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Blood Vessels

Chapter 19 – Day 1

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Blood Vessel Structure

Fig. 19.1

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Blood Vessels - Intro

Blood vessels are essentially a “pipeline” to:♦Carry blood TO parts of the body = arteries♦Carry blood BACK FROM parts of the body = veins

Subdivisions♦Pulmonary blood vessels: blood to the lungs and back♦Systemic blood vessels: blood to and from the rest of the

body

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Blood Vessels - Intro

Veins = mostly deoxygenated – except pulmonary vein & umbilical vein

Arteries = mostly oxygenated – except pulmonary artery & umbilical artery

Capillaries = interconnecting vessels♦Enable gas exchange, etc.

Blood vessel structure and comparison activity in lab

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Blood Vessel Structure

Fig. 19.1

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Arteries vs. Veins - Similarities 3 LayersTunica Externa

♦Connective TissueTunica Media

♦Smooth muscle cells ♦Elastic fibers (arteries)♦Collagen fibers

Tunica Interna♦Elastic layer♦Endothelial cells & connective tissue with elastic fibers

(arteries)

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Arteries vs. VeinsArteries are thick walledLarger arteries have more elastic fibers

♦Tunica media – thicker, concentric & longitudinal♦Tunica interna – internal elastic membrane

ARTERIES♦Elasticity

•Ability to stretch when full = high pressure•Return to their original state when relaxed

♦Contractability•More smooth muscle (than veins)•Vasodilation, Vasoconstriction

Both veins & large arteries need O2 – supplied by vaso vasorum

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Arteries vs. VeinsHierarchy of organization

♦(learn examples from text)Largest vessels coming out of heart or to heartThese carry the most volume

♦If arteries – they have the highest pressureDiagram on board and Fig. 19.2

Be able to work though these – know order and characteristics

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Blood Vessel Hierarchy

Fig. 19.2

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Capillaries

Fig. 19.5

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Arteries vs. VeinsDifferent jobs and different driving forcesArteries

♦Force of contraction pushes blood forward♦Blood pressure = driving force♦Moves downhill to lower extremities - gravity

Veins ♦Lower extremities to heart = against gravity♦Low pressure♦Relies on other driving forces

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VeinsTwo features help to push blood forward:

♦Valves – keep blood from flowing backward (flow is possible in 1 direction only)

♦Skeletal muscle contraction•Helps to push blood forward

♦Breathing action•Pressure in chest helps venous flow

♦All contribute to venous return

Fig. 19.6

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Blood vessel functionUltimately blood delivers O2 & nutrients to tissues as

well as removing wastes How does this happen?Any organ:

♦Blood vessels (in & out): arteries – smallest branch = capillary

♦The organ is infused with capillaries♦Nutrient exchange occurs at this level

In the capillaries – only the endothelial layer is presentSubstances in the capillaries move to the Interstitial

Fluid → then into cells

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O2, Nutrient, and Waste ExchangeWaste products are released into the interstitial fluid

Waste products are then taken up by fenestrated capillaries because they are typically large molecules (recall differences between fenestrated & continuous capillaries)

Fig. 19.4

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O2, Nutrient, and Waste Exchange Exchange between blood and interstitial fluid

1. Simple (& Facilitated) Diffusion:♦In response to a concentration gradient

2. Filtration♦Force pushes out substances – based on pressure

3. Osmosis♦Reabsorption of water

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Diffusion Ions and small organic molecules (glucose, amino

acids, urea – move through pores in fenestrated capillaries or move via diffusion between endothelial cells of adjacent capillaries

Ions (Na+, K, etc.) diffuse across endothelial cells by passing through channels in cell membranes

Large water-soluble compounds can only work enter or leave blood stream via fenestrated capillaries

Lipids (FAs, steroids) and lipid-soluble compounds (esp. CO2, O2) cross capillary walls by diffusion through endothelial cell membranes

Plasma proteins can only diffuse through in sinusoids (such as those in the liver)

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Filtration Driving force =

PRESSURE in capillary = Capillary Hydrostatic Pressure (CHP)

Water is forced across a capillary wall and small solutes travel with the water♦Through endothelial cells

or pores of fenestrated capillaries

Fig. 19.11

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Reabsorption Occurs as a result of osmosis

♦Diffusion of water across selectively permeable membrane•Remember, water molecules move toward soln with higher

solute concentration Process by which dissolved solutes is moved Osmotic pressure = amount of pressure that must be

applied to prevent osmotic movement across a membrane (Blood Osmotic Pressure = BOP; IOP=?)♦BCOP = blood colloid osmotic pressure = osmotic pressure

of blood (also BOP) Remember…hydrostatic pressure forces water OUT

of solution, whereas osmotic pressure draws water INTO a solution (BHP vs. IOP; BOP vs. IFHP)

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Pressures have to be balanced so that fluid in and out can be coordinated – refer to handout (review!!)

