Excretory System Flashcards
What are the functions of the excretory system?
- maintain proper internal levels inorganic solutes
- maintain proper plasma and water volume
- removal of waste
- maintain osmotic balance
What are the functions of the excretory system?
- maintain proper internal levels inorganic solutes
- maintain proper plasma and water volume
- removal of waste
- maintain osmotic balance
What are nitrogenous wastes the result of?
metabolism of proteins and nucleic acids
What does the choice of primary nitrogenous waste correlate with?
water availability
Name and describe the nitrogenous waste from most toxic to least.
- Ammonia: MOST toxic; expelled by most aquatic animals that breathe water (ammonotely); can’t be broken down so it gets diluted to a non-toxic concentration.
- Urea: expelled by most terrestrial animals (humans included) [ureotely], more expensive metabolically but is less toxic than ammonia.
- Uric Acid: expelled by insects, reptiles, & birds (uricotely); most expensive metabolically, highly insoluble, highly non-toxic; makes water conservation for animals (semi-solid form).
Explain the process of transport epithelia.
There is a Na+/K+ ATPase pump on the basolateral (top) side of the membrane, making the Na+ concentration inside the cell lower (because pumps Na+ out of cell and K+ into). Na+ then enters the apical (bottom) side by diffusing through ENaC (epithethial Na channel). Cl- wants to counteract the outside charge (attracted to Na+), so it goes through CIC or CFTR channels and changes the gradient produced by the Na+ efflux. This increases the extracellular solute concentration, which attracts water (osmosis, low solute concentration to high to dilute) across basolateral membrane. This occurs on the PCT.
What is filtration?
water and small solutes can pass through a barrier, while cells and larger molecules remain behind (comes from the blood and goes into another area)
What is secretion?
transport epithelia move specific solutes into tubule for lumen secretion
What is reabsorption?
transport epithelia move specific solutes and water back into the body from the lumen
What is osmoconcentration?
water is removed from lumen, laving solutes behind, producing more concentrated excretory fluid (hyper osmotic)–> goal to concentrate urine and reabsorb water to avoid dehydration
What are the parts of the excretory system?
- kidneys: urine forming organ, have 2 one on each side of vertebral column (houses renal pelvis where kidney stones develop)
- ureters: tube like things that urine drains into from the kidneys (have 2)
- urinary bladder (or hindgut in reptiles and birds) ureters empty urine here
- urethra: bladder empties urine into and urine goes out through
What are the regions of the kidney?
- renal cortex (outer portion)
- renal medulla (inner- divided into renal pyramids in larger mammals)
- renal pelvis (drainage area in the center of the kidneys, collects urine and releases it–where kidney stones occur)
What is a nephron and how many are in the human body?
smallest functional unit of the kidney we have ~1 million
afferent arteriole
supplies each nephron by bringing dirty blood in, made of smooth muscle
glomerulus
ball-like knot of capillaries in renal cortex, site of filtration of blood, its twisted to increase SA
efferent arteriole
exits the glomerulus and carries semi-clean blood
pertitubular capillaries
surrounds tubules, puppies renal tissue with blood and exchanges materials with tubular fluid
Bowman’s (glomerular) capsule
site of glomerular filtration
proximal (convoluted) tubule
PCT, involved in tubular reabsorption and secretion
loop of Henle
part of osmoconcentration, descending limb (plunges into medulla), ascending limb (returns to the cortex)
distal (convoluted) tubule
DCT, involved in reabsorption/secretion and osmoconcentration
collecting duct
involved in osmoconcentration, empties into renal pelvis
juxtaglomerular apparatus
JGA, sensor in osmoregulation and blood pressure regulation, on DCT near glomerulus, wants to dictate what the afferent arteriole does
Describe elasmobranch urinary systems.
- isosmotic or hyper osmotic relative to seawater
- fish itself is hyper osmotic, lots of solute–water wants to go into, blocks Na+
- retain urea and trimethylamine oxide (TMAO)–breaks down, gives off fishy smell, uses compound to bring water in
- hindgut excretes hypertonic fluid high in salt
Describe marine bony fish urinary systems.
- hyposmotic (not much solute, drink salt water)
- drink salt water to reverse water loss through gills
- gills actively transport salt outward and excrete nitrogenous wastes
- kidneys remove divalent ions
Describe fw bony fish urinary systems.
- hyperosmotic (will drink water in and it dilutes urine)
- takes water in through gills and mouth
- excretes a large volume of highly diluted urine
- gills take in salt and excrete ammonia and ammonium
Describe urinary systems of amphibians.
