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HUMAN BIOLOGYLECTURE 1
HEART
− located between the lungs pointing towards the left
− 4 chambers: 2x atria (upper) + 2x ventricle (lower)
COMPARTMENTS
− valves:
o semilunar valves: pulmonary & aortic
o atrioventricular (AV) valves: left – bicuspid &
right – tricuspid → reinforced by chordae
tendineae = strong connective tissue that is also
in tendons
− coronary circulation:
o heart’s blood supply
o supplied by coronary arteries → the first branches of aorta
o drained by coronary veins → emptying into the right atrium
o myocardial infarction = heart attack, blockage in the coronary
arteries
BLOOD FLOW
− heart:
o superior vena cava & inferior vena cava carry deoxygenated
blood from the body to the right atrium → right AV valve →
right ventricle
o right ventricle → pulmonary valve → pulmonary trunk →
right & left pulmonary arteries → lungs
o lungs → right & left pulmonary veins → left atrium
o blood flows from the left atrium through the left AV valve to
the left ventricle
o the left ventricle pumps blood through the aortic valve into
the aorta
− pulmonary circuit:
o circulating blood through the lungs
o right atrium pumps deoxygenated blood into the right
ventricle which pumps it into the pulmonary trunk
o pulmonary trunk splits into right & left pulmonary arteries
which go to the lungs
, o in the lungs, pulmonary arteries branch into
arterioles which lead to capillaries → gas exchange
o pulmonary capillaries lead to venules which merge
into pulmonary veins
o 4 pulmonary veins empty into the left atrium
− systemic circuit = circulating blood through the body tissues
CARDIAC CYCLE
− atria contract together → ventricles contract together →
heart relaxation
− systole = heart contraction
− diastole = heart relaxation
− intrinsic control:
o right atrium
o sinoatrial (SA) node / pacemaker initiates the
heartbeat → sending out an electric signal → atria
contraction
o the impulse reaches the atrioventricular (AV) node →
a signal down the AV bundle and Purkinje fibers →
ventricular contraction
o ECG (electrocardiography) peaks: P = atrial
contraction, QRS = contraction of the ventricles, T =
relaxation of ventricles
− extrinsic control: cardiac control centre in the brain increases
or decreases the heart rate depending on body’s needs
BLOOD PRESSURE
− the pressure blood exerts against a blood vessel wall
− contraction of ventricles creates blood pressure → propels blood through the arteries
− highest in the aorta → gradually decreases as it flows through the vessels in the body
− slowest in the capillaries to increase the exchange of gases, nutrients, and waste → adjusted by
precapillary sphincters
− pulse = surge of blood into an artery that causes its walls to stretch and then recoil, 60-80 beats per
minute
− venous return:
o skeletal muscle contraction
o respiratory pump (breathing)
o valves
,HEART WALL
− endocardium = 1 flat layer of epithelium → endothelium, always bordering the lumen, also some
connective tissue
− myocardium = long heart muscle cells, connected with each other via intercalated disc (dark lines in
microscopy) that consists of cell-cell connections → adherens, desmosome, and gap junctions →
united contraction
− desmosome = arrangements of protein fibres tightly holding the membranes together to prevent
overstretching
− epicardium/pericardium = connective tissue, location of the big blood vessels, secretes pericardial
fluid for lubrication
− a lot of capillaries → continuous need for oxygen and glucose since the heart works nonstop
− left ventricle myocardium is thicker than the right ventricle since it pumps blood to the entire body,
not just the lungs
− ventricle myocardium is thicker than the atria one
BLOOD VESSELS
− aorta – muscular artery (1 cm) – arteriole (30-300 μm) – capillary (10 μm) – venule (30-300 μm) –
vein – vena cava (1 cm)
WALL
− tunica intima/internal layer:
o bordering the lumen
o endothelium with basal lamina
o subendothelial layer – connective tissue
o lamina elastica interna
− tunica media:
o mostly smooth muscle cells in circular layers
o surrounded by a bit of elastic and collagen fibres
− tunica adventitia/external layer:
o connective tissue – elastin and collagen fibres
o longitudinal smooth muscle cells
o vasa vasorum = small blood vessels in the external
layer
, − elastic & muscular arteries
− aorta: the only elastic artery in the body → a lot of extra amounts of elastic fibre in media since it
receives a lot of blood
− arteriole:
o small diameter
o endothelium, elastica
interna
o very few layers of
smooth muscle cells in
the media
− venule:
o small diameter
o endothelium, NO
elastica interna
o very few layers of
smooth muscle cells in
the media
− veins:
o relatively wide lumen
o valves = intima extensions helping blood flow from the bottom to the top (opposite of
gravity) towards the heart
o NO elastic interna
o thin media with circular smooth muscle cells
o thicker external layer
− capillaries:
o very small diameter
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