6.2 The blood system Flashcards
1
Q
When is systolic pressure exerted?
A
When the heart pumps blood into the aorta, the main and biggest artery connecting the heart with the rest of the body, it exerts a systolic pressure of between 120 and 200 mm Hg.
2
Q
What does systolic mean?
A
This refers to the part of the heartbeat when the muscle is contracting.
3
Q
What is the diastolic portion?
A
When cardiac muscle is relaxing, that part of the heartbeat is called the diastolic portion.
4
Q
Which is lower: diastolic pressure or systolic pressure?
A
Diastolic pressure is lower than systolic pressure.
5
Q
Why do blood pressure measurements have two systole/diastole?
A
Because diastolic pressure is lower than systolic pressure.
6
Q
Diagram of blood flow in the aorta
A
7
Q
Why can the aorta and all arteries in the body cope with the pressure that is exerted on their walls?
A
Because they are elastic.
8
Q
Describe the structure of the walls of the aorta and arteries
A
-The walls contain elastic fibers formed from elastin protein, which are stretched at every heartbeat when the pressure is highest.
-Arteries also have muscular walls to help propel the blood.
9
Q
What happens to the aorta and arteries when the walls return to their normal shape?
A
This recoil helps to propel the blood forward.
10
Q
What is the overall function of the muscle and elastic fibers present in the wall of the arteries?
A
They assist in maintaining blood pressure between pump cycles.
11
Q
What is the role of the arterial muscle?
A
To keep the arteries narrow enough to maintain the high pressure needed to ensure that the blood has the speed and pressure required to reach all parts of the body.
12
Q
Does blood flow in “bursts” or continuously like a river?
A
In “bursts”.
13
Q
What are the three main layers that the arterial walls are classified as?
A
-Tunica intima
-Tunica media
-Tunica adventitia (also known as the tunica externa).
14
Q
The part of the tunica intima facing the lumen is lined with the ___
A
Endothelium
15
Q
Diagram of the layers of an artery
A
16
Q
Cross-section of the wall of an artery
A
17
Q
Describe the composition of the tunica intima
A
-This is the innermost layer and is in direct contact with the blood in the lumen.
-It includes the endothelium that lines the lumen of all vessels; thus forming a smooth, friction-reducing lining.
18
Q
Describe the composition of the tunica media
A
-This is also known as the middle coat and is mainly made up of smooth (involuntary) muscle cells and elastic fibers arranged in roughly spiral layers.
-This layer is usually the thickest of the three layers.
19
Q
Describe the composition of the tunica adventitia
A
This is also known as the outermost coat and is a tough layer consisting largely of loosely woven collagen fibers that protect the blood vessel and anchor it to surrounding structures.
20
Q
Explain what happens to the arteries when the heart contracts
A
-The arteries experience the highest pressure: systolic blood pressure.
-The circular muscles surrounding the arteries resist the outward pressure and constrict.
-This is called vasoconstriction.
21
Q
Explain what happens to the arteries when the heart relaxes
A
-When the heart relaxes between beats, the pressure in the arteries is lowest: diastolic blood pressure.
-The smooth muscles surrounding the arteries can also relax, and this is called vasodilation.
22
Q
What are arterioles?
A
-Smaller arteries branch off in the body to supply blood to organs, limbs, etc.
-These smaller forms of arteries are called arterioles.
23
Q
Diagram of vasodilation and vasoconstriction in arteries
A
24
Q
What is the role of vasoconstriction and vasodilation?
A
-They directly control the flow of blood through the body.
-They play a role in regulating body temperature and are involved in slowing the flow of blood when a person is severely wounded.
25
What is the pulse and how can it be detected?
-When an artery lies near the surface of the skin, the pulse can be felt; for example, at the wrist or neck.
-The pulse or heart rate refers to the number of times the heart beats per minute.
-It is the result of the alternate expansion and contraction of the arterial wall as the beating heart forces blood into the system of arteries via the aorta.
26
Define stroke volume
The volume of blood pumped out of the left ventricle of the heart during each contraction (or heartbeat).
27
Define cardiac output
The volume of blood the heart pumps through the circulatory system in a minute.
28
A patient with a pulse rate of 40 beats/minute and a stroke volume of 75 ml/beat will have a cardiac output of ___
3,000 ml/minute
Cardiac output is the amount of blood the heart pumps through the circulatory system in a minute.
29
What is usually the thickest layer of the wall of arteries?
