6.2 The Blood System Flashcards
What did William Harvey find?
- The heart acted as a pump for the circulation of blood
- Demonstrated that blood flow through the larger vessels is unidirectional, with valves to prevent backflow
- Predicted the presence of numerous fine vessels too small to be seen with contemporary equipment that linked arteries to veins in the tissues of the body
After some simple experiments and observations, what did Harvey propose? (3)
- Arteries and veins were part of a single connected blood network (he did not predict the existence of capillaries however)
- Arteries pumped blood from the heart (to the lungs and body tissues)
- Veins returned blood to the heart (from the lungs and body tissues)
How many chambers do the heart have? What are they?
The human heart is a four chambered organ, consisting of two atria and two ventricles
What do atria and ventricles act as? What do they do?
Atria: acts as reservoirs, by which blood retuning to the heart is collected via veins (and passed on to ventricles)
Ventricles: acts as pumps, expelling the blood from the heart at high pressure via arteries
Why are there two sets of atria and ventricles?
Because there are two distinct locations for blood transport
What does the left and right side of the heart do?
The left side of the heart pumps oxygenated blood around the body (systemic circulation)
The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation)
Why does the left side of the heart have a much thicker muscular wall?
It pumps the blood much further - to the body compared to the just the lungs for the right side
What is the function of arteries?
To convey blood at high pressure from the heart ventricles to the tissue of the body and lungs
What are the characteristics of artery structure?
- Narrow lumen (relative to wall thickness) to maintain a high blood pressure
- Have think wall containing an outer layer of collagen to prevent the artery from rupturing under the high pressure
- The arterial wall contains a inner layer of muscle and elastic fibres to help maintain pulse flow (it can contract and stretch)
How does blood flow through the arteries?
In repeated surges called pulses
This blood flows at a high pressure and the muscle and elastic fibres assist in maintaining this pressure between pumps
How does muscle fibres in arteries help withstand high blood pressure and also increase pressure?
- help form a rigid arterial wall that is capable of withstanding the high blood pressure without rupturing
- Muscle fibres also contract to narrow the lumen, which increases the pressure between pumps and helps to maintain blood pressure throughout the cardiac cycle
What benefit comes from the elastic and muscular tissues contributing to the toughness of the walls?
Strong enough to withstand the constantly changing and intermittently high blood pressure without bulging outwards (aneurysm) or bursting
What does the pulse reflect?
each heartbeat and can easily be felt in arteries that pass near the body surface, including those in the wrist and the neck
What do elastic fibres do upon the flow of a pulse through the lumen?
They allow the arterial wall to stretch and expand
What is elastic recoil and how they help?
When the pressure exerted on the arterial wall is returned to the wall and the artery returns to its normal size
The elastic recoil helps to push the blood forward through the artery as well as maintain arterial pressure between pump cycles
What does the contraction of smooth muscle in the artery wall determine?
The diameter of the lumen and to some extent the rigidity of the arteries, thus controlling the overall flow through them
What artery supplies the powerful, continuously active muscles of the heart with blood?
Coronary arteries
What is systolic pressure?
The peak pressure reached in an artery
- It pushed the wall of the artery outwards, widening the lumen and stretching elastic fibres in the wall, this storying potential energy
What happens at the end of each heartbeat?
Pressure in the arteries falls sufficiently for the stretched elastic fibres to squeeze the blood in the lumen
- This mechanism save energy and prevents the minimum pressure inside the artery, called the diastolic pressure, from becoming too low.
What is diastolic pressure?
The lowest arterial blood pressure of a cardiac cycle occurring during diastole of the heart.
When does pressure change during the cardiac cycle?
Left atrium, left ventricle and aorta
What are the 3 layers of the artery wall?
- Tunica Externa - a tough outer layer of connective tissue
- Tunica Media - A thick layer containing smooth muscle and elastic fibres made of the protein elastin
- Tunica Intima - a smooth endothelium forming the lining of the artery.
What do the circular muscles in the wall of the artery form?
A ring
What is vasoconstriction?
When the circular muscles in the wall of the artery contract and the circumference is reduced, and the lumen is narrowed
What does vasoconstriction increase in the arteries?
Blood pressure
What are capillaries?
the narrowest blood vessels with a diameter of about 10um
How are capillary network formed?
Capillaries branch and rejoin repeatedly
What is the function of capillaries?
to exchange materials between the cells in tissues and blood travelling at low pressure
- Transport blood through almost all tissues in the body
What is split in order to turn into capillaries?
Arteries split into arterioles which split into capillaries, decreasing arterial pressure as total vessel volume is increased
What dos the branching of arteries into capillaries ensure?
It ensures blood is moving slowly and all cells are located near a blood supply
What happens to capillaries after material exchange has occured?
The capillaries will pool into venules which will in turn collate into larger veins
What are characteristic of the capillaries structure? (4)
- very small diameter which allows passage of only a single red blood cell at a time (optimal exchange)
- The capillary wall is made of a single layer of thin endothelium cells to minimise the diffusion distance for permeable materials
- coated by a filter-like protein gel, with pores between the cells, thus very permeable and allows part of the plasma to leak out and form tissue fluid
- May contain pores to further aid in the transport of materials between tissues fluid and blood
What is plasma?
The fluid in which the blood cells are suspended
What do tissue fluid contain?
Oxygen, glucose, and all other substances in blood plasma apart from large protein molecules, which cannot pass through the capillary wall.
What does tissue fluid do?
Flows between the cells in a tissue, allowing the cells to absorb useful substances and excrete waste products. The tissue fluid then re-enters the capillary network.
What is the effect of the differing permeabilities of capillary walls?
Enabling particular proteins and other large particles to reach certain tissues but not others.
How may capillaries structure vary depending on its location in the body and specific role?
- The capillary wall may be continuous with endothelial cells held together by tight junctions to limit permeability of large molecules
- In tissues specialised for absorption (e.g. intestine, Kidney), the capillary wall may be fenestrated (containing pores)
- Some capillaries are sinusoidal and have open spaces between cells and be permeable to large molecules and cells
What is the flow of blood like in capillaries?
- Very slow
- Low pressure
→ allow for maximal material exchange
How is the high blood pressure in arteries dissipated?
By extensive branching of the vessels and the narrowing of the lumen
What kind of materials do the blood capillaries exchange?
Oxygen and nutrients to cells for respiration