Human Anatomy and Physiology Unit IV Circulation and Body Defense Part III Blood Vessels

Blood Vessel Topics Components of the blood vessel system Basic structures of blood vessels Blood distribution Capillary exchange Factors affecting blood pressure and flow Control of blood pressure and flow Circulatory routes

Components of the Blood Vessel System The circulatory system is composed of: Arteries Arterioles Capillaries Venules Veins

Components of the Circulatory System Heart Arteries Arterioles Capillaries Venules Veins

Circulatory System Systemic Circulation Pulmonary Circulation

Blood Vessel Topics Components of the blood vessel system Basic structures of blood vessels Blood distribution Capillary exchange Factors affecting blood pressure and flow Control of blood pressure and flow Circulatory routes

Basic Blood Vessel Structure Specializations of the blood vessel wall gives different types of vessels their unique functions.

Basic Blood Vessel Structure Tunica Interna Endothelium Basement membrane Internal elastic lamina Tunica Media Smooth muscle External elastic lamina Tunica Externa Connective tissue

Figure 21.1 Comparative structure of blood vessels

Arteries Arterial Tunica Interna Arterial Tunica Media Internal elastic lamina Strength Elasticity Arterial Tunica Media Elastic Fibers Compliance Thick smooth muscle Vasoconstriction Vasodilation External elastic lamina Arterial Tunica Externa Thick and protective

Arteries Functional Properties Elasticity Contractility

Arteries Elastic Muscular Well-defined elastic laminae Thick tunica media dominated by elastic fibers Act as pressure reservoirs Muscular Well-defined internal elastic lamina but thin external elastic lamina Thick tunica media dominated by smooth muscle Maintain vascular tone

Figure 21.2 Pressure reservoir function of elastic arteries https://www.youtube.com/watch?v=PLM-e_TAhmI

Elastic Artery

Muscular Artery

Figure 21.1 Comparative structure of blood vessels

Anastomoses Collateral circulation End arteries Occlusion = necrosis

Arterioles Almost microscopic Control blood flow into capillary beds

Arterioles Arteriolar Tunica Interna Arteriolar Tunica Media Poorly defined internal elastic lamina Arteriolar Tunica Media Thin layer of smooth muscle Precapillary sphincter Arteriolar Tunica Externa Well innervated for good control of BF

Arterioles Figure 21.3 Arterioles, capillaries, and venules Metarteriole Precapillary sphincter Resistance vessels Figure 21.3 Arterioles, capillaries, and venules

Figure 21.3 Arterioles, capillaries, and venules Decrease blood flow by contracting sphincters = closing taps = limit blood flow Control blood flow to a tissue as need be

Capillaries Microscopic; smallest vessels in body Arterial outflow  venous return Microcirculation Metarteriole  capillaries  postcapillary venules Distribution varies with metabolic activity of tissues. Exchange vessels

Capillaries Capillary Tunica Interna Capillary Tunica Media Endothelium Basement membrane Capillary Tunica Media None Capillary Tunica Externa

Figure 21.1Comparative structure of blood vessels

Three Types of Capillaries Continuous Leaky Muscle, CT, lungs, CNS, Skin Fig 21.4

Three Types of Capillaries 2. Fenestrated Leakier Kidneys, S.I, brain, eye, endocrine glands Fig 21.4

Three Types of Capillaries 3. Sinusoids Leakiest Liver, red bone marrow, spleen Fig 21.4

1-2 layers of smooth muscle Venules (muscular) Microscopic Pass blood to veins Venule Tunica Interna Endothelium Basement membrane Venule Tunica Media 1-2 layers of smooth muscle Venule Tunica Externa Sparse

Venules No more gas exchange Act as blood reservoirs Helps regulate blood volume

Postcapillary Venules Tunica Interna Endothelium Basement membrane Tunica Media None Tunica Externa Sparse Microscopic

Postcapillary Venules Pass blood into muscular venules Permit exchange of nutrients and wastes between blood and interstitial fluid Very porous - Permit white blood cell immigration

Veins Venous Tunica Interna Venous Tunica Media Venous Tunica Externa Endothelium Valves Large lumen Basement membrane No internal elastic lamina Venous Tunica Media Much thinner than arteries No external elastic lamina Venous Tunica Externa Thickest layer

Veins Range from 0.5mm-30mm Return blood to heart Little compliance and vascular tone Valves Regulate blood flow Vascular (venous) sinuses Varicose veins

Blood Vessel Topics Components of the blood vessel system Basic structures of blood vessels Blood distribution Capillary exchange Factors affecting blood pressure and flow Control of blood pressure and flow Circulatory routes

Blood Distribution Because systemic veins and venules contain more than half the total blood volume, they are called blood reservoirs.

Figure 21.6 Blood distribution in the cardiovascular system 21_06