6.2 The blood system Flashcards
What is our modern understanding of circulatory system based upon?
The discoveries of william harvey
What were the beliefs of the circulatory system prior to harveys findings?
- arteries and veins were separate blood networks
- veins were though to pump natural blood
- arteries were thought to pump heat via the lungs
What were the three findings Harvey proposed?
- arteries and veins were part of a single connected blood network
- arteries pumped blood from heart
- veins returned blood to the heart
What is the heart?
A four chambered organ
What are the four chambers of the heart?
Right ventricle
Left ventricle
Right Atria
Left atria
What do the atria act as?
Resevoirs
How do atria act as reservoirs?
By which blood returning to the heart is collected via veins
What do the ventricles act as?
Pumps
How do the ventricles act as pumps?
Expelling the blood from the heart at high pressure via arteries
Why are there two sets of atria and ventricles?
As there are two distinct locations for blood transport
What does the left side of the heart do?
Pump oxygenated blood around the body
What does the right side of the heart do?
Pump deoxygenated blood to the lungs
What are the two types of circulation?
Systemic and pulmonary circulation
What side of the body is systemic circulation?
Left
What side of the body is pulmonary circulation?
Right
Why does the left side of the heart have a much thicker muscular wall?
As it must pump blood much further
What is the function of the arteries?
To convey blood at high pressure from the heart ventricles to the tissues of the body and lungs
What is the three structures of arteries to match their functions?
- narrow lumen to maintain a high bp
- thick wall with an outer layer of collagen to prevent artery from bursting under the high pressure
- arterial wall has an inner layer of muscle and elastic fibres to maintain pulse flow
When is blood expelled from the heart?
Upon ventricular contraction
How does blood flow from the heart?
Through the arteries in repeated surges called pulses
What helps maintain the pressure in arteries?
Muscle and elastic fibres
What do the muscle fibres help to form in arteries?
A rigid arterial wall capable of withstanding the high bp without bursting
What do the elastic fibres allow the arterial wall to do?
Stretch and expand upon the flow of a pulse through the lumen
What happens when the lumen is narrowed in the arteries?
Pressure increases between pumps to maintain bp throughout cardiac cycle
When is the pressure exerted on the arterial wall returned to the blood?
When the artery returns to its normal size
What does the elastic recoil in arteries help to do?
Push the blood forward through the artery as well as maintain arterial pressure between pump cycles
What is the function of capillaries?
To exchange materials between the cells in tissues and blood travelling at low pressure
What do arteries split into?
Arterioles
What do arterioles split into?
Capillaries
What decreases as total vessel volume is increased?
Arterial pressure
What does the branching of arteries into capillaries ensure?
Blood is moving slowly and all cells are located near a blood supply
What do capillaries pool into after material exchange?
Venules which in turn collate into larger veins
What are the four key structures of capillaries?
- small diameter
- capillary wall is made of a single layer of cells
- surrounded by a basement membrane
- may contain pores
What does the fact capillaries have a small diameter allow?
Passage of only a single red blood cell at a time
Why does the capillary wall being a single layer of cell minimise?
Diffusion distance for permeable materials
What is the basement membrane surrounding capillaries permeable to?
Necessary materials
What do the pores in capillaries aid with?
The transport of materials between tissue fluid and blood
What are the three types of capillary structure?
Continuous
Fenestrated
Sinusoidal
What is a continuous capillary wall?
Continuous with endothelial cells held by tight junctions
What do the tight junctions limit?
Permeability of large molecules
When will the capillary be fenestrated?
In tissues specialised for absorption
What do sinusoidal capillaries have?
Open spaces between cells and may be permeable to large molecules and cells
How does blood flow through capillaries?
Very slowly and at low pressure
Why does blood flow through capillaries at slowly and at low pressure?
To maximise material exchange
What is the high blood pressure in arteries dissipated by?
The extensive branching of vessels and narrowing of the lumen
What does the higher hydrostatic pressure at the arteriole end of the capillary force?
Material from the bloodstream into the tissue fluid
What are examples of materials that exit the capillaries at body tissues?
Oxygen and nutrients
What does the lower hydrostatic pressure at the venule end of the capillary allow?
Materials from the tissue to enter the bloodstream
What are examples of materials that enter the capillaries at body tissues?
Carbon dioxide and urea
What is the function of veins?
To collect blood from the tissues and convey it at low pressure to the atria of the heart
WHat are the the three key structures veins have?
- very wide lumen
- thin wall with less muscle and elastic fibres
- valves
Why do veins have a very wide lumen?
To maximise blood flow for more effective return
Why do veins have less muscle and elastic fibres?
As blood is flowing at a very low pressure
Why do veins have valves?
As pressure is low, to prevent backflow and stop blood pooling at the lowest extremities
Why can blood flow in veins be difficult to move against the downward force of gravity?
As blood is at a very low pressure
How do veins maintain the circulation of blood by preventing backflow?
Contain numerous one-way valves
Where do veins typically pass between?
Skeletal muscle groups
How do skeletal muscle groups facilitate venous blood flow?
Via periodic contractions
