Urinary/Excretory System Flashcards
metabolism
reactions in a cell
secretion vs. excretion
secretion: releasing substance by exocytosis
excretion: eliminating metabolic wastes
Excretory organs maintain homeostasis by…
- regulating body fluids
- removing metabolic wastes from blood
- controlling rate of RBC formation
- regulating blood pressure
- regulating absorption of calcium
water is a by-product of…
dehydration synthesis & respiration
CO2 is a by-product of…
cellular respiration
salts are a by-product of…
neutralization
urea is a by-product of…
amino acid metabolism
deamination
removing amino group from amino acid & converting it into ammonia
3 ways the liver helps with homeostasis
- removes bilirubin
- produces urea
- detoxifies blood
How do drugs/alcohol affect the liver?
They kill liver cells, so the liver struggles to detoxify substances
the body system our skin belongs to
integumentary system
urine has the same components as what?
sweat (made of water, salts, and urea… aka metabolic wastes)
4 main structures of urinary system
kidneys, ureters, urinary bladder, urethra
urinary system
organs that produce, store, & rid the body of urine
functions of urinary system
excretion, maintenance of water-salt balance, maintenance of acid-base/pH balance, secretion of hormones & enzymes
excretion
- removal of metabolic wastes (NOT defection!)
- ex. ammonia, urea, uric acid
ammonia
formed from breakdown of amino groups in a.a.’s… very toxic
urea
liver converts ammonia into less toxic urea
uric acid
- formed from breakdown of nucleotides
- too much uric acid causes gout
gout
- formed by excess of uric acid
- painful arthritis-like condition that affects joints, esp. big toe
maintenance of water-salt balance
- kidneys regulate NA+, K+, HCO3, and Ca2
- balance of ions affects osmotic concentration of blood
maintenance of acid-base (pH) balance
keeps blood pH at 7.4 by excreting H+ and reabsorbing HCO3
renin
affects release of aldosterone -> regulates blood pressure
erythropoietin (EPO)
tells bone marrow to produce RBC
calcitrol
helps intestine absorb calcium from food
kidneys
- primary organs of urine production
- on either side of spine below diaphragm & anterior to deep back muscle
hilium
- part of the kidney
- renal artery enters & renal vein leaves
ureters
- small muscular tubes that transport urine from kidney to bladder
- peristalsis moves urine
urinary bladder
- muscular organ that expands as urine enters
- holds up to 600ml of urine
urethra
- extends from bladder to external opening
- 4cm in females, 20cm in males
- shorter length in females makes them more prone to UTI
- in males, urethra is surrounded by prostate gland & also carries sperm
What problem can arise with the prostate gland?
As males age, the prostate gland can enlarge and restrict urine flow
3 major regions of kidney
- renal cortex: outer layer
- renal medulla: inner layer, consists of cone-shaped renal pyramids
- renal pelvis: central cavity leading to ureter
nephron
microscopic units of kidneys that produce urine… one million per kidney
Blood supply pathway
renal artery -> kidneys -> afferent arteriole -> glomerulus -> efferent arteriole -> peritubular capillary -> venule -> renal vein
glomerulus
capillary knot inside nephron
path of filtrate
nephron -> collecting ducts -> renal pelvis -> ureter
characteristics of urine
- 95% water
- 5% solutes
solutes include
- ions: H, K, Na, Ca, Cl, Mg
- ammonia, sulphates, phosphates
- urea
- creantinine
- uric acid (organic compound from purine breakdown)
- others: carbs, enzymes, fatty acids, hormones, pigments & mucins
colour of urine
- old decomposed RBC -> bilirubin -> urobilin = yellow
- urinate less = less yellow (diluted urobilin)
- if urine stored for a while (ie. overnight) = darker yellow
changes to smell
- diabetics have a sugary smell to their urine
- asparagus can also cause a strong odor
Process of urine formation
- waste-filled blood enters kidneys
- glomular or pressure filtration occurs
- tubular or selective reabsorption
- loop of henl
- tubular secretion
Waste-filled blood enters kidneys
- afferent arterioles enter Bowman’s capsule & form a ball of capillaries called glomerulus
- efferent arteriole is smaller diameter than the arteriole so blood pressure builds up in glomerulus
- blood pressure forces substances from blood into Bowman’s capsule
