Blood Vessels

1. FunctionsA) conduit for blood flowB) site of exchange of nutrients and

wastes2. Structure of Vessels

A) all vessels except capillaries have the same basic structure

Blood Vessels

1) Tunica Interna (Intima)a) innermost layer composed of simple

squamous = endotheliumb) remains unchanged in thickness

throughout the circulation pathway

Blood Vessels

2) Tunica Mediaa) middle layer composed mostly of

smooth muscle and elastin3) Tunica Externa (Adventitia)

a) outermost layer composed of areolar CT

Blood Vessels

3. Types of VesselsA) arteries

1) carry blood away from the heart2) thick tunica externa & media with

narrow, circular lumen3) two types

Blood Vessels

a) elastic arteriesi) large diameter arteries leaving the

heartii) their elasticity helps propel blood

when heart is relaxed

Blood Vessels

b) muscular arteries i) branch off of elastic arteriesii) distribute blood to different areas of

the bodyiii) capable of great vasoconstriction &

vasodilation to control the rate of blood flow to these areas

Blood Vessels

B) arterioles1) very small arteries that deliver blood

to the capillaries2) also capable of vasoconstriction &

vasodilation and control blood flow into the tissues, as well as systemic blood pressure

Blood Vessels

C) capillaries1) connect arterioles to venules2) composed of a simple squamous

and a thin basal lamina3) site of nutrient and waste exchange

in the tissues4) three types

Blood Vessels

a) continuous capillaryi) complete cells

with small intercellular clefts (gaps)

ii) found in skeletal muscle, smooth muscle, and lungs

Blood Vessels

b) fenestrated capillaryi) cells contain

small pores (fenestrations) with small intercellular clefts

ii) found in kidney, small intestine and brain

Blood Vessels

c) sinusoidsi) cells have very

large fenestrations and wide intercellular clefts

ii) found in spleen, liver and bone marrow

Blood Vessels

5) Capillary Bedsa) metaarteriole

i) vessel that connects an arteriole to 10-100 capillaries (capillary bed)

ii) passes directly thru the capillary bed(a) also known as the vascular shunt or

thoroughfare channel(b) directly connects the arteriole to the

venule

Blood Vessels

b) precapillary sphinctersi) found at the junction of the

metaarteriole and the capillary bedii) controls blood flow into the capillary

bed

Blood Vessels

D) venules1) collect blood from capillaries2) primarily serve as a conduit for blood3) no vasoconstriction/vasodilation

Blood Vessels

E) veins1) carry blood back to the heart2) have thin tunica media which contains

little smooth muscle & elastina) no vasoconstriction/vasodilation

3) thick tunica externa composed of collagen and elastin

Blood Vessels

4) large, collapsed lumens5) have valves in their lumen to prevent the

backflow of blood

Blood Vessels

4. Capillary Exchange – 3 main processesA) diffusion (simple & facilitated)

1) O2, CO2, glucose, amino acids, hormones & urea

B) transcytosis1) protein hormones and antibodies

Blood Vessels

C) bulk flow (filtration)1) a large numbers of ions and molecules

move within a fluid2) fluid may move out (filtration) or back into

(reabsorption) the capillary 3) responsible for the relative volumes of the

blood and interstitial fluid4) driven by a pressure difference

a) NFP = (BHP + IFOP) - (BOP + IFHP)

Blood Vessels

i) NFP – net filtration pressure(a) difference between the forces favoring

filtration and those opposing itii) BHP – blood hydrostatic pressure

(a) created by blood pushing against the walls of the vessel

(b) favors filtration(c) only pressure to change significantly from

one end of the capillary to the other

Blood Vessels

iii) BOP – blood colloid osmotic pressure(a) created by plasma proteins in the blood(b) favors reabsorption

iv) IFHP – interstitial fluid hydrostatic pressure(a) created by the interstitial fluid pushing on

the walls of the vessel(b) favors reabsorption

Blood Vessels

v) IFOP – interstitial fluid osmotic pressure(a) created by plasma proteins that have

leaked out of the vessel (into the interstitial fluid)

