Describe the flow of blood through the body from the heart to capillary beds and return to the heart.
2) Describe the flow of blood through the body from the heart to capillary beds and return to the heart.
The heart is a large muscular organ which constantly pushes oxygen-rich blood to the brain and extremities and transports oxygen-poor blood from the brain and extremities to the lungs to gain oxygen.
The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.
Blood comes into the right atrium from the body, moves into the right ventricle and is pushed into the pulmonary arteries in the lungs. After picking up oxygen, the blood travels back to the heart through the pulmonary veins into the left atrium, to the left ventricle and out to the body's tissues through the aorta.
The blood when pumped away from the heart, it travels through the aorta to arteries, arterioles, and the capillary beds.
Flowing through the capillary beds, blood almost reaches every cell in the body, and is controlled to divert blood according to the need of the body.
After oxygen is used up, the deoxygenated blood flows to the lungs, where it is reoxygenated and sent through the veins back to the heart.
- With the help of each rhythmic pump of the heart, blood is pushed under high pressure and velocity away from the heart, initially along the main artery, the aorta. In the aorta, the blood travels at 30 cm/sec.
- From the aorta, blood flows into the arteries and arterioles and, ultimately, to the capillary beds. As it reaches the capillary beds, the rate of flow is dramatically (one-thousand times) slower than the rate of flow in the aorta.
- While the diameter of each individual arteriole and capillary is far narrower than the diameter of the aorta, the rate is actually slower due to the overall diameter of all the combined capillaries being far greater than the diameter of the individual aorta.
- The slow rate of travel through the capillary beds, which reach almost every cell in the body, assists with gas and nutrient exchange.
- Blood flow through the capillary beds is regulated depending on the body’s needs and is directed by nerve and hormone signals. For example, after a large meal, most of the blood is diverted to the stomach by vasodilation of vessels of the digestive system and vasoconstriction of other vessels.
- During exercise, blood is diverted to the skeletal muscles through vasodilation, while blood to the digestive system would be lessened through vasoconstriction. The blood entering some capillary beds is controlled by small muscles called pre-capillary sphincters. A sphincter is a ring-like band of muscle that surrounds a bodily opening, constricting and relaxing as required for normal physiological functioning.
- If the pre-capillary sphincters are open, the blood will flow into the associated branches of the capillary bed. If all of the sphincters are closed, then the blood will flow directly from the arteriole to the venule through the thoroughfare channel. These muscles allow the body to precisely control when capillary beds receive blood flow.
- At any given moment, only about 5-10 percent of our capillary beds actually have blood flowing through them.
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