Heart

Question 1

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

Answer 1

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

Question 2

What are the two layers of the serous pericardium?

Answer 2

1. Parietal layer - adjacent to fibrous pericardium

2. Visceral layer - adjacent to myocardium also called epicardium

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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

Question 5

What is pericarditis?

Answer 5

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

Question 6

What is pericardial effusion?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What are the three components of the cardiac skeleton?

Answer 8

1. Annuli fibrosi
2. Trigona fibrosi
3. Septum membranaceum

Question 9

What is the annuli fibrosi?

Answer 9

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

Question 10

What is the trigona fibrosi?

Answer 10

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

Question 11

What is the septum membranaceum?

Answer 11

An extension of the cardiac skeleton into the IV septum

Question 12

What are the functions of the cardiac skeleton?

Answer 12

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

Question 13

What are the three components of the heart wall?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What is found in the epicardium?

Answer 15

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.

Question 16

What is the myocardium and what is it analogous to?

Answer 16

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

Question 17

What defines cardiac muscle cells?

Answer 17

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

Question 18

What are the components of the intercalated discs?

Answer 18

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

Question 19

How does myocardial thickness vary between atria and ventricles?

Answer 19

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

Question 20

How do atrial myocardial cells differ from ventricular?

Answer 20

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

Question 21

What is ANF and its function?

Answer 21

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

Question 22

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

Answer 22

Arranged into complex spiral / helical patterns called trabeculae carneae

Question 23

What are papillary muscles?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

What is the endocardium and what is it analogous to?

Answer 25

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

Question 26

What does the endocardium consist of?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

What is an EKG / ECG?

Answer 28

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

Question 29

Where are SA nodal cells and what is their function?

Answer 29

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

Question 30

How do SA nodal cells look like histologically?

Answer 30

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

Question 31

Where are AV nodal cells and what is their function?

Answer 31

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

Question 32

How do AV nodal cells look like histologically?

Answer 32

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.

Question 33

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

Answer 33

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.

Question 34

Where do the left and right bundle branches run?

Answer 34

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

Question 35

How do cells of the bundles appear?

Answer 35

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

Question 36

Where are Purkinje fibers located and what is their function?

Answer 36

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

Question 37

What are the characteristics of Purkinje fibers histologically?

Answer 37

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

Question 38

What is the structure of valves?

Answer 38

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

Endocardium - covers the free atrial and ventricular surfaces.

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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