D4 The heart Flashcards
1
Q
What is cardiac muscle unique to?
A
The heart
2
Q
What are the similarities between cardiac muscle and skeletal muscle?
A
- striated in appearance
- the arrangement of the contractile proteins actin and myosin is similar
3
Q
What are the similarities between cardiac muscle and skeletal muscle?
A
- striated in appearance
- the arrangement of the contractile proteins actin and myosin is similar
4
Q
What are the differences between cardiac and skeletal muscle? (4)
A
Cardiac muscles are
* shorter and wider
* most commonly have just one nucleus per cell
* Not under voluntary control
* Can contract even in the absence of sitmulation by nerves for the entire life of the organism
5
Q
What shape are cardiac muscles cells?
A
Y-shaped
6
Q
How are cardiac muscles cells joined?
A
are joined end to end in a complex network of interconnected cells
7
Q
What is an intercalarted disc?
A
A specialized junction where the end of one cell contacts the end of another cell
8
Q
What structure only appears in cardiac muscles?
A
Intercalated discs
9
Q
What does the intercalated disc consist of?
A
double membrane containing gap junctions
10
Q
What does the gap junctions in the double membrane of intercalated disc provide?
A
A connected cytoplasm between the cells
11
Q
What does a connected cytoplasm between cells in an intercalated disc allow for?
A
- rapid movement of ions
- low electrical resistance
12
Q
What allows for the synchronization of cardiac muscle contraction?
A
- Being connected because of their Y shapes and being electrically connected due to gap junctions
- Allows a wave of depolarization to pass easily from one cell to a network of other cells
- Leading to the synchronization of muscle contraction
13
Q
What does the network of cardiac muscle cells contract like?
A
As if it was one large cell
14
Q
What does the orange and blue represent?
A
Cardiac muscle fibrils
15
Q
What does the red represent? What does it do?
A
Mitochondria
* supply the muscle cells with energy
16
Q
What are the narrow dark blue lines representing? What do they mark?
A
Transverse tubules
* they mark the division of the myofibrils into contractile units (sarcomeres)
17
Q
What are the narrow dark blue lines representing? What do they mark?
A
Transverse tubules
* they mark the division of the myofibrils into contractile units (sarcomeres)
18
Q
What is the wavy dark blue line representing?
A
In the centre is the intercalated disc
19
Q
What is the wavy dark blue line representing?
A
In the centre is the intercalated disc
20
Q
What is the cardiac cycle?
A
- A repearting sequence of actions in the heart which result in the pumping of blood to the lungs and all other parts of the body
- Represents all of the events from the beginning of one heartbeat to the beginning of the next
21
Q
What do cardiologists refer to contraction and relaxation of the heart’s chamber as?
A
Contraction: systole
Relaxation: Diastole
22
Q
What happens in atrial systole?
A
- When ventricles are ~70% full,
- atria will contract (atrial systole),
- increasing pressure in the atria
- forcing blood into ventricles
23
Q
What happens in ventricular systole?
A
- ventricles contract
- ventricular pressure exceeds atrial pressure and AV valves close to prevent back flow
- With both sets of heart valves closed, pressure rapidly builds in the contracting ventricles (isovolumetric contraction)
- When ventricular pressure exceeds blood pressure in the aorta, the aortic valve opens and blood is released into the aorta
24
Q
What happens during diastole?
A
- ventricular pressure falls as blood exits the ventricle and travels down the aorta
- When ventricular pressure drops below aortic pressure, the aortic valve closes to prevent back flow (second heart sound)
- When the ventricular pressure drops below the atrial pressure, the AV valve opens and blood can flow from atria to ventricle
25
What is the SA node?
* a collection of uniquely structured cardiac cells that spontaneously initiate action potentials without stimulation by other nerves
26
Where is the SA node?
In the wall of the right atrium
27
What is the SA node sometimes referred to as?
The pacemaker of the heart
28
What allows the contraction which originated in the SA node to spread rapidly across the entire atrium?
**Gap junctions** allow **electric charges** to **flow freely between cells**, the contraction which originated in the SA node spreads very rapidly
29
What does the SA node cause?
causes the atria to undergo systole and contract as if it were one cell
30
What can the signals from the SA node not travel to?
Signal from the SA node that cause the atria to contract cannot pass directly from the atria to ventricles
31
Where does the signal from the SA node reach after causing the atria to contract?
the signal from the SA node reaches the atrioventricular (AV) node
32
How does the electrical signal form the SA node spread throughout the heart?
* it reaches the AV node
* via specialized Purkinje fibres spread through the heart
33
What are purkinje fibres?
specialized heart muscle tissue that spreads the signal from the SA node and AV node throughout the heart
34
What does signal from the prukinje fibres cause?
* causes the ventricle to undergo systole
* snaps the AV valves shut
* after the ventricles are emptied, the semilunar valves close
35
What does the AV valve do when the ventricle begins diastole?
