Urinary System

what’s affected by kidney function

all body systems either directly or indirectly affected

urinary system function

excrete metabolic waste

urinary system components

kidneys, ureters, bladder, urethra

urinary system filters

US filters blood and returns most of the water and solutes in it to blood stream

ureters function

tubes that take urine to bladder

what protects the kidneys

11th and 12th ribs

kidney’s cortex

outer zone of kidney

renal columns

extensions of the cortex that divide the medulla into 6-10 renal pyramidds

calyces

papilla of renal pyramid nestled into cup; calyces converge to form renal pelvis

parenchyma

functional portion of kidney

renal medulla

inner portion consisting of 8-18 cone-shaped renal pyramids Separated by renal columns

minor calyces

part of drainage system collecting urine from the papillary ducts of the papilla

where major and minor calyces empty into

renal pelvis which empties into the ureter

ureters length & diameter

10-12 inches long, 1-10 mm

where do ureters extend

retroperitoneal from renal pelvis to posterior bladder

how ureters flow

due to peristalsis, gravity and hydrostatic pressure

what funnels urine to paired ureters

renal pelvis

ureter layers

mucosa, muscularis, adventitia

bladder capacity

hollow, distensible muscular organ with capacity 800 ml or 24 oz voluntarily

up to 2000 ml or 60 oz when obstructed

bladder layers

mucosa, submucosa, muscularis, serosa

are the bladder’s sphincters voluntary

involuntary internal & voluntary external urethral sphincters

bladder volume exceeds 200 ml

conscious desire to urinate when stretch receptors in wall stimulated

bladder location

posterior to pubic symphysis, inferior to uterus, anterior to vagina, and anterior to rectum for males

who’s more prone to UTIs and why

women since their urethra’s are much shorter

male urethra dual function

rid the body of urine and release seminal fluid during orgasm

nephron overview

functional unit of the kidney removing waste and excess substances

number of nephrons in each kidney

one million

nephron parts

renal corpuscle & renal tubule

renal corpuscle - blood plasma filtered

glomerulus and Bowman’s capsule

renal tubule - filtered fluid passes

proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT)

Bowman’s capsule

cup shaped mouth of nephron (usually in cortex)

proximal convoluted tubule (PCT)

attached to Bowman’s capsule, highly coiled (convoluted), inner surfaces contains microvilli

loop of Henle

large loop consisting of descending limb & ascending limb, extends down into medulla

collecting tubule

part of nephric tubule where DCT drains into; bundles of collecting tubules is a pyramid

where do pyramids drain into

calyces

glomerular capsule

visceral layer, parietal layer, Bowman’s space

visceral layer of glomerular capsule

has modified simple squamous epithelial cells called podocytes and many wrap around the single layer of endothelial cells to form an inner layer

parietal layer of glomerular capsule

simple squamous epithelium

why 2-3 yr olds have urinary incontinence

neurons to sphincter muscle is not developed

what causes stress incontinence in adults

bladder pressure can result in leaking due to coughing, sneezing, laughing, exercise, walking

what causes injury urinary incontinence

injury to nerves, loss of bladder flexibility, damage to sphincter, pregnancy

diuretic definiton

substances that slow renal reabsorption of water & cause diuresis (increased urine flow rate)

diuretic examples

Caffeine inhibits Na+ reabsorbtion, alcohol inhibits secretion of ADH, prescription medicines can act on the PCT/loop of Henle/DCT

Glomerular disease

inability to maintain balance of some substances

polycystic kidney disease

inherited disorder that causes cysts to form inside the kidney

kidney stones secondary name

renal calculi

aging kidneys

kidneys shrink from 260g to 200g

urinary system age-related diseases

acute and chronic inflammation of canaliculi, infections, nocturia, polyuria, dysuria, incontinence, diminished thirst equaling dehydration, lowered filtration and flow

what do sweat glands eliminate

heat, water, salt, urea

what GI tract eliminates

solid wastes, CO2, water, salt, heat

what is the site for metabolic recycling

liver controls conversion of amino acids into glucose, glucose into fatty acids or toxic into less toxic substances

what also transports wastes

blood

dialysis therapy

artificially cleaning blood by separating large solutes from small ones by selectively permeable membrane

hemodialysis

directly filters blood because blood flows through tubing surrounded by dialysis solution and cleansed blood goes straight back to body

what do blood tests do

* Blood urea nitrogen test (BUN) measures urea in blood (rises steeply if GFR decreases severely)


