Chapter 18: Blood Vessels

Question 1

Blood flow

Answer 1

• volume of blood going through a vessel, organ or system within measurable time period (ml/min)
• thru entire system fairly constant at rest=CO
• varies thru organs

Question 2

Blood pressure(BP)

Answer 2

• force per unit area exerted on vessel wall by blood within
• expressed as a millimeters of mercury (mm Hg). So BP of 120 mmHg= pressure exerted by column of mercury 120 mm high
• BP= your systemic arterial BP, found in large arteries near the heart
• blood moves from higher pressure to lower pressure

Question 3

Resistance

Answer 3

• opposition to flow, amount of friction blood is encountering on the vessel walls
• more resistance is encountered in the peripheral (systemic) circulation so the common term is PERIPHERAL RESISTANCE
• sources of resistance : viscosity (1-3)

Question 4

Systolic pressure

Answer 4

• highest pressure, when your ventricles are contracting and blood is being pushed into aorta
• in healthy adults avg. systolic is 120mmHg
• Blood moves forward because pressure is higher at aorta than vessels away from the heart

Question 5

diastolic pressure

Answer 5

• when heart is relaxing; semilunars closed, aortic pressure at its lowest point
• in healthy adults average diastolic pressure is 70~80mmHg. The elastic walls of the aorta recoil and maintain enough pressure to keep blood flowing forward

Question 6

pulse pressure

Answer 6

-difference between systolic and diastolic pressure; felt as a throbbing pulsation during systole as the elastic arteries expand due to blood being forced into them

Question 7

mean arterial pressure (MAP)

Answer 7

• pressure that propels blood to the tissues
  -MAP= diastolic pressure + pulse pressure/3
  -so what is normal MAP for a person of systolic 120 mmHg and diastolic 80 mmHg?
  MAP= diastolic pressure +(pulse pressure/3)
  MAP= 80+(40/3)=93.33 mmHg
  -MAP and pulse pressure decline with increasing distance from the heart, MAP due to friction between blood and the vessel walls and pulse pressure due to reduction in elasticity of arteries farther along
  -once blood crosses from arteries into arterioles, it has evened out to a steady pressure

Question 8

vasomotor tone

Answer 8

• arteries are almost always moderately constricted because the vasomotor center sends impulses at a steady state along the vasomotor fibers
• vasomotor activity is modified by inputs from: 1. Baroreceptors 2. Chemoreceptors 3. Higher Brain Centers

Question 9

Baroreceptors

Answer 9

• located in the coratid sinuses to supply the brain and in the aortic arch and walls of the larger arteries in the neck & thorax to supply the systemic circuit
• excitement of vasomotor center would cause vasoconstriction

Question 10

orthostatic hypotension

Answer 10

-temporary - you stand up too fast and get dizzy

Question 11

chronic hypotension

Answer 11

-long term-caused by poor nutrition, Addison’s disease, or hyperthyroidism

Question 12

acute hypotension

Answer 12

-circulatory shock, extreme blood loss

Question 13

chronic hypertension

Answer 13

• -BP 140/90 or higher
• prolonged hypertension is the major cause of heart failure, vascular disease, renal failure and stroke
• 10-20 years before detection-“silent killer”

Question 14

essential hypertension

Answer 14

• no identified cause, but several factors are believed to be involved:
  1) hereditary
  2) diet increase in: salt, fat, cholesterol foods
  3) obesity
  4) Age 40+ yrs
  5) Diabetes Mellitus
  6) stress
  7) smoking

Question 15

secondary hypertension

Answer 15

-obstruction of renal arteries, kidney disease, hyperthyroidism, Cushing’s Disease

Question 16

Nitric Oxide

Answer 16

causes vasodilation in blood vessels & temporarily increases blood flow

Question 17

endothelins

Answer 17

-vasoconstrictors, decrease blood flow

Question 18

hypovolemic shock

Answer 18

• most common form of shock
• “low” “blood volume”
• this results in large scale blood loss of blood, as might follow acute hemorrage, severe vomiting or diarrhea, or extensive burns

Question 19

cardiogenic shock

Answer 19

• or “pump failure”
• occurs when the heart is so ineffecient that it cannot sustain adequate circulation
• its usual cause is myocardial damage, as might follow numerous myocardial infarcts

Question 20

vascular shock

Answer 20

-blood volume is normal, but circulation is poor a result of an abnormal expansion of the vascular bed caused by extreme vasodilation

Question 21

what 3 sources of resistance and which is most important?

Answer 21

1) Blood viscosity
2) Total blood vessel length
3) Blood vessel diameter-*most important

Question 22

Blood viscosity

Answer 22

• thicker the blood the more resistance you will get, usually will be constant but RBC can thicken blood (blood doping, polycithemia)
• too little or too many RBC, thicken or thin the blood

Question 23

Total blood vessel length

Answer 23

• the longer the vessel the greater the resistance, changes during development

Question 24

Blood vessel diameter

Answer 24

• unlike the blood viscosity and blood vessel length, blood vessel diameter changes frequently, making it the biggest determinant of resistance
• the smaller the vessel, the greater the resistance by friction when blood contacts the wall

Question 25

What is the relationship between flow, pressure and resistance?

Answer 25

• F=(change in P/r)
• therefore increased decreases in pressure mean increase or decrease flow (direct) and increased resistance means increased flow (inversely proportional)

Question 26

What 2 factors control arterial blood pressure?

Answer 26

1) COMPLIANCE OR DISTENSIBILITY- amount the elastic arteries near the heart can stretch
2) The volume the blood being forced into them at any time.

Question 27

How do arteriol, capillary and venous pressure differ?

Answer 27

• ARTERIOL-(SYSTOLE)-120mmHg (DIASTOLE)-70~80mmHg
• CAPILLARY-(initial)-35mmHg-(initial)- 15mmHg
• VENOUS- 15 mmHg

Question 28

Ways the body assists blood in getting back through the veins to the heart?

Answer 28

1. Respiratory Pump-when we inhale, abdominal pressure increases, squeezes blood out to the heart
   2) Muscular or pump-skeletal around veins contracting and relaxing, “milks” blood toward heart
   3) Smooth Muscle- around veins will constrict, increase venous return.
   * sympathetic nervous system

Question 29

What factors maintain BP? How are these related?

Answer 29

• BP is maintained by CO, peripheral resistance, blood volume
• F=(change in P/R)
• CO=(change in P/R)
• (change P)= CO X R

Question 30

How Chemoreceptors modify vasomotor activity?

Answer 30

• when CO2 level rise, or pH falls, or O2 content of blood drops sharply, chemoreceptors in the aortic arch and large arteries of the neck transmit impulses to cardiacceleratory center, increase CO and to the vasomotor center, which causes reflex vasoconstriction, this increases BP leading to faster return of blood to the heart and lungs

Question 31

How do the higher brain centers modify vasomotor activity?

Answer 31

• BP is regulated through the medulla, but the hypothalamus and cerebral cortex can modify BP by relaying through the medulla
  ex. fight or flight mediated by the hypothalamus