- kidneys maintain constant ECF
- metanephric nephrons: (excrete water and reabsorbs ions, it can also exert urea–checks and balances system)
- urinary bladder: serves as a temporary water reservoir in case of dehydration
- arginine vasotocin (AVT): triggers water uptake through aquaporins in bladder wall (similar to our vasopressin/ADH)
Describe urinary systems of reptiles.
- nephrons resemble aquatic vertebrates
- ureters carry urine in liquid/semi-solid form into cloaca (all waste out at same time, excretory & digestive)
- NO loop of Henle
- primary nitrogenous waste: uric acid (no need to dilute it)
What can the cloaca and lower intestine do in reptiles?
reabsorb water
What do the nasal salt glands in reptiles do?
secrete highly salty fluid
Describe avian (bird) urinary systems.
- resemble reptiles
- some mammalian-type nephrons WITH loop of henle
- uric acid crystals are covered with proteins to form rate balls (can easily pass)
What do marine birds have that are different from non-marine ones?
nasal salt glands near the eyes
- contain blind end tubules lined with active salt secreting cells
- excrete excess salt out of nasal passages
Explain the difference between cortical and juxtaglomerular nephrons.
- cortical: glomeruli in outer cortex, short loops of henle that dip only into outer medulla (humans mainly have)
- juxtaglomerular: glomeruli in inner cortex near medulla, long loops of helm plunge into inner medulla (more time to reabsorb good stuff, birds and desert animals-need to reabsorb more water); peritubular capillaries form hairpin vascular loops (vasa recta)
What are the 3 layers of the molecular sieve for filtration?
1) glomerular capillary wall: consists of a singly layer of flattened endothelial cells, perforated with pores (too small for proteins to pass)
2) basement membrane: gelatinous layer composed of collagen and glycoproteins (further limit protein movement)
3) inner layer of Bowman’s capsule: consists of podocytes with filtration slits
filtration is a…… process
exclusively extracellular and its VERY selective
What are the driving forces of glomerular filtration?
- glomerular capillary blood pressure
- plasma colloid osmotic pressure
- Bowman’s capsule hydrostatic pressure
- net filtration
glomerular capillary blood pressure
is higher than capillary blood pressure elsewhere (ex 50mmHg), major determinant of filtration
- afferent arteriole is larger in diameter than efferent to bring more blood into glomerulus
- FAVORS filtration
plasma colloid osmotic pressure
protein remains in blood, it increases osmotic pressure (ex: 30mmHg) ; wants things to move-impedes filtration to go back in
-OPPPOSES filtration
Bowman’s capsule hydrostatic pressure
pressure exerted by tubular gland (ex: 15 mmHg)
-OPPOSES filtration
net filtration
net= glomerular cap. pressure–(colloid + Bowmans)
= 55mmHg – (30mmHg + 15mmHg)
= + 10 mmHg (FAVORS filtration)
What is the glomerular filtration rate?
GFR, amount of pressure in glomerulus dictates GFR
-depends on net filtration, SA, permeability of glomerular membrane, and hydrostatic pressure
GFR= filtration coefficient x net filtration pressure
What happens when a person has long term high blood pressure and it goes undiagnosed?
higher pressure, enlarges pores and allows proteins and RBC to get into the urine, can cause kidney failure
If resistance in the afferent arteriole is increased, what will happen to blood flow and GFR?
blood flow will decrease to glomerulus, thus decreasing GFR
What is autoregulation and what are two types of it?
intrinsic control, doesn’t care what’s happening to the rest of the body, just wants to maintain its workload, no more, no less–> prevents unintentional shifts in GFR
-myogenic mechanisms and tubuglomerular feedbacks
myogenic mechanism
smooth muscle contracts when afferent is stretched–> increase in blood pressure, increase blood through glomerulus, causes afferent to stretch and constricts on blood, decreases GFR back to normal by lowering the pressure
tubuglomerular feedback
juxtaglomerular apparatus (DCT) there are granular cells with macula densa that sense when Na+/water content changes
- too high, PCT didn’t absorb efficiently, macula densa will release adenosine/ATP to constrict afferent arteriole, decreasing GFR
- too low, macula densa will release nitric oxide (NO) to dilate afferent arteriole, increasing GFR
What does an increase in sympathetic activity do to GFR?
contributes to long-term maintenance of blood pressure by restoring plasma volume
- constricts afferent arteriole, lowering GFR, decreasing urine output
- extrinsic control, doesn’t care about what happens at kidneys, only cares about the rest of the body
What happens if sympathetic activity is maintained for too long?
increases BP, increases toxins, won’t produce as much urine and urine that is produced will be super concentrated, can cause kidney stones and kidney failrue
What happens when arterial blood pressure increases?
increases blood flow in afferent, increases glomerular pressure and net filtration, thus increasing GFR
What happens when the afferent arteriole is constricted?
blood flow decreases, the glomerular pressure and net filtration decreases, thus decreasing GFR
What happens when the afferent arteriole is dilated?
blood flow increases, glomerular pressure and net filtration increases, thus increasing GFR
What happens when the efferent arteriole is constricted?
increases GFR, and decreases blood exit
What happens when the afferent and efferent arterioles are constricted?
GFR stays the same, goes back to norm
What happens in the short term when arterial blood pressure decreases? In the long term?
short term, heart wants to fix it
long term, kidneys take a while to correct it (~7 days)
mammalian tubular reabsorption…..
is HIGHLY selective
mammals reabsorb …. of filtered salt and water and …… of filtered glucose and amino acids
99% of filtered salt and water
100% of filtered glucose and amino acids
Where does the reabsorption of most substances occur?
at the proximal convoluted tubule (PCT)– 2/3!
80% of kidney’s total energy requirement is used for…?
Na+ transport
Is Na+ reabsorption passive or active?
active (ATP) in most sections of tubule, but passive (rest) in some
What percentages of Na+ reabsorption do the PCT, loop of henle, and DCT contain?
- PCT, 67% of filtered Na+
- loop of henle (ascending) 25%
- DCT, 8%
The active step of Na+ reabsorption involves……?
Na+/ATPase pump in basolateral membrane
The passive part of Na+ reabsorption involves….?
transport of Na+ across apical membrane
What occurs in the descending loop of henle?
- fluid entering loop is isotonic
- water reabsorption=permeable to water, drawn out into interstitial space and quickly goes into vasa recta as to not dilute interstitial
- becomes more solute concentrated as go down because not permeable to Na+
- hypotonic to environment
What occurs in the ascending loop of henle?
- salt (NaCl) actively pumped into interstitial space
- walls not permeable to water, osmosis doesn’t occur
- highly solute concentrated interstitial space at bottom
- hypertonic to environment
What is the countercurrent multiplier system?
- water is not actively pumped out of tubes, will not cross if it is isotonic to ECF
- structure of loop allows for concentration gradient to be set up for osmosis of water
- ascending limb, sets up gradient
What is countercurrent multiplication?
positive feedback created between 2 portions of loop of henle
-more sodium ascending limb removes, the saltier the fluid entering will be (more Na+ out, more water it can retain)
What is the vasa recta?
- specialized blood vessels around the loop of henle with ascending/descending portions
- increased salt concentration at beginning of ascending region, pulls in water, removed from interstitial space
- keeps Na+ concentration in interstitial high=hypertonic
Explain the collecting duct and ADH>
- last step in urine formation
- influenced by hypertonicity of interstitial space, water will leave via osmosis if able
- permeability to water depends on number of aquaporin channels in cells of collecting duct (determined by ADH)
What happens in dehydration?
ADH secretion is high and water is reabsorbed from the collecting duct
What happens in over hydration?
ADH secretion is low and water is not reabsorbed
What happens to ADH when one drinks alcohol?
alcohol is a diuretic and it blocks the production of ADH, meaning no aquaporins are present, no water is reabsorbed (dehydration) because water goes into the urine
How does the reabsorption of water occur?
passively reabsorbed by osmosis
- ascending limb of loop impermeable to water
- reabsorption from DCT and collecting duct is subject to hormonal control
- water passes through aquaporin channels (AQPs)
What are the types of aquaporin channels?
- AQP1- channels in PCT are ALWAYS open
- AQP2- changes in DCT and collecting duct are regulated by vasopressin (ADH)
How much of glucose and amino acids are reabsorbed?
100%
-VITALLY IMPORTANT and reflects nutritional value
Describe the secondary active transport of glucose/amino acids?
- symporter in apical membrane simultaneously transports Na+ down its concentration gradient and a specific organic molecule (glucose) up its gradient from the lumen into tubular cell (glucose follows Na+)
- basolateral Na+/K+ pump indirectly drives cotransport system
Once inside the cell, the organic molecule is transported into ECF by….?
facilitated diffusion
All actively reabsorbed substances exhibit a ……… ?
tubular maximum (Tm)
Plasma membrane carriers exhibit….?
saturation
How does glucose reabsorption occur in diabetes mellitus?
plasma glucose is increased (hyperglycemia), glucose is filtered into Bowman’s capsule at same concentration as plasma–> when filtered, glucose load exceeds tubular maximum for glucose reabsorption and the excess spills over into the urine
What is a diagnosis of diabetes mellitus?
glucose in the urine (both types)
What is the only waste product to be reabsorbed?
urea, passively as the filtrate is progressively concentrated by reabsorption of water from proximal tube
-40% of filtered is reabsorbed, adds in water reabsorption at loop of henle and collecting duct
How does urea recycling contribute to medullary hypertonicity?
- top and middle portions of the collecting duct are impermeable to urea
- urea concentration in collecting duct increases as water is reabsorbed
- lowest section of collecting duct is PERMEABLE to urea, so urea diffuses out, increasing the solute concentration of medulla
- some urea is recycled into loop of henle
Regulation of plasma …… is important for blood pressure regulation.
Na+
What does RAAS stand for?
Renin-angiotensin-aldosterone-system
What signals the secretion of Renin?
- granular cells of JGA, secrete renin into blood in response to a fall in Na+, ECF volume, or blood pressure
- granular cells secrete renin in response to fall in pressure in afferent
- macula densa cells respond to fall in DCT salt and stimulates renin secretion
- baroreceptor reflex triggers increase sympathetic activity, stimulates renin secretion
How does renin convert angiotensinogen?
renin catalyzes conversion of angiotensin, cleaves it and converts it to Ang I (active but not the best), angiotensin converting enzyme then reacts with Ang I and converts it to Ang II (major bioactive player in the body)
What is responsible for the primary secretion of aldosterone in the adrenal cortex?
Ang II
What are the effects of aldosterone?
- increase in Na+ reabsorption by DCT and collecting duct
- stimulates secretion of vasopressin (ADH) and promotes water retention by kidneys
- potent constrictor of systemic arterioles, directly increasing BP
What effects does Ang II have on the body?
- goes to brain and triggers thirst and salt hunger
- increases sympathetic activity, increasing HR
- Na+ reabsorbs, K+ excreted, water retention
- aldosterone secretion
- vasoconstriction of arterioles, increases BP
- ADH secretion increases (renal collecting duct reabsorption)
What is initiated when blood pressure drops?
hormone cascade, brings bp up because targets multiple systems (RAAS)
Natriuretic peptides do what to RAAS?
oppose it
atrial natriuretic peptide (ANP)
secreted by atrial cardiac muscle cells
-inhibts Na+ reabsorption in DCT and collecting duct (decreases)
-inhibits secretion of renin, aldosterone, vasopressin (ADH) (decreases)
-decreases cardiac output and inhibits sympathetic activity
OPPOSITE OF ALDOSTERONE
What do diuretics do?
- used clinically to control BP and relieve edema
- increase urine volume, decrease blood volume, and interstitial fluid volume
What are loop diuretics?
most powerful, inhibits Na+ transport out of the loop of henle
- used for extreme hypertension
- example: Lasix
- can inhibit up to 25% of water reabsorption, blocks countercurrent multiplier system
What are thiazide diuretics?
inhibits Na+ transport in DCT
- used for slight hypertension
- can inhibit up to 8% of water reabsorption
Pharmaceutically speaking, why are diuretics not prescribed more than ACE inhibitors or Ang II drugs?
- actually safer than the two because it doesn’t affect multiple systems
- make one urinate more because increases urine volume, not prescribed as much because of patient in compliance, people don’t want to pee all the time
What is the bladder wall made up of?
smooth muscle lined with transitional epithelium
What makes the bladder wall impermeable?
umbrella cells joined with tight junctions
Can the bladder accommodate large fluctuations in volume?
YES
What is the bladder opening guarded by and what are they made of?
- internal urethral sphincter (smooth muscle- we don’t control it, ANS and parasympathetic do)
- external urethral sphincter (skeletal muscle-we control dilation/contraction of this)
Describe micturition.
Urination
- stretch receptors in bladder wall stimulated by distended bladder
- stimulates parasym. neurons that originate in lower spinal cord
- bladder wall contracts due to parasym. stimulation, mechanically pulling internal urethral sphincter open
- external urethral sphincter opens and urine is expelled through urethra
-condensed version: bladder contracts due to parasym. activity by stretch receptors in bladder wall, pressure increases, pushed out external sphincter (we control)
