Physiology Flashcards
define human physiology
study of the normal function of the human body and the mechanisms that control it
define homeostasis
stable internal environment
two classes of homeostatic control
- intrinsic
2. extrinsic
define feedforward
responses made in anticipation of a change
define feedback
responses made after the change has been detected
define positive feedback
amplifies the initial change
define negative feedback
opposes the initial change by shutting off the system
reasons the cell membrane is important
outer boundary (maintaining concentrations), selectively permeable, joins cells and responds to signals
two classes of membrane proteins
- integral
2. peripheral
functions of membrane proteins are
- ligand-binding receptors
- adhesion molecules
- allows movement of water-soluble substances
- enzymes
- intracellular signalling
name of the layer of glycoproteins and glycolipids
glycocalyx
model to describe the cell membrane
fluid-mosaic model
two types of gradients that drive transport across the membrane
- concentration gradient
- electrical gradient
Ficks law of diffusion takes into consideration
- magnitude of the concentration gradient
- SA
- lipid solubility
- molecular weight
- diffusion distance
define osmosis
net diffusion of water via a selectively permeable membrane. channels for water are called aquaporins
define osmolarity
concentration of osmotically active particles present in solution
define tonicity
effect of solution on cell volume
define hypotonic
increase in cell volume
define hypertonic
decrease in cell volume
define isotonic
equal volume/ no effect on cell size
mechanisms for selective transport are
- carrier-mediated transport
2. vesicular transport
describe carrier-mediated transport
substances bind to specific carriers causing them to undergo conformational changes
the molecules that bind must have three characteristics to cause conformational change
- specificity
- saturation
- competition
two forms of carrier-mediated transport
- facilitated diffusion
2. active transport
two forms of active transport
- primary: direct energy
2. secondary: second-hand ATP
define symport
same direction
define antiport
different directions
define blood pressure
outward (hydrostatic) pressure exerted by the blood on the vessel walls.
define systemic systolic arterial blood pressure
pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts (<140mmHg)
define systemic diastolic arterial blood pressure
pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes (<90mmHg)
define hypertension
blood pressure of 140/90 mmHg
define pulse pressure
difference between systolic and diastolic blood pressures
define mean arterial blood pressure
average arterial blood pressure during a single cardiac cycle. diastole is twice as long as systole
receptors that detect stretch/ pressure
baroreceptors
control centre of the baroreceptor reflex
medulla
effectors of the baroreceptor reflex
heart and blood vessels
location of the baroreceptors
carotid arteries and aorta
what happens in the medulla during the baroreceptor reflex
medulla receives CVS afferent information. the nucleus tracts solitarius (NTS) relays information to other areas of the brain. this generates vagal outflow (parasympathetic)
mean arterial blood pressure can be regulated by
- heart rate
- stroke volume
- systemic vascular resistance (SVR)
define autorhythmicity
heart is capable of beating rhythmically in the absence of external stimuli.
two divisions of the autonomic nervous system
- sympathetic (speeds up the heart)
2. parasympathetic (slows the heart- vagus nerve)
define stroke volume
volume of blood pumped out of the left ventricle
how is stroke volume regulated?
sympathetic nerves supply the ventricular myocardium and increase force of contraction. parasympathetic has little effect.
how is systemic vascular resistance regulated
vascular smooth muscles constrict and dilate
define vasomotor tone
tonic (continuous) discharge of sympathetic nerves resulting in continuous release of noradrenaline
increased sympathetic discharge causes?
increased vasomotor tone which leads to vasoconstriction
decreased sympathetic discharge causes?
vasodilation by decreasing vasomotor tone (there is no parasympathetic intervention)
baroreceptors can re-set blood pressure if?
a new blood pressure is maintained.
commonly assessed vital signs
pulse, temperature, blood pressure, respiratory rate, capillary refill time, oxygen saturation and consciousness
define core body temperature
temperature of structures deep within the body. the outer shell consists of skin and subcutaneous tissue.
