Cardiovascular System Flashcards
(179 cards)
1
Q
Which organs make up the cardiovascular system, and what are their functions?
A
Heart- pumps blood to lungs and rest of body
Arteries- supply oxygenated blood to rest of body
Capillaries- exchange nutrients and gases with tissues
Veins/ lymphatics- drain blood/ fluid from tissues
2
Q
What is vascular tissue made up of?
A
Connective tissues (elastin and collagen), epithelial cells and muscle cells (smooth in capillaries, cardiac in heart).
3
Q
Define the mechanism of the blood vascular system.
A
A closed supply and drainage system forming a continuous loop.
4
Q
Define the mechanism of the lymphatic vascular system.
A
An open-entry, one-way system.
5
Q
What is the purpose of the lymphatic system?
A
It accumulates and drains the fluid that escapes from the blood vascular system back to the heart.
6
Q
Name and define the two circulation pathways within the blood and lymph vascular systems.
A
Pulmonary circulation- deoxygenated blood is received from the right ventricle and is pumped to the lungs for oxygenation.
Systemic circulation- oxygenated blood is received from the lungs and pumped through the LHS of the heart, out the aorta to the rest of the body.
7
Q
What function do lymph nodes play in the systemic circuit?
A
They surveil the lymph fluid for any microbes, venom etc., before it goes back into the blood vascular system.
8
Q
Where are major arteries found? Why?
A
They are situated to avoid damage: e.g. deep in the trunk, on flexor aspect of limbs like behind the knee
The blood flowing through arteries is travelling at high velocity and high pressure, so damage to the artery would be life-threatening.
9
Q
How many arteries supply each structure?
A
One, unless it is an important structure such as the brain or hand, of which there are two.
10
Q
Name the three types of capillaries in order of increasing permeability.
A
Continuous
Fenestrated
Sinusoidal
11
Q
Name the three pathways for drainage, and their locations.
A
Deep veins- next to supply artery
Superficial veins- just below dermis
Lymphatics
12
Q
Why are superficial veins near the surface of the skin?
A
The blood is flowing at low pressure and low velocity, so damage to the veins would not be life-threatening.
13
Q
How large are veins in comparison to arteries? Why?
A
Twice the cross-sectional surface area is needed in order to shift the same volume of blood per second, since the pressure and velocity of blood is lower in veins than arteries.
14
Q
Describe the shape of the heart.
A
Blunt and cone-shaped. It has a pointed end (apex) and a broad end (base).
15
Q
Where is the heart located, and how is it positioned?
A
In the mediastinum (chest cavity).
The apex is in line with the midclavicular line between the 5th and 6th ribs on the LHS. This is the called the point of maximal impulse (PMI).
The base sits level between the 2nd and 3rd ribs. 2/3rds of the heart is on the LHS of the body.
The heart is rotated so the RHS is facing more anteriorly, and the LHS is facing more posteriorly.
16
Q
What is the apex beat?
A
The location where the greatest visual and aural heartbeat can be observed. (At the PMI)
17
Q
Name the four chambers of the heart, and their functions.
A
Right atrium- receives deoxygenated blood from the body
Right ventricle- pumps deoxygenated blood to the lungs
Left atrium- receives oxygenated blood from the lungs
Left ventricle- pumps oxygenated blood to the body
18
Q
Name the two septums of the heart, and their functions.
A
Interventricular septum- blocks any movement of blood between the left and right ventricles
Interatrial septum- blocks any movements of blood between the left and right atriums
19
Q
Name the two veins feeding the right atrium, and where they transport blood from.
A
Superior vena cava- head, neck, chest, upper limbs
Inferior vena cava- below diaphragam
20
Q
How does venous blood drain from the heart itself?
A
Through the opening of the coronary sinus into the right atrium.
21
Q
Through which structures does the left atrium receive its oxygenated blood?
A
The four pulmonary veins.
22
Q
Name the three layers of the heart wall.
A
Endocardium
Myocardium
Epicardium
23
Q
What is the pericardium?
A
A lubricated sac which acts as a protective layer around the heart.
24
Q
What makes up the endocardium?
A
Endothelium- a thin, delicate layer of squamous epithelium
Loose irregular FCT (supports endothelium)
Blood vessels
Purkinje fibres- modified cardiac muscle cells that carry electrical activity
25
What prevents blood from clotting up against the heart wall?
