PHYS 1302 Lecture Notes - Lecture 10: Afferent Arterioles, Proximal Tubule, Active Transport
Ch. 20: Integrative Physiology II: Fluid and Electrolyte Balance (pg.
618-651)
(Remember to check end of textbook chapter for sample chapter Qs)
Fluid and Electrolyte Homeostasis
● Human body is in state of constant flux
● Body must maintain mass balance
○ What comes in must go out (if body does not need it)
ECF Osmolarity Affects Cell Volume
● If ECF osmolarity decreases as a result of excess water intake, water moves into
cells and they swell
● If ECF osmolarity increases as result of salt intake, water moves out of cells and
they shrink
Multiple Systems Integrate Fluid and Electrolyte Balance
● Fluid and electrolyte balance involves respiratory, cardiovascular, renal, and
behavioral responses
Water Balance
● Water is the most abundant molecule in the body
● Standard 70-kg man has about 40L
● Daily Water Intake and Excretion Are Balanced
○ Input must equal output
○ Metabolism, food, and drink can increase water while we lose water via
sweating, breathing, urinating, and pooping
■ Most water is lost via urination
■ A small amount is lost while pooping
●Diarrhea is a serious problem for infants → disrupts
water balance
● The Kidneys Conserve Water
○ Kidneys can remove excess fluid by excreting it into urine
■ Kidneys CANNOT replace lost volume
● The Renal Medulla Creates Concentrated Urine
○ The kidneys control urine concentration by varying the amounts of water
and Na+ reabsorbed in the distal portion of nephron (Distal Tubule and
Collecting Duct)
○ Water reabsorption in kidneys conserves water and can decrease body
osmolarity when coupled with solute excretion via urine
Distributing prohibited | Downloaded by Cfisd Center ([email protected])
lOMoARcPSD|2520155
Vasopressin Controls Water Reabsorption
● Distal Tubule and Collecting Duct alter their permeability of water via
adding/removing water pores in the apical membrane under direction of
Vasopressin (AVP, ADH)
■ Also referred to arginine vasopressin (AVP) or antidiuretic hormone
(ADH)
● Vasopressin acts on target cells to allow them to become permeable to water
○ Allows water to move out of lumen via osmosis
Vasopressin and Aquaporin
● Water pores are aquaporins
○Aquaporin-2 (AQP2) is the water channel controlled by Vasopressin
● When vasopressin levels and collecting duct water permeability are low, the
collecting duct cell has few water pores and AQP2 is stored in cytoplasmic
storage vesicles
● When vasopressin arrives at collecting duct, binds to V2 receptors on basolateral
side of cell which causes G-protein/cAMP second messenger system to cause
AQP2 to move to membrane and fuse with it
○ Cell becomes permeable to water
■ Process is known as membrane recycling
Blood Volume and Osmolarity Activate Osmoreceptors
● Plasma osmolarity, blood volume, and blood pressure control vasopressin
secretion
● Osmolarity is monitored by osmoreceptors in hypothalamus
○ When plasma osmolarity is low (>280mOsM), osmoreceptors do not fire
and vasopressin release from posterior pituitary ceases
○ When plasma osmolarity is high (>280mOsM), osmoreceptors shrink and
fire to stimulate vasopressin release
● Decreases in BP and blood volume are less powerful stimuli for vasopressin
release
○ Atrial stretch receptors detect decreased volume
○ Carotid and aortic baroreceptors detect decreased blood pressure
○ When BP/blood volume is low, these receptors signal to hypothalamus to
secrete Vasopressin in order to conserve fluid
The Loop of Henle Is A Countercurrent Multiplier
● Vasopressin is the signal for water reabsorption out of nephron
● Countercurrent Exchange Systems
○ Require arterial and venous blood vessels that pass very close to each
other, w/ their fluid flow moving in opposite directions
● The Renal Countercurrent Multiplier
Distributing prohibited | Downloaded by Cfisd Center ([email protected])
lOMoARcPSD|2520155
Document Summary
20: integrative physiology ii: fluid and electrolyte balance (pg. 618-651) (remember to check end of textbook chapter for sample chapter qs) Human body is in state of constant flux. What comes in must go out (if body does not need it) If ecf osmolarity decreases as a result of excess water intake, water moves into cells and they swell. If ecf osmolarity increases as result of salt intake, water moves out of cells and they shrink. Fluid and electrolyte balance involves respiratory, cardiovascular, renal, and behavioral responses. Water is the most abundant molecule in the body. Daily water intake and excretion are balanced. Metabolism, food, and drink can increase water while we lose water via sweating, breathing, urinating, and pooping. A small amount is lost while pooping. Diarrhea is a serious problem for infants disrupts. Kidneys can remove excess fluid by excreting it into urine. The kideeys caeeot replace lost water; all they cae do is coeserve water.
