Flashcards in Introduction to the Cardiovascular System Deck (107):
What is true of all living cells?
They are metabolically active
What is the result of living cells being metabolically active?
They use oxygen and nutrients, and produce carbon dioxide and other waste
How can single celled or tiny organisms get oxygen and nutrients?
Directly by diffusion from the environment
What is diffusion?
Random movement that results in an overall movement from high concentration to a low concentration
What is the result in small organisms being able to get oxygen and nutrients directly by diffusion?
They don’t require a cardiovascular system
How many cells are in the human body?
10^14 (100 million)
What is the problem with the human body having so many cells?
Most are far away from a source of oxygen and nutrients, and therefore can’t obtain them from diffusion
Why does the body cells being far away from a source of oxygen and nutrients mean that it can’t get them by diffusion?
Because diffusion is proportional to distance squared, so it works well over short distances, but not larger distances as it takes far longer to travel across
What is the result of large cells being unable to get oxygen and nutrients by direct diffusion?
They need a gas exchange and circulatory system to carry oxygen and nutrients to cells, and carry waste produces away
What does the right heart do?
Pumps blood to the lungs
What happens to blood at the lungs?
Gas exchange takes place and blood becomes oxygenated
What happens to blood once it has become oxygenated?
It passes from the lungs to the left heart
What does the left heart do?
Pumps blood to the body cells
What happens to blood at the body cells?
Oxygen is released
What does deoxygenated blood return to the right heart via?
The kidneys and the gut
Why does blood return via the kidneys?
Why does blood return via the gut?
What is the pulmonary circulation?
The circulation of blood form right heart to lungs, to left heart
Where is blood pumped in the pulmonary circulation?
Why is blood pumped to the alveoli?
So gas exchange can take place by diffusion
What is the systemic circulation?
The circulation of blood form left heart, to body, to right heart
How does blood in circulation travel?
By convective transport (flow)
What is the advantage of convective transport?
It works quickly over long distances
What is essential to allow diffusion to take place?
The mechanism for transporting substances close to cells
What is the distribution system?
Vessels and blood
What is the heart?
Effectively, two pumps
What is the exchange mechanism?
What does blood transport around the body?
How does exchange of substances between the blood and body cells occur?
What does the cardiovascular system provide?
The correct conditions for diffusion to take place at the tissues and lungs
Where does diffusion between blood and tissues take place?
What are capillaries composed of?
A single layer of endothelial cells, surrounded by a basal lamina
What is the advantage of capillaries being one cell thick?
There is a short distance for diffusion to take place
What molecules can directly diffuse through the lipid bilayer?
Those that are lipid soluble, e.g. oxygen and carbon dioxide
How do molecules that can’t diffuse through the lipid bilayer get through?
Small aqueous pores between endothelial cells in capillaries
What molecules can’t diffuse through the lipid bilayer?
Those that are hydrophilic and not lipid soluble, e.g. glucose, amino acids and lactate
In what direction do all molecules move?
Down their concentration gradient
What does how easily molecules diffuse through pores depend on?
Size and charge of molecule
Why are special transport molecules sometimes needed to get through pores?
In some places, e.g. the brain, the pores are tighter
What do leaky pores allow?
More molecules to move in and out of the capillary lumen
What does rate of diffusion depend on?
Area, diffusion ‘resistance’, and concentration gradient
What does a larger area available for exchange result in?
A faster rate of diffusion
What does the area of exchange between capillaries and tissues depend on?
What will be true of a tissue that is more metabolically active?
It will have more capillaries (a higher capillary density)
What does diffusion resistance pertain to?
The nature of the molecule, the nature of the barrier, and the path length
Give an example of what is meant by the nature of the molecule?
Is it hydrophilic or lipophilic
Give an example of what is meant by the nature of the barrier
Larger pores mean hydrophilic molecules and larger molecules can diffuse more readily
What does a greater path length lead to?
A slower rate of diffusion
What is the rate of diffusion proportional to?
The square of the distance it needs to travel
What does the path length depend on?
Where is path length shortest?
The most active tissues
What is normally the rate limiting factor of diffusion?
What does a greater concentration gradient lead to?
Greater rate of diffusion
What is the concentration gradient that matters in the human body?