The endothelium, because it provides a non-stick surface.
26
What tissue makes up the myocardium?
Cardiac muscle tissue
27
How thick is the myocardium layer in the left and right ventricles? Why?
LHS: 0.5cm
RHS: 1.5cm
More cardiac muscle tissue is required in the RHS, because it must pump the same volume of blood to the body that the LHS is pumping just to the lungs.
28
What makes up the epicardium?
Visceral pericardium
Blood vessels
Loose irregular FCT
Adipose tissue
29
Name the four components of the pericardium and their locations.
Visceral pericardium- part of epicardium/ envelops the heart
Pericardial cavity- between two layers (filled with fluid)
Parietal pericardium- faces wall of mediastinum
Fibrous pericardium- leathery bag surrounding other layers
30
Name the types of valves in the heart, and their functions.
Semilunar valves- prevent blood returning to ventricles during filling (diastole)
Atrioventricular (AV) valves- prevent blood returning to atria during ventricular contraction
31
Name the two AV valves and their positions.
Tricuspid valve- between right atrium and right ventricle
| Mitral/ bicuspid valve- between left atrium and left ventricle
32
Name the two semilunar valves and their positions
Pulmonary valve- between right ventricle and pulmonary arteries
Aortic valve- between left ventricle and aorta
33
Describe diastole in terms of valves.
The phase where the ventricle is filled with blood. The AV valves are open and the semilunar valves are closed.
34
Describe systole in terms of valves.
The phase in which the ventricular muscle contracts and exerts pressure on the ventricle. The AV valves are closed and the semilunar valves are open, so blood has to move through the arteries.
35
Why doesn't blood fall back into the ventricles?
The semilunar valves close as blood starts to backflow.
36
How are the AV valve leaflets prevented from slamming up the atrium when the pressure gets too high in the ventricle?
Papillary muscles- fingerlike projections- in the ventricular wall attach the leaflets through chordae tendineae. They develop tension early in systole.
37
Why don't semilunar valves need chordae tendineae?
The valve is smaller and the leaflets support each other up.
38
Name the arteries that supply the heart.
Right coronary artery
| Left coronary artery- splits into circumflex artery and anterior interventricular artery
39
Where does the right coronary artery run?
From the root of the aorta- in the epicardium- down the coronary groove between the right atrium and right ventricle to the posterior aspect of the heart. It branches off and supplies the bulk of the muscle- ventricular chamber.
40
Where does the anterior interventricular artery run?
From the left coronary artery- in the epicardium- across the anterior of the heart, over the interventricular septum.
41
Where does the circumflex artery run?
From the left coronary artery- in the epicardium- down the coronary groove between the left atrium and left ventricle to the posterior aspect of the heart.
42
Name the veins that drain the heart, and which parts they drain.
Great cardiac vein (LHS) and small cardiac vein (RHS).
43
Where do the cardiac veins run and collect?
Up the coronary grooves to the posterior of the heart, arriving in a big bulging vein called the coronary sinus- into the right atrium.
44
How does cardiac muscle differ from other types of muscle?
```
They are striated, unlike smooth muscle.
The nucleus (one, occasionally two) is in the centre of the cell, unlike pushed to the periphery in muscle cells.- organelles are at poles of nucleus
Consists of short. branched cells, unlike long skeletal fibres.
```
45
Why are capillaries in cardiac muscle so narrow?
They are the diameter of one red blood cell to force them to travel in single file. This ensures they are as close to the wall of the capillary as possible, so gas exchange is improved.
46
Why are there many capillaries in cardiac muscle?
It needs a good blood supply because its metabolism is very oxygen-dependent.
47
Which organelle takes up 20% volume of a cardiac muscle cell and why?
Mitochondria- because cardiac muscle has a very oxygen-dependent, ATP-driven metabolism.
48
How are the sarcomeres in cardiac muscle organised and why?
Irregularly (they are also branched), so the force of contraction is spread out
49
What is the name for a cardiac muscle cell?
Cardiomyocyte
50
Name the three types of intercalated disks (ICD's) between cardiomyocytes.
Adhesion belts
Desmosomes
Gap junctions
51
Describe adhesion belts.
Links the actin filaments of neighbouring cardiomyocytes by transmembranous proteins. This transfers force from the contractile apparatus of one cell to that of the next- creating a physical propagation of force.
