Lecture 4: Cardiac Histology

Question 1

What are some characteristics of smooth muscle?

• Type of cell
• Nucleus
• Striated or not?

Answer 1

• Elongated fusiform cells with tapered ends
• One elongated, nucleus that is located centrally
• Not striated

Question 2

How are cells in smooth muscle connected?

What does this permit?

Answer 2

They are connected by gap junctions, which allows them to contract at the same time with a low force.

Question 3

What controls the contractions of smooth muscle? (2)

Answer 3

1. Autonomic NS

2. Enteric NS

Question 4

How are the contractile filaments in smooth muscle organized?

Answer 4

Smooth muscle has thick and thin filaments (actin and myosin) that is anchored to cytoplasmic densities/dense bodies.

Tension is then transmitted from the densities–> membrane, allowing uniform contraction.

Question 5

Contractile elements (thick and thin filaments) in smooth muscle are connected to dense bodies/cytoplasmic bodies in smooth muscle. What are the dense bodies made up of?

Answer 5

1. Desmin
2. Vimentin intermediate filaments

Question 6

When the thin and thick filaments contract, it causes the fusiform cells to change shapes. Describe the change in shape.

Answer 6

Cells go from a thick body with tapered ends–> globular (ball like).

Question 7

What are some characteristics of cardiac muscle?

• What does it look like?
• Nucleus?
• What else can you find in the muscle? (3)

Answer 7

• Short, branched, Y shaped
• 1 or more nucleus that are more round
• Many capillaries, intercalated discs, purkinje cells

Question 8

What allows the passage of electrical currents in cardiac muscle?

Answer 8

Intercalated discs–> transverse junctions at the end of cells that allow currents to be passed from cell–> cell.

Question 9

Cardiac muscle consists of purkinje cells. What are they?

Answer 9

Purkinje cells are

modified cardiac muscle that act as the “pacemaker for the heart”.

They prevent cardiac muscle from tearing.

Question 10

What are the layers of pericardium of the heart?

Answer 10

Outermost–> innermost

1. Fibrous pericardium

2. Parietal serous pericardium

3. Visceral serous pericardium.

Question 11

What kind of tissue is the fibrous pericardium?

Answer 11

dense connective tissue.

Question 12

Visceral layer of the serous pericardium is also called what?

Answer 12

Epicardium.

It is the outer surface of the heart.

Question 13

What are the 3 layers of the heart wall?

Answer 13

1. Epicardium
2. Myocardium
3. Endocardium

Question 14

What are the characteristics of epicardium (visceral serous pericardium)?

Answer 14

• Outermost layer of the heart
• Dense CT with elastic fibers, lined with simple squamous epithelium (mesothelium).

+ Adipose tissue ( with coronary arteries embedded in it)

Question 15

What is mesothelium?

Answer 15

Simple squamous epithelium thiat is located in pericardium, pleura, peritoneum

Question 16

What cells are located in myocardium, the thiccest layer of the heart?

Answer 16

1. Cardiomyocytes (which are contractile)
2. Nodal cardomyocytes (these are purkinje cells, located in the SA and AV node)
3. Myoendocrine cardiomyocytes

Question 17

Myocardium is characterized by (6):

Answer 17

1. Striated

2. Intercalated discs

3. DYAD t-tubule system

4. mT

5. Lipofuscin granules

6. Atrial granules (myoendrocrine granules)

Question 18

Where are intercalated discs located?

Answer 18

In between 2 cardiomyocytes; always coincide with the Z-disk.

They always coincide with the Z disc.

Question 19

What are the components of the intercalated discs, interdigitating junctions located between cardiomyocytes?

Answer 19

The components of intercalated discs are organized into a transverse region and a longitudinal region.

Transverse region (percendicular to the length of the cell)

1. Fascia adherens

2. Desmosomes

Longitudinal region (parallel to the length of the cell)

3. Gap (nexus ) junctions

Question 20

Interacalated discs are made up of fascia adherens located in the transverse region of the cardiomyocyte. What are they?

Answer 20

Fascia adherens are most predominant contact, made up of actin filaments junctions, located at the end of the terminal sarcomere that help cells contract.

They transmit contractile forces between cells.

Question 21

Interacalated discs are made up of desmosomes located in the transverse region of the cardiomyocyte. What are they?