The tunica media
30
Which layer of the artery contains muscle fibers and elastic fibers?
The tunica media
31
Which process occurs when arteries must maintain high pressure of the blood?
Vasoconstriction
32
What is the overall purpose of veins?
To transport blood back from the tissues of the body and return it to the atria (upper chambers) of the heart.
33
How does the pressure of blood in veins compare to that in arteries and how does this affect the structure of veins?
-The pressure of blood is much lower than in arteries, and blood flows far more slowly.
-This means that the veins do not need thick walls with lots of muscle fibers.
34
Diagram of the different layers of a vein
35
Because the pressure in veins is lower than in arteries, veins need other ways to ensure that blood flows back to the heart.
What are the two ways in which this happens?
Through the skeletal muscles next to veins, and valves found inside veins.
36
Explain how blood flow in veins is helped by pressure exerted by skeletal muscles
-When you move around, especially during vigorous exercise, the muscles squeeze the veins like a pump.
-Sitting still or lying flat on your back does not assist blood flow.
-So patients that have to remain immobilized for long periods of time or are in a coma, need manual manipulation of the muscles to help the flow of blood, preventing blood boils and bed sores.
37
What danger is posed by the fact that blood pressure in veins is much lower than in arteries?
-There is a danger of backflow due to gravity when blood is returning to the heart from the lower part of the body.
-To solve this problem, veins have valves that close to prevent backflow.
38
Valves in veins ensure that blood flows in ___
One direction only, that is towards the heart, by preventing backflow.
39
Diagram of valves in veins
40
What does blood consist of?
-A liquid portion, called plasma,
-Cells: including red blood cells, white blood cells, and cell fragments called platelets.
41
What does plasma carry?
Dissolved substances such as proteins, hormones, carbon dioxide, glucose, and vitamins and minerals.
42
What do red blood cells contain?
Hemoglobin proteins to transport oxygen.
43
What is the function of while blood cells?
They are part of the immune system and help to defend the body from disease.
44
What is the function of platelets?
They are involved in the mechanisms that clot blood when blood vessels break.
45
What is the connection between arteries and veins formed by?
By a capillary network.
46
Why are arterioles needed?
-The nutrients and oxygen in blood need to reach each and every cell of the body.
-However, the size and wall structure of arteries are too big for that purpose.
-Arteries cannot fit between individual cells if they are large, and they cannot allow for efficient diffusion if there are many cells through which substances must diffuse.
-Thus, the arteries divide to form smaller arterioles that in turn divide successively to form very fine blood vessels called capillaries.
47
What do arterioles divide to form?
Capillaries
48
What do capillaries fuse together to form?
Venules?
49
What do many venules fuse together to form?
Veins
50
Diagram of a capillary network connecting arteries with veins
51
Describe the structure of capillaries
-Capillaries have walls that are only one-cell thick with a diameter of around 3–4 µm; they have no muscle fibers or other layers.
-In fact, capillary walls are rather leaky.
52
What does the leakiness of capillary walls allow?
-This allows the exchange of materials; oxygen and nutrients with cells in tissues, and waste products, such as carbon dioxide and urea, back into the capillaries to be transported by blood.
-White blood cells can also exit capillaries through gaps between the endothelial cells.
53
Diagram of a capillary
54
Blood flows through tissues in ___
Capillaries
55
Describe the walls of capillaries and what this allows
Capillaries have permeable walls that allow the exchange of materials between cells in the tissue and the blood in the capillary.
56
Capillaries connect ___
Arterioles to venules
57
Blood flow is slowest in the ___, to allow time for ___.
Capillaries
Exchange with tissues
58
What is tissue fluid or interstitial fluid?
The liquid part of blood that passes through the capillary wall to bathe tissue cells.
59
What is tissue fluid or interstitial fluid mainly composed of?
Water, sugars, salts, fatty acids, amino acids, coenzymes, and hormones, as well as waste products from the cells.
60
How does the exchange of materials between cells and fluid occur?
By diffusion or active transport
61
Since tissue fluid containing dissolved nutrients is in direct contact with tissue cells, the exchange of materials between cells and fluid is ___
Greatly enhanced.
62
What happens to tissue fluid after the exchange has taken place?
Tissue fluid is mostly reabsorbed into capillaries, which ultimately drains into venules.
63
Diagram showing exchange between capillary and body tissue
64
What is present in all arterioles but not in all capillaries?
