6.2 The Blood System Flashcards
Who developed today’s understanding of the circulatory system?
Our modern understanding of circulatory system is based upon the discoveries of 17th century English physician, William Harvey
Where were Harvey’s findings published?
Harvey’s findings were published in a book commonly called De Motu Cordis – On the Motion of the Heart and Blood
Whose findings were popular before Harvey?
Prior to Harvey’s findings, scientists held to the antiquated views of the Greek philosopher Galen, who believed that:
What 3 things did Galen believe?
Arteries and veins were separate blood networks (except where they connected via invisible pores)
Veins were thought to pump natural blood (which was believed to be produced by the liver)
Arteries were thought to pump heat (produced by the heart) via the lungs (for cooling – like bellows)
What 3 findings did Harvey state?
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)
What are the different types of blood vessel present in the body?
Arteries Arterioles Capillaries Venules Veins
How do the vessels differ? (general)
Each type of blood vessel has a specialised structure that relates to the function of that vessel
What is the function of arteries?
Arteries transport blood away from the heart at high pressure
Where does blood travel from the ventricles?
Blood travels from the ventricles to the tissues of the body
What 3 layers do artery walls consist of?
tunic intima
tunica media
tunica externa
What is the tunica intima and what is composed of?
The tunica intima is the innermost layer and is made up of an endothelial layer, a layer of connective tissue and a layer of elastic fibres
Describe the endothelium/tunica intima? (thickness - why is it smooth?)
The endothelium is one cell thick and lines the lumen of all blood vessels. It is very smooth and reduces friction for free blood flow
What is the composition of the tunica media?
The tunica media is made up of smooth muscle cells and a thick layer of elastic tissue
What is the thickness of the tunia media in arteries?
Arteries have a thick tunica media
Why is the tunica media thick for arteries?
The layer of muscle cells strengthen the arteries so they can withstand high pressure
Blood leaves the heart under high pressure
What can also control the diameter of the lumen of arteries?
Muscles cells/fibres can also contract or relax to control the diameter of the lumen and regulate blood pressure
Muscle fibres can also contract to narrow the lumen, which increases the pressure between pumps and helps to maintain blood pressure throughout the cardiac cycle
What is the role of elastic tissue in arteries?
The elastic tissue helps to maintain blood pressure in the arteries. It stretches and recoils to even out fluctuations in pressure
What is the composition of the tunica externa?
The tunica externa covers the exterior of the artery and is mostly made up of collagen
What is the role of collagen in artery structure?
Collagen is a strong protein and protects blood vessels from damage by over-stretching
What is the lumen like in arteries?
Arteries have a narrow lumen which helps to maintain a high blood pressure
Why is a pulse present? What is it?
Blood is expelled from the heart upon ventricular contraction and flows through the arteries in repeated surges called pulses
A pulse is present in arteries due to blood leaving the heart under high pressure
What is the role of muscle fibres in the arterial wall?
The muscle fibres help to form a rigid arterial wall that is capable of withstanding the high blood pressure without rupturing
What is elastic recoil?
The pressure exerted on the arterial wall is returned to the blood when the artery returns to its normal size (elastic recoil)
What is the role of elastic recoil?
The elastic recoil helps to push the blood forward through the artery as well as maintain arterial pressure between pump cycles
What are arterioles?
Arterioles branch off from arteries forming narrower blood vessels which transport blood into capillaries
What are arterioles similar in structure to? What is the difference?
Arterioles are similar in structure to arteries, but they have a lower proportion of elastic fibres and a large number of muscle cells
Why are muscle cells present in arterioles?
Give an example
The presence of muscle cells allows them to contract and close their lumen to regulate blood flow to specific organs
Eg. during exercise blood flow to the stomach and intestine is reduced while blood flow to the muscles increases
What must arteries and to a certain extent arterioles withstand?
Arteries, and to a slightly lesser extent arterioles, must be able to withstand high pressure generated by the contracting heart, and both must maintain this pressure when the heart is relaxed
What is important in maintaining the blood pressure?
Muscle and elastic fibres in the arteries help to maintain the blood pressure as the heart contracts and relaxes
What is systolic pressure?
Systolic pressure is the peak pressure point reached in the arteries as the blood is forced out of the ventricles at high pressure
What does systolic pressure cause?
At this point, the walls of the arteries are forced outwards, enabled by the stretching of elastic fibres
What is diastolic pressure?
