Chapter 9 - Circulatory Systems in Mammals Flashcards
Past Paper Question - June 2018 AS2 Q2 a)
Q2 The diagram below represents sections through an artery and a vein.
a) Describe and explain two structural differences shown between the artery and vein. [2]
(Go do this past paper question)
Q2 a) Any two from:
• the arteries have thicker muscular walls to withstand the high
pressure blood/smooth muscle allows for vasodilation/constriction
• veins have a larger lumen which reduces friction/resistance to blood
flow
• arteries have more elastic tissue to allow for distension/stretch and
recoil [allow converse] [2]
Past Paper Question - June 2018 AS2 Q2 b)i)
Q2 The diagram below represents sections through an artery and a vein.
b)i) Distinguish between the terms ‘atherosclerosis’ and ‘atheroma’, and explain their effect on blood flow in the artery. [3]
Q2 b)i) Atherosclerosis is the disease that is caused by the thickening/ hardening/reduced elasticity of the artery wall through the development of atheromas/plaques;
atheroma is a term used to describe the build-up of fatty deposits under the endothelium layer of the artery;
they narrow blood vessels and restrict blood flow/making blockages more likely; [3]
Past Paper Question - June 2018 AS2 Q2 b)ii)
Q2 b)ii) The blood vessels of the heart can be investigated to diagnose atherosclerosis by injecting radioactive dye and taking an X-ray.
Name this procedure and the blood vessels involved. [2]
Test __________________________
Blood vessels _________________________
Q2 b)ii) Angiograph;
coronary arteries; [2]
Past Paper Question - June 2018 AS2 Q2 c)
Q2 c) Capillaries are involved in the production of tissue fluid.
State the difference in composition between tissue fluid and blood. [1]
Q2 c) (Plasma) minus blood cells (and large proteins); [1]
Why do mammals require a circulatory system?
Mammals have small surface area to volume ratios. A circulatory system is necessary to transport materials to and from the large volume of metabolically active tissue.
Mammals have a (blank) circulatory system
Double
Why are mammals described as having a ‘double circulatory system’?
As blood goes through the heart twice for each complete circuit of the body.
Mammals have a double circulatory (cardiovascular) system - this means that blood goes through the heart twice for each complete circuit of the body. In effect, the heart pumps the blood through …
Two circuits, the pulmonary and systemic circuits
Mammals have a double circulatory (cardiovascular) system - this means that blood goes through the heart twice for each complete circuit of the body. In effect, the heart pumps the blood through two circuits. What are the names of these two circuits?
The pulmonary and systemic circuits
What are the pulmonary and systemic circulations?
The pulmonary circulation supplies the lungs and the systemic circulation supplies the other organs and the rest of the body.
What are the two major differences between the pulmonary and systemic circulation?
The pulmonary circulation is a relatively small circuit (relative to the systemic circulation) and the blood is pumped at lower pressure
Why is blood pumped at lower pressure in the pulmonary circuit?
The lower pressure allows the blood to pass relatively slowly through the capillaries in the lungs, allowing more time for gas exchange.
In addition, high pressure is not necessary to pump the blood over the shorter distances involved.
Furthermore, the higher pressure could damage the delicate pulmonary capillaries.
Why is blood pumped at higher pressure in the systemic circuit?
A higher pressure in the systemic circuit ensures that blood is pumped to all the other organs in the body at a pressure sufficient to deliver metabolites and remove waste, at the rate required, and also at a pressure that maintains the blood/tissue fluid balance in each organ.
Blood going through the pulmonary circulation is pumped by what side of the heart?
Right side of the heart
Blood going through the systemic circulation is pumped by what side of the heart?
Left side of the heart
Blood going though the pulmonary circulation is pumped by the right hand side of the heart and blood going through the systemic circulation is pumped by the left side of the heart. Hence, or otherwise, comment on the distribution of cardiac muscle in the walls of the left and right ventricle.
Cardiac muscle in the wall of the left ventricle is much thicker than that of the right ventricle.
What is a single circulatory system?
Blood goes through the heart once for each complete circuit of the body.
Give an example of an animal with a single circulatory system
Fish
Why is a double circulatory system more efficient than a single circulatory system?
- The double circulatory system is a very efficient system necessary in meeting the high metabolic needs of mammals.
- In animals with a single circulatory system, such as fish, the blood is pumped through the gas exchange surface (the gills) and the rest of the body in the same circuit.
- This means that following the loss of pressure associated with passage through the gill capillaries, there is no further increase in pressure before the blood continues through the remaining organs.
What are the three main types of blood vessels that occur in mammals?
Arteries
Veins
Capillaries
Draw a diagram showing the main blood vessels of the thorax and abdomen
Textbook page 151
Describe the structure of an artery
Thick wall consisting of:
- An outer thin layer of fibrous tissue (consisting of the structural protein collagen). [Arteries contain less fibrous tissue than veins].
- A thick middle layer of smooth muscle and elastic tissue
- An inner layer of squamous endothelium
Narrow lumen
Arteries usually retain an overall rounded shape
Small lumen-wall ratio
Describe the structure of a vein
Thin wall consisting of:
- An outer thin layer of fibrous tissue (consisting of the structural protein collagen). [Veins contain more fibrous tissue than arteries].
- A thin middle layer containing some smooth muscle and very little elastic tissue
- An inner layer of squamous endothelium
Large lumen
Valves at intervals along their length
Much less regular in shape compared to arteries
Describe the structure of a capillary
Microscopic vessels with one cell thick walls, consisting of squamous (pavement or flattened) endothelium.
Describe blood pressure in arteries
High in pulses
Describe blood pressure in veins
Low
Describe blood pressure in capillaries
Blood pressure in capillaries is relatively low, with a gradual reduction in pressure across the capillary network.
What are some of the adaptations of arteries?
- The elastic tissue in the thick middle layer
- Maintains size and shape
- Allows the artery to stretch as the blood pulses out of the heart, through the arterial system, following the contraction of the ventricle muscles.
- The elastic tissue recoils between heartbeats which helps to push blood along the artery, maintaining blood pressure. - The muscle tissue in the middle layer
- Provides support
- Can constrict (vasoconstriction) or dilate (vasodilation), to provide less or more blood to an organ depending on metabolic needs
- Contraction of the muscle and the narrowing of the lumen can help maintain blood pressure, further aided by the small lumen-wall ratios characteristic of arteries. - Fibrous tissue
- Protection - Squamous endothelium layer
- Creates a smooth surface which reduces friction as blood flows through - Furthermore, the elastic and smooth muscle tissue in the thick middle layer of arteries maintains a constant blood velocity by providing a smoothing effect (i.e. the pulse effect in blood pressure is not matched by a pulse effect in blood velocity).
Give an example of where vasoconstriction and vasodilation may occur in the body
The skin during temperature regulation
What are some of the adaptations of veins?
- Large lumen
- Offers little resistance to blood flow, which is essential as the blood is at low pressure in the veins - Valves
- Prevent the backflow of blood - Elastic tissue
- Limits vessel expansion
- Due to the low pressures involved, there is much less muscle tissue and very little elastic tissue compared to arteries. - Fibrous tissue
- Protection - Squamous endothelium layer
- Creates a smooth surface which reduces friction as blood flows through
What are some of the adaptations of capillaries?
- It’s small size allows an extensive network of capillaries, providing a large surface area for the diffusion of materials (no cell is far from a capillary).
