Section 3: Cardiovascular System Flashcards
1
Q
Human heart contains __ muscular pumps
A
2 muscular pumps, which each have a daily output of 7,000L of blood
2
Q
Consequence of stoppage of heart’s muscular pumps
A
Unconsciousness in 10 seconds
Death in 4 minutes
3
Q
Arteries vs veins
A
Arteries bring blood away from heart
Veins bring blood towards heart
4
Q
Heart - circuits
A
Pulmonary circuit:
Only pumps to lungs
Medium resistance
Medium pressure
Systemic circuit:
Lots of systems involved
High resistance
High pressure
5
Q
(Hepatic) portal veins
A
Veins don’t go straight back to heart
e.g. heptic portal vein - goes from gut to liver
6
Q
Blood volume
A
9% pulmonary
7% pumps
84% systemic
Total 5L
7
Q
Blood volume output
A
5L per minute for 1 pump
Can increase by 4 times if exercising, but trainable to up to 8x
8
Q
Building a ventricular pump - phases
A
Filling phase:
Venous inlet on left side and arterial outlet on right
While ventricle is filling from venous end, an outlet valve is essential to prevent arterial blood from returning to the pump
Ejection phase:
Inlet valve necessary to prevent high-pressure blood in pumping chamber from returning to veins
Improvement #1:
An atrium is a reservoir upstream of the pump
During ejection phase, the atrium accumulates venous blood, which can enter the ventricle quickly during the filling phase
Improvement #2:
If inlet and outlet of pump are moved to lie close tgt, the walls of the pumping chamber can shorten in length and width
Adding an appendage = auricle also increases the capacity of the atrium
9
Q
Auricle
A
An extension of the side of the atrium
10
Q
Blood flow through heart - arrangements
A
Deoxygenated blood has a vertical arrangement
Oxygenated blood has a horizontal arrangement
11
Q
Peak pressures (mmHg) - averages
A
Right atrium: 5 mmHg
Right ventricle: 27 mmHg
Left atrium: 8 mmHg
Left ventricle: 120 mmHg
Left higher as it must go through high resistance
12
Q
Ventricular ejection - valves
A
Not actively opening valves - we’re actively preventing them from pushing too far
13
Q
Ventricular inlet valves
A
AKA atrioventricular valves
Constructed from 2 or 3 flat flaps of fibrous CT
Free edge of each flap is tethered by tendinous cords - prevent it from bursting upwards into atrium during systole
14
Q
Inlet valves
A
Tricuspid valve (right) Bicuspid/Mitral valve (left)
15
Q
Left ventricle
A
Forms core of heart
Hollow cone with thick, muscular walls
16
Q
Right ventricle
A
Sits on the side of left ventricle, much smaller
17
Q
Open ends of ventricles are subdivided into…
A
An inlet and an outlet
18
Q
Inlets and outlets - diameter
A
Inlets: large diameter to admit blood at low pressure
Outlets: small diameter because blood leaves ventricles at high pressure
19
Q
Outlet valves
A
Pulmonary valve (right) Aortic valve (left)
20
Q
Valves are essential for…
A
The operation of the pumps
21
Q
Pathway taken by blood through ventricles
A
Approximately V-shaped
22
Q
Ventricles in transverse section - peak pressure and wall thickness ratio
A
Peak pressure ratio (L:R) = 5:1
Wall thickness ratio (L:R) = 3:1 - main structural difference
23
Q
Opening the pulmonary trunk
A
Shows three cusps of pulmonary valve
Shape = ‘semi-lunar’ - sometimes used to describe outlet valves
24
Q
Outlet valves - number of cusps
A
Both outlet valves have three cusps, but unlike inlet valves, the cusps are each shaped like a pocket and lack cords
When inflated with blood, they gain strength from their 3D shape
25
Outlet valves - closed position
Ventricular filling
Pressure of blood trying to re-enter the ventricle forces the free edges of the cusps tightly together
Pressure in ventricle decreases
Pockets/cusps inflated
26
Where does the heart lie in our body
1/3 of mass of heart lies to right of mid-line of body and about 2/3 to the left
27
Apex of heart
Points inferiorly, anteriorly and to the left
| So, heart is slightly rotated
28
Right border of heart
Formed mainly by right atrium
29
Inferior border of heart
Formed mainly by right ventricle
30
Left border of heart
Formed mainly by left ventricle (and in part, the left atrium/auricle)
31
Superior border of heart
Blood vessels = base
32
The heart is enclosed in a...
