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Flashcards in Body Fluids and Renal Function Deck (43):


the number of solute particles per 1L of water



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





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



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



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)



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