Diastolic pressure is the lowest pressure point reached within the artery as the heart relaxes
What happens to the arterial wall during diastolic pressure?
At this point, the stretched elastic fibres recoil and force the blood onward through the lumen of the arteries
What does the arterial wall’s response to systolic and diastolic pressure maintain?
This maintains high pressure throughout the heart beat cycle
What is vasoconstriction?
Vasoconstriction of the circular muscles of the arteries can increase blood pressure by decreasing the diameter of the lumen
What is vasodilation?
Vasodilation of the circular muscles causes blood pressure to decrease by increasing the diameter of the lumen
What are capillaries and what is their function?
Capillaries provide the exchange surface in the tissues of the body through a network of vessels called capillary beds
What is the wall of a capillary made of?
The wall of a capillary is made from a single layer of endothelial cells (this layer is also found lining the lumen in arteries and veins)
Why is the wall of a capillary one cell thick?
Being just one cell thick reduces the diffusion distance for oxygen and carbon dioxide between the blood and the tissues of the body
What is between the endothelial cells of a capillary? What does this form?
The thin endothelium cells also have gaps between them called pores which allow blood plasma to leak out and form tissue fluid
What does tissue fluid contain?
Tissue fluid contains oxygen, glucose and other small molecules from the blood plasma
What does tissue fluid not contain?
Large molecules such as proteins usually can’t fit through the pores into the tissue fluid
Where is tissue fluid found? Why?
Tissue fluid surrounds the cells, enabling exchange of substances such as oxygen, glucose, and carbon dioxide
What regulates the amount of tissue fluid that seeps out?
The permeability of capillaries can vary depending on the requirements of a tissue
What is the diameter of the lumen of capillaries?
Capillaries have a lumen with a small diameter
What does the small diameter of capillaries allow for?
Red blood cells squeeze through capillaries in single-file
This forces the blood to travel slowly which provides more opportunity for diffusion to occur
What is a capillary bed?
Capillaries form branches in between the cells; this is the capillary bed
What is the purpose of capillary beds?
These branches increase the surface area for diffusion of substances to and from the cells
Being so close to the cells also reduces the diffusion distance
How does pressure change from arterioles to capillaries?
Arteries split into arterioles which in turn split into capillaries, decreasing arterial pressure as total vessel volume is increased
Why is it useful for blood pressure to decrease from arterioles to capillaries?
The branching of arteries into capillaries therefore ensures blood is moving slowly and all cells are located near a blood supply
What do capillaries join back into?
After material exchange has occurred, capillaries will pool into venules which will in turn collate into larger veins
What are capillaries surrounded by? What is the purpose?
They are surrounded by a basement membrane which is permeable to necessary materials
What may be present in the endothelial layer of capillaries?
They may contain pores to further aid in the transport of materials between tissue fluid and blood
What holds endothelial cells together?
The capillary wall may be continuous with endothelial cells held together by tight junctions to limit permeability of large molecules
What may capillaries look like in kidneys?
In tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores)
What does it mean if a capillary is sinusoidal? Where might it be found?
Some capillaries are sinusoidal and have open spaces between cells and be permeable to large molcules and cells (e.g. in liver)
What forces materials into tissue fluid?
The higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid
What is carried in tissue fluid back into the venules?
Materials that enters the capillaries at body tissues include carbon dioxide and urea (wastes produced by the cells)
What is the function of veins?
Veins transport blood to the heart at low pressure
What blood pressure do veins recieve?
They receive blood that has passed through capillary networks, across which pressure has dropped due to the slow flow of blood
How does the structure of the tunica media differ in veins?
The tunica media is much thinner in veins
WHy is the tunica media thinner in veins?
There is no need for a thick muscular and elastic layer as veins don’t have to maintain or withstand high pressure
How does the lumen of veins differ from arteries?
The lumen of veins is much wider in diameter than that of arteries
What is the purpose of the larger lumen in veins?
3
A larger lumen helps to ensure that blood returns to the heart at an adequate speed
A large lumen reduces friction between the blood and the endothelial layer of the vein
The rate of blood flow is slower in veins but a larger lumen means the volume of blood delivered per unit of time is equal
What special feature do veins have?
These prevent the back flow of blood that can result under low pressure, helping return blood to the heart
What helps push blood through veins?
