BIO210Y5 Chapter Notes - Chapter 17: Posterior Interventricular Sulcus, Superior Vena Cava, Pulmonary Valve

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18 Feb 2016
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Heart Notes
19.1 – THE HEART HAS A SUPERIOR BASE, AN INFERIOR APEX, AND FOUR BORDERS
The heart is located near the anterior chest wall, directly posterior to the sternum
The base of the heart is at its superior border, where the great veins and arteries are
attached
oThe base sits posterior to the sternum at the level of the third costal cartilage
The inferior, pointed tip of the heart is the free apex
The base of the heart forms the superior border
The right border of the heart is formed by the right atrium
The left border is formed by the left ventricle and a small portion of the left
atrium
oThe left border extends to the apex, where it meets the
inferior border
The inferior border is formed mainly by the inferior wall of the right ventricle
19.2 THE HEART WALL CONTAINS CONCENTRIC LAYERS OF CARDIAC MUSCLE
TISSUE
Pericardium The pericardium is the serous membrane that lines the pericardial cavity and covers
the heart.
Parietal Pericardium
The parietal pericardium is the portion of the serous membrane that lines the outer
wall of the pericardial cavity. The parietal pericardium is reinforced by a dense fibrous
layer; together they form the pericardial sac that surrounds the heart.
Epicardium
The epicardium, or visceral pericardium, covers the outer surface of the heart. This
portion of the serous membrane consists of an exposed mesothelium and an underlying
layer of areolar tissue that is attached to the myocardium.
Myocardium
The myocardium, or muscular wall of the heart, forms both atria and ventricles. This
middle layer contains cardiac muscle tissue, blood vessels, and nerves. The
myocardium consists of concentric layers of cardiac muscle tissue.
Endocardium
The inner surfaces of the heart, including those of the heart valves, are covered by the
endocardium, a simple squamous epithelium and underlying areolar tissue. The
squamous epithelial lining of the cardiovascular system is called an endothelium. The
endothelium of the heart is continuous with the endothelium of the attached great
vessels.
Each cardiac muscle cell is connected to several others at specialized sites known as intercalated discs
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Like skeletal muscle fibers, cardiac muscle cells contain organized myofibrils, and the presence of many
aligned sarcomeres gives the cells a striated appearance
They are almost totally dependent on aerobic metabolism to obtain the energy they need to continue
contracting
The sarcoplasm of a cardiac muscle cell contains many mitochondria and abundant reserves of myoglobin that
store oxygen
Because these cells are metabolically very active and have high demand for oxygen and nutrients, cardiac
tissues are richly supplied with capillaries
At an intercalated disc, the plasma membranes of two adjacent cardiac muscle cells are extensively
intertwined and bound together by gap junctions and desmosomes
oThese connections help stabilize the positions of adjacent cells
The gap junctions allow ions and small molecules to move from one cell to another
oThis creates a direct electrical connection between the two muscle cells
An action potential can travel across an intercalated disc, moving quickly from one cardiac muscle cell to
another
19.3 – THE HEART IS LOCATED IN THE MEDIASTINUM, AND ENCLOSED BY THE PERICARDIAL CAVITY
The heart, surrounded by the pericardial cavity, sits in the anterior portion of the mediastinum, the region
between the two pleural cavities
The pericardial sac surrounds the heart
oThe pericardial sac consists of a dense network of
collagen fibers
oIt attaches to the central tendon of the diaphragm
and sternum, and stabilizes the positon of the heart
and associated vessels within the mediastinum
The parietal pericardium lines its inner surface
The pericardial cavity contains 15-50mL of pericardial fluid,
secreted by the pericardial membranes
oThis fluid acts as a lubricant that reduces friction between the
opposing surfaces as the heart beats
Pathogens can infect the pericardium, producing the condition pericarditis
oThe inflames pericardial surfaces rub against one another, producing a distinctive scratching sound
that can be heard through a stethoscope
19.4 – THE BOUNDARIES BETWEEN THE CHANBERS OF THE HEART CAN BE IDENTIFIED ON ITS EXTERNAL
SURFACE
Shallow grooves, called sulci, mark the boundaries between the atria and ventricles and between the left and
right ventricles
The connective tissue of the epicardium generally contains substantial amounts of fat, especially along the
sulci
These sulci also contain the arteries and veins that carry blood to and from the cardiac muscle
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19.1
19.2
19.3
19.4
19.5
19.6
19.7
19.9
19.10
19.16
19.12
19.11
19.5 – THE HEART HAS AN EXTENSIVE BLOOD SUPPLY
The heart works continuously, so cardiac muscle cells require reliable supplies of oxygen and nutrients
Although a great volume of blood flows through the chambers of the heart, the myocardium needs its own,
separate blood supply
The coronary circulation supplies that blood to the muscle tissue of the heart
During maximum exertion, blood flow to the myocardium may increase to nine times that of resting levels
The left and right coronary arteries originate at the base of the ascending aorta, where blood pressure is
highest in the systemic circuit
Myocardial blood flow is not steady, it peaks while the heart muscle is relaxed and almost ceases while it
contracts
Each time the left ventricle contracts, it forces blood into the aorta
The arrival of additional blood at elevated pressures stretches the elastic walls of the aorta
When the left ventricle relaxes, pressure decreases, and the walls of the aorta recoil
oThis recoil, called elastic rebound, pushes blood both forward, into the systemic circuit, and
backward, into the coronary arteries
The combination of blood pressure and elastic rebound ensures a continuous flow of blood to meet the
demands of active cardiac muscle tissue
19.6 – INTERNAL VALVES CONTROL THE DIRECTION OF BLOOD FLOW BETWEEN THE HEART CHAMBERS
The atria are separated by the interatrial septum
The ventricles are separated by the much thicker interventricular septum
Atrioventricular valves (AV valves), folds of fibrous tissue, extend into the openings between the atria and
ventricles
oThese valves permit blood flow in one direction only: from the atria to the ventricles
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