Lecture: Blood Vessels and Circulation

Question 1

What are the 3 layers of a blood vessel?

Answer 1

from inside to outside:
tunica interna (tunica intima)
tunica media
tunica externa (tunica adventitia)

Question 2

Describe the composition of the tunica interna (tunica intima).

Answer 2

endothelium: simple squamous epithelium
- continuous layer of cells throughout system
- layer in contact with the blood

Question 3

What are the 4 functions of the tunica interna (tunica intima)?

Answer 3

1) selectively permeable barrier
2) secretion of chemicals
3) repels blood cells and platelets
4) inflammation

Question 4

Describe the composition of the tunica media.

Answer 4

smooth muscle (amount varies)
elastic tissue
collagen

Question 5

What are the 2 functions of the tunica media?

Answer 5

1) strengthens vessels / prevents rupture

2) vasomotion (vasoconstriction / vasodilation)

Question 6

Describe the composition of the tunica externa (tunica adventitia).

Answer 6

loose CT

Question 7

What are the 3 functions of the tunica externa (tunica adeventitia)?

Answer 7

1) protects and anchors blood vessel
2) passage for nerves & lymphatic vessels
3) smalls vessels called vaso vasorum supply blood to outer walls of larger vessels

Question 8

What are the 3 categories of arteries?

Answer 8

1) conducting arteries (elastic, large)
2) distributing arteries (muscular, medium)
3) resistance arteries (arterioles, small)

Question 9

Comment on the composition of conducting arteries. Give some examples of conducting arteries.

Answer 9

largest diameter
elastic tunica media
ex. aorta, pulmonary trunk, common carotid, subclavian, common illiac

Question 10

What is the function of conducting arteries?

Answer 10

reduce effects of BP surgers

• expand during systole, recoil during diastole
• helps maintain blood flow

Question 11

Comment on the composition of distributing arteries. Give some examples of distributing arteries.

Answer 11

thicket smooth muscle

ex. brachial, femoral, renal, splenic

Question 12

What is the function of distributing arteries?

Answer 12

distribute blood to specific organs and adjust flow based on demand

Question 13

Describe the composition of resistance arteries.

Answer 13

smooth muscles layers variable;

little elastic tissue

Question 14

Define: arterioles.

Answer 14

smallest resistance vessels

lead into capillary bed

Question 15

Define: metarterioles.

Answer 15

link arterioles to capillaries

Question 16

What is the function of resistance arteries? What vital signs does it influence?

Answer 16

primary control of blood flow
most responsible for PR
significantly affects BP

Question 17

Describe the composition of capillaries.

Answer 17

single layer of endothelial cells

small lumen

Question 18

What is the function of capillaries?

Answer 18

to exchange materials, accomplished by their close proximity to nearly all cells

Question 19

What are the 3 types of capillaries?

Answer 19

1) continuous
2) fenestrated
3) sinusoid

Question 20

Describe the composition of continuous capillaries.

Answer 20

present in most tissues, such as skeletal muscle;
tight junctions hold endothelial cells together
intracellular clefts
pericytes

Question 21

Define: intracellular clefts

Answer 21

spaces between endothelial cells in continuos capillaries;
allow small molecules (ex. glucose) to pass through;
retrain larger molecules such as plasma proteins and formed elements

Question 22

Define: perictyes

Answer 22

contractile proteins in continuous capillaries

Question 23

Describe the composition of fenestrated capillaries.

Answer 23

endothelial cells covered in filtration pores (fenestrations);
greater permeability
allow rapid passage of small molecules but retain formed elements

Question 24

What are some examples of organs/tissues perfused by fenestrated capillaries?

Answer 24

kidneys
endocrine glands
small intestine
choroid plexus

Question 25

Describe the composition of sinusoids.

Answer 25

a.k.a. discontinuous capillaries; irregular, blood-filled spaces; endothelial cells have large filtration pores (fenestrations) through which formed elements can pass

Question 26

What are some examples of organs/tissues perfused by sinusoids?

Answer 26

liver bone marrow spleen

Question 27

Define: capillary beds.

Answer 27

networks of capillaries; not all are perfused at any given time; they drain into a distal continuation of the metarteriole called a thoroughfare channel, which then leads to a venule

Question 28

Define: capillary sphincter.

Answer 28

smooth muscle cell that wraps around the opening to each capillary and regulates blood flow

Question 29

Describe the composition of postcapillary venules.

Answer 29

smallest veins only tunica intima often have pericytes extremely porous

Question 30

Describe the composition of muscular venules.

Answer 30

thin tunica media | thin tunica externa

Question 31

Describe the composition of medium veins.

