties; converge to form papillary ducts to drain urine to renal pelvis and ureter)
What are the 2 types of nephrons?
cortical and juxtamedullary
How do cortical and juxtamedullary nephrons differ?
cortical - short nephron loop, receives blood from peritubular capillaries, creates urine with similar osmolarity to blood
juxtamedullary - long nephron loop, receives blood from peritubular cap & vasa recta, thick/thin ascending limbs, secrete concentrated urine
What do efferent arterioles around the nephron give rise to?
peritubular cap & vasa recta
What does the glomerular capsule comprise of?
- visceral layer: consists of podocytes (modified simple sq cells)
- parietal layer: consist of simple sq e that forms outer wall of capsule
What is the JG apparatus?
macula densa + JG cells that regulate BP in kidney (with ANS)
What is the macula densa? JGC?
macula densa - where ascending loop contacts the afferent arteriole
JGC - smooth musc cells on wall of afferent arteriole
What are the 3 basic processes of nephrons/collecting ducts?
- glomerular filtration - portion blood plasma filters into kidney
- tubular reabsorption - water & substances are reabsorbed into blood
- tubular secretion - wastes are removed from blood and secreted in urine
What is the rate of excretion?
filtration + secretion - reabsorption
What is glomerular filtrate?
fluid that enters the capsular space
What is the filtration fraction?
fraction of plasma in kidney’s aff arteriole that becomes filtrate
What are the 3 barriers filtered substances must cross?
- glomerular endothelial cells
- basal lamina
- filtration slit formed by podocytes
What are mesangial cells?
contractile cells that increase glomerular filtration when relaxed
- located bt aff and eff arterioles, among glomerular cap
What is the purpose of the basal lamina? What is it composed of?
prevents filtration of larger proteins; collagen fibers and proteoglycans
What is the slit membrane? Filtration slits?
thin membrane that extends across filtration slit; permits passage of molec that have a smaller diameter; spaces between pedicels
What are the 3 pressures that compose net filtration pressure (NFP) ?
- glomerular BHP (GBHP)
- capsular hydrostatic pressure CHP)
- blood colloid osmotic pressure (BCOP)
What is GBHP?
BP in glomerular capillaries; promotes filtration by pushing water and solutes out of cap through filtration membrane
What is CHP?
hydrostatic pressure exerted against filtration membrane by fluid already in capsular space of glomerular capsule; opposes filtration
What is BCOP?
pressure due to presence of proteins in blood plasma; opposes filtration
What is the equation of NFP?
NFP = GBHP - CHP - BCOP
What is GFR?
glomerular filtration rate; amount of filtrate formed in all renal corpuscles of both kidneys each minute
What are 2 mechanisms that regulate GFR?
- change rate of blood flow into or out of glomerulus (GFR increases when blood flow increases)
- change amount of SA avail for filtration
What are 3 ways that control blood flow through glomeruli?
- renal autoregulation by kidneys (myogenic mech, tubuloglomerular feedback)
- hormonal regulation
- neural regulation by sym NS
What is myogenic mechanism?
response to stretching of walls of aff arteriole due to increase in BP
- sm muscle contacts, decreasing GFR
What are 2 hormones that contribute to GFR regulation?
angiotensin II, atrial natriuretic peptide
How does angiontensin II contribute to GFR?
decreases GFR; strong vasoconstrictor reducing blood flow
How does ANP contribute to GFR?
increases GFR; increase in blood vol stretches atria, stimulating ANP release
How does ANP contribute to GFR?
increases GFR; increase in blood vol stretches atria, stimulating ANP release
How does neural regulation control GFR?
BV of kidneys supplied by sym ANS release NE; causing vasoconstriction of sm muscle in aff arterioles
- requires strong sym stimulation such as exercise or hemorrhage
What is reabsorption?
returning most of filtered water and solutes back to bloodstream
In what part of the nephron does reabsorption occur the most?
epithelial cells with microvilli in PCT
How is water reabsorbed? Solutes?
osmosis; active/passive processes; proteins/peptides reabsorbed via pinocytosis
What are the 2 reabsorption routes from fluid in tubular lumen to a peritubular capillary?
- paracellular reabsorption - reabsorbed mat moves bt cells via diffusion
- transcellular reabsorption - material moves through both apical and basal membranes of tubule cell via active or passive transport
Where does the apical membrane face? Basolateral?
tubular lumen; IS fluid
How is Na+ reabsorbed via primary active transport?
- Na+ diffuses into tubule cell
- Na+/K+ pumps in (only) basolateral membrane; pump Na+ from tubule cell cytosol to IS fluid, where it diffuses into peritubular capillary (Na+ is one way process!!!)
How are solutes reabsorbed via secondary active transport?