Double-walled bag
33
Pericardium - inner and outer walls is made of what?
Both inner and outer pericardium are made of a single layer of squamous mesothelial cells
Walls are continuous where the great vessels enter and leave the heart
34
Pericardium - inner and outer wall - where
```
Inner wall (visceral pericardium) adheres to heart and forms heart's outer surface (epicardium)
Outer wall (parietal pericardium) lines the fibrous pericardium
```
35
Fibrous pericardium
A tough fibrous sac
Outermost layer
Composed of collagen - doesn't like to stretch
36
Parietal and visceral pericardium are made of...
Serous membrane
37
Pericardial space
Space between the visceral and parietal layers
Contains serous fluid, secreted by serous membrane
Allows parietal and visceral surfaces to slide without friction as the heart beats
38
What is 'inside' the pericardial space
Heart is NOT inside the pericardial space - excluded by visceral pericardium
Only pericardial fluid is inside the pericardial space
39
Fat
Good electrical insulator between atria and ventricles
40
Inlets and outlets - plane
Inlets and outlets on same plane with each other
| Attach to fibrous skeleton - doesn't allow inlet and outlet to stretch
41
Fibrous skeleton of heart
Fibres forming tricuspid ring are incomplete
Pulmonary ring is absent
Fatty CT present in areas where fibrous skeleton is incomplete
42
Sinoatrial (SA) node
Can depolarise and repolarise themselves (autonomic)
Pacemaker - determines heart rate
Influenced by hormones and nerve impulses
43
Atrioventricular (AV) node
Can depolarise and repolarise themselves, but not as fast as SA node
44
Purkinje fibres
Made of purkinje cells, which conduct APs very quickly and aren't branched
45
Conduction system of heart: SA node --> Atrial muscle - speed and result
Speed - slow
| Result - atrial contraction
46
Conduction system of heart: Atrioventricular node - speed and result
Speed - very slow
| Result - 100ms delay in AP getting to ventricles
47
Conduction system of heart: AV bundle --> Purkinje fibres - speed and result
Speed - fast
| Result - complete and even ventricular contraction, known as systole
48
The cardiac cycle
Ventricular filling:
Commences as pressure in ventricle drops below that of atrium
Mitral valve opens quietly and blood enters ventricle
Ventricle fills to ~80% of its capacity
Atrial contraction:
Left atrium contracts to complete filling of ventricle
Rise in atrial pressure is small for 2 reasons;
- atrial muscle layer is thin
- no valves where pulmonary veins enter atrium (so nothing to prevent backflow into veins)
Isovolumetric ventricular contraction (systole):
~0.05s
Ventricle starts to contract
Blood within it lifts backwards towards atrium and mitral valve closes (first heart sound)
Ventricular pressure still below aorta's so aortic valve remains closed
Atrial P < ventral P (increasing) < arterial P
Ventricle is isolated from rest of circulation (inlet and outlet closed)
Ventricular ejection:
Systole continues, but ventricular pressure now exceeds aortic pressure and aortic valve cusps open quietly
Blood leaves ventricle
Since blood is ejected into aorta faster than it can run-off into distributing arteries, the pressure in ventricle and aorta continues to rise steeply
Later in this phase, rate of ejection falls below rate of run-off and aortic and ventricular pressures level-off, then decrease
Isovolumetric ventricular relaxation:
As ventricle relaxes, ventricular pressure drops suddenly, flow reverses in aorta and aortic valve closes (second heart sound) as blood tries to re-enter ventricle
Mitral valve is closed because ventricular pressure still exceeds atrial pressure
Atrial P < ventral P (increasing) < arterial P
Ventricle is isolated from rest of circulation (inlet and outlet closed)
Once ventricular pressure drops below pressure in atrium, cycle repeats
49
Heart sounds
First heart sound: lub
| Second heart sound: dub
50
Do we need atria to survive
No, we don't need atria for the last 20% filling
| Can fill up some without it
51
Classes of blood vessels
```
Elastic artery
Muscular artery
Arteriole
Capillary
Venule (collecting part)
Vein (collecting part)
Coronary arteries
```
52
Blood vessels: Elastic artery - structure and function
Structure: Many thin sheets of elastin in middle tunic, quite big - can fit finger inside
Function:
