Chapter 18: The Vascular System

blood vessels are the…

delivery system, begins and ends at the heart, works along with lymphatic system to circulate fluids

arteries

1. carry blood away from heart

   1. oxygenated except pulmonary

capillaries

1. direct contact with tissue cells

   1. directly serve cellular needs

veins

1. carry blood toward heart

   1. deoxygenated except for pulmonary

veins

1. carry blood toward heart

   1. deoxygenated except for pulmonary

vessel lumen

central space, surrounded by a wall

3 layers of a blood vessel

1. tunica intima

2. tunica media

3. tunica externa

tunica intima

1. innermost layer

   1. direct contact with blood

2. endothelium

   1. simple squamous

   2. continuous with endocardium

tunica media

1. middle, bulkiest layer

2. smooth muscle

3. ANS control

4. vasoconstriction/vasodilation

5. maintains blood flow and BP

tunica externa

1. outermost layer of wall

   1. collagen fibers

      1. protects, reinforces, and anchors

3 groups of arteries

1. elastic arteries

2. muscular arteries

3. arterioles

elastic arteries (conducting)

1. thick wall and large lumen

2. elastin

3. aorta

4. pressure reservoirs: expand and recoil as blood is ejected from heart

muscular arteries

1. deliver blood to organs

2. thickest tunica media—vasoconstriction

arterioles (resistance)

1. smallest

   1. smooth muscle around endothelial cells

2. control flow into capillary beds

   1. vasodilation or vasoconstriction

capillaries

1. microscopic vessels

2. tunica intima only

function of capillaries

exchange of gases, nutrients, hormones, waste between blood and interstitial fluid

capillary endothelial cells are joined by…

tight junctions with gaps known as intercellular clefts

3 types of capillaries

1. continuous

2. fenestrated

3. sinusoidal

continuous capillaries

1. most abundant, least permeable

2. skin, muscles, lungs, CNS

3. pinocytotic vesicles ferry fluid

4. intercellular clefts between endothelial cells

basis of blood-brain barrier (continuous capillaries)

brain capillary epithelial cells lack intercellular clefts and have TJs around their perimeter

fenestrated capillary

1. fenestrations are pores

2. filtration (kidneys)

3. absorption (intestines)

4. secretion (endocrine)

sinusoidal capillaries

1. few TJs

2. fenestrated with larger intercellular clefts

3. liver, bone marrow, spleen, and adrenal medulla

4. sluggish blood flow

5. macrophages

terminal arteriole

branches into 10 to 20 capillaries (exchange vessels)—capillary bed

postcapillary venule

drain into venule

capillary beds

flow controlled by diameter of terminal arteriole and upstream arterioles

veins

carry blood toward the heart

venules

smaller veins

postcapillary venules structure

1. consist of endothelium

2. very porous

veins (capactiance) description

1. large lumen and thin walls

2. storage

3. blood reservoirs (65% of blood supply)

blood pressure in veins are … than in arteries

lower due to large-diameter lumens that offer little resistance; helps get blood back to heart

venous valves

1. prevent backflow of blood

2. most abundant in veins of limbs

systemic veins

1. supply all of the body except the lungs

2. distensible

3. large proportion of blood volume

4. blood reservoirs

pulmonary blood vessels supply the…

lungs

blood flow

1. CO for entire vascular system

2. ml/min

blood pressure (BP)

1. force on blood vessel wall by blood

2. mmHg

resistance (peripheral resistance)

opposition to flow

3 sources of resistance

1. blood viscosity

2. total blood vessel length

3. blood vessel diameter

blood viscosity

1. thickness of blood

2. directly proportional

total blood vessel length increases…

resistance

blood vessel diameter

1. has greatest influence on resistance

2. resistance varies inversely

3. as vessel gets wider, resistance declines

blood flow is…..to blood pressure gradient

directly proportional

blood flow is … to peripheral resistance

inversely proportional

what influences blood flow (R)

altering blood vessel diameter

systemic pressure through circulation

1. highest in aorta

2. lowest in vena cavae

2 factors of arterial blood pressure

1. elasticity of arteries close to heart

2. volume of blood forced into them at any time

blood pressure near heart is….

