Urinary system Flashcards
6 Functions of the Kidneys
Filters: blood plasma
Regulates: blood volume and BP, osmolarity, PCO2 and acid base balance
Secretes: renin (controls BP and electrolytes), and erythropoietin
Processes: separates waste from useful (waste is removed, useful is returned) and gluconeogenesis
Nitrogenous wastes
Urea, Uric acid, creatinine
Uric acid formation
Proteins > Amino acids > Remove NH2 > ammonia > liver converts ammonia to Urea
Urea
Product of nucleic acid catabolism
Creatinine
Product of creatinine phosphate catabolism
Urinary excretes
Metabolic wastes, toxins, drugs, hormones, salts, H+, water
Renal circulation
Aorta > renal artery > segmental artery > interlobar artery > arcuate artery > interlobular artery > afferent arteriole > glomerulus > efferent arteriole > vasa recta| > peritubular capillaries > interlobular vein > arcuate vein > interlobar vein > renal vein > inf vena cava
Vasa recta
- Specialized capillary bed
- ONLY in medulla
Proximal Convoluted Tubule (PCT)
Longest, most coiled
Simple cuboidal epithelium
With microvilli
Largest amount of recovery
Nephron loop/ Loop of Henle
Salt - water gradient
Distal convoluted tubule (DCT)
Shorter, less coiled
WITHOUT microvilli
End of nephron
Last effort for recovery
Cortical nephrons
85% of all nephrons
Short nephron loops
Efferent > branch into peritubular capillaries
Juxtamedullary nephrons
- 15 % of all nephrons
- long nephron loops, maintain salinity gradient in medulla»_space; helps to conserve water
- Efferent branch into vasa recta around long nephron loop
Basic stages of Urine Formation
- Glomerular filtration - create filtrate
- Tubular reabsorption - remove useful sources from filtrate, return to blood for use
- Tubular secretion - remove additional wastes from blood, add to filtrate
- Water conservation - remove water from urine, return to blood (concentrates waste)
Name the fluid by location/phase
In capsular space: glomerular filtrate
In PCT»_space; DCT: tubular fluid (substances are removed/added)
In collecting duct: urine (no other changes in composition)
Glomerular filtrate membrane: what is turned back
Blood cells
Plasma proteins large anions
Protein-bound minerals and hormones
Molecules > 8nm in diameter
Glomerular filtrate membrane: passed through filter
Water Electrolytes Glucose Amino acids Fatty acids Vitamins Urea Uric acid Creatinine
Glomerular filtration
Capillary fluid exchange process: some diluted pass from capillaries into capsular space of nephron
Kidney infections and trauma—
Damage filtration membrane:
» allow aluminum or blood cells to filter
> > proteinuria (albuminuria) : protein in urine
> > hematuria : blood in urine
Forces in Glomerular Filtratiob
Blood hydrostatic pressure : 60mmhg
Colloid osmotic pressure :
-32mmHg
Capsular pressure :
-18mmHg
Net filtration pressure :
10mmHg
High BP in glomerulus
Hypertension in kidneys
» tears in basement membrane
»_space; rupture of glomerular capillaries
»_space; scarring of kidneys (nephrosclerosis)
»_space; atherosclerosis of renal blood vessels
»_space; renal failure!
Blood hydrostatic pressure
- higher than in most capillaries
- afferent arteriole larger than efferent arteriole
- larger inlet, smaller outlet
Capsular pressure
18mmHg due to high filtration rate and continual accumulation of fluid in the capsule
Colloid osmotic pressure
Glomerular filtrate is almost protein free and has no COP
We want bc it will affect pressure if proteins get stuck
Glomerular filtration rate GFR
Amount of filtrate formed per minute by the two kidneys combined
Male: 180 L/day
Female: 150L/day
Total amount: 50-60x amount of blood in body
- 99% of filtrate reabsorbed since 1-2 L of urine excreted per day
GFR too HIGH
What happens:
- fluid flows thru tubules too rapidly
- urine output ^
- may cause dehydration and electrolyte depletion
GFR too low: what happens
- wastes are reabsorbed
- Azotemia may occur ***
GFR controlled by adjusting glomerular blood pressure. 3 mechanisms:
- Renal autoregulation
- Sympathetic control
- Hormonal control
Renal autoregulation
Ability of the nephrons to adjust own blood flow
Maintains relatively stable GFR
2 methods: myogenic (muscular) and tubuloglomerular feedback
Renal autoregulation: antigenic mechanism
Smooth muscle tends to contract when stretched
-inc arterial blood pressure stretches afferent arteriole
-arteriole constricts and prevents blood flow to glomerulus from changing
-» when blood pressure FALLS: afferent arteriole relaxes
»_space;> allows blood flow more easily into glomerulus
filtration remains stable!
Renal autoregulation: tubuloglomerular feedback
Glomerulus receives feedback of tubular fluid and adjusts filtration to regulate the COMPOSITION of the fluid, stabilize its performance, and compensate for fluctuation
- -juxtaglomerular apparatus: @ end of nephron loop
- loop comes into contact w afferent and efferent arterioles
internal sensing system
Renal autoregulation: 3 specialized cells
- Macula densa: sense
- Juxtaglomerular cells: constrict afferent arteriole
- Mesangial: capillaries
Macula densa
Slender closely spaced epithelial cells at the end of nephron loop
Senses variations in flow or fluid composition
» secretes paracrine that stimulates JG cells
JG cells
Enlarges smooth muscle cells in afferent arteriole
Stimulated by macula > dilate/constrict arteriole, secrete renin in drop of low pressure
JG apparatus: if GFR rises
- flow of tubular fluid inc and more NaCl is reabsorbed
- Macula densa stimulates JG cells w paracrine
- JG cells contract, construct afferent arteriole, reduce GFR to normal OR
- mesangial cells contract, construct capillaries and reducing filtration
JG apparatus: if GFR falls
- macula densa relaxes afferent arterioles and mesangial cells
- blood flow inc and GFR rises back to normal
PCT
- reabsorbs __%
- removes:
- secretes into _____ for ______
- 65% of glomerular filtrate
- substances from blood
- secretes into tubular fluid for DISPOSAL in urine
Proximal Convoluted Tubule
- prominent microvilli
- lots of mitochondria for ATP for active transport
- account for 6% of resting ATP and calorie consumption
