blood vessels

Question 1

Bblood vessels

• examples
• when aren’t arteries carrying oxygenated blood?

Answer 1

• delivery system of dynamic structures that begins and ends at the heart
• arteries, capillaries, veins
• pulmonary circulation and umbilical vessels of fetus

Question 2

structures of blood vessel walls

Answer 2

• lumen
• tunica intima
• tunica media
• tunica externa

capilaries = endothelium with sparse basal lamina

Question 3

Tunica intima

Answer 3

• endothelium lines lumen of all vessels
• continuous with endocardium
• slick surface reduces friction
• subendothelial layer in cessels larger than 1 mm = CT basement membrane
• internal elastic lamina in arteries

Question 4

Tunica media

Answer 4

smooth muscle and sheets of elastin
-sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels (affects blood flow and pressure)

Question 5

Tunica externa (tunica adventitia)

Answer 5

• collagen fibers protect and reinforce; anchor to surrounding structures
• contain nerve fibers and lymphatic vessels
• vaso vasorum of larger vessels nourishes external layer

Question 6

Elastic arteries

Answer 6

• “conducting arteries”
• large, thick-walled arteries with elastin in all three tunics
• aorta and its major branches
• large lumen offers low resistance
• inactive in vasoconstriction
• acts as pressure reservoirs - expand and recoil as blood ejected from heart
• smooth pressure downstream
• diameter = 1.5 cm; thickness = 1 mm

Question 7

muscular arteries

Answer 7

• “distributing arteries”
• distal to elastic arteries
• deliver blood to body organs
• thick tunica media with more smooth muscle
• active in vasoconstriction
• diameter = 6 mm; thickness = 1 mm

Question 8

arterioles

Answer 8

• -“resistance vessels”
• smallest arteries
• lead to capillary beds
• control flow into capillary bed via vasodilation and vasoconstriction
• diameter = 37 um; thickness = 6 um

Question 9

capillaries

-walls and size

Answer 9

• microscopic blood vessels
• walls of thin tunica intima
• in the smallest, one cell forms entire circumference
• diameter allows only one rbc to pass at a time

Question 10

capillaries
-where?
function?

Answer 10

in all tissues except cartilage, epithelia, cornea, and lens of eye

• provide direct access to almost every cell
• func: exchange of gases, nutrients, wastes, hormones, etc… bt blood and interstitial fluid

Question 11

Three types of capillaries

Answer 11

• continuous= least permeable; most common; tight junctions; small intercellular cleft; skin and muscle
• fenestrated = large fenestration; tight junctions; intercellular cleft; kidney and small intestine
• sinusoid = few tight junctions; pores and intercellular cleft; big lumen; macrophages in lining; liver and bone marrow and spleen and adrenal medulla

Question 12

blood flow in sinusoid capillaries

Answer 12

• slugginsh –> allows modification

- big molecules and blood cells pass bt blood and surrounding tissues

Question 13

Microcirculation in capillary beds

Answer 13

• interwoven networks of capillaries between arterioles and venules
• teminal arteriole –> metarteriole –> throughfare channel –> postcapillary venule

Question 14

two types of vessels in capillary beds

Answer 14

• vascular shunt (metarteriole to thoroughfare channel) - directly connects terminal arteirole and postcapillary venule
• true capillaries = 10-100 exchange vessels per capillary bed –> branch off metarteriole or terminal arteriole and return to thoroughfare channel

Question 15

precapillary sphincters

Answer 15

• regulate blood flow into true capillaries
• blood may go into true capillaries or to shunt
• regulated by local chemical conditions and vasomotor nerves

Question 16

venules

Answer 16

• formed when capillary beds unite
• smallest postcapillary venules = endothelium and a few pericytes - very porous, allowing fluids and wbcs into tissues
• larger venules have 1-2 layers of smooth muscle cells

Question 17

veins

• anatomy
• pressure

Answer 17

• formed when venules converge
• have thinner walls, bigger lumens than arteries
• BP is lower than arteries
• thin tunica media; thick tunica externa of collagen fibers and elastic networks
• “capacitance vessels” (blood reservoirs) w/ up to 65% of blood supply

Question 18

% of blood everywhere

Answer 18

capillaries = 5%
heart = 8%
pulmonary blood vessels = 12%
systemic arteries and arterioles = 15%
systemic veins and venules = 60%

