Excretory System Flashcards
Kidney portal system
2 capillary beds in series: vasa recta capillary bed for providing oxygen to kidneys, peritubular capillary bed for nutrients
Bladder
has muscular lining (detrusor muscle); urine must pass through internal and external urethral sphincters
Internal urethral sphincter
smooth muscle, involuntary control
External urethral sphincter
skeletal muscles, voluntary control
Micturition reflex
when bladder is full:
1) nervous system alerted-parasympathetic neurons fire-detrusor muscle contracts-internal sphincter relaxes
2) invididual must choose to relax external sphincter to urinate or maintain discomfort
Filtration
- blood from glomerulus filtered as fluid into Bowman’s space
- fluid collected=filtrate
- movement of fluid due to Starling forces
- hydrostatic pressure much higher in glomerulus so net flow of fluid into nephron
Kidney stones
obstruct ureter causing buildup of urine; high hydrostatic pressure in Bowman’s space so filtration can’t occur
Secretion
Kidneys can secrete salts, acids, bases, and urea as needed in body, to be eliminated in urine, mechanism for excreting waste
Reabsorption
Some compounds such as glucose, amino acids, and vitamins that are filtered are usually taken back up for use in the body; water is also reabsorbs depending on the blood pressure
Interstitium
connective tissue surrounding nephrons where reabsorbed water and ions enter before being returned to circulation
Descending limb of Henle
Water leaves due to increasing interstitial concentation after the release of substances in the proximal convoluted tubule
Ascending limb of Henle
only permeable to salts; increasing amounts of salts removed as move up; filtrate becomes hypotonic
Aldosterone mechanism
1) Low blood pressure stimulates release of renin from kidneys
2) renin cleaves angiotensinogen to form Ang I
3) Ang I metabolized by ACE in lungs to form Ang II- promotes release of aldosterone
4) Aldosterone causes reabsorption of Na+ which causes water to also be reabsorbed
ACE inhibitors
Used to lower blood pressure by prohibiting conversion of Ang I into Ang II
ADH/vasopressin
Released when high blood osmolarity to retain water in the body; alters permeability of collecting duct to allow more water to reabsorb; inhibited by caffeine and alcohol
Acid-Base balance
kidneys can excrete bicarbonate and increase reabsorption of H+ if pH too high
If pH too low, excretes more H+ and increases reabsorption of bicarbonate
Glomerulus
main site of filtration; blood enters through afferent arteriole, leaves through efferent arteriole; filtrate that is filtered out falls into Bowman’s capsule; acts like a sieve-small molecules dissolved in blood can go through pores, but large proteins and blood cells can’t
Proximal convoluted tubule
filtrate from glomerulus enters; amino acids, glucose, and vitamins are reabsorbed with water here, as well as most of sodium; waste products such as hydrogen ions, potassium ions, ammonia and urea are secreted into the tubule
distal convoluted tubule
responds to aldosterone, which promotes sodium reabsorption, causing water to follow; causes a lower volume of concentrated urine
osmotic pressure
sucking pressure that draws water into the vasculature caused by concentration of dissolved solutes
oncotic pressure
osmotic pressure that is due specifically to dissolved proteins
osmolarity
concentration of a solution, in solute particles per volume
when blood osmolarity is low
excess water is excreted and solutes reabsorbed in higher concentrations
when blood osmolarity is high
increased water reabsorption and solute excretion increases
