renal 5 Flashcards
homeostatic mechanisms for fluid/electrolyte balance focus on maintaining four parameters:
- fluid volume
- osmolarity
- concentrations of individual ions
- pH
the body is in a state of ________________
CONSTANT FLUX
-we ingest 2L of fluid containing 6-25 grams of NaCl
-we take in varying amount of other ions (K, H, Ca, HCO3 and phosphate ions)
whatever comes in must be ______________
EXCRETED IF NOT NEEDED (mass balance)
-kidneys are the primary route
-small amounts lost in feces and sweat
-the lungs lose water and help remove H and HCO3 by excreting CO2
____________also play an essential role
BEHAVIORAL MECHANISMS
-thirst, salt appetite
why are we concerned with homeostasis of these substances?
-H2O and Na determine ECF volume and osmolarity
-K balance can cause problems with cardiac and muscle function
-Ca is involved in many processes in the body
-H and HCO3 determine the body pH
how does ECF osmolarity affects cell volume?
-maintaining osmolarity in the body is important because water can cross most cell membranes freely
maintaining cell volume is important, some cells have independent mechanisms for doing so:
-renal tubule cells are constantly exposed to hypertonic ECF and produce organic solutes such as sugar alcohols and amino acids to match their intracellular osmolarity to the ECF
-some cells use changes in cell volume to initiate cellular responses, liver cells beginning protein and glycogen synthesis (swell)
what systems integrate fluid and electrolyte balance?
-is an integrative process involving the respiratory, cardiovascular and renal systems as well as behavioral responses
-cardio and resp systems are under neural control and are quite rapid. renal responses occur more slowly because kidneys are primarily under endocrine and neuroendocrine control
-overlap between pathways
what is the response to elevated blood pressure and volume graph?
what is our water balance?
-water makes up 50-60% of our body weight
-2/3 is intracellular fluid
-1/3 extracellular
-water intake must match excretion
what is water loss regulated by?
-under normal conditions water loss in urine is a regulated mechanism
-other mechanisms become significant during conditions, like excessive sweating and diarrhea (drop blood pressure, increase osmolarity)
what is the graph of how the kidneys conserve water?
-the kidneys can remove excess fluid or conserve what is in the bod but cannot replace what is lost to the environment
how to the kidneys conserve water?
-volume gain will offset with increase loss
-volume loss results in reduced flow through the “handle”, volume loss in urine is reduced, also reabsorption is regulation and can be increased
-volume loss must be replaced through behavioral mechanisms to maintain homeostasis
the renal medulla creates ____________
CONCENTRATED URINE
-the concentration, or osmolarity, of urine is a measure of how much water is excreted by the kidneys
what is diuresis?
-when removal of excess water required, the kidneys produce large volume of dilute urine (osmolarity as low as 50 mOsM)
-removal of excess urine is known as diuresis
-if the kidneys need to conserve water, low volume of concentrated urine is produced (up to 1200 mOsm)
what is the graph of osmolarity changes through the nephron?
how do the distal tubule and collecting duct alter their permeability to water?
-by adding or removing water pores in the apical membrane under the direction of the posterior pituitary hormone vasopressin (AVP), aka antidiuretic hormone (ADH)
what is AVP induced AQP2 insertion graph?
-insertion of AQP2 is graded, depends on the amount of AVP present
what stimuli control vasopressin secretion?
-blood volume, pressure and osmolarity activate osmoreceptors
-increased osmolarity is the most potent stimulus of AVP secretion
-AVP secretion also shows a circadian rhythm (increases at night)
how is AVP produced and secreted?
magnocellular neurosecretory cells (MNC’s) produce and release AVP
-osmolarity is monitored by osmoreceptor neurons
-stretch sensitive neurons that increase their firing rate as osmolarity increases (shrink)
-signal to the MNC’s, AP’s fire in the MNC’s causing release of AVP containing vesicles
-baro and atrial receptors also signal to MNC’s
what creates the hyperosmotic interstitium and why isn’t it reduced as water is reabsorbed?
- countercurrent exchange systems
-evolved in mammals and birds to reduce heat loss from flippers, tails, wings that are poorly insulated and have a high surface-area-to-volume ratio - urea contributes to hyperosmotic interstitium
what is the renal countercurrent exchange system?
-two components: the loop of henle that is referred to as the countercurrent multiplier and the peritubular capillaries (vasa recta) that are referred to as the countercurrent exchanger
-nephrons and vasa recta of juxtamedullary nephrons extend deep into the medulla and are responsible for the high osmolarity deep in the medulla
what is the countercurrent multiplier?
-the descending limb of the loop of henle allows water to follow its osmotic gradient into the increasingly hypertonic interstitium but does not allow solutes to be transported
-the ascending limb of the loop of henle actively transports solutes (Na, Cl and K) into the interstitium
what is the active transport in the loop of henle?
-although majority of reabsorption takes place in the proximal tubule, about 25% of Na and K reabsorption occurs in the ascending limb of the loop of henle
-NKCC transporter on apical membrane uses energy stored in the Na concentration to move Na, K and 2 CL into the epithelial cells
-Na is actively transported against concentration gradient on basolateral membrane
-NKCC is target of loop diuretic drugs for treatments of hypertension and edema (prevents generation of hyperosmotic medulla)
what is the full graph of countercurrent graph?
why doesn’t the water entering interstitium via the descending limb dilute the hyperosmotic medulla?
-the opposite direction loops of the vasa recta picks some solute up and loses some water as it travels by the ascending limb creating hyperosmotic blood
-this then creates a gradient allowing much of the water transported from the descending limb to move into vasa recta
-vasa recta removes water graph
