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
What happens when the skeletal muscles contract?
The squeeze the vein and cause the blood to flow from the site of compression
In what direction do veins run to arteries?
Parallel
How can an effect similar to skeletal muscle groups be caused by arteries?
By the rhythmic arterial bulge created by a pulse
What blood vessels transport blood at low pressures?
Veins
What blood vessels send blood at high pressure?
Arteries
How many wall layers do veins and arteries have?
Three
What does the left side of an image of the heart represent?
The right side of the heart
What are the three overall main features of the heart structures?
Chambers
Heart valves
Blood vessels
How many atria does the heart have?
Two
What are the atria?
Smaller chambers near the top of the heart that collect blood from body and lungs
What are ventricles?
Larger chambers near bottom of heart that pump blood to body and lungs
Where are the atrioventricular valves?
Between atria and ventricles
What is the atrioventricular valve on the left side?
Bicuspid valve
What is the atrioventricular valve on the right side?
Tricuspid valve
Where are semilunar valves found?
Between ventricles and arteries
What is the semilunar valve on the left side of the heart?
Aortic valve
What is the semilunar valve on the right side?
Pulmonary valve
What are the four main blood vessels in the heart?
Vena cava
Pulmonary artery
Pulmonary vein
Aorta
What does the vena cava do?
Feeds into the right atrium and returns deoxygenated blood from the body
What does the pulmonary artery do?
Connects to the right ventricle and sends deoxygenated blood from the lungs
What does the pulmonary vein do?
Feeds from the left atrium and returns oxygenated blood from the lungs
What does the aorta do?
Extend from the left ventricle and send oxygenated blood around the body
What word describes the contraction of the heart?
Myogenic
What does myogenic mean?
That the signal for cardiac compression arises within the heart tissue itself
Where does the signal for a heart beat initiate?
In the cardiomyocytes
What is within the wall of the right atrium?
A cluster of specialised cardiomyocytes that direct the contraction of the heart
What is the cluster of specialised cells in the right atrium called?
Sinoatrial node
What does the sinoatrial node act as?
The primary peacemaker
What does the sinoatrial node control?
The rate at which the heart beats
How many cardiac contractions does the SA node trigger per minute?
60 - 100
What happens if the SA node fails?
A secondary pacemaker maintains contractions at 40 - 60
What would the interference of pacemakers lead to?
The irregular and uncoordinated contraction of the heart muscle
How may normal sinus rhythm be re-established when fibrillation occurs?
With a controlled electrical current
What causes the two heart sounds?
The delay between atrial and ventricular contractions
What does the sinoatrial node send out?
An electrical impulse
What does the electrical impulse from the SA node stimulate?
The contraction of the myocardium
What does impulse directly cause the atria to do?
Contract and stimulare another node at the junction between the atrium and ventricle
After the electrical impulse, what does the AV node do?
Sendss signals down the septum via a nerve bundle
What causes ventricular contraction?
The bundle of his innervates nerve fibres in the ventricular wall
What does the delay between atrial and ventricular contractions allow?
Time for the ventricles to fill with blood following atrial contractions so as to maximise blood flow
Whilst the heart rate can be determined within the heart what else can regulate it?
External signals
How can nerve signals from the brain affect heart rate?
It can trigger rapid changes
How can endocrine signals affect heart rate?
By triggering sustained changed
What will bp levels or Co2 conces trigger changes in?
Heart rates
What is the pacemaker under autonomic control from?
The brain stem
How do the two nerves connected to the medulla regulate the heart rate?
By speeding it up or slowing it down
How does the sympathetic nerve increase heart rate?
By releasing the neurotransmitter noradrenaline
How does the parasympathetic nerve decrease heart rate?
By releasing the neurotransmitter acetylcholine
What are hormones?
Chemical messengers released into the bloodstream that act specifically on distant target sites
What can heart rate undergo in order to prepare for vigorous physical activity?
A sustained increase to hormonal signalling
Where is the hormone adrenaline released from?
Adrenal glands
How does adrenaline affect heart rate?
Increases it by activating the same chemical pathways as noradrenaline
What does the cardiac cycle describe?
The series of events that take place in the heart over the duration of a single heart beat
What is the cardiac cycle comprised of?
Systole and diastole
Where will blood returning to the heart flow into?
The atria and ventricles
Why will blood returning to the heart flow into the atria and ventricles?
As the pressure in them is lower
What happens when the ventricles are 70% full?
Atria will contract
When the atria contract what happens?
Increasing pressure in the atria and forcing blood into ventricles
What happens to the ventricular pressure as the ventricles contract?
It exceeds atrial pressure and AV valves close to prevent back flow
What happens to pressure when both sets of heart valves close?
Pressure rapidly builds in the contracting ventricles
What happens when the ventricular pressure exceeds blood pressure in the aorta?
The aortic valve opens and blood enters the aorta
What happens to ventricular pressure when blood exits the ventricle and travels down the aorta?
It falls
What happens when ventricular pressure drops below aortic pressure?
The aortic valve closes to prevent back flow
What happens when the ventricular pressure drops below the atrial pressure?
The AV valve opens and blood can flow from atria to ventricle
Why does aortic pressure stay quite high throughout the cardiac cycle?
As muscle and elastic fibres in the artery wall maintain bp
What are coronary arteries?
The blood vessels that surround the heart and nourish the cardiac tissue to keep the heart working
What happens if the coronary arteries become occluded?
The region of heart tissue nourished by the blocked artery will die and cease to function
What is athersclerosis?
The hardening and narrowing of the arteries due to the deposition of cholesterol
What do atheromas do?
Develop in the arteries and reduce the diameter of the lumen
In atherosclerosis, what does the restricted blood flow do?
Increases pressure in the artery causing arterial wall damage
How is damaged region due to atherosclerosis repaired?
With fibrous tissue which reduces the elasticity of the vessel wall
What happens as the smooth lining of the artery is progressively degraded?
Lesions form called atherosclerotic plaques
What happens if the atherosclerotic plaque ruptures?
Blood clotting is triggered forming a thrombus which restricts blood flow
What happens if the thrombus is dislodged?
It becomes an embolus and can cause a blockage in a smaller arteriole
What can atherosclerosis lead to?
Blood clots, which cause CHD when in coronary arteries
What does the myocardial tissue require to function?
The oxygen and nutrients transported via the coronary arteries
What happens if a coronary artery becomes completed blocked?
A heart attack will happen
How are blockages of coronary arteries typically treated?
By by-pass surgery or creating a stent
What are the risk factors for CHD ( a goddess)
Age
Genetics
Obesity
Diseases
Diet
Exercise
Sex
Smoking
How does age affect CHD?
Blood vessels become less flexible with advancing age
How does genetics affect CHD?
Having hypertension predisposes individuals to developing CHD
How does obesity affect CHD?
Being overweight places additional strain on the heart
How does diseases affect CHD?
Certain diseases increase the risk of CHD
How does diet affect CHD?
Diets rich in saturated fats, salts and alcohol increases the risk
How does exercise affect CHD?
Sedentary lifestyles increase the risk of CHD
How does sex affect CHD?
Males are at a greater risk due to lower oestrogen levels
How smoking age affect CHD?
Nicotine causes vasoconstriction raising blood pressure
