lecture 11

Question 1

how to calculate cardiac output and stroke volume

Answer 1

• Cardiac output = heart rate x stroke volume
  Stroke volume = end diastolic volume (relaxation of heart) - end systolic volume (contraction of heart)

Question 2

describe the cardiovascular system

Answer 2

• From lungs, oxygenated blood goes through pulmonary veins to left atrium, goes through bicuspid valve to left ventricle to aortic valve (note right and left ventricles contract at the SAME time, and eject the SAME amount of blood)
  
  • Then goes through aorta and systemic arteries in systemic capillaries to organs
    Arranged in parallels
  • Gets deoxygenated, then blood empties from veins into superior, inferior vena cava and the coronary sinus
    Then goes to right atrium, through tricuspid valve to right ventricle, to pulmonary valve to pulmonary trunk and pulmonary arteries back into the lungs

Question 3

describe venous return

Answer 3

• Is the blood flow returning to the heart in the venous system
  CO = VR (e.g. If 5L/min cardiac output, then have 5L/min venous return)

Question 4

why does blood flow in 1 direction

Answer 4

1. Pressure gradient
   ○ Is created by the heart pumping
   ○ Blood goes from high gradient to low gradient
   2. One-way valves
      ○ Prevents blood from back flowing
      Heart has AV valve, in veins- venous valves are bicuspid

Question 5

describe one-way valves

Answer 5

AV valves go down, semilunar valves go across

Question 6

what are the determinants of blood flow

Answer 6

pressure + resistance

Question 7

describe pressure: in systemic vs pulmonary systems

Answer 7

○ Delta P = P1-P2
○ Is the difference in blood pressure between 2 points
○ Blood flows from areas of high pressure to areas of low pressure
○ Blood travels from left ventricle to right atrium (120mmHg to 2mmHg) due to the pressure gradient of the SYSTEMIC CIRCULATION
The blood travels from the right atrium to the left ventricle (25mmHg to 8mmHg) due to the pressure gradient of the PULMONARY CIRCULATION

Question 8

describe resistance

Answer 8

○ Is the impediment to blood flow through a vessel due to friction of blood with vessel walls
○ Cannot be directly measured, instead calculated using Ohm’s law (delta P = F x R)
○ Most resistance is located with in the peripheral systemic circulation (arterioles), so resistance for the whole body is called the total peripheral resistance (TPR)
○ Blood flow is inversely proprtional to resistance (as resistance increases, blood flow decreases)
So resistance increases as diameter decreases due to increase friction + decrease laminar flow

Question 9

3 factors that vascular resistance depends on

Answer 9

1. Lumen diameter (eg. Big vs small straw, bigger straw easier to drink from due to less resistance)
   2. Blood viscosity (if thicker, travels slower because resistance higher because more friction) note: haematocrit increases viscosity
   Length of blood vessel (longer = more resistance, gaining weight increases blood vessel length, so obesity can lead to hyper tension)

Question 10

poiseuille’s law

Answer 10

• Relates to lumen diameter
  Flow is proportional to vessel radius to the 4th power

refer to onenote for a formula

* Vasoconstriction (contractions) = increase resistance = decrease blood flow
* Vasodilation = decrease resistance = increase blood flow
* So blood closet to vessel wall is slower (hgiher resistance) due to greater friction, while the blood in the middle is faster due to less friction (lower resistance) Bigger the diameter, greater % of blood NOT touching walls

Question 11

describe arterial tones

Answer 11

• Normal arteriole = normal tone
  
  • Vasoconstriction = INCREASED tone
    Vasodilation = REDUCED tone

Question 12

describe total peripheral resistance (TPR)

Answer 12

• Is ALL the vascular resistance from systemic vessels
  
  • Arterioles constrict + relax the most, so TPR is controlled here
    ONLY slight changes in radius can lead to large effects on TPR