Movement of the skeletal muscles pushes the blood through the veins, and any blood that gets pushed backwards gets caught in the valves; this blood can then be moved forwards by the next skeletal muscle movement
Can a pulse be found in veins?
A pulse is absent in veins; the pressure changes taking place due to the beating of the heart are no longer present
What is the role of venules?
Venules connect the capillaries to the veins
What is the composition of venules?
They have few or no elastic fibres and a large lumen
Why do venules have few or no elastic fibres ?
As the blood is at low pressure after passing through the capillaries there is no need for a muscular layer to maintain pressure
Why do venules have a large lumen?
The large lumen enables a large volume of blood to be transported
How do skeletal muscles help in the passage of blood?
When the skeletal muscles contract, they squeeze the vein and cause the blood to flow from the site of compression
Apart from skeletal muscles, what other contraction can help push blood up veins?
Veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse
Why is a circulatory system needed?
All organisms need to transport materials to where they are needed inside their tissues
What is the alternative to a circulatory system and when is it used?
Small organisms (or relatively inactive animals like jellyfish) can rely on diffusion alone to transport oxygen, carbon dioxide and nutrients around their bodies
Why can larger organisms not rely on diffusion?
Larger organisms have more layers of cells, so diffusion alone is insufficient for transport of materials between cells further from the exchange surface of the organism
What are circulatory systems?
Circulatory systems are systems which transport fluids containing materials needed by the organism, as well as waste materials that need to be removed
What do circulatory systems ensure?
Circulatory systems ensure that fluids containing these substances reach all of the cells in an organism quickly enough to supply their needs and remove waste
What is a closed circulatory system?
A closed circulatory system is one in which blood is contained within a network of blood vessels
What is an open circulatory system?
As opposed to an open circulatory system in which the fluid fills the body cavity e.g. as in insects
What is a double circulatory system?
A double circulatory system passes through the heart twice for every one complete circuit of the body, with blood passing through two separate circuits known as pulmonary and systemic circulation
What side of the heart is related to the pulmonary circulatory system?
In the pulmonary circulatory system
The right side of the heart pumps deoxygenated blood to the lungs for gas exchange
What is the pressure of the blood in the pulmonary system?
Blood pressure is lower in the pulmonary system; this prevents damage to the lungs
What part of the heart is involved in the systemic circulation?
In the systemic circulatory system
Oxygenated blood returns to the left side of the heart from the lungs
What chamber of the heart is responsible for pushing blood around the body?
The left ventricle then pumps the oxygenated blood at high pressure around the body
What is the structure and function of the heart?
A hollow, muscular organ located in the chest cavity which pumps blood. Cardiac muscle tissue is specialised for repeated involuntary contraction without rest.
What is the structure and function of arteries?
Blood vessels which carry blood away from the heart. The walls of the arteries contain lots of muscle and elastic tissue and a narrow lumen to maintain high blood pressure. Arteries range from 0.4 - 2.5 cm in diamter.
What is the structure and function of arterioles?
Small arteries which branch from larger arteries and connect to capillaries. There are around 30 μm (micrometre) in diameter
What is the structure and function of capillaries?
Tiny blood vessels (5-10μm in diameter) which connect arterioles and venules. Their size means they pass directly past cells and tissues and perform gas exchange and exchange of substances such as glucose
What is the structure and function of venules?
Small veins which join capillaires to larger veins. they have a diameter of 7μm - 1mm
What is the structure and function of veins?
Blood vessels which carry blood back towards the heart. The walls of the veins are thin in comparison to arteries, having less muscle and elastic tissue and a wider lumen. Valves help maintain blood flow back towards the heart.
What do atria act as? What collects and delivers blood to them?
The atria act as reservoirs, by which blood returning to the heart is collected via veins (and passed on to ventricles)
What do the ventricles act as?
The ventricles act as pumps, expelling the blood from the heart at high pressure via arteries
Why are there two distinct sets of atria and ventricles?
The reason why there are two sets of atria and ventricles is because there are two distinct locations for blood transport
What is the left side of the heart responsible for?
The left side of the heart pumps oxygenated blood around the body (systemic circulation)
What is the right side of the heart responsible for?
The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation)
How does the left side of the heart differ from the right side, in terms of structure and why?
he left side of the heart will have a much thicker muscular wall (myocardium) as it must pump blood much further
What separates the chambers of the heart?
The left and right sides of the heart are separated by a wall of muscular tissue called the septum.