Between the capillary blood and the tissues
What must happen to the concentration gradients for exchange to continue
The gradient between capillary blood and tissues must be maintained
What will happen to concentrations when a substance is used by tissues?
It will have a lower concentration in capillary blood that arterial blood
What happens to the concentration of oxygen as it’s used by tissues?
It falls in the blood
What does the extent of oxygen concentration decrease depend on?
Rate of use by tissue
Rate of blood flow through capillary bed
What does a higher rate of flow through the capillary bed mean?
The more the concentration gradient can be maintained to match the rate of use in tissues
What is the result of a lower blood flow at any rate of use?
The lower the capillary concentration
What must the rate of blood flow do?
Be high enough to maintain a sufficient concentration gradient for diffusion
What does the rate of blood flow determine?
The concentration gradient driving oxygen or nutrient diffusion into cells
What must blood flow match?
The tissues metabolic needs
What is the result of a higher rate of metabolism?
The greater the demand for oxygen and nutrients, and so an increase in blood flow
What is the rate of blood flow known as?
What is the perfusion rate of the brain?
Needs constant high flow
0.5ml per min per gram
What is the perfusion rate of heart muscle?
0.9ml per min per gram at rest
3.6ml per min per gram during exercise
What is the perfusion rate of kidneys?
Need high, constant flow
3.5ml per min per gram
Give two places where blood flow varies?
When is skeletal muscle blood flow high?
When is gut blood flow high?
After a meal
What is the cardiac minimum flow in for a 70kg man?
5 litres per min
What is the cardiac maximum flow in for a 70kg man?
24.5 litres per min
What must the cardiovascular system do?
Supply between 5 and 25 litres per minute of blood to the tissue, whilst at all times maintaining perfusion to vital organs such as the brain, heart and kidneys
How long would the heart have to stop beating for you to go unconscious?
2 to 4 secs
What happens once the heart stops beating for a minute?
Neurones start to die
What are the components of the cardiovascular system?
Pump- the heart
Distribution system- vessels and blood
Exchange mechanisms- capillaries
What acts as the flow control in the cardiovascular system?
What do pre-capillary sphincters and specialised arterioles have?
Lots of smooth muscle cells
How do pre-capillary sphincters and arterioles control flow?
The smooth muscle cells tense to restrict blood flow, or relax to increase blood flow to the area
What would happen if there was no flow control?
Blood would only flow to the parts that are easier to perfuse
What is the problem with blood flowing only to the easiest to perfuse areas?
The brain is harder to perfuse, due to gravity
What needs to be added to the system to regulate blood flow?
What is meant by adding resistance to the system?
Reducing the ease with which some reasons are perfused, in order to direct blood flow to the more difficult to perfuse regions
What are the resistance vessels?
Why are the arterioles the resistance vessels?
As they narrow flow to one area, and therefore allow it to go to other areas
What is the heart made up of?
Two pumps in series
What does the left heart do?
Pumps blood around the systemic circulation
What does the right heart do?
Pumps blood around the pulmonary circulation
What does the heart pump to in the systemic circulation?
Arteries via the aorta
What do the arteries supply?
What do arterioles supply?
What do capillaries produce?
A branching network
What does the capillaries branching network provide?
A large surface area for diffusion
What do capillaries drain into?
What do venules drain into?
What must the total flow in the system be able to do?
What does the ability to change the total flow in the system require?
A temporary store of blood, which can be returned to the heart at a different rate
Why does a change in total flow in the system require a temporary store of blood?
The heart can only pump more blood through if it has more blood going into it
What provides the temporary store of blood?
The capacitance of veins
Why are veins able to provide a temporary store of blood?
Because they have thin walls with smooth muscle in them, so they can easily distend of collapse, enabling them to act as a variable reservoir
In what direction does blood flow?
From high to low pressure
How does the pressure of blood change as it goes through the system?
The heart increases the pressure of the blood to push it into the high pressure arterial system
Blood goes to resistance vessels, to exchange vessels, to capacitance vessels, resulting in blood being in the low pressure venous system
What causes the highest drop in blood pressure?
What is the result in drop in blood pressure caused by arterioles?
By the time that blood reaches capillaries, its at low pressure
What is the distribution of blood in the body?
It varies, but it is approximately-
11% in arteries and arterioles
5% in capillaries
17% in heart and lungs
67% in veins