Glomular or pressure filtration
- material forced out of blood = filtrate
- has h2o, a.a.’s, glucose, salts, & urea
- larger particles (blood cells, proteins, & fats) can’t leave capillaries, so they stay in blood & leave via efferent arteriole
- efferent arteriole branches into peritubular capillaries which form a mesh around nephron
- filtrate moves into proximal convoluted tubule
Tubular or selective reabsorption
- in proximal convoluted tubule where some filtrate returns to bloodstream
- lined with villi to enhance absorption
- active transport moves glucose, a.a’s, and Na back into blood
- Cl follows passively because it’s attracted to Na
- with salt leaving (NaCl), h2o follows by osmosis
- if amount of substance exceeds number of carrier proteins, not all can be reabsorbed so it ends up in urine
Loop of Henle
its main job is to regulate water concentration
Tubular secretion (excretion)
- 2nd place where substances leave blood & enter nephron
- distal convoluted tubule not permeable to H20, so H20 enters capillaries, not nephron
- excess H & K ions, drugs, uric acid, products from the breakdown of hemoglobin, histamines, etc. move by active transport from blood to nephron
- distal tubules drain into collective duct where more H20 diffuses back into surrounding tissue makes urine more concentrated than blood
- fine-tuning of H20 concentration occurs in distal convoluted tubule & collecting tubule
osmolarity
- number of particles per volume of fluid
- maintaining osmolarity in tissues involves h20 regulation
H20 regulation occurs through…
- direct control using ADH
- indirectly through aldosterone
Anti-diuretic hormone (ADH)
- control of h20 excreted relies on ADH (aka vasopressin)
- diuresis means “water-loss”, so ADH mean “anti-water-loss hormone”
- ADH is made in hypothalamus & stored in posterior pituitary gland
- makes you thirsty -> you’ll drink more
Steps of ADH secretion
h20 level drops -> osmolarity increases -> osmoreceptors in hypothalamus direct ADH to be released from pituitary -> ADH binds to receptors of cell on collecting tubule in nephron -> triggers chain of events that lead to insertion of aquaporin channels in collecting duct & distal tubule -> membrane becomes more permeable to water -> water flows out of tube into capillaries to be reclaimed by body -> H20 builds up in body -> osmoregularity back to normal -> shuts down hypothalamus… until the cycle begins again
If blood is too dilute (ie. after large intake of H20)…
- ADH secretion is inhibited
- aquaporin channels removed by endocytosis
- h20 can’t leave nephron -> large volume of urine
How to alcohol & caffeine affect urination?
- inhibit ADH
- urine volume remains large & dehydration can result
Aldosterone
- low Na concentration in blood sensed by kidney
- through chain of complex chemical signals, kidney sends message to adrenal cortex which releases aldosterone
- aldosterone causes nephrons to reabsorb more Na and water back into blood and to excrete more K in urine
- when blood Na concentration returns to normal, aldosterone release is stopped
acid-base balance
- pH maintained by controlling H levels
- only urinary system can eliminate excess H
a) HCO3 from nephron moves to capillaries -> resupplies the blood with buffers
b) H removed from blood & excreted
loop of henle - water control
- descending limb permeable to H20, so it diffuses into surrounding fluids
- filtrate becomes more concentrated as it moves down DL
- ascending limb impermeable to H20, but pumps out Na and Cl by active transport
- due to that ^, as filtrate moves along AL, it comes less concentrated
- at top of AL, there’s less filtrate, but it’s almost as concentrated as it was at the start of DL
- in tissue surrounding loop of Henle, salt gradient is established, increasing concentration from top to bottom of loop & establishing countercurrent multiplying effect
- fluid at top of collecting duct has salt concentration about equal to beginning of the loop of Henle
- as fluid descends collecting duct, it’s exposed to the surrounding salt gradient established by loop of Henle
- without ADH, collecting duct is impermeable to H20. 2 outcomes are possible:
a) if H20 is needed, ADH simulates opening of aquaporins, allowing H20 to move out of duct and into surrounding tissues
b) if h20 not needed by body, no ADH & duct allows h20 to drain out of body