What is the role of the septum?
The septum is very important for ensuring blood doesn’t mix between the left and right sides of the heart
What is the role of valves?
Valves are important for keeping blood flowing forward in the right direction and stopping it flowing backwards. They are also important for maintaining the correct pressure in the chambers of the heart
What are the atria and ventricles separated by>?
The atria and ventricles are separated by the atrioventricular valves
What are the ventricles and arteries that leave the heart separated by?
atrioventricular valves
The ventricles and the arteries that leave the heart are separated by semi-lunar valves
What is the right ventricle and pulmonary artery separated by?
The right ventricle and the pulmonary artery are separated by the pulmonary valve
What is the left ventricle and aorta separated by?
The left ventricle and aorta are separated by the aortic valve
What two blood vessels bring blood to the heart?
There are two blood vessels bringing blood to the heart; the vena cava and pulmonary vein
What two blood vessels transport blood away from heart?
There are two blood vessels taking blood away from the heart; the pulmonary artery and aorta
What is systole?
The contraction of the heart is called systole,
What is diastole?
while the relaxation of the heart is called diastole
What is atrial systole?
Atrial systole is the period when the atria are contracting
What is ventricular systole?
ventricular systole is when the ventricles are contracting
Approx. haw many seconds does atrial systole happen after ventricular systole?
Atrial systole happens around 0.13 seconds after ventricular systole
What does atrial systole do?
Atrial systole forces blood from the atria into the ventricles
What does ventricular systole do?
During ventricular systole, blood is forced from the ventricles into the pulmonary artery and aorta
What is a heartbeat composed of and how long does it last?
One systole and diastole makes a heartbeat and lasts around 0.8 seconds in humans.
What is systole and diastole (a heartbeat) called?
This is the cardiac cycle
What does it mean that the heart muscle is myogenic?
The heart muscle is myogenic, meaning that the heart will beat without any external stimulus from other organs or the nervous system
What is the normal heart rate?
This intrinsic control causes the heart to beat at around 60 beats per minute
What initiates the heart beat?
The heart beat is initiated by a group of cells in the wall of the right atrium called the sinoatrial node (SAN)
What does the SAN do to initiate the heartbeat?
The cells of the sinoatrial node depolarise, reversing the charge across their membranes
What does the depolarisation of the SAN cause?
This triggers a wave of depolarisation that spreads across the rest of the heart
Why is the SAN termed the pacemaker?
The sinoatrial node is considered to be the pacemaker of the heart because it initiates the heart beat and so controls the speed at which the heart beats
What are artificial pacemakers?
Note that artificial pacemakers are electronic devices implanted just underneath the skin. They can be used to replace or regulate the sinoatrial node if it becomes defective
What is the cardiac cycle?
The cardiac cycle is the series of events that take place in one heart beat, including atrial and ventricular systole
What is the cardiac cycle controlled by?
The cardiac cycle is controlled by electrical signals that are initiated in the sinoatrial node
What causes atrial systole?
Depolarisation of the cells in the sinoatrial node sends an electrical signal over the atria, causing them to contract in atrial systole
Does ventricular systole occur straight after atrial systole?
NO
The electrical signal then reaches a region of non-conducting tissue which prevents it from spreading straight to the ventricles; this causes the signal to pause for around 0.1 s
Why is there a pause after atrial systole?
This delay means that the atria can complete their contraction before the ventricles begin to contract
What is the role of the AVN?
The electrical signal is carried to the ventricles via the atrioventricular node (AVN)
What is the AVN? (structure)
This is a region of conducting tissue between atria and ventricles
How does the signal from the AVN travel further?
The signal then travels to the base of the heart via conductive fibres in the septum known as the bundle of His
What causes ventricular systole once the electrical signal reaches the base of the heart?
The electrical signal is then carried through another set of conductive fibres called Purkyne fibres which spread around the sides of the ventricles, causing contraction of the ventricles from the apex, or base, of the heart upwards
Where is blood forced after ventricular systole?
This is called ventricular systole
Blood is forced out of the heart into the pulmonary artery and aorta
State the 5 simple stages of electrical control of the cardiac cycle
- sinoatrial node sends out a wave of excitation/depolarisation
- atria contract
- atrioventricular node sends out a wave of excitaion/depolarisation
- Purkinje fibres conducts wave of excitation/depolarisation
- ventricles contract
What is the (v. general) change in pressure of the heart?