AV valves open and ventricles start filling with blood
36
Near the end of diastole, what happens to all four chambers of the heart?
all four chambers are in diastole and filling
37
When does the a cardiac cycle end?
when the **atria are filled** and the **ventricles are 70% filled**
38
How do the mechanisms in place stagger the contraction of the atria and the ventricle?
The fibres which connect the SA node to the AV node carry the action potential relatively slowly
* delays by ~0.12s between the arrival of the stimulus from the SA node and initiation of the impulse with the ventricles
39
Which node takes longer to become excited?
Cells of the AV node take longer to become excited than the cells of the SA ndoe
40
What are 4 features of the AV node that lead to the delayed initiation of contraction of ventricles by the AV node?
* AV node cells have a **smaller diameter** and **do not conduct as quickly**
* There is a relatively **reduced number of Na+ channels** in the membranes of AV node cells, a **more negative resting potential** and a **prolonged refractory period** within the cells of the AV node
* There are **fewer gap junctions** between the cells of the AV node
* There is relatively **more non-conductive connective tissue** in the node
41
Why is the delay in the initiation of contraction caused by the AV node important?
* ensures the atria contract and empty the blood they contain into the ventricle first before the ventricles contract
* contraction of ventricles causes the AV valve to snap shut
* so contraction too early would lead to too small a volume of blood entering the ventricles
(allow time for atrial systole before AV valve close)
42
Describe the pathway of the electric impulse initiated by the SA node?
* SA node in the wall of the right atrium to AV node
* AV node send impulse to the atrioventricular bundle (AV bundle)
* AV bundle conducts the signal rapidly to a point where it splits into the right and left bundle branches
* Bundle brances conduct the impulses through the wall between the two ventricles
* signal reaches the base/apex of the heart and connects to the Purkinje fibre
* Purkinje fibre conduct signal even more rapidly to the ventricles
43
What are 4 modifications of Purkinje fibres that facilitate them to conduct signals at high speed?
* They have relatively **fewer myofribrils**
* They have a **bigger diameter**
* They have **higher densities of voltage-gated sodium channels**
* They have **high numbers of mitochondria** and **high glycogen stores**
44
Where does the contraction of the ventricle begin?
at the apex/base of the heart
45
What is a stethoscope?
A tool that allowed for non-invasive investigation of internal anatomy that detects different sounding heartbeats which can indicate different types of heart abnormalities
46
What is a stethoscope?
A tool that allowed for non-invasive investigation of internal anatomy that detects different sounding heartbeats which can indicate different types of heart abnormalities
47
Prior to the stethoscope, practitioners would place their ears directly on the best of patients to listen to the heart beat, why was that impractical?
* Most patients were too obese for sound to be heard
* Washing was not the social norm and some patients were "invested with vermin"
* Modesty was an issue for female patients
48
What are the two normal heartbeat sounds from?
From the closing of valves
* AV valves shut = "lub"
* Semilunar valves shut = "dub"
| Semilunar valves close after the ventricles are emptied
49
What are the two normal heartbeat sounds from?
From the closing of valves
* AV valves shut = "lub"
* Semilunar valves shut = "dub"
| Semilunar valves close after the ventricles are emptied
50
What are some examples of how heart rate can be influenced?
* Exercise: intensity, recovery
* relaxation
* body position: lying down, breathing and breath holding
* Exposure to a cold stimulus
* facial immersion in water
51
How can heart rate be detected?
* Pulse of an artery in the wrist and the side of the neck below the jaw
* Hand-grip heart monitors
* ear clips
* EKG sensors
* Wrist watches
* built-in cameras on some tablet computers
52
What are artificial pacemakers?
* medical devices
* surgically fitted in patients with a malfunctioning SA node or with a block in the signal conduction pathway within the heart, which impairs the nerve impulses generated by the node
53
What are the purpose of artificial pacemakers?
Maintain the rhythmic nature of the heart beat
* when its not beating fast enough
* when there is a fault in the heart's electrical conduction system
54
What do pacemakers provide?
* provide a regular impulse or discharge only when a heartbeat is missed so that it beats normally
55
How does the most common, basic pacemaker do compare to more complex forms?
* basic pacemakers monitors the heart's rhythm and when a heartbeat is not detected, the ventricle is stiulated with a low voltage pulse
* More complex forms stimulate both the atria and the ventricles
56
What does the leads from the pacemaker do?
Supply regular electrical impulses to the heart
57
How can electrical signals that makes cardiac muscle contract be detected and quantified?
Using an electrocardiogram (ECG or EKG)
58
What is the P-wave, QRS wave, and the T wave caused by?
P-wave = by atrial systole
QRS wave = by ventricular systole
T-wave = coincides with ventricular diastole
59
When can an electrocardiogram be compared to?
The overall pattern can be compared before and after mild exercise
60
When does cardiac arrest occur?
when the blood supply to the heart becomes reduced and the heart tissues are deprived of oxygen
61
What is ventricular fibrillation?