Fig. 19.11

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Filtration & Reabsorption If BHP > BOP in the blood vessel, fluid is pushed out If BHP < BOP fluid enters in

IFHP & IOP – low & stable because there are fewer proteins in interstitial fluid

Net Filtration Pressure is the difference between the net hydrostatic pressure and the net osmotic pressure: ♦Net filtration = net hydrostatic – net colloid pressure pressure osmotic pressure

If positive fluid moves OUT of capillary If negative fluid moves INTO capillary

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Equilibrium Analogy to filtration experiment

♦Charcoal = cells & proteins♦CuSO4 = nutrients & O2

Cells & Proteins remain in blood vessel H2O, hormones, other chemicals, nutrients, O2,

glucose, ions = pushed out Equilibrium between arterial & venus ends maintains

proper pressure differences (Starling’s Law of Capillaries)

Excess fluid expelled into tissues causes an increase in interstitial fluid – if in excess, causes EDEMA♦Excess fluid buildup, swollen ankles, etc

Read in book and follow handout

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Equilibrium Equilibrium between arterial & venus ends maintains

proper pressure differences Excess fluid expelled into tissues causes an increase

in interstitial fluid – if in excess, causes EDEMA♦Excess fluid buildup, swollen ankles, etc

Read in book and follow handout Different demands for gas and nutrient exchange For proper delivery – the cardiovascular system

depends on:1. Cardiac Output2. Peripheral Resistance3. Blood Pressure

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St

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Blood Pressure and Blood Vessels Blood Pressure

♦Pressure within blood vessels♦Influenced by cardiac output, but other factors are involved

as well

1. Vasomotor tone♦Muscle tone of smooth muscle♦Resistance against blood♦This is controlled by the medulla in the brain♦VASOCONSTRICTION - ↑ sympathetic impulse♦VASODILATION - ↓ sympathetic impulse♦THESE CHANGES AFFECT BLOD PRESSURE

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Blood Pressure and Blood Vessels Blood Pressure1. Vasomotor tone2. Baroreceptors

♦Monitor the degree of stretch♦Special receptor nerve cells in specific areas of the body♦Baroreceptors adjust cardiac output & resistance

3. Chemoreceptors♦Special nerve cells sensitive to chemical concentrations♦These sense arterial levels of CO2, O2, H+ (pH),♦Can adjust constriction based on the concentration of these

chemicals

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Blood Pressure and Blood Vessels Blood Pressure4. Cerebral Cortex

♦Stress, anger, depression♦All of these emotions affect the sympathetic division of the

nervous system♦The cerebral cortex alters blood pressure/flow by altering

levels of vasoconstriction/vasodilation

5. Local Changes♦Sphincters near capillaries

6. Chemicals♦Drugs♦Alter vasodilation & constriction

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Hypertension Abnormally high BP levels (>150/90)

♦Approximately 25% of the population suffers from hypertension

Cause & Effects♦uncertain♦Heart works harder – O2 demand is high ♦Hypertension: accelerates artherosclerosis, increases clot

formation, causes kidney damage Treatment

♦To reduce heart workload♦Diuretics - ↓ blood volume (increasing urine output)♦Vasodilators – relax smooth muscle♦β – blockers: affects sympathetic receptors (reduces cardiac

output)♦CA2+ blockers: reduce cardiac output

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Other Vessel Disorders Varicose veins

♦Hemorrhoids Circulatory Shock

♦Hematogenic Shock♦Cardiogenic Shock♦Neurogenic Shock♦Septic Shock

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Equilibrium Need constant control of these factors to maintain

homeostasis= CARDIOVASCULAR REGULATION

Controlled by♦Autoregulation Mechanisms

•Local factors change pattern of blood flow w/in capillary beds•Response to chemical changes in interstitial fluids

♦Neural Mechanisms•Respond to changes in arterial pressure or blood gas levels @

a specific site stimulates cardiovascular centers of ANS♦Endocrine Mechanisms

•Releases hormones that enhance short-term adjustments and direct long-term changes in cardiovascular performance

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Auto Regulation Local changes

♦Sphincters near capillaries are adjusted♦Depend on local VASODILATION & VASOCONSTRICTION

chemicals (nitrous oxide) – know examples from text (p 547)•Vasodilator: factor(s) that promote the dilation of precapillary

sphincters•Local vasodilators act at the tissue level & accelerate blood

flow through the tissue of origin

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Neural Mechanisms Neural Mechanisms

♦Sympathetic division controls…•Smooth muscle tone (vasomotor tone)•Increased sympathetic impulses ( vasoconstriction)•Decreased sympathetic impulses ( vasodilation)

♦Receptors

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Capillaries

Fig. 19.5