Urinary System - A&P II

Why is maintaining a minimal blood pressure essential for kidney function? In other words, what does GFR have to do with RBF?

a minimal blood pressure is essential for kidney function as it ensures there is enough pressure to push fluid through the glomerulus.

What are the 2 major functions of kidneys?

filter blood to produce urine and regulate blood pressure

What are the effects of diuretics on kidney function? On blood pressure?

diuretics increase urine output, essentially enhancing kidney function and decreasing blood pressure

to remove liquid wastes from the blood and regulate blood volume (and therefore pressure)

urinary system function

the urinary system excretes these wastes

excess electrolytes and nitrogenous and other metabolic wastes (urea)

main organs of blood filtration

kidneys

carry urine from kidneys to bladder

ureters

stores urine prior to micturition (urination)

bladder

carries urine out of the body

urethra

micturition

urination

kidneys consume roughly 20-25% of ____ used by the body at rest

oxygen

why do kidneys use so much oxygen

they are extremely metabolically active

why do the kidneys filter your entire blood volume roughly 60 times a day

to keep the blood free from waste products and to conserve as much water as possible

kidneys are highly dependent on…

blood pressure

how many layers of connective tissue surround each kidney

three

name the three layers of connective tissue surrounding each kidney

renal fascia, perirenal fat capsule, fibrous capsule

anchors kidney and adrenal gland to surrounding structures

renal fascia

surrounds kidney and protects it from damage

perirenal fat capsule

impermeable connective tissue that protects kidney from infections

fibrous capsule

why are kidneys considered “retroperitoneal”

they are not located within the abdominal (peritoneal) cavity, but in the lining behind the cavity

supplies blood to be filtered

renal artery

filtered blood returns to circulation

renal vein

concave surface (medial surface)

hilum

distal tissue layer (outside layer)

renal cortex

renal pyramids (lobes)

renal medulla

renal medulla drains into the…

renal pelvis

why do the blood vessels in the kidneys get really small

increased surface area allows for rapid filtration

brings blood to kidney - up to ¼ total CO per minute

renal artery

renal artery branches into ____ that branch smaller and smaller, eventually to capillaries around each nephron

segmental arteries

list the three steps to urine formation

1. “squeeze” liquid from the blood (filtrate)

2. reabsorb necessary components (still filtrate)

3. actively secrete wastes into liquid that is left over (urine)

“squeeze” liquid from the blood (filtrate)

step 1 of urine formation

reabsorb necessary components (filtrate)

step 2 of urine formation

actively secrete wastes into liquid that is left over (urine)

step 3 of urine formation

the functional unit of filtration in the kidney

nephron

about _______ nephrons per kidney

1 million

fluid collected from _____ is sent to the renal pelvis via collecting ducts

nephrons

tuft of capillaries that removes wastes from blood via hydrostatic pressure

glomerulus

renal corpuscle

nephron

fluid leaves the capillaries and goes into the…

glomerular capsule

fluid leaves the glomerular capsule and passes into the _____ to be processed into urine

renal tubules

tuft of fenestrated capillaries inside the Bowman’s capsule

glomerulus

fenestrated capillaries are very _____, allowing liquids to move out under pressure

porous

fenestrae (holes) are restrictive, meaning…

only very small solute molecules should pass through (H20, sugars, salts, etc.), not large ones (e.g. proteins)

form a network of spaces surrounding the capillaries that limits diffusion of large molecules

podocytes (“foot cells”)

visceral layer clings to the capillaries and contains podocytes

glomerular capsule

collected filtrate from the glomerular capsule is transported via the collecting duct called the…

renal tubule

blood (hydrostatic) pressure gives the glomerular capillaries high enough pressure to squeeze liquid out of the blood and enhance filtrate formation

outward pressure

capsule pressure and osmotic pressure in blood hinders filtrate formation

inward pressure

describe the sum of glomerular pressures

high pressure forces liquid out of the blood (~+55), osmotic pressure making liquid go back in the blood (~-30), hydrostatic pressure from capsule forcing liquid back into capillaries (~-15), resulting in ~+10 mm/Hg moving liquid out of the capillaries

explain how altered blood pressure affects glomerular pressures

for instance, if someone were hypotensive, the pressure forcing liquid of the blood would be lower than normal, so there would not be enough pressure to force liquid out of the capsule, meaning there is no urine production

