Lecture 26 Flashcards
Antidiuretic Hormone:
- Increases water permeability = regulates facultative water reabsorption
- Stimulates the insertion of aquaporin-2 channels into the membrane
When osmolarity of plasma & interstitial fluid decreases,
more ADH is secreted and facultative water reabsorption increases.
Dilute =
having fewer solutes than plasma
Water reabsorbed in thin limb, but ions reabsorbed in thick limb of loop of Henle create
a filtrate more dilute than plasma
- can be 4x as dilute as plasma
- as low as 65 mOsm/liter
Principal cells do not
reabsorb water if ADH is low
Compensation is for
low water intake or heavy perspiration
Urine can be
up to 4 times greater osmolarity than plasma
It is possible for principal cells & ADH to
remove water from urine to that extent
- Long loop juxtamedullary nephrons make that possible
- Na+/K+/Cl- symporters reabsorb Na+ and Cl- from tubular fluid to create osmotic gradient in the renal medulla
Urea recycling causes
a buildup of urea in the renal medulla
Diuretics:
Substances that slow renal reabsorption of water & cause diuresis
Examples of diuretics:
- caffeine which inhibits Na+ reabsorption
- alcohol which inhibits secretion of ADH
- prescription medicines can act on the PCT, loop of Henle or DCT
Dialysis Therapy:
- Kidney function is so impaired the blood must be cleansed artificially
- -separation of large solutes from smaller ones by a selectively permeable membrane
Artificial kidney machine performs
hemodialysis
Hemodialysis:
- directly filters blood because blood flows through tubing surrounded by dialysis solution
- cleansed blood flows back into the body
Micturition Reflex:
-urination
Stretch receptors that signal spinal cord and brain
-when volume exceeds 200-400mL
Impulses sent to
micturition center in sacral spinal cord & reflex is triggered
parasympathetic fibers cause
detrusor muscle to contract, external & internal sphincter muscles to relax
Filling causes a
sensation of fullness that initiates a desire to urinate before the reflex actually occurs
Filling also causes
- conscious control of external sphincter
- cerebral cortex can initiate micturition or delay its occurrence for a limited period of time
Urinary Incontinence:
Lack of voluntary control over micturition
Incontinence is normal in 2 or 3 year olds because
neurons to sphincter muscle is not developed
Stress incontinence in adults caused by
increases in abdominal pressure that result in leaking of urine from the bladder
Ex. coughing, sneezing, laughing, exercising, walking
Stress incontinence in adults =
injury to the nerves, loss of bladder flexibility, or damage to the sphincter
Body fluid:
all the water and dissolved solutes in the body’s fluid compartments
Mechanisms regulate
total volume
distribution
concentration of solutes and pH
Regulation of Water Gain:Formation of metabolic water is
not regulated
-function of the need for ATP
Main regulator of water gain is
intake regulation
Stimulators of thirst center in hypothalamus:
dry mouth, osmoreceptors in hypothalamus, decreased blood volume causes drop in BP & angiotensin II
When Drinking occurs
body water levels return to normal
Elimination of excess water or solutes occurs through
urination
Consumption of very salty meal demonstrates
function of three hormones
Demonstrates how:
- “water follows salt”
- excrete Na+ and water will follow and decrease blood volume
Intracellular and interstitial fluids normally have the same
osmolarity,so cells neither swell nor shrink
Swollen cells of water intoxication because
Na+ concentration of plasma falls below normal
Swollen cells happen because =
- drink plain water faster than kidneys canexcrete it
- replace water lost from diarrhea or vomitingwith plain water
- may cause convulsions, coma & death unless oral rehydration includes small amount salt in water intake
Functions of electrolytes
- control osmosis between fluid compartments
- help maintain acid-base balance
- carry electric current
- cofactors needed for enzymatic activity
Concentration expressed in
mEq/liter or milliequivalents per liter for plasma, interstitial fluid and intracellular fluid
Plasma contains proteins, but interstitial fluid
does not
-producing blood colloid osmotic pressure
Extracellular fluid contains
Na+ and Cl-
Intracellular fluid contains
K+ and phosphates