During systole - expand to store blood leaving ventricle
During diastole - push blood out into arterial tree by elastic recoil
Smooth the pulsatile flow of blood leaving ventricles
53
Transition between elastic and muscular artery
Gradual
54
Blood vessels: Muscular artery - structure and function
Structure: many layers of circular smooth muscle wrapped around vessel in middle tunic, varies in size from pencil to pin
Function: distribute blood around body at high pressure and lungs at medium pressure
Rate of blood flow is adjusted by using smooth muscle to vary radius of vessel
Controls bulk flow of blood - go where needed
55
Blood vessels: Muscular artery - flow rate
Flow is proportional to fourth power of radius (Poiseuille's law)
Small change in radius has a large effect on flow rate
56
Blood vessels: Muscular artery - parts
```
Inner tunic (tunica interna/intima)
Middle tunic with smooth muscle (tunica media)
Outer tunic (tunica externa/adventitia)
```
57
Blood vessels: Arteriole - structure and function
Structure: 1-3 layers of circular smooth muscle wrapped around vessel in middle tunic
Have a thicker muscular wall relative to their size than other blood vessels
Function: control blood flow into capillary beds
Where greatest pressure drop occurs and where there is greatest resistance to flow
58
Blood vessels: Degree of constriction of arterioles throughout body determines...
Total peripheral resistance, which in turn affects;
Mean arterial blood pressure - the more arterioles open, the more the heart has to pump blood into the big vessel to keep pressure up
59
Which blood vessels are endothelial cells found in
All blood vessels
60
Which blood vessels are the tunica interna found in
All blood vessels
61
Blood vessels: Capillary - structure and function
Structure: diameter just wide enough to admit one RBC
Wall is a single layer of endothelium with an external BM
No smooth muscle in wall and no CT --> can't adjust diameter
Function: tiny vessels which are thin-walled to allow exchange of gases, nutrients and wastes between blood and surrounding tissue fluid
Blood flow is slow to allow time for exchange to occur
Leaky - plasma escapes, but most is immediately recovered due to osmosis
62
Blood vessels: Venule - structure and function
Structure: small venules have endothelium plus a little CT
Larger ones have a single layer of smooth muscle
Vary in size
Function: low-pressure vessels which drain capillary bed
During infection and inflammation, venules are the site where WBCs leave the blood circulation to attack bacteria
Very slow flow
63
Blood vessels: Vein - structure and function
```
Structure: similar to a muscular artery but much thinner-walled for their size (less muscle and CT)
Larger veins (especially in legs) have valves which prevent backflow
```
Function: thin-walled, low-pressure, high V vessels which drain blood back to atria (except portal veins)
Walls are thin and soft --> stretch easily
Small change in venous BP causes large change in venous V
Act as a blood reservoir
64
Coronary arteries - location
Arise from the aorta just downstream from aortic valve
| Underneath fibrous pericardium
65
What do coronary arteries supply
Muscles of the heart (myocardium), which is what makes them important
66
Reduction of coronary artery size
If narrows to ~20% its normal X-section by atheroma, significant obstruction to blood flow occurs
During exercise, the myocardium supplied by the diseased artery runs low on oxygen (ischemia) causing chest pain (angina) - may result in death of a local area of myocardium
67
Deoxygenated blood is drained from the ___ by ____
Myocardium
| Cardiac veins, which return the blood to the right atrium
68
What function does the heart serve?
Demand --> Supply
Oxygen use --> Oxygen demand
More in --> More out
69
Cardiac output (CO) = ?
heart rate (HR) x stroke volume (SV)
At rest CO is between 4-7 litres / min
70
What is stroke volume (SV)
The volume of blood ejected by the left ventricle for 1 cardiac cycle
71
What is venous return
The volume of blood returning to the heart from the vasculature every min and is linked to CO
72
What is cardiac output (CO)
The volume of blood ejected into the aorta (or ejected from the left ventricle) per min (mL / min)
73
Cardiovascular system - flow
High flow
74
The more blood that returns to the heart during diastole...
