S1: structure and function of CVS Flashcards
What is the course of blood flow into and out of the heart through the major vessels?
The right side of the heart consists of the right atrium which receives deoxygenated blood from the body and the right ventricle which pumps the deoxygenated blood out through the pulmonary artery to the lungs. The left side of the heart consists of the left atrium which receives oxygenated blood from the lungs and the left ventricle which pumps the oxygenated blood out through the aorta to the body
What does the pericardium enclose?
The heart and roots of the great vessels are enclosed by a fibroserous sac called the pericardium.
What are the two layers of the pericardium?
Fibrous pericardium = strong, outer fibrous layer made of tough connective tissue
-prevents overfilling of the heart
Serous pericardium = two different layers: visceral & parietal
-outer parietal layer: lines the internal surface of the fibrous pericardium
-internal visceral layer: forms the outer layer of the heart (epicardium)
-between the two layers there is a small amount of lubricating serous fluid (heart beats in a minimised friction environment)
What is in between the two layers of the pericardium? What is the function?
The space between the visceral and parietal layers contains a thin film of pericardial fluid that allows the heart to beat in a minimal-friction environment.
What are the four recognised borders of the heart?
Right
Left
Inferior
Superior
Describe the four borders of the heart
Left border = left ventricle (& some of left atrium)
Right border = right atrium
Superior border = right and left atria (& great vessels)
Inferior border = left and right ventricles
Describe problems associated with accumulation of fluid in the pericardial sac
Rapid fluid accumulation in the pericardium can cause cardiac tamponade, a severe compression of the heart that impairs its ability to function
Cardiac tamponade resulting from pericardial effusion can be life-threatening.
Describe the relationship between the pericardium and the phrenic nerves
Sensory fibres from the phrenic nerve supply the central part of the diaphragm, including the surrounding pleura and peritoneum. The nerve also supplies sensation to the mediastinal pleura and the pericardium.
What are the three layers that large blood vessels have and their structure?
Tunica intima – consists of endothelium and the internal elastic lamina. Tunica media – smooth muscle with elastic fibres. This layer is responsible to vasoconstriction and vasodilation. Tunica adventitia (also called externa) – connective tissue consisting of collagen and elastic fibres. It can anchor the vessel to nearby structures.
What is the cardiac / thoracic ratio?
The cardiothoracic ratio is the ratio of the transverse diameter of the heart to the maximum internal diameter of the thoracic cavity.
What does an increased cardiac / thoracic ratio mean?
Increased cardiothoracic ratio describes widening of the cardiac silhouette on a chest radiograph. This is of use when making an assessment of a PA chest x-ray since the AP chest x-ray causes the artefactual magnification of the heart and the cardiothoracic ratio is altered.
What different imaging techniques can be used to assess cardiac structure and functioning?
X-rays Ultrasound Nuclear CMR CT
Define haemodynamics
Physical factors that control blood flow
What is the difference between serum and plasma?
Plasma is the fluid collected from unclotted blood
Serum is the fluid collected from clotted blood
Name some diseases where whole blood viscosity changes
Polycythaemia
Thrombcythaemia
Leukaemia
Define flow
Volume transferred per unit time
Define pressure
Force per unit area
Define resistance
Measure of difficulty of flow
What is the relationship between flow, conductance and pressure difference?
F = K * P F = flow K = conductance P = change in pressure
What is Darcy’s law and what is it similar to?
Flow = change in pressure / resistance
Analogous to Ohm’s law (I = V/R)
What is vascular resistance?
Resistance to flow in blood vessels
What is the relationship between flow and resistance?
What is the relationship between resistance and change in pressure?
Flow and resistance are reciprocally related (if one goes up the other one goes down)
At any given flow, increased resistance = increase in pressure gradient
What is laminar flow?
Laminar flow is smooth, silent maintaining energy
Typical of most arteries, arterioles, venules and veins
Moves in ‘stream lines’ = centre has the greatest velocity
What is turbulent flow?
Turbulent flow is disorganised and noisy
Energy is lost
Causes of turbulent flow
Branching of a vessel
Change in direction of blood
Stenosis (eg. atheroma building up in a vessel)
Define stenosis
Abnormal discrete narrowing of an artery or open area of a heart valve
What is Reynolds number?
There is a pressure increase beyond which flow can match it linearly
What are the main factors of resistance to flow?
Diameter
Length of vessel
Viscosity
What contributes the greatest component of total peripheral resistance?
Smallest arteries and arterioles = biggest jump in pressure across vessel class
Define velocity
The distance fluid moves in a given time
Why is lower velocity useful in capillaries?
Diffusion of nutrients
Delivering of oxygenated blood
What is pulse pressure?
The difference between systolic blood pressure and diastolic blood pressure
PP = SBP - DBP
What is mean arterial pressure?
MAP = DBP + 1/3 PP
What is the relationship between cardiac output, heart rate and stroke volume?
CO = HR * SV
What is the relationship between mean arterial pressure, cardiac output and total peripheral resistance?
MAP = CO * TPR
Define pulse
Shock wave that arrives slightly before the blood itself
What factors govern pulse pressure?
Volume of blood ejected
Compliance of the arterial system
What is a strong pulse described as and reasons why someone may have one?
What is a weak pulse described as?
Strong pulse = bounding
Bradycardia, vasodilation and elite athletes
Weak pulse = thready
Relating to blood flow, what can be heard and what can be felt?
THRILL can be felt
BRUIT can be heard
What are the names of the sounds generated when a blood pressure cuff changes the flow of blood through the artery?
Korotkoff sounds (change from laminar flow to turbulent flow)
Describe taking blood pressure using a cuff
1) pressure in cuff > systolic pressure: no blood flow can take place
2) pressure in cuff < systolic pressure: blood can begin to flow, but artery is partially compressed -> flow is turbulent and korotkoff sounds can be heard
3) pressure in cuff < diastolic pressure: sounds will disappear as blood can now flow in a laminar fashion
What is the effect of gravity on blood pressure?
Pressure below the level of the heart greater and above the level of the heart lower
Effects of gravity maintains a pressure gradient allowing blood flow from heart to foot when standing
Pooling of blood occurs below the level of the heart upon standing in the venous system
Postural hypotension: dizziness upon standing -> lower stroke volume
Factors that affect venous pressure
Venous constriction
Changing body position
Total peripheral resistance
Cardiac output
Factors that affect arterial pressure
Total peripheral resistance
Cardiac output
Name the 5 surfaces of the heart
Anterior = right ventricle Inferior = left and right ventricles Posterior = left atrium Right pulmonary = right atrium Left pulmonary = left ventricle
List 4 functions of the pericardium
Fixes the heart in the mediastinum and limits its motion
Prevents overfilling of the heart
Lubrication
Protection from infection