- A capillary has a very thin wall (one cell thick), which facilitates exchange of materials with surrounding cells and tissues as:
- It is permeable to water and solutes.
- There is a short diffusion distance. - Narrow capillary lumen
- Red blood cells are just about able to ‘squeeze’ their way through the narrow capillaries, further reducing the diffusion distances between the red blood cells and the lungs or the tissues. - Squamous endothelium layer creates a smooth surface which reduces friction as blood flows through.
Draw a diagrammatic representation of an artery
Textbook page 152
Draw a diagrammatic representation of a vein
Textbook page 152
Draw a diagrammatic representation of a capillary
Textbook page 152
Elastic tissue in photomicrograph/microscope images of cross-sections of arteries and veins often appear as …
Wavy lines
Which blood vessel contains more elastic tissue?
Arteries or veins
Arteries
Which blood vessel has a thicker wall?
Arteries or veins
Arteries
Which blood vessel has a characteristic round shape?
Arteries or veins
Arteries
Which blood vessel has a more irregular shape?
Arteries or veins
Veins
Which blood vessel contains more fibrous tissue?
Arteries or veins
Veins
Which blood vessel has a larger lumen?
Arteries or veins
Veins
What causes the difference in thickness between the vessel walls of arteries and veins?
The difference in thickness between the vessel walls is largely due to much more smooth muscle being present in the artery.
Comment on the proportion of elastic tissue to muscle tissue in arteries close to the heart and in arteries close to the organs
High proportion of elastic tissue to muscle tissue in the arteries close to the heart
Lower proportion of elastic tissue to muscle tissue in the arteries close to the organs
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Textbook page 153
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Why does blood remain at high pressure while it travels through the aorta and the main arteries?
Textbook page 153
As it is still close to the heart and there is no significant increase in cross-sectional area.
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Why is the pulse effect in the blood pressure not matched by a pulse effect in blood velocity?
Textbook page 153
Due to the smoothing effects of the elastic and muscle tissue in the artery wall.
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
What causes the significant reduction in pressure between the arteries and arterioles?
As the main arteries branch into a large number of smaller arterioles, the increased cross-sectional area causes a significant reduction in pressure.
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Why is there a further increase in cross-sectional area between the arterioles and capillaries?
As the arterioles subsequently branch into millions of capillaries.
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Why is it crucial that the blood in the capillaries moves with low pressure and low velocity?
The low pressure, and consequent reduction in blood velocity, facilitates the exchange of materials between the blood and the surrounding tissue flood as the blood flows through the capillaries.
What helps transport the blood in veins?
Valves prevent backflow.
With blood pressure being very low in the veins, it is gravity and the force created by the contraction of surrounding muscles that helps transport the blood.
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Why does the overall cross-sectional area of the blood vessels decrease between the capillaries, venules and veins?
As the capillaries unite to form venules, which in turn unite to form veins.
Draw a graph showing the changes in blood pressure, blood velocity and total cross-sectional area of blood vessels across the circulatory system
Why does blood velocity increase after reaching the veins?
The large lumen in each vein ensures that friction between the blood and the wall of the vein is reduced to the extent that blood velocity can increase even though blood pressure is still low.
What is the heart?
A highly specialised muscular organ
What is the function of the heart?
Pumping blood through the body.
As mammals have a double circulation, the heart consists of …
Two pumps, with each side of the heart pumping blood through two separate circulatory systems.
The two sides of the heart are separated by …
A thick muscular wall (the septum) that runs through the centre of the heart.
As mammals have a double circulation, the heart is really two pumps, with each side of the heart pumping blood through two separate circulatory systems (the pulmonary and systemic systems).
Describe the structure of each ‘pump’
Each ‘pump’ has an upper chamber, the atrium, and a lower chamber, the ventricle.
Describe the structure of atria
Atria - are relatively thin walled, as they receive blood from the lungs (left atrium) or the body (right atrium) and pump blood into the ventricles that lie directly below them.
Why do the atria walls have similar thicknesses?
As they contract with equal force, forcing blood into the adjacent ventricle
Describe the structure of ventricles
Ventricles - have much thicker walls compared to atria as they pump blood to the lungs (right ventricle) or around the body (left ventricle).
The muscular wall of the left ventricle is considerably thicker than the wall of the right ventricle.
The blood leaves the heart in …
Pulses
The blood leaves the heart in ‘pulses’ that coincide with …
Each heartbeat
The blood leaves the heart in ‘pulses’ that coincide with each heartbeat and it functions as a …
One-way pump
What are the two types of valve present in the heart?
The atrioventricular (bicuspid and tricuspid) valves
The semilunar (arterial and aortic) valves
Give two examples of where backflow could occur in the heart if valves were absent
The flow of blood back into the atria when the ventricles contract to pump blood out of the heart.
The return of blood from the arteries back into the heart when the pressure falls between pulses.
Where are the atrioventricular valves situated in the heart?
The atrioventricular (tricuspid and bicuspid) valves lie between the atria and the ventricles
What is the role of the atrioventricular valves?
Prevent the backflow of blood into the atria when the ventricles contract.
Where are the semilunar valves situated in the heart?
The semilunar (arterial and aortic) valves lie at the base of the aorta and the pulmonary artery.
What is the role of the semilunar valves?
Prevent the backflow of blood from the arteries into the ventricles
Where can papillary muscle be found in the heart?
Papillary muscles are embedded in the ventricle walls
The atrioventricular valves are anchored by …
The papillary muscles
What links the atrioventricular valves and the papillary muscles?
Chordate tendinae
How are the chordate tendinae adapted for their role?
They are thin (resembling short lengths of thread or string) and can therefore function without impeding the flow of blood through the ventricle.
They are extremely tough and flexible, but not elastic, ensuring that when the ventricles contract (resulting in an increased pressure in the ventricles forcing the AV-valves shut) they prevent the valves turning ‘inside out’, which would allow blood to flow back into the atria.
What are chordae tendinae?
Valve tendons that link the papillary muscle and the atrioventricular valves.
Sometimes referred to as the ‘heart-strings’ as they resemble short lengths of thread or string.
What is the role of the chordae tendinae?
Prevent the backflow of blood from the ventricles into the atria by preventing the AV-valves from turning inside out
What are the semilunar valves?
The semilunar valves are pocket valves on the artery walls that only close when the blood pressure in the arteries exceeds the pressure in the ventricles. When blood is being pumped out of the ventricles they are pushed flat against the artery walls and do not impede blood flow.
What are the names of the four major blood vessels that enter or leave the heart?
Aorta
Pulmonary artery
Vena cava
Pulmonary vein
What is the role of the aorta?
The aorta is the major artery that carries oxygenated blood out of the left ventricle. Arterial branches leading from the aorta carry blood to all the major organs of the body except the lungs.
What is the role of the pulmonary artery?
Carries deoxygenated blood from the right ventricle to the lungs
What is the role of the vena cava?
Brings deoxygenated blood back from the body, returning blood into the right atrium
What is the role of the pulmonary vein?
Transports oxygenated blood from the lungs to the left atrium.
What arteries supply the heart with glucose and oxygen for respiration?
Coronary arteries
The heart itself has a very high …
Metabolic rate
Why does the heart have a very high metabolic rate?