Answer 31

``` have all 3 tunics -thin tunica media -thick tunica externa -large lumen -tunica intima folds inward, forming valves; relatively thin wall vessel -BP much lower, collapses when empty; blood "reservoirs" (large % of total blood supply) ```

Question 32

Where are venous valves found/ not found in the body?

Answer 32

abundant where upward flow opposed by gravity; | not present in small/large veins, abdominal/thoracic cavities, and the brain

Question 33

Describe the composition of large veins. Name some examples of large veins.

Answer 33

v. thin tunica intima, v. thick tunica externa; | ex. venae cavae, pulmonary, internal jugular, renal

Question 34

Describe the 5 different types of circulatory routes.

Answer 34

1) simple pathway: 1 network of capillaries 2) portal system: 2 networks of capillaries (ex. kidneys, hypophyseal portal system) 3) arteriovenous anastomosis (a.k.a. shunt): artery directly to vein 4) venous anastomosis: alternative drainage 5) arterial anastomosis: collateral supply

Question 35

Define: anastomosis.

Answer 35

point of convergence between 2 blood vessels other then capillaries

Question 36

Define: flow.

Answer 36

vol. of blood through an organ, tissue, or vessel in a given amt. of time; expressed in ml/min

Question 37

Define: perfusion.

Answer 37

flow per given volume or mass of tissue; | expressed in ml/min/g

Question 38

Define: pressure.

Answer 38

force of blood exerted on vessel wall; | expressed in mmHg

Question 39

Define: hemodynamics.

Answer 39

study of physical principles of blood flow; based on pressure and resistance F ≈ ΔP / R where F = blood flow, ΔP = difference in pressure, R = resistance to flow

Question 40

How does blood pressure vary throughout the body / circulatory system?

Answer 40

highest pressure immediately after systole; highest pressure proximal to heart; arteries > capillaries > veins

Question 41

What 3 factors is blood pressure influenced by?

Answer 41

elasticity of arteries: recoil maintains pressure and facilitates flow; blood volume; kinetic energy of blood stretching the aorta

Question 42

Define: pulse pressure (PP).

Answer 42

measure of pressure surges | PP = SBP - DBP

Question 43

Define: mean arterial pressure (MAP).

Answer 43

avg. of pressures | MAP = DBP + 1/3 (PP)

Question 44

BP depends on what 3 organs coordinated by what 1 organ?

Answer 44

brain - heart - blood vessels - kidneys

Question 45

What are the 3 main variables determining blood pressure?

Answer 45

1) cardiac output 2) blood volume 3) resistance to flow

Question 46

Define: resistance.

Answer 46

measure of friction encountered by blood through vessels; | opposition to flow

Question 47

Define: peripheral resistance.

Answer 47

opposition to blood flow encountered away from the heart, generally from smaller vessels and arterioles

Question 48

What are 3 sources of resistance?

Answer 48

1) blood viscosity 2) blood vessel length 3) blood vessel diameter (most dynamic)

Question 49

Define: blood viscosity. What contributes to it? What is its relationship to resistance and flow?

Answer 49

"thickness" of blood; results from RBC and albumin; directly proportional to resistance (which is usually constant); inversely proportional to flow

Question 50

What effect does blood vessel length have on friction, resistance, and flow?

Answer 50

longer distance = more cumulative friction; directly proportional to resistance; inversely proportional to flow

Question 51

What are the terms for blood vessel diameter changes? What effect does this have on peripheral resistance?

Answer 51

vasoreflexes: vasodilation & vasoconstriction; | constantly alters peripheral resistance

Question 52

Differentiate laminar and turbulent flow.

Answer 52

laminar flow: layered flow, faster in center and slower near the walls; turbulent flow: at higher velocities, flow becomes rougher and lateral mixing occurs

Question 53

What is the most significant variable of Poiseuille's Law?

Answer 53

vessel radius (to the fourth power!)

Question 54

What are the 3 reasons that arterioles are the most significant point of control over peripheral resistance and blood flow?

Answer 54

1) location proximal to capillary beds makes them best positioned to regulate flow into the capillaries 2) greatly outnumber any other class of arteries 3) more muscular in proportion to their diameters than any other class of blood vessel, and are highly capable of changing radius

Question 55

Name the 3 mechanisms for regulating pressure and flow.

Answer 55

1) local control 2) neural control 3) hormonal control

Question 56

Explain local control.

Answer 56

autoregulation; myogenic control: vasoreflexes metabolic control; -CO2, H+, K+, lactic acid -vasoactive chemicals: histamine, prostaglandins, bradykinin; angiogenesis: growth of new blood vessels

Question 57

Define: autoregulation.

Answer 57

ability of tissues to regulate their own blood supply; | corresponds to local control

Question 58

Define: angiogenesis.

Answer 58

growth of new blood vessels; | corresponds to local control

Question 59

Explain neural control.

Answer 59

``` vasomotor center in medulla sends sympathetic impulses to smooth muscle, constricting most vessels, but dilating some cardiac and skeletal muscles; regulated by 3 autonomic reflexes 1) baroreflex 2) chemoreflex 3) medullary ischemic reflex ```

Question 60

Define: baroreflex.

Answer 60

``` autonomic, negative feedback response in response to BP (detected by baroreceptors); BP increase inhibits SNS, including cardiac and vasomotor centers; BP increase excites vagal fiber; effects: -reduce HR -reduce cardiac output -dilates vessels -reduces BP ```

Question 61

Define: chemoreflex.

Answer 61

autonomic response to chemical changes; chemoreceptors activated by low pH, low O2, and high CO2; primary role of chemoreceptors = adjust respiration; secondary role = vasomotor -vasoconstriction -increases perfusion

Question 62

Define: medullary ischemic reflex.

Answer 62

autonomic response to brain hypoperfusion; cardiac and vasomotor centers increase HR & contractile force and cause widespread vasoconstriction; these centers also receive input from higher brain centers: stress, arousal, anger can stimulate them and raise BP

Question 63

Name 6 hormones and their effects on vascular smooth muscle.

Answer 63

1) Angiotensin II: vasoconstriction 2) Aldosterone: sodium retention by kidneys 3) Atrial natriuretic peptide: increases sodium excretion 4) Antidiuretic hormone: water retention 5 & 6) epinephrine and norepinephrine: vasoconstriction in most vessels; vasodilation in coronary and skeletal muscle blood vessels

Question 64

Explain how blood flow can be redirected.

Answer 64

local vasoconstriction of an artery; downstream of site of constriction, pressure decreases; upstream of site of constriction, pressure increases; blood takes path of least resistance