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What is the definition of hyperplasia?

Hyperplasia is the increase in number of cells


What are the two types of Hyperplasia?

What are the two causes of hyperplasia?

Two types of hyperplasia: Nodular or cystic

Two causes of hyperplasia:  Physiologic and pathologic


What are some characteristics of physiologic hyperplasia?

Physiologic hyperplasia

  • Often a response to hormones
  • Often compensatory
  • May be regenerative, acting to repair a site


What are some characteristics of pathologic hyperplasia?

Pathologic hyperplasia:

  • Due to Inappropriate or excessive hormones (ACTH -> Adrenal cortex)
  • Due to Irritation
  • Unknown/idiopathic cause



What organs are commonly affected by hyperplasia?

Common examples:

  • Liver
  • Spleen
  • Pancreas
  • Lymph node/spleen

Very common example: Cystic endometrial hyperplasia


Why do we care about hyperplasia?

Why do we care? 

We need to know what the cause is.  What is this in response to?

Also, possibly preneoplastic.


Hyperplasia vs neoplasia?


  • Controlled growth, normal process
  • Reversible, if the inciting cause is determined and removed
  • The cause is known.



  • May be harder to recognized the cause, may not see a justification for an increase in cell number. 
  • Unregulated, unorganized. 
  • May not be reversible, if it's a genetic change



Is hypertrophy cell swelling?

No, hypertrophy is an increase in the size of cells or organ. 

This is not cell swelling.

Cells swell because they are taking on water, or lipids.  The cells got very big, but it's not because they were able to do more a job.  They were very fragile.


Why does hypertrophy happen?

Hypertrophy is an increase in the size of cells or organ, due to the increase in volume of organelles.  The increase in organelles leads to an overall increase in cell size.


What are the two types of hypertrophy?

Two types of hypertropy are physiologic or compensatory.

In response to work/increased demand


What types of cells can't undergo hyperplasia?

"Permanent" cells, like neurons or myocardiocytes.  These cells don't regenerate, so they can't become hyperplastic. 

They could potentially become hypertrophic.


When labile cells (skin, GI, respiratory, or hematopoietic) become hyperplastic, what are they typically working to do?

When labile cells become hyperplastic, they are typically working to repair something.


(From review session, not from lecture)


When a stable cell type (glandular, liver, kidney, or endocrine) undergoes hyperplasia, what type of hyperplasia will that typically be?

The hyperplasia of stable cell types typically results in nodular hyperplasia.


(from review session, not lecture)


How would you describe the circled kidney?

The circled kidney is a hypoplastic kidney. 

The contralateral kidney had more work to do, so it increased in size as an organ to handle the increased workload

Sometimes we see this change in a cat/animal that has no renal abnormalities in the bloodwork at all

Can be an incidental finding


What's happening in this image?

This is hypertrophic cardiomyopathy. 

For reasons we don't always understand, the myocardium of the left ventricle becomes very large, due to the increased size of the myofibers.  The cats can be asymptomatic until you go to do a dental, or spay.

We don't have a good antemortem test at this time.


What is an example of both hypertrophy and hyperplasia?

Prostatomegaly would be an example of this.

The entire size of the organ may increase.  There would be an increase in cell size and cell number. 


Metaplasia is when one adult cell type is replaced by another adult cell type of the same ________ _______,


Metaplasia is when one adult cell type is replaced by another adult cell type of the same germ line.


So, an epithelial cell wouldn't be replaced with a lymphocyte, for example.


What are two broad categories through which metaplasia can be induced? 

What are some examples of each?

Metaplasia can be:

  • induced (due to increases in estrogen, or a vitamin A def.)
  • caused by irritation (in the trachea of a smoker, normal ciliated columnar cells become stratified squamous epi)


When you have metaplasia in epithelial tissue, what are some pros/cons to it?

It's protective.  Great for skin, not great for trachea, other organs that interface with the environment


Loss of cilia, loss of clearance

When you lose a special feature of those cells, like cilia, then you're also losing an important clearance mechanism for the resp. tract


Can be preneoplastic


What are some characteristics of metaplasia in mesenchymal tissue?

Mesenchymal tissue = connective tissue

Mesenchymal metaplasia may indicate:

  • An altered cellular environment (May be hormonal, may be constant mechanical trauma)
  • Decreased or increased oxygen in the tissue
  • Example?  Osseous metaplasia. 


Osseous metaplasia?  In the face of chronic stress and perhaps overexposure to corticosteroids, one skin lesion that can occur is the formation of bone within skin.  Hematopoetic cells in the bone marrow, of bone that shouldn't be there in the first place!!   Common in oral masses in dogs.


What the significance of metaplasia?

Metaplasia may be:

Reversible, if the inciting cause is removed

May be protective or harmful

May be a preneoplastic lesion, like a carcinoma in situ.


An organ that is enlarged due to an increased number of cells is:

a. Hyperplastic

b. Hypertrophic

c. Metaplastic



An organ that is enlarged due to an increased number of cells is:

a. Hyperplastic

b. Hypertrophic

c. Metaplastic


What is atrophy?

Atrophy is the decrease in cell size or number of cells, tissue, or organ after normal growth has been reached.

