The cardiovascular system

The Cardiovascular system, comprising both the heart and the blood vessels, circulates blood throughout the body. It carries essential supplies of food and fuel to every living cell and exchanges them for potentially harmful waste products.

The heart is a hollow muscular organ about the size of a clenched fist. Inside, the heart is divided vertically by a muscular wall called the septum. On each side of this wall is an upper chamber (atrium) and a thicker, lower chamber (ventricle). Blood moves through each side of the heart systematically. Deoxygenated blood is delivered into the right atrium. It then enters the right ventricle, from where it is pumped out into the pulmonary artery and to the lungs. Oxygenated blood returning in the pulmonary veins flows into the left atrium. This blood enters the left ventricle and is then pumped into the aorta for circulation.

Blood is made up of plasma, red blood cells (RBC), white blood cells (WBC) and platelets.

In its passage through the body blood is carried in arteries and veins. Most arteries transport oxygenated blood, and most veins transport deoxygenated blood. The largest artery is the aorta. Arteries split into narrow branches called arteriols, which in turn divide into capillaries. It is through the very thin capillary walls that the blood gives up its oxygen and nutrients and receives carbon dioxide and wastes. Deoxygenated blood in the capillaries flows into venules, and then into veins. The two largest veins, the Venae cavae, return this blood to the heart.

To ensure reoxygenation, the circulation has a second “loop”. In this part of the system, blood rich in carbon dioxide travels from the heart along the pulmonary artery to the lungs, where carbon dioxide is exchanged for oxygen breathed in. The newly oxygenated blood is carried back to the heart along the pulmonary vein, the only vein to transport oxygenated blood.

The flow of blood in each side of the heart is controlled by a series of valves. The pumping action of the heart is achieved by the contraction of the cardiac muscle. The rhythm of the heartbeat is regulated by the pacemaker, a concentration of specialized heart tissue. The pacemaker also helps to ensure the correct sequence of activities during each heart beat. The period of contraction (systole) is followed by a period of relaxation (diastole), during which the heart refills. The electrical activity of the heart is monitored as an electrocardiogram (EKG).

Heart disease is the ordinary term used to describe a variety of heart disorders. These include arteriosclerosis, coronary heart disease, coronary thrombosis, hypertension, angina pectoris and many others.

Endocrine system

The endocrine system is a network of ductless glands of internal secretion. The endocrine glands produce and store various hormones, which are secreted directly into the bloodstream and influence body activities. There are seven glands that make up the endocrine system: thyroid, parathyroids, ovaries and testes, adrenals, pineal, pituitary, and pancreas islet cells.

The chief endocrine gland is the pituitary, governed by the hypothalamus and situated beneath the brain and divided into lobes. The front (anterior) lobe produces a group of stimulating (tropic) hormones that are carried to the thyroid, adrenals and sex glands to trigger hormone production. Other anterior pituitary hormones include prolactin, which maintains milk production from the breasts , and growth hormone. The back (posterior) lobe of the pituitary stores two hormones: vasopressin, which is carried to the kidneys to help control water content; and oxytocin, which assists the contraction of the uterus during labor and encourages the flow of milk from the breasts after the birth of a baby.

The pineal gland secretes melatonin, which may help regulate sexual development and menstruation.

Each of the adrenal glands, situated over the kidney, is divided into outer (cortex) and inner (medulla) region. The medulla makes the hormones adrenaline and noradrenaline, which help to prepare the body for “fight or flight” in responses to danger. The hormones of the cortex include steroids involved in the metabolizing of sugars and proteins and in balancing body water content.

The thyroid lies below the voicebox and secretes hormones that control the rate at which cells use nutrients, and the body burns and stores sugars. Attached to the back of the thyroid are the four parathyroid glands whose hormones regulate the amounts of calcium and phosphate in the blood.

The amount of glucose in the blood is governed by cells in the pancreas, situated beside the duodenum. The endocrine cells of the gland make two hormones: glucagons, which raises blood levels, and insulin, which decreases them. The gland also secretes digestive enzymes.

The sex glands – ovaries in a female and testes in a male – produce hormones that control the production of mature sex cells and help to determine a person’s total sexual development.

The most serious diseases affecting the endocrine glands are thyroiditis (an inflammation of the thyroid gland) and diabetes (a disorder in which the body can not make use of sugars & starches in a normal way). The science which studies the endocrine glands & the treatment of their diseases is called Endocrinology.

To affect поражать (о болезни)

Diabetes диабет

Endocrinology эндокринология

Hypothalamus гипоталамус

Thyroiditis тиреоидит