The more blood is ejected during the next systole
75
Regulation of SV: Intrinsic regulation of force of contraction
Governed by degree of stretch of myocardial fibre at end of diastole
76
Regulation of SV: Extrinsic regulation
Determined by activity of ANS and circulating levels of various hormones
77
Starling's Law
The energy of contraction of the ventricle is a function of the initial length of the muscle fibres comprising its walls
i.e. a greater force of contraction can occur if the heart muscle is stretched first
78
SV and diastole
As blood returns to the heart in diastole, it begins to fill the ventricle --> pressure rises --> stretches myocardial fibres, placing them under a degree of tension (preload)
79
What 3 factors regulate SV
Preload on heart (mmHg) - stretch on left ventricle before it contracts
- increased V --> increased pressure --> increased preload --> increased SV --> increased force of contraction
Contractility - ability of nervous system to increase contractility
Afterload (mmHg) - the pressure the heart has to work at to eject left ventricle, through aortic valve, into aortic arch (work heart must do) to pump blood out
- refers to arterial pressure in left ventricle
80
What is inotrophy
Force of a contraction / contractility
81
Ejection fraction
SV/EDV
60-70%
i.e. 60-70% of blood that comes into left ventricle is pumped out per cardiac cycle
<25% = heart failure
82
Pressure-volume curve
Shows the work performed by the heart each time it beats
83
Contractility - intropic agent
The SV increase when a +ve inotropic agent is present
These agents often promote Ca2+ inflow during cardiac AP, which strengthens the force of the subsequent muscle fibre contraction
84
Contraction of left ventricle requires...
Co-ordination (electrical activity)
85
Positive inotropic agents
A slight increase in Ca2+ plasma promotes Ca2+ inflow in AP --> increased inotrophy
K+ slows heart rate
Na+, K+ and Ca2+ highly regulated
86
Causes of heart failure
Ejection fraction decrease:
High blood pressure
Viruses
Coronary artery disease
Responds by increasing heart rate
87
What is the rhythmic pulsation of heart maintained by
Excitatory signals generated within the heart
88
Heart electrical activity
1.5 mV
89
Intrinsic HR
90-100 bpm (higher than resting)
Generated by pacemaker cells (e.g. SA node) which self-discharge
Causes ventricular myocytes to contract
90
What does an ECG measure
Sum of all electrical activity spreading over heart walls
91
Why does heart require electrical activity
To get to the right myocytes at the right time to allow them to contract
92
Which part of the heart is the last to contract
Apex of heart (base)
93
If measuring electrical activity in myocyte, you are measuring the...
Cardiac AP
94
Steps in cardiac muscle contraction (basic)
Depolarisation
Plateau
Repolarisation
95
Steps in cardiac muscle contraction (detail)
Excitation is initiated by specialised cells in SA node which lies close to right atrium
A wave of depolarisation is conducted throughout the myocardium
MP between successive APs show a progressive depolarisation - this is the pacemaker
When threshold is reached, an AP is triggered
Myocytes of atria, ventricle and conducting system have APs with a fast initial depolarisation followed by a pleateau phase prior to repolarisation
Since muscle is refractory during and shortly after the passage of an AP, the long plateau phase ensures unidirectional excitation of myocardium
Repolarisation of myocardial cells occur when V-gated Ca2+ channels inactivate and additional V-gated K+ channels open
96
SA node - resting potential
Cells of SA node have an unstable resting potential
97
Cardiac muscle contraction - Ca2+
Responsible for plateau phase (inward movement of Ca2+, as well as some K+ channels opening)
- ensures the AP lasts almost as long as the contraction
98
Electrocardiogram (ECG)
```
P wave = atrial depolarisation (atrial contraction)
QRS complex (R wave) = onset of ventricular depolarisation (ventricular contraction)
T wave = ventricular repolarisation
```
99
ECG - 'leads'
12 leads give diff views of atria and ventricles (L and R)
100
Fibrilation
If atria stops working --> atria fibrilation --> can still function / walk around
Ventricular fibrilation --> heart attack --> must reset / use defibrillator
101
ECG - steps
1. Depolarisation of atrial contractile fibres produce P wave
2. Atrial systole (contraction)
3. Depolarisation of ventricular contractile fibres produce QRS complex
4. Ventricular systole (contraction)
5. Repolarisation of ventricular contractile fibres produce T wave
6. Ventricular diastole (relaxation)
102
Autonomic Nervous System (ANS)
A branch of the CNS
| Involves brainstem - helps regulate cardiovascular system
103
Components of ANS
```
Parasympathetic:
Increased parasympathetic --> decreased HR
Quick acting
Neurotransmitter ACh
e.g. vagus nerve - slows HR
```
```
Sympathetic:
Increased sympathetic --> increased HR
Increased sympathetic --> increased SV (also increased by parasympathetic but v little)
Slower acting (5-10s to change HR)
Neurotransmitter NE
```
104
ANS - goes to...