Contraction of the heart muscle causes an increase in pressure in the corresponding chamber of the heart, which then decreases again when the muscle relaxes
What does the change in pressure do to a specific structure of the heart?
Throughout the cardiac cycle, heart valves open and close as a result of pressure changes in different regions of the heart:
When do valves open?
Valves open when the pressure of blood behind them is greater than the pressure in front of them
When do valves close?
They close when the pressure of blood in front of them is greater than the pressure behind them
Why are valves in the heart important?
Valves are an important mechanism to stop blood flowing backwards
State the stages of the cardiac cycle shown on a graph of pressure
- end of diastole
- atrial systole
- beginning of ventricular systole
- ventricular systole
- early diastole
- diastole
- late diastole
COMPARE WITH GRAPH!!!!!
How is the pressure of the atria affected by diastole?
During diastole, the heart muscle is relaxing
During this period, blood begins to flow into the atria from the veins, increasing the atrial pressure
Overall, how does diastole affect the pressure of the heart?
Relaxed muscle in the heart walls recoils, increasing the volume of the chambers of the heart:
volume up, pressure down (inverse)
What valves open during diastole and why?
The atrioventricular valves open as the pressure in the atria is higher than the pressure in the ventricles
What valves close during diastole and why?
The semilunar valves close as the pressure in the pulmonary artery and aorta is higher than the pressure in the ventricles
What is the general pressure change during systole?
The contraction of the muscles in the wall of the heart reduces the volume of the heart chambers and increases the pressure within that chamber
What valves are open during atrial systole and why?
The atrioventricular valves are open as the pressure in the atria exceeds the pressure in the ventricles
What valves are closed during atrial systole and why?
The semilunar valves are closed as the pressure in the ventricles is less than the pressure in the aorta and pulmonary artery
What valves are closed during ventricular systole and why?
The atrioventricular valves are closed as the pressure in the ventricles exceeds the pressure in the atria
What valves are open during ventricular systole and why?
The semilunar valves are open as the pressure in the ventricles exceeds the pressure in the aorta and pulmonary artery
- What happens at the end of diastole?
+ pressure
The atrium has filled with blood during the preceding diastole
Pressure is higher in the atrium than in the ventricle, so the AV valve is open
- What happens at atrial systole + pressure?
Left atrium contracts, causing an increase in atrial pressure and forcing blood into the left ventricle
Ventricular pressure increases slightly as it fills with blood
Pressure is higher in the atrium than in the ventricle, so the AV valve is open
What happens at the beginning of ventricular systole + pressure?
Left ventricle contracts causing the ventricular pressure to increase
Pressure in the left atrium drops as the muscle relaxes
Pressure in the ventricle exceeds pressure in the atrium, so the AV valve shuts
What happens at ventricular systole + pressure?
The ventricle continues to contract
Pressure in the left ventricle exceeds that in the aorta
Aortic valve opens and blood is forced into the aorta
What happens at beginning of diastole + pressure?
Left ventricle has been emptied of blood
Muscles in the walls of the left ventricle relax and pressure falls below that in the newly filled aorta
Aortic valve closes
What happens at early diastole + pressure?
The ventricle remains relaxed and ventricular pressure continues to decrease
In the meantime, blood is flowing into the relaxed atrium from the pulmonary vein, causing an increas
What happens at diastole + pressure?
The relaxed left atrium fills with blood, causing the pressure in the atrium to exceed that in the newly emptied ventricle
AV valve opens
What happens to left ventricle in late diastole? How does this affect pressure?
There is a short period of time during which the left ventricle expands due to relaxing muscles
This increases the internal volume of the left ventricle and decreases the ventricular pressure
What may increase pressure in late diastole?
At the same time, blood is flowing slowly through the newly opened AV valve into the left ventricle, causing a brief increase in pressure in the left atrium
What causes the pressure to slowly rise at late diastole?
The pressure in both the atrium and ventricle then increases slowly as they continue to fill with blood
What may cause an individual’s heart rate to change?
Although the heart muscle maintains a base heart rate via myogenic stimulation, there are several circumstances that can cause an individual’s heart rate to change, e.g.
Exercise
Stress
Relaxation
What organ is involved in the regulation of the heart rate?
The brain is involved in the regulation of heart rate, though it does not require conscious thought
WHat branch of the nervous system increases heart rate?
