Adaptation of Cells and Tissues在线视频

Hello everyone Today I am going to introduce you adaptation of cell and tissue

So what is adaption

Under the conditions of the external environment changes cells can alter their metabolism structure and biochemical process to avoid injury

This process of change is called adaptation

Adaptation can be divided into four categories including atrophy hypertrophy hyperplasia and metaplasia

Atrophy hypertrophy and hyperplasia mainly focus on changes in cell number and volume

Metaplasia refers to change of the cell type

Let's look at those specific changes

The first one is atrophy

Atrophy refers to the normal formed organ or tissue diminished in size due to decrease in the size of the parenchymal cells or in the number of cells

The key point of this definition is the organ should be normal developed

Aplasia or hypoplasia organ or tissue don't belong to this category even if they have smaller size than normal

According to different causes atrophy can be divided into physiological and pathological atrophy

Pathological atrophy can be furtherly classified according to different causes into six categories including malnutrition atrophy denervation atrophy disuse atrophy pressure atrophy endocrine atrophy and ischemic atrophy

Next let's look into this

For an atrophic tissue or organ

Grossly the volume will decrease the mass will also decrease together with a darker color

It's because of the microscopical changes of each parenchymal cell that decreasing both in volume and in size

On one hand the decreasing volume and number of cells involve the parenchyma

On the other stromal fibrous tissue such as adipose tissue will increase

Meantime we can occasionally find a kind of special pigment granules called lipofucin

We'll talk about that later

According to different causes as we have learned it can be divided into into two categories as physiological atrophy and pathological atrophy

Physiological atrophy literally means it's normal

For examples thymus undergoes atrophy after adolescence and this is called restitution

Uterus and mammary gland of adult female undergo atrophy after giving childbirth and lactation period respectively which also belongs to physiological atrophy

We call it regression

With the increasing of age organs and tissues gradually become smaller which is called senile atrophy

These are all normal phenomenon so they are called physiological atrophy

There is another type called malnutrition atrophy

This type of atrophy is usually seen in long-term starvation or cachexia state of patient suffering from late stage malignant tumor

In such case for example the patient with esophageal cancer

may have dysphagia and long-term pain which result in malnutrition and atrophy of various organs

The second one is called disuse atrophy

For example patient with bone fractures may be restricted to complete bed rest

Consequently the skeletal muscle will become smaller and thinner which belongs to disuse atrophy

That is use it or lose it

The third classification is also called denervation atrophy

It's necessary for normal skeletal muscle to be supported nourished or regulated by nerve endings

For example there is a disease called polio

The patient's motor neurons of the front spinal cord were damaged thus the skeletal muscles which controlled by the nerve endings will undergo atrophy

We call it denervation atrophy because the atrophy is due to nerve damage

The fourth is called pressure atrophy

The organs atrophy is associated with compression by high pressure

We take stone in urinary tract for example

Here we see a case with hydronephrosis

As we can see here urine can not be discharged and then accumulated in the renal pelvis because of the stone obstruction

Accumulated urine increased the pressure then lead to renal cortex shrunkage

This is hydronephrosis also known as pressure atrophy

The fifth is called endocrine atrophy

Endocrine atrophy is mainly caused by certain malfunction of endocrine organ which leads to decreasing volume of target organ

For example pituitary injury resulting from a hemorrhagic peripartum event is called Sheehan's syndrome

Hereby causing a atrophy in one or more organs such as gonads adrenal gland and thyroid

The sixth category is called ischemic atrophy

Let's take a look at this picture

This is brain tissue

When cerebrovascular ischemia like atherosclerosis occurs

Certain part of the brain parenchema will undergo atrophy due to insufficient blood supply

It shows deep sulci and narrowed gyri

It is the same with heart besides brain

When cornary atherosclerosis result in blood supply insufficiency certain area of myocardium will undergo atrophy

This concludes the six categories of pathological atrophy

Next in this picture we can see the striated muscle fiber became thinner obviously

When atrophy occurs the interstitial connective tissue may proliferate between the striated muscle fiber

This is one of the signs of atrophy

Here we can see the normal structure of myocardium form by striated muscle

Therefore when the striated muscle fibe underwent atrophy they bacame thinner accompanied by volume decrease and fading cytoplasmic staining

This is the change of atrophy

Next picture

As we mentioned before in the event of atrophy

Lipofucin will appear inside the cytoplasm

So in this picture we can find accumulated brown pigment in the cytoplasm of myocardial cells

It is the accumulation of lipofucin

When causes of atrophy are eliminated the original normal size and morphology can be restored

However if the pathological agents persist the atrophic cells may gradually disappear

So overall it shows decreased volume and hardening of organs after atrophy occurs

Consequently it will show defect of function

The second category is called hypertrophy

Hypertrophy refers to an increase in the size of tissue or organs

Why does the volume increase?

It mainly due to increase amount of cytoplasmic organells which makes the volume of tissue or organ increase uniformly

More nutrition and oxygen are needed in order to adapt the change of environment

Similarly hypertrophy can also be divided according to the cause as physiological hypertrophy and pathological hypertrophy

First is physiological hypertrophy

For example the volume of the uterus during pregnancy will increase

It shows in this slide

The relatively smaller uterus is of normal size while during pregnancy its volume can obviously increase which belongs to physiological hypertrophy

Next this is the normal morphology of uterine striated muscle fiber

During pregnancy the muscle fiber became thick and cytoplasm increased

On the other hand there is pathological hypertrophy

Pathological hypertrophy can be classified as two categories including compensatory hypertrophy and endocrine hypertrophy

What is compensatory hypertrophy?

