1. Introduction

Fig. 21-1

II. The Anatomy of Blood Vessels

1. Tunica Interna (Intima)

• innermost layer
• include endothelium, connective tissue and underlying elastic fibers (internal elastic membrane)

1. Tunica Media

• middle layer
• concentric sheets of smooth muscle in a loose connective tissue
• collagen and elastic fibers bind three layers together
• thickest layer of an artery
• separated by externa by a band of elastic fibers (external elastic membrane)

1. Tunica Externa (Adventitia)

• outermost layer
• form C.T. sheath around vessel

1. Arteries vs. Veins

• walls of arteries thicker - tunica media contains more smooth muscle and elastic fibers
• arterial walls contract when not opposed by pressure - arteries are more resilient
• endothelium of an artery folded when the artery is contracted
• arteries and veins usually run together

1. Arteries

• Elasticity and Contractility
• Vasodilation and Vasocontraction

1. Elastic arteries

• conducting arteries
• transport large volumes of blood away from heart
• pulmonary trunk, aorta, common carotid, subclavian
• walls are extremely resilient
• large amounts of elastic fibers

1. Muscular Arteries

• medium-sized arteries
• distribute blood to skeletal muscle and internal organs
• more smooth muscle than elastic arteries
• external carotid, brachial and femoral arteries

1. Arterioles

• poorly defined tunica externa
• tunica media consists of one or two layers of smooth muscle fibers
• resistance vessels (change diameter to affect blood flow)

1. Capillaries

• gas exchange
• do not contain a tunica media or tunica externa

1. Continuous Capillaries

• endothelial cells connected by intermediate junctions
• Connective tissue, muscle tissue, neural tissue
• permit exchange of water, small molecular weight solutes and lipid-soluable materials
• Plasma proteins are too big to fit through cell junctions

1. Fenestrated Capillaries

• contain pores for exchange of larger molecules
• kidney, choroid plexus, hypothalamus and pitiutary

1. Capillary Beds

• interconnected network of capillaries
• entrance guarded by a pre-capillary sphincter

1. Veins

• collect blood from tissues and organs and return it to the heart
• blood pressure lower than in the corresponding artery

1. Venules

• collect blood from capillary beds

1. Medium-sized Veins

• tunica media thin
• tunica externa thick

1. Large Veins

• superior and inferior vena cavae
• all tunica layers present

1. Venous Valves

• blood pressure low in veins
• can’t oppose force of gravity
• valves prevent backflow - allow one-way blood flow
• valves => folds of tunica interna
• movement of muscles pushes blood toward heart

III. Cardiovascular Physiology

1. Pressure

• Hydrostatic pressure => pressure of the blood inside pushing out against the wall of the vessel
• circulatory pressure => pressure difference between base of aorta and right atrium
• arteries > capillaries > veins

1. Resistance

• pressure of the wall of the vessel squeezing in on the blood

1. Vascular resistance

• friction between blood and vessel walls
• change with alterations in vessel length and diameter
• Increase length - Increase resistance
• Increase diameter - Decrease resistance

1. Viscosity

• Increase viscosity - Increase resistance
• polycythemia

1. Turbulence

• Increase turbulence - Increase resistance
• Atherosclerosis

1. Overview of Circulatory Pressures and Exchanges

1. Fluid Compartments

1. Intravascular
2. Extracellular (Interstitial)
3. Intracellular

blood vessel

1. Capillary-Interstitial Fluid Dynamics

1. Diffusion - movement from area of high to low concentrations
2. Filtration - net flow of water due to effect of pressure
3. Hydrostatic Pressure - fluid pressure
4. Osmotic Pressure - pressure that accompanies a movement of water across a membrane
5. Oncotic Pressure - pressure that results from a difference in protein concentration
6. Normal capillary dynamics

IV. Cardiovascular Regulation

• Local, central and hormonal regulation

1. Local Regulation

1. Local Vasodilation (increase blood flow)

• Decreased oxygen or pH
• Increased carbon dioxide, potassium or hydrogen ions
• Nitric oxide
• Inflammatory agents (histamine)
• Temperature increase

1. Local Vasoconstrictors (decrease blood flow)

• Prostaglandins
• Thromboxanes

1. Neural Regulation

1. Vasomotor Centers (Sympathetic)

1. Vasoconstriction

• Norepinephrine

1. Vasodilation

• Nitric oxide (ACh)
• Nitroxidergic (NO is the neurotransmitter)

1. Cardiac Centers

1. Baroreceptors - monitor degree of stretch of vessel

• Carotid sinuses - head
• Aortic sinuses - systemic circuit
• Atrial reflex - monitor blood in/blood out ratio

1. Chemoreceptors - monitor levels of oxygen, carbon dioxide or pH

• Carotid - monitor arterial blood to head
• Aortic - monitor arterial blood to systemic circuit
• Medulla - monitor CSF

1. Hormonal Regulation

1. ADH

• decrease in blood pressure
• vasoconstriction/absorption of water at kidneys

1. Angiotensin II

• release of renin in response to a decrease in blood pressure
• vasoconstriction/increase cardiac output
• stimulate secretion of ADH/stimulate thirst

1. Erythropoietin

• decrease in blood pressure/decrease in oxygen content of blood
• stimulate red cell production

1. Atrial Natriuretic Peptide (ANP)

• right atrium/stretch receptor
• decrease blood volume/decrease blood pressure
• increase water loss at kidneys/decrease thirst/ decrease ADH
• vasodilation