Histology- Blood and Nerves

Question 1

General structure of blood vessels:

Answer 1

LUMEN: the channel through which blood flows

This is bounded by a layer of squamous endolthelial cells which rest on a basement membrane

The basement membrane is surrounded by a layer of loose connective tissue called the intima

The intima is bound by a layer of elastic tissue called the Internal elastic lamina.

MEDIA OF BLOOD VESSEL: Around the internal elastic lamina there is a thick layer of connective tissue generally made up of smooth mucle with some fibroblasts and variable amounts of collagen and elastin
The media of a blood vessel is surrounded by another layer of elastic tissue called the external elastic lamina

ADVENTITIA: A layer of loose connective tissue

Question 2

Elastic Arteries

Answer 2

Large arteries near the heart. e.g. aorta, pulmonary artery

Question 3

Structure of elastic arteries

Answer 3

Have a layer of vascular endothelial cells resting on a basement membrane underneath which there is a layer of loose finrous connective tissue, the intima

There is then an internal elastic lamina, followed by the media

Question 4

Structure of Muscular arteries:

Answer 4

Most arteries are muscular arteries

They still have a lumen, an intima lined on its inner surface by vascular endothelial cells resting on a basement membrane, underneath which there is an intima of loose fibrous connecrive tissue and then a muscular media

Media comprises concentric layers of smooth muscle
The media is bounded by an internal and external elastic lamina

The entire vessel is surrounded by a layer of loose connective tissue, the adventitia.

Little elastin still found in the media

examples; radial artery and splenic artery

Question 5

Arterioles

Answer 5

Arterioles are the resistance vessels of the circulation

Question 6

What is the distinction between a muscular artery and an arteriole?

Answer 6

Arbitrarily

Question 7

Define arbitrarily

Answer 7

Defined as a vessel having 3 or fewer muscle layers in their media

Also defined as an artery that is less than 100 microns in diametre

Question 8

Staining and seeing elastic laminae in arteriole

Answer 8

with special stains it can be seen that elastic laminae in arterioles are generally poorly defined

Question 9

Structure of capillaries

Answer 9

Capillaries do not have an adventitia and external lamina or media or internal elastic lamina or intima.

They are made up of only a layer of vascular endothelial cells resting on the inside of a basement membrane

Question 10

How is the size of the capillaries regulated?

Answer 10

The vascular channels are contricted or relaxed in order to regulate capillary size.

This is achieved by a layer of cells that are present on the outside of capillaries. These are the pericytes

Question 11

Structure of pericytes:

Answer 11

In the smallest capillaries the pericytes form a discontinous layer on the outside of the capillary which becomes continous as the capillaries get larger.

Question 12

Fenestrated capillaries

Answer 12

In some capillaries, the vascular endolthelial layer is incomplete, forming windows that facilitate the movement of materials out of the circulation and into surrounding tissues.

Such capillaries are found in the tissues of kidney and liver

Question 13

Histologic structure of capillaries

Answer 13

Composed entirely of thin-walled endothelial cells resting on a basement membarne, with no surrounding muscle or connective tissue

Most tissues have closed capillaries. The layer of vascular endothelial cells is complete.

But in some tissues the endothelial layer is incomplete, creating more “leaky” fenestrated ones

Question 14

Structure of veins

Answer 14

There is no external elastic lamina

Arteries and arterioles have a thicker muscular wall and a smaller lumen than their corresponding veins and venules

In veins, the lumen is larger and the media is thinner

Question 15

Venules

Answer 15

Found associated with arterioles

Thin walled vessels

The contractile pericytes found along capillaries form continual layer around the venules first and as the venules get larger these cells are replaced by a muscular smooth muscle media

Question 16

Veins

Answer 16

In larger veins the media becomes thicker (compared to venules)
Still thinner that the corresponding artery

Smooth muscle in the wall of a large vein, such as the inferior vena cava, may be circular around the vein or in a longitudanal orientation

Question 17

Lymphatics

Answer 17

Thin walled, similar to capillaries and veins

Have valves

Do not contain blood- contain lymph (fluid found in blood plasma)

Red blood cells are not found in lymphatics but some blood cells (lymphocytes) will be found here
Lymphocytes do not primaliry travel around the body through the lymphatics, they circulate in the blood

Contains eosinophilic lymph and may contain lymphocytes

Question 18

Peripheral nerves

Answer 18

Composed of axons

Axons are the bulk of the peripheral nerve

Axons are supported by schwann cells

Most have myelinated axons- acts as an insulating sheath

Myelin is produced by the schwann cells

Peripheral nerves are also made of connctive tissue that binds individual axons together to form fascicles, and binds fascicles together to form nerve fibres

Question 19

Myelinated peripheral nerve

Answer 19

The white circles are the axons which do not stain readily with H or E

The thin circles are the myelin sheath

On good notes

Question 20

Small neuro-vascular bundle

Answer 20

nerve

arteriole

venule

Question 21

Myelin

Answer 21

Does not stain readily with H&E but can be more easily seen with silver stains

Myelin insulates axons

Formed from a spiral of apposed schwann cell membranes

An individual schwann cell wraps itself around part of an individual axon multiple times to produce the myelin layer.
Multiple schwann cells per myelinated axon. One axon per schwann cell

This means when multiple

Question 22

role of schwann cells

Answer 22

Both myelinated and unmyelinated axons are supported by schwann cells

Schwann cells support one or more axons and produce myelin in some cases

Question 23

Difference between myelinated and unmyelinated axons

Answer 23

Myelinated axons are larger and transmit impulses faster than unmyelinated ones

When an axon is myelinated at any given point along the axon, there is a single axon related to a single schwann cell

In contrast in an unmyelinated fibre or axon there are multiple axons associated with a single schwann cell at any one point.

Question 24

How do neurones convey information?

Answer 24

Partly through the conduction of electrical impulses and then by the relase of neurochemicals at synapses which form junctions between adjacent neurones or between neurones and effector organs

Question 25

Where are motor neurons found in peripheral nerves?

Answer 25

cell bodies in grey matter of spinal cord

Question 26

Where are Sensory neurons found in peripheral nerves?

Answer 26

Cell bodies in dorsal root ganglion

Question 27

Where are sympathetic neurons found in the peripheral nerves?

Answer 27

Cell bldies in grey matter of cord AND in adjacent sympathetic ganglia

Question 28

Where are parasympathetic neurons found in peripheral nerves

Answer 28

Cell bodies in brain and local ganglia