52
Describe desmosomes.
Link the internal cytoskeletons (cytokeratin) of neighbouring cardiomyocytes- keeps cells stuck together.
53
Describe gap junctions.
Fuses the plasma membranes of neighbouring cardiomyocytes and forms small porous openings. The junction connects cells horizontally (parallel to contractile plane) to avoid force because of its fragility. Allows electrochemical communication.
54
What is the purpose of the heart's conduction system?
It greatly increases its pumping efficiency.
| Responsible for co-ordination of AV valves and heart contraction.
55
Which tissue makes up the conduction system of the heart?
Modified cardiac tissue (not nervous).
56
Describe Purkinje cells.
Cardiac cells that no longer contract- few desmosomes and adhesion belts.
Surrounded by myofibrils.
Filled with mitochondria and glycogen- function is very energy-dependent.
Lots of desmosomes- communicating cells.
57
Name the branches of the aorta.
Thoracic aorta: Ascending aorta
Aortic arch
Descending aorta
Abdominal aorta, then bifurcates at bellybutton level
58
Name the arteries between where the aorta bifurcates, and the foot.
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Common iliac artery
External iliac artery
Femoral artery
Popliteal artery
Posterior tibial artery
Plantar arch
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59
Name the deep veins between the foot and the inferior vena cava.
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Plantar venous arch
Posterior tibial vein
Popliteal vein
Femoral vein
External iliac vein
Common iliac vein
```
60
What is the great saphenous vein, and where does it run?
```
Superficial vein (hypodermis)- longest vein in the body
Drains the medial aspect of ankle, medial aspect of knee, and groin, then joins femoral vein in the groin.
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61
Name the layers of a blood vessel.
Tunica intima
Tunica media
Tunica adventitia/ externa
62
What comprises the tunica intima?
Endothelium- thin, squamous epithelium
Sub-endothelium- sparse pad of loose FCT that cushions the endothelium
Internal elastic lamina (IEL)- thin, condensed sheet of elastic tissue (more distinct in arteries than veins)
63
Why is the tunica media thicker in arteries than veins?
The blood is under higher pressure.
64
What comprises the tunica adventitia/ externa?
Loose FCT- high collagen content and varying elastin, determines how far the blood vessel can dilate (collagen fibres get taut)
Vasa vasorum- small blood vessels that supply the smooth muscle of large blood vessels (need their own supply)
Lymphatics and autonomic nerves
65
What comprises the tunica adventitia/ externa?
Loose FCT- high collagen content and varying elastin, determines how far the blood vessel can dilate (collagen fibres get taut)
Vasa vasorum- small blood vessels that supply the smooth muscle of large blood vessels (need their own supply)
Lymphatics- drain any fluid that has left the blood vascular space
Autonomic nerves- control constriction and dilation of the smooth muscle in the media
66
What is the difference between elastic arteries and muscular arteries?
Elastic arteries are near the heart, and have elastic tissue all through the tunica media because they require a lot of elasticity (during systole) and recoil (during diastole). Because of this abundance in the media, they don't need connective tissue in the tunica adventitia.
In muscular tissue, most of the tunica media is smooth muscle, with a few connective fibres (most are in the adventitia).
67
How do elastic arteries dampen the pulsatility of the blood before it gets to the capillaries?
By taking up some of the energy into the elastic tissue of the vessel walls in diastole, then re-exerting it into the lumen during systole.
68
Why do muscular arteries constrict or relax to change the size of their lumen?
To distribute the blood however necessary, e.g. to leg muscles when working out.
69
Describe arterioles.
Last vessels of the supply network, feed into capillary beds. Their smooth muscle tone determines blood pressure.
70
Describe venules.
First vessels of the drainage system, drain capillary beds. Valves ensure low pressure blood travels in the right direction.
71
Why is the tunica adventitia/ externa the thickest layer of a vein?
Veins are capacitance vessels- they can hold extra blood volume (e.g. if standing for long period). Collagen in the adventitia prevents over-distension of the vein when it's holding extra blood.
72
How does the tunica media of veins differ from arteries? What does this cause for some veins?
Thinner- only a few layers of smooth muscle. Usually two distinct ones- circumferential and longitudinal.
Because the media is thinner, veins collapse on themselves post-mortem, giving wrinkly shape.
73
Define vascular bundle.
