CV physiology I Flashcards
what are the main functions of the CV system
- O2 and substrate delivery
- removal of CO2 and metabolic by products
- transport of hormones and other molecules
- thermoregulation
- maintaining acid base balance
- regulation of immune function
what are the components of the CV system
- pump - heart
- high pressure circuit - arteries and arterioles
- arteries = bulk flow
- arterioles = start to distribute
- exchange vessels - capillaries
- low pressure circuit - veins and venules
- fluid - blood
how is velocity related to the total CSA of blood vessels
inversely related
- as total CSA increases, velocity decreases
why is blood flow the slowest in the capillaries
allows time for exchange of gases and nutrients
- largest total CSA
why does velocity goes up on the venous side
- skeletal muscle pumps
- total CSA decreases
- higher volume of blood in vessels
- heart pump pulls the blood back up
what is the pathway of blood through the heart
right side:
- atrium receives deO2 blood from body
- ventricle pumps deO2 blood to the lungs
left side:
- atrium receives O2 blood from lungs
- ventricle pumps O2 blood to body
what is the structure of the myocardium
- shorter than skeletal muscles
- homogenous (all type I)
- cells are connected by intercalated discs (mechanical connection between cells)
- connected fibres connect as a unit (no size principle)
why are there no satellite cells in the myocardium
only one type of muscle fibres - therefore not needed
what are the mechanics of the myocardium
- involuntary contraction
- calcium induced calcium release
what is calcium induced calcium release
- electrical activity into t tubules and then a little calcium is released at the beginning
- little calcium activates the SR and more calcium is released
- SR not activated by electrical activity like skeletal muscle is
what is the intrinsic control of electrical activity (HR)
myocardium generates its own electrical signals
- due to anatomical coupling of the myocardial cells via gap junctions
- conveys electrical discharge from cell to cell in heart (not in muscle cells - APs propagate)
what is the function of the SA node
- specialised fibres that are special groups of cardiac muscles
- don’t contribute to contraction directly
- initiate the electrical discharge
- adapted to generate automatic impulses only (~100bpm)
why does the SA node depolarise at a greater rate than other cells
- leaky to Na+ compared to K+ that leaves the cell
- easier and faster for Na+ to leak into the SA node
- pushes K+ out which is the mechanism to create electrical discharge
why is ithe delay between the AV node and AV bundle important
allows blood from the atria to completely empty to ventricles before contraction
what are the 4 players in extrinsic control of HR
parasympathetic NS
sympathetic NS
endocrine system
mechano/chemoreceptors in muscle and heart
how does parasympathetic NS contribute to extrinsic control of HR
REDUCES HR
- originate from medulla oblongata (CV and resp control)
- vagus nerve sends signals to SA and AV nodes and releases ACh
- activation of vagus nerve (vagal tone)
- ACh released from vagus nerve
- vagal tone (at rest) sets HR around 60-80 bpm
how does sympathetic NS contribute to extrinsic control of HR
INCREASES HR
- increase the rate of depolarisation of SA node
how does endocrine system contribute to extrinsic control of HR
- epi and norepi (catecholamines) from adrenal glands released = increased HR
- triggered by sympathetic stimulation during stress
what is diastole
relaxation phase
- ventricles fill with blood
- passive flow (70%) and contraction of atria (30%)
- twice the duration of systole at rest
what is systole
contraction phase
- ventricles contract
- occurs ~100ms after atrial contraction at rest
- ejects 2/3 blood out of ventricles when ventricular pressure exceeds the pressure of the pulmonary artery and aorta (cardiac afterlload)
- half duration of diastole at rest
what is the difference in length of diastole and systole during exercise
systole is slightly reduced in duration and diastole is way shorter
- HR goes up because of significant decrease in diastolic phase
