Anatomy Notes Essay

Chapter 17: Blood Vessels 1. Hemostasis * Stops blood loss from damaged blood vessel walls * Establishes framework for tissue repairs * Usually divided into 3 phases but continuous process 1. Vascular phase 2. Platelet phase 3. Coagulation phase 2. Events of the vascular phase * Endothelial cells contract exposing underlying basal lamina to bloodstream * Endothelial cells release chemical factors, local hormones, and endothelins (stimulate smooth muscle and vascular spasms) * Endothelial cells become sticky * In capillaries, cell can reduce flow in vessel * Can cause platelets to attach 3. Events of the platelet phase * Begins with platelet attachment to endothelial cells, basal lamina, exposed collagen fibers, and each other * Platelets become activated and accumulate large numbers 4. Events of coagulation phase * Starts 30 seconds or more after damage * Involves complex sequence of steps leading to conversion of circulating fibrinogen to insoluble fibrin * Blood cells and platelets are trapped in fibrin network * Blood vessels conduct blood between heart and peripheral tissues * Two circuits 1. Pulmonary circuit (to and from lungs) 2. Systemic circuit (to and from rest of the body) * Each circuit begins and ends with the heart * Occurs in sequence * Specific vessels * Arteries (transport blood away from the heart * Veins (transport blood to the heart) * Capillaries (exchange substances between blood and tissues) * Interconnect smallest arteries and smallest veins * General circulation pathway through circuits 1. Right atrium (entry chamber) 2. Pulmonary circuit * Pulmonary arteries to pulmonary capillaries to pulmonary veins 3. Left atrium 4. Systemic circuit * Systemic arteries to systemic capillaries to systemic veins * Both arteries and veins have three layers 5. Tunica intima (tunica interna) * Endothelial cells in contact with blood 6. Tunica media * Contains concentric sheets of smooth muscle * Capable of vasoconstriction or vasodilation * Most variable layer 7. Tunica externa * Connective tissue sheath with collagen and elastic fibers * Five general blood vessel classes 8. Arteries * Elastic arteries (large vessels close to the heart that stretch and recoil when heart beats) * Muscular arteries (medium sized arteries, distribute blood to skeletal muscles and internal organs) 9. Arterioles * Poorly defined tunica externa and tunica media only 1-2 smooth muscle cells thick 10. Capillaries * Thin, exchange vessels 11. Venules * Small veins lacking tunica media 12. Veins * Medium sized veins (tunica media is thin but tunica externa is thick with longitudinal collagen fibers * Large veins ( superior + inferior vena cava and tributaries having thin tunica media) * Typical capillary consists of tube of endothelial cells with delicate basal lamina * Neither tunica media nor externa are present * Average diameter= 8 um * About the same as an RBC * Three types of capillaries 13. Continuous capillaries 14. Fenestrated capillaries 15. Sinusoid capillaries 1. Continuous capillaries * Endothelium is a complete lining * Located throughout body in all tissues except epithelium and cartilage * Permit diffusion of water, small solutes and lipid-soluble materials. 2. Fenestrated capillaries * Contain windows or pores penetrating endothelium * Permit rapid exchange or water and larger solutes * Examples: capillaries in brain and endocrine organs, adsorptive areas if GI

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