Heart Flashcards
Elastic Artery- function
Very large arteries near the heart which have elastic walls. During systole they expand to store bolus of blood leaving the ventricle; then during diastole they push blood out into the arterial tree by elastic recoil. Thus they have smooth pulsatile flow of blood leaving the ventricle.
Elastic Artery-structure
Many thin sheets of elastin in the middle tunic
Muscular Artery- function
Distribute blood around the body around the body at high pressure (and lungs at medium pressure). Rate of blood flow is adjusted by using smooth muscle to vary the radius of the vessel.
Flow is proportional to the fourth power of radius
A small change in radius has a large effect on flow rate
Muscular artery- structure
Many layers of circular smooth muscle wrapped around the vessel in the middle tunic
Arteriole- function
Control blood flow into capillary beds. They have a thicker muscular wall relative to their size than any other blood vessel. These are the vessels in the circulation where the greatest pressure drop occurs, and where there is the greatest resistance to flow. The degree of constriction of arterioles throughout the body determines:
Total peripheral resistance which in turn affects mean arterial blood pressure.
Arteriole-structure
Between one and three layers of circular smooth muscle wrapped around the vessel in the middle tunic
Capillary- function
Tiny vessels which are thin-walled to allow exchange of gases, nutrients, and wastes between blood and the surrounding tissue fluid. Blood flow is slow to allow time for exchange to occur. Capillaries are leaky vessels; plasma escapes (but not blood cells). Most of the lost plasma is immediately recovered due to an osmotic gradient.
Capillary- structure
Diameter just wide enough to admit one red blood cell. The capillary well is a single layer of endothelium (with an external basement membrane). No smooth muscle is present within the wall, (therefore no ability to adjust diameter), and no connective tissue
Cardiac cycle
Ventricular filling Atrial contraction Isovolumetric ventricular contraction (systole) Ventricular ejection Isovolumetric ventricular relaxation
Venule- function
Low-pressure vessels which drain capillary beds. During infection and inflammation, venules are the site where white blood cells leave the blood circulation to attack bacteria in the tissue alongside. The drawing shows a neutrophil which, having first adhered to the endothelium, is now squeezing its way between two endothelial cells to exit the vessel.
Venule- structure
Small venules have usual endothelium plus a little connective tissue. Larger ones have a single layer of smooth muscle.
Vein- function
Thin-walled, low-pressure vessels which drain blood back to the atria (except portal veins which drain blood to another capillary bed). Their walls are thin and soft; they stretch easily (i.e. They’re compliant). A small change in venous blood pressure causes a large change in venous volume. Therefore veins act as a reservoir which stores blood, (64% of blood occurs in systemic veins and venules compared to 13% in systemic arteries and arterioles).
Vein-structure
Similar to a muscular artery but much thinner-walled for their size, (much less muscle and connective tissue). Larger veins (especially in the legs) have valves which prevent back flow. As leg muscles alongside the vein alternately contract and relax during walking, the system acts as a venous pump which returns blood to the right atrium.
Coronary arteries-function
Downstream from the aortic valve and supply the muscle of the heart (myocardium). They are ordinary small muscular arteries but critically important because of the tissue they supply.
Deoxygenated blood is drained from the myocardium by cardiac veins which return the blood to the right atrium.
Coronary arteries- damage
If a coronary artery is narrowed to about 20% of its normal cross-section by atheroma, significant obstruction of blood flow occurs. During exercise the myocardium supplied by the diseased artery runs low on oxygen (ischemia) causing chest pain (angina). Severe ischemia results in death (infarction) of local area of myocardium. Sometimes artery-to-artery junctions (anastomoses) between small penetrating branches of the main coronary arteries widen slowly so that an ischaemic area of muscle can be supplied by a distant artery.
Dyspnoea
Discomfort during breathing, consciousness of laboured breathing
P wave
The P wave in ECG represents atrial depolarisation which results in atrial contraction
QRS complex
Combination of 3 of the graphical deflections seen on a typical ECG. It corresponds to the depolarisation of the right and left ventricles of the heart
T wave
Positive deflection after each QRS complex
-Represents ventricular repolarisation
Autonomic nervous system
Part of the nervous system, responsible for the control of the bodily functions not consciously directed e.g. Heart beat
Parasympathetic nervous system
Part of the autonomic nervous system
Responsible for regulating the body’s unconscious actions
Sympathetic nervous system
Part of the autonomic nervous system
Activates during ‘fight or flight response’
Vagus nerve
Originates in the Medulla oblongata- a nerve that supplies nerve fibres to the heart
Chronotrophy
Things that change heart rate