Answer 21

Desmosomes are where intermediate filaments anchor to the cytoskeleton

Question 22

Interacalated discs are made up of gap (nexus) junctions located in the longitudinal region of the cardiomyocyte. What are they?

Answer 22

Allows excitation to pass between cells.

They are sites of low electrical resistance.

Question 23

The mycardium is made up of dyad T-tubules. Describe these?

Answer 23

Dyad T-tubules= 1 T-tubule and 1 SR cisterna.

invaginations of the sarcolemma that are found at the Z-line. Thus, they allow uniform contraction within one cardiomyocyte

Question 24

Because the dyad T-tubules in myocardium located at the Z-line. What does this allow?

Answer 24

It allows the uniform contraction of myofibrils within one cardiomyocyte.

Question 25

Lipofuscin granules are located in the myocardium. What is their role?

Answer 25

Lipofuscin granules are small bodies that consist of material from residual bodies after they are ingested by lyosomes. They accumulate with age in stable, non-dividing cells.

Question 26

Myocardium contains atrial granules. What are atrial granules?

Answer 26

Atrial granules (myoendocrine cardiomyocytes) are atrial cardiomyocytes that contain membrane-bound granules that contains the PRECURSOR to **ANF (atrial natriuretic factor).**

Question 27

What is **atrial natriuretic factor (ANF)**?

Answer 27

**ANF** is released from atrial granules. It goes to the kidneys **decreases retention of H20 and Na+.**

Question 28

What is **endocardium** made up of?

Answer 28

**1. Endothelium** **2. Thin layer of loose CT**

Question 29

How does endocardium differ in the ventricles and atria?

Answer 29

Endocardium **differs in thickness** in the ventricles and atria. In the ventricles, it contains a **subendocardial layer**.

Question 30

The endocardium located in the \_\_\_\_\_\_\_\_\_, has a subendcardial layer.

Answer 30

ventricles.

Question 31

What is the subendocardial layer of endocardium in the ventricles look like?

Answer 31

- Thin layer of CT with smooth muscle, that has **purkinje fibers.**

Question 32

What does the **endocardium** in the **atria** look like?

Answer 32

Purkinje fibers are closer to the endothelium and intermixed with the myocardium.

Question 33

Describe the conducting system of the heart. Are intercalated discs present?

Answer 33

The conducting system is made up of **nodal cardiomyocytes**, innervated by the the parasympathetic and sympathetic NS. **Does not** have intercalated discs!

Question 34

What are nodal cardiomyocytes?

Answer 34

Modified cells located in the SA/AV node that initate and relay electrical signals.

Question 35

**T/F:** The parasympathetic NS and sympathetic NS only **MODIFIES** the intrisic cardiac muscle contraction.

Answer 35

**T**

Question 36

Conduction pathway of the heart:

Answer 36

**SA node --\> AV node--\> AV bundle (bundle of his)--\> LR bundle branches--\> purkinje fibers**

Question 37

Describe purkinje fibers. Where are they typically found?

Answer 37

- Fibers that conduct impulses - typically adjacent to endocardium and at the periphery of the myocardium. - do not have t-tubules.

Question 38

How can we distinguish purkinje fibers from myocardium?

Answer 38

- Cell is larger with LOOKS like it lacks nuclei. - less intercalated discs that myocardium - more rounded - located at the periphery of myocardium

Question 39

What is the cardiac skeleton

Answer 39

A fibrous skeleton with - 4 rings, one around each valve - 2 trigons, which connects the valves. - membranous portion of the septum

Question 40

What is the function of the **cardiac skeleton**?

Answer 40

1. Anchors the valves 2. Surrounds the AV canals to maintain shape 3. Makes the interventricular and interatrial septa, creating the electrical insulator between the atria and ventricle 4. Insertion point for cardiac muscle

Question 41

What kind of tissue is the cardiac skeleton and where is it located?

Answer 41

**-Dense irregular CT located in the endocardium**

Question 42

Describe the structure of heart valves.

Answer 42

Extensions of endocardium (**endothelium** located on both sides) with a **core of fibroelastic CT (lamina fibrosa**) that condenses --\> **valve ring**

Question 43

**Heart valves** are continous with the \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 43

**Cardiac skeleton.**