Chapter 21 - Blood Vessels and Circulation:
- Introduction
Fig. 21-1
II. The Anatomy of Blood Vessels
A. Structure of Vessel Walls
- Tunica Interna (Intima)
- innermost layer
- include endothelium, connective tissue and underlying elastic fibers (internal elastic membrane)
- 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)
- Tunica Externa (Adventitia)
- outermost layer
- form C.T. sheath around vessel
- Arteries vs. Veins
Fig. 21-2
- 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
veins often contain valves to prevent backflow
- Arteries
Fig. 21-3
- Elasticity and Contractility
- Vasodilation and Vasocontraction
- 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
- 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
- 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)
- Capillaries
- gas exchange
- do not contain a tunica media or tunica externa
- 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
- Fenestrated Capillaries
- contain pores for exchange of larger molecules
- kidney, choroid plexus, hypothalamus and pitiutary
- Capillary Beds
- interconnected network of capillaries
- entrance guarded by a pre-capillary sphincter
- Veins
- collect blood from tissues and organs and return it to the heart
- blood pressure lower than in the corresponding artery
- Venules
- collect blood from capillary beds
- Medium-sized Veins
- tunica media thin
- tunica externa thick
- Large Veins
- superior and inferior vena cavae
- all tunica layers present
- 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
- 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
- Resistance
- pressure of the wall of the vessel squeezing in on the blood
- Vascular resistance
- friction between blood and vessel walls
- change with alterations in vessel length and diameter
- Increase length - Increase resistance
- Increase diameter - Decrease resistance
- Viscosity
- Increase viscosity - Increase resistance
- polycythemia
- Turbulence
- Increase turbulence - Increase resistance
- Atherosclerosis
- Overview of Circulatory Pressures and Exchanges
- Fluid Compartments
- Intravascular
- Extracellular (Interstitial)
- Intracellular
cells
blood vessel
Capillary-Interstitial Fluid Dynamics
- Diffusion
- movement from area of high to low concentrations
- Filtration
- net flow of water due to effect of pressure
- Hydrostatic Pressure
- fluid pressure
- Osmotic Pressure
- pressure that accompanies a movement of water across a membrane
- Oncotic Pressure
- pressure that results from a difference in protein concentration
- Normal capillary dynamics
IV. Cardiovascular Regulation
- Local, central and hormonal regulation
- Local Regulation
- Local Vasodilation (increase blood flow)
- Decreased oxygen or pH
- Increased carbon dioxide, potassium or hydrogen ions
- Nitric oxide
- Inflammatory agents (histamine)
- Temperature increase
- Local Vasoconstrictors (decrease blood flow)
- Prostaglandins
- Thromboxanes
- Neural Regulation
- Vasomotor Centers (Sympathetic)
- Vasoconstriction
- Vasodilation
- Nitric oxide (ACh)
- Nitroxidergic (NO is the neurotransmitter)
- Cardiac Centers
- Baroreceptors - monitor degree of stretch of vessel
- Carotid sinuses - head
- Aortic sinuses - systemic circuit
- Atrial reflex - monitor blood in/blood out ratio
- 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
- Hormonal Regulation
- ADH
- decrease in blood pressure
- vasoconstriction/absorption of water at kidneys
- Angiotensin II
- release of renin in response to a decrease in blood pressure
- vasoconstriction/increase cardiac output
- stimulate secretion of ADH/stimulate thirst
- Erythropoietin
- decrease in blood pressure/decrease in oxygen content of blood
- stimulate red cell production
- Atrial Natriuretic Peptide (ANP)
- right atrium/stretch receptor
- decrease blood volume/decrease blood pressure
- increase water loss at kidneys/decrease thirst/ decrease ADH
- vasodilation