(b) favors filtration

Blood Vessels

5. Blood Flow (Circulation) & Blood PressureA) Blood flow – volume of blood that flows

thru any tissue1) total blood flow = cardiac output2) distribution of blood throughout the

body is dependent on:a) a pressure difference at the tissues

(blood pressure)b) vascular resistance

Blood Vessels

B) Blood Pressure – pressure of the blood on the walls of the vessel1) decreases as you move away from the

heart2) 2 components

a) systolic pressure (100-120mmHG)b) diastolic pressure (70-80mmHG)

Blood Vessels

4) pulse pressurea) pulse P = systolic P – diastolic P

5) mean arterial blood pressure (MABP)a) MABP = diastolic P + (pulse pressure/3)

6) dependent on total blood volumea) small decrease ( < 10%)b) large decrease ( > 10%)c) any increase

Blood Vessels

C) Resistance1) created by friction between blood and

walls of vessels2) dependent on:

a) blood viscosity (thickness) i) ratio of RBC to plasma

(a) dehydration increases(b) anemia decreases

b) total blood vessel length

Blood Vessels

c) blood vessel diameteri) controlled by sympathetic NS through

vasoconstriction/vasodilation3) total peripheral resistance

a) the total resistance of all systemic blood vessels combined

b) controlled by altering arteriole diameteri) controlled by vasomotor center

c) determines localized blood pressure and flow to particular tissues & systemic BP

Blood Vessels

D) Venous Return1) requires pressure difference2) heart normally creates enough

pressure to keep blood moving3) aided by:

a) skeletal muscle pumpb) respiratory pump

Blood Vessels

6. Control of Blood Flow & PressureA) 3 mechanisms

1) alter cardiac output (addressed during heart lecture)

2) adjust total blood volume 3) change vascular resistance

B) Autonomic NS – Short-Term1) via cardiovascular center

Blood Vessels

2) inputa) baroreceptors

i) blood pressureb) chemoreceptors

i) O2, CO2, H+

Blood Vessels

3) outputa) sympathetic fibers

i) cardiac accelerator nerves(a) innervates the conduction

system & ventricular myocardium

Blood Vessels

ii) vasomotor nerves (sympathetic)(a) innervate the tunica media of most

systemic arterioles(i) vasoconstriction

(b) innervate the tunica media of the blood vessels in heart & skeletal muscle(i) vasodilation

Blood Vessels

b) parasympathetic fibersi) Vagus nerves

(a) innervates the conduction system(b) doesn’t innervate any blood vessels

Blood Vessels

4) Vasomotor Reflexesa) baroreflex

i) triggered by increased stretch (BP)ii) inhibits sympathetic output and

stimulates Vagus nerve (parasympathetic)

Blood Vessels

b) chemoreflexi) triggered by hypoxia, acidosis, or

hypercapniaii) stimulates sympathetic output

Blood Vessels

c) medullary ischemic reflexi) triggered by hypoxia or hypercapnia at

the brainstemii) stimulate vasomotor center

(a) vasoconstriction of vessels in lower parts of the body

Blood Vessels

C) Hormonal Control – Long-Term1) renin-angiotensin system

a) increases blood volume i) renin

(a) released from the kidney in response to decreased blood volume

(b) converts angiotensinogen (plasma protein) to angiotensin I

Blood Vessels

ii) ACE (angiotensin converting enzyme)(a) found primarily in the lungs(b) converts angiotensin I to angiotensin II

iii) angiotensin II(a) systemic vasoconstrictor(b) causes aldosterone release from adrenal

cortex(i) increases Na+ & H2O reabsorption by

the kidneys

Blood Vessels

2) Atrial Natriuretic Peptide (ANP)a) decreases blood volume

i) released from the ventricles of the heart in response to an increase in blood volume

ii) decreases Na+ & H2O reabsorption by the kidneys and inhibits the release of aldosterone

Blood Vessels

7. Blood Vessel DisordersA) Atherosclerosis – plaque build-up (fat and

cholesterol) within the vessel1) The plaque obstructs the vessel

causing increased blood pressure and a reduction in elasticity

B) Aneurysm – ballooning of a blood vessel which increases risk of rupture

Blood Vessels

C) Hypotension – low blood pressure1) systolic below 90 or diastolic below 60

D) Hypertension – high blood pressure1) Prehypertension – systolic 120-139 or

diastolic 80-892) Stage 1 Hypertension – systolic 140-159

or diastolic 90-993) Stage 2 Hypertension – systolic 160 & up

or diastolic 100 & up