As it continually contracts throughout the life of the individual concerned
The heart itself has a very high metabolic rate, as it continually contracts throughout the life of the individual concerned and consequently has …
High respiratory demands
Describe the distribution of the coronary arteries
The coronary arteries branch off the aorta shortly after it leaves the heart and travel over the heart muscle
Describe two similarities and one difference between the pulmonary artery and vein and other arteries and veins in the body
Similarities
- Both carry blood away from and to the heart as normal
- Both are histologically (structurally) similar to other arteries and veins
Difference
- The pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood, which is different from normal arteries (which carry oxygenated blood) and veins (which carry deoxygenated blood).
Label the different structures present in the heart on the diagram provided
[Do not draw on the diagram]
[Use blank sheet of white paper which is pre-drawn]
Textbook page 155
What is the cardiac cycle?
The cardiac cycle describes the sequence of events that occur during one heartbeat.
How often does the cardiac cycle take place in a human heart per minute?
70 times
What are the two main stages within the cardiac cycle?
Diastole
Systole
What does the phase ‘diastole’ describe?
Diastole describe a phase when the heart muscle is relaxed.
What does the phase ‘systole’ describe?
Systole indicates a contraction phase
What are the three stages of the cardiac cycle in chronological order?
Diastole
Atrial systole
Ventricular systole
What happens in the atria during diastole?
- Atrial walls relaxed.
* Blood enters the atria from the venae cavae and the pulmonary vein.
What happens in the ventricles during diastole?
- Ventricle walls relaxed and semilunar valves closed, as arterial pressure > ventricular pressure preventing reflux of blood back into the ventricles.
- As atrioventricular valves are open, blood enters the ventricles from the atria.
What happens in the atria during atrial systole?
- Walls of the atria contract forcing more blood into the ventricles.
- AV valves remain open as the pressure in the atria still exceeds the pressure in the ventricles.
- Blood continues to enter the atria from the venae cavae and the pulmonary vein.
What happens in the ventricles during atrial systole?
- Walls of the ventricles remain relaxed.
- Ventricle volume continues to increase as they fill with blood.
- Semilunar valves remain closed.
What happens in the atria during ventricular systole?
• Walls of atria relax
What happens in the ventricles during ventricular systole?
- Walls of ventricles contract.
- AV valves close as the pressure in the ventricles now exceed the pressure in the atria.
- The chordae tendinae prevent the AV valves ‘blowing inside out’.
- As ventricle pressure reaches its peak, semilunar valves are forced open, forcing blood into the arteries.
- By the end of ventricular systole, the ventricles will be at their smallest volume.
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
Explain what happens during stage A.
A - atrial walls contract, increasing atrial pressure. AV valves are open (as atrial pressure > ventricular pressure) and semilunar valves remain closed (as aortic pressure > ventricular pressure).
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
Explain what happens at stage B
B- atrial contraction complete (atria are empty of blood) and ventricles begin to contract - ventricular pressure > atrial pressure - AV valves close (first heart sound)
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
Explain what happens at stage C
C - continued contraction of ventricles - ventricle pressure > arterial pressure - semilunar valves open
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
Explain what happens at stage D
D - arterial pressure > ventricular pressure - semilunar valves close due to loss of blood from ventricles (second heart sound)
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
Explain what happens at stage E
E - ventricular pressure falls as little blood present and walls begin to relax - atrial pressure > ventricular pressure - AV valves open
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
Explain what happens during stage F
F - atrial pressure > ventricle pressure as blood flowing into atria - AV valves remain open - blood passively flows into the ventricles from the atria.
Turn to textbook page 157
The diagram shown at the top of the page shows the pressure changes in the left side of the heart during the cardiac cycle (left atrium, left ventricle and aorta).
What causes the changes in atrial pressure between B and E?
The changes in atrial pressure between B and E are caused by:
- the increased pressure of the contracting ventricle causing back pressure of the contracting ventricle on the atria (B-C) [i.e. the force of the AV valves shutting will temporarily increase atrial pressure].
- the subsequent fall in pressure is caused by the relaxation (and increase in volume) of the atria.
- the increase in pressure between 0.2 seconds and E is cause by the atria filling with blood.
When is the first heart sound heard?
At the end of atrial systole / start of ventricular systole
When ventricular pressure > atrial pressure
What causes the first heart sound?
When the heart valves close, the flaps of tissue bang together to make a sound.
Closure of the atrioventricular (tricuspid and bicuspid) valves.
When is the second heart sound heard?
End of ventricular systole
When arterial pressure > ventricular pressure
What causes the second heart sound?
When the heart valves close, the flaps of tissue bang together to make a sound.
Closure of the semilunar (arterial and aortic) valves
When the heart valves close, the flaps of tissue bang together to make a sound. How often does this occur in each cardiac cycle?
Twice
When the heart valves close, the flaps of tissue bang together to make a sound. This occurs twice in each cycle. The sounds can be shown in a …
Phonocardiogram
What does ECG stand for?
Electrocardiogram
What is an ECG?
An electrocardiogram (ECG) is a graphical representation of the electrical activity in the heart
Do the heart valves control the cardiac cycle?
The valves do not control the cardiac cycle, they open and close (passively) due to pressure changes within the heart.
Both sides of the heart contract at …
The same time
Both sides of the heart contract at the same time, with the same part of …
The cardiac cycle occurring simultaneously in each
In general, when heart chambers relax they have …
A larger volume than when they are contracting
In general, when heart chambers have a large volume they are …
Relaxed
In general, when heart chambers have a reduced volume they are …
Contracting
The sequences within the cardiac cycle are stimulated by …
A co-ordinated wave of electrical excitation through the heart.
Cardiac muscle is …
Myogenic
Cardiac muscle, unlike other muscle, is myogenic. What does this mean?
The heart can beat on its own and does not require external stimulation.
What does SAN stand for?
Sinoatrial node
The sinoatrial node (SAN) is often referred to as …
A pacemaker
How does the heartbeat start?
The heartbeat starts with an electrical signal, originating from an area of muscle in the wall of the right atrium, the sinoatrial node (SAN) or pacemaker
Where is the sinoatrial node found?
The sinoatrial node (SAN) can be found in an area of muscle in the wall of the right atrium.
Outline the sequence of events that occur during the electrical stimulation of the heart
- The SAN sends out a wave of electrical activity over the atria, causing contraction (atrial systole). This wave of electrical activity travels rapidly, causing the atria to contract simultaneously.
- Between the atria and the ventricles is a layer of non-conductive tissue that prevents the wave of excitation passing directly through to the ventricles. The only way the electrical activity can pass through to the ventricles is via the atrioventricular (AV) node that conducts very slowly. As a result the contraction in the ventricles (ventricular systole) is delayed relative to the atria. This ensures that when ventricular systole begins, atrial systole is complete and the ventricles are filled with blood.
- The electrical activity passes down the septum of the ventricles in special tissue called the Bundle of His to the bottom of the ventricles. The stimulation then spreads up through the walls of the ventricles in special tissue called Purkinje fibres, causing contraction of the ventricle walls and forcing blood up through the arteries (ventricular systole).
Although the heart is myogenic and can beat without nervous stimulation, the sinoatrial node is under …
Nervous system control
Although the heart is myogenic and can beat without nervous stimulation, the sinoatrial node is under nervous system control. What does this mean?
This means that the rate of heartbeat can be increased (or decreased) in time of need through external nervous control.
Give an example of when the rate of heartbeat may be increased by external nervous stimulation.
During periods of exercise the rate of heartbeat is increased to ensure that the muscles receive increased glucose and oxygen for their increased respiratory needs.
