Wandering Cells在线视频

Hello, everyone,

welcome to the world of Clinical Histology.

We will divide this chapter into four sessions :

wandering cells，

fibers and ground matrix, cartilage & bone,

and the last one is blood and hematopoiesis.

They all originate from embryonic mesenchyme,

a tissue derived mainly from the middle layer

of the embryo, the mesoderm.

This session will focus on wandering cells.

What we need to learn during this session

is that connective tissue consists of cells,

fibers and matrix.

The dominating component among these three

dictates the type of connective tissue.

The sorts of fibers in connective tissue

and also the nature of the matrix will help you learn

how connective tissues become very specialized

in very different parts of the body.

There are also lots of cell types in connective tissue,

some of which are resident cells.

Other are cells which wander in from the blood.

Today I will discuss those that are resident

in the connective tissue,

and the cells that wander in from blood.

We will also talk about their functions.

In the last session,

we mentioned that there are no blood vessels

in the epithelial tissue.

Then, what supports its metabolism ?

This diagram shows connective tissue

that underlies the epithelial layer.

Here, connective tissue produces interstitial fluid

that serve as the medium for diffusion of nutrients

and waste products.

Connective tissue is every where in the human body.

Bacteria and other pathogens travel along

connective tissue channels and cause

damage to our organs and tissues.

Consequently,

connective tissue is also where the immune

and inflammatory responses occur in the body.

There are 7 types of cells in connective tissue.

Some of these cells are resident cells,

including fibroblasts, adipocytes,

and mesenchymal cells.

Other cells, for instance,

macrophages, plasma cells,

mast cells

and leukocytes wander in from the blood.

Here,

I'll share with you a story about 18-year-old Huqi.

She had allergic rhinitis.

'Allergic' means it is caused by 'allergens'.

Allergens are harmless (or neutral) substances

that can trigger an

excessive immune reaction

in an individual after contact.

Huqi was fine during her first contact with flowers.

But the second time

she smelled and touched it,

she experienced a serious runny nose

and developed a rash on her skin.

The rash

was so itchy that she could not help scratching.

Pollen from flowers is a common allergen.

Let's look at the details of the

cells involved in this process.

Once inside the nose an allergen

will meet members of the immune system

particularly mast cells attached to IgE antibodies.

Allergen will bind to these antibodies,

which will then activate and alert mast cells.

In a person without allergy,

the reaction is minimal,

but in those suffering from allergic rhinitis,

this response is exaggerated.

It signals to all cells

in the surrounding

environment by releasing 'histamine'.

Histamine will now cause inflammation

and swelling of the nasal mucosa,

with excessive mucus production.

The first time Huqi was exposed to the pollen,

plasma cells in the nasal mucosa received

this message and produced IgE.

Plasma cells are derived from B lymphocytes

and are responsible for the synthesis of

immunoglobulin antibodies.

each antibody is specific for one antigen

that originally stimulated a clone of B cells and reacts

only with that antigen or molecules resembling it.

These relatively large,

ovoid plasma cells have basophilic cytoplasm rich

in RER and a large Golgi apparatus near the nucleus,

which may appear pale in routine

histologic preparations.

Then the antibodies will be captured

by a mast cell with specific receptors

express on the cell surface.

Mast cells are oval or irregularly shaped cells

of connective tissue,

filled with basophilic secretory granules,

which often obscure the central nucleus.

The granules are poorly preserved by common fixatives,

so that mast cells may be difficult to identify

in routinely prepared slides.

Mast cells function through the release of many

bioactive substances important

in the local inflammatory response,

innate immunity, and tissue repair.

Some of these molecules produced

by mast cell secretory granules include the following:

Heparin, a sulfated glycosaminoglycan

that acts locally as anticoagulant

Histamine, which promotes increased

vascular permeability and smooth muscle contraction

Serine proteases, which activate

various inflammatory mediators

Eosinophil and neutrophil chemotactic factors,

which attract leukocytes.

When the allergic reaction combines with

bacteria-mediated inflammation,

the leukocytes and macrophages

will be attracted and wander to this site.

There are 3 types of leukocytes in connective tissue.

Neutrophilic leukocytes participate

in this process and phagocytose bacteria.

Eosinophils modulate allergic reactions,

and lymphocytes also exert defense functions.

Macrophages have highly developed

phagocytic ability

and specialize in turnover of protein fibers

and removal of dead cells,

tissue debris,

or other particulate material,

being especially abundant at sites of inflammation.

In connective tissue,

cells are arranged separately in the loose,

water-based environment.

When the body senses imminent danger,

cells would start their protective actions.

For example,

plasma cells will produce antibodies

to which mast cells will bind.

The mast cells will prepare specific

substances with protective functions.

Leukocytes and macrophages can also

kill or remove the harmful materials.

That's all for this session,

thank you!