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Histology / Embryology Unit 3 > Heart > Flashcards

Heart Flashcards

1
Q

What are the two layers of the pericardial sac? What are they made of?

A
  1. Fibrous pericardium - dense fibroelastic connective tissue
  2. Serous pericardium - Loose connective + squamous epithelium called mesothelium
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2
Q

What are the two layers of the serous pericardium?

A
  1. Parietal layer - adjacent to fibrous pericardium

2. Visceral layer - adjacent to myocardium also called epicardium

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3
Q

Where are the parietal and visceral layers of serous pericardium continuous?

A

At the reflexion at that base of the heart called the superior reflexion. Because they are continuous, they form the pericardial sac

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4
Q

What is the pericardial cavity and what is in it? What is its function?

A

A narrow space formed by the serous pericardium, containing a thin film of pericardial fluid (several mL). Function is to prevent friction during heart beating

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5
Q

What is pericarditis?

A

Inflammation of the pericardium that causes friction between layers and restricts beating of heart

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6
Q

What is pericardial effusion?

A

Abnormal collection of fluid in pericardial cavity which interferes with normal heart contraction

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7
Q

What is the cardiac skeleton? What is it composed of?

A

Central supporting structure of heart which some of the cardiac muscle fibers are attached to, and what supports the valves

Made of dense irregular connective tissue

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8
Q

What are the three components of the cardiac skeleton?

A
  1. Annuli fibrosi
  2. Trigona fibrosi
  3. Septum membranaceum
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9
Q

What is the annuli fibrosi?

A

Part of the cardiac skeleton - surrounds each of the four cardiac valves to stabilize them. Its connective tissue also gives rise to the core of the leaflets / cusps of the valves

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10
Q

What is the trigona fibrosi?

A

Part of cardiac skeleton, consists of right and left fibrous trigones. They are triangular islands of connective tissue which serve to strengthen the annuli fibrosi.
The right one has an opening for the bundle of His

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11
Q

What is the septum membranaceum?

A

An extension of the cardiac skeleton into the IV septum

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12
Q

What are the functions of the cardiac skeleton?

A
  1. Separate atrial from ventricular musculature
  2. Origin of cardiac muscle
  3. Localizes / stabilizes valves
  4. Limits valve diameter
  5. Prevents spread of electrical impulses except via the conducting system of heart
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13
Q

What are the three components of the heart wall?

A
  1. Epicardium (visceral layer of serous pericardium)
  2. Myocardium
  3. Endocardium
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14
Q

What makes up the epicardium and what is it analogous to? What its inner layer called?

A

Simple squamous epithelium called mesothelium associated with its basal lamina.
Epicardial connective tissue with collagen, elastic fibers, arteries, veins, nerves, and FAT

Analogous to tunica adventitia

Inner layer bordering the myocardium is sometimes called the subepicardium

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15
Q

What is found in the epicardium?

A

Coronary arteries, cardiac veins, and nerves that supply the heart. They are located in the connective tissue and are typically surrounded by adipose.

It is the only place of fat storage for the heart.

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16
Q

What is the myocardium and what is it analogous to?

A

Middle layer of heart wall containing cardiac muscles, analogous to the tunica media

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17
Q

What defines cardiac muscle cells?

A

One or two centrally located nuclei, packed with myofibrils and large mitochondria, connected to eachother via intercalated discs

18
Q

What are the components of the intercalated discs?

A
  1. Fascia adherens (FA) - connect two cells and anchor actin filaments in each cell
  2. Desmosomes - connect two cells via intermediate filaments desmin and vimentin
  3. Gap junctions - ionic communication and coupling between cardiac muscle cells
19
Q

How does myocardial thickness vary between atria and ventricles?

A

Atrial myocardium is thinner than ventricular, since it only needs to provide the force to open the AV valves to let blood in.

Left ventricle myocardium is 3x thicker than right ventricle

20
Q

How do atrial myocardial cells differ from ventricular?

A

They are smaller than ventricular. They thus have less elaborate T-tubule system, but more gap junctions (perhaps for electrical communication)

Also, they produce, store, and secrete ANF

21
Q

What is ANF and its function?

A

Atrial natriuretic factor. It is stored in electron dense granules in atrial cardiomyocytes and released into surrounding continuous capillaries.