Name the three key elements of the ECG
- P wave
- QRS complex
- T wave
Draw a sketch of an ECG
Textbook page 158
What does the P wave represent in an ECG?
The P wave represents the wave of electrical stimulation that triggers the contraction of the atria.
What does the QRS complex represent in an ECG?
The QRS complex represents the electrical activity that stimulates contraction of the ventricles.
What does the T wave represent?
The T wave represents the relaxation of the ventricles (the ventricles are repolarised).
Why does the R peak have a much greater amplitude than the P peak?
The R peak has a much greater amplitude than P as there is much greater electrical activity in the ventricles (reflecting their larger size and thicker muscle).
What does the short straight section between the P wave and the QRS complex represent?
The wave of excitation passing through the AV node.
What can doctors use ECG traces for?
To identify irregularities in the heartbeat.
What is blood?
A suspension of cells (red and white blood cells) in a pale yellow liquid (plasma).
What is the role of blood?
Primary role = Transport
Secondary role = Defence against disease
Name the three major components of the blood
Platelets
Cells
Plasma
What are platelets?
Platelets are cell fragments that have an important role in the clotting process and in repairing minor breaks in blood vessels.
What is plasma?
Pale yellow liquid
Transports blood cells plus Glucose Amino acids And other products of digestion Ions Carbon dioxide Urea Heat Prothrombin Fibrinogen Clotting factors And many other substances
Name the two major types of blood cells
Red blood cells
White blood cells
What are the adaptations of red blood cells?
- Their number - about 500 million in each mm3 of blood.
- Small size - haemoglobin molecules must be close to the cell surface to aid diffusion. Also it makes it easier to flow through narrow capillaries.
- Shape - High SA/V ratio due to biconcave shape.
- No nucleus or organelles - so more room for haemoglobin.
- Haemoglobin - to carry oxygen. Being in the RBC affects the water potential of the blood less and makes it less viscous. Also more can be packed in than dissolved in plasma. Each RBC has nearly 300 million molecules of haemoglobin.
Why is it beneficial that haemoglobin is stored within the red blood cell as opposed to being dissolved in the plasma?
- Affects the water potential of the blood less.
- Makes the blood less viscous.
- More can be packed inside red blood cells than can be dissolved in the plasma.
What are white blood cells?
Larger than red blood cells with a nucleus. Much less numerous than red blood cells.
What are the three types of white blood cell?
Polymorphs (microphages)
Monocytes
Lymphocytes
What is the most common white blood cell?
Polymorphs (microphages) [70% of all white blood cells]
What are polymorphs?
Polymorphs (microphages)
- The most common white blood cell (70% of all white blood cells).
- They have a distinctive multi-lobed nucleus and granular cytoplasm.
- They are phagocytic and can pass between the squamous endothelium capillary cells, and destroy bacteria and other foreign bodies by phagocytosis at the sites of infection (for example, outside the blood system).
What are monocytes?
Monocytes
- Largest but least common white blood cell (5%)
- They have a bean-shaped nucleus
- They are phagocytic and can move out of the blood at sites of infection and develop into phagocytic macrophage cells, which destroy bacteria and other foreign material.
- They are longer lived than polymorphs.
What are lymphocytes?
Lymphocytes
- Around 20-25% of white blood cells are lymphocytes.
- They have a very large nucleus leaving only a small amount of cytoplasm.
- There are two types:
• B-cells are involved in antibody production
• T-cells are involved in cell-mediated immunity (destroying infected and foreign cells).
What are the two types of lymphocyte?
B-cells
T-cells
Draw a diagram of a polymorph
Textbook page 159
Draw a diagram of a lymphocyte
Textbook page 159
Draw a diagram of a monocyte
Textbook page 159
Draw a diagram of red blood cell
Textbook page 159
What is tissue fluid?
The fluid that lies immediately outside the capillaries and surrounds the cells of the tissues.
What is the function of tissue fluid?
Osmoregulation of the cells
Facilitation of the transport of substances between the blood and body cells
Provides a stable environment for the cells
White blood cells are also known as …
Leucocytes
What substances does the tissue fluid supply to the tissues?
Oxygen Glucose Amino acids Salts Many other substances
What substances does the tissue fluid supply back to the blood?
Carbon dioxide
Many other substances
What is ultrafiltration?
Filtration under pressure
What force pushes liquid and small molecules out of capillaries?
Hydrostatic (blood) pressure
What creates the hydrostatic (blood) pressure present in the capillaries?
As blood travels through the arteries, the arterioles and then into the arteriole end of the capillary network, the narrowing of the blood vessels creates a pressure called hydrostatic (blood) pressure.
As blood travels through the arteries, the arterioles and then into the arteriole end of the capillary network, the narrowing of the blood vessels creates a pressure called …
Hydrostatic (blood) pressure
What effect does the hydrostatic (blood) pressure have on the blood in the capillary network?
The pressure will force liquid and small molecules out of the capillaries at the arteriole end of the capillary network. Plasma proteins and red blood cells are too large to be filtered through in this process of ultrafiltration.
What are the two forces which oppose hydrostatic (blood) pressure?
- The lower water potential of the blood, due to the presence of plasma proteins, that tends to pull the tissue fluid back by osmosis.
- The hydrostatic pressure of the tissue fluid opposes the inward flow of liquid from the capillaries.
Why do liquids and small molecules leave the blood at the arteriole end of the capillary network?
At the arteriole end of the capillary network, the hydrostatic pressure of the blood exceeds the two other forces.
How do the substances filtered out of the blood at the arteriole end of the capillary network enter the cells of the tissue?
Liquid rich in oxygen and other materials is filtered out of the blood and into the tissue fluid that bathes the cells. Oxygen, glucose and other materials then enter the cells by diffusion.
It is important that the liquid filtered out of the capillary at the arteriole end is returned to the capillary after the tissue have been supplied with essential metabolites. The returning fluid transports …
Carbon dioxide and other wastes to the capillary.
What causes the tissue fluid to return to the blood?
- The loss of fluid from the capillary causes a reduction in hydrostatic (blood) pressure, with the result that by the time the blood reaches the venule end of the capillary, the hydrostatic pressure of the tissue fluid exceeds the hydrostatic pressure of the blood.
- The return of tissue fluid to the capillaries is aided by the difference in water potential between the blood in the capillaries and the tissue fluid.
- The water potential gradient is maintained along the length of the capillary but is much reduced at the venule end, by which time much of the filtered liquid has returned.
What is the function of blood clotting?
Reduces the loss of blood through injury (as blood is an essential body fluid)
The repair and sealing of wounds prevents the entry of pathogens.
The process of blood clotting operates on a …
Cascading principle
The process of blood clotting operates on a cascading principle, with the presence of certain compounds …
Catalysing reactions further down the chain.
What is a blood clot made of?
A mesh of insoluble fibrin containing trapped blood cells.
As the blood clot dries, it forms …
A scab
What is the role of a scab formed from a blood clot?
Prevents blood loss
Prevents the entry of microbes
The clotting process is aided by …
The fact that as soon as a blood vessel is damaged, it vasoconstricts thus reducing blood flow to the damaged area.
How are the platelets activated?
The exposed collagen fibres of the damaged blood vessel activate the platelets.
Once the platelets are activated they release …
Clotting factors
What is the role of platelets in blood clotting?
Once activated, the platelets realise clotting factors (which catalyse the conversion of prothrombin to thrombin).
The platelets can also form a plug (minor clot) to seal minor damage or reduce the rate of blood loss if greater damage is present.