Every arteriole in the body
105
What is the apex formed by
The tip of the left ventricle and rests on the diaphragm
106
Layers of the heart wall
Epicardium (external)
Myocardium (middle)
Endocardium (inner)
107
Layers of heart wall - myocardium
Responsible for pumping action of heart
Composed of cardiac muscle tissue
Makes up approx 95% of heart wall
108
Layers of heart wall - endocardium
A thin layer of endothelium overlying a thin layer of CT
Provides a smooth lining for chambers of heart
Continuous with endothelial lining of large blood vessels attached to heart
109
Coronary sulcus
Encircles most of the heart
| Marks the external boundary betwen the superior atria and inferior ventricles
110
Anterior interventricular sulcus
A shallow groove on the anterior surface of the heart that marks the external boundary between the right and left ventricles
Continuous with posterior interventricular sulfucs
111
Which veins does the right atrium receive blood from
Superior vena cava, inferior vena cava and coronary sinus
112
Right atrium - anterior and posterior walls
Very different
Inside of posterior wall is smooth
Inside of anterior wall is rought due to presence of muscular ridges
113
Valves of the heart are composed of...
Dense CT covered by endocardium
114
Chordae tendineae
Tendon-like cords connected to cusps of the inlet valves
115
Pathway of blood from right ventricle
Blood passes from right ventricle through the pulmonary valve into pulmonary trunk, which divides into right and left pulmonary arteries and carries blood to the lungs
116
How many veins does the left atrium receive blood from
4
117
Blood passes from the left atrium into the left ventricle through the...
Bicuspid (mitral) valve
118
How are the systemic and pulmonary circuits arranged
Arranged in series; output of one becomes the input of the other
119
What blood do venules carry
Venules carry deoxygenated blood away from tissues and merge to form larger systemic veins
120
What does blood pressure measure
Pressure in arteries (arterial pressure, i.e. pulsatile pressure)
121
BP = ?
BP = CO x TPR (total peripheral resistance) = MAP
122
High levels of BP for long periods of time can cause...
Weakness in blood vessels --> may burst or become occluded --> coronary or stroke
123
What does BP drive
Exchange
124
Where does exchange occur
Capillaries
| The rest is just transport
125
What is the driving force pushing blood through
Pressure
126
Arterioles provide lots of...
Resistance
Are small vessels with lots of smooth muscle --> have a degree of tension/tone --> provides a shock absorption --> decreased pulsatility
127
Does pressure increase or decrease in capillaries
Pressure continues to decrease in capillaries (was initially decreasing in arterioles) because we're taking fluid out
128
Venous pressure - level
Low
129
Cardiovascular system - flow and pressure
Flow rate is same even though pressure changing
| 5L in and 5L out
130
Capillary exchange - in and out?
At one end of capillary bed, we're squeezing fluid out, but at other end we're absorbing it back in
i.e. high V out and high V in
131
Capillary exchange - lymphatic system
A certain amount of fluid passes out from capillaries into lymphatic system and is transported away
132
Capillary exchange - BHP
Blood hydrostatic pressure
| The driving force for exchange in arterial end of *capillaries*
133
Capillary exchange - IFHP
Interstitial fluid hydrostatic pressure
Opposing pressure of interstitial fluid
Close to zero
134
Capillary exchange - BCOP
Blood colloid osmotic pressure
Have proteins dissolved in plasma all the time but aren't pushed out of capillaries --> act as a restraint for fluid going out - opposes BHP
135
Capillary exchange - IFOP
Interstitial fluid osmotic pressure
Some proteins dissolve in interstitial fluid that isn't reabsorbed back into capillaries
Normally very small
136
Capillary exchange - NFP
Net filtration pressure
137
Edema
Where you are pushing out more fluid than you are reabsorbing
Interstitial spaces between cells have lots of fluid in there
Net filtration increases --> extrudes more fluid out of plasma
Tissue in legs and limbs get swollen
138
Arterioles - constriction?
