29 Questions
What is the main function of the lymphatic system in relation to the capillaries?
To return lost plasma protein to the blood circulation
What is the primary mechanism by which gas and nutrient exchange occurs in the capillaries?
Diffusion
What is the role of the veins in the circulatory system?
To return deoxygenated blood from the tissues to the heart
How do the valves in the veins assist in the return of blood to the heart?
They open when the venous pressure is driving blood flow towards the heart, and close when pressure drops to prevent backflow
What is the role of the precapillary sphincters and arterioles in the circulatory system?
To control the amount of blood that flows into the capillaries
What are the local metabolic changes that occur in skeletal muscle during activity, and how do they affect the smooth muscle of the arterioles?
Decreased PO2, increased PCO2, increased acid production, and increased temperature, leading to arteriolar smooth muscle relaxation and increased blood flow
What is the main function of the heart according to the text?
To circulate blood around the body
Where does blood get oxygenated in the circulatory system?
In the lungs
What happens during atrial systole?
Atria contract
What occurs during ventricular diastole?
Blood returning to the heart
Which chamber of the heart receives deoxygenated blood from the periphery?
Right atrium
What allows us to return blood from the lower limb to the heart, especially when we are standing upright?
Valves in the veins and skeletal muscle contraction
Who was the first to recognize the role of valves in the veins in assisting blood flow back towards the heart?
William Harvey
Where does the major pressure drop occur in the circulatory system?
Arteries
Which part of the nervous system controls the diameter of arterioles to match tissue needs?
Sympathetic nervous system
What causes the smoothing of blood flow by the time it reaches the capillaries?
Elastic nature of vessels
Why is diastolic blood pressure in the left ventricle different from diastolic pressure in the arteries?
Elastic nature of vessels and aortic valve function
What is the primary function of the arterial system?
To act as a pressure reservoir for blood flow
What causes the semilunar valves to open during systole?
Increased pressure in the ventricles
What happens to the major arteries during systole?
They bulge or stretch like a balloon being inflated
What causes the aortic valve to close at the start of diastole?
Increased pressure in the aorta
What drives the continuous flow of blood through the arteries during diastole?
Elastic recoil of the major arteries
What does the term 'diastolic pressure' refer to?
The lowest pressure in the arteries before ventricular contraction
What happens when the ventricles begin to contract?
The pressure in the ventricles rises and exceeds the pressure in the atria.
What happens to the AV valves when the ventricular pressure exceeds the atrial pressure?
The AV valves slam shut, creating the first heart sound.
What happens to the semilunar valves during the isovolumic phase of ventricular contraction?
The semilunar valves remain closed until the ventricular pressure exceeds the pressure in the arteries.
What happens to the semilunar valves when the ventricular pressure exceeds the pressure in the arteries?
The semilunar valves open to allow blood flow.
What happens at the end of systole, when diastole begins?
The ventricular pressure drops below the arterial pressure, and the semilunar valves are pushed shut, creating the second heart sound.
What can happen to diseased or damaged heart valves?
They can become stiff or leaky, causing a murmur.
Study Notes
Smooth Muscle Activity
- Smooth muscle activity can be affected by local metabolic products and hormones
- Localized skeletal muscle activity leads to:
- Decreased PO2
- Increased PCO2
- Increased acid production
- Raised temperature
- Arteriolar smooth muscle relaxation
- Decreased resistance
- Increased flow of oxygenated arterial blood to the working muscle
Blood Circulation
- Precapillary sphincters and arterioles control the amount of blood that flows into the capillaries
- Flow through capillaries is slow, allowing for efficient exchange of gases and nutrients by diffusion
- Capillary walls are slightly leaky, allowing some plasma protein to leak into the interstitial fluid
- The lymphatic system returns lost protein to the blood circulation
Veins
- Veins provide a low resistance, low pressure pathway for blood to return to the heart
- Valves in the veins are oriented to open when venous pressure is driving blood flow towards the heart
- Valves close when pressure drops, preventing backflow
Heart
- The heart is a dual pump that circulates blood around the body and through the lungs
- Blood enters the atrial chambers at a low pressure and leaves the ventricles at a higher pressure
- High arterial pressure provides energy to force blood through the circulatory system
Cardiac Cycle
- Ventricular diastole (relaxation):
- Blood returns to both sides of the heart
- Deoxygenated blood from the periphery enters the right atrium
- Oxygenated blood from the lungs enters the left atrium
- Atrial contraction (atrial systole):
- Filling of the ventricles is completed
- Accounts for only 20% of ventricular filling in the resting state
- Ventricular contraction (ventricular systole):
- Contraction of the ventricles
- The combination of veins with valves and skeletal muscle contraction allows for blood return from the lower limb to the heart
Blood Flow
- Pressure gradient generated by ventricular contraction drives blood flow through the circulation
- Blood flow is pulsatile in the arteries but becomes smoothed by the time it reaches the capillaries
- The major pressure drop occurs in the arterioles, which provide the single largest resistance to flow
- Arterioles are controlled by the sympathetic nervous system, adjusting blood flow to match tissue needs for oxygen and energy
Arterial System
- The arterial system functions as a pressure reservoir
- Blood leaves the arterial system continuously through the capillaries, but enters only intermittently from the heart
- The ventricles contract during systole, causing the semilunar valves to open and blood to flow into the arterial system
- The aortic valve closes at the start of diastole, preventing blood from flowing back into the ventricles from the aorta
Blood Pressure
- Systolic pressure is defined as the peak pressure reached during the cardiac cycle
- Diastolic pressure is the lowest pressure reached during the cardiac cycle, immediately before the contracting ventricle pushes blood into the arteries again
- The arterial pressure decreases during diastole due to the elastic recoil of the major arteries
Learn about the dual pump function of the heart that circulates blood around the body and through the lungs. Understand how blood flows from atrial chambers to ventricles at different pressures, providing energy to force blood through the circulatory system.
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