physiology Flashcards
what is osmolarity
the concentration of osmotically active particles present in a solution
unit of osmolarity used for body fluids
mosmol/l
how would you calculate the osmolarity of 150mM of NaCl
molar concentration of the solution x number of osmotically active particles present
2 x 150 = 300 mosmol/l
name the 3 main types of osmotically active particles
ions, small molecules and proteins
what is the difference between osmolarity and osmolality
osmolarity - number of osmoles per litre of solution
osmolality - number of osmoles per kilogram of solvent
what is tonicity
the effect a solution has on the cell volume
isotonic solution
causes no change in cell volume
hypotonic solution
causes an increase in cell volume as water enters the cell
consequence of a hypotonic solution
cell lysis
hypertonic solution
causes a decrease in cell volume as water leaves the cell
consequence of hypertonic solution
cell shrinkage
what are the 2 major compartments of total body water
intracellular fluid - fluid inside the cells
extracellular fluid - plasma, interstitial fluid + lymph, CSF
what can be useful when determining the volume of body fluid compartments
tracers
what is the volume of distribution
determines how a drug distributes itself within the body
what does it mean if a drug has a low Vd
mainly stays in the plasma
what does it mean if a drug has a moderate Vd
distributes into extracellular fluid
what does it mean if a drug has a high Vd
drug extensively enters tissues
what can be used as a tracer in extracellular fluid
inulin
what can be used as a tracer in plasma
labelled albumin
what are the 3 main ions found in extracellular fluid
Na+, Cl- and HCO3-
what is interstitial fluid
the fluid surrounding the cells in tissues
describe the relationship between ICF, interstitial fluid and blood plasma
ICF | (plasma membrane) | interstital fluid
interstital fluid | (capillary wall) | plasma
what is fluid shift in the body
movement of water between the ICF and the ECF in response to an osmotic gradient
what happens to the ECF in a patient who is dehydrated and what is the consequence of this
becomes hypertonic
water moves out of cells into ECF so cells shrink
what happens to the ECF in a patient who is overhydrated and what is the consequence of this
becomes hypotonic
water moves into the cells from the ECF so cells swell
what is the key role of K+
establishes membrane potential
what are the 2 main clinical consequences of change in K+ plasma concentration
muscle weakness and cardiac irregularities
why is Na+ so important anyway?
major determinant of ECF volume
what is the primary function of the kidney
regulate the volume, composition and osmolarity of body fluids
what is the functional unit of the kidney
nephron
what are the 2 main types of nephron and their role
cortical nephrons (**): filtration and reabsorption
juxtamedullary nephrons: urine collection
describe where nephrons are found
cortex = renal corpuscle and the PCT and DCT
medulla = loop of henle and collecting ducts
what is the glomerulus
loop of capillaries twisted into a ball
what surrounds the glomerulus
bowmans capsule
what happens in the glomerulus
ultrafiltration
what does the glomerulus connect to
proximal convoluted tubule
what is the justamedullary unit
structure formed by the macula densa and the glomerular afferent arteriole
what is the role of the juxtamedullary unit
regulate blood pressure and the filtration rate of the glomerulus
what are the 3 stages of urine production
glomerular filtration
tubular reabsorption (back into the blood)
tubular secretion
what is GFR
how much plasma if filtered per minute
how do we calculate rate of filtration in the kidney
plasma concentration of substance x GFR
what is Vu
urine flow rate - volume of urine produced per minute
how do we calculate the rate of excretion of a substance
concentration or substance in urine x urine flow rate
how do we calculate rate of reabsorption
rate of filtration - rate of excretion
what does it mean if filtration of a substance > excretion
the kidney has absorbed some of the substance back into the blood
how do we calculate the rate of secretion
rate of excretion - rate of filtration
what does it mean if excretion > filtration
additional substance must have been secreted into the tubules
what are the 3 layers of the glomerular membrane
glomerular capillary endothelium
basement membrane
podocytes
how is the glomerular capillary endothelium adapted for its role
fenestrae (pores) act as a barrier to red blood cells
how is the basement membrane in the glomerulus adapted for its role
negatively charged - prevents the movement of plasma proteins across it
what are podocytes and what is their role
epithelial cells of the bowmans capsule - prevent plasma proteins passing through
forces that encourage filtration in the glomerulus
glomerular capillary blood pressure
bowman’s capsule oncotic pressure
forces that oppose filtration in the glomerulus
capillary oncotic pressure
bowmans capsule hydrostatic pressure
what is the major determinany of GFR
glomerular capillary fluid pressure
how do we calculate GFR
Kf (filtration coefficient) x net filtration pressure
what is Kf
filtration coefficient - how ‘holey’ the glomerular membrane is
what is the macula densa
group of cells in the distal convoluted tubule
what are the 2 main intrinsic mechanisms that regulate GFR
myogenic
tubuloglomerular feedback
what is the myogenic mechanism used to regulate GFR
increased blood pressure in afferent arteriole causes stretch
sensed by vascular smooth muscle which contracts to reduce blood flow to the glomerulus
what is the juxtaglomerular feedback mechanism used to regulate GFR
increased BP causes increased filtration so more NaCl moves through the DCT
macula densa notices an increase in NaCl (Na+ increase) and releases adenosine
causes vasoconstriction of the afferent arteriole
what effect does diarrhoea have on GFR
decreases
dehydration increases plasma protein concentration - increases capillary oncotic pressure which pushes fluid back into the arteriole
what is plasma clearance
a measure of how effectively the kidneys can clean the blood of a substance
