Cardiovascular Histology

Question 1

What are the layers of the heart and blood vessels?

Answer 1

Endocardium = T. intima (endothelium, BM, CT).
Myocardium = T. media (muscle, elastic tissue).
Epicardium = T. external / adventitia (fibrous CT).
The epicardium has epithelium.

Question 2

What is the endocardium?

Answer 2

Lines the heart chambers.
SImple squamous epithelium sitting on BM, which sits on CT.
Forms valves.

Question 3

What is the myocardium?

Answer 3

The thick middle layer of the heart wall.
Arranged in a spiral around a fibrous CT skeleton.
Has a rich capillary bed.
Has myocytes - forms branching fibres, connected by intercalated discs.
Striated muscle with lots of mitochondria and a single central nucleus.

Question 4

What is the epicardium?

Answer 4

The outer layer of the heart wall.
A visceral layer of serous pericardium.
Contains main branches of coronary arteries.
May be fatty.

Question 5

What are capillaries?

Answer 5

The main exchange site for nutrients and gases.
A very thin T. intima.
No T. media or T. adventitia.

Question 6

What are pericytes?

Answer 6

Incomplete cell layers that surround capillaries.
Has contractile properties that control BP.

Question 7

What are continuous capillaries?

Answer 7

Controls what is exchanged via junctions.
Material must pass through or between the cell.
Selective transport mechanisms.
Found in muscle.

Question 8

What are fenestrated capillaries?

Answer 8

Has pores.
Diaphragms filter molecules by weight and charge.
Found in endocrine glands and renal corpuscles.

Question 9

What are discontinuous capillaries?

Answer 9

Has gaps between the endothelial cells and BM that allow for free passage of fluid and cells.
Found in the liver, spleen, and bone marrow.

Question 10

What are sinusoids?

Answer 10

Large diameter type of discontinuous capillaries.
Where a lot of exchange occurs (liver).
T. intima - contains phagocytes.

Question 11

What are AV shunts?

Answer 11

Bypasses capillary beds.
Found in the skin for thermoregulation.

Question 12

What are the differences between arteries and veins?

Answer 12

A - thick muscle wall, small lumen, thin adventitia, no valves.
V - thin muscle wall, large lumen, thick adventitia, valves (endothelial projections).

Question 13

What are elastic arteries?

Answer 13

Large and conducting.
A pressure reservoir.
Aorta, common carotid, pulmonary.

Question 14

How is the structure of elastic arteries related to its function?

Answer 14

Extensive amounts of elastic fibres in the T. media are in the form of layers (laminae). Secreted by smooth muscle cells.

Question 15

What happens to elastic arteries in systole and diastole?

Answer 15

Systole - stretches.
Diastole - recoils when the heart relaxes and pressure falls, maintains pressure on the blood.

Question 16

What are muscular arteries?

Answer 16

Controls the distribution of blood.
Coronary, radial, femoral.
Thick T. media, due to smooth muscle cells (no elastic laminae).

Question 17

How are elastic fibres concentrated in muscular arteries?

Answer 17

Two well-defined sheets.
Internal elastic lamina - under epithelium.
External elastic lamina - thin, between T. media and T. externa.

Question 18

What are arterioles?

Answer 18

From smaller muscular arteries.
Controls systemic BP and local blood flow to capillary beds.
Has a rich sympathetic nerve innervation.
Only 1-2 layers of smooth muscle in T. media.
No IEL, OEL, or T. adventitia.

Question 19

What are veins and venules?

Answer 19

Thin tunica layers.
Folds of T. intima form valves.
Larger and less rounded lumen than arteries.

Question 20

What are superficial veins?

Answer 20

Thick walled.
No surrounding support.
Drains into deep veins.

Question 21

What are deep veins?

Answer 21

Thin walled.
Has surrounding support from deep fascia and muscles.

Question 22

What is the lymphatic system?

Answer 22

Drains tissue fluid lost from blood capillaries.
Drains into the systemic venous system.
Valves direct flow.

Question 23

What are lymphatic capillaries?

Answer 23

Blind-ended.
Lined by thin endothelium.
Anchoring filaments - fine collagenous filaments that link endothelial cells to surrounding tissue, keeping lumens open.
No RBCs.

Question 24

What supply do blood vessels get?

Answer 24

Sympathetic and parasympathetic fibres.
Blood supply from vasa vasorum.
Lymphatics (T. adventitia).

Question 25

What is the histology of the heart and blood vessels?

Answer 25

Similar histology - the heart is just an expanded, partitioned, folded, muscular blood vessel.