Target: Adrenal cortex, kidney, and vascular smooth muscle

Function: Decreases arterial blood pressure by stimulating kidney to secrete Na+, and regulates fluid balance / electrolyte balance

22
Q

How are muscle cells / fibers arranged in the ventricular wall?

A

Arranged into complex spiral / helical patterns called trabeculae carneae

23
Q

What are papillary muscles?

A

Fingerlike projections from the ventricular wall into the lumen of the ventricle, which hold onto the chordae tendineae

24
Q

How are muscle cells / fibers arranged in the atrial wall?

A

In a latticework that gives a ridged appearance known as the pectinate musculature

25
Q

What is the endocardium and what is it analogous to?

A

Internal layer of heart wall, borders anything that touches blood. It is analogous to the tunica intima of blood vessels

26
Q

What does the endocardium consist of?

A
  1. Endothelium - Simple squamous + basal lamina
  2. Endocardial connective tissue - fibroblasts, collagen, elastic fibers, smooth muscle.
    - >3. Subendocardial layer - deepest layer of endocardial connective tissue, where it connects to myocardium
27
Q

What is the path of the conduction system in the heart?

A

SA node (pacemaker under sympathetic control) -> atrial muscle and internodal fibers -> AV node -> Bundle of His -> left and right bundle branches -> Purkinje fibers (very fast, 4 m/s) -> gap junctions in ventricular cardiac muscles stimualte others

28
Q

What is an EKG / ECG?

A

Electrocardiogram - voltage trace of depolarization in heart can be traced via PQRS waves

29
Q

Where are SA nodal cells and what is their function?

A

Located in the wall of the right atrium close to the SVC, often surrounding a branch of the coronary artery.

They are the pacemaker cells which initiate the contraction of the heart, which spreads along the tracts of modified cardiac muscle fibers (internodal fibers) to AV node

30
Q

How do SA nodal cells look like histologically?

A

They are modified cardiac muscle cells which are spindle-shaped and smaller than normal cardiac muscle cells since they are not contracticle. They are fewer in number and less organized than cardiomyocytes. Also have less developed intercalated discs: only the gap junctions are developed

31
Q

Where are AV nodal cells and what is their function?

A

Located in the floor of the right atrium just above the tricuspid valve. They function to delay the impulse to allow ventricular filling, and then pass the impulse to the Bundle of His

32
Q

How do AV nodal cells look like histologically?

A

They are small, pale-staining cells isolated by connective tissue, similar to SA nodes. They are roughly spindle-shaped and form a reticular meshwork, with poorly developed intercalated discs.

33
Q

Where do the AV bundle / bundle of His fibers run?

A

Run from AV node to the IV septum, traversing the right fibrous trigone of the cardiac skeleton and runs along margin of septum membranaceum. It will divide here into the left and right bundle branches.

34
Q

Where do the left and right bundle branches run?

A

They terminate in the connective tissue between the endocardium and myocardium, often called the subendocardium. They connect here to the bundle of His.

35
Q

How do cells of the bundles appear?

A

Larger than nodal cells, but still have fewer myofibrils than typical cardiac muscle cells since they are not contractile.

36
Q

Where are Purkinje fibers located and what is their function?

A

Located in subendocardial connective tissue of ventricular endocardium.
Function: Transmit impulses to a subset of cardiac muscle cells at the endocardium / myocardium interface. These will transmit the electric signal through the intercalated discs

37
Q

What are the characteristics of Purkinje fibers histologically?

A

They are larger than normal cardiac muscle cells, and have a large amount of glycogen inclusions. Cells and nuclei are more rounded in appearance.

  • > Glycogen inclusions, staining pale with vacuoles
  • > Lack T-tubules entirely, but contain few myofibrils
  • > Less developed intercalated discs
38
Q

What is the structure of valves?

A

Fibrosa - core of dense irregular connective tissue, continous with annuli fibrosi of the cardiac skeleton.

Endocardium - covers the free atrial and ventricular surfaces.

39
Q

What are the chordae tendineae made of and what is their function?

A

They are attached to the AV valves and held by papillary muscles.

Made of dense REGULAR connective tissue, like a tendon.

Function to prevent eversion of valve leaflets during ventricular contraction

40
Q

Where is the endocardium thicker, the atrium or the ventricle?

A

The atrium. It is relatively thin all around the ventricle, except it gets slightly thicker wherever there are Purkinje fibers

Histology / Embryology Unit 3 (9 decks)

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