Page 155 - 84 human physiolofy part-1

The Cardiovascular System

myocardium depends on its blood supply, and with age there is greater likelihood that arthrosclerosis
will narrow the coronary arteries. Arthrosclerosis is the deposition of cholesterol on and in the walls of
the arteries, which decreases blood flow and forms rough surfaces that may cause intravascular clot
formation High blood pressure (hypertension) causes the left ventricle to work harder. It may enlarge
and outgrow its blood supply, thus becoming weaker. A weak ventricle is not an efficient pump, and
may progress to congestive heart failure. This process may be slow or rapid. The heart valves may
become thickened by fibrosis, leading to heart murmurs and less efficient pumping. Arrhythmias are
also more common with age, as the cells of the conduction pathway become less efficient.

Shock

Physiological stress can be any kind of injury form burns, to broken bones; the body's response to
stress is categorized in two phases the ebb phase (early phase) begins immediately after the injury. And
the second phase is about 36 to 48 hours after injury is called the flow phase. In the ebb (shock) phase
there is Inadequate circulation, decreased insulin level, decreased oxygen consumption, hypothermia
(low body temperature), hypovolemia (low blood volume), and hypotension (low blood pressure). In
the flow phase there is increased levels of catecholamine, glucocorticoids, and glucagons, normal or
elevated insulin levels, catabolic (breakdown), hyperglycemic (high blood sugar), increased oxygen
consumption/respiratory rate, hyperthermia (high body temperature) fever sets in, hypermetabolism,
increased insulin resistance, increased cardiac output.

Premature ventricular contractions (PVC's)

Excitation occurs through the SA node to the AV node if there are abnormalities or drug
interference that malfunctions the AV node the ventricles will not receive the initiating stimuli and the
autorhythmic cells in the bundle branches begin to initiate actions on their own rate becoming the
pacemakers for the ventricles. This in turn will cause conduction disorder. With conduction that causes
problems with the bundle branches there is the right and the left premature ventricular contractions.
Right is most common and may go untreated. Left is always a serious problem and must be treated.

Intrinsic Control of heartbeat

• SA node (located in the right atrium near the entrance of the superior vena cava)
• AV node (located at the base of right atrium)

• AV bundle (located in the intraventricular septum between the two ventricles that go in two directions
right and left bundle branches that leave the septum to enter the walls of both ventricle)
• Bundle Branches (the branching off the septum to the walls of the ventricles that run into the purkinje
fibers that then make contact with ventricular myocardial cells to spread the impulse to the rest of the
ventricles)

Electrocardiogram

• The P is the atrial depolarization

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