This is due to the increasing workload of certain tissue or organ

For example hypertrophy of ventricular wall occurs in patient with hypertension

The higher pressure requests more workload of myocardium thus needs more systolic activity eventually results in myocardial hypertrophy

There is another example

When one of the kidney was removed for treatment purpose the other one shall compensate the loss of function

Therefore there are more units of nephrons from the residual kidney becoming functional accompanied by the increased renal function

The second category is called endocrine hypertrophy

It is due to the hyperplasia or tumor of endocrine organ

Excessive secretion of hormones cause organ hypertrophy

Let's take a look at this compensatory hypertrophy of heart

This is a normal microscopic view of myocardium

We can see that each individual cells underwent hypertrophy with pink stained and abundant cytoplasm

On the gross view the thickness of the myocardial wall including interventricular septum became thickening obviously

That is because of the size increase of each individual cells

The third category is called hyperplasia

Hyperplasia constitude an increase in the number of cell

Similar to hypertrophy increase in numbers of parenchymal cells can also result in volume increase of the tissue or organ

Actually increase of size of the tissue is due to combination of hypertrophy and hyperplasia

For exampleas we have just learned that

the volume increase of uterus during pregnancy not only associates with increased cell volume but also number of the cells

These hormone-related hyperplasia can be seen in uterine smooth muscle cell during pregnancy and breast ductal epithelial cell during lactating peroid

These are both hormone-induced physiological hyperplasia

There is another type called compensatory hyperplasia

For example after partial hepatectomy

The liver will grow back to its original cell number and volume by the remaining stem cells after certain period of time

This is called compensatory proliferation

Pathological hyperplasia can be devided into endocrine hyperplasia and inflammatory repair hyperplasia

For example excessive secretion of estrogen may cause endometrial hyperplasia and breast hyperplasia

These are very common diseases

Excessive androgen secretion may cause prostate hyperplasia

The other type is inflammatory repair hyperplasia which we are going to learn later

When inflammatory occurs various cells like fibroblast and endothelial cells will fix the injured tissue

Then the original structure and function are able to be restored

This also belongs to pathological hyperplasia

This slide shows an inflammatory repair hyperplasia

There is normal gastric epithelium at both sides

This polypoid protrution here is the gastric inflammatory repair polyp

This is also known as proliferative polyp

On the high power view there are increased number of glandular structure and epithelial hyperplasia as well

The last category of adaptation is called metaplasia

It refers to a process in which one matured tissue type is replaced by another matured tissue type

In this process the transformation goes only between tissues with similar properties

It means metaplasia occurs between epithelial tissue or between mesenchymal tissues

Metaplasia does not occur between epithelial and mesenchymal tissues

This is the first key point we shall remember

Then the second key point is

during the process of metaplasia

The metaplastic cells are not coming from mature cells

Instead metaplasia results from the differetiation of undifferented cells or stem cells

This picture below shows columnar epithelium

Normally there are some reserve cells at the base part of columnar epithelium which is called stem cells

Stem cells have the potential to divide and differentiate

Mature squamous epithelium are actually differentiated from reserve cells

It's not coming from the mature columnar epithelium

There are several common types of metaplasia

The first type is important and is called epithelium metaplasia

Bronchial columnar epithelium may turn into squamous epithelium after a long-term stimuli of chronic inflammation in patient such as heavy smoker

It's very important because the squamous metaplasia is a sort of precancerous lesion of squamous cell carcinoma of bronchus

We take chronic cervicitis as another example

Columnar epithelium on cervix may undergo squamous metaplasia

which is also the precancerous lesion of cervical squamous cell carcinoma

Let's first take a look at the bronchial squamous cell metaplasia

Under normal circumstances the bronchial mucosa is covered by pseudostratified columnar epithelium

However entirely replaced by squamous epithelium under the microscopic view

which is called squamous metaplasia

This slide shows the squamous metaplasia of cervical mucosa

The normal columnar epithelium has been replaced by squamous epithelium

The second category is intestinal metaplasia

which happens on cases with chronic atrophic gastritis or gastric ulcer

Epithelium of gastric mucosa is replaced by small intestinal or colorectal like mucosa

It's believed to be the precancerous lesion of intestinal type gastric cancer especially for the colorectal epithelial metaplasia

Under the microscopic view

We can find here the gastric mucosa

Meantime we see a lot of goblet cells

which is the characteristic feature of intestinal epithelium

So we say this is intestinal metaplasia

The second category happens between mesenchymal tissues

which means one kind of mesenchymal tissue turns into another

For example fibroblasts can turn into osteoblasts or chondroblast

Then turns into bone or cartilage tissue

This slide shows the myositis ossificans

Just as the term tells us that myositis ossificans occurs when there is tissue injury

bone tissue forms inside muscle or other connective fibrous tissue

As we can see that there are formation of trabecular bone tissue

This is the mataplasia between mesenchymal tissue

Muscle turn into connective tissue with the calcium deposition bone tissue gradually formed

Here is the summary of the adaptation

There are four kinds of adaptation for a normal cell

Atrophy refers to a decrease in the volume or number of cells

Hypertrophy refers to an increase of cell size

Hyperplasia refers to the increase of number of cells

Metaplasia is different from those

Metaplasia is the change of cell type without affecting the number or volume of cells

That's all for today