Histology of the Circulatory system

Question 1

Name the 2 division of the circulatory system

Answer 1

• Cardiovascular system

- Lymphatic system

Question 2

List the roles of the cardiovascular system

Answer 2

• Transporting nutrients and oxygen to tissues
• Transporting CO2 and waste away from tissues
• Temperature regulation
• Distribution of hormones
  and immune cells
• Reproductive function (penile erection)

Question 3

List the 3 layers of a blood vessel and describe their layering

Answer 3

• Tunica intima (innermost)
• Tunic media (middle)
• Tunica adventitia (outermost)

Question 4

Describe the tunica intima

Answer 4

Innermost layer

Consists of:

• Single layer of squamous epithelial cells (endothelial cells)
• Supported by a basal lamina
• Thin layer of connective tissue (internal elastic lamina)

Question 5

Describe the tunica media

Answer 5

Middle layer

The layers thickness varies greatly in different vessel types

Consists of:

• Mainly smooth muscle
• Some elastic fibres (external elastic lamina)
• Can have lots of elastic fibres (e.g. elastic arteries)

Question 6

Describe the tunica adventitia

Answer 6

Outer layer

Consists of:
- supporting connective tissue

Question 7

Describe the:

• Internal elastic lamina (membrane)
• External elastic lamina (membrane)

Answer 7

Internal elastic lamina (membrane):

• outermost bit of the tunica intima
• separates the intima from the media

External elastic lamina (membrane):

• outermost bit of the tunica media
• separates the media from the adventitia

Question 8

Describe elastic arteries

Answer 8

The largest arteries (e.g. aorta)

• Have many sheets of elastic fibres in their tunic media
• These provide elastic recoil, maintaining MAP during diastole

Question 9

Describe arterioles

Answer 9

Only have 1 or 2 layers of smooth muscle in their tunica media

Have almost no tunica adventitia

Question 10

Describe capillaries

Answer 10

Consist of:

• Endothelial cells
• Basal lamina
• Pericytes

Question 11

Describe a pericyte

Answer 11

• Connective tissue cells
• Wrap around the outside of the basal lamina
• Have contractile properties

Question 12

List the 3 types of capillary

Answer 12

• Continuous
• Fenestrated
• Discontinuous (sinusoidal)

Question 13

Describe continuous capillaries

Where are they found?

Answer 13

• No gaps in endothelium
• Basal lamina complete
• Found in muscle, skin, lung, nervous and connective tissues

Question 14

Describe fenestrated capillaries

Where are they found?

Answer 14

• Small pores in endothelium
• Basal lamina complete
• Found in gut mucosa, endocrine glands, and kidney glomeruli

Question 15

Describe discontinuous (sinusoidal) capillaries

Where are they found?

Answer 15

• Large gaps in epithelium that macromolecules (sometimes cells) can fit through
• The basal lamina is discontinuous or absent
• Found in liver, spleen, and bone marrow

Question 16

Describe microvascular networks and their structure

Answer 16

Connect small arterioles with small venules

Made up of:

• Metarterioles
• Capillary bed
• Thoroughfare channels

Question 17

Describe metarterioles and their structure

Answer 17

Links arterioles with capillaries

• Has no continuous tunica media
• Has a precapillary sphincter

Question 18

Describe a precapillary sphincter and its structure

Answer 18

Individual smooth muscle cells (close together)

Found in metarterioles

Controles blood entrance to the capillary bed

Question 19

Describe the thoroughfare channels found in microvascular networks

Answer 19

A direct channel that connects a metarteriole to a venule

• has capillaries surrounding it

Question 20

Describe a postcapillary venule

Answer 20

Consist of:

• Endothelial lining
• Thin layer of connective tissue
• Pericytes (sometimes)

Capillary networks drain into post-capillary venules

(important site for diapedesis)

Question 21

Describe venules and their structure

Answer 21

Consist of:

• Endothelial lining
• Thin layer of connective tissue
• Pericytes (sometimes)
• Tunica media that contains myocytes

Question 22

Describe veins and their structure

Answer 22

Consist of:

• Tunica intima
• Tunica media (much thinner that that in arterioles)
• Tunica adventitia

Question 23

Describe the tunica adventitia found in the largest veins (e.g. vena cava)

Answer 23

Very thick

Bundles of longitudinal smooth muscle

Question 24

Describe the composition of venous valves

Answer 24

• In most small to medium sized veins

- Are extensions of the tunic intima

Question 25

List the 3 layers of the heart

Answer 25

Endocardium (inner) Myocardium (middle) Epicardium (outer)

Question 26

Describe the structure of the endocardium

Answer 26

``` Endothelium --> Basal lamina --> Thin layer of collagen fibres --> Denser layer of connective tissue ```

Question 27

Describe the subendocardium and its structure

Answer 27

In some areas there is also a subendocardium Consists of loose connective tissue containing: - small blood vessels - nerves - branches of the impulse conducting system (e.g. Purkinje fibres)

Question 28

Describe the structure of the myocardium

Answer 28

Thick central layer of heart - Bundles and layers of contractile muscle fibres - Individual fibres are surrounded by a collagenous connective tissue with capillaries

Question 29

Describe the surroundings of individual muscle fibres

Answer 29

each fibre is surrounded with a delicate collagenous connective tissue This supports a rich capillary network

Question 30

Describe the nuclei found in contractile cardiac myocytes

Answer 30

They have a small central nucleus (sometimes 2) Unlike skeletal myocytes

Question 31

Describe the intercalated discs between cardiac myocytes

Answer 31

Boundary between cardiac myocytes Have: - Gap junctions (for transmitting impulses) - Desmosomes (for attaching cells together) - Zonula adherens (for attaching cells together)

Question 32

Describe the contractile cardiac myocytes found in the myocardium

Answer 32

- Large cells - Uninucleate (sometimes 2 nuclei) - Some have branches - Attached via intercalated discs

Question 33

Describe the structure of the epicardium (serous visceral pericardium)

Answer 33

``` A single layer of simple squamous epithelium (mesothelium) --> basal lamina --> Fibroelastic connective tissue --> adipose tissue (in some places) ```

Question 34

Describe the structure of the pericardium

Answer 34

Fibrous pericardium: - Sac of fibrocollagenous connective tissue Serous pericardium: - single layer of simple squamous epithelium (mesothelium) - -> - basal lamina - -> - connective tissue

Question 35

In what layer of the heart do the coronary arteries and veins flow?

Answer 35

Epicardium In the adipose tissue deep to the mesothelium, basal lamina, and connective tissue

Question 36

Describe the fibrous skeleton of the heart

Answer 36

- Made of bands of connective tissue - Supports the valves - Electrically insulates the atria and ventricles - Supports myocardium

Question 37

Describe the histology of the heart valves

Answer 37

A core lamina fibrosa: - dense irregular connective tissue - is continuous with the fibrous skeleton The lamina fibrosa is covered on both sides by endothelium: ``` Endothelial layer --> Basal lamina --> Collagen and elastin fibres ```

Question 38

Is there a vascular supply to the heart valves?

Answer 38

No

Question 39

What do the chordae tendineae attach to?

Answer 39

on one side the papillary muscles on the other they merge with the lamina fibrosa of the valve

Question 40

List the 3 types of cardiac myocyte

Answer 40

- Contractile cardiac myocytes - Pacemaker cells - Conducting cells

Question 41

Describe pacemaker cells

Answer 41

- Much smaller than contractile cardiac myocytes - appear paler - very few myofibrils - Found in AV and SA nodes

Question 42

Describe Purkinje fibres

Answer 42

- Larger than contractile cardiac myocytes - In subendocardium - No intercalated discs - They are NOT nerves

Question 43

Describe lymph vessels

Answer 43

- This walled - Walls a bit like those of a vein - drain some of the ECF and return it to circulation - transport lymphatic fluid - passes through lymph nodes

Question 44

Describe what makes lymphatic fluid move

Answer 44

- Skeletal muscle movement | - pressure from incoming fluid