Physiology Flashcards
Autorhythmicity
The capability of the heart to beat rhythmically in the absence of an external stimuli
Where does the excitation of the heart originate?
Pacemaker cells in the SA node
What is the parasympathetic supply to the heart?
Vagus nerve
What is the neurotransmitter and receptor in parasympathetic?
ACh acting on M2 muscarinic receptors
What does atropine do?
Speeds up the heart
What does increasing vagal stimulation do to the slope of the pacemaker?
Decreases slope
What does increasing sympathetic stimulation do to the slope of the pacemaker?
Increases slope
What is the neurotransmitter and receptor in sympathetic?
NA acting on beta1 adrenoreceptors
What is blood pressure?
The outwards pressure exerted by the blood on the vessel walls
Which Korotkoff sound is hear when diastolic pressure is estimated?
Fifth
Pressure gradient between the aorta and the right atrium
Mean arterial pressure - central venous (right atrial) pressure
What is mean arterial blood pressure?
The average arterial blood pressure during a single cardiac cycle
Calculate mean arterial blood pressure
[(2 x diastolic) + systolic] / 3
What is the normal range of MAP?
70-105 mmHg
Relationship between MAP, TPR and CO
MAP = CO x TPR
What is cardiac output?
The volume of blood pumped by each ventricle of the heart per minute
Relationship between CO, SV and HR?
CO = SV x HR
What is stroke volume?
The volume of blood pumped by each ventricle per beat
What are the major resistance vessels?
Arterioles
Which cranial nerve is involved in transmission from the carotid baroreceptors?
IX th CN
Which cranial nerve is involved in transmission from the aortic baroreceptors?
X th CN
What are the two main factors which affect extracellular fluid volume?
- Water excess/deficit
2. Na+ excess/deficit
Which hormones regulate extracellular fluid volume?
- Renin angiotensin aldosterone system
- Atrial Natriuretic peptide
- Antidiuretic hormone
What is the rate limiting step for RAAS?
Renin secretion
What regulates total peripheral resistance?
Vascular smooth muscle
What type of autonomic supply is given to the vascular smooth muscle?
Sympathetic
What is vasomotor tone?
When the vascular smooth muscles are partially constricted at rest
Which receptor causes vasoconstriction of arterioles when acted on by adrenaline?
alpha adrenoreceptors
Which receptor causes vasodilation of arterioles when acted on by adrenaline?
beta 2 adrenoreceptors
Which two hormones (other than adrenaline) cause vasoconstriction?
Angiotensin
Antidiuretic hormone
Name 3 local humeral agents which cause vasodilatation
Histamine
Bradykinin
Nitric oxide
Name 4 humoral agents which cause vasoconstriction
Serotonin
Thromboxane A2
Leukotrines
Endothelin
What does sympathetic stimulation do to the heart?
Increases SA node firing
Decreases AV node delay
What is the refractory period?
A period following an action potential in which it is not possible to produce another AP
What is after load?
The resistance into which the heart is pumping
What does inotropic relate to?
FORCE
What does chronotropic relate to?
RATE
What does vagal stimulation have major influence on?
Rate
What does adenosine do to blood vessels in the coronary system?
Vasodilator
When does peak left coronary blood flow occur?
Diastole
Where does the brain receive its blood supply from?
Internal carotids and vertebral arteries
Which part of the brain is sensitive to hypoxia?
Grey matter
What is the purpose of the circle of Willis?
So that if one carotid artery is obstructed, cerebral perfusion is maintained
If MABP rises, what is the effect on the auto regulation of resistance vessels to cerebral flow?
Constricts
If MABP falls, what is the effect on the auto regulation of resistance vessels to cerebral flow?
Dilate
Why can hyperventilating lead to fainting?
Too much CO2, so causes cerebral vasodilation
What MABP causes fainting, confusion etc.
50mmHg
What is the normal inter cranial pressure?
8-13 mmHg
What do cerebral capillaries contain?
Tight intercellular junctions which make up the blood brain barrier
What is the typical pulmonary artery BP?
20-25/6-12 mmHg
What does hypoxia do to pulmonary arterioles?
Vasoconstriction - to divert blood from poorly ventilated areas
What does hypoxia do to systemic arterioles?
Vasodilation
what is interstitial fluid?
Fluid which bathes the body cells - it acts as a go between blood and body cells
which type of cells make up capillaries?
endothelial cells
what determines blood flow in the capillaries?
Contractile state of arterioles
what regulates blood flow in the mesentery?
Precapillary sphincters
What cannot cross the capillary wall?
Plasma protein
Net Filtration Pressure
Force favouring filtration - force opposing filtration
which forces favour filtration?
capillary hydrostatic pressure
Interstitial fluid osmotic pressure
which forces oppose filtration?
capillary osmotic pressure
Interstital fluid hydrostatic pressure
which end favours filtration in the capillaries
Arteriolar end
which end favours reabsorption in the capillaries?
Veules
Which end has the lower pressure of the capillaries?
Venules
Define Oedema
Accumulation of fluid in the interstitial space