An artery flanked by two veins. (Neurovascular bundle includes a nerve)
74
What occurs in veins when the skeletal muscle around them contracts?
The blood is pushed in both directions, but valves prevent in from flowing away from the heart. Varicose veins involve valves which leak, and the vein is stretched outwards and lengthways.
75
Briefly describe the function of capillaries.
Site of exchange between blood and tissues.
76
What does capillary function require?
Very thin walls
Slow, smooth blood flow
Large cross sectional area
77
How is slow, smooth blood flow ensured in capillaries?
The area of the capillary bed is very large, so that when it spills out of the low-area arterioles, it flows like a river running into a calm lake.
78
What does a capillary consist of?
Endothelial cell(s)- usually just one- that wraps around and binds to itself with tight junctions, forming a tube.
Nucleus
Lumen
Basement membrane- thin extracellular layer of connective tissue
79
Describe a vascular shunt, and its components.
The structure blood flows through when precapillary sphincters constrict and prevent blood from entering the capillary bed. Goes straight from supply to drainage- to prevent heat loss through epidermis.
Consists of the metarteriole (off the terminal arteriole), and the thoroughfare channel (into the postcapillary venule).
80
Describe the properties of a continuous capillary.
```
Most common type of capillary- seen in skeletal and cardiac muscle
Lumen is 8-10μm in diameter
Endothelial cell(s) has no openings- just tight junctions
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81
Describe the properties of a fenestrated capillary.
Lumen is 8-10μm in diameter
Fenestrations/ porous openings in the cytoplasm of the endothelial cell
Maintain extracellular barrier of the basement membrane
82
Give an example of a fenestrated capillary bed.
The glomerulus in the kidney. Capillary bed of fenestrated capillaries that allow fluid to leave and accumulate. This forms the primary filtrate for urine.
83
Describe the properties of a sinusoidal capillary.
Lumen is 30-40μm in diameter
| Intercellular gaps and incomplete basement membrane
84
Give an example of a sinusoidal capillary bed.
Liver sinusoids- blood transports toxins and nutrients from mucosa of the gut to the sinusoidal capillary beds in the liver for processing.
This bathes the liver cells in blood (but blood cells don't escape), and allows free and easy exchange.
85
Which types of transport can occur in all three types of capillaries? Which type can only occur in fenestrated and sinusoidal capillaries?
Diffusion through membrane- lipid-soluble substances
Movement through intercellular cleft (larger no. of tight junctions= less permeability)- water-soluble substances
Transport via vesicles- large substances
Movement through fenestrations- water-soluble substances
86
Name the functions of the lymph vascular system.
Drains excess tissue fluid and plasma proteins from tissues, and returns them to the blood.
Filters foreign material from the lymph.
Screens lymph for foreign antigens and responds by releasing antibodies and activated immune cells.
Absorbs fat from intestine and transports it to blood.
87
Define lacteals.
A special group of lymphatic vessels that drain fat-laden lymph- from the small intestine- into a collecting vessel called the cisterna chyli.
88
Describe the properties of lymphatic vessels.
Commence as large, blind ending capillaries.
Thin wall with large lumen diameter.
Larger vessels have numerous valves ensuring unidirectional flow towards the heart.
89
Describe an edema.
Swelling of the tissue by excess fluid in the interstitial space.
90
What separates a lymph vessel from arteries and veins?
Very thin walled
No red blood cells
High number of valves
91
Describe the pathway of lymph fluid from the RHS side of the body/ LHS below the diaphragm.
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Interstitial space
Lymphatic collecting vessels
Thoracic duct
Left subclavian vein- valve between duct and vein
Blood vascular system
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92
Describe the pathway of lymph fluid from the RHS side of the body above the diaphragm.
Interstitial space
Lymphatic collecting vessels
Right lymphatic duct
Right subclavian vein
93
Name the lymph node clusters.
Cervical nodes
Axillary nodes
Inguinal nodes
94
Where does lymph fluid in the cisterna chyli drain into?
Thoracic duct
95
Describe the structure of a lymph node.
A kidney bean shaped structure, consisting of a network of connective fibres that hold lymphoid cells. Afferent lymphatics carry lymph in, and efferent lymphatics carry lymph out.
96
How can breast cancer metastasise?
Lymphatic drainage can carry cancer cells through the axillary lymph nodes, through the lymphatic ducts into the blood vascular system.
