Week 3 - Lesson 1 (Part 3) Flashcards
What is the essential principle in circulation?
That a pressure gradient must be created in order for blood to flow
How is a pressure gradient produced?
By the contraction of the heart and the resultant ejection of blood into the aorta and systemic vessels
How is energy lost in circulation?
In the form of heat
Vascular resistance
Is the resistance to flow that must be overcome to push blood through the circulatory system and create flow
Systemic vascular resistance (SVR)
Is the resistance offered by the peripheral circulation
What is net flow controlled by? (2)
- Arterial resistance
2. Arteriolar resistance
What kind of diameters and resistance to flow do non diseased circulation on arteries have? (2)
- Diameter = relatively large
2. Resistance = small
What are the main resistance vessels?
Arterioles
How do you preserve blood flow to the capillary bed?
With an increase in resistance in a large distributing artery because of atheroma they must be compensated by a decrease in the resistance of the small arteries and arterioles
How is flow maintained as a diseases progresses?
By arteriolar dilatation
- until a point is reached where the arteriolar network is fully dilated
What happens when there is an increase in a degree of stenosis?
It leads to a reduction in flow
What is the major determinant of vascular resistance?
Precapillary arterioles
What kind of vessels are precapillary arterioles?
Autoregulatory
Autoregulatory
Vessels that can dynamically change in diameter to increase or reduce blood flow
What is an example of autoregulatory?
During exercise the arterioles will increase in diameter to allow for increased flow to the muscles
- the peripheral flow then becomes low resistant with continuous flow throughout systole and diastole
What are 3 sources of peripheral resistance?
- Blood viscosity
- Blood vessel diameter
- radius - Total vessel length
Blood viscosity
Is a measure of the resistance of blood to flow
What is an example of a biophysical property? (2)
- Thickness of blood
2. Stickiness of blood
What does viscosity determine? (4)
- Friction against vessel walls
- Rate of venous return
- Work required to pump the heart
- How much oxygen is transported to tissues and organs
What is blood viscosity affected by? (9)
- Hypertension
- Cholesterol and triglycerides
- LDL and HDL - Diabetes
- Obesity
- Cigarette smoking
- Male gender
- Aging
- Temperature
- Anemia
When does blood viscosity increase?
As blood is more hemoconcentrated
- as red blood cell concentration increases
When does blood viscosity decrease?
As blood is more diluted
- red blood cell concentration decreases
Hemodilute
Blood will flow more readily
- thinner
Hemoconcentrated
Blood will flow more steadily
- thicker
Hematocrit
Is the percentage of red cells in the total blood volume
What does hematocrit affect?
The bloods viscosity
- therefore the resistance to flow
What does it mean if the blood is more viscous? (2)
- The greater the resistance it encounters
2. The higher the blood pressure
When can the hematocrit increase? (2)
- More red blood cells
2. Less plasma in the blood
When can the hematocrit decrease? (2)
- Fewer red blood cells
2. More plasma
What is blood strongly dependent on?
Hematocrit
Polycythemia
Is a condition of abnormal elevation in red cell hematocrit causing higher blood viscosity
What does polycythemia do? (3)
- Increases the resistance to flow
- Increases the work of the heart
- Can impair organ perfusion
What does anemia cause? (2)
- Low hematocrit
2. Reduced blood viscosity
