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| Friday, August 04, 2006 |
| Circulatory System |
THE CIRCULATORY SYSTEM
The circulatory system, also called the vascular system, consists of blood, heart, and blood vessels. The circulatory system is close circuited (i.e., there is no opening to external environment of the body).
Function
- To move blood between the cells and the organs of the integumentary, digestive, respiratory, and urinary system that communicate with the external environment of the body.
- This function is facilitated by the heart pumping blood through blood vessels.
- The blood travels throughout the body transporting nutrients and wastes, and permitting the exchange of gases (carbon dioxide and oxygen).
Component
i. Blood
- Is fluid tissue composed of formed elements (i.e., cells) suspended in plasma. It is pumped by the heart through arteries, capillaries, and veins to all parts of the body. Total blood volume of the average adult is 5 to 6 liters.
ii. Heart
- The heart is a hollow, muscular organ, somewhat larger than the closed fist, located anteriorly in the chest and to the left of the midline. Lying obliquely in the chest, much of the base of the heart is immediately posterior to the sternum.
iii. Blood Pressure
- Is the pressure the blood exerts on the walls of the arteries. The highest pressure is called systolic pressure when the heart is in systole, or contraction. A certain amount of blood pressure is maintained in the arteries even when the heart is relaxed i.e. diastolic pressure. The difference between systolic and diastolic pressure is known as pulse pressure.
- Normal blood pressure vary with an individual's age, weight, and general condition e.g. young adults systolic pressure is 120 to150 mm of mercury, and the diastolic pressure is between 70 and 90 mm of mercury. On average, women have lower blood pressure than men.
i.v Blood Vessels
- Is a closed circuit of tubes that transport blood between the heart and body cells. The several types of blood vessels include arteries, arterioles, capillaries, venules, and veins.
- Blood Vessel Classifications
- Arteries and arterioles—distributors
v Arteries are elastic tubes constructed to withstand high pressure that carry blood away from the heart to all parts of the body.
v The smooth muscles of arteries and arterioles constrict and dilate in response to electrical impulses received from the autonomic nervous system.
- Arteries and Arterioles Capillaries—exchangers
v At the end of the arterioles is a system of minute vessels that vary in structure, but which are spoken of collectively as capillaries from which the tissues of the body are fed.
v There are approximately 60,000 miles of capillaries in the body. As the blood passes through the capillaries, it releases oxygen and nutritive substances to the tissues and takes up various waste products to be carried away by venules.
v Venules continue from capillaries and merge to form veins
- Veins and venules—collectors
v Veins and venules form the venous system that comprised of vessels that collect blood from the capillaries and carry it back to the heart.
v The force of muscles contracting adjacent to veins aids in the forward propulsion of blood on its return to the heart. Valves, spaced frequently along the larger veins, prevent the backflow of blood.
v The walls of veins are similar to arteries, but are thinner and contain less muscle and elastic tissue.
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posted at 10:54 AM   |
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