Change in radius = big effect on resistance
| Blood flow decrease = vasoconstriction
139
Renal blood flow
Renal blood flow can go from 1L/min to 50mL/min
140
What happens if pressure decreases
No longer drives exchange
141
What happens to blood vessels when you're hot
Vasodilation (regulates temp)
142
How is the cardiovascular system arranged
Anatomically arranged in parallel (not series) --> all receive same amount of pressure
143
Cardiovascular system - arterioles in diff organs
Constriction of arterioles in diff organs helps redistribute blood flow to other organs
144
Blood pressure - main points
Exchange
| Stability
145
General pathway for inputs and outputs
Input --> CNS (particularly ANS) --> Output
146
Why don't you faint when you stand up
Input: senses BP using arterial baroreceptors -->
CNS/ANS -->
Output:
- decrease in parasympathetic NS --> increase HR
- increase in sympathetic NS --> increase HR and SV
-->
Increased CO
BP = CO x TPR
Both CO and TPR increase --> increase BP
147
Arterial baroreceptors
Y-shaped
Have afferent nerves entering which are stretch sensitive (stretch every heartbeat)
Increased BP activates more
Baroreceptors also found in aortic arch
148
Arterioles and sympathetic nerves
Arterioles have sympathetic nerves branching throughout the muscle
Sympathetic nerves have varicosities that release NE --> vasoconstriction
149
CNS: types of outputs
Neural and hormonal
150
CNS: Output - angiotensin II
Important hormone for vasoconstriction
Ace inhibitor if you have high BP --> decrease angiotensin II --> vasodilation
Related to renin (produced in kidneys)
151
Inputs to CNS
Multiple inputs which give rise to an output
152
Vasoconstriction/dilation of organs
Vessels in some organs will vasoconstrict and other vessels in other organs will vasodilate
i.e. tailored response
153
Cardiopulmonary receptors
Receptors found in major veins around the heart (especially SVC)
Respond to stretch of veins
154
Cardiopulmonary receptors - drinking fluid process
Drinking fluid increases venous pressure --> receptor is stretched and fires off -->
CNS --decreases renal SNS activity-->
Kidney:
- increase renal blood flow
- increase filtration
- increase urine flow rate
-->
Venous pressure returns to normal (homeostasis)
Slow / long-term process compared to arterial baroreceptors
155
CNS: Drinking fluid - hormonal response
Also slow activity
Antidiuretic hormone (ADH) decreases urine production
Decreased ADH --> allows you to excrete urine more
156
Stable BP is important for...
Exchange
157
When you almost get into an accident, you have elevated HR for a while (longer lasting) - why?
Increased sympathetic NS
CNS triggers adrenal gland via SNS
- secretes NE into bloodstream --> acts on α-receptor --> vasoconstriction --> increased HR and SV
158
Blood vessels: Tunica interna/intima
Forms inner lining of blood vessel
In direct contact with blood as it flows through the lumen
Contributes minimally to thickness
159
Blood vessels: Tunica media
Muscular and CT layer
Greatest variation among diff vessel types
In most vessels, relatively thick
Substantial amounts of elastic fibres
160
Blood vessels: What separates the tunica media from the tunica externa?
External elastic lamina
161
Blood vessels: Tunica externa
Consists of elastic and collagen fibres
Contains numerous nerves and tiny blood vessels
Helps anchor vessels to surrounding tissues
162
Elastic arteries - elastic lamellae
The thick tunica media, dominated by elastic fibres
163
Examples of elastic arteries
Aorta and pulmonary trunk
164
Elastic arteries - important function
Help propel blood onward while ventricles are relaxing
165
Elastic arteries AKA...
Conducting arteries
166
Muscular arteries are also called...