Question 19

vein adaptations to ensure return of blood to heart despite low pressure

Answer 19

• big diameter lumens offer little resistance
• venous valves prevent backflow of blood (most abundant in veins of limbs)
• venous sinuses = flattened veins with extremely thin walls (coronary sinus of the heart and dural sinuses of the brain)

Question 20

dimmensions of capillary, venule and vein

Answer 20

capillary: D = 9 um; T = 0.5 um
venule: D = 20 um; T = 1 um
vein: D = 5 mm; T = 0.5 mm

Question 21

vascular anastomoses

Answer 21

• interconnections of blood vessels
• Arterial anastomoses provide alternate pathways (collateral channels) to a given body region (joinds, abdominatl orgains, brain, and heart –> NOT retina, kidney or spleen)
• Venous anastomoses are common

Question 22

Blood flow

Answer 22

• volume of blood flowing through a vessel, organ, or entire circulation in given period
• measured in ml/min
• CO for entire system
• constant at rest
• varies widely through individual organs based on needs

Question 23

blood flow vs blood pressure vs resistance

Answer 23

• blood flow (F) is directly proportional to blood pressure gradient (delta P)
• Blood flow inversely proportional to peripheral resistance (R)
• F = (delta P)/(R)
• R is more important in influencing local blood flow because its easily changed by altering blood vessel diameter

Question 24

Resistance

• definition
• sources

Answer 24

• opposition to flow
• amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation
• 3 sources:
  1. blood viscosity
  2. total blood vessel length (every 2.2 lb of adipose tissue contains 400 miles of blood)
  3. blood vessel diameter

Question 25

factors affecting resistance that remain relatively constant

Answer 25

blood viscosity - "stickiness" of blood due to formed elements and plasma proteins - increased viscosity = increased resistance blood vessel length -longer vessel = greater resistance encountered

Question 26

how does blood vessel diameter impact resistance (use math)?

Answer 26

resistance varies inversely with the fourth power of vessel radius -e.g. if radius doubles, resistance is 1/16 what it used to be

Question 27

Atherosclerosis

Answer 27

- increase in plaque in blood vessels - increases resistance - disrupts laminar flow and causes turbulent flow - irregular fluid motion --> increased resistance

Question 28

Blood pressure

Answer 28

- force per unit area exerted on wall of blood vessel by blood - pressure results when flow is opposed by resistance - mm Hg - measured as systemic arterial BP in large arteries near heart - Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas

Question 29

systemic blood pressure

Answer 29

- highest in aorta - declines throughout pathway - 0 mm Hg in right atrium - steepest drop occurs in arterioles

Question 30

Arterial blood pressure | -what it reflects

Answer 30

reflects 2 factors of arteries close to heart: - elasticity (compliance or distensibility) - volume of blood forced into them at any time -BP near heart is "pulsatile"

Question 31

Arterial BP - systolic pressure - diastolic pressure - pulse pressure

Answer 31

Systolic = pressure exerted in aorta during ventricular contraction (about 120 mm Hg in normal adult) Diastolic = lowest level of aortic pressure Pulse pressure = dif bt systolic and diastolic pressure -"pulse" = throbbing of arteries

Question 32

Mean arterial pressure

Answer 32

- pressure that propels blood into tissues - MAP = diastolic pressure + 1/3 pulse pressure - pulse pressure and MAP both decline with increasing distance from heart - BP: 120/80 and MAP = 93 mm Hg near heart

Question 33

capillary blood pressure

Answer 33

- ranges from 17 to 35 mm Hg - low capillary pressure is desirable - high BP would rupture the thin walls - most are very permeable, so low pressure forcesfiltrate into interstitial spaces

Question 34

venous BP

Answer 34

- changes little during cardiac cycle - smallest pressure gradient: about 15 mm Hg - low pressure due to cumulative effects of peripheral resistance (energy of blood pressure lost as heat during each circuit)

Question 35

Factors aiding venous return

Answer 35

1. muscular pump: contraction of skeletal muscles "milks" blood toward heart; valves prevent backflow 2. Respiratory pump: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand 3. Venoconstriction: under sympathetic control pushes blood toward heart

Question 36

Maintaining BP - requirements - factors influencing BP

Answer 36

Requirements - cooperation of heart, blood vessels, and kidneys - supervision by brain Main factors influencing BP 1. Cardiac output (CO) 2. Peripheral resistance (PR) 3. Blood volume - change in one variable quickly compensated for by change in another