Name some clotting factors necessary to catalyse the conversion of prothrombin to thrombin
Calcium ions
Vitamin K
Factors VIIIa, Xa and XIII (XIIIa in its activated form)
Thromboplastin/thrombokinase (enzyme)
What is prothrombin?
A soluble plasma protein
What is prothrombin converted to?
Thrombin (an enzyme)
What is the role of XIII?
Clotting factor
XIIIa in its activated form
Catalyses the conversion of prothrombin to thrombin.
XIIIa helps bind the fibrin polymers in a clot together helping to ensure the integrity of the clot.
What is the role of thrombin?
An enzyme which catalyses the conversion of fibrinogen to fibrin.
What is fibrinogen?
A soluble plasma protein
What is fibrin?
Insoluble protein.
Fibrous strands form a mesh that traps red blood cells to form a clot.
What is haemophilia?
Medical condition which prevents the blood from clotting due to the absence of factor VIII
Why do some medical conditions prevent the blood from clotting?
Due to there being a particular part of the cascade reaction missing.
Give an example of a medical condition which prevents the blood from clotting
Haemophilia
In what case may a blood clot form despite the blood vessel not being damaged?
Certain types of medical treatment can increase the risk of a clot forming within the blood vessel (even if the vessel is not damaged).
Certain types of medical treatment can …
Increase the risk of a clot forming within the blood vessel (even if the vessel is not damaged).
Oxygen is transported in (blank) through the blood system
Red blood cells
How does oxygen reach the cells of the tissue?
In the capillaries the oxygen leaves the red blood cells and enters the plasma, where it is carried into the tissue fluid by the ultrafiltration of the plasma. The oxygen diffuses through the tissue fluid to the cells.
What molecule within the red blood cells is responsible for oxygen transport?
Haemoglobin
What is haemoglobin?
A respiratory pigment
Responsible for oxygen transport
Consists of four polypeptide chains
- 2 alpha chains and 2 beta chains
Each polypeptide chain has a haem group (prosthetic group) attached, which contains iron (Fe2+)
Conjugated protein with quaternary structure
What part of the haemoglobin molecule does a molecule of oxygen bind to?
The haem group
Each haem group can bind to an oxygen molecule to form …
Oxyhaemoglobin
Write down an equation showing the reaction between haemoglobin and oxygen to from oxyhaemoglobin
Textbook page 162
Each molecule of haemoglobin can carry up to …
Four molecules of oxygen
The reaction between haemoglobin and oxygen to form oxyhaemoglobin is …
Reversible
How are respiratory pigments specialised for the transport of oxygen?
Their structure is that it’s affinity for oxygen changes as the concentration of oxygen changes.
What does each haem group contain?
Iron (Fe2+)
When is oxyhaemoglobin formed?
In conditions where oxygen levels are high/ high partial pressures of oxygen
When does oxyhaemoglobin dissociate?
When oxygen levels are low/ low partial pressure of oxygen
What does ‘dissociate’ mean?
Breaks down releasing oxygen
In mammals, where is oxyhaemoglobin formed?
In the lungs where oxygen levels in the blood are high due to the rapid gaseous exchange in the lungs.
In mammals, where does oxyhaemoglobin dissociate?
Dissociation takes place in the tissues where oxygen levels are low due to respiration.
How many oxygen molecules does haemoglobin transport on average?
In reality, haemoglobin is either deoxygenated or fully oxygenated with four oxygen molecules. It seldom transports one, two or three oxygen molecules around the body.
When one oxygen molecule is taken up by a haemoglobin molecule, there is a …
Conformational change (distortion) in the haemoglobin molecule
When one oxygen molecule is taken up by a haemoglobin molecule, there is a conformational change (distortion) in the haemoglobin molecule, resulting in …
An easier (faster) uptake of the remaining three oxygen molecules (cooperative loading)
What is cooperative loading?
When one oxygen molecule is taken up by a haemoglobin molecule, there is a conformational change (distortion) in the haemoglobin molecule, resulting in an easier (faster) uptake of the remaining three oxygen molecules.
When one oxygen molecule binds, this distorts the shape and facilitates binding of the second oxygen molecule. Further structural alterations occur when oxygen molecules attach to the second and third haem groups, each one facilitating much faster uptake of oxygen than the preceding one.
If every molecule of haemoglobin in the blood is carrying four oxygen molecules, the blood is said to be …
100% saturated
What does 100% saturation of the blood mean?
If every molecule of haemoglobin in the blood is carrying four oxygen molecules, the blood is said to be 100% saturated.
If only 50% of the haemoglobin is carrying oxygen (assuming they are all carrying four molecules), the blood is said to …
50% saturated.
What does 50% saturation of the blood mean?
If only 50% of the haemoglobin is carrying oxygen (assuming they are all carrying four molecules), the blood is 50% saturated.
The degree of saturation of haemoglobin is dependent on …
The amount of oxygen available in the environment in which the haemoglobin is in at that time.
The oxygen concentration in the environment is referred to as its …
Partial pressure (pO2) or oxygen tension
What is partial pressure?
The partial pressure of any gas is the proportion of total air pressure that is contributed to by that gas and is measured in kilopascals (kPa).
What is partial pressure measured in?
Kilopascals (kPa)
If haemoglobin molecules are exposed to a range of partial pressures of oxygen, their percentage saturation (with oxygen) can be plotted on a graph known as a …
(Haemoglobin) oxygen dissociation curve
Describe the characteristic shape of oxygen dissociation curves
S-shape (sigmoidal)
What does the characteristic S-shape (sigmoidal) of the (haemoglobin) oxygen dissociation curve reveal about the process of oxygen transport?
It shows that in high oxygen partial pressures, such as 14 kPa (as found in the lungs), oxyhaemoglobin is readily formed and the haemoglobin approaches full saturation - ie every haemoglobin molecule is fully saturated with oxygen.
The haemoglobin remains saturated as the partial pressure falls (as it travels through the pulmonary vein, heart, aorta, other arteries and arterioles).
However, in low partial pressures, for example, 2-5 kPa (as found in respiring tissues), dissociation takes place and the oxygen is released and diffuses into the respiring cells.
The sigmoidal pattern makes the process even more efficient, as over the range of partial pressures typical of respiring tissues there is rapid dissociation, making large quantities of oxygen available to the tissues, even though there is a relatively small fall in partial pressure.
How does the sigmoidal shape of the (haemoglobin) oxygen dissociation curve make the process of oxygen transport even more efficient?
Over the range of partial pressures typical of respiring tissues there is rapid dissociation, making large quantities of oxygen available to the tissues, even though there is a relatively small fall in partial pressure.
What is the partial pressure of oxygen in the lungs?
14 kPa
What is the partial pressure of oxygen in respiring tissue?
2-5 kPa
What variables and units go on the x and y axes of a (haemoglobin) oxygen dissociation curve?
X-axis = Partial pressure of oxygen/ kPa Y-axis = Saturation of haemoglobin/ %
Definition of terms
Loading tension:
The loading tension is the partial pressure at which the haemoglobin is 95% saturated with oxygen.
Definition of terms
Unloading tension:
The unloading tension is the partial pressure at which haemoglobin is 50% saturated with oxygen.
What factors affect the physiological ability of haemoglobin to bind with or release oxygen?
- Partial pressure of oxygen (pO2)
- Partial pressure of carbon dioxide (pCO2)
- Blood pH
- Blood temperature
What is the Bohr effect?