97
Which type of blood flows away from the heart? Which flows towards?
Arterial
| Venous
98
Define the thin and thick filaments of cardiac muscle and their functions.
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Thin= actin, structural element that runs the length of the cell
Thick= myosin, the motor that generates force by pulling
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99
Briefly describe cardiac muscle contraction at the cellular level.
Ca2+ levels increase
Myosin binds to actin to form cross-bridges
Myosin pulls on the actin which shortens the sarcomere and generates force
100
How many myocytes are activated during each heartbeat?
All of them.
101
How is the force of muscle contraction increased?
Increase cytosolic Ca2+ level which increases number of cross-bridges formed.
102
Briefly describe cardiac muscle relaxation of the cellular level.
Ca2+ levels decrease
ATP binds to myosin and cross-bridges release
Reduction in force allows the muscle to relax
103
How many myocytes relax each heartbeat?
All of them.
104
Describe diastole in two terms.
Relaxation
| Falling pressure
105
Describe systole in two terms.
Contraction
| Rising pressure
106
Name the order of phases of the cardiac cycle.
1. Atrial systole
2. Atrial diastole
3. Ventricular systole 1st phase- isovolumetric contraction
4. Ventricular systole 2nd phase- ventricular ejection
5. Ventricular diastole- early
6. Isovolumetric relaxation
7. Ventricular diastole- late
107
Describe atrial systole.
Atria contract while ventricles remain relaxed. AV valves open to allow blood to flow into ventricles, while semilunar valves stay closed to prevent blood from flowing into the arteries.
108
Describe atrial diastole.
Atria relax and AV valves shut. Ventricular contraction occurs at the same time.
109
Describe isovolumetric contraction.
1st phase of ventricular contraction. The AV valves shut and the ventricles contract. Since both sets of valves are shut, the pressure on the blood in the ventricle increases.
110
Describe ventricular ejection.
2nd phase of ventricular contraction. The pressure in the ventricle rises higher than that of the aorta and pulmonary arteries. The semilunar valves open to allow most of the blood to flow into the arteries.
111
Describe early ventricular diastole.
Semilunar valves shut to prevent blood returning to the ventricle, when the pressure in the ventricle is lower than that of the arteries.
112
Describe isovolumetric relaxation.
Ventricles relax. Since both valves are shut, the pressure on the small amount of blood left in the ventricle falls.
113
Describe late ventricular diastole.
The longest phase. AV valves open to allow blood to fill the ventricles.
114
Which is higher, the pressure of the systemic or pulmonary circuit?
Systemic circuit.
115
Where is mean blood pressure in relation to the individual's pulse?
Closer to diastolic pressure, since the heart spends more time in diastole than systole.
116
Define hypertension and hypotension.
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Hypertension= high blood pressure
Hypotension= low blood pressure
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117
Why is hypotension dangerous?
The pressure on the blood isn't high enough to move enough of it up to the brain, against gravity.
118
Define pulse blood pressure.
The difference between the highest and lowest points of blood pressure (systolic and diastolic).
119
Explain the equation Q̇ = ΔP/R in terms of the two cardiovascular circuits.
Q̇ is the blood flow (volume per sec)
ΔP is the change in pressure along the blood vessel
R is the resistance
We know the systemic circuit has a higher pressure, since it has to move blood all through the body. To ensure the blood flow is the same throughout both circuits, there must be more resistance in the systemic circuit.
120
Why do the electrical cells of the heart have a 'pale' striated appearance?
They have a low amount of actin and myosin. The signal they conduct is Ca2+ based, and a larger amount of contractile units in these cells would use up more of the signal.
121
How does depolarisation result in contraction on the cellular level?
Conduction cells pass the signal, Ca2+, onto the bordering contractile cells through the gap junctions of intercalated disks. These have low resistance to ionic current. This increases cytosolic Ca2+ level, cross-bridge attachment, and contraction.
122
Explain what the heart being a functional syncytium means.
Millions of cardiac cells working as one unit to produce contraction.
123
Describe the conduction pathway of the heart.
1. Sinoatrial (SA) node spontaneously generates contraction potentials (doesn't need any signalling from the brain).
2. These potentials are conducted into the right atrium, across the interatrial bundle to the left atrium, and across the internodal bundles to the AV node. Atria contract, while AV node pauses the signal.
