CVS Physiology 1-5 Flashcards
Define the function of the cardiovascular system.
Function of the CVS - bulk flow system: transports Oxygen and Carbon dioxide, nutrients, metabolites, hormones and provides heat.
The heart can vary it’s output - vessels can redirect blood-flow to where it is needed most and vessels can store blood.
Indicate the significance of vascular beds being arranged in parallel or in series.
Pumps are in series output=input, therefore:
Output of right side of heart must be equal to left side to prevent accumulation of blood in pulmonary and systemic circulations.
Most vascular beds are in parallel (receive blood at the same time) therefore:
All tissues get oxygenated blood
Allows regional redirection of blood
Most vascular beds are arranged in parallel however there are some exceptions to this rule, most notably the gut and the liver which are arranged in series.
Describe the importance of resistance with respect to the cardiovascular system.
Resistance is a measure of how difficult it is for blood to flow through the circulation.
To allow redirection of blood flow there must be a change in resistance. The main thing that influences this is the diameter of the blood vessel that you’re trying to push blood through. Resistance controlled by radius^4, selectively redirects flow. Arterioles act as the taps, controlling resistance and therefore flow to each vascular bed.
Justify the significance of pressure with respect to the cardiovascular system.
To allow fluid to be transported through a tube there must be a difference in pressure. High pressure side on the left and lower pressure side on the right. High pressure side on the left pushes blood into the arteries out of the left side of the heart and into systemic circulation. Lower pressure on the right to allow blood to return to the right side of the heart.
What is darcy’s law
Flow = Difference in Pressure/Resistance
Pressure difference = mean arterial pressure - central venous pressure, affects all tissues.
What does regional distribution of blood describe?
This describes the ability of the body to constrict and dilate arterioles supplying different vascular beds to redirect blood flow to different body regions.
Describe the importance of capacitance with respect to CVS.
In electrical circuits, capacitance describes the ability of a component to store electrical charge. By analogy, capacitance vessels (the venules and veins) have the ability to store blood and may contain two thirds of the total blood volume.
Explain the functions of elastic arteries, muscular arteries, resistance vessels, exchange vessels and capacitance vessels.
Aorta - elastic arteries, wide lumen, thick elastic wall, damp pressure variations.
Arteries - Muscular arteries, wide lumen, strong, thick, non-elastic wall, low resistance conduit.
Arterioles - resistance vessels, narrow lumen, thick contractile wall, control resistance and therefore flow, allow regional redirection of blood.
Capillaries - exchange vessels, narrow lumen, thin wall.
Veins and Venules - Capacitance vessels, wide lumen, thin, distensible wall, low resistance conduit and reservoir, allows fractional distribution of blood between veins and rest of circulation.
Describe the flow of blood through the heart.
List the sequence of events occurring during excitation-contraction coupling.
When a motor neurone fires an action potential, you get release of the neurotransmitter acetylcholine from its axon terminal, that will diffuse across the synaptic cleft where it binds to cholinergic nicotinic receptors on the end plate. This triggers endplate potential and that is enough to get muscle cell membrane to threshold to evoke an action potential. This is propagated along the sarcolemma, that’s mediated by voltage gated sodium channels and it will be propagated down into these T-tubules. Then calcium is released from these stores in the sarcoplasmic reticulum. That calcium binds to binding sites on troponin, and that then allows the actin and myosin filaments to interact with each other and they form cross-bridges. Essentially myosin grabs actin and pulls it which causes muscle contraction.
List the differences between excitation contraction coupling in cardiac muscle and skeletal muscle.
Cardiac muscle forms a functional syncytium:
- Electrically connected via gap junctions
- Physically connected by desmosomes
- These form the intercalated discs
Cardiac muscle has a long action potential (~250 ms vs. ~2 ms in skeletal muscle)
- Long refractory period, so cannot exhibit tetanic contraction
- Ca2+ entry from outside cell can regulate contraction
- - Ca2+ release does not saturate the troponin, so regulation of Ca2+ release can be used to vary the strength of contraction
What is the function of pacemakers.
Send electrical signals to heart to make it beat at the correct pace.
Describe the basis of the action potential in non pacemaker tissue.
Non pacemaker:
- Resting membrane potential
High resting PK+
- Initial depolarisation
Increase in PNa+ - Plateau
Increase in PCa2+ (L-type) and decrease in PK+ - Repolarisation
Decrease in PCa2+ and increase in PK+
Describe the basis of the action potential in pacemaker tissue.
Action potential
Increase in PCa2+ (L-type)
Pacemaker potential (= pre-potential)
Gradual decrease in PK+
Early increase in PNa+ (= PF)
Late increase in PCa2+ (T-type)
Pacemaker explains autorhythmicity
Also a basis for understanding modulation of the activity of the heart (see directed work)
Describe the functions of the components of the special conducting system.
Sinoatrial node
- Pacemaker
~0.5 m/s
Annulus fibrosus
- Non-conducting
Atrioventricular node
- Delay box
~0.05 m/s
Bundle of His and Purkinje fibres
Rapid conduction system
~5 m/s
Ensures coordinated contraction of the heart
Describe the initiation and spread of electrical activity throughout the heart.
An action potential in a single myocyte evokes a very small extracellular electrical potential.
However, lots of small extracellular electrical potentials evoked by many cells depolarising and repolarising at the same time can summate to create large extracellular electrical waves.
These can be recorded at the periphery as the electrocardiogram.
Correlate the various components of the electrocardiogram with the electrical events in the heart.
Identify the P-wave, QRS-complex and T-wave in a normal ECG and what heart events they respond to.
Identify the PR interval, QT interval, PR segment and ST segment
Describe how to measure heart rate from an ECG
Heart rate:
Measure the RR interval and work out how many occur in 60 s, or better…
Count the R waves in 30 large squares (= 6 s) and multiply by 10
Illustrate the sequence of changes in pressure and volume in the chambers of the heart throughout the cardiac cycle.
Interpret and label a pressure-volume loop.
