Chapter 19 Anatomy & Physiology Blood Vessels: Notes Chapter 19 Anatomy & Physiology

The blood vessels of the body form a closed circulatory system that begins and ends at the heart. In the 1620’s, scientist William Harvey discovered how the circulatory system works, before his discovery, it was thought that the blood moved like a tide, moving out from the heart then returning.

The 3 major types of blood vessels are the arteries, capillaries and veins. As the heart contracts. It forces blood out under high pressure into arteries which then branch into smaller arteries called arterioles. The arterioles then branch into smaller vessels called capillaries, which supplies all the body’s cells with oxygen and nutrients.

The capillaries then collect into small veins called venules, which then converge into veins that carry the blood back to the heart. This is the order the blood flows in the blood vessels. The adult human body has about 60,000 miles of blood vessels that cover every area of the body.

Because arteries carry blood away from the heart, they are said to branch or fork as they form smaller divisions. Veins on the other hand carry blood to the heart and so they are said to merge or join as they collect into larger vessels. Only capillaries have direct contact with cells and directly serve their nutrients needs.

Arteries Arteries can be divided into 3 groups – elastic arteries, muscular arteries and arterioles. Elastic arteries – These are thick walled arteries near the heart – the aorta and its branches. These arteries are the largest in diameter ranging from 1 to 2.5 cm. They are also elastic which allow them to expand and recoil to accommodate changes in blood flow. Muscular arteries – Deliver blood to specific body organs and account for most of the “named” arteries. Range in size form 1/3mm to 1cm. Arterioles – The smallest arteries, smaller than 1/3mm. These supply the capillary beds.

Capillaries The smallest blood vessels. Their average length is 1mm and they are just large enough in diameter for red blood cells to flow through single file. Their role is the exchange of materials between the blood and the cells. There are 3 types of capillaries: Continuous – Most common type. Common in skin and muscles. Fenestrated – Found primarily in the small intestines where they absorb food molecules. Sinusoids – Found mainly in liver, bone marrow and endocrine organs. Have larger pores. Capillary beds – interweaving network of capillaries that supply a region with nutrients. Why do sinusoids have large pores? The excrete

Veins Venules are the smallest veins. They are microscopic and carry nutrient-spent blood to the veins. 65% of the body’s blood supply is found in veins. We have more veins than arteries and the blood in them is under much less pressure so their walls are much thinner. Veins have valves in them to help ensure blood does not back flow. This is important due to the lack of pressure. Varicose veins are veins that become overly dilated because of faulty valves. Can be caused by standing in one position too often, obesity or pregnancy.

Varicose veins

Hemorrhoids – varicose veins in the anus caused by over straining during bowel movements and childbirth. Blood flow – The volume of blood flowing through the circulatory system at a given time. Blood Pressure – The force per unit area exerted on a vessel wall. Measured in mm of mercury. Blood pressure is usually measured by the auscultatory method. The cuff is placed around the arm and tightened to limit blood flow, the nurse slowly relieves pressure until they can start to hear blood flow with a stethoscope. This is the systolic pressure. They keep releasing pressure until the sound disappears, this is the diastolic pressure.

Hypotension – Low blood pressure. Systolic blood pressure is below 100 Hypotension – Low blood pressure. Systolic blood pressure is below 100. Usually no cause for concern. Can be cause by poor nutrition or anemia. Hypertension – High blood pressure. Major causes are: Diet – High fat, high cholesterol and high sodium can increase blood pressure. Obesity – The more fat, the more blood vessels, the harder the heart has to work. Age – The onset of hypertension usually appears after 40. Race – More common in blacks than whites. Least common in Asians. Heredity – If parents have it you have a greater risk. Stress – Especially common in “hot-tempered” people. Smoking – Nicotine enhances the blood vessels vasoconstrictors effects.

Pulse – The alternating expansion and recoil of elastic arteries during each heart beat. Circulatory shock – This is any condition where the blood vessels are inadequately filled and blood can’t circulate normally. Hypervolemic shock – results from large scaled blood loss. Vascular shock – blood volume is normal but poor circulation is a result of extreme vasodilation (blood vessels dilate) causes drop in blood pressure. Most common causes are; anaphylactic shock (a systemic allergic reaction) and septicemia (a severe systemic bacterial infection)

Vocabulary (use your book to define these terms on pg. 741)   Aneurysm - ______________________________________________________ Angiogram - __________________________________________________ Diuretic - ___________________________________________________ Phlebitis - ____________________________________________________ Phlebotomy __________________________________________________