Body Fluids and Renal Function Flashcards
osmolarity
the number of solute particles per 1L of water
osmolality
the number of solute particles in 1 Kg of water
osmotic pressure
results with concentration difference and specific permeability
oncotic pressure
osmotic pressure generated by large molecules in solution
van’t Hoff’s Law
osmotic pressure may be predicted on the basis of the concentration of the osmotically active substances
π = RT(ions*concentration)
What is the fluid distribution in an average 70 Kg person?
42 L total body water
14 L ECF and 28 L ICF
10.5 L interstitial fluid and 3.5 L plasma
What is the normal osmolarity in the body?
285 mOsm/L
composition of body fluid compartments
sodium is the major cation of the ECF
chloride and bicarbonate are the major anions
plasma has high concentration of proteins
What assumptions are made in fluid shift calculations?
intracellular osmolarity = extracellular osmolarity
water moves freely across membranes
solutes (NaCl, NaHCO3, Mannitol) do not move across membranes
isosmotic volume contraction
loss of ECFV and solute
ECFV decreases
no decrease in ECF osmolarity
ICFV remains unchanged
hyperosmotic volume contraction
loss of hyposmotic ECFV = sweat
ECFV decreases
increase in ECF osmolarit
ICFV decreases
hyposmotic volume contraction
decreased aldosteron, loss of NaCl and water
ECFV decreases
ECF osmolarity decreases
ICFV increases
isosmotic volume expansion
increasing NaCl and water in the ECF
ECFV osmolarity unchanged
ECFV increased
ICFV unchanged
hyperosmotic volume expansion
increasing NaCl in the ECF
ECF osmolarity increases
ECFV increases
ICFV decreases
hyposmotic volume expansion
inappropriately high levels of ADH
excess water is reabsorbed by the kidney
ECFV increases
ECF osmolarity decreases
ICFV increases
three processes of renal function
filtration
secretion
reabsorption
glomerular filtration
180 liters perday of plasma filtered through glomerular capillaries into the renal tubules
this represents filtration of the entire plasma volume almost 60 times each day once every 24 min
secretion
some substances secreted from peritubular capillaries into the renal tubule
represents a method for quickly removing foreign substances from the body fluids and also another means to regulate the excretion of certain endogenous substances
reabsorption
over 99% of filtered fluid is reabsorbed by the renal tubule
returned to the circulation through the peritubular capillaries
three layers of the filtration membrane
capillary endothelial cells - gross filters, excludes cells, 500-1000 Angstrom diameter pores
basement membrane (basal lamina) - main bariier, excludes most plasma proteins, network of mucopolysaccharide filaments embedded in a gel-like matrix
epithelial cells lining Bowman’s capsule (podocytes) - additional barrier, cells have foot processes that are in contact with the basement membrane
slit pores
spaces inbetween foot processes
250-400 A diameter and covered by a thin membrane or diaphragm which also contains pores of 40-140 A diameter
What are the components of glomerular filtrate? What are the mechanisms of formation of filtrate?
basically same composition as plasma with respect to water and low molecular weight solutes
solutes with a molecular weight above 5500 are not freely filtered and there is essentially no filtration of solutes with molecular weights of 70,000 and higher
filtrate is considered protein-free because 70,000 is the molecular weight of albumin, the smallest plasma protein
How does the structure of proteins affect how they are filtered in the glomerulus?
molecules with a radius <20 A are freely filtered
molecules with a radius >42 angstroms are not filtered
molecules between 20-42 A are filtered to various degrees
electrical charge of membrane associated glycoproteins (sialic acid) restricts filtering of negatively charged proteins
two factors impeding filtration of proteins
structure and electrical charge
How does loss of electrical charge inthe membrane affect filtration?
increases the filterability of large molecules
may occur in ccertain disease conditions characterized by protein in the urine (proteinuria)
What controlls the bladder?
reflex pathays in the spinal cord
supraspinal center
bladder functions
storage of urine (holding phase)
elimination pf urine (voiding phase)
urination can be triggered automatically at large bladder volumes (involuntary)
holding phase
urine storage
urine is produced continuously by kidneys
bladder storage converts excretion of uring to intermittent process
voiding phase
normal urination depends upon an intact micturition reflex
urination can be activated at will at any bladder volume (voluntary)
What are the muscles of the bladder?
detrusor muscle - main body
trigone muscles - internal sphincter (smooth muscle)
urogenital diaphragm muscle - external sphincter (skeletal muscle)
What is the role of the trigone muscles?
close off urethra during passive bladder filling
close off ureters during reflex bladder empy
nervous innervation of the bladder
lumbar sympathetic (L2, L3, L4)
sacral parasympathetics (S2, S3, S4)
Describe the role of the lumbar sympathetic innervation of the bladder.
bladder inhibition and relaxation
hypogastric nerve innervates detrusor and trigone muscles (involuntary visceral efferents)
Describe the role of the sacral parasympathetics in the bladder.
bladder stimulation and contraction
pelvic nerves innervate detrusor and trigone muscles (involuntary visceral afferents and efferents)
pudendal nerves innervate the urogenital diaphragm muscle (involuntary somatic efferent)
ureters
small smooth-muscle conduits for urine from the renal pelvis to the bladder
How does urine get pushed out of the body?
increased renal pelvic pressure leads to peristaltic wave in ureter resulting in urine propulsion
velocity of 3 cm/sec
frequency of 0.5-5 every minute
increased frequency by parasympathetic and decreased by sympathetic
bladder compliance
very compliant, capable of holding large volumes at low pressures (<25 mmHg)
cystometrograms used to measure the pressure-volume relationship
sympathetic innervation of the bladder
postganglionic sympathetic neurons act on the detrusor muscle, stimulating beta2 receptors with norepinephrine
stimulates alpha receptor in the internal urethral sphincter
net result is relaxation of the bladder muscle and constriction of the internal sphincter
parasympathetic innervation of the bladder
postganglionic parasympathetic neurons innervate the detrusor muscle, the trigone, and the sphincter
increased activity of the parasympathetic neurons results in contraction of the detrusor muscle, and relaxation of the tirgone and sphincter
phases of cystometrograms
phase I - initial rise in pressure
phase II - initial limb of pressure (pressure slope is proportional to bladder tone)
phase III - ascending limb of pressure (peak pressure is proportional to micturition contraction)
key points for micturition
300 mL - sensation of fullness, brief micturition contraction, tonic c ontraction of external sphincter insures continence
350 mL - micturition contractions become stronger and longer, tonic contraction of external sphincter still insures continence
400 mL - micturition contractions become very strong and polonged, person experiences very strong sensations of discomfort, continenct of external sphincter may fail, involuntary urination follows
Law of Laplace
P = 2T/R
micturition reflex
depends on CNS
intact visceral afferents and efferents
once initiated, the reflex will continue through at least one cycle - involuntary reflex depends on volume bladder and continues automatically until the bladder is completely empty