Distributing arteries - continue to branch and ultimately distribute blood to each of the various organs
167
Arterioles - metarteriole
Terminal end of arteriole
| Tapers toward the capillary junction
168
Capillary bed
A network of 10-100 capillaries that arise from a single metarteriole
169
Cardiac conduction system
A network of specialised cardiac muscle fibres that provide a path for each cycle of cardiac excitation to progress through the heart
170
Where is the only site where APs can electrically conduct from atria to ventricles?
Atrioventricular (AV) bundle
171
Nervous system regulation of the heart originates in...
The cardiovascular centre in the medulla
172
Capillary exchange
The movement of substances between blood and interstitial fluid
173
3 basic mechanisms by which substances enter and leave capillaries
Diffusion
Transcytosis
Bulk flow
174
Bulk flow
A passive process where large numbers of ions, molecules, or particles in a fluid move tgt in the same direction
Move at faster rates than with diffusion alone
175
What is bulk flow more important for
Regulation of relative volumes of blood and interstitial fluid
176
Filtration vs reabsorption
Filtration: pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid
Reabsorption: pressure-driven movement from interstitial fluid into blood capillaries
177
What does net filtration pressure (NFP) determine
Whether volumes of blood and interstitial fluid remain steady or change
178
Within vessels, what is hydrostatic pressure due to
Pressure that water in blood plasma exerts against blood vessel walls
179
NFP (net filtration pressure) = ?
(BHP + IFOP) - (BCOP + IFHP)
i.e. pressures that promote filtration minus pressures that promote reabsorption
If +ve = net outward pressure (filtration)
If -ve = net inward pressure (reabsorption)
180
Systolic BP vs diastolic BP
Systolic: highest pressure attained in arteries during systole
Diastolic: lowest arterial pressure during diastole
181
Mean arterial pressure (MAP) is roughly...
1/3 of the way between diastolic and systolic pressures
182
Another way of calculating cardiac output = ?
CO = MAP / R
183
Vascular resistasnce depends on...
Size of lumen
Blood viscosity
Total blood vessel length
184
Total peripheral resistance
Refers to all vascular resistances offered by systemic blood vessels
185
Circulation time
The time required for a drop of blood to pass from the right atrium, through the pulmonary circulation, back to the left atrium, through the systemic circulation down to the foot, and back again to the right atrium
In a resting person, usually ~1 min
186
Proprioceptors
Monitor movements of joints and muscles and provide input to cardiovascular centre during physical activity
187
Baroreceptors
Monitor changes in blood pressure and stretch in walls of blood vessels
188
Chemoreceptors
Monitor conc of various chemicals in blood
189
Baroreceptors - when BP falls...
Baroreceptors are stretched less --> send nerve impulses at slower rate to cardiovascular centre, which decreases parasympathetic stimulation of heart and increases sympathetic stimulation
190
Where is the bicuspid valve located
Between the left atrium and the left ventricle
191
Where does deoxygenated blood returning from the systemic circulation flow into
Right atrium
192
Blood flows from the pulmonary veins into the..
Left atrium
193
The outlet valves lack chordae tendinae because...
When the valves close, the cusps remain stable because of their cup shape
194
Where the great arteries and veins attach at the base of the human heart, the aorta is...
Posterior to the pulmonary trunk
195
There is a semilunar valve between the..
Right ventricle and the pulmonary trunk
196
Does the left ventricle expel a greater volume of blood per beat than the right ventricle
No
197
When do the atrioventricular valves close
The ventricles contract
198
Where does blood flow into the coronary arteries from
The ascending aorta
199
What component of the conduction system provides the only electrical connection between the atria and the ventricles
AV bundle
200
A decrease in arterial blood pressure would most likely and immediately lead to...
Decreased afterload
201
Blood flow to muscles increase if _______ in arterioles supplying the muscles increase
Vasodilation
202
An increase in cardiac sympathetic activity would most likely and immediately...
Increase SV
203
Increased stimulation of the heart by cardiac accelerator nerves causes...
Stimulation by NE of the SA node and of the beta receptors on the cardiac muscle fibres of the ventricles
204
Where does blood flow most slowly through
Capillaries because their total cross-sectional area is the largest
205
In terms of the structural organisation of the cardiovascular system, what factor contributes most to BP
The parallel arrangement of the vascular beds
206
Stimulation of the heart by autonomic nerves fibres traveling with the vagus nerve causes...