Circular smooth muscle cells
65
The set of blood vessels with the slowest velocity of blood flow is ___
The capillaries
66
What is the function of the gaps between the endothelial cells of capillaries?
Permitting exchange of materials between the blood and the tissue cells
67
Which of these structural aspects of veins contribute to ensuring that blood flows in one direction through veins?
I valves
II their position next to skeletal muscles
III thin layer of muscle and elastic fibers
I and II
Valves do have the function of ensuring the one-way flow of blood. Skeletal muscles squeeze veins, pushing blood along.
68
Cross-section of walls of an artery
69
Cross-section of walls of a vein
70
Cross-section of walls of capillary
71
How many layers are there in an artery and what are they?
Three layers: tunica externa, media and intima (from outer to inner)
72
How many layers are there in a vein and what are they?
Three layers: tunica externa, media and intima (from outer to inner)
73
How many layers are there in a capillary and what is it?
One layer of endothelial cells
74
Tunica media in an artery
Thicker than in vein
75
Tunics media in a vein
Thinner than artery
76
Tunica media in a capillary
Absent
77
Muscle and elastin fibers in an artery
Thick layer
78
Muscle and elastin fibers in a vein
Relatively thin compared to artery
79
Muscle and elastin fibers in a capillary
None
80
Valves in an artery
Absent
81
Valves in a vein
Present at intervals
82
Valves in a capillary
Absent
83
Diameter of an artery
Can be greater than 10 mm
84
Diameter of a vein
Can be greater than 10 mm
85
Diameter of a capillary
Between 2 and 10 μm
86
Wall thickness of an artery
Generally have thicker walls with narrower lumens than veins
87
Wall thickness of a vein
Generally have thinner walls with larger lumens than arteries
88
Wall thickness of a capillary
Wall is one cell thick with a lumen of about 5 μm
89
Tips to help you identify blood vessels
-Check the number of layers.
-If the wall of a vessel is one cell thick, the vessel is a capillary.
-If you are provided with two vessels, compare:
-The relative thickness of the middle and outer layers (these are thicker in the artery).
-The diameter of the lumen (veins normally have larger lumen).
-Check for the presence of valves.
90
The figure below shows the cross-section of a blood vessel.
Name the layer labeled X.
Tunica media
91
The figure below shows the cross-section of a blood vessel. What type of vessel is it?
Capillary
Because the outer layer is so thin, and because the vessel is not much wider than a single blood cell, this vessel is a capillary.
92
Who discovered that the heart acted as a pump to help blood circulate throughout the body?
William Harvey
93
What did William Harvey's discovery provide an explanation for?
-How nutrients, oxygen, carbon dioxide, hormones, and blood cells could be transported to and from body tissues.
-The application of William Harvey's knowledge about the circulatory system also helped to explain how body temperature and pH are stabilized in the process of homeostasis.
94
Describe the overall structure of the heart
There are two ventricles, two atria and a number of valves which prevent blood from flowing backwards.
95
What do valves in the heart ensure?
That circulation of blood occurs in only one direction by preventing backflow.
96
Diagram of the human heart
97
What are the tricuspid and bicuspid valves sometimes called?
The right and left atrioventricular valves.
98
What does it mean that the human body has a double circulatory system?
The blood flows through the heart twice before it is distributed to tissues.
99
What is pulmonary and systemic circulation?
The circulation of blood from the heart to the lungs and back forms the pulmonary circulation, while the circulation of blood from the heart to the body tissues and back forms the systemic circulation.
100
Explain how blood flows through the body (right side of the heart)
-Blood enters the heart through the inferior and superior vena cava, with oxygen-poor blood from the body tissues flowing into the right atrium of the heart.
-As the atrium contracts, blood flows from the right atrium into the right ventricle through the open tricuspid valve.
-When the ventricle is full, it begins to contract. The increased pressure of blood against the tricuspid valve forces it shut. This prevents blood from flowing backward into the atrium.
-As the ventricle contracts, blood leaves the heart through the pulmonary valve, into the pulmonary artery and flows to the lungs where it is oxygenated.
101
Explain how blood flows through the body (left side of the heart)
-The pulmonary vein carries oxygen-rich blood from the lungs into the left atrium of the heart.
-As the atrium contracts, blood flows from the left atrium into the left ventricle, through the open bicuspid (also called mitral) valve.
-When the ventricle is full, it begins to contract. The increased pressure of blood against the bicuspid valve causes it to close.
