Heart Histology

Question 1

What is a pericardium?

Answer 1

A double-walled sac containing the heart and the roots of great vessels

Question 2

What are the 2 types of pericardium?

Answer 2

Fibrous pericardium

Serous pericardium

Question 3

What is the fibrous pericardium?

Answer 3

The tough, external fibrous layer

• made from thick connective tissue
• attached to the diaphragm

Question 4

What is the function of the fibrous pericardium?

Answer 4

To hold the heart in place in the chest cavity and protects from infections

Question 5

What 2 layers does the serous pericardium consist of?

Answer 5

Parietal pericardium

Visceral pericardium

Question 6

What is the parietal pericardium?

Answer 6

The serous membrane on the inside of the fibrous pericardium

Question 7

What is the visceral pericardium?

Answer 7

The serous membrane on the surface of the heart

Question 8

What is the function of the serous pericardium?

Answer 8

Helps to lubricate the heart which prevents friction

Question 9

What are the 3 layers to the heart?

Answer 9

Endocardium (inner)-thin layer
Myocardium (middle)-thick layer
Epicardium (outer)

Question 10

What does the endocardium consist of?

Answer 10

3 distinct layers:

• Inner endothelial layer- containing flat endothelial cells
• Middle subendothelial layer- containing regularly shaped collagen and elastic fibres
• Outer subendocardial layer (in some areas)- irregularly shaped collagen, and may contain elements of the cardiac conducting e.g purkinje fibres

Question 11

What are myofibroblasts?

Answer 11

Myofibroblasts are a differentiated cell type essential for wound healing, participating in tissue remodelling following insult

Question 12

What does the myocardium consist of?

Answer 12

Composed of cardiac muscle:

• myofibrils and sarcomeres
• central nucleus
• intercalated discs

Variable thickness ( thicker in ventricles as they need to contract)

Question 13

What is another name for the epicardium?

Answer 13

The visceral pericardium

Question 14

What does the epicardium consist of?

Answer 14

Flattened mesothelial cells
Vessels supplying the heart
Adipose tissue

Question 15

What is the significance of the heart having a fibrocartilagenous structure?

Answer 15

• Provides a solid structure for the muscle to contract against
• Means the atrial and ventricular sides of the heart are electrically isolated by the fibrous skeleton

Question 16

What are the features of cardiac muscle?

Answer 16

• Striated like skeletal muscle
• Single centrally placed nucleus
• Connected by intercalated discs to ensure electrical continuity

Question 17

What is the contractile mechanism of cardiac muscle?

Answer 17

Ca2+ binds to troponin and exposes myosin-binding site on actin

Question 18

What is the name of the contractile unit within cardiac (and skeletal) muscle?

Answer 18

Sarcomere

Question 19

What is the structure of a sarcomere?

Answer 19

Composed of 2 main protein filaments, actin and myosin. These are the structures responsible for muscular contraction.

Question 20

What is the sliding filament theory?

Answer 20

The sliding filament theory explains the mechanism of muscle contraction.
The theory explains how myosin binds to actin, and the myosin then alters its configuration, resulting in a ‘stroke’ that pulls the actin filament causing it to slide across the myosin filament

Question 21

How is filament sliding a Ca2+ dependant process?

Answer 21

As the binding of Ca2+ facilitates the myosin and actin-binding

Question 22

What 3 structures bind together adjacent cardiac myocytes?

Answer 22

Desmosomes
Adherens junctions
Gap junctions

Question 23

What is the function of the structures binding adjacent cardiac myocytes together?

Answer 23

The arrangement of structures increase the transmission of electrical impulses as there is a direct connection between the cells
As well as increasing structural strength and integrity

Question 24

What is a desmosome?

Answer 24

A desmosome is a cell structure specialised for cell to cell adhesion

• a type of anchoring junction
• Intermediate filaments of each cell connect to a plaque containing transmembrane proteins. These transmembrane proteins attach 2 adjacent cell surfaces

Question 25

What is an adherens junction?

Answer 25

Type of anchoring junction which connects adjacent cell surfaces
-Actin filaments of each cell connect via proteins to adjacent cells

Question 26

What are gap junctions?

Answer 26

A type of junction associated with communication

• contain intercellular channels for passage of ions
• as ions can flow through the gaps, it permits changes in membrane potential to pass from cell to cell

Question 27

What is meant by functional syncytium?

Answer 27

It is the term used to describe how the entire myocardium behaves as a single unit
-due to all the cardiac myocytes being electrically coupled via the gap junctions