Circulatory system Flashcards
Heart Location
- The heart is located in the mediastinum (prosteriorly extends
from the sternum anteriorly to the vertebral column, and lies medially
between the two lungs and the pleural membranes that
cover them)
Heart Angle
The base of the heart is
tipped up medially and
posteriorly, while the apex
projects inferiorly and
laterally.
The Pericardium
- membrane that
surrounds and
protects the heart - helps retains its
position in the
mediastinum,
while allowing for
some freedom of
movement
The Pericardium - structure
- The pericardium is composed of a tough
outer fibrous layer lined by a delicate serous membrane. - The fibrous pericardium is a very dense
and non-flexible connective tissue that
helps protect and anchor the heart. - The inner serous pericardium is
subdivided into a parietal layer which
adheres to the outermost fibrous layer
and a visceral layer which is also viewed
as the outer surface of the heart wall. - A thin pericardial fluid lubricates the
space between the visceral and parietal
pericardium.
Layers of the Heart Wall
- The epicardium, the thin, transparent
outer layer of the heart wall, is also called
the visceral layer of the serous pericardium. - The myocardium, the thick middle layer, is
composed of cardiac muscle. - The endocardium is a simple squamous
epithelium that is known throughout the
circulatory system as endothelium
Chambers of the Heart
- The heart has 4 Chambers:
- The upper 2 are the right
and left atria. - The lower 2 are the right
and left ventricles.
The right heart consists of the
right atrium and right
ventricle, taking venous blood
from the body and pumping it
to the lungs for oxygenation.
The left heart consists of the
left atrium and left ventricle,
taking freshly oxygenated
pulmonary
blood and pumping it
systemically to the body.
Arteries
- always conduct blood
away from the heart
– mostly contain oxygenated blood. - Mostly thick-walled
- exposed to high pressures
and friction forces.
Veins
- Veins are vessels that always bring blood back to the heart
- mostly contain deoxygenated blood.
- thin-walled
- exposed to low pressures
- minimal friction forces.
major arteries attach to…
attach to the heart are the arch of the aorta ,the
pulmonary trunk and the coronary arteries
major veins that attach to…
attach to the heart
are the superior and inferior vena cava,
the four pulmonary veins and the coronary sinus.
Arterioles
- Have thin tunica interna with thin fenestrated
internal elastic lamina. - Tunica media consists of one or two layers of
smooth muscle cells - Tunica externa consists of connective tissue
and sympathetic nerve supply that can vary
rate of flow.
Capillaries
- Smallest vessels that have narrow diameters, red blood cells pass single file through the lumen of
vessel. - Allow exchange of
substances between the
blood and interstitial
fluid. - Lack both tunica media
and externa. - Single layer of endothelial cells.
Venules
- Post capillary venules have thin walls that do not readily maintain shape (exchange of nutrients & wastes, white blood cell emigration).
- Muscular venules one or two smooth muscle layers, no exchanges now possible.
- Drain capillary blood and begin return flow back toward the heart.
Blood flow (2 circuits)
- The body’s blood flow can best be understood as two circuits arranged in series. The output of one becomes the input of the other:
- Systemic circuit ejects blood into the aorta, systemic arteries, and arterioles and is powered by the left side of the heart.
- Pulmonary circuit ejects blood into the pulmonary trunk and is powered by the right side of the heart.
Coronary Circulation (info)
- Only the innermost tissues lining the chambers of the heart can derive oxygen from the blood flowing through those chambers.
- The myocardium and other tissues of the thick cardiac walls must get nutrients from blood flowing through the coronary circulation.
- Even then, only during the relaxation phase of ventricular diastole, will blood actually flow through the coronary circulation
Coronary Circulation (route)
Starting at the aortic root, the
direction of blood flow is
from the aorta to the left and
right coronary arteries (LCA,
RCA):
* LCA to anterior
interventricular and
circumflex branches
* RCA to marginal and posterior
atrioventricular branches
- Coronary veins all
collect into the coronary
sinus on the back part of
the heart: - The coronary sinus empties into the right
atrium where the deoxygenated coronary
blood joins with oxygendepleted blood from the rest of the body.
Name 2 coronary arteries:
left coronary artery & right coronary artery
Cardiac Muscle Tissue
- Cardiac muscle, like skeletal muscle, is
striated. Unlike skeletal muscle, its fibres are shorter, they branch, and they have only one centrally located nucleus. - Cardiac muscle cells connect to and
communicate with neighbouring cells
through gap junctions in intercalated discs.
Autorhythmicity
- The rhythmical electrical activity they produce is called autorhythmicity. Because heart muscle is autorhythmic, it does
not rely on the central nervous system to sustain a lifelong heartbeat. - Autorhythmic cells spontaneously depolarise at a given rate, some groups faster, some groups slower. Once a group of autorhythmic cells reaches threshold and starts an action potential (AP), all of the cells in that area of the heart also depolarise.
Cardiac Conduction
- The self-excitable myocytes that
‘act like nerves’ have the 2 important roles of forming the conduction system of the heart and acting as pacemakers within
that system. - Because it has the fastest rate of
depolarisation, the normal pacemaker of the heart is the sinoatrial (SA) node, located in the right atrial wall just below
where the superior vena cava enters the chamber.
Spontaneous Depolarization of autorhythmic fibres in the SA node firing about once every 0.8 seconds, or 75 action potentials per minute
- The action potential generated from the SA node reaches the next pacemaker
by propagating throughout the wall of the atria to the AV node in the interatrial
septum. - At the AV node, the signal is slowed, allowing the atrium a chance to mechanically move blood into the
ventricles. - From the AV node, the signal passes through the AV bundle to the left and
right bundle branches in the interventricular septum towards the apex
of the heart. - Finally, the Purkinje fibres rapidly conduct the action potential throughout the
ventricles (0.2 seconds after atrial contraction)
Co-ordinating Contractions
- Although anatomically the heart consist of individual cells, the bands of muscle
wind around the heart and work as a unit – forming a functional syncytium . - This allows the top and bottom parts to contract in their own unique way.
Describe contraction of the heart
what is stroke volume