3. The AV bundle branches down from the AV node, running down the interventricular septum.
5. AV bundle branches into right and left bundle branches, and terminate in Purkinje fibres at the bottom of the ventricles. Ventricles contract.
124
Why is the signal brought all the way down to the bottom of the ventricles?
By contracting from the bottom, the ventricles are able to eject the maximum amount of blood possible.
125
Define quiescence in the heart.
The period when nothing is happening electrically- no signals are being conducted, and the chambers are being passively filled with blood.
126
Describe the cycle of the heart in terms of depolarisation and contraction.
1. Depolarisation spreads from the SA node to the atria, which contract.
2. Atria repolarise and relax, AV node sends excitation to the ventricles to prepare for contraction.
3. Ventricles fully depolarise and contract.
4. Ventricles begin to repolarise and relax.
5. Ventricles are fully repolarised and relaxed, heart is in quiescence.
127
Describe an ECG.
The electrocardiogram is a way of monitoring changes in the electrical activity of the heart. It doesn't measure the exact electrical signal the heart is producing, it measures the changes- if it is depolarising or repolarising.
128
Describe the key features of the ideal ECG.
P wave- atria depolarising (atrial contraction)
QRS complex- atria repolarising and ventricles depolarising (isovolumetric contraction phase)
T wave- ventricles repolarising (isovolumetric relaxation)
129
Name the two sounds of the heart and at which stages they are present.
'Lubb' at the isovolumetric contraction phase
| 'Dupp' at the isovolumetric relaxation phase
130
What is the most important determinant of blood flow?
MAP mean arterial blood pressure
131
Why will the body do everything to keep pressure at MAP?
Because blood supply- especially to the brain- relies on the pressure difference between arteries and veins to drive blood flow.
And, this high pressure allows full control of the distribution of blood flow to different organ systems.
132
What is MAP determined by?
The balance between blood flow in and out of the arteries.
133
What is the "blood flow in" component of MAP determined by?
Cardiac output- flow of blood out of ventricles into arteries.
134
What is the "blood flow out" component of MAP determined by?
Arterial resistance
135
Explain the formula MAP = CO x TPR.
MAP= mean arterial blood pressure
CO= cardiac output
TPR= total peripheral resistance
A version of Q=P/R
136
What determines cardiac output? What is the formula?
CO= stroke volume x heart rate= SV x HR
137
Define stroke volume.
The contraction strength/ amount of blood pushed out of the ventricle with each contraction (L/beat).
138
Describe the cardiac output of a failing heart.
The stroke volume is decreased, even halved, so the heart rate increases to keep cardiac output up, to keep MAP up. This increased heart rate puts the heart under a lot of stress.
139
Is cardiac output constant in an individual?
No- it changes with exercise and rest.
140
Briefly describe homeostasis of arterial blood pressure.
The brainstem:
- receives afferent information from the CNS and periphery
- sends efferent information to the heart and blood vessels
141
Name the sensors for blood pressure and why they are concentrated in specific regions.
Baroreceptors, embedded in the walls of the carotid arteries (sense changes in blood flow to the brain) and the aortic arch (sense changes in pressure of aorta after each heartbeat).
142
How do baroreceptors react to high blood pressure?
They sense the extra stretch of the blood vessel wall, and send signals of higher frequency to the brainstem.
143
How do baroreceptors react to low blood pressure?
They sense the reduced stretch of the blood vessel wall, and send less frequent signals to the brainstem.
144
How does the brain decrease heart rate?
Increases signalling on the parasympathetic vagus nerve (nucleus in medulla oblongata), which communicates with:
- SA node to signal more slowly
- AV node to pause for longer
145
How does the brain increase heart rate?
Increases signalling on the sympathetic cardiac nerves (nucleus in sympathetic trunk ganglion), which communicate with:
- SA node to signal more quickly
- AV node to pause for a shorter time
- ventricular walls to increase number of cross bridges, which increases stroke volume
146
Briefly describe how both the brain and SA node contribute to brain signalling.
The SA node controls when the signal starts and ends.
| The brain tells the SA node to speed up and slow down.
147
What changes when the body moves from horizontal to vertical?
Stroke volume falls, because the blood vessels are working against gravity. To compensate, heart rate increases. Cardiac output still falls slightly, so vascular resistance increases (vessels contract) to keep MAP constant.
