Phys 3 Flashcards
Reabsorption in PCT
- location of most active reabsorption
- all glucose and aa
- 60-80% of Na+
- 75-85% of water
- K+
- Urea
PCT
- overall change to filtrate
- secretion
- filtrate volume reduced by 80%
- secretion of nitrogenous wastes
Descending loop of Henle
- permeability
- filtrate changes
- freely permeable to water
- not permeable to NaCl
- filtrate is concentrated by water resorption
why does water exit descending loop of Henle?
exits based on osmotic gradient of cortical and medullary interstitial fluid
Ascending loop of Henle
- permeability
- filtrate changes
- freely permeable to NaCl
- not permeable to water
- dilute filtrate formed
Why does Na+ leave the Ascending loop of Henle, what does it contribute to
actively transported out
- contributes to high osmolarity of the medullary ECF
DCT
- absorption
- secretion
selective absorption and secretion Absorption - HCO3- - Na+ (under Aldosterone control) - Water (ADH control)
secretion:
- NH4 and H+
What happens to filtrate as it moves through DCT
becomes more concentrated as water is absorbed
CD reabsorption & secretion
- urine is concentrated along medulla
- reabsorption/secretion to maintain blood pH (K+, H+, HCO3-, Cl-)
- urea diffuses via transporters to medulla, helps contribute to high osmolarity
Tubular secretion
- functions
- dispose of unwanted substances not in filtrate such as drugs
- eliminate unwanted substances that have been reabsorbed by passive processes
- K+ elimination (via aldosterone)
- Control of blood pH
How does tubular secretion change as blood becomes acidic
- actively secrete H+ into filtrate (acidify urine)
- reabsorb HCO3- and K+
How does tubular secretion change as blood becomes alkaline
- HCO3- is secreted
How is the flow of blood related to the flow through the nephron?
countercurrent
- creates opportunities for osmotic movement with help from highly osmotic gradient of medullary interstitium
- as blood flows past ascending limb absorbs ions, becomes hypertonic
- then when passes descending limb water easily moves into blood dt osmotic pressure of ions
Vasa recta
- function
- maintain osmotic gradient
- deliver nutrient supply
- sluggish blood flow
- freely permeable to water and salt (vs. loop of Henle which is differentially permeable)
Volume of water in
- the body
- ICF
- ECF
Total: 40 L
ICF: 25 L
ECF: 15 L (interstitial fluid and plasma)
Composition of body fluids
- what maintains
- ICF ion
- ECF ion
- Na/K pump
- ICF: K+
- ECF: Na+
*bc osmolality is equal between ECF and ICF, the NET change between the two is zero even though lots of ion, etc. flow between
Tonicity
definition
ability of a solution to change the tone of cells
Isotonic
- example
Physiological saline soln (PSS)
- 0.9% sodium w/v, 308 mOsmol
what happens to cells in solutions that are:
Hypotonic
Hypertonic
hypo: swell, lysis
hyper: shrivel, crenation
What happens when there is a mismatch in osmolality of body fluids between electrolyte intake and loss
change in osmolality of body fluids - physiologic issues that must be fixed
What two things happen when there is an increase osmolality of ECF?
- thirst: drink more water, dilute ECF
- ADH secretion: water retention, dilute ECF
Thirst drive for water balance
- two stimuli
- decreased volume of ECF
- increased osmolality of ECF
What happens when increased osmolality of ECF occurs?
- decreased saliva secretion
- dry mouth
- drink
- increased water = decreased osmolality
what happens when decreased volume of ECF occurs
- stim osmorelceptors in hypothalamic thirst center
- sensation of thirst,
- drink
- increased water = increased volume
ADH
- released from what
- why released?
- released from posterior pituitary
- in response to hypothalamic stimulus
ADH
- 2 receptor types
Osmoreceptors
- in hypothalamus
- depolarize when >285 mOsm/kg
Baroreceptors
- great veins, L/R atria, PV
- respond to low volume
ADH
- what other stimuli cause release
- pain
- nausea
- surgical stress
- Ang II in response to hypovolemia
ADH
- principle effect
- water retention by kidney
- causes filtrate to become concentrated
ADH
- receptor
- V2 receptor
- on CD cells
- stimulates insertion of aquaporin 2 into the apical membranes
where are aquaporins stored
endosomes
- ADH causes rapid translocation to cell membrane
ADH
- effects
- water enters hypertonic interstitum of renal pyramids, is reabsorbed
- osmotic pressure of body fluids decreases
- urine concentrates, volume decreases
In conditions of good hydration and no ADH describe the
- urine
- water loss/gain
- urine is hypotonic to plasma
- urine volume is increased
- net water loss
what is the most important determinant of ECF volume
Na+
Sodium
- regulation linked to what
- regulated by what 3
- regulation linked to blood pressure and blood volume
- regulated by aldosterone, renin, natriuretic peptides (ANP, BNP)
what regulatory molecule has the most influence over sodium in the ECF?
Aldosterone
Aldosterone
- steroid hormone
- produced and released by adrenal cortex
Aldosterone is released in response to (2)
- renin from kidney (via angiotensin II)
2. High serum K+
Function of aldosterone
- increase renal Na+ reabsorption and K+ secretion (water follows Na+)
- receptors on DCT and CT
Renin
- released from what
- in response to what
- released from juxtaglomerular cells in response to: 1. decreased stretch due to low volume/bp 2. decreased filtrate osmolarity 3. direct SNS stimulation
What is the function of Renin/angiotensin system
- cleave angiotensinogen to release angiotensin I
- ACE action produces angiotensin II
Functions (3) of Angiotensin II
- vasoconstriction
- increases peripheral vascular resistance (after load)
- increases bp - aldosterone secretion from renal cortex
- reabsorb Na+, increase blood volume and bp
- secretion of K+ - feedback inhibition of renin
Natriuretic peptides
- two types
- ANP: atrial natriuretic peptide (atrial myocytes)
2. BNP: B-type natriuretic peptide (ventricle)
Natriuretic peptides
- released in response to what
stretch - increased blood volume/bp
Natriuretic peptides
- action
- decrease blood volume/bp
- kidney:
- increase GFR dt vasodilation
- inhibit Na+ reabsorption by tubules
- decrease renin - inhibit aldosterone
- vascular smooth muscle relaxation (vasodilation)
Potassium
- essential for what
- other very important function
- essential for membrane potential, esp in heart
- important in pH buffering systems (H+ movement is balanced by K+ countermovement)
What controls K+ balance
renal mechanisms under influence of aldosterone (directly sensitive to increased K+)
How does body remove excess K+?
Aldosterone causes increased Na+ reabsorption by tubules
- concomitant secretion of K+ due to Na/K pump
