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Human Physiology 2 > Week Two > Flashcards

Week Two Flashcards

1
Q

Describe the location of the heart

A

Located in the thoracic cavity, the heart sits behind the sternum, between the two lungs in an area called the mediastinum. It is centered in the rib cage but favours the left side.

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2
Q

What is the fibrous pericardium?

A

outer layer of connective tissue

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3
Q

What is the serous pericardium?

A

Inner membrane that folds under itself to form 2 layers: called the parietal and visceral layer

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4
Q

What is the parietal layer of the pericardium?

A

fused to the inner surface of the fibrous pericardium

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5
Q

What is the visceral layer (epicardium) of the pericardium

A

inner layer closest to the heart wall

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6
Q

What is the pericardial cavity and what is its function?

A

between the parietal & visceral layer, filled with serous fluid (pericardial fluid)
- lubricated to decrease friction as the heart beats

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7
Q

What are the layers of the heart wall in order?

A

epicardium → myocardium → endocardium

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8
Q

Describe the Epicardium

A

includes a thin layer of connective tissue containing fat deposits

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9
Q

Describe the myocardium

A

the main component that makes up the wall of the heart; mostly cardiac muscle cells (myocytes); also contains specialized pacemaker cells & connective tissue

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10
Q

Describe the Endocardium

A

Innermost layer of the heart, faces the lumen of the heart chamber; simple squamous epithelium (endothelium) and layers of connective tissue containing collagen & elastic fibers

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11
Q

Describe the chambers of the heart

A
  • two atria and two ventricles
  • the atria receive blood from veins and pump blood into ventricles through one-way valves
  • the ventricles eject blood into arteries → carry blood through either systemic or pulmonary circuit
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12
Q

Where does gas exchange occur to pick up oxygen?

A

between air in the alveoli and blood in the pulmonary capillaries

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13
Q

Where does gas exchange occur to provide tissues with oxygen?

A

between tissues and blood in the systemic capillaries

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14
Q

Name the major systemic veins

A

superior and inferior vena cava

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15
Q

Name the major systemic artery

A

aorta

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16
Q

Name the major vessels of pulmonary circulation

A
  • right and left pulmonary arteries
  • right and left pulmonary veins
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17
Q

What separates the right and left ventricles?

A

interventricular septum

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18
Q

Describe the chambers of the heart

A
  • the ventricles are larger than the atria and have thicker walls → much stronger pumps
  • the atria are not symmetrical in size, shape of location; right atirium is larger, thinner walled, more anterior; left atrium is smaller, thicker-walled and more posterior
  • the ventricles are not symmetrical
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19
Q

Describe the shape of the right ventricle

A

thin-walled and crescent shaped

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20
Q

Describe the shape of the left ventricle

A

thicker-walled and circular

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21
Q

What is the name of the valves between the atria and ventricles? describe them

A

Atrioventricular valves
tricuspid: between right atrium and right ventricle (contains 3 cusps)
bicuspid: between left atrium and left ventricle (contains 2 cusps)

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22
Q

What is the name of the valve between the ventricles and the pulmonary artery/aorta? Describe them

A

semilunar valves
pulmonary valve: between right ventricle and pulmonary trunk
aortic valve: between left ventricle and aorta

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23
Q

Describe pressure changes and blood flow in the heart

A

blood flows in response to pressure gradients. As ventricles contract and relax, pressure in chambers changes, causing blood to push on valves and open or close them

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24
Q

WHat happens if pressure in the ventricles is larger than pressure in the aorta/pulmonary arteries

A

aortic/ pulmonary valve opens

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25
Q

What happens if pressure in the aorta/pulmonary arteries is greater than pressure in the ventricles?

A

aortic/pulmonnary valve closes

26
Q

What happens if pressure in the atrium is greater than in the ventricles?

A

AV valve opens

27
Q

What happens if pressure in the ventricles is greater than pressure in the atrium?

A

AV valve closes

28
Q

Describe the ratio of cells that make up the heart

A
  • most of the cells are myocytes (99%(
  • 1% are pacemaker cells
29
Q

Describe myocytes

A
  • striated muscle fibers
  • generate action potentials when membrane is depolarized to threshold
  • the source of force-production (contraction) of the heart muscles
30
Q

Describe pacemaker cells

A
  • generate spontaneous, rhythmic action potentials
  • the signal for myocyte contraction
  • these cells do not contribute to the contractile force of the heart
31
Q

What are the intercalated discs made up of?

A

desmosomes: hold cells together
gap junctions: allow ions to pass rapidly from one cell to another

32
Q

Describe the histology of cardiac myocytes

A
  • contain contractile proteins (actin & myosin) that are organized in the same way as skeletal muscle fibers, producing the characteristic striations
  • they are branched muscle fibers with only 1 nucleus and fibers are shorter and wider than skeletal muscle fibers
  • each myocytes contains many mitochondria → high energy demands
  • unique structures called intercalated discs join myocytes together and also connect pacemaker cells to contractile cells
33
Q

How do pacemaker cells set the pace of the heart?