- relies on ion gradient created by Na+/K+ pumps
- Na+ drags another solute molec as it moves down conc gradient into tubular cell via symporters or antiporters
What are symporters?
2 or more solutes go in same direction
What are antiporters?
2 or more solutes go in opposite directions
What are the 2 patterns of H2O reabsorption?
1) obligatory 2) facultative
What is obligatory water reabsorption?
when water is obliged to follow solutes being reabsorbed
- occurs in PCT and descending limb of nephron loop bc both are permeable to water
What is facultative water reabsorption?
capable of adapting to need
- occurs in collecting duct under control of ADH
What is tubular secretion?
transfer of materials from blood and tubular cells into tubular fluid; eventually becomes urine
- controls blood pH via H+ secretion; eliminate certain substances (H+, NH4+, K+)
Where does most water and solute reabsorption occur?
PCT
What is the difference of Na+ symporters and antiporters?
S - help reabsorb substances from tubular filtrate (glucose, aa, SO4)
A - reabsorb Na+ and secrete H+ for elimination through urine (HCO3)
How do reabsorbed solutes increase osmolarity?
- in tubule cell, then IS fluid, then in blood
- reabsorption of solutes create osmotic gradient that promotes reabsorption of water via osmosis in PCT
Which limbs in the nephron loop are (im)permeable to water? Solutes?
thin - permeable to H2O, impermeable to solutes
thick - impermeable to H2O, permeable to solutes
- pumps Na+ and Cl- from tubular fluid to IS fluid
What is countercurrent multiplication?
osmotic gradient generated in IS fluid via movement of Na+, Cl-, H2O in nephron loop
- essential for concentrated urine production when ADH is present!
How is PTH activity related to the DCT?
DCT is the major site where PTH stimulates Ca2+ reabsorption
What are the 2 types of cells in the collecting duct and what do they do?
- principal cells - reabsorb Na+ and secrete K+ under control of aldosterone; increase H2O movement if ADH is present
- intercalated cells - reabsorb K+ and HCO3-, secrete H+
What are the 4 hormones that affect reabsorption (of Na+, Cl-, H2O) and secretion (of K+) ?
angiotensin II, aldosterone, ADH, ANP
How does angiotensin II affect reabsorption/secretion?
- decreases GFR by causing vasoconstriction of aff arteriole
- enhances reabsorption of Na+, Cl-, H2O in PCT by stimulating Na+/H+ antiporter activity (BP, blood vol increase!)
- stimulates aldosterone release from adrenal cortex (Na+ reabsorption, K+ secretion)
How does aldosterone affect reabsorption/secretion?
regulates electrolyte reabsorption and secretion
How does ADH affect absorption/secretion?
- increases water permeability of principal cells in last part of DCT and collecting duct (stimulates insertion of aquaporin-2 into membrane)
- increases facultative water reabsorption
How does ANP affect absorption/secretion?
ANP is released in response to large increase in blood vol stretching atrial cells
- inhibits Na+ and H2O reabsorption in PCT and collecting duct
- suppresses secretion of aldosterone and ADH
- natriuresis + diuresis leads to decreased blood vol/BP
How does ADH control whether dilute or concentrated urine is formed?
low ADH - dilute urine
high ADH - concentrated urine bc more water reabsorbed
Describe negative feedback control of ADH
- osmoreceptors in hypothalamus detect increase in plasma osmolarity
- stimulate ADH release
- principal cells more permeable and reabsorb more water
- plasma osmolarity decreases
What is urinalysis?
measuring vol and physical/chem/microscopic characteristics of urine
What are 2 blood tests used to evaluate kidney function?
1) blood urea nitrogen (BUN) test 2) plasma creatine
What is renal plasma clearance?
measure how fast a particular substance is removed from blood plasma by kidneys
How are kidneys capable of compensation in the event of dysfunction?
- individual nephrons can increase in size/workload (i.e. increase filtration/urine production)
- removal of one kidney causes enlargement of remaining kidney
What is the trigone?
smooth flat triangular area in floor of bladder
- 2 ureteral openings in posterior corners
- internal urethral orifice in anterior corner
Where is the urethra located in females?
post to pubic symphysis, orifice between clitoris and vagina
Where is the urethra located in males?
passes through prostate and penis
- 3 regions: prostatic, intermediate, spongy
Describe the urination reflex
- stretch receptors signal SC and brain when volume exceeds ~200-400 mL
- impulses sent to urination center (in S2 and S3) to trigger reflex
- parasympathetic fibers cause detrusor muscle to contract, ext/int sphincter muscles to relax
- filling causes sensation of fullness that initiates desire to urinate before reflex occurs
- conscious control of ext sphincter
