m11 + 12 lecture - urinary system Flashcards
what organ does the urinary system include?
kidneys
- smaller than a fist
- covered in fat
what are the functions of the kidney?
- clean the blood of waste
maintain:
- BP (RAAS)
- O2 concentration in the blood (RBC production)
- pH and electrolyte balance (albumin, K+, Na+, Cl-, Ca++)
what is the nephron?
- functional unit of the kidneys
- responsible for urine formation
- mainly in cortex of kidney, a portion extends into the medullary region (loop of Henle)
what are the steps of urine formation by the nephron?
1) filtration
2) reabsorption
3) excretion/secretion
how many nephrons are in each kidney?
- 1 million per kidney
about how many nephrons are cortical and juxtamedullary ?
cortical nephron - 85%
juxtamedullary nephron - 15%
- long loop
- helps to concentrate urine
what are the parts of the nephron?
- renal corpuscle
- glomerulus (podocytes)
what is the renal corpuscle?
- made from the glomerulus and the bowman’s capsule
- this is the filtration unit of the kidneys
what is the glomerulus?
- a network of very porous fenestrated capillaries, held together by podocytes
- receives blood from the afferent arteriole and is drained by the efferent arteriole (only kind of capillary bed drained by an arteriole)
what is a podocyte?
- helps prevent rupture of the glomerulus
- reinforces the membrane and has filtration slits
what is the JG apparatus made of?
- macula densa cells of DCT
- juxtaglomerular cells (granular cells of afferent arteriole)
what do the juxtaglomerular cells do?
- monitor the BP and O2 content in the afferent arteriole
- release renin to increase BP (RAAS)
- produce EPO to increase RBCs and O2
what do the macula densa cells do?
- tubuloglomerular feedback mechanism (TGFM)
- cells of the DCT which lie close to the glomerulus
- these cells act as chemoreceptors that sense the concentration of the filtrate
- change the flow of blood thru the afferent arteriole and the filtration rate thru the glomerulus
what is filtrate formation?
- driven by hydrostatic pressure (BP)
- kidneys form 180L of filtrate per day
—-> we reabsorb 178.2L = 99%
—-> we only secrete 1.8L = 1% in our urine - filtrate is the same as plasma except without any protein/cells
- anything not reabsorbed = considered urine
equation for net filtration pressure (NFP)?
glomerular filtration pressure –> GFP
(+/-) colloid osmotic pressure –> COP
(+/-) capsular hydrostatic pressure –> CHP
= net filtration pressure –> NFP
why is filtrate formed?
- due to glomerular filtration pressure - this is the same as glomerular hydrostatic pressure
- pressure in the glomerulus is much higher than regular capillaries at 55mmHg (vs. 15mmHg normally)
- this pressure will force fluid and small particles out of the blood into the bowman’s capsule
two factors will oppose this:
- capillary osmotic pressure = around 30 mmHg
- capsular hydrostatic pressure = usually 15 mmHg
what is the glomerular filtration rate (GFR)?
- the rate at which filtrate forms
- 125mL/min
what factors affect filtrate formation?
- BP changes in the afferent arteriole
- hydration
- health of glomerular capillaries
- age
what happens when BP increases?
- filtrate formation increases
- reabsorption decreases
—> urine formation increases and becomes more dilute
—> nephron does not have time to reabsorb the fluid
* if greatly affected by how much water you take in per day*
through what mechanisms is regulation of GFR done?
intrinsic and extrinsic mechanisms
where does renal autoregulation, an intrinsic control of filtrate formation, occur?
it is myogenic, in the muscles
how does renal autoregulation occur?
- done by controlling the BF through the afferent and efferent arterioles
- reflex action monitors stretch in the afferent arteriole and will adjust to changes in pressure
—> maintains BF through the kidneys => maintains GFR if active/resting or in positional changes
what is tubuloglomerular feedback mechanism (TGFM)?
- the macula densa cells monitor the concentration (osmotic pressure) of the filtrate in the DCT (quality control)
–> the GFR influences the reabsorption rate and affects the amt. of materials we lose or reabsorb - the goal of TGFM is to maintain an even GFR to prevent a loss or excessive gain in electrolytes
what happens to reabsorption if filtration is low? (TGFM)
reabsorption is high, the concentration is low and the MD will increase BF - in the afferent arteriole
what happens to reabsorption if filtration is high? (TGFM)
reabsorption is low, the concentration is high and the MD will decrease BF - in the afferent arteriole
what is reabsorption?
