anatomy 2 exam 2

• function of blood vessels:

  • transport and distribute blood throughout the body
  • deliver oxygen, nutrients, and hormones to cells and carry away CO2 and wastes
  • return blood to heart
• tunica interna: surrounds lumen, in direct contact with blood; endothelium, basement membrane and internal elastic lamina
• tunica media: smooth muscle fibers and external elastic lamina; stretch and recoil, and exchange diameter of lumen through vasoconstriction or vasodilation
• tunica externa: anchor vessel to surrounding fibers; elastic and collagen fibers
• blood vessel walls from deep to superficial: tunica interna, tunica media, tunica externa
• arteries carry blood away from heart
• elastic arteries:

  • close to the heart
  • have highly elastic walls to accommodate the surge of blood and project blood onward when ventricles are relaxing
• muscular arteries:

  • have lots of smooth muscle in tunica media for greater vasoconstriction and vasodilation to adjust blood flow to various regions of the body
• anastomosis: form alternate route of blood flow to body part through collateral circulation
• arterioles: abundant microscopic vessels from small arteries branching from muscular arteries that deliver blood to capillaries
• in arterioles, the tunica interna is thinner with fenestrated internal elastic lamina
• metarteriole

  • tapers toward junction with capillary
  • precapillary sphincter (single muscle fiber) at junction regulates blood flow through capillary bed by regulating resistance
  • also effects blood pressure
• capillaries: network of microscopic vessels that connect outflow from heart (arterioles) to return to heart (venules); exchange of materials between blood and interstitial fluid bathing tissue cells
• capillary bed: 10-100 capillaries arise from single metarteriole, blood flow controlled by precapillary sphincters of metarteriole
• thoroughfare channel: distal end with no smooth muscle that provides capillaries direct route to venule
• autoregulation: tissues automatically adjust blood flow to match its metabolic demands
• continuous capillaries: endothelial cells for continuous tubes, intercellular clefts between adjacent cells allow only a few substances to move across (like in blood brain barrier)
• fenestrated capillaries: endothelial cell membranes have many fenestrations, allow greater exchange of materials, such as in kidneys for filtration
• sinusoids capillaries: endothelial cells with large fenestrations, incomplete basement membrane, and large intercellular clefts; allows all components of blood to pass through
• capillary exchange is the movement of substances between blood and interstitial fluid

  • diffusion
  • across endothelial cell membranes: gases and lipid soluble
  • through intercellular clefts or fenasterations: water soluble
  • transcytosis: pinocytic vesicles across a membrane
• influences on exchange in capillaries

  • filtration: capillary blood pressure (hydrostatic) "pushes" fluid out of capillary into interstitial fluid
  • reabsorption: blood colloid osmotic pressure (due to plasma proteins) "pulls" fluid into capillary bed
  • filtration greater at arteriole end, reabsorption greater at venule end
• most capillaries reunite to form venules

  • thin walls that don't maintain shape
  • merge to form veins
  • close to capillary, very porous, function as exchange of nutrients and wastes and movement of WBCs from bloodstream into inflamed or infected tissue
  • acquire thicker walls as enlarge with no exchange of nutrients
• in some parts of body, blood passes from one capillary bed to another instead of a venule, portal system

  • portal vein connects the two capillary beds
  • in hepatic and hypophyseal (hypothalamus and pituitary)
• veins: bring blood from tissues back to the heart, thinner tunica interna and tunica media than arteries, lack elastic lamina

  • distensible with variations in volume and pressure
  • not able to withstand high pressure
• veins have valves

  • flap-like cusps of tunica interna into lumen
  • prevent backflow of blood in segments of vein
• vascular sinus:

  • vein with thin endothelial wall, such as coronary sinus
  • lacking smooth muscle, so unable to alter its diameter
• venous return: volume of blood flowing back to the heart through systemic veins, limited pressure remaining from heart pump
• skeletal muscle pump:

  • skeletal muscle compression pushes blood through valve closer to heart, "milking"
  • valves further away close as some blood is pushes back against it
• respiratory pump: during inhalation, diaphragm moves downward, decreases pressure in thoracic cavity and increase pressure in abdominal cavity

  • blood flows into decompressed veins and into right atrium
• at rest, 64% of blood volume is in systemic veins and venules
• blood reservoir

  • blood can be diverted quickly as needed arises
  • brainstem sympathetic impulses can vasoconstrict veins, allowing greater blood volume to flow to skeletal muscle as needed during increased activity
  • similar mechanism during hemorrhage, to counteract blood loss and associated decrease in blood volume and pressure
• blood flow in any given tissue

  • varies with blood pressure gradient and resistance
  • in all systemic vessels is equal to cardiac output
• blood pressure: hydrostatic pressure exerted by blood on blood vessel walls

  • generated by ventricular contraction
  • measures in mmHg
• systemic blood pressure: highest arterial pressure during systole
• diastolic blood pressure: lowers arterial pressure during diastole
• measuring blood pressure is highest at aorta and falls profressibly with fluctuations disappearing at the capillaries
• blood pressure influenced by cardiac output, blood volume, and vascular resistance
• vascular resistance: opposition to blood flow due to friction between blood and walls of blood vessel

  • an increase decreases blood flow and increase blood pressure
• 3 factors affecting vascular resistance

  • size of lumen: higher resistance as vasoconstrict
  • blood viscosity: higher resistance as ratio of blood cells and plasma proteins increases
  • total blood vessel length: higher resistance if longer
• systemic vascular resistance: total peripheral resistance from all systemic vessels, slight change in arteriole diameter has large effect