Blood Vessels

1. Blood Vessels

2. Anatomy: 3 layers Tunica externa (adventitia): outer layer; dense to loose connective tissue lotsa collagen, bits of elastin, few smooth muscles (veins) Tunica media: middle layer; concentric rings of smooth muscle within CT framework External elastic membrane in arteries (thickest layer) Tunica intima: inner layer; simple, squamous epithelium (endothelial lining), basement membrane, some elastic fibers Internal elastic membrane in arteries

3. Artery vs. Vein

5. Arteries vs. Veins Arteries Contractile (thick, muscular walls) & elastic Passive changes in diameter In response to changes in BP Active changes in diameter Vosoconstrict Vasodilate Veins Few muscles & little elastic Passive blood collectors Little diameter change Larger lumen than corresponding arteries

7. Elastic arteries Large diameter, conducting arteries. Take blood away from heart. Ex: Aorta, pulmonary trunk, common carotid, subclavian, & common iliac arteries Tunica media has many elastic fibers, few smooth muscle cells

8. Muscular arteries Medium-sized, distribution arteries Distribute blood to skeletal muscles & internal organs Ex: external carotid, brachial, mesenteric, femoral Muscular (smooth) tunica media, few elastic fibers

9. Arterioles Small arteries, resistance vessels 1 or 2 layers of smooth muscle; usually incomplete Change diameter in response to sympathetic & hormonal stimulation or 02 levels. Produce resistance to blood flow and affect BP

10. Capillaries Simple, squamous epithelial cells + CT layer Blood flow regulated by precapillary sphincters. Only vessel that allows exchange between blood & interstitial fluid

11. Continuous capillaries Widespread Limited permeability Permit diffusion of small solutes & lipid soluble material

12. Fenestrated capillaries Distribution limited to areas of absorption or secretion Very permeable Permit rapid diffusion of H20 & large solutes Surrounding glands, intestinal tract, filtration areas Hypothalamus, pituitary, thymus

13. Venous return Valves & skeletal muscle contraction return blood to the heart

14. Blood flow Aorta Arteries Arterioles Capillaries Venules Veins Vena cava

15. Capillary exchange About 10 billion capillaries in the body Blood pressure Forces fluid (but not dissolved solutes) into interstitial space Osmosis Fluid (lacking dissolved blood proteins) moves back into capillaries along solute concentration gradient

16. Capillary exchange

17. Effects of diameter & distance F ? ?P/R Increased Pressure = increased Flow Increased Resistance = decreased Flow Cardiovascular Pressure Blood Pressure (BP); arterial ?P = 65mm Hg Capillary hydrostatic pressure (CHP) ?P = 17mm Hg Venous pressure; ?P = 18mm Hg

18. Effects of diameter & distance F ? ?P/R Increased Resistance = decreased Flow Vascular Resistance Vessel Length Longer vessel = more friction; more SA in contact with blood Diameter Smaller diameter = more friction; more blood in contact with vessel walls Viscosity; R caused by interaction of suspended molecules & solutes Turbulence; irregular surfaces, high flow rates, changes in diameter.

19. BP changes with distance From arterioles to capillaries: BP drops quickly ?P drops quickly

20. Taking BP

21. Local control of blood vessels Sphincters contract or relax based on demand for: nutrients (AA, glucose, fatty acids) Dissolved gases (O2, CO2 load, lactic acid) Additional capillaries grow in to area to satisfy increased energy demands

22. Nervous Control of BP Controlled by vasomotor center (pons & medulla oblongata, MO) Carried out primarily by sympathetic vasoconstrictor fibers Constitutively active = Vasomotor tone Allows shunting of blood to/from major regions of body

23. Regulation of Arterial Pressure Baroreceptor reflex Stretch receptors; autonomic control Chemoreceptor reflex Stimulated by change in CO2, O2 or pH; autonomic control Hormonal control Adrenal Medullary; Renin-Angiotensin-Aldosterone (RAA); Vasopressin; Atrial Natiuretic; autonomic control

24. Acronyms Heart rate (HR) Blood Pressure (BP) Stroke Volume (SV) Medulla oblongata (MO) Vasomotor Center (VaC) Cardiovascular Center (CaC) Vasomotor Tone (VaT)

25. Baroreceptor Carotid sinus & aortic arch baroreceptors Increase stretch = increased AP frequency to MO Increases HR, SV, VaT Increase BR

26. Chemoreceptor Carotid & aortic bodies have receptors Communicate with MO O2 drops, or CO2 or pH increases Increase AP frequency CaC & VaC decrease parasympathetic stimulation & increases sympathetic stimulation of heart Increase HR, SV, VaT Increase BP and blood flow to lungs = MORE O2

27. Hormonal Adrenal Medullary Mechanisms that increase sympathetic stimulation of heart & vessels, also stimulate adrenal medulla Adrenal medulla releases epinephrine Epinephrine increases HR, SV; causes vasoconstriction of blood vessels in skin & viscera; vasodilation of blood vessels in skeletal & cardiac muscle

28. Hormonal RAA BP drops kidney secretes renin which turns on angiotensin Angiotensin increase vasoconstriction; BP rises Angiotensin encourages adrenal medulla to produce aldosterone. Aldosterone increases Na+ and H20 reclamation @ kidney; BP rises

29. Hormonal Vasopressin (ADH) mechanism plasma solute concentration increases or BP decreases ADH released from pituitary ADH stimulates vasoconstriction & water reclamation at kidney; BP rises