The branch of the nervous system that does not require conscious thought is known as the autonomic nervous system
What area of the brain controls heart rate?
The area of the brain that controls heart rate is the cardiovascular centre, located in a region of the brain called the medulla
Where is the medulla found?
The medulla is found at the base of the brain near the top of the spinal cord
What connects the medulla to the SAN? (v.basic)
Two nerves connect the medulla with the sinoatrial node (SAN):
Where does one of the nerves connecting the medulla to the SAN connect to, that involves speeding up heart rate?
One nerve connects to the acceleratory centre, which causes the heart to speed up
What causes nerve to send impulses to acceleratory centre?
This happens in response to low blood pressure, low oxygen concentrations and low pH
These changes might occur during exercise
What happens to blood vessels during exercise?
The blood vessels dilate, causing a decrease in blood pressure
What do muscles do during exercise?
The muscle cells are using up oxygen at a faster rate, causing blood oxygen levels to drop
What does co2 produced during exercise do?
The production of carbon dioxide by respiring cells causes blood pH to decrease
Where does one of the nerves connecting the medulla to the SAN connect to, that involves slowing down heart rate?
The other nerve connects to the inhibitory centre, which causes the heart to slow down
What may cause heart rate to slow down?
This happens in response to high blood pressure, high oxygen concentrations and high pH
These changes are likely to occur when the body is at rest
What hormone is produced during times of excitement/fear?
Epinephrine, also called adrenaline, is produced by the adrenal glands, located above the kidneys, in times of fear, stress, or excitement
What controls the release of epinephrine?
The brain controls the release of epinephrine from the adrenal glands
What is the role of epinephrine in relation to heart rate?
Epinephrine increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’
Why is glucose production a response to epinephrine?
Increased glucose and oxygen are needed by the cells for aerobic respiration to release energy, e.g. to fuel the muscles to move/run away!
What is the right atrium and ventricles separated by?
The right atrium and ventricle are separated by the tricuspid valve
What is the left atrium and ventricles separated by?
The left atrium and ventricle are separated by the bicuspid valve
What is the first step of the pathway of blood through the heart?
Deoxygenated blood coming from the body flows through the vena cava and into the right atrium
What happens to the blood coming from the vena cava once its in the atrium?
The atrium contracts and the blood is forced through the atrioventricular (tricuspid) valve into the right ventricle
Where does blood from the right ventricle travel?
The ventricle contracts and the blood is pushed through the semilunar valve into the pulmonary artery
Where does the pulmonary artery transport blood to?
The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place
What is the pressure of the blood in the right ventricle and why?
Low pressure blood flow on this side of the heart prevents damage to the capillaries in the lungs
How does oxygenated blood from the lungs return to the heart?
Oxygenated blood returns via the pulmonary vein to the left atrium
What happens to blood in the left atrium?
The atrium contracts and forces the blood through the atrioventricular (bicuspid) valve into the left ventricle
Where does blood go from the left ventricle?
The ventricle contracts and the blood is forced through the semilunar valve and out through the aorta
Which heart chamber has the thickest wall and why?
Thicker muscle walls of the left ventricle produce a high enough pressure for the blood to travel around the whole body
What does the heart require to keep beating?
The heart is a muscle and so requires its own blood supply to enable its cells to carry out aerobic respiration
What is the blood supply to the heart called?
The heart receives blood through arteries on its surface called coronary arteries
What is important about the coronary arteries’ health?
It’s important that these arteries remain clear of blockages called plaques, as this could lead to angina or a heart attack (myocardial infarction)
What can occlusion be defined as?
The narrowing of the arteries due to a blockage
What can cause blockage of the arteries?
The arteries can be blocked by the process of atherosclerosis
What does atherosclerosis result in?
Atherosclerosis results in a build-up of layers of fatty material known as plaque inside arteries
What is the main cause of atheroma development? (atherosclerosis)
The main cause of atheroma development is the presence of low-density lipoprotein (LDL) which forms from saturated fats and cholesterol
What is done to the LDL build-up in coronary arteries? (atherosclerosis)
LDL builds up in regions of the arteries and phagocytes move to these areas, engulfing the LDL by endocytosis
What happens to the phagocytes that engulf the LDLs? (atherosclerosis)
The enlarged phagocyte cells are then covered by smooth muscle cells which cause a bulging of the endothelium in the artery
What else can decrease the diameter of the artery and how? (atherosclerosis)
Deposition of calcium ions can worsen the situation by hardening the endothelium
This narrows the lumen of the artery, reducing the space for blood flow
What happens when an atheroma gets too big and starts almost fully blocking an artery?
