Histology 2016-2017Department of Anatomy &Histology: Dr.Rajaa Ali*************************************************************

Cardiovascular SystemIntroductionThe human body is made up of 70 to 80 trillion cells. All of these cells need to be fed oxygen and nutrients. These are provided by the cardiovascular system (CVS), (fig. ).The body’s cells must also get rid of waste materials. The CVS does this jobtoo, at the same time it delivers oxygen and nutrients.

12.1 Major Organs of the Cardiovascular System The heart pumps blood. It beats 60 to 90 times every minute for whole life.Each beat pumps blood throughout the body. The blood flows through blood vessels.12.2 Structures of the Heart1. superior vena cava (VE-nah KAY-vah)2. pulmonary semilunar valve (POOL-mon-ayr-ee seh-me-LOO-nar VALV)3. right atrium (AY-tree-um)4. tricuspid valve (trigh-KUS-pid)5. right ventricle (VEN-trih-kul) 6. inferior vena cava (VE-nah KAY-vah)7. septum (SEP-tum)8. left ventricle (VEN-trih-kul)9. bicuspid (bye-KUS-pid) or mitral (MY-tral) valve10. aortic semilunar valve (ay-OR-tick seh-mee-LOO-nar VALV)11. left atrium12. aorta (ay-OR-tah)

The large blood vessels include the aorta, superior vena cava (SVC), inferior vena cava (IVC), and pulmonary artery.

Heart ChambersThe heart contains four cavities. They are calledchambers. The upper chambers are called atria (singular is atrium). Thelower chambers are called ventricles (singular is ventricle).Figure also illustrates that the heart is separated into the right and left sections.The wall dividing them is called the septum.

In Brief

Atria are the upper chambers.Ventricles are the lower chambers.Septum separates the right and left sides of the heart.

Heart ValvesThere are four valves in the heart. They open to let blood in, and then they close tightly to ensure there is no backward flow of blood (Figure ).Two of the valves are called semilunar valves (Figure 12-4A). The semilunar valve at the entrance of the pulmonary artery is called the pulmonary semilunar valve. The one at the entrance of the aorta is called the aortic semilunar valve.

In Brief

Semilunar valvespulmonary valveaortic valveAtrioventricular (AV) valvestricuspid valvebicuspid valve

Walls of the HeartThe heart has three walls (Figure ). The outer wall is the epicardium um). The middle wall is the myocardium . It is composed of the muscle that contracts the ventricles, pumping the blood out of the heart. The innerwall is the endocardium .Pericardium: The heart is surrounded by a sac called the pericardium.(Figure). It has two layers. Pericardial fluid lies between the layers. This fluid prevents friction between the two layers when the heart beats.

In Brief

Epicardium outermost wall of the heartMyocardium muscle wall of the heartEndocardium innermost wall of the heartPericardium sac surrounding the heart

How the Heart BeatsElectrical impulses stimulate the heart to beat. Unlike other nerve impulses, they do not come from the brain. They are created in special tissue in the atrium called the pacemaker. They then follow a trail through the heart to the Purkinje fibers, which extend throughout the ventricles. When the impulses reach the Purkinjefibers, the ventricles contract and push blood out of the heart into arteries.The trail the impulses follow from the pacemaker to the ventricles is called the conduction pathway. It is illustrated in Figure . When the electrical impulses follow the conduction pathway properly, the heart will beat in a regular way, 60 to 90 beats per minute. This is called normal sinus rhythm.The electrical activity of the heart can be recorded in a procedure called electrocardiography (Figure). The record of such a test is called an electrocardiogram . It is usually referred to as an ECG or EKG. Figure

shows a record of a normal ECG. The spikes or waves on the record represent the strength of contraction of the atria and ventricles.

In Brief

Electrical impulses travel through the heart from the pacemaker to the Purkinje fibers, causing the ventricles to contract and the heart to beat. An ECG monitors the electrical impulses as they travel through the heart.

Blood Pressure and PulseOn each ventricular contraction, blood is pumped through an artery. It pushes on the artery wall. The pressure this creates is called blood pressure (BP).Blood pressure is measured with an instrument called a sphygmomanometer.When the blood pressure (BP) is taken manually, as shown in Figure 12-9, a stethoscope is used to listen to blood sounds. When using a digital sphygmomanometer, which is automated, no stethoscope is used.

A normal blood pressure reading is written like this: 115/75 mm Hg. The first number is the systolic (SIS-tohl-ick) pressure, the pressure against the arterial wall when the ventricles contract and pumps blood out of the heart. The second number is the diastolic pressure, the pressure against the arterial wall when the ventricles relax. High blood pressure is called hypertension (high-per-TEN-shun).Low blood pressure is called hypotension . If high blood pressure affectsthe heart, the condition is called hypertensive heart disease.A BP reading between 120/80 to 139/89 is considered prehypertension. A reading over 140/90 is hypertension. BP of 90/60 is hypotension.Many experts now suggest that 115/75 is the optimum. The arteries dilate and constrict in unison with the heartbeat. These movements, knownas a pulse, can be readily detected at several sites. Figure 12-10 illustrates the following pulse sites: temporal, carotid, brachial, radial, femoral, popliteal, and dorsalis pedis.

In BriefSphygmomanometer

A device used to measure blood pressure. Optimum blood pressure reading is 115/75 mm Hg.

In Brief