In higher concentrations of carbon dioxide, ie higher than ‘normal’ levels in the blood, the oxygen dissociation curve moves to the right.
The partial pressure of oxygen, the partial pressure of carbon dioxide, blood temperature and blood acidity all affect …
The physiological ability of haemoglobin to bind with or release oxygen
What is the advantage of the Bohr effect?
The advantage of the Bohr effect is that oxygen is released more readily from haemoglobin at a particular partial pressure of oxygen, ie the haemoglobin has reduced affinity for oxygen.
The unloading tension shifts to the right and occurs at higher partial pressures of oxygen. Therefore there is more oxygen available for the respiring tissues at times of greatest need.
The Bohr effect occurs when …
Carbon dioxide levels increase, such as when high rates of respiration are taking place, for example, during strenuous exercise.
What factors, other than the partial pressure of carbon dioxide (pCO2), produce the Bohr effect?
Higher blood temperature
Increased blood acidity
When does blood temperature rise?
During times of strenuous exercise when the rate of respiration increases (respiration is an exothermic reaction).
When does blood acidity rise?
During times of strenuous exercise when the rate of respiration increases (leading to increased carbon dioxide transport in the plasma).
Draw a (haemoglobin) oxygen dissociation curve showing the % saturation of haemoglobin with oxygen in low pCO2 and in high pCO2 over a range of partial pressures
Textbook page 164
What is myoglobin?
Respiratory pigment
Does not circulate in the blood
Found in ‘red’ muscle (skeletal and heart muscle)
Consist of one polypeptide chain with a single haem group
Myoglobin’s affinity for oxygen is (blank) than haemoglobin’s affinity for oxygen
Higher
If the oxygen dissociation curve for a respiratory pigment is shifted to the left, the respiratory pigment has an (blank) affinity for oxygen
Increased
If the oxygen dissociation curve for a respiratory pigment is shifted to the right, the respiratory pigment has a (blank) affinity for oxygen
Decreased
Draw an oxygen dissociation curve for both myoglobin and haemoglobin
Textbook page 165
The oxygen dissociation curve for myoglobin is situated to the (blank) of haemoglobin
Left
Explain the differences in the oxygen dissociation curves for myoglobin and haemoglobin
- Myoglobin has a greater affinity for oxygen than haemoglobin. This means it will remain saturated with oxygen even at relatively low partial pressures of oxygen.
- The myoglobin will only release oxygen if the pO2 becomes very low - lower than normally found in respiring tissues. This means that it serves as an oxygen store - it has no role in oxygen transport - and only releases oxygen when blood oxygen levels are very low (less than 1kPa), such as during very strenuous exercise.
How is myoglobin adapted for its role as an oxygen store?
- It is situated in the skeletal muscle, where respiratory demands are greatest during vigorous exercise.
- The physiological (biochemical) differences between haemoglobin and myoglobin ensures that it only begins to release oxygen when the haemoglobin reserves are depleted.
- The oxygen reserve released by the myoglobin allows aerobic respiration to continue for longer during strenuous exercise, thereby delaying the onset of less efficient anaerobic respiration.
What is the role of the oxygen reserve released by myoglobin during strenuous exercise after the haemoglobin reserves have been depleted?
The oxygen reserve released allows aerobic respiration to continue for longer during strenuous exercise, thereby delaying the onset of less efficient anaerobic respiration.
What makes skeletal and heart muscle red?
The myoglobin and its stored oxygen
Myoglobin is particularly abundant in the muscles of what animals?
In the muscles of diving mammals such as seals and whales.
How does the myoglobin store become replenished following depletion, particularly as it is found in muscles only and does not travel in the blood to the lungs?
- Myoglobin has a greater affinity for oxygen than haemoglobin.
- In the period following exercise, blood flows through the muscle.
- The pO2 will have stabilised, returning to a normal 2-5 kPa.
- Oxygen will dissociate from the haemoglobin (as is typical).
- At these partial pressures, the myoglobin is physiologically capable of remaining fully saturated (with no dissociation).
- Oxygen freed from the haemoglobin readily combines with any unsaturated myoglobin molecules until the myoglobin store is fully replenished.
- The effect of altitude on oxygen transport by haemoglobin
What happens as height above sea level increases?
Overall atmospheric pressure and pO2 is reduced
- The effect of altitude on oxygen transport by haemoglobin
As height increases above sea level, overall atmospheric pressure and pO2 is reduced. What effect will this have on the saturation of haemoglobin?
If the lungs have a pO2 environment around 7 kPa, which is typical in very high altitudes, compared to around 13 kPa in more lowland altitudes, the human haemoglobin cannot become fully saturated.
- The effect of altitude on oxygen transport by haemoglobin
As height increases above sea level, overall atmospheric pressure and pO2 is reduced. What effect will this have on the human body?
At high elevations the human haemoglobin cannot become fully saturated. The reduced oxygen levels can significantly affect normal activity and altitude sickness can result.
- The effect of altitude on oxygen transport by haemoglobin
What occurs after a period of time at high altitude?
Acclimatisation
- Effect of altitude on oxygen transport by haemoglobin
What is acclimatisation?
After a period of time (even a few days) at high, acclimation can occur.
Acclimatisation involves:
- An increase in the number of red blood cells
- This allows for more efficient transport of the oxygen that is available in the atmosphere (compensating for the reduced saturation of haemoglobin in the lower pO2). - Increased ventilation
- To maximise the diffusion of oxygen into the blood. - Other subtle changes to the physiology of respiration in the cells.
- Effect of altitude on oxygen transport by haemoglobin
Why do many athletes spend time training in high altitudes?
To increase their red blood cell count
- Effect of altitude on oxygen transport by haemoglobin
Populations that have lived in high altitudes for many generations have …
Evolved a type of haemoglobin that saturates at lower pO2 levels than the more typical lower altitude population.
Give an example of a mammal species that is adapted to live at high altitudes
Llama
How are some mammal species adapted to living at high altitudes?
They have haemoglobin that is specialised and highly adapted for high altitude environments.
Their haemoglobin has a greater affinity for oxygen.
Draw a (haemoglobin) oxygen dissociation curve for both human haemoglobin and llama haemoglobin over a range of partial pressures
Textbook page 166
The oxygen dissociation curve for the llama is to the (blank) of the ‘normal’ human oxygen dissociation curve.
Left
What is the advantage of the oxygen dissociation curve for the llama haemoglobin being to the left of the ‘normal’ human oxygen dissociation curve?
The llama haemoglobin therefore has a greater affinity for haemoglobin, allowing it to become fully saturated at lower partial pressures of oxygen (typical in high altitude environments).
What does CHD stand for?
Coronary Heart Disease
What disease kills more people than any other disease in the British Isles?
Cardiovascular disease
What causes coronary heart disease (CHD)?
Damage to the coronary arteries that supply the heart muscles with blood, carrying oxygen and glucose, for respiration.
What is an atheroma?
A build-up of fatty deposits that form within the wall of an artery
What increases the likelihood of development of atheromas in arteries?
Risk factors
The likelihood of development of atheromas in arteries can be increased by a number of …
Risk factors
Give some examples of risk factors which can increase the likelihood of development of atheromas in arteries
Smoking Lack of exercise Too much salt in the diet Stress High blood cholesterol levels
What are risk factors?
Factors which can increase the likelihood of development of atheromas in arteries
Outline the sequence of events which leads to the development of an atheroma
- The squamous endothelium cells that line the artery lumen become damaged.