filtration rate factors

pressure, total surface area, filtration membrane permeability

volume of filtrate produced each minute by both kidneys

glomerular filtration rate (GFR)

these factors lead to glomerular filtration rate (GFR)

pressure, total surface area, filtration membrane permeability

what is the most clinically important feature on this chart

the point at which GFR is 0 (60 mm/Hg) because it shows there is not enough pressure to produce filtrate/urine

what resorbs everything the body needs during step 2 of urine formation

tubules

what do the tubules resorb during step 2 of urine formation

water and other important dissolved solutes

what happens to everything the tubules do not resorb during step 2 of urine formation

becomes urine

what sort of things become urine after tubules do not resorb them during step 2 urine formation

glucose, vitamins, electrolytes, etc.

how is reabsorption in step 2 urine formation accomplished

by both active diffusion and passive diffusion

what are the three distinct sections of the renal tubule

proximal tubule, nephron loop (loop of Henle), distal tubule

what is the difference between the proximal tubule and distal tubule

proximal tubule is closest to the glomerulus

why is the renal tubule so long

more surface area for diffusion

cling to and readily absorb water and solutes from the filtrate in the renal tubules

peritubular capillaries

peritubular capillaries serve to further…

remove water and useful substances from the filtrate collected from the renal capsule

summarize the glomerular capsule’s role in renal circulation

only arterioles transport blood to the glomerular capsule, very high pressure, allowing water and wastes to be collected in the nephron by diffusion AND physical pressure, producing filtrate

summarize the role peritubular capillaries play in renal circulation

they run along tubules to reabsorb water from waste, under low pressure, longer to produce more concentrated urine, and they reclaim most of the filtrate from the capsule while the rest is excreted as urine

what are the two ways filtrate can be reabsorbed into the renal tubule

transcellular route (across the membrane) and paracellular route (through cellular junctions and interstitial fluid)

please explain how filtrate from step 1 starts at low concentration, increases in concentration, and then decreases again

• during step 1, the concentration increases as the solvent (water) decreases (gets resorbed)

• during steps 2 and 3, the concentration decreases as the solutes (Na+ and Cl-) decrease (get resorbed)

reabsorption is limited by the number of…

primary transport proteins for each substance (e.g. sodium- potassium pump)

solutes are co-transported back into the blood with sodium

secondary active transport

water follows solutes into the blood via _____, helping to maintain blood pressure

passive diffusion

these add substances to urine by secreting them during step 3 of urine formation

capillaries

what is the purpose of secreting substances into urine

1. eliminate drugs and toxic metabolites

2. regulate K+

3. control blood pH levels

secretion (step 3) is the opposite of…

resorption (step 2)

increases permeability of the collecting ducts to water, putting water back into the blood

anti-diuretic hormone (ADH)

when ADH is stimulated, it…

increases blood solutes and decreases blood pressure

reduces Na+ secretion (stimulates resorption)

aldosterone

when aldosterone is stimulated, it…

increases K+ and lowers blood pressure (via renin-angiotensin mechanism)

after processing, urine is collected from several nephrons into…

collecting ducts

in each kidney, collecting ducts empty into the…

ureter

reduces urine output resulting in a reduction or stop to urine production

kidney damage

how to treat kidney damage

dialysis, sometimes for life

medication that enhances water excretion

diuretics

how do diuretics enhance water excretion

inhibits ADH secretion and Na+ resorption into the blood

need to test BOTH _____ to clinically evaluate kidney function

blood and urine

urine characteristics

sterile, pale yellow, specific gravity greater than that of water

urine composition

water (95%), urea, uric acid, creatinine, Na+, K+, PO4, SO4

from breakdown of amino acids

urea

transport urine from the renal pelvis to the bladder

ureters

how do the ureters transport urine

peristalsis

what is the diameter of ureters like

VERY thin (1 mm)

precipitated minerals can cause…

kidney stones

three tissue layers of the bladder

mucosa (epithelia), detrusor (smooth muscle layer), adventitia (connective tissue)

allow the bladder to stretch when filling with urine

rugae

flexes and squeezes the bladder to get urine out of the body

detrusor muscle

should have 5 mL or less of urine

empty bladder

what is the danger of having urine stay in the bladder too long

bacterial infection

can hold 500 mL of urine

full bladder

can hold ~1000 mL or urine

distended bladder

what is the danger of a distended bladder

bladder can herniate or rupture