Fibers and Ground Substances在线视频

Hello, everyone,

welcome to the world of Clinical Histology.

In the last session,

we talked about the wandering cells

in connective tissue.

These cells live in a basic water environment.

which contains three types of fibers

and cellular matrix,

that is the ground substance.

There are different fibers

in connective specialized tissue.

It is important that you understand

when these fibers are needed,

what their structural specifications are,

and therefore what roles are they have

in various connective tissues.

Connective tissue is an abundant supportive tissue

found throughout the body.

It provides structural support to organs

and connects tissues together like tape.

There are three main types of fibers include collagen,

reticular, and elastic fibers in the connective tissue

that you should be familiar with.

Let's discuss collagen fiber first.

Collagen is the most abundant protein

in the human body,

representing 30% of its dry weight.

A major product of fibroblasts,

collagens are also secreted

by several other cell types

and are distinguishable

by their molecular compositions,

morphologic characteristics,

distribution, functions, and pathologies.

A family of 28 collagens exists in vertebrates.

They can be grouped into the following categories

according to the structures formed

by their interacting subunits as the slide shows.

Fibroblasts are targets of many families

of proteins called growth factors

that influence cell growth and differentiation.

In adults,

connective tissue fibroblasts rarely undergo division.

However,

upon stimulation by locally released growth factors,

cell cycling and mitotic activity resume

when the tissue requires additional fibroblasts,

for example,

to repair a damaged organ.

Fibroblasts involved in wound healing,

sometimes called myofibroblasts,

have a well-developed contractile function

and express a form of actin (α-smooth muscle actin)

also found in smooth muscle cells.

Okay, let's look at this case:

a 71-year-old man is brought

to the emergency department

by his daughter due to tender gums

and bruising over his legs.

He has lived alone for the past two years

after his wife passed away.

He has been struggling with depression

and finds little pleasure in eating.

He mostly eats meat, bread and dessert.

The doctor suspects a nutritional deficiency

resulting in impaired synthesis

of an important molecule.

Which nutrient is lacking

and what molecule cannot be synthesized ?

Hopefully you know that the case

description is consistent

with scurvy or vitamin C deficiency.

Vitamin C is a cofactor for these hydroxylation reactions,

which means that patients

who are deficient in vitamin C

may have impaired collagen synthesis.

Vitamin C comes from our diet,

mainly fruits and vegetables.

Lack of vitamin C causes decreased

production of collagen

and hence weaker connective tissues.

As a result,

these patients have poor wound healing

and commonly present with swollen gums and bruising.

The collagens constitute a family of proteins selected

during evolution for their ability

to form various extracellular fibers,

sheets, and networks,

all of which are extremely strong

and resistant to normal shearing

and tearing forces.

Collagen is a key element of all connective tissues,

as well as epithelial basement membranes

and the external laminas of muscle and nerve cells.

Okay let's move on and discuss the elastic fibers.

This is a diagram of elastin synthesis.

Please note that elastin is synthesized

in a very similar way to collagen.

One difference is that elastin relies

on a scaffold of microfibril molecules

which you can see right here.

Fibrillin-1 is a component of the microfibrils

and defects in fibrillin-1 can result

in a disorder called Marfan syndrome

which we'll discuss in a minute.

The main difference between collagen

and elastic fibers is that

collagen provides strength and flexibility,

whereas elastin returns stretched structures

to their original shape.

Marfan syndrome is a genetic disorder

that results in defect in fibrillin-1.

The patient has impaired elastin synthesis

and weak connective tissue.

Fibrillin-1 is particularly abundant in the heart,

lens of the eyes and the periosteum.

So defects

in the protein primarily affect these tissues.

The last type of fiber

we are going to introduce today,

reticular fibers is a type of fiber

in connective tissue composed of type III collagen.

Type III collagen produces a network

of delicate reticular fibers.

This network acts as a supporting mesh

in soft tissues such as liver,

bone marrow, and the tissues

and organs of the lymphatic system.

So let's summarize this session.

Connective tissue contains fibers,

including collagen, elastic and reticular fibers.

Fibroblasts synthesize procollagen

and forming proper collagen is the key

to maintaining normal body functions.

Thanks for joining us.