- This damage can be caused by a number of reasons including toxins in the blood from tobacco smoke or high blood pressure that applies a greater force on the artery walls. - Following damage to the endothelial lining, the atheroma builds up within the wall of the artery (beneath the endothelium).
- Macrophages (having developed from monocytes) migrate from the blood into the damaged artery wall and are involved in the accumulation of materials within the wall, particularly cholesterol, but including dead muscle cells, salts and fibrous tissue.
- In due course, the atheroma builds up into hardened plaques. - As they increase in size and toughness, the atheromas (plaques) bulge into the lumen of the artery, causing a narrowing that restricts blood flow.
- The fibrous material causes the artery to become less elastic and less able to regulate blood flow through vasodilation or vasoconstriction. - The ‘hardening (and narrowing) of the arteries’ tends to raise blood pressure further, and as a consequence further atheromas and plaques are more likely to form.
What is atherosclerosis?
The disease that is caused by the thickening of the artery wall through the development of atheromas and plaques.
The artery wall becomes less elastic, the artery lumen gets narrower and an increase in blood pressure results.
What is thrombosis?
The formation of blood clots within the blood vessels
Where can thrombosis occur in the circulatory system?
The formation of blood clots within the blood vessels (thrombosis) can happen anywhere in the circulatory system.
When can thrombosis (the formation of blood clots within the blood vessels) be particularly problematic?
In narrow arteries, such as the coronary arteries, or in arteries that have been narrowed as a result of heart disease.
If a thrombosis occurs in the coronary arteries, it is known as a …
Coronary thrombosis
What is coronary thrombosis?
The formation of blood clots within the coronary arteries
What will increase the likelihood of a thrombosis occurring in the coronary arteries?
Damage to the artery wall (for example, as a result of atheromas/atherosclerosis).
What happens if a coronary thrombosis occurs?
The area of the heart affected fails to receive blood, and therefore oxygen and glucose for respiration, and the cells die if the blockage is prolonged.
If a large area of the heart is affected (ie the thrombosis occurs near the origin of the coronary artery rather than near the tip) a myocardial infarction (heart attack) results.
What is an angiograph?
An angiograph is a medical imaging technique that allows doctors to ‘see’ inside blood vessels; it is a specialised type of X-ray.
How is the investigation of blood vessels by angiograph carried out?
A contrast agent (dye) that will show up in angiograph imaging is added to the blood via a thin tube (catheter) that is inserted into a blood vessels in, for example, the forearm or groin.
The tube is pushed through the blood vessels until it reaches the part of the body under investigation so that the contrast agent is placed only where needed.
What can an angiograph identify in the blood vessels?
The extent of blood vessel narrowing, blockage or damage.
What medical conditions can an angiograph diagnose through the investigation of blood vessels?
Coronary heart disease (CHD)
Aneurysm
Atherosclerosis
What is an aneurysm?
An aneurysm is a bulge in a large blood vessel (often the aorta) due to weakness of the vessel wall.
Why is it important that aneurysms are identified in their early stages?
As rupture of the wall (of the aorta) is often fatal.
What is a heart attack?
Myocardial infarction
What is a myocardial infarction?
Heart attack
Practical work - Mammalian heart dissection
External anatomy and orientation
Traditionally when drawing diagrams of the heart (and the circulatory system), the diagram is drawn as …
If we are facing the heart.
Practical work - Mammalian heart dissection
External anatomy and orientation
Traditionally when drawing diagrams of the heart (and the circulatory system), the diagram is drawn as if we are facing the heart. This means …
That the left side of the heart is actually on the right side of the diagram and the right side of the heart is on the left side of the diagram.
Practical work - Mammalian heart dissection
External anatomy and orientation
Traditionally when drawing diagrams of the heart (and the circulatory system), the diagram is drawn as if we are facing the heart. This means that the left side of the heart is actually on the right side of the diagram and the right side of the heart is on the left side of the diagram. The same principle applies when …
Dissecting the heart
Practical work - Mammalian heart dissection
External anatomy and orientation
The back of the heart is known as the …
Dorsal side
Practical work - Mammalian heart dissection
External anatomy and orientation
The front of the heart is known as the …
Ventral side
Practical work - Mammalian heart dissection
External anatomy and orientation
The back of the heart, the dorsal side, is …
The part closest to the back of the animal
Practical work - Mammalian heart dissection
External anatomy and orientation
The front of the heart, the ventral side, is …
The part closest to the front of the animal.
What side of the heart faces uppermost when placed on the dissecting board?
The front, ventral side, faces uppermost
Practical work - Mammalian heart dissection
External anatomy and orientation
The major blood vessels are at the …
Top of the heart so it should be straightforward to place the heart the correct way up.
Practical work - Mammalian heart dissection
External anatomy and orientation
The major blood vessels are at the top of the heart so it should be straightforward to place the heart the correct way up. It is more difficult to distinguish between the front and back of the heart but a good clue is …
That there is a diagonal line of blood vessels running across the front of the heart. These vessels (coronary arteries) run down from the base of the aorta (top right as you examine it) across the front of the heart.
Practical work - Mammalian heart dissection
External anatomy and orientation
The coronary arteries run from …
The base of the aorta diagonally down the heart.
Practical work - Mammalian heart dissection
The major blood vessels
Once the heart is positioned correctly, the next stage is …
To identify the major blood vessels
Practical work - Mammalian heart dissection
The major blood vessels
Once the heart is positioned correctly, the next stage is to identify the major blood vessels. The pulmonary artery and aorta are …
Very close to each other at the very top of the heart.
Practical work - Mammalian heart dissection
The major blood vessels
Once the heart is positioned correctly, the next stage is to identify the major blood vessels. The pulmonary artery and aorta are very close to each other at the very top of the heart. How can the pulmonary artery be distinguished from the aorta?
- The aorta is the larger of the two vessels.
- Depending on how close the aorta was cut to the heart it may or may not have a branch (often appearing as a second opening).
- The pulmonary artery is adjacent to the aorta but is smaller with thinner walls.
Practical work - Mammalian heart dissection
The major blood vessels
Once the heart is positioned correctly, the next stage is to identify the major blood vessels. How can the superior and inferior venae cavae be identified?
- The two venae cavae often appear more like flaps rather than discrete blood vessels, when they are cut close to the heart.
- One returns blood from the upper part of the body and the other returns blood from the lower part of the body.
- The two venae cavae are on the tip right hand side of the heart (top left as you examine it), with the vena cava coming from the lower part of the body being slightly lower and further back in the heart.
Practical work - Mammalian heart dissection
The major blood vessels
Once the heart is positioned correctly, the next stage is to identify the major blood vessels. How can the pulmonary vein be identified?
The pulmonary vein is on the top left of the heart (top right as you examine it).
Practical work - Mammalian heart dissection
Examining the circulation of blood in and through the heart
With a gloved finger or a probe, it is possible to trace the path through which the blood flows.
Describe the path through which blood flows in the heart.
- The venae cavae lead to the right atrium which in turn leads to the right ventricle.
- The flow from the right ventricle is back up through the pulmonary artery and out of the top of the heart.
- Similarly, the pulmonary vein leads to the left atrium.
- It is possible to trace the path through the pulmonary vein, left atrium, left ventricle and back up through the aorta.
Practical work - Mammalian heart dissection
Examining the circulation of blood in and through the heart
How can the path through which blood flows in the heart be traced?
With a gloved finger or a probe, it is possible to trace the path through which the blood flows.