* Abnormalities in the cardiac cycle
* twitching of the ventricles due to rapid and chaotic contraction of individual muscle cells
62
How do first responders treat a victim in cardiac arrest?
* apply two paddles of a defibrillator to the chest of the patient
* setting up a diagonal line between the two paddles with the heart in the middle
* the device will first detect whether fibrillation is happening
* if it is, an electric discharge is given off to restore a normal heart rhythm
63
What is atherosclerosis?
Hardening of the arteries caused by the formation of plaques, or atheromas, on the inner linning of the arteries
64
What are plaques?
Areas that are swollen and accumulate a diversity of debris
65
Why do plaques often develop?
Because of high circulating levels of lipids and cholesterol
66
What can plaques do to vessels?
It can reduce the speed at which blood moves through the vessels
67
How can plaques block the blood flow through the artery?
* plaques can trigger a clot, or thrombosis
* which can block the blood flow through the artery and deny the tissue access to oxygen
68
If there is a thrombosis, blood clot on the surface of the heart, what is the consequence?
Myocardial infarction, or heart attack
69
What is hypertension?
When there is a greater pressure on the walls of arteries caused by slow flow of blood caused by a resistance to the flow of blood
70
What are the 4 consequnces of hypertension?
* **Narrowing or stiffening of the arteries** - from a cascade of events initiated by having damage to the cells that line arteries.
* **Aneurysm** - a bulge (an enlarged section of the artery wall) caused by constant high blood pressure weakening an artery. Can form in any artery in the body but are most common in the aorta which can burst and cause internal bleeding.
* **Stroke** - from chronic high blood pressure that weakens the blood vessels in the brain, causing them to narrow, leak or rupture. If leads to a blood clot in the arteries leading to the brain, it can potentially cause a stroke.
* **Kidney failure** - chronic high blood pressure damages both the arteries leading to the kidney and the capillaries within the glomerulus
71
What are the factors correlated with a greater incidence of thrombosis and hypertension?
* **Genetic precondition** - having parents who experienced it
* **Old age** - leads to less flexible blood vessels
* **post-menopause** - correlated with a fall in estrogen levels in females, increasing risk
* **Male** - greater risk compared to females correlated with lower levels of estrogen
* **Smoking** - raise blood pressure because nicotine causes vasoconstriction
* **A high-salt diet** - excessive amounts of alcohol and stress are also correlated with hypertension
* **Too much saturated fat and cholesterol** - promotes plaque formation
* **Height** - afffects blood pressure
* **Sedentary lifestyle** - correlated with obesity and prevents the retun of venous blood from the extremitites leading to a greater risk of clot formation
72
What is blood pressure?
More accurately is arterial pressure
* the pressure that circulating blood puts on the walls of arteries
73
How does the pressure of blood within arteries vary?
Peak - during ventricle systole
Minimum - beginnning of the cardiac cycle when the ventricles are filled with blood and are in systole
74
How are blood pressure measurements often quotes?
In the pressure unit "mm Hg"
75
What does a blood pressure of "120 over 80" mean?
The higher number - the pressure in the artery caused by ventricular systole
The lower number - the pressure in the artery due to ventricular diastole
76
What is high blood pressure during preganancy called?
Pre-eclampsia
* can be life threatening condition if not treated
77
How is blood pressure measured?
* a cuff is placeod on the bicep and inflated so that it constricts the arm and prevents blood from entering the forearm
* The cuff is slowly deflacted
* Nurse listens for the occurence of a sound (this occurs when the cuff pressure is lowered below the systolic pressure
* The sound is caused by the opening and closing of the artery
* The cuff is further deflated until normal blood flow returns and there is no longer a sound
* The absence of sound occurs when the cuff pressure is less than the diastolic pressure
78
When does the absence of sound occur when measuring blood pressure?
When the cuff pressure is less than the diastolic pressure because the sound is caused by the opening and closing of the artery
79
What intrument is used by doctors to measure blood pressure?
Sphygmomanometer/blood pressure monitor
80
What is the normal blood pressure?
Systolic - less than 120
Diastolic - less than 80
81
What does coronary heart disease (CHD) refer to?
the damage to the heart as a consequence of **reduced blood supply to the tissues of the heart** itself.
Often caused by **narrowing and hardening of the coronary artery**.
82
What does coronary heart disease (CHD) refer to?
the damage to the heart as a consequence of **reduced blood supply to the tissues of the heart** itself.
Often caused by **narrowing and hardening of the coronary artery**.
83
How do ethnic groups differ in their predisposition to CHD?
Different diets and lifestyles
84
What groups can have different probabilities of experiencing CHD?
* age
* gender
* level of physical activity
* different genotypes
* differing medical histories
* ethinic
85
What groups can have different probabilities of experiencing CHD?
* age
* gender
* level of physical activity
* different genotypes
* differing medical histories
* ethinic