When an atheroma builds up enough to cause impeded blood flow, tissues do not receive the required level of oxygen and nutrients
This can inhibit cell functions
What disease can occlusion of coronary arteries lead to?
Occlusion of the coronary arteries in particular can lead to significant health issues such as coronary heart disease
What is the main result of coronary heart disease? (v. basic)
The flow of blood through the coronary arteries is reduced, resulting in a lack of oxygen and nutrients for the heart muscle
What does partial blockage of coronary arteries create?
Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina as the heart muscle beats faster to try to increase blood supply
What does complete blockage of coronary arteries create?
Complete blockage means cells in the area of the heart not receiving blood will not be able to respire aerobically; these cells will be unable to contract, leading to a heart attack
What happens when an atheroma ruptures?
Atheromas can sometimes rupture, leading to the development of a blood clot
Why can blood clots worsen the occlusion of ateries?
Blood clots can worsen existing blockages, or break off and travel into smaller blood vessels
What 2 events can travelling blood clots cause?
Blood clots that travel to the coronary arteries can cause a heart attack
Blood clots that travel to the brain can lead to a stroke
What are the 6 risk factors of coronary heart disease? (v1 savemyexams)
consumption of trans-fats constant high blood sugar high blood pressure high blood concentrations of LDL smoking infection by certain microbes
How is the consumption of trans fats a risk factor for coronary heart disease?
These damage the endothelium of the artery initiating formation of an atheroma
How is constant high blood sugar causes?
This is usually the result of consumption of foods high in carbohydrate
How is high blood pressure a risk factor for coronary heart disease?
This increases the force of the blood against the artery walls and consequently leads to damage of the vessels
Blood pressure can increase due to smoking or stress
How is high blood concentrations of LDls a risk factor for coronary heart disease?
Speeds up the build up of fatty plaques in the arteries, leading to blockages
How is smoking a risk factor for coronary heart disease?
Chemicals in smoke cause an increase in plaque build up and an increase in blood pressure
Carbon monoxide also reduces the oxygen carrying capacity of the red blood cells
How is infection by certain microbes a risk factor for coronary heart disease?
Chlamydia pneumoniae can infect the arterial wall and trigger inflammation which promotes atherosclerosis
Microbes of the small intestine produce the chemical trimethylamine N-oxide which promotes atherosclerosis
Summarise the structure of the artery
Three thick layers in their walls
A high proportion of muscle and elastic fibres
Narrow lumen
No valves
Summarise the structure of capillaries
Walls are only one cell thick (endothelial layer only)
No muscle or elastic fibres
No valves
Summarise structure of veins
Thin walls with three layers
Low proportion of muscle and elastic fibres compared to arteries
Large lumen
Valves (usually) present
What does the sympathetic nerve release?
The sympathetic nerve releases the neurotransmitter noradrenaline (a.k.a. norepinephrine) to increase heart rate
What does the parasympathetic nerve release?
The parasympathetic nerve (vagus nerve) releases the neurotransmitter acetylcholine to decrease heart rate
Apart from narrowing lumen, what other feature of the artery changes due to atherosclerosis?
The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall
What is the scientific name of a blood clot, and what is its name when it travels?
If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole
What is an atherosclerotic plaque?
As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques
How can atherosclerosis be treated?
Blockages of coronary arteries are typically treated by by-pass surgery or creating a stent (e.g. balloon angioplasty)
bioninja what are the risk factors of coronary heart disease?
Age – Blood vessels become less flexible with advancing age
Genetics – Having hypertension predispose individuals to developing CHD
Obesity – Being overweight places an additional strain on the heart
Diseases – Certain diseases increase the risk of CHD (e.g. diabetes)
Diet – Diets rich in saturated fats, salts and alcohol increases the risk
Exercise – Sedentary lifestyles increase the risk of developing CHD
Sex – Males are at a greater risk due to lower oestrogen levels
Smoking – Nicotine causes vasoconstriction, raising blood pressure
Mnemonic: A Goddess
bioninja summary of atherosclerosis
Atheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen (stenosis)
The restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress)
The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall
As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques
If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole
