The Circulatory System 2 Flashcards
what is the arctic arch?
fat covered on the heart
what is the heart?
a hollow, 4 chambered muscular organ
where is the heart located?
in mediastinum
(section of thoracic cavity)
midline between sternum + vertebrae
what is the heart surrounded by?
double layered membrane - pericardium
- inner, visceral pericardium covers full heart (epicardium)
- outer parietal pericardium attaches to vessels, sternum + diaphragm
- pericardial activity contains 30-50 ml serous fluid
the heart functions as 2 separate functional pumps.
describe this?
- each pump divided into upper chamber + lower chamber
- upper chambers open into lower chambers via valve (tricuspid / mitral)
- left + right pumps separated by septum
right sided pump
pulmonary circulation + gaseous exchange
- receives DE-OXYGENATED blood from systemic circulation
- pumps into lungs for re-oxygenation + CO2 removal
ventricle opens into pulmonary artery via pulmonic valve
left sided pump
systemic circulation + O2 + nutrient supply
- receives re-oxygenate blood from lungs (p.circulation)
- pumps into systemic circulation
ventricle opens into aorta via aortic valve
what are the 2 main types of blood vessels in the heart?
- great cardiac vessels
- the coronary vessels
great cardiac vessels
carry blood to + from heart chambers and systemic + pulmonary circulations
inc:
- superior + inferior vena cava
- pulmonary artery
- pulmonary veins
- aorta
coronary vessels
= coronary circulation - specialised blood supply system of heart
inc:
- left + right coronary arteries
- coronary sinus, great/middle/anterior + posterior cardiac veins, thebesian veins
aorta
- accepts output of left ventricle
- 1st vessel of systemic circulation
- has highest systolic pressure ~140mmHg
pulmonary artery
- accepts output of right ventricle
- 1st vessel of pulmonary circulation
- has peak pressure ~25mmHg
superior vena cava / inferior vena cava
largest vessels returning deoxygenated blood to right atrium from s.circulation
pulmonary veins
largest vessels returning oxygenated blood to left atrium from p.circulation
coronary arteries + veins
supply blood to cardiac muscle tissue
branch off from aorta above aortic valve
veins drain blood into right atrium
coronary circulation
myocardial O2 + nutrient demand
- heart beats constantly through life
- needs constant + adequate supply of oxygen + nutrients
coronary circulation
myocardial O2 + nutrient supply
- supplied by special network of blood vessels
- made of left + right coronary arteries
coronary circulation
delicate balance between demand + supply
- reduced coronary blood flow during systole
- disproportionate share of cardiac output
- high O2 extraction -> low O2 reserve
what are the benefits of having a one-way opening valve?
- prevents back flow of blood
- ensures unidirectional flow of blood through heart
AV valves
- TRISCUPID valve - bet. right atrium + ventricle
- BICUSPID/MITRAL valve - bet. left atrium + ventricle
semilunar valves
- PULMONIC valve - bet. right ventricle + pulmonary artery
- AORTIC valve - bet. left ventricle + aorta
AV heart valves in function process
- blood returns to heart
- fills atria
- puts pressure against AV vales -> open
- as ventricles fill, AV valves flap -> hang limply into ventricles
- atria contract -> forcing extra blood into ventricles
- ventricles contract -> forcing blood against AV valves cusps
- AV valves close
- papillary muscles contract + chordae tendineae tighten
- prevents valve flaps everting into atria
semilunar heart valves in function process
- ventricles contract, intraventricular pressure rises
- blood pushed up against SL valves—> open
- as ventricles relax, intraventricular pressure falls
- blood flows back from arteries
- fills cusps of SL valves + forces them to close
what are the 3 layers the heart wall consists of?
- endocardium
- myocardium
- epicardium
endocardium
- innermost thin lining of endothelial cells
- allows smooth flow of blood
- prevents clotting
myocardium
- middle layer - made of cardiac muscle
- forms bulk of heart wall
epicardium
- protective outer layer
- embeds coronary blood vessels
what are the 2 main SPECIALISED types of heart cells?
- contractile cells
- electrical / autorhythmic cells
contractile cells
- 99% of heart cells
- mainly in myocardium + septum
- mediate mechanical, pumping work of heart
- form interlacing bundles - arranges spirally around circumference of heart
- electrically quiescent
- comprise: atrial + ventricular muscle cells
what does electrically quiescent mean?
do not normally initiate own AP
electrical/autorhythmic cells
- don’t contract
- specialised for initiating + conducting AP -> activation + contract of muscle cells
inc: SAN, AVN, Bundle of His, purkinje fibres
cardiacs RMP
- at rest = POLARISED
(inside = NEG) - unequal distrib of ions across membrane
- opening + closing of ion channels = voltage + time-dependent
- K+ channels selectively open in memb at rest (RMP = CLOSER to K+ equilib potential)
- slow spontaneous depolarisation in automatic cells
define excitability?
ability of cardiac cells to respond to electrical stimulus by firing AP
fast AP
high conduction velocity ~1-4m/s
slow AP
slow conduction velocity ~0.02-0.1m/s
- more easily blocked
- liable to conduction failure at high repetition rates
define refractoriness?
inability of more than enough stimulus to elicit an AP
refractoriness of cardia cells
- happens for some time after previous AP
- gives rise to ABSOLUTE/EFFECTIVE ARP/ERP + relative refractory periods
what are the benefits of the refractory period?
protects against premature excitation + tetany
time of recovery for fast response
faster recovery of excitability
time of recovery for slow response
slower recovery of excitability —> inc risk of conduction block