Practical work - Mammalian heart dissection
The internal anatomy
To examine the heart’s interior it is necessary to …
Make incisions (cuts) with a scalpel or dissecting scissors through the ventral wall from the top of each atrium to the base of the ventricle.
Practical work - Mammalian heart dissection
The internal anatomy
To examine the heart’s interior it is necessary to make incisions (cuts) with a scalpel or dissecting scissors through the ventral wall from the top of each atrium to the base of the ventricle.
Outline the steps taken when making incisions to study the internal anatomy of the heart
- From the base of the upper vena cava, cut through the wall down through the right atrium and right ventricle. Keep the cut as close as possible to the septum.
- After making the cut pull the two sides apart to expose the two heart chambers on the right side of the heart.
- It should be possible to identify the papillary muscles, the chordae tendinae (‘heart-strings’) and the tricuspid valve (an atrioventricular valve, seen as three flaps).
- Identify the origin of the pulmonary artery, leading out of the left ventricle, and follow it up until you find the semilunar valve.
- Repeat for the left side of the heart. The bicuspid valve, the atrioventricular valve on the left side of the heart only has two flaps.
- Identify the origin of the aorta, leading out of the right ventricle, and following it up until you find the semilunar valve.
Practical work - Mammalian heart dissection
The internal anatomy
To examine the heart’s interior it is necessary to make incisions (cuts) with a scalpel or dissecting scissors through the ventral wall from the top of each atrium to the base of the ventricle.
When dissecting the heart you should be able to observe …
The difference in wall thickness between the atria and ventricles.
Practical work - Mammalian heart dissection
The internal anatomy
To examine the heart’s interior it is necessary to make incisions (cuts) with a scalpel or dissecting scissors through the ventral wall from the top of each atrium to the base of the ventricle.
When dissecting the heart you should be able to observe the difference in wall thickness between the atria and ventricles. It is also apparent that …
Most of the heart consists of heart (cardiac) muscle, with the chambers appearing relatively small in comparison.
Practical work - Mammalian heart dissection
The internal anatomy
To examine the heart’s interior it is necessary to make incisions (cuts) with a scalpel or dissecting scissors through the ventral wall from the top of each atrium to the base of the ventricle.
The walls of the left side of the heart are …
Thicker than the walls on the right.
Practical work - Mammalian heart dissection
The internal anatomy
To examine the heart’s interior it is necessary to make incisions (cuts) with a scalpel or dissecting scissors through the ventral wall from the top of each atrium to the base of the ventricle.
The walls of the left side of the heart are thicker than the walls on the right. Other structures such as the chordae tendinae are also …
Larger and stronger on the left side of the heart.
Knowledge check 22
Explain why large, active animals need a transport system.
Substances enter the blood at the exchange (absorptive) surface. These substances have to be transported quickly enough to satisfy the organism’s requirements (which will be great if it is large and active). Diffusion alone is not rapid enough.
Knowledge check 23
What are the advantages of a double circulatory system over a single circulatory system?
A double circulation allows a two-pressure system with higher pressure to the body cells and lower to the lungs. High pressure in the systemic (body) circulation ensures that oxygenated blood is pumped efficiently to the body cells and allow the formation of tissue fluid. Low pressure in the pulmonary (lung) circulation ensures that fluid is not forced out into the alveoli and the slower flow of blood allows more time for gaseous exchange.
Knowledge check 24
Describe the pathway that blood takes between the vena cava and the aorta
Vena cava ––> right atrium ––> right ventricle ––> pulmonary artery ––> capillaries in lung ––> pulmonary vein ––> left atrium ––> left ventricle ––> aorta
Knowledge check 25
Why is the maximum pressure similar in both atria?
They have the same thickness of muscle and contract so equal force, since they only have to pump blood into the ventricles below.
Knowledge check 26
What causes the atrioventricular valves to close?
They close when the pressure in the ventricles is greater than the pressure in the atria.
Knowledge check 27
During which stage(s) in the cardiac cycle are the semilunar valves closed? Explain your answer.
They are closed during diastole and atrial systole when the ventricle muscle is relaxed. They are also closed during the initial part of ventricular systole when the ventricle muscle contracts without raising the ventricular pressure above that in the artery. They are closed as long as the arterial pressure exceeds that in the ventricles.
Knowledge check 28
Figure 21 shows a heartbeat of duration 0.8 seconds. Calculate the heart rate in beats per minute.
60s
––– = 75 beats min-1
0.8s
Knowledge check 29
List the functions of the SAN, AVN and the bundle of His.
The SAN initiates the heartbeat by emitting impulses over the atria. The AVN delays these impulses and relays them to the bundle of His, which conducts them to the base of the ventricles (to the Purkinje fibres).
Knowledge check 30
Explain the advantages of:
a) the delay in the impulse through the AV node
b) the ventricles contracting from the base upwards
a) The delay allows time for the atria to empty before the ventricles contract.
b) By contracting from the base upwards, each ventricle forces all the blood towards the arteries.
Knowledge check 31
Which possess more elastic tissue, the aorta or the pulmonary artery? Explain your answer.
The aorta, because the aortic pressure is much greater than that in the pulmonary artery.
Knowledge check 32
State where the red blood cells ‘pick up’ oxygen and where they are likely to release it again.
They pick up oxygen in the lungs and release it in respiring tissues.
Knowledge check 33
How is a red blood cell adapted to carry haemoglobin and facilitate its functioning in oxygen transport?
It has no nucleus, so has more room for haemoglobin (each red blood cell contains around 250 million haemoglobin molecules). It is small and flattened, so has a large surface area-to-volume ratio. Being thin means that oxygen does not have to diffuse far to reach a haemoglobin molecule.
Knowledge check 34
Which white blood cells are involved in phagocytosis? How do they differ in activity?
Polymorphs and monocytes (which develop into macrophages). Polymorphs are short-lived, while monocytes are long-lived.
Knowledge check 35
In what form is carbohydrate transported in plants and animals?
Sucrose is transported in plants; glucose is transported in animals.
Knowledge check 36
Name two enzymes invoked in clotting and describe their action.
Thromboplastin (thrombokinase) converts prothrombin (a blood protein) to thrombin (another enzyme) which converts fibrinogen (another blood protein) to fibrin (which forms the fibres of the clot).
Knowledge check 37
Explain how haemoglobin supplies more oxygen to actively respiring tissues to those with lower levels of respiration.
There are two factors - actively respiring tissues consume more oxygen and release more carbon dioxide. Both a decrease in pO2 and an increase pCO2 cause more oxygen to be released from the haemoglobin.
Knowledge check 38
Explain why fetal haemoglobin must have a higher affinity for oxygen than adult haemoglobin.
At the pO2 found in the placenta, fetal haemoglobin must be able to pick up oxygen when the maternal haemoglobin is releasing oxygen.
Knowledge check 39
It may soon be possible to have your DNA analysed to see if you have genes that increase the risk of cardiovascular disease. Suggest a benefit and a potential problem of this.
Benefit: if you know you are at high risk of cardiovascular disease, you can take action to reduce other risk factors.
Potential problem: insurance companies might want to know if you are at high or low risk, which would affect the premiums that you pay.
What is infarction?
The death of tissue resulting from oxygen deprivation
If a small branch of an artery is blocked, only a small amount of muscle dies, causing a small heart attack; if large artery is blocked, the whole heart may stop beating. This is known as …
A cardiac arrest.
