6.2 - the blood system Flashcards
1
Q
who discovered the circulation of blood and that the heart pumped blood?
A
- William Harvey
- found that blood had unidirectional flow, veins returned blood to heart and valves prevented backflow of blood
- blood flowed too high to be consumed by body
2
Q
what are arteries?
A
- type of blood vessel that carries blood from the heart to the tissue of body.
3
Q
how does an artery work?
A
- blood flows through the lumen (middle)
- ventricles of the heart pump high volumes of blood at high pressures
- so the walls of arteries are elastic and have muscle cells that facilitate and control this blood flow.
- elastin fibres in walls to help propel the blood through artery
- contraction of muscle in walls controls overall flow
- tough walls from elastic and muscular tissue, needed for pressure
- blood pulsates from contractions
- coronary arteries supply heart with blood
4
Q
whats the structure of the artery wall?
A
- several layers
- tunica externa is a tough outer layer of connective tissue
- tunica media is a thick layer containing smooth muscle and elastic fibres made of protein elastin
- tunica intima is the internal layer of smooth endothelium that lines the lumen of the artery
5
Q
how does arterial blood pressure work?
A
- blood enters artery at high pressure form heart
- peak pressure is called systolic pressure
- This pushes the wall of artery out, widening the lumen and stretching the elastic fibres in the wall, storing potential energy.
- end of a heartbeat, the pressure in arteries falls and the stretched
elastic fibres squeeze the blood in the lumen, saving energy and preventing the minimum pressure (called diastolic pressure) from getting too low. - lumen narrows when circular muscles contract, vasoconstriction
- vasodilation causes an increase in
blood flow and decreases blood pressure.
6
Q
what is a capillary?
A
- tiny blood vessel
- they branch and connect to form a network of capillaries
- they transport blood to most tissue of the body except the lens and cornea of the eye
- link arteries and veins in the tissue
7
Q
structure of a capillary?
A
- wall consists of one very thin layer of endothelium cells coated with a protein gel and pores between the cells
- wall is very permeable and plasma can leak out from the lumen to form tissue fluid
- Tissue fluid contains oxygen, glucose and other things found in plasma but not plasma proteins
- tissue fluid flows between cells in tissue so they can absorb useful substances and secrete waste
- tissue fluid then re-enters the capillary network
- blood pressure in capillaries is extremely low due to the excessive branches of capillaries (lower volume).
- slows the movement of blood for efficient exchange of materials
8
Q
what is the structure veins?
A
- blood from capillaries enters veins to be transported back to the atria of the heart
- blood pressure is low in veins
- walls contain less muscle and elastic fibres bc less pressure
- the lumen of veins becomes wider
as they can dilate so to hold more blood than arteries. - Gravity and skeletal muscle contractions allow for blood to flow through veins.
- Muscle contractions act as a pump during movement to move blood.
9
Q
what do valves do?
A
- low pressure in veins can flow backwards to the capillaries and not enough blood is returned to the heart.
- To prevent this, veins have valves which are 3 cup-shaped flaps of tissue without muscle.
- Valves open when blood flows towards the heart as it pushes the flaps to the side of the vein
allowing blood to flow freely. - If blood flows back, it is caught in the flaps of the pocket valve, which fills with blood and is blocking
the lumen of the vein. - As a result, blood is circulated in one direction.
10
Q
what is a single circulation system?
A
- when blood flows in one direction to the gills to be oxygenated before flowing to the organs and heart
11
Q
what is the double circulation system?
A
- a separate circulation for gas exchange
- blood capillaries in lungs cant have high pressure, so pumped to lungs at low pressure
- blood from lungs goes back to heart oxygenised to pump to other organs at high pressure
- There is pulmonary circulation to and from the lungs, and systemic circulation to and from the other organs
- Blood is delivered under different pressures and separately in the two
circulations in mammals
12
Q
explain the heart structure.
A
- right side pumps to the pulmonary circulation
- left side pumps to systemic circulation
- atriums collect blood from veins and pumps it into the ventricle
- ventricle pumps blood into the arteries of each circulation
- Each side of the heart has two sets of valves: an atrioventricular valve between the atrium and ventricles, and semilunar valves between the
ventricles and arteries - Deoxygenated blood flows into the right side and oxygenated blood flows through the left side
13
Q
what is Atherosclerosis?
A
- a chronic disease caused by elevated serum cholesterol levels (in blood) that result in lipids deposited in walls of arteries
- releases growth factors that stimulate the muscle and fibrous tissues in the artery wall to thicken
14
Q
what is the sinoatrial node? (SA node)
A
- a group of specialised muscle cells in the wall of the right atrium with the fastest contraction rate
- they have few proteins but many membranes that cause other cells to contract, it initiates heartbeat
- Contractions of the heart muscle can occur without external stimulation from motor neurons
- This contraction is called myogenic, where the muscle generates the contraction
- The membrane of the heart muscle cell depolarises, when the cell contracts, and this activates adjacent cells to also contract
15
Q
SA node initiating heartbeat.
A
- it sets the pace for the regular beating (sinus rhythm) of the heart and is often referred to as the pacemaker
- each impulse will spread across the wall f the heart, and stimulates the chamber to contract
- defective SA node can be replaced with an artificial pacemaker where electrodes are implanted into the wall of the heart to initiate each heartbeat
16
Q
what is the Atrial and ventricular contraction?
A
- the electrical signal of beat spreads across the branches of muscle fibre, across the walls of both the atria to
cause the atria to contract - contraction will pass the atrioventricular (AV) node extremely quickly (0.03s)
- AV node is positioned in the wall of the right atrium, near the junction
between the atrium and ventricle - electrical impulse has a time delay of 0.09 seconds at the AV node so that there is sufficient time for blood to fill the ventricles before contraction
- impulse travels from the AV node along fibres in the ventricular wall to the Bundle of His (specialised cardiac fibres) that branches into the Purkinje fibres
- This impulse is propagated so that the ventricle contracts to push blood into the arteries.
17
Q
Explain the cardiac cycle.
A
0.00-0.10: Atria contract causing small bp increase, blood is pumped from atria to ventricles, Semilunar valves closed, bp in arteries drops
0.10-0.15: Ventricles contract causing rapid pressure build-up, making atrioventricular valves close, Semilunar valves stay closed
0.15-0.40: Pressure in ventricles rises and semilunar valves open, blood is pumped from ventricles into
arteries, Pressure rises in arteries and atria
0.40-0.45: Contraction in ventricles lessens and pressure rapidly drops in ventricles, semilunar valves close
Atrioventricular valves remain closed
0.45-0.80: Pressure in ventricles drops, atrioventricular valves open
Blood from veins drains into atria then ventricles, slowly increasing pressure
18
Q
how does the heartrate change?
A
- Nerves from a region in the medulla of the brain transmit messages to the SA node to either increase or
decrease the rate - Impulses travel from the medulla via the vagus nerve in the parasympathetic nervous system to decrease heart rate.
- Impulses travel from the medulla via sympathetic cardiac nerves to increase heart rate.
19
Q
what causes heart rate change?
A
- Low blood pressure, low pH and low oxygen concentration cause an increased heart rate
- high blood pressure, high pH and high oxygen concentration will decrease heart rate.
20
Q
what is epinephrine?
A
- a hormone that affects heart rate
- known as the “fight or flight” hormone that is produced by the adrenal gland in the kidneys
- secretion is controlled by the brain and is caused by physical activity or serious situation
- makes heart beat faster and get more oxygen
- acetylcholine returns it to normal