- an active process occurring at the PCT and the loop of Henle
- 80% of energy expenditure is devoted to the reabsorption of Na+
solute pump
- reabsorb Na+
- consume ATP
- generates osmotic pressure
- helps to reabsorb H2O
what is reabsorbed in the PCT?
- K+, Na+
—> glucose, amino acids, vitamins thru co-transport w/ Na+ - H2O along w/ Na+ (osmosis)
- small proteins that endocytosed
- anions –> Cl- and HCO3-
- Ca+, P, Mg+ are absorbed due to plasma concentrations and hormone stimulus (PTH, testosterone, estrogen)
what is absorbed in the loop of henle?
- descending limb - permeable to H2O
- ascending limb - Na+ reabsorbed
—> K+ secreted here - Na+ reabsorbed by the Na+/K+ pump along the length of the loop of Henle and DCT
—> as these are reabsorbed, H2O will move along w/ this due to osmotic pressure
what is the transport maximum?
- the maximum concentration of a molecule or compound that can be reabsorbed — any concentration above this will be excreted
example: glucose - norm: 110, too much = 300
multivitamins
what happens to the CD when dehydrated?
- when a person is dehydrated, ADH makes the CD permeable
what are tubular secretions?
secretions from the tubes - PCT, DCT
what are the actively secreted substances from the PCT and DCT?
- K+
- drug waste molecules
ex.) tylenol = hard on the liver
ibuprofen = hard on the kidneys
what are the monitored substances of the PCT and DCT?
- H+ and HCO3- to balance pH
what substances are waste from the PCT and DCT?
nitrogenous wastes
- urea
- uric acid
- ammonia
- creatinine
what processes are activated when a person is dehydrated (forming concentrated urine)?
- hypothalamus to release ADH, increasing permeability of the CD to water (better reabsorption of H2O from urine)
- RAAS
what happens with the hypothalamus when a person is dehydrated? (forming concentrated urine)
- hypothalamus triggers thirst and releasing ADH
- ADH increases permeability of the CD to water
- helping us to reabsorb water from the urine
- ADH is secreted in small amts. to maintain fluid volume in the plasma
what happens in RAAS? (Renin Angiotensin-Aldosterone System)
- triggered by loss of pressure and volume
- JG cells release renin to stimulate the liver to release angiotensin I
- at the lungs, ACE (angiotensin converting enzyme) changes angiotensin I to angiotensin II, stimulating three things:
1) vasoconstriction - increases BP to norm.
2) reinforces ADH prod.
3) aldosterone prod.
what does the release of aldosterone do?
- promotes the reabsorption of Na+ at the loop of Henle to increase H2O reabsorption
ex.) norm. 1200mL, so it increases to 1600-2400mL
which is produced more, ADH or aldosterone?
- ADH is prod. more often throughout the day and affects water reabsorption more than aldosterone
- w/o these two working together, we would dehydrate quickly
what blocks ADH?
alcohol and caffeine affect the absorption of water in the urine
what is the normal amt. of urine formation? and the amt. with diuretic?
norm. = 2-3mL/min, go every 3hrs
w/ diuretic (alcohol) = 20-30mL/min, go every 30 min.
how much urine is normally produced in a day?
1.5L/day
what is polyuria?
- more than 2.5L/day is prod.
due to DM, DI
what is oligouria?
less than 500mL.day
what is anuria?
no urine output - kidney failure
what is the composition of urine?
- 95-99% water
- urea, creatinine, uric acid, ammonia, Ca+, Mg+, H+, HCO3-, Na+, K+ and other ions
- urine is sterile until exiting the body
what is renal calculi?
- stones caused by the build up of uric acid salts/Ca++
- will block the pelvis and get stuck in the ureters
about the bladder?
- controlled by the PSNS and the pons
- internal urethral sphincter relaxes as the bladder contracts
- external urethral sphincter is done by voluntary control
about the urethra?
carries urine out the body
- surrounded by the internal and external urethral sphincter
male urethra extends abt 20cm
- surrounded by the prostate gland, which lies just below the bladder
female urethra extends abt 3-4cm
- this accounts for the higher incidence of UTIs in women
what is incontinence?
- inability to control micturition
- happens in: old age, holding it in too long (overflow), stress, pregnancy
what is nocturia?
urinating at night
what is nocturnal enuresis?
wetting of the bed
