Lecture 18 : Cardiovascular Overview Flashcards
(28 cards)
What 3 components make up the circulatory system?
- Heart - pump
- Blood vessels - pipes
- Blood - fluid to be moved
What other systems/organs affect the function of the cardiovascular system?
- Endocrine system
- Nervous system
- Kidneys
What is blood made up of?
- Formed elements 45% - cells and cell fragments
- Plasma 55% - mostly water
What is the role of plasma?
Carries blood cells, proteins, nutrients, metabolic wastes, and other molecules being transported around the body
What is bulk flow?
Rapid flow of blood throughout the body is produced by the pressure created by the pumping action of the heart
Describe how each bulk flow distributes contribute to homeostasis:
- Ions, water, CO2 - regulates pH, osmolarity, body water
- Heat - regulates temperature
- Hormones, O2, CO2, substrates - regulate metabolism
Describe the contribution of the circulation of the blood to homeostasis:
Lung: O2, CO2 (pH)
Gut: Nutrients, ions, water
Skin: Heat
Kidney: Water, ions (pH & osmolarity)
Describe the basic design of the circulation:
- Double circulation
- The right heart pumps the cardiac output through the lungs via the pulmonary circulation
- The left heart pumps the cardiac output through the body via the systemic circulation
What is cardiac output?
The amount of blood pumped by each side of the heart EACH MINUTE
What is the cardiac output of an average person?
- 5 to 6 litres/minute (in a ~70 kg person)
- This will depend on body size - a smaller person will have a proportionally smaller SV and CO
What is stroke volume? Give the value at rest.
The amount pumped out of each side of the heart EACH BEAT
* At rest SV= 60 - 80 mL
What is heart rate (HR)?
At rest the heart beats 50 to 80 times per minute
Give the equation for working out cardiac output:
CO = HR x SV
Describe the series flow in the circulatory system:
Blood flows sequentially through the pulmonary and systemic circuits, which are arranged in series
Describe the parallel flow in the circulatory system:
- In the systemic circuit blood can flow through a ‘choice’ of paths that originate at branches
- These branch circuits are arranged in parallel
Describe the blood flow in the different organs:
- Flow is not the same in all organs
- Flow is dynamic
- At rest the total blood flow in the body is ~5000mL/min
Describe the resistance, flow, and pressure of blood around the body (hemodynamics):
- To start or maintain blood flow, energy must be put into the system – heart generates pressure
- Blood flows from a region of high to low pressure
- Energy is lost from flowing blood through friction - resistance to blood flow
Describe the relationship between blood flow, pressure, and resistance:
- Blood flow = drop in blood pressure/ resistance to flow
- F = ΔP/R
- F ∝ ΔP
- F ∝ 1/R
- ΔP ∝ R
What factors affect resistance?
- Length of tube
- Viscosity of liquid
- Radius of tube
* In physiology we can only change radius
- R = 1/r4
- If radius doubles, resistance decreases by 16 times
What is the sequence of vessels in the systemic and pulmonary circuits?
- Aorta
- Arteries
- Arterioles
- Capillaries
- Venules
- Veins
- Vena cava
Where is most of the blood volume located?
Veins (40%)
Where is least of the blood volume located?
Aorta (2%)
Arterioles and capillaries (3%)
Describe the relationship between cross-sectional area and the velocity of blood flow?
- CSA of capillaries is massive compared to aorta as we have heaps of capillaries but one aorta
- Blood velocity starts high through the aorta
- Blood moves away and branches so blood velocity within each blood vessel gets slower
- Very slow in capillaries so exchanges can occur
- Coming back to the heart, velocity is half as what it was at beginning because the vena cava is bigger than the aorta so blood doesn’t need to move as fast to move the same volume
What determines the blood pressure gradient through each circuit?
- More resistance causes lower blood pressure
- Lowest bp entering the heart
- Highest bp as it leaves
- Systemic circuit has a much higher pressure than the pulmonary circuit
- Pressure dampens as blood moves away from the heart
