CV system anatomy and physiology Flashcards
Function of the cardiovascular system is to circulate to achieve?
- Transport of oxygen, nutrients, electrolytes and hormones
- Return of blood to lungs to be re-oxygenated
- Removal of metabolic by-products
- Maintenance of fluid balance and acid-base balance
- Immune function
- Thermoregulation
Systemic and pulmonary circulations
Systemic • High pressure system • LV wall 8-10mm thick • Systolic BP - 120mmHg Pulmonary • Low pressure system • RV wall 2-3mm thick • Systolic BP - 25mmHg
Layers of the heart wall
Epicardium
- serves as a lubricating outer covering
Myocardium
- provides muscular contractions that eject blood from the heart
Endocardium
- serves as protective inner lining of the chambers & valves
Conduction system of the heart
Autorhythmicity –action potentials are initiated by pacemaker cells in sinoatrial (SA) node and travel via conduction fibres
Stroke volume
EDV
ESV
Volume of blood pumped per contraction
volume of blood in ventricle just before contraction
volume of blood in ventricle just after contraction
SV = EDV – ESV
Cardiac output
Total volume of blood pumped by the ventricle per minute
Q = HR x SV
EF
Proportion of blood pumped out of the left ventricle with each beat Ø EF = SV / EDV
• Averages 60% at rest
• Assessment of EF: Ø “Good” if at least 50% (≥50%) Ø “Moderate” if 40-49% Ø “Poor” if less than 40% (<40%)
SBP
DBP
- Systolic blood pressure (SBP) is the highest pressure within the vascular system generated during cardiac contraction
- Diastolic blood pressure (DBP) is the lowest pressure within the vascular system when the heart is relaxed
MAP
MAP = 2/3 DBP + 1/3 SBP
Hemodynamics
Pressure gradient across the entire cardiovascular system = 100 mmHg
Resistance to blood flow = [ηL / r4],
• η = viscosity of the blood
• L = length of the vessel
• r4 = radius of the vessel to the 4th power
Changing blood flow
Blood Flow = Δpressure / resistance
Ø Blood flow can change by either changing pressure or resistance or a combination of the two
Ø Changing resistance has a larger effect on blood flow because of the fourth power mathematical relationship between vascular resistance and vessel radius
Ø Vasoconstriction: radius of the vessel decreases, decreasing blood flow
Ø Vasodilation: radius of the vessel increases, increasing blood flow
Intrinsic Control of Blood Flow
Stimuli to increase local blood flow
1. Metabolic factors Øincreased oxygen demand
Øincreases in metabolic by-products
Øinflammatory chemicals
2. Endothelium released factors
ØNitric oxide ØProstaglandins ØEndothelium-derived hyperpolarization factors (EDHF)
3. Myogenic responses
Extrinsic Neural Control
Accomplished by the autonomic nervous system through vasoconstriction or vasodilation.
Ø Sympathetic branch – vasoconstriction
Ø Parasympathetic branch - vasodilation
Integrative Control of Blood Pressure
Ø Blood pressure is maintained and controlled by the autonomic nervous system
Ø BP = Q X TPR (total peripheral resistance)
Ø Receptors that modify blood pressure control through the cardiovascular control centers:
• Baroreceptors: stretch receptors in the aortic arch and carotid arteries that are sensitive to changes in blood pressure
• Chemoreceptors: chemical receptors that relay information about the chemical environment
• Mechanoreceptors: receptors that sense changes in muscle length and tension
Endothelial functions
The endothelium serves critically important functions:
• Barrier restricting passage of large molecules and cells
• Resist thrombosis through anti-clotting factors and platelet inhibitors
• Regulate blood flow to meet metabolic demands by secreting vasodilator substances
• Inhibits the migration and proliferation of smooth muscle cells
