Cardiovascular System Introduction For Nursing

The Heart
•    The heart is a cone-shaped, muscular organ located between the lungs behind the sternum.
•    The heart muscle forms the myocardium,
•    the inner lining of the myocardium is called Endocardium and the outer layer cells is called the Epicardium.
•    The pericardium (visceral) is the outer membranous sac with lubricating fluid.
•    The heart has four chambers: two upper, thin-walled atria, and two lower, thick-walled ventricles.
•    The ventricle are, the chambers that eject blood in to arteries. The functions of the atrium are to receive the incoming blood from the vein.
•    The septum is a wall dividing the right and left sides.
•    Coronary arteries: the vessels that supply blood to the heart muscle.

Cardiac Valves:
Cardiac valves permit blood to flow in only one directions through
•    Atrioventricular Valves:
1] Tricuspid valve: separates the Rt atrium from the
Rt  ventricle
2] Bicuspid valve [Mitral valve]: lies  Lt atrium and
Lt ventricle.
•     Semilunar valves:
1] Pulmonic valve: the valve between the Rt ventricle
and the pulmonary artery.
2] Aortic valve: the valve between the Lt ventricle and
the aorta.
Internal view of the heart

CardioDiagram

The Heartbeat
•    Each heartbeat is called a cardiac cycle.
•    When the heart beats occur, the two atria contract together, then the two ventricles contract; then the whole heart relaxes.
•    Systole is the contraction of heart chambers; diastole is their relaxation.
•    The heart sounds, lub-dup, are due to the closing of the atrioventricular valves, followed by the closing of the semilunar valves.

Conducting system of the heart
Intrinsic Control of Heartbeat

•    The SA (sinoatrial) node, or pacemaker, initiates the heartbeat approximately 60-100 impulses / min.
•    The AV (atrioventricular) node conveys the stimulus and initiates contraction of the ventricles, located right Atrial wall, similar to S.A node but with impulses about 40-60/ min..
•    The signal for the ventricles to contract travels from the AV node through the atrioventricular bundle to the smaller Purkinje fibers.

Conduction system of the heart
Control-of-heart-by-heart-conduction-system_

Extrinsic Control of Heartbeat
•    A cardiac control center in the medulla oblongata speeds up or slows down the heart rate by way of the autonomic nervous system branches: parasympathetic system (slows heart rate) and the sympathetic system (increases heart rate).
•    Hormones epinephrine and norepinephrine from the adrenal medulla also stimulate faster heart rate.

The Vascular Pathways
•    The cardiovascular system includes two circuits:
•    Pulmonary circuit which circulates blood through the lungs, and
•    Systemic circuit which circulates blood to the rest of the body.
•    Both circuits are vital to homeostasis.

The Pulmonary Circuit
•    The pulmonary circuit begins with the pulmonary trunk from the right ventricle which branches into two pulmonary arteries that take oxygen-poor blood to the lungs.
•    In the lungs, oxygen diffuses into the blood, and carbon dioxide diffuses out of the blood to be expelled by the lungs.
•    Four pulmonary veins return oxygen-rich blood to the left atrium.

The Systemic Circuit
•    The systemic circuit starts with the aorta carrying O2-rich blood from the left ventricle.
•    The aorta branches with an artery going to each specific organ.
•    The vein that takes blood to the vena cava often has the same name as the artery that delivered blood to the organ.
Note:
•    Stroke volume: the amount of blood ejected per heart beat.    (Cardiac output)  CO = SV X HR

Passage of Blood Through the Heart

blood_flow

•    Blood follows this sequence through the heart: superior and inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk and arteries to the lungs → pulmonary veins leaving the lungs → left atrium → bicuspid valve → left ventricle → aortic semilunar valve → aorta → to the body.

External heart anatomy

heart_external

Diagnostic Test
1] Cardiac enzyme:
–     CPK : creatinine phosphate kinase. 50-350
–     LDH: lactic dehydrogenase 100-135
–     SGOT: 0-40
–    Blood level rise in 2 to 3 days.
2] Total cholesterol, Triglycerides and lipoproteins to evaluate atherosclerotic diease.
3] Serum electrolyte:
–    Na : ↓ Na : hyponatremia.    ↑ Na : hypernatremia.
–    Ca: ↑ Ca : causes ECG changes or dysrhythmias
–    K: ↓ K cause cardiac irritability.
–    Glucose: many cardiac patients also have serum glucose level will ↑ with stress.
4] Chest x-ray:
     Usually used to determine size and position of the heart. E.g CHF, placement of cardiac catheters.
5] Cardiac catheterization:
     Invasive diagnostic procedure in which one or more catheters are introduced into the heart, used to assess the patency of the patient coronary arteries.
6] Angiography:
     x-ray examination of blood vessels.
7] Rt heart catheterization:
     Involve passing a catheter from femoral vein- Rt atrium → Rt .ventricular → tricuspid valve.
8] Lt heart catheterization:
   The same but passing a catheter through femoral artery.

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