Histology

Question 1

What is the role of the heart?

Answer 1

1. Transport of oxygen and nutrients to the tissues.
2. Transport of CO2 and other metabolic waste from the tissues.
3. Temperature regulation.
4. Distribution of hormones and immune cells.
5. Reproductive function in males: penile erection

Question 2

What are the three basic layers of the blood vessels?

Answer 2

1. Tunica intima - single layer of squamous epithelial cells (endothelial cells) supported by basal lamina. has connected tissue
2. Tunica media - made up of mainly smooth muscle
3. Tunica adventitia - made up of supporting tissue

Question 3

How are the three basic layers of blood vessels separated?

ii. how can they be stained?

Answer 3

1. The tunica intima is separated from the tunica media by a layer of elastic tissue called the internal elastic membrane.
2. The tunica media is separated from the tunica adventitia by a layer of elastic tissue called the external elastic membrane.
   ii. Elastic fibres are not stained using most common stains (including H&E) but can be visualized with special stains

Question 4

What are the largest arteries known as?

ii. why?

Answer 4

elastic artery

ii. has many sheets of elastic fibres.

Question 5

What is the typical diameter for arterioles?

Answer 5

20 to 300 micrometers

Question 6

What are the types of capillaries?

Answer 6

1. Continuous capillaries are the more common. Found: muscle, connective tissue, lung, skin, nerve.
2. Fenestrated capillaries have ~50nm pores in wall. Found: mucosa of the gut, endocrine glands, glomeruli of the kidney.
3. Sinusoidal or Discontinuous capillaries have large gaps through which macromolecules, and in some cases even cells, can pass; the basal lamina is discontinuous or even absent. Found: liver, spleen and bone marrow.

Question 7

What do capillaries consist of?

ii. What is its typical diameter?

Answer 7

endothelial cells and basal lamina

ii. 4-8 micrometer

Question 8

Define what perictyes are.

ii. where are they found?

Answer 8

These are connective tissue cells that have contractile properties

ii. in capillary intervals just outside the basal lamina

Question 9

How do arterioles connect to post capillary venules?

Answer 9

via metarterioles, thoroughfare channels and capillaries

Question 10

What is the role of precapillary sphincters

Answer 10

composed of smooth muscle, at the beginning of the capillary help control flow through the network

Question 11

What is the typical diameter of a post capillary venule.

ii. what do they consist of?

Answer 11

10-30µm diameter

ii. which are endothelial cell-lined and contain a thin layer of connective tissue and occasional pericytes

Question 12

When does a post capillary venule get classified as a venule?

Answer 12

Once the vessel begins to acquire intermittent smooth muscle cells in a tunica media layer, they are referred to as venules (generally >50µm).

Question 13

Describe the characteristics of veins.

Answer 13

in addition to the tunica intima, have a relatively thin but continuous tunica media typically consisting of a few layers of smooth muscle. The tunica media is markedly thinner than would be found in a muscular artery.

The largest veins (e.g. vena cava or hepatic portal vein) have a thick tunica adventitia which incorporates bundles of longitudinally oriented smooth muscle.

Veins are flexible and can accommodate expansion and thus contain most of the blood in the body.

Most small to medium sized veins have valves that are inward extensions of the tunica intima.

Question 14

What are the three layers which make up the heart?

Answer 14

Endocardium: inner layer

Myocardium: middle layer

Epicardium: outer layer

Question 15

Describe the structure of the endocardium.

Answer 15

1. Endothelium
2. Basal lamina
3. Thin layer of collagen fibres
4. Layer of denser connective tissue
5. In some areas there is also a subendocardium of loose connective tissue containing small blood vessels and nerves and the branches of the impulse conducting system.

Question 16

Describe the structure of the myocardium

Answer 16

1. Bundles and layers of contractile cardiac muscle fibres.
2. Individual muscle fibres are surrounded by delicate, collagenous connective tissue with a rich network of capillaries.

Question 17

Cardiac muscles sometimes have 2 nucleus and not always just one true or false?

Answer 17

true.

Question 18

What is the role of the intercalated disks?

Answer 18

to attach fascia adherens and desmosomes to allow joining of cells.

Allow for passing of electrical activity.

Question 19

Describe the structure of the epicardium

Answer 19

1. On the surface of the heart: A single layer of flattened epithelium called mesothelium.
2. Basal lamina
3. Fibroelastic connective tissue and, in some places, adipose tissue.

Question 20

What are the two types of pericardium?

Answer 20

Fibrous pericardium is a sac of tough fibrocollagenous connective tissue.

Serous pericardium is made up of a layer of simple squamous epithelium (termed mesothelium), backed by a basal lamina and connective tissue.

Question 21

what is the role of the ‘fibrous skeleton’ in the heart?

ii. what is it made of?

Answer 21

This connective tissue supports the valves, but also provides the attachment for the cardiac muscle fibres.

ii. The heart has a fibrous ‘skeleton’ formed by thick bands of fibrous connective tissue around the heart valves, between the atria, and between the ventricles.

Question 22

What is the structure of the valves?

Answer 22

Have an outer endothelial layer with basal lamina.

Layer of collagen and elastin fibres.
A core of dense connective tissue, called the lamina fibrosa, that is in continuity with the fibrous skeleton.

The leaflets of the valves separating the atria from the ventricles (the mitral and tricuspid) are anchored to papillary muscles in the wall of the ventricle by collagenous strands called the chordae tendineae, which merge with the lamina fibrosa.

There are no blood vessels in the valves.