A

they undergo rhythmic, spontaneous depolarizations that lead to action potentials → the APs spread quickly from cell-to-cell via gap junctions through the cardiac conduction system

34
Q

Describe the three steps of the cardiac conduction system

A
  1. the sinoatrial node generates potential, which spreads to the atrial cells and the AV node
  2. After the AV node delay, the action potential is conducted to the AV bundle and then to the right and left bundle branches
  3. The action potential spreads from the bundle branches along the Purkinje fibers to the contractile cells of the ventricles
35
Q

Why is there a delayed conduction through the AV node?

A

allows that atria to full depolarize and contract before the ventricles; gives the ventricles time to fill with blood

36
Q

Describe the pathway of cardiac conduction

A

SA node → AV node → AV bundle → right/left bundle branches → Purkinje fibers → contractile cells of the ventricles

37
Q

Describe the first step in Pacemaker cell action potentials

A

HCN (hyperpolarization-activated) channels open in response to membrane hyperpolarization → allow Na+ in and K+ out (more NA+ in than K+ out lead to depolarization threshold)

38
Q

Describe the second step in pacemaker cell action potentials

A

Ca2+ comes in via Ca2+ channels causing the depolarization phase of the action potential in pacemaker cells

39
Q

Describe the third step pace maker cell action potentials

A

K+ flows out via K+ channels causing the repolarization phase of the action potentials in pacemaker cells

40
Q

Describe the fourth step in pacemaker cell action potentials

A

HCN channels open again in response to the hyperpolarization from K+ flowing out

41
Q

How are action potentials transmitted from pacemaker cells to myocytes?

A

through gap junction that unite them
- these APs potentials in myocytes are the signals for contraction (excitation-contraction coupling)

42
Q

Describe the first step in Myocytes action potentials

A

voltage-gated Na+ channels open and Na+ rushes into the cell

43
Q

Describe the second step in Myocyte action potentials

A

NA+ channels close and K+ channels open, K+ begins to leave the cell, causing some repolarization

44
Q

Describe the plateau phase (3rd step) in myocytes action potentials

A
  • due to Ca2+ in balancing K+ out, the plateau phase lengthens the cardiac AP to 200-300msec. This keeps the heart rate slow enough to allow enough to allow enough time for the heart to fill with blood for next contraction
  • also prevents tetanus (another AP can’t fire right after)
45
Q

Describe the 4th phase in myocytes action potentials

A

Na+ and Ca2+ channels close as K+ continue to exit, causing repolarization

46
Q

True or False: Mechanism for cardiac muscle cell contraction is very similar to that of skeletal muscle fibers

A

true

47
Q

What is the perfect sequence and synchrony of the contraction and relaxation of the heart a result of?

A
  1. the cardiac conduction system that focuses the electrical signal long a given path and allows for a delay at the AV node
  2. gap junctions that allow the electrical signal to spread quickly through myocytes
  3. the orientation of myocytes in the myocardium
48
Q

What is an electrocardiogram?

A

-an important clinical tool for examining the function of the heart- gives us a picture of the electrical activity occurring in all cardiac muscle cells over a period of times
- recorded by placing electrodes on the surface of your skin
- electrical changes shown on the ECG reflect the depolarization and repolarization of cells in different areas of the heart

49
Q

What does the P wave reflect?

A

depolarization of all the myocytes of the left and right atria

50
Q

What does the QRS complex reflect?

A

depolarization of all the myocytes of the left and right ventricles; the myocytes of the atria are in the process of repolarizing at the same time

51
Q

What does the T wave reflect?

A

repolarization of all myocytes of the left and right ventricles

52
Q

What do period between waves on an ECG represent?

A

important phases of action potentials and of spread of electrical activity through the heart

53
Q

What is the cardiac cycle?

A
  • describes mechanical events of the heart
  • each cardiac cycle consists of one period of contraction (systole) and one period of relaxation (diastole) from each chamber of the heart
  • atrial and ventricular systoles and diastoles occurs at different times due to AV node delay
  • both sides of the heart are working to pump blood into their respective circuits simultaneously
54
Q

Name the four main phases of the cardiac cycle

A

filling, contraction, ejection, and relaxations

55
Q

Describe the ventricular filling phase

A
  • ventricles fill with blood and are in diastole
  • AV valves are open
  • atrial systole occurs
  • semilunar valves are closed
56
Q

What is end-diastolic volume?

A

the total amount of blood in the ventricles at the end of ventricular diastole

57
Q

Describe the isovolumetric contraction phase

A
  • ventricular systole begins
  • AV and semilunar valves close when enough pressure fills in the ventricles
  • atrial diastole begins
58
Q

What does isovolumetric mean

A

the pressure in the ventricles is not yet high enough to push open the semilunar valves and blood is neither being ejected from nor entering into the ventricles; volume briefly remains contract in the ventricles

59
Q

Describe the ventricular ejection phase

A
  • ventricular systole continues (70ml of blood pumped from each ventricle)
  • AC valves are still closed
  • atrial diastole contributes
  • pressure opens SL valves and blood is ejected into pulmonary trunk and aorta
60
Q

What is end-systolic volume?

A

the amount of blood remains in the ventricles at the end of ventricular ejection (about 50 ml at rest)

61
Q

Describe the isometric relaxation step

A
  • ventricular diastole begins
  • AV valves are still closed
  • Atrial diastole continues
  • SL valves close

Human Physiology 2 (9 decks)

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