Body Fluids and Renal Function

Question 1

osmolarity

Answer 1

the number of solute particles per 1L of water

Question 2

osmolality

Answer 2

the number of solute particles in 1 Kg of water

Question 3

osmotic pressure

Answer 3

results with concentration difference and specific permeability

Question 4

oncotic pressure

Answer 4

osmotic pressure generated by large molecules in solution

Question 5

van’t Hoff’s Law

Answer 5

osmotic pressure may be predicted on the basis of the concentration of the osmotically active substances

π = RT(ions*concentration)

Question 6

What is the fluid distribution in an average 70 Kg person?

Answer 6

42 L total body water

14 L ECF and 28 L ICF

10.5 L interstitial fluid and 3.5 L plasma

Question 7

What is the normal osmolarity in the body?

Answer 7

285 mOsm/L

Question 8

composition of body fluid compartments

Answer 8

sodium is the major cation of the ECF

chloride and bicarbonate are the major anions

plasma has high concentration of proteins

Question 9

What assumptions are made in fluid shift calculations?

Answer 9

intracellular osmolarity = extracellular osmolarity

water moves freely across membranes

solutes (NaCl, NaHCO3, Mannitol) do not move across membranes

Question 10

isosmotic volume contraction

Answer 10

loss of ECFV and solute

ECFV decreases

no decrease in ECF osmolarity

ICFV remains unchanged

Question 11

hyperosmotic volume contraction

Answer 11

loss of hyposmotic ECFV = sweat

ECFV decreases

increase in ECF osmolarit

ICFV decreases

Question 12

hyposmotic volume contraction

Answer 12

decreased aldosteron, loss of NaCl and water

ECFV decreases

ECF osmolarity decreases

ICFV increases

Question 13

isosmotic volume expansion

Answer 13

increasing NaCl and water in the ECF

ECFV osmolarity unchanged

ECFV increased

ICFV unchanged

Question 14

hyperosmotic volume expansion

Answer 14

increasing NaCl in the ECF

ECF osmolarity increases

ECFV increases

ICFV decreases

Question 15

hyposmotic volume expansion

Answer 15

inappropriately high levels of ADH

excess water is reabsorbed by the kidney

ECFV increases

ECF osmolarity decreases

ICFV increases

Question 16

three processes of renal function

Answer 16

filtration

secretion

reabsorption

Question 17

glomerular filtration

Answer 17

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

Question 18

secretion

Answer 18

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

Question 19

reabsorption

Answer 19

over 99% of filtered fluid is reabsorbed by the renal tubule

returned to the circulation through the peritubular capillaries

Question 20

three layers of the filtration membrane

Answer 20

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

Question 21

slit pores

Answer 21

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

Question 22

What are the components of glomerular filtrate? What are the mechanisms of formation of filtrate?

Answer 22

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

Question 23

How does the structure of proteins affect how they are filtered in the glomerulus?

Answer 23

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

Question 24

two factors impeding filtration of proteins

Answer 24

structure and electrical charge

Question 25

How does loss of electrical charge inthe membrane affect filtration?

Answer 25

increases the filterability of large molecules may occur in ccertain disease conditions characterized by protein in the urine (proteinuria)

Question 26

What controlls the bladder?

Answer 26

reflex pathays in the spinal cord supraspinal center

Question 27

bladder functions

Answer 27

storage of urine (holding phase) elimination pf urine (voiding phase) urination can be triggered automatically at large bladder volumes (involuntary)

Question 28

holding phase

Answer 28

urine storage urine is produced continuously by kidneys bladder storage converts excretion of uring to intermittent process

Question 29

voiding phase

Answer 29

normal urination depends upon an intact micturition reflex urination can be activated at will at any bladder volume (voluntary)

Question 30

What are the muscles of the bladder?

Answer 30

detrusor muscle - main body trigone muscles - internal sphincter (smooth muscle) urogenital diaphragm muscle - external sphincter (skeletal muscle)

Question 31

What is the role of the trigone muscles?

Answer 31

close off urethra during passive bladder filling close off ureters during reflex bladder empy

Question 32

nervous innervation of the bladder

Answer 32

lumbar sympathetic (L2, L3, L4) sacral parasympathetics (S2, S3, S4)

Question 33

Describe the role of the lumbar sympathetic innervation of the bladder.

Answer 33

bladder inhibition and relaxation hypogastric nerve innervates detrusor and trigone muscles (involuntary visceral efferents)

Question 34

Describe the role of the sacral parasympathetics in the bladder.

Answer 34

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)

Question 35

ureters

Answer 35

small smooth-muscle conduits for urine from the renal pelvis to the bladder

Question 36

How does urine get pushed out of the body?

Answer 36

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

Question 37

bladder compliance

Answer 37

very compliant, capable of holding large volumes at low pressures (\<25 mmHg) cystometrograms used to measure the pressure-volume relationship

Question 38

sympathetic innervation of the bladder

Answer 38

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

Question 39

parasympathetic innervation of the bladder

Answer 39

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

Question 40

phases of cystometrograms

Answer 40

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)

Question 41

key points for micturition

Answer 41

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

Question 42

Law of Laplace

Answer 42

P = 2T/R

Question 43

micturition reflex

Answer 43

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