148
Why do we need higher pressure in the arteries than the veins?
We want more control over where we're sending it- lots of different directions.
149
Describe the design of the systemic circulation- what kind of circuits?
Parallel circuits to and from each organ system- can direct individual supplies of different flows.
150
How does the distribution of blood flow change during exercise?
Increases to muscle, heart and skin.
Decreases to GI tract and kidneys.
Constant to brain.
151
How does arterial pressure change during exercise?
Increases to kidneys and GI tract.
| Decreases to muscle, heart and skin.
152
Describe the relationship between arteriole diameter and resistance.
R=1/(r^4)
153
What is the 'rule of 16'?
If the diameter changes by a factor of 2, the resistance of the vessel changes by a factor of 16.
154
How are arterioles able to make such an effective change in resistance, even though they are small?
The rule of 16- even a small change in diameter evokes a large change in resistance.
155
How do vessels increase their diameter?
Smooth muscle relaxation/ vasodilation.
156
How do vessels decrease their diameter?
Smooth muscle constriction/ vasoconstriction.
157
Where is our extra blood stored, and why do we need it?
In systemic veins, in case of injury to blood vessels- we won't run out of blood.
158
What proportion of our total blood volume is the stored blood?
2/3rds
159
How are veins able to store more blood, while keeping low pressure?
Their thin walls are very compliant- they can hold a lot of volumes, by stretching, without changing the pressure much.
160
Define the formula for compliance.
ΔV/ΔP
161
What occurs in the veins if there is arterial puncture, and loss of blood?
They receive a signal from the brain, and venoconstrict, contracting on the extra pool of blood to move it up to the heart and into arteries. This keeps MAP up.
162
Define venous pooling.
Collection of blood towards the bottom of the body, and the veins stretching to accommodate.
163
When is venous pooling common?
When upright, and not moving muscles.
164
What counteracts venous pooling, and how?
Venous valves- stop the blood from falling very far.
| Muscle tone- stiffens the veins to make them less compliant
165
Why are some elderly prone to fainting?
They have lost skeletal muscle tone, so cannot counteract venous pooling as well.
166
How do we increase venous return to the heart?
Skeletal muscle contraction- forces valves above the contraction to open which allows blood to flow to the heart, and valves below contraction to close which prevents backflow into capillaries.
167
Which muscles (other than skeletal) contract additionally when we are exercising?
Diaphragm and intercostal muscles- deeper breaths work these muscles harder, increasing blood flow back to the heart.
168
Define and explain Starling's Law of the Heart.
The more stretched muscle fibres are before a contraction, the stronger the contraction will be.
The sarcomeres will be more stretched out- myosin further from actin, allowing for generation of more force from the powerstroke.
Increased venous return= increased ventricular volume= increased stroke volume
169
Define three general functions of the blood.
Transport- of O2, CO2, nutrients, waste products, water, heat, ions, hormones, immune cells and coagulation factors
Immune response- largely via white blood cells
Coagulation- platelets and coagulation factors prevent bleeding
170
Name the two general components of the blood.
Plasma
| Formed elements
171
What makes up the formed elements of the blood?
Platelets
White blood cells
Red blood cells
172
What makes up the blood plasma, and what are their functions?
Plasma proteins- maintain osmotic pressure, immune response, coagulation factors
Solutes- maintain pH and ion balance
Water- hold a lot of heat
173
Define hematopoiesis.
The formation of red blood cells from hemocytoblasts in the red bone marrow.
174
How is red blood cell production increased?
Erythropoietin (EPO) stimulates the hemocytoblasts to produce more RBC.
175
What is the shape of red blood cells, and why?
Biconcave disc shape gives large surface area to volume ratio, which allows efficient gas diffusion. The shape also gives flexibility which allows the cells to squeeze through narrow capillaries.
176
Why don't red blood cells have nuclei?
They don't need to divide and produce more of themselves. The hemocytoblasts do this.
177
Define packed cell volume PCV.
PCV, or hematocrit, is the fraction of blood occupied by red blood cells.
178
Why is PCV higher in men than women?
They have more testerone, which augments the EPO mechanism of stimulating RBC production.
179
How does the body produce more red blood cells at high altitudes?
The kidneys sense the drop in blood O2 and release erythropoietin, which travels to the red bone marrow where it stimulates hemocytoblasts to produce more RBCs.
