Physiology Flashcards
what is the spread of excitation in the heart
1 - Across the atria mainly cell-to-cell conduction via gap junctions
2 - From SA node to AV node: mainly cell-to-cell conduction via gap junctions; but there is also some internodal pathways
3 - The conduction is delayed in the AV node.
4 - The Bundle of His and its branches and the network of Purkinje fibers allow rapid spread of action potential to the ventricles
5 - Ventricular muscle: cell-to-cell conduction
Diastole
what stimulation decreases the HR
Parasympathetic
what is classified as bradycardia
HR less than 60
what is classified as tachycardia
HR more than 100
what does a negative chronotropic effect do
slows down HR (parasympathetic)
what does a positive chronotropic effect do
increases HR (sympathetic)
what is an ECG a record of
depolarization and repolarization cycle of cardiac muscle obtained from the skin surface
what values shut together
Tricuspid and Mitral
Pulmonary and aortic
how long does diastole and systole last for
diastole - 0.5sec
systole - 0.3sec
what happens in systole
the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery (RV)
what happens in diastole
the heart ventricles are relaxed and fill with blood
what is the process of Isovolumetric Ventricular Contraction
- Ventricular pressure rises
- When ventricle pressure exceeds atrial pressure the AV values shut
- produces first heart sound (‘lub’)
when does the aortic/pulmonary value open
When the ventricular pressure exceeds aorta/pulmonary artery pressure
what does the T wave on an ECG represent
ventricular repolarisation
what happens after the aortic/pulmonary value open
Ventricles relax
ventricular pressure start to fall
what happens when the ventricular pressure falls below aortic/pulmonary pressure
aortic/pulmonary valves shut
this produces the second heart sound (dub)
what does the Closure of aortic/and pulmonary valves signal
isovolumetric ventricular relaxation
what happens when the ventricular pressure falls below atrial pressure
AV valves open and the heart starts a new cycle
what are the 5 stages of the cardiac cycle
1 - Passive Filling 2 - Atrial Contraction 3 - Isovolumetric ventricular Contraction 4 - Ventricular Ejection 5 - Isovolumetric ventricular Relaxation
how does arterial pressure not fall to zero during diastole
elastic tissue
when does JVP appear
after right atrial pressure waves
what is the a wave on the JVP
atrial contraction
what is the c wave on the JVP
bulging of tricuspid valve into atrium during ventricular contraction
what is the v wave on the JVP
rise of atrial pressure during atrial filling: release as AV valves open
what happens in diastole (in relation to ions)
sodium enters the cell
Calcium exits the cell
Calcium enters the SR
what does stretch do in relation to calcium
increases the affinity of troponin for Ca++
when is the optimal length in cardiac muscle achieved
by stretching the muscle
what happens if venous return to right atrium increases
EDV of right ventricle increases
Starling’s Law leads to increased SV into pulmonary artery
when does EDV of left ventricle increase and what does this cause
Venous return to left atrium from pulmonary vein increases
Starling’s Law leads to increased SV into aorta
what does sympathetic stimulation do
increases the force of contraction (positive inotropic effect)
what is the effect of sympathetic stimulation on ventricular contraction
1 - Force of contraction increases
2 - peak ventricular pressure rises
3 - Rate of pressure change (dP/dt) during systole increases
4 - reduced the duration of systole
5 - Rate of ventricular relaxation increases
6 - reduces duration of diastole
how is force of contraction increased in sympathetic stimulation and what mediates it
activation of Ca++ channels - greater Ca++ influx
cAMP
how is the rate of ventricular relaxation increased in sympathetic stimulation
increased rate of Ca2+ pumping
what does the Frank-Straling curve shifted to the right
heart failure
what should systolic and diastolic BP not exceed
s - 140mmHg
d - 90mmHg
what is the effect of the parasympathetic stimulation on the heart
decreases HR
decreases CO
decreases MAP
what is the effect of the sympathetic stimulation on the heart
increases HR-increases CO-increases MAP
increases contractile strength of heart-increases SV-increases CO-increases MAP
what is the effect of the sympathetic stimulation on the arterioles
increases vasoconstriction-increases TPR- increases MAP
what is the effect of the sympathetic stimulation on the veins
increases vasoconstriction-increases Venous return-increases stroke volume-increases cardiac output- increases MAP
what causes postural hypotension
failure of Baroreceptor responses to gravitational shifts in blood, when moving from horizontal to vertical position
what are the two main factors affect Extracellular Fluid volume
Water excess or deficit
Na+ excess or deficit
what affect does angiotensin II have on the systemic system and how does it achieve this
vasoconstriction -increases TPR and BP
increases ADH and thirst -increases Plasma Volume and BP
what does aldosterone do
acts on the kidneys to increase sodium and water retention increases plasma volume
therefore, increases BP
where does aldosterone come from
adrenal cortex
where does ACE come from
lung vascular endothelium
what stimulates the release of rennin from the juxtaglomerular apparatus in the kidneys
1 - Renal artery hypotension -caused by systemic hypotension (↓ blood pressure)
2 - stimulation of renal sympathetic nerves
3 - Decreased [Na+] in renal tubular fluid
where is ADH synthesised and where is it stored
hypothalamus
posterior pituitary
what is ADH also known as
vasopressin
what is plasma osmolality monitored by
osmoreceptors in the brain in close proximity to hypothalamus
when is the release of ADH stimulated
when there is an increased plasma osmolality
mechanism of action of ADH
1 - increase reabsorption of water
2 - increase extracellular and plasma volume
3 - increases CO and BP
affect of ADH on blood vessels
vasoconstriction - increase TPR and BP
important in hypovolaemic shock e.g. haemorrhage
what does contraction and relaxation of vascular smooth muscle cause
vasoconstriction - increases TPR and MAP
vasodilatation - decreases TPR and MAP
what is the effect of increase sympathetic discharge on vascular smooth muscle
vasoconstriction
what factors causes relaxation of arteriolar smooth muscles resulting in VASODILATATION
Decreased local PO2 Increased local PCO2 Increased local [H+] (decreased pH) Increased extra-cellular [K+] Increased osmolality of ECF Adenosine release (from ATP)
where is NO produced and from what
vascular endothelium from the amino acid L-arginine through enzymatic action of Nitric Oxide Synthase (NOS)
what is the mechanism of action of NO
1 - diffuses from the vascular endothelium into the adjacent smooth muscle cells
2 - activates the formation of cGMP
3 - serves as a 2nd messenger for signalling smooth muscle relaxation
what causes increased venous return
increase venomotor tone
increased skeletal muscle pump
increased resp pump
increased blood volume
what does increased venous return causes
increased atrial pressure-increase EDV-increased SV
what does increased venomotor tone causes
increased venous return, SV and MAP
what does increased vasomotor tone causes
increases TPR and MAP
how does contraction of muscles aid venous return
large veins lie in between skeletal muscle
One-way venous valves allow blood to move towards the heart
Muscle Activity increases VENOUS RETURN to heart
how does sympathetic stimulation increase HR
INCREASING THE RATE OF FIRING OF SA NODE and DECREASES AV NODAL DELAY
Increases force of contraction
what happens when slope of pacemaker potential increases
pacemaker potential reaches threshold quicker
frequency of action potentials increases
what does adequate tissue perfusion depend on
adequate blood pressure and adequate cardiac output
where do the right and left coronary arise from
the base of the aorta
what is the mechanism of adenosine
potent vasodilator
cause vasodilation of coronary arteries
increase blood flow to cardiac muscle
what does shortening diastole cause
very fast heart rate ↓ coronary flow
