The Cardiovascular System Chapters 19, 20, 21

The Closed Circulatory System Blood is confined to vessels Heart pumps blood into large vessels that branch into smaller ones leading into the cells Nutrients & wastes are exchanged by diffusion

Three Major Elements: Blood Vessels, Blood, Heart I. Blood Vessels 3 layers: 1.Endothelim - epithelial inner lining (tunica intima) 2.smooth muscle & elastic connective tissue (tunica media) 3.connective tissue covering (tunica externa) Types of blood vessels: Arteries → Arterioles → Capillaries → Venules →Veins

Arteries: Carry oxygenated blood away from the heart Thicker & more elastic walls than veins Arteries are thicker and more elastic because they are closer to the pumping action of the hear

Veins: Carry deoxygenated blood towards the heart Less elastic and thinner walls than arteries Valves prevent backflow of blood When valves don’t close properly = varicose veins When you walk and your leg muscles squeeze, the venous pump works well. But when you sit or stand, especially for a long time, the blood in your leg veins can pool and the pressure in your veins can increase. If you are a susceptible individual, your veins can stretch if you repeatedly sit or stand for a long time. This stretching can sometimes weaken the walls of your veins and damage your vein valves. Varicose veins may result. Spider veins are mild varicose veins.

Capillaries: Smallest blood vessels found almost near all body cells Exchange of nutrients, gases & metabolic wastes (through diffusion) Only one cell thick – contain only tunic intima Link arteries & veins

II. Blood A. Plasma 55% of blood Liquid portion of the blood 91.5% of plasma = water Also contains dissolved hormones, antibodies, nutrients, wastes, gases

Blood Cont. B. Erythrocytes - Red Blood Cells (RBCs) Formed in the bone marrow Hemoglobin carries oxygen Do not have a nucleus and live only about 120 days

Blood Cont. C. Leukocytes – White Blood cells (WBCs) Fight infection and are formed in the bone marrow Many types

Blood Cont. D. Thrombocytes – Platelets Clot blood by sticking together via protein fibrin