BI 411 - Fine Tuning of Vertebrates

what type of urine can all basic vertebrates produce?

all vertebrates can produce isotonic or hypotonic urine (more dilute than blood)

what type of urine can birds and mammals produce?

birds and mammals can produce hypertonic urine through loop of henle

how does sodium reabsorption work in tubules?

• Active process using NaK pump

• Occurs everywhere in the basic nephron

• Key uptake of other solutes

how does water reabsorption work in tubules?

• Passive osmosis (so only as concentrated as the surrounding tissues)

• Depends on salt concentrations

what happens in the proximal tubule?

• Uptake of salt and water

• NaK ump in basolateral membrane moves Na+ into interstitial fluid to capillaries 

• Secondary transport coupled with Na+

  • Cotransport moves glucose and amino acids

  • Countertransport is used to get rid of certain substances

what happens when membranes are permeable to water?

water follows NaCl by osmosis

what can basic vertebrates do to adjust their urine?

• Can adjust permeability

• High permeability: take water into capillaries to conserve (isosomotic)

• Low permeability: excrete water (dilute)

• In nephron, sodium moves into blood vessels and water follows

  • Water cannot go from blood vessel into nephron

what does the proximal tubule do in basic vertebrates?

• NaCl (active transport) and H20 absorbed equally

• Glucose taken up with secondary active transport

• Urea moves by simple diffusion

• Filtrate isosmotic with plasma

what does the distal tubule do in basic vertebrates?

• Fine tune and then filtrate

• Active secretion to get rid of wastes (always coupled with NaK pump)

• Absorption of key solutes

what does the final urine in the collecting duct look like for basic vertebrates?

• Low NaCl, no glucose

• Modify permeability to adjust water loss

  • High: water taken back into body (isosmotic)

  • Low: lots of dilute urine

how do kidneys work in birds and mammals?

• Ultrafiltration: creates lots of pre-urine

• Proximal tubule: reabsorption of most water and salt – no change in osmolarity

• Loop of henle: create osmotic gradient in surrounding fluids

• Distal tubule: fine tune the filtrate by active secretion and absorption

• Collecting duct: modify water content

what does the osmotic gradient in the renal medulla look like?

• Tissue becomes more concentrated as you go in

• Concentration gradient made by loop of henle

how does countercurrent multiplication in the loop of henle work?

• Descending loop of henle

  • No NaCl uptake

  • Permeable to water → no active transport

• Ascending loop of henle

  • NaCl uptake

  • Impermeable to water 

what is the loop of henle responsible for?

• This system established the osmotic gradient required for the formation of hyperosmotic urine 

• Loop of henle concentrates tissues of kidney, not urine

what does the permeability of the collecting duct determine?

Permeability of collecting duct is determined by how dilute or concentrated urine is

why doesn’t water movement dilute interstitial fluid?

• Much higher volume of blood leaving the bloop due to taking up H20 and NaCl by diffusion 

• Net outcome → descending = lose water, ascending = lose salt

what is another name for anti-diuretic hormone?

vasopressin

what does ADH do?

• Water excess = no ADH present, moves water out

• Water deficit = ADH present, aquaporins inserted and keep water in

• High ADH, high permeability = concentrated urine

• Low ADH, low permeability = dilute urine

how is ADH regulated?

• Osmoreceptors in hypothalamus signals ADH release from pituitary gland if ECF is too concentrated 

• Baroreceptors in cardiovascular system 

  • Low BP = more ADH to save water

  • High BP = less ADH, lots of dilute urine

what is the effect of alcohol and caffeine?

Inhibit ADH production to get dilute urine

what animals have longer loops of henle?

desert animals

how is sodium excreted calculated?

Na excreted = Na filtered - Na reabsorbed

what is never secreted?

sodium

how is salt monitored?

• NaCl is linked to blood pressure → walt follow salt

• Low NaCL = low BP = decrease excretion

• Low BP will also decrease H20 excretion

• Long term control of BP depends on Na regulating mechanisms

what is the renin-angiotension-aldosterone system in response to?

In response to low BP or low Na+

what does the renin-angiotension-aldosterone system do?

• Alter NaCl absorption

  • Aldosterone (adrenal gland) stimulates Na reabsorption

  • More transport proteins in distal convoluted tubule and collecting ducts 

  • Impacts K+ secretion (NaK pump)

  • Also in intestine, sweat glands, and salivary glands

• Decrease NaCl filtered (angiotension system)

  • Decrease GFR by vasoconstriction of renal aterioles (also increase BP0

  • Stimulate ADH release

  • Stimulate thirst and salt cravings

what does potassium do?

• Linked to salt absorption by NaK ATPase

• Secretion in collecting duct

• Increase aldosterone, Na+ absorption, and K+ secretion

what is thirst craving stimulated by?

Stimulated by increase in osmolarity or decrease in volume

what is salt craving stimulated by?

• Stimulated by increase ADH

• Most mammals eat it whenever they can

what animals excrete ammonia?

Ammonia excreted by aquatic invertebrates, bony fish, and tadpoles (not a lot of energy)

what animals excrete urea?

Urea excreted by sharks, rays, amphibians, and mammals

what animals excrete uric acid?

• Uric acid excreted by insects, reptiles, and all birds (most energy)

how does urea move through the kidneys?

• 50% taken up by diffusion in proximal tubules

• Then reabsorbed by facilitation diffusion into loop

• More reabsrobed from collecting duct 

• Only about 15% actually excreted → rest helps build up gradient in loop of henle

what are kidney stones?

xcess solutes crystallize in kidney

what causes kidney stones?

• Excess calcium and vitamin D

• Struvite (due to infection in women)

• Uric acid (high protein diet = gout)

• Cysteine (genetic)

what is diabetes insipidus?

failure to release of respond to ADH; constant water loss

what is diabetes mellitus (sugar diabetes)?

failure of cells to reabsorb glucose; extra sugar and solutes in urine, which disrupt osmotic gradient

what is micturation?

control release of urine

how do the internal and external sphincters work?

• Internal sphnicter 

  • Smooth, radial fibers

  • Relax = closed

• External sphnicter 

  • Skeletal, circular fibers

  • Contract = closed (voluntary control)

what do stretch receptors do?

• Stretch receptors respond to volume in bladder

  • If reach 300-400 ml, sends message to contract (open) internal sphincter and inhibit (open) external