-This prevents blood from flowing backward into the atrium while the ventricle contracts.
-As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the body.
102
Why is the human circulatory system called a double circulatory system?
Because there are two separate pathways that the blood follows.
103
What is the purpose of the two separate pathways that the blood follows in the human body?
-One pathway is to absorb oxygen and dump carbon dioxide into the lungs.
-The other pathway is to supply all the tissues with oxygen and to remove waste from the same tissues.
104
Which side of the heart is responsible for pulmonary circulation and which is responsible for systemic circulation?
The right side of the heart is responsible for pulmonary circulation, and the left side of the heart is responsible for systemic circulation: blood does not cross the septum in a normal heart.
105
Pulmonary artery and pulmonary vein
-It is easy to think that the way to differentiate arteries and veins is that the former carries oxygenated blood, and the latter carries deoxygenated blood.
-However, the pulmonary artery and pulmonary vein show that this is not always the case.
-Instead, arteries and veins are defined by the directions in which they carry blood: arteries carry blood away from the heart, and veins return blood to the heart.
106
Diagram of the double circulatory system
107
Blood returning to the mammalian heart in a pulmonary vein drains first into the ___
Left atrium
108
In the diagram shown, the blood vessels X and Y carry ___
Deoxygenated blood to the lungs
X and Y represent the left and right pulmonary arteries that carry deoxygenated blood to the lungs for oxygenation.
109
The heart is myogenic, which means that it can ___
Generate its own contractions.
110
What is the SA (sinoatrial) node?
A group of specialized muscle cells in the wall of the right atrium.
111
Explain how the SA node works
-This SA node initiates (starts) each heartbeat and sets the heart rate, so it is often called the pacemaker.
-The SA node 'fires' (sends electrical signals) at regular intervals to cause the heart to beat with a rhythm of about 60 to 70 beats per minute for a healthy, resting heart.
112
Diagram of initiation and propagation of the signal in heart contraction
113
Steps of the propagation through the heart of the electrical signal initiated in the SA node
-The SA node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria.
-The signal then passes via the interatrial septum to reach the atrioventricular (AV) node.
-From the AV node, the signal is relayed via the bundle of His located in the interventricular septum to the top of each ventricle (confusingly, the top of the heart, or apex, is the bottom-most part where the two ventricles meet in a shape somewhat like a point).
-At the top of the ventricles, the signal spreads from the bundle of His (also called the atrioventricular (AV) bundle), to the ventricles via the Purkinje fibres located in its wall.
114
Define the cardiac cycle
The complete sequence of events in the heart from the start of one beat to the beginning of the following beat.
115
Diagram of the 5 steps of the cardiac cycle
116
How can the cardiac cycle be illustrated?
-As a graph in which the pressure and volume changes inside the atria and ventricles are shown.
-These events coincide with heart sounds.
117
How can the cardiac cycle be illustrated?
-As a graph in which the pressure and volume changes inside the atria and ventricles are shown.
-These events coincide with heart sounds.
118
What are systole and diastole?
Systole refers to the heart muscles contracting (atrial and ventricular systole), and diastole is the relaxation of the heart muscles (atrial and ventricular diastole).
119
Diagram of pressure and volume change during the cardiac cycle
.
120
Steps of cardiac cycle
1. Atrial contraction begins ( atrial systole) .
2. Atria eject blood into ventricles ( atrial systole).
3. Atrial systole ends; AV valves close ('lubb' sound).
4. Isovolumetric contraction of the ventricles occurs ( ventricular systole).
5. Ventricular ejection occurs.
6. Semilunar valves close ('dupp' sound).
7. Isovolumetric relaxation of the ventricles occurs ( ventricular diastole.
8. AV valves open; passive ventricular filling occurs.
121
What is isovolumetric contraction?
An event occurring at the beginning of systole, during which the ventricles contract with no corresponding volume change.
122
Why can isovolumetric contraction occur and what does it lead to?
-This can occur because the valves are closed.
-This type of contraction makes the pressure in the heart chamber rise so that the blood can be forced out of the ventricle into the artery in a one-way direction.
123
Damage to the sinoatrial node in humans would ___
Disrupt the rate and timing of cardiac muscle contractions.
124
What is the sequence of events for the propagation of the electrical signals initiated in the SA node to the ventricles?
SA node → AV node → Bundle of His → Purkinje fibres → Walls of the ventricles
125
What does a person's resting heart rate depend on?