pulsatile, rises and falls with each heartbeat

systolic pressure

pressure exerted in aorta during ventricular contraction

diastolic pressure

lowest level of aortic pressure when heart is at rest

pulse pressure

systolic - diastolic pressure

pulse

throbbing of arteries due to differences in pulse pressures

mean arterial pressure (MAP)

pressure that propels blood to tissues

Atrial systole time

0.1 s

ventricular systole time

0.3 s

diastole time

0.4 s

MAP equation

Diastolic pressure + Pulse Pressure/3

venous blood pressure

1. changes little during cardiac cycle

2. low pressure, 15 mmHg

3. adaptations to help with venous return

   1. muscular pump

   2. respiratory pump

factors that increase MAP

1. CO

2. Peripheral resistance

3. blood volume

short-term regulations of BP

1. neural controls

2. hormonal controls

long-term regulation of BP

renal controls

neural controls

1. cardiovascular center of medulla

2. baroreceptors

3. chemoreceptors

cardiovascular center of medulla

cardioinhibitory and cardioacceleratory centers

vasomotor center (neural)

1. sends steady impulses to blood vessels

2. continuous moderate constriction called vasomotor tone

baroreceptor reflexes (neural)

1. located in carotid sinuses, aortic arch

2. respond to stretch

chemoreceptor reflexes (neural)

1. respond to chemical signals

2. stimulated by increased CO2, decreased pH + O2

3. signal cardioacceleratory center to increase CO

4. signal vasomotor center to increase vasoconstriction

hormonal controls

epinephrine and Ne from adrenal medulla increase CO

renal regulation

alter blood volume in kidneys

1. direct renal mechanism

2. indirect renal mechanism renin-angiosin-aldosterone

direct renal control of BP

1. decrease in arterial pressure

2. decrease filtration by kidneys

3. decrease urine

4. increase blood volume (BV)

5. increase MAP

indirect renal regulation—renin-angiotensin-aldosterone mechanism

decreased BP causes

1. release of renin from kidneys

2. renin enters blood and converts angiotensinogen (from liver) into angiotensin I

3. angiotensin-converting enzyme (ACE, lungs) converts angiotensin I into angiotensin II

angiotensin II functions

1. stimulates aldosterone secretion

2. ADH release from post pituitary

3. triggers hypothalamic thirst center to drink water

4. vasoconstrictor, increases BP

atrial natriuretic peptide (ANP)

if heart is stretched

1. antagonizes aldosterone

2. tells kidneys to get rid of Na+ and water

3. decreases BV and BP

BP to brain is too low

person loses consciousness

BP to brain is too high

stroke

primary hypertension

1. common—90%

2. heredity, diet, obesity, age, diabetes

controlling primary hypertension

1. restrict salt, fat, cholesterol intake

2. increase exercise, lose weight, quit smoking

3. antihypertensive drugs

hypotension

1. low BP below 90/60 mmHg

2. not a concern unless it causes inadequate blood flow to tissues

systemic veins

1. supply all the body except the lungs

2. distensible

3. contain a large proportion of BV and are called capacitance vessels or blood reservoirs

tissue perfusion

transport of blood to tissues

rate of blood flow is…

precisely right amount to provide proper function to that tissue

capillary transport mechanisms

1. diffusion through plasma membrane (lipid-soluble)

2. movement through intercellular clefts (water-soluble)

3. movement through fenestrations (water-soluble)

4. transport via vesicles (large substances)

bulk flow

1. movement of large materials

2. forced out clefts at arterial end

3. most returns to blood at venous end

direction and amount of fluid depends on…

1. hydrostatic pressures

2. colloid osmotic pressures

capillary hydrostatic pressure (HPc)

1. force exerted by fluid pressing against capillary wall

2. pushes fluid out of capillary

HPc force distribution

greater at arterial end of bed

capillary colloid osmotic pressures (OPc)

1. pulls fluid into capillary

2. created by nondiffusible plasma proteins albumins

3. 26 mmHg

hydrostatic-osmotic pressure interactions

1. net fluid flow out at arterial end (filtration)

2. net fluid flow in at venous end (reabsorption)

bulk flow and fluid

more fluid leaves than is returned

what happens to excess fluid

returned to blood via the lymphatic system

edema

abnormal increase in amount of IF

cause of edema

1. increase in outward pressure

2. decrease in inward pressure

3. lymphatics