The human cardiovascular system consists of the heart, blood vessels and blood. The heart is located in the mediastinum on the left side of the thorax, posterior to the sternum and is divided into four chambers. Two atria (left and right) are located superiorly in the heart, and inferior to these are the powerful left and right ventricles (Vickers). A ventricular septum divides the left and right ventricles, and the atrial septum separates left and right atria. The heart and lungs are contained within the pericardium, a membranous sac filled with a serous fluid that serves to reduce friction during heart contractions.
Physiology Deoxygenated blood is returned from the body via the large vena cavae and enters the right atrium. During diastole, blood flows downwards, through a one-way atrioventricular valve to the right ventricle. Systolic heart contractions eject blood from the right ventricle into the cardio-pulmonary circuit. Blood is oxygenated in the lungs and returns to the left atrium via the pulmonary vein. Oxygen rich blood is sent to the muscular left ventricle, where it is ejected into the body during systole. Twenty major arteries carry blood into the tissues, branching into smaller vessels called arterioles and capillaries.
As blood in the capillaries becomes nutrient-deprived, it is collected by venules, which join to form the larger veins that transfer blood back to the heart, where the cycle begins again (Vickers). Contraction of the heart is controlled by electrical impulses (action potentials) which are generated by the sinoatrial (SA) node. Located superior to the right atrium, the SA node initiates impulses that cause the myocardium of the atria to contract. The impulses are propagated through bundles of nervous tissue to the atrioventricular (AV) node.
The AV node checks the integrity of the signals and passes them on to the ventricular myocardium, which then contracts. Whilst electrical impulses occur at a standard rate, hormonal changes, stress or physical demands may cause the heart rate to increase or decrease. Pathology Since the cardiovascular system provides oxygen and nutrients to all body tissues, pathologies of the cardiovascular system are serious and have wide-reaching consequences. All the components of the cardiovascular system are subject to pathology.
Congenital abnormalities, such as valvular or septal defects are relatively common and affect the structural integrity of the heart. These are often corrected surgically. Cardiac arrhythmias are a group of conditions that occur when the heartbeat is irregular, faster (tachycardia) or slower (bradycardia) than usual. Fibrillation occurs when the contractile units of the myocardium do not operate in synchronicity. Atrial fibrillation often indicates a serious underlying pathology, but is not typically life-threatening. By contrast, ventricular fibrillation can lead to cardiac arrest and should be treated as a medical emergency.
Cardiovascular disease is the leading cause of death in the United States. The condition refers to disease of the entire cardiovascular system, however the major pathology is a chronic inflammatory response (atherosclerosis) in the walls of the arteries. This inflammation occurs in response to the deposition of lipoproteins. Lipoproteins form hard, plaques on the arterial walls and cause them to harden and narrow (stenosis). The body may attempt to compensate for stenosis by arterial enlargement, which weakens the arterial walls. Since arteries are high pressure vessels, weakened arterial walls often fatally rupture (aneurysm).
When fragments of arterial plaques dislodge, they commonly travel to the heart and lodge in the small-gauge coronary arteries that supply the heart. This causes a sudden decrease in coronary blood flow and a heart attack (infarction) typically results. Reproductive system Anatomy Both the male and female reproductive systems include primary sex organs (gonads) and secondary organs. The female gonads (ovaries) are located in the ovarian fossae on either side of the uterus in the lateral walls of the pelvic cavity. The ovaries are held in place by peritoneal ligaments and are connected to the uterus by the fallopian tubes.
Other female sex organs include the external genitalia (vagina, labia minora and majora and the clitoris) and the mammary glands, or breasts. The primary sex organs of the male reproductive system are the testicles (or testes) which are contained within the scrotal sac on the exterior of the body. Each testicle is partitioned into lobules, each of which contains highly coiled seminiferous tubules. Spermatic fluid is collected by short efferent ducts, which exit the testes via the urethra. Secondary sex organs in the male include the penis and accessory glands, including the prostate and bulbourethral glands.