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Physiology of the Heart and Circulation, Summaries of Physiology

The physiology of the heart and circulation. It describes the capillaries, the circulation, and the properties of the myocardium. It also explains the cardiac action potential and the cardiac cycle. useful for students studying physiology, anatomy, and medicine.

Typology: Summaries

2020/2021

Available from 06/12/2022

enriquediaz99
enriquediaz99 🇺🇸

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Physiology :
System Nervous :
III.1.2.3. Capillaries
Are tiny blood vessels, 50 times smaller than a hair, connecting arteries
and veins together. Blood flows through them very slowly, allowing
exchanges between the blood and the cells. Oxygen and nutrients are
delivered to the cell while waste products from the cell are collected by
the blood.
III.2 The circulation
The heart is in fact a double pump: one pump, the right heart. The other,
the left heart. Each of the pumps has specific functions:
- The right heart: is the pump that handles the pulmonary circulation
to send blood (not oxygenated) to the lungs.
- The left heart: is the pump that deals with the systemic circulation, which
is responsible for distributing blood (oxygenated) to the whole body
(Figure 32).
III.3. Properties of the myocardium
III.3.1. Nodal tissue and cardiac automatism
The heart has a mechanical activity which is electrically controlled.
Cardiac automaticity: existence of myocardial cells spontaneously
producing an electrical signal that stimulates neighboring cells. This set of
cells constitutes the nodal tissue.
Two cell clusters:
Sinus node or Keith and Flack.
Atrioventricular node or Aschoff-Tawara node.
Extension by the His bundle, division into 2 branches: Purkinje fiber
network. Birth of the heart stimulation process in the sinus node.
Sinus node = pace-maker imposes its rhythm to the whole heart = sinus
rhythm.
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Physiology :

System Nervous : III.1.2.3. Capillaries Are tiny blood vessels, 50 times smaller than a hair, connecting arteries and veins together. Blood flows through them very slowly, allowing exchanges between the blood and the cells. Oxygen and nutrients are delivered to the cell while waste products from the cell are collected by the blood. III.2 The circulation The heart is in fact a double pump: one pump, the right heart. The other, the left heart. Each of the pumps has specific functions:

  • The right heart: is the pump that handles the pulmonary circulation to send blood (not oxygenated) to the lungs.
  • The left heart: is the pump that deals with the systemic circulation, which is responsible for distributing blood (oxygenated) to the whole body (Figure 32). III.3. Properties of the myocardium III.3.1. Nodal tissue and cardiac automatism The heart has a mechanical activity which is electrically controlled. Cardiac automaticity: existence of myocardial cells spontaneously producing an electrical signal that stimulates neighboring cells. This set of cells constitutes the nodal tissue. Two cell clusters: Sinus node or Keith and Flack. Atrioventricular node or Aschoff-Tawara node. Extension by the His bundle, division into 2 branches: Purkinje fiber network. Birth of the heart stimulation process in the sinus node. Sinus node = pace-maker imposes its rhythm to the whole heart = sinus rhythm.

Propagation to the atria which contract en bloc. Relayed by the atrioventricular node, reaches both ventricles through the His bundle and the Purkinje network (figure 33). III.3.2. The cardiac action potential III.3.2.1. The electrocardiogram Any working muscle is the site of a depolarization wave, i.e. a current that can be recorded by two judiciously placed electrodes (figure 34). The heart, like any other muscle, produces a current. Because of its crucial role in the body and the complexity of its functioning, the electrical study of the heart, or electrocardiography, has become very important in cardiac physiology and pathology. The electrocardiogram is the result of recording the electrical activity of the heart, studied from <> different points. The more numerous and overlapping these different points of study, called leads (points where electrodes are placed), the more accurate the <> of cardiac activity thus obtained. Electrocardiogram (ECG): a recording of the electrical activity of the heart. Cardiac electrical activity can be tracked from the skin (Marey, Waller 1880). Each phase of the beat has a particular electrical trace. III.3.2.2. The cardiac cycle Alternating contractions and relaxations: pump propelling the blood. The cardiac cycle is the pattern of repeated contractions and relaxations (figure 35). Two main phases: diastole and systole. Blood flows from a high pressure system to a low pressure system. Phase 1: General diastole - Passive flow of blood from atria to ventricles. Phase 2: Atrial systole - Contraction of the atria and active filling of the ventricles. Phase 3: Atrial diastole - relaxation of the atria. Phase 4: Ventricular systole - Contraction of the ventricles and passive blood flow into the atria. Ejection of blood into the aorta Phase 5: Ventricular diastole: relaxation of the ventricles.