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Anatomy and Physiology 1 > 4. Cardiac Muscles > Flashcards

4. Cardiac Muscles Flashcards

1
Q

What are intercalated discs?

A
  • Cell membranes that separate individual cardiac muscle cells.
  • Cell membranes fuse here to from communicating/gap junctions - which allow cardiac muscle to act as a syncytium
  • Allow almost totally free diffusion of ions
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2
Q

Name the two syncytia of the heart.

A

Atrial and ventricular syncytium

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3
Q

Through what feature is the action potential passed from the atria to the ventricles?

A

Through the A-V bundle (atrial to ventricular syncytium)

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4
Q

What is the role of the A-V node?

A
  • Conducts action potential from atrial side to ventricle side
  • The A-V node delays electrical signals from the atria to the ventricles, ensuring the ventricles contract after the atria, allowing proper blood flow.
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5
Q

What causes the action potential plateau in cardiac muscle?

A
  1. Calcium: Slow calcium channels (calcium-sodium channels) that open slower and remain open longer than the fast sodium channels.
  2. Potassium: A decrease in the permeability of the cardiac muscle to potassium immediately after the onset of the action potential.
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6
Q

What is the main source of calcium for causing excitation-contraction in cardiac muscle?

A
  1. T-tubules
  2. ECF
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7
Q

What event is associated with each of the following parts of the
EKG?
a. P wave
b. QRS wave
c. T wave

A

P: depolarization of atria - atrial contraction (slight rise in a pressure after P)
QRS: depolarization of ventricles - ventricle contraction ( v pressure rises)
T: repolarization of ventricles

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8
Q

On the following chart indicate where each of the following events
occur.
a. Depolarization of the atria
b. Contraction of the atria
c. Depolarization of the ventricles
d. Contraction of the ventricles
e. Closing of the AV valves
f. Opening of the AV valves
g. Closing of the aortic valves
h. Opening of the aortic valves

A

a. P
b. Slightly after P
c. QRS
d. right after S
e. right after a (before big hump)
f. right after v (after big hump)
g. right before T ends
h. right at S

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9
Q

On the atrial pressure curve, what is causing the changes in atrial pressure at a, c and v.

A

A wave: Caused by atrial contraction.
C wave: Caused by bulging of the A-V valves during early ventricular contraction.
V wave: Caused by atrial filling while A-V valves are closed during ventricular systole

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10
Q

What is the Frank-Starling Mechanism of the heart? (4)

A
  • The heart’s ability to adapt to increasing volumes of inflowing blood.
  • The greater the heart muscle stretched during filliing, the greater the force of contraction - has limits
  • Stretch of atria increases rate of contractions
  • Cardiac output is determined almost entirely by venous return
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11
Q

What is the pacemaker of the heart?

A

The sinus node (sinoatrial node) because it controls the rate of beat and self-excites.

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12
Q

What is the role of the internodal pathway?

A
  • To provide a pathway for rapid conduction of the action potential from the sinus node to the A-V node.
  • One way conductance
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13
Q

What are the Purkinje fibers of the heart and what is their role.

A
  • Large fibers in the heart’s ventricular system with a high level of gap junctions.
  • Allow almost instantaneous transmission of the cardiac impulse throughout the entire ventricular muscle.
  • Causes synchronous contraction of the ventricular muscle, making more efficient pumping
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14
Q

What percent of the total blood is found in each of the following parts
of the circulatory system?
a. Heart and lungs
b. Veins
c. Arteries
d. Arterioles and capillaries

A

a. 16%
b. 64%
c. 13%
d. 7%

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15
Q

Define cardiac output. What is one of the main determinants of cardiac output?

A
  • The quantity of blood pumped into the aorta each minute by the heart.
  • Venous return - the quantity of blood flowing from the veins into the right atrium each minute.
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16
Q

Give Ohm’s law

A

F = ∆P/R
- Flow (F) through a conductor is directly proportional to the potential difference (∆P) across its ends and inversely proportional to the resistance (R) offered by the conductor.

17
Q

Using Poiseuille’s law demonstrate the effect of the pressure gradient and radius of the vessel on blood flow. What is one of the factors related to blood flow that makes small radius vessels slow flowing?

A

F = π∆Pr4/8ηl
- A more detailed relationship between blood flow, pressure gradient, and vessel radius, considering other factors like blood viscosity and vessel length.
- Blood flow is directly proportional to the fourth power of the radius of the vessel.
- Blood cells can get caught up and slow blood flow in vessels with a smaller radius.

18
Q

What are two reasons that blood flow increases when arterial pressure increases?

A
  1. Higher pressure in the arteries pushes blood faster through the veins.
  2. When arteries expand slightly due to higher pressure, the wider vessels allow blood to flow more easily.
19
Q

At any arterial pressure would you get more or less blood flow when the sympathetic system was activated?

A

Less blood flow because stimulation of the sympathetic system causes vasoconstriction

20
Q

What functions to return venous blood to the heart?

A

Venous pump
- When muscles contract, they squeeze veins, pushing blood toward the heart, while valves prevent backflow.

21
Q

Describe the baroreceptor reflex.

A
  • The baroreceptor reflex helps maintain short-term blood pressure stability by detecting changes in arterial pressure through baroreceptors in the carotid sinus and aortic arch.
  • When blood pressure rises, baroreceptors send signals to the brain to reduce heart rate and cause vasodilation; when blood pressure drops, they trigger increased heart rate and vasoconstriction.
  • This reflex quickly adjusts blood pressure but adapts to long-term changes, making it less effective for chronic regulation.
  • It has spray type nerve endings
  • Signals travel via Herings nerve to Glossopharangeal nerve or Vagus nerve
22
Q

Describe the atria or volume reflex.

A
  • The atria stretches causing an increase in blood flow to kidneys (increase in filtration), and decrease secretion of antidiuretic hormone (decreases reabsorption of water)
23
Q

Describe the Bainbridge reflex.

A
  • The increase in atrial pressure (up to 75%) and sends signals via vagus nerve
  • the efferent signals come back via vagus and sympathetic nerves to increase heart rate and strength of contractions
24
Q

What is the effect of arterial pressure on renal output?

A
  • Too much ECF, the blood volume and arterial
    pressure rise - causes kidneys to excrete excess fluid
  • Pressure diuresis: increase in arterial pressure can double the renal output
  • Pressure natriuresis: also double output of salt
25
Q

What are the two primary determinants of long-term arterial pressure?

A
  1. The degree of pressure shift of the renal output curve for water and salt.
  2. The level of intake of water and salt.
26
Q

What enzyme is released by the kidney when the arterial pressure falls too low?

A

Renin

27
Q

Describe the renin-angiotensin system

A
  1. Renin is a protein enzyme released by the kidney when arterial pressure falls too low
  2. Angiotensin: acts directly on the kidney to cause salt and water retention
  3. This causes adrenal glands to secrete aldosterone, which increases salt and water re-absorption in the kidney

Anatomy and Physiology 1 (17 decks)

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