* Plasma creatinine--from skeletal muscle breakdown
* Renal plasma clearance of substance from the blood in ml/minute (important in drug dosages)

urinalysis

analysis of the volume and properties of urine

normal urine is protein free, but includes filtered & secreted electrolytes

(electrolytes, urea, creatinine, uric acid, urobilinogen, fatty acids, enzymes & hormones)

dilute urine

has not had enough water removed, although sufficient ions have been reabsorbed

how much water does PCT reabsorb

65%

how much water does loop of Henle reabsorb

15%

how much water does DCT reabsorb

10-15%

how much water does collecting duct reabsorb

5-10% w ADH

how does ADH work

increases water permeability of principal cells so regulates facultative water reabsorption and stimulates aquaporin-2 channels so H2O moves more rapidly

what happens when osmolarity of plasma and interstitial fluid decreases

more ADH is secreted and H2O reabsorption increases

what do principal cells of the collecting duct do

principal cells reabsorb Na+ and secrete K+

what do intercalated cells of the collecting duct do

reabsorb K+ and bicarbonate HCO3- (bicarbonate)

secrete H+

ADH controls permeability of tubules

w/out ADh tubules are practically impermeable to water

what is the DCT a major site for

parathyroid hormone to stimulate reabsorption of Ca+

how are Na+ and Cl- reabsorbed in the DCT

symporters

what sets the stage for independent regulation of both volume and osmolarity of body fluids

loop of Henle

what does the PCT have that you WON’T forget

the inner surface has microvilli

what does glomerular filtration prevent from leaving the body

most plasma proteins, blood cells, and platelets

what are the 3 barriers of glomerular filtration

glomerular endothelial cells, basal lamina, pedicels

what type of capillaries does the glomerulus have

fenestrated capillaries that allow molecules less than 10k MW

pressure is very high in glomerulus

55mm Hg versus 35mm Hg in most capillaries

what produces glomerular filtrate

BP

what enhances glomerular filtration

glomerular capillary BP is high due to small size of efferent arteriole

thinness of membrane & large surface area of glomerular capillaries

glomerular blood hydrostatic pressure (GBHP)

55mm Hg pressure in glomerular capillaries, **promotes filtration** by forcing water/solutes in blood plasma through the filter membrane

capsular hydrostatic pressure (CHP)

15mm Hg, hydrostatic pressure exerted against the filtration membrane in capsule and tubule space, **opposes filtration**

blood colloid osmotic pressure (BCOP)

30mm Hg, due to presence of proteins (albumin, globulins, fibrinogen) in blood plasma, **opposes filtration**

10mm Hg causes normal blood plasma filtration

NFP = GBHP - CHP - BCOP

what mean arterial pressures keep GFR normal

80-180

what happens when GFR is too high

useful substances are lost due to the speed of fluid passage through nephron

what happens when GFR is too low

sufficient waste products may not be removed from the body

what mechanisms keep GFR constant despite arterial BP changes

myogenic mechanism and tubuloglomerular feedback

myogenic mechanism

systemic increases in BP, stretch the afferent arteriole and smooth muscle contraction reduces the diameter of the arteriole returning the GFR to its previous level in seconds

tubuloglomerular feedback

if BP is too high, the macula densa detects that difference & releases a vasoconstrictor from the juxtaglomerular apparatus allowing afferent arterioles constrict & reduce GFR

renal BV at rest

maximally dilated because sympathetic activity is minimal (renal autoregulation prevails)

moderate sympathetic stimulation of the GFR

both afferent & efferent arterioles constrict equally, hence decreasing GFR equally

extreme sympathetic stimulation of GFR (exercise or hemorrhage)

vasoconstriction of afferent arterioles reduces GFR, lowers urine output & permits blood flow to other tissues

hormonal atrial natriuretic peptide (ANP)

increase GFR

* when stretching of the atria BV increase causes hormonal release which **relaxes glomerular mesangial cells increasing capillary surface area and increasing GFR**

hormonal angiotensin II

reduces GFR as a potent vasoconstrictor that narrows both afferent & efferent arterioles reducing GFR

creatinine

normal end product of muscle metabolism

uric acid

end product of nucleic acid metabolism (some is secreted by PCT)

urea

main nitrogen containing waste produced during metabolism formed in the liver as a result of protein breakdown

* highly dependent on dietary intake

paracellular reabsorption 

50% of reabsorbed material moves between cells by diffusion in some parts of \n tubule

transcellular reabsorption

material moves through both the apical and basal membranes of the tubule \n cell by active transport

secondary active transport

symporters is membrane protein moving in same direction and antiporters are opposite direction

how much reabsorption occurs in the PCT

80%

where are all small proteins, glucose, and amino acids reabsorbed?

PCT