Cardiovascular System, Lecture 8

Question 1

Venous - venules and veins

Answer 1

blood pressure
- minimal pressure; enough to get back to right atrium of heart (never gets to zero)
- enough pressure to get back (low)
- factors to assist return
total cross sectional area
* branches rejoining - decreasing area - lowering resistance ( 3 passageways left to head back to the heart)
- results in increased velocity of blood flow from capillaries as heading back to heart (resistance is less so we pick up velocity - flowing better)

Question 2

Alter vasomotor nerves (symapathetic) to veins:

Answer 2

alter vasomotor nerves (sympathetic) to veins:
- venous vessels represent “blood reservoir” (volume of blood held in veins and venules) (alter blood reservoir)
- amount of blood the veins hold at a particular point in time - Blood reservoir
- veins are container holding certain amount of blood, we can make it larger or smaller
◦ can hold large amount of blood with little pressure (high compliance)
◦ compliance = △volume/△pressure
◦ very little pressure is needed to get a high amount of volume (high compliance)
◦ a changeable variable
Venoconstriction (less, extra venous return) - increase in sympathetic activity /venodilation (larger container, smaller venous return) - decrease in sympathetic activity
-> manipulating volume of blood
* alters volume in blood reservoir
* alters venous return
* alters stroke volume
* alters cardiac output

Question 3

Alter skeletal muscle pump:

Answer 3

• ones running between muscles (preferred) or between bones
• veins are very complaint meaning that will listen to outside forces
• muscle contract, squeeze vein which will lead to pressure change, with resulting high pressure
• we do not want to squeeze pushing blood pack down the feet instead up to the heart
• when muscle contracts the valves close as the cusp fills and pushes it upwards, when relaxed leg then cusp is not filled allowing blood flowing downward
  alter skeletal muscle pump:
• contracting skeletal muscles creates pressure changes
• pressure changes squeeze compliant venous and increase venous pressure locally
• aid pressure gradient for blood flow back to heart
• valves to prevent backflow

Question 4

alter respiratory pump:

Answer 4

• diaphragm - dome (relaxed), contracted (flat shape) - divides the thoracic and abdominal cavity
• inspiration allows air to flow into the lungs
• expiration involves gases leaving the lungs
  alter respiratory pump (pump based on breathing):
• breathing diaphragm movement creates pressure changes
  ◦ inspiration (flattening): abdominal pressure > thoracic pressure (gradient that favours blood moving back to heart
  ◦ expiration (dome): abdominal pressure < thoracic pressure (valves to then prevent backflow because there is space lower now when blood would want to go) (gradient decrease)
• pressure changes squeeze compliant venous and increase venous pressure locally
• aid pressure gradient for blood flow back to heart
• valves to prevent backflow

Question 5

Alter blood volume (BV) -> indirectly

Answer 5

• long term regulation -> blood volume
  alter blood volume (BV):
• hormones - indirect mechanism on BV by altering kidney reabsorption (altering kidney output) (quicker pathway)
  increasing BV
• if you increase plasma volume you can increase blood volume
• angiotensin ll:
  ◦ secretion of aldosterone - greater sodium and water reabsorption
  ◦ increased signal to hypothalamus thirst center (stimulate thirst center -> consume more water) - greater water consumption
• ADH - greater water reabsorption (reabsorped more water, more PV -> more BV)
  decreasing BV
• ANP - reduced sodium and water reabsorption
• will see more detail of mechanisms with urinary system

Question 6

Alter blood volume -> direct

Answer 6

• difference is not outcome, its the starting point
• indirect have to do something that alters hormones that then alters urinary system
• directly change the kidney - not a hormone involved
  ◦ directly change blood volume
  ◦ alter arterial pressure
  alter blood volume (BV):
• kidneys - direct mechanism on BV by altering urinary excretion
  blood volume - arterial pressure
• working together for regulation
• both directly affect each other