average core body temperature
37.8 degrees
sites for monitoring body temperature are
ear drum, recut, oral
internal heat gain
oxidation of food, BMR, muscle activity, shivering and brown fat
external heat exchange
- radiation: absorbing and emitting radiation
- conduction: transfer of heat between objects in contact
- convection: transfer by air or water currents
- evaporation: conversion of water into vapour
sensors for body temperature
thermoreceptors
location of thermoreceptors
hypothalamus, abdominal organs, skin
control centre for core body temperature
hypothalamus
effectors for core body temperature
skeletal muscles, skin arterioles and sweat glands
two centres of the hypothalamus
- posterior- activated by cold
2. anterior- activated by warmth
how is fever produced?
macrophages are stimulated by the infection. they act as endogenous pyrogens (cytokines) and stimulate the release of prostaglandins. this increases the body temperature (fever)
define hyperthermia
elevation of body temperature (above 40 degrees)
define hypothermia
reduction in body temperature (below 35 degrees)
define membrane potential
separation of opposite charges across the membrane on immediate sides of the membrane
is the membrane itself charged
no
concentration gradient across the membrane of K+
movement outwards
concentration gradient across the membrane of Na+
movement inwards
at rest what ion is the membrane more permeable to?
K+
at rest what is the membrane impermeable to?
large, negatively charged (anionic) intracellular proteins (A-)
resting membrane potential
-70mV
what can the nerst equation be used for?
calculate equilibrium potential of a given ion
equilibrium potential of Na+
+60mV
what can the GHK equation be used for?
calculates Em (membrane potential)
function of the Na+/K+ pump
3Na+ and 2K+
potassium equilibrium potential
-90mV
what does the magnitude of the potential depend on?
number of charges that are separated
define depolarisation
membrane potential becomes less negative
define hyperpolarisation
membrane potential becomes more negative
the driving force for Na+ influx
Vm - ENa (membrane potential - equilibrium potential for Na+)
define the ‘all-or-nothing’ principle
the action potential must be above the threshold value
define an action potential
momentary reversal of charge across the membrane
activation of Na+ channels causes?
an influx of Na+ which stimulates more channels to open
define the absolute refractory period
no stimulus, no matter how strong can elicit a second action potential
define the relative refractory period
a stronger stimulus than normal is required to elicit a second action potential
problem with passive signals
cell membrane is leaky so the signals do not spread far from the site of origin
factors that affect the speed of nerve impulses
- axon diameter
- leakiness
- myelin sheath
define saltatory conduction
action potentail jumps from one node of Ranvier to the next
define the autonomic nervous system
transports efferent impulses to tissues other than striated muscle
three subdivisions of the autonomic nervous system
- enteric (GI tract)
- sympathetic division
- parasympathetic division
functions of the ANS
- regulates activities not requiring conscious effort
- training allows some degree of control
neurotransmitters in the sympathetic motor ANS
preganglionic neurone it is acetylcholine and postganglionic neurone it is noradrenaline
two divisions of the motor ANS
- sympathetic
2. parasympathetic
neurotransmitters in the parasympathetic motor ANS
acetylcholine
location of synapses in the sympathetic ANS
- paravertebral ganglia
2. prevertebral ganglia
location of synapses in the parasympathetic ANS
terminal ganglia
name of myelinated preganglionic fibres
motor B-fibres
name of unmyelinated postganglionic fibres
motor C-fibres
describe sympathetic outflow
thoracolumbar outflow T1-L2
describe parasympathetic outflow
cranial nerves III, VII, IX and X and sacral spinal nerves S2-S4
examples of rapid neurotransmitters
ACh and ATP
examples of intermediate speed transmitters
NO and NA
examples of slow neurotransmitters
VIP and NP-gamma
which type of channels are nicotinic ACh receptors
ligand-gated ion channels
which type of channel are muscarinic ACh receptors
G-protein-coupled receptors
clinically important receptors for sympathetic stimulation are?
beta-1 (heart rate increase)
beta-2 (relaxation of bronchi)
clinically important receptors for parasympathetic stimulation are?
M2 (decrease heart rate)
M3 ( constricts bronchi)
three ways blockage of cholinergic transmission may be achieved
- depolarisation
- competitive antagonism
- non-competitive antagonism
which substance can block all ganglionic transmission?
hexamethonium
the effects of cocaine on the ANS
increases NA causing vasoconstriction
effects of amphetamine on ANS
displaces NA into the cytoplasm which increases adrenoceptor stimulation