Age, gender and fitness level.
126
Explain how an increase in physical activity will increase your heart rate
-Two nerves that originate in the medulla oblongata of your brain, in an area called the cardiovascular center, can signal the SA node to speed up the heart or to slow it down.
-The cardiac accelerator nerve stimulates the heart to beat faster, while the vagus nerve reduces the heart rate.
-Blood pressure, pH, and carbon dioxide concentration of the blood are all monitored by the cardiovascular center to determine whether impulses should be sent along the cardiac accelerator nerve or vagus nerve to the heart.
127
Increased activity means more ___, and this causes a greater need for ___.
Respiration
Oxygen and causes increased production of waste products, such as carbon dioxide.
128
What does increased carbon dioxide in the blood do and what does this lead to?
-This decreases the pH
-This decrease in pH will be sensed by the cardiovascular center.
-This will then send impulses along the cardiac accelerator nerve to the SA node to increase heart rate.
129
As the heart pumps faster, more ___ is sent to body tissues and more ___ is removed.
Oxygen
Carbon dioxide
130
What happens to the heart once the physical activity stops?
-Once the activity stops, the heart can slow down, which the vagus nerve controls.
-The speed at which your heart rate slows down after activity is a measure of your fitness.
131
What is another factor (other than an increase in activity) that influences the SA node?
Epinephrine (also known as adrenalin) – the 'flight or fight' hormone secreted by the medulla of the adrenal glands.
132
What can cause epinephrine to be released into the bloodstream?
Strong emotions such as fear or anger
133
What happens when epinephrine is released into the bloodstream?
-The bloodstream carries it to all parts of the body, including the heart.
-Epinephrine increases the heart rate by stimulating the SA node to emit electrical signals at a faster rate as well as by increasing the conduction speed of impulses generated by both the SA and AV nodes.
134
Why is epinephrine called the 'flight or fight' hormone?
-Because it speeds up the heart rate to ready the body for either of these two actions.
-Other than triggering a rise in heart rate, epinephrine also increases muscle strength, blood pressure, and sugar metabolism: all of which prepare the body for immediate action.
135
How does epinephrine affect the heart rate?
It increases the heart rate to prepare for vigorous physical activity.
136
As an athlete starts to exercise, his heart rate slowly increases.
Explain this increase in heart rate.
Due to the lowered blood pH caused by carbon dioxide production during exercise, impulses are sent along the cardiac accelerator nerve to the SA node.
137
What structure is used to send messages to the heart to slow down after vigorous exercise?
Vagus nerve
138
Why does the human body need fats?
For energy, insulation, and as starting material for certain hormones and anti-inflammatory compounds.
139
What are atheromas and what are they caused by?
-These are fatty deposits caused by high blood concentrations of low-density lipoprotein (LDL) in the arterial walls next to the endothelial cells.
-LDL consists of cholesterol and fats.
-The deposits build up and eventually block an artery.
140
Diagram showing the gradual build-up of plaques (fatty deposits) in arteries
141
What is thrombosis?
The forming of a clot in the blood vessel that can block the blood vessel entirely.
142
What happens if the artery blocked by a clot is a coronary artery (an artery supplying the heart with oxygen and nutrients)?
The cells in that part of the heart will die, and the result is a myocardial infarction (heart attack).
143
Explain how the buildup of plaque occurs
-The buildup of plaque takes time and, initially, the restricted flow of blood in such an artery will cause pain due to heart cells being deprived of oxygen and nutrients.
-Medically, the pain is known as angina.
144
What is plaque formation?
Building up of fatty deposits in arteries
145
What are the causes of plaque formation that lead to atherosclerosis and the increase in cardiovascular disease?
-High blood concentrations of LDL
-Diabetes causing high blood glucose concentrations
-Smoking and stress cause high blood pressure
-Diets containing high levels of trans fats
-Recent research indicates that certain infections with bacteria, such as Chlamydia pneumoniae, can also play a role.
146
Why is atherosclerosis especially dangerous when found in the coronary arteries?
It can restrict blood flow to the heart muscle.
147
What is atherosclerosis?
Plaque formation
148
What type of pressure causes the loss of water and other molecules from capillaries in order to facilitate the production of tissue fluid?
Hydrostatic pressure
A drop in hydrostatic pressure allows water and other molecules and ions to move out of the blood within capillaries in order to form tissue fluid to bathe cells.
149
What did Harvey propose about the blood system?
-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)
