Unit 6.2 - The Heart Flashcards
Harvey and Blood circulation
Until 17th century - thought that blood is produced in the liver, pumped out by the heart and consumed in other organs of the body.William Harvey usually credited with the discovery - demonstrated that blood flow through vessels is unidirectional with valves to prevent back flow and that the rate of flow through major vessels is far too high for blood to be consumed in body after being pumped by heart. Heart pumps blood out through arteries and comes back through veins.
What allowed for Harveys discovery
predicted the presence of numerous fine vessels too small to be seen with contemporary equipment. Microscopes had not been invented when he published his theory but it was only proved after his death that he was correct.
Double Circulation method
seperate circulations for the lungs (pulmonary) and for the body (systemic). Heart is a double pump with left and right sides - right side pumps deoxygenated blood to the lungs via the pulmonary artery. Oxygenated blood return to the left side in the pulmonary vein. Left side pumps this blood via the aorta to all organs apart from lungs. Deoxygenated blood pumped back through the right side in vena cava.
Arteries
convey blood at high pressure by the ventricles of the heart. Carry blood to the tissues of the body.
Tough outer coat, Thick layer containing elastic fibres (high pressure), Thick walls, Narrow lumen to help maintain high press
Veins
collect blood at low pressure from the tissues of the body and return to the atria of the heart . Thin layers of tissues (few/no elastic fibres), wide lumen (low pressure), valves, Thin walls, outer coat is thin (no danger of veins bursting)
Capillaries
carry blood through tissues, permeable walls allows for exchange of materials between the cells of tissues and the blood in capillaries. single layer of thing cells, very narrow lumen (fit in small spaces), Pores between cells (allows some plasma to leak out and form tissue fluid)
Outline the structure of cardiac Muscle
The walls of the heart made from cardiac muscle (special property - can contract on it’s own without being stimulated by a nerve). There are many capillaries in the muscular wall of the heart - blood running through these supplied by coronary arteries which branch off the aorta.
What is brought by the coronary arteries
brings nutrient rich blood as well as oxygen for cell respiration providing energy for cardiac muscle contraction
What is the purpose of valves
ensure circulation of blood flow by preventing back-flow, the atria are collecting chambers and the ventricles pumping chambers
Structure of the Heart
right side:
vena cava (inferior and superior)
right atrium
right ventricle
pulmonary artery
Left side:
pulmonary veins
left atria
left ventricle
aorta
Valves:
atrioventricular valves
semilunar valves
Outline the Cardiac Cycle
- The walls of the atria contract, pushing blood from the atria into the ventricles through atrio-ventricular valves (open). Semilunar valves are closed so the blood fills in ventricles
- walls of ventricles powerfully contact and the blood pressure rapidly rises - first causes AV valves to close and then causes SL valves to open allowing blood to be pumped out. atria starts to refill
- Ventricles stop contracting so pressure falls inside them. Semilunar valves close preventing back flow to ventricles. when the ventricular pressure drops below the atrial pressure the AV valves open
Pressure in Cardiac Cycle
atrium - stays relatively low throughout
ventricles - peak when semi-lunar valve opens
Aorta - relatively high pressure increases when SL valves open
Control of Heart Rate
specialised cardiac muscle in the wall of the right atrium acts as a pacemaker of the heart. (sinoatrial node (SA node)). SA node sends out electrical signal that stimulates contraction as it is propagated first through the walls of the atria and then through walls of ventricles. Messages carried to SA node through nerves and hormones - impulses brought from the medulla of the brain by two nerves can cause heart rate to increase /decrease.
What hormones control heart rate
Epinephrin = increases heart rate to help prepare for vigorous activity
Coronary Artery Disease
caused by fatty plaque building up in the inner lining of the coronary arteries which become occluded (narrowed) - blood flow to cardiac muscle is restricted causing chest pain - mineraly often become deposited in the plaque making it hard and rough.