Decreased HR but no change in ventricular contractility
207
What happens if heart rate increases to very high levels
End-diastolic volume drops because ventricular filling time is so short
208
Moderator band is part of..
The heart's conduction system
209
With regard to resistance, the parameter with the largest effect is...
Radius / diameter
210
If plasma proteins are lost due to kidney disease, which of the following pressure changes occur as a direct result
Blood colloid osmotic pressure (BCOP) decreases
211
The vasomotor region of the cardiovascular centre directly controls...
Peripheral resistance by changing diameter of blood vessels
212
Where are baroreceptors located
In the walls of the aorta (aortic arch) and carotid arteries/sinus
213
End-systolic volume
The amount of blood remaining in the ventricle when the semilunar valve closes
214
What is angina pectoris
The pain accompanying myocardial ischemia
215
Pons - grey or white matter?
Both
216
Fibrous skeleton - function
Insulates the ventricular myocardium from electrical activity of the atria, so wave of electrical activation can only propagate between the 2 chambers via the AV node - prevents simultaneous contraction of atria and ventricles
Vital for coordination of mechanical contraction and thus ejection of blood
217
Mitral regurgitation
Blood regurgitation from LV into LA during ventricular systole due to failure of valves to close properly
As soon as pressure in ventricle exceeds that of the atria (isovolumetric ventricular contraction), regurgitation may occur
218
When does atrial diastole first occur
During isovolumetric ventricular contraction
219
Longest phase in cardiac cycle
Ventricular filling
| ~0.4s
220
What is the valve immediately upstream of the coronary arteries
Aortic semi-lunar valve
221
Cardiac reserve
The difference between the rate at which the heart pumps blood and its max capacity for pumping blood at any given time
222
Hypothermia ____ HR
Decreases
223
Hypertension
Abnormal higher BP
224
Bradycardia
Abnormally slow HR
225
Tachycardia
Abnormally rapid HR
226
Poiseuille's law
States the velocity of a liquid flowing through a capillary is directly proportional to the pressure of the liquid and the fourth power of the radius of the capillary
227
Hemorrhage
Blood loss
228
Chronotropy
Heart rate
| i.e. +ve chronotropic effect = increased HR
229
Starling's Law of the Capillaries
States that the V of fluid reabsorbed at the venous end of a capillary is nearly equal to the V of fluid filtered out at the arterial end
230
Arterioles - nerves
Only contain sympathetic nerves (so there is a constant degree of tension)
Doesn't contain parasympathetic nerves
231
Chordae tendineae when valves are open
Chords are relaxed and closer to the middle of the lumen of the ventricle
232
For no ventricular filling to occur...
Ventricular P must be higher than peak atrial pressures to keep inlet valves closed
233
Upstream vs downstream
```
Upstream = closer to heart
Downstream = further from heart
```
234
Afterload and BP
Increased afterload = increased BP = hypertension
235
Decreased BP and baroreceptors
Decreased BP --> baroreceptors fire less and upregulate sympathetic nervous activity
236
Why is resting HR slower than intrinsic HR
Due to activity of parasympathetic NS
237
Most anterior structure at base of heart
Pulmonary trunk
238
Fibrous skeleton is made of...
CT
239
Pulmonary veins drain into the...
LA --> LV
240
Atria contract when initially stimulated by...
SA node
241
Initiation of heartbeat is the responsibility of...
SA node
242
Increase in venous return results in...
Increased end-diastolic volume --> increased preload
243
Alpha vs beta receptors
Alpha receptors affect skin
| Beta receptors affect cardiac muscle
244
Vasomotor nerves
Activated by sympathetic activity --> vasoconstriction --> increased resistance
245
Arteries and veins - pressure
```
Arteries = high pressure
Veins = low pressure
```
246
Standing still for long periods of time
Lack of skeletal muscle pumping of veins --> venous return decreases --> SV decreases --> CO decreases
247
What happens during diastole
Relaxes and fills with blood
248
End-systolic volume
The amount of blood remaining in the ventricle when the semi-lunar valve closes