what does it mean if clearance = GFR
the substance is being filtered and is neither reabsorbed nor secreted
what does it mean if clearance is 0
substance is filtered, completely reabsorbed and not secreted
what does it mean if clearance < GFR
the kidneys are reabsorbing the substance after filtration rather than excreting it into the urine
what does it mean if clearance > GFR
substance is being secreted into the urine as well as being filtered
what is used clinically to measure renal plasma flow
PAH
what is tubular reabsorption
water and solutes within the tubule are transported into the blood stream
what is the role of the proximal tubule
reabsorbs filtered fluid
where in the nephron is Na+ not reabsorbed
descending loop of henle
how is Na+ reabsorbed in the nephron
transcellularly - active transport
what is the renal threshold
the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine
what is the role of the loop of henle
concentrating urine and maintaining the body’s water and salt balance
what happens in the descending limb of the loop of henle
water moves out of the filtrate by osmosis leading to concentration of the tubular fluid
what happens in the thin limb of the ascending loop of henle
passive reabsorption of NaCl into the interstitium - causes filtrate in the tube to dilute
which part of the loop of henle is impermeable to water
ascending limb
what happens in the thick limb of the ascending loop of henle
active transport of Na+, K+ and Cl- out of the tubule
what is the importance of substance exchange in the thick limb of the ascending loop of henle
generates the osmotic gradient needed for water absorption in the collecting duct
what drives the reabsorption of water in the descending limb of henle
countercurrent flow
what is the role of the early distal tubule
reabsorption of ions via active transport
what are the 3 substances that influence the distal convoluted tubule
aldosterone
PTH
ADH
what are the 2 main types of cells found in the late DCT and collecting duct
principal cells and intercalated cells
what is the role of principal cells in the DCT and CD
uptake of sodium ions and the extrusion of potassium ions
what is the role of intercalated cells in the DCT and CD and how do they do it
acid base control - control levels of H+ and HCO3-
what is the main role of the collecting duct
reabsorption of water
what influences the reabsorption of water in the collecting duct
anti-diuretic hormone
where is ADH released from
posterior pituitary gland
what is the role of ADH
increases water reabsorption in the kidney
what triggers the production of ADH
high plasma osmolarity detected by hypothalamic osmoreceptors
where is ADH synthesised
hypothalamus
what is the effect of ADH on the collecting duct
triggers the insertion of aquaporin channels which allow water to be reabsorbed
what is the result of high ADH on urine
small volume of hypertonic urine
what is aldosterone
steroid hormone secreted by the adrenal cortex
when is aldosterone secreted (3)
in response to an increase in [K+] or a decrease in [Na+] in the blood or due to activation of the RAAS
where is aldosterone secreted from
zona glomerulosa of the adrenal cortex
what are the 3 main functions of aldosterone
sodium reabsorption in DCT and CD
potassium secretion
increases H+ secretion from intercalated cells in the collecting duct
what are the 3 main hormones in the RAAS system
renin, angiotensin 2, aldosterone
what can prevent the release of renin and why would this happen
ANP released in response to increases in blood pressure
where is ANP released from
atria
where is renin released from
granular cells in the juxtaglomerular apparatus of the kidney
what causes renin to be released
reduction in blood pressure (NaCl reduced)
what is the role of ANP
promotes excretion of Na+ and diuresis -> decreases plasma volume
describe how the micturition reflex is triggered
bladder gets full - detected by stretch receptors
sends information to the spinal cord triggering the reflex
describe the micturition reflex
bladder contracts and internal and external urethral sphincters relax leading to urination
what can override the micturition reflex
contraction of the external urethral sphincter
what can acidosis of ECF lead to
depression of the CNS
what can alkalosis of the ECF lead to
overexcitability of the PNS
what is the most important physiological buffer system
CO2 - HCO3- buffer
what is respiratory acidosis
retention of CO2 by the body
name some conditions that can cause respiratory acidosis
chronic bronchitis or emphysema, airway restriction, chest injuries, respiratory depression
what causes respiratory alkalosis
excess removal of CO2 by the body
name some conditions that can cause respiratory alkalosis
low inspired pO2 at altitude, hyperventilation
what causes metabolic acidosis
excess H+ from any source OTHER THAN CO2
name some conditions that can cause metabolic acidosis
ingestion of acids or acid-producing food
lactic acid during exercise, ketoacidosis
loss of base: diarrhoea
how do we compensate for metabolic alkalosis
blowing off CO2
what causes metabolic alkalosis
excessive loss of H+ from the body
name some conditions which can cause metabolic alkoalosis
vomiting - loss of HCl from stomach
ingestion of alkali or alkali-producing foods
aldosterone hypersecretion
how can we compensate for metabolic alkalosis
CO2 retention by decreased ventilation
what are the 5 basic structures of the nephron
glomerulus, proximal tubule, loop of henle, distal tubule and collecting duct
where are the juxtaglomerular cells found
at the afferent arteriole
what is the main role of the juxtaglomerular cells
sense blood pressure and secrete renin in response
low blood pressure = more renin
where is angiotensinogen produced
liver
what converts angiotensinogen to angiotensin 1
renin
what converts angiotensin 1 to angiotensin 2
ACE
where is ACE produced
in the lungs
what are the 2 main short-term effects of angiotensin 2
vasoconstriction
aldosterone release by the adrenal glands
what is the long term effect of angiotensin 2
hypertrophy of the myocardium and vascular smooth muscle - leading to cardiac remodelling