The key feature is that the cell has to have reached its normal size at some point, and then gotten smaller


What are some types of atrophy, by mechanism?

i.e. what's a mechanical reason why a cell would atrophy?

Types of atrophy, by mechanism:

  • Disuse
  • Denervation
  • Pressure - decreased blood flow due to a decrease in oxygen or nutrients
  • Reduced work load
  • Decreased hormones
  • Any reduction in nutrition/oxygen
  • Aging/senility


What are the morphologic types of atrophy?

Types of atrophy, by morphology:

  • Simple atrophy
  • Fatty atrophy
  • Fibrous atrophy
  • Serous atrophy


What is fatty atrophy?

Fatty atrophy is fat replacement in connective tissue.  Adipocytes replace myofibers.


What is fibrous atrophy?


Fibrous atrophy is when something is decreasing in size, and there's fibrous replacement

Increased fibrous tissue within connective tissue.


(She literally said "something" in lecture and didn't elaborate on what, so.....)


Atrophy vs. involution?  Discuss.

Atrophy is the decrease in cell size or number of cells, tissue, or organ after normal growth has been reached.  The term "atrophy" implies an adverse situation/environment.

Involution is the reduction in cell number without degeneration.  Involution in a normal physiologic process that involves apoptosis.  Examples: How the thymus involutes with age, or how the uterus shrinks/involutes after birth.


What do you need to ask yourself when you see atrophy?

Presence of atrophy?  Ask yourself:

Where is this happening?

What exactly is happening?

Are there any indicators of disease?


What are some potential fates of atrophic tissues?

Atophy could:

  • Be reversible.  For example, muscle atrophy in a broken limb
  • Persist, as it is
  • Progress into serious bad news, like fat (serous) atrophy or fibrosis atrophy


What type of atrophy is the brain on the right undergoing?

Pressure atrophy.

Dog brain, blockage of CSF in one of the ventricles.  Result: Severe hydrocephalus.  Remaining cerebrum collapsed on itself.


What is the gross morphology of atrophy?

Grossly, you'll see a decrease in the weight and volume of the organ.

Loose covering

Tortuous vessels (over the surface of the organ.  What used to be fully expanded, has collapsed)

Firm +/- fatty


What is the microscopic morphology of atrophy?

Microscopically, you'll see either a decrease in the number of cells, a decrease in the cell sizes, or potentially both.


What is the EM morphology of atrophy?

EM morphology of atrophy?

Decreased organelles:  Less ER, fewer mitochondria, less intracellular filaments

Increased autophagocytic vacuoles, lipofuscin


What are the last fat stores, that atrophy in serous atrophy of fat?

Last fat stores:



Bone marrow


Why do we care about serous atrophy of fat?

Important to recognize because it implies a severe caloric deficiency

When we see an animal that's thin, we know that there's been a severe lack of nutrients if we see a lack of fat around the heart and the kidneys

If there's been a rapid decrease in availability of food, then we see serous atrophy of fat, when those fat stores are gone so rapidly that the remaining stroma around it is filled in with clear, gelatinous fluid

If you shake it back and forth, you'll see what used to be fat is instead clear, pale yellow, very fragile substance

Would see there anywhere we would expect to see fat, esp. around the heart and the kidneys

Not uncommon for animals.   Perhaps not always in an intentional or malicious way, but people may not feed adequately.

Upon necropsy, may not able to prove intent, but you can prove that the animal was severely malnourished.


This can NOT occur postmortem


What does lipofuscin represent, in a cell?

Lipofuscin is essentially the break down product of chronic cell stress

Long term phagocytosis


May see it in a cell, but it doesn't indicate why the cell was stressed.

Called a "wear and tear" pigment for that reason


There are a lot of Cellular Adaptation images at the end of the lecture that were too big to put on here.  Look through them! 

You are a champion!



What is the lesion in A



This is a rabbit

  1. What organ?

  2. Describe lesions?

  3. What is the most common cause of these lesions in a rabbit

  1. Liver
  2. Multifocal, pale circular nodular lesions
  3. tularemia


this is a rabbit

  • What organ?
  1. What is seen at 1?
  2. ?

  • liver
  1. Normal bile duct

  2. Hyperplastic bile ducts


  • What organ?
  1. What is seen at 1
  2. What is the name of this disease

  • uterus
  1. Cycts
  2. Endometrial cystic hyperplasia


this is a canine

  • What tissue is this?
  1. What layer is this?
  2. What layer is this?
  3. What is this?

  • uterus
  1. Myometrium

  2. Endometrium

  3. Cyst Filled with exudate and mucous


  1. what is seen here
  2. ?
  3. ?

  1. Hyperplasia, Projectile increase in number of cells

  2. neutrophils

  3. normal epithelium


  1. What organ is this
  2. What is seen here

  1. prostate
  2. hypertrophy and hyperplasia


this is a canine prostate

  1. what is seen here
  2. what is this?

  1. Cellular hypertrophy

  2. Normal cuboidal


What is seen at 1

hypertrophy of bladder wall


  1. ?
  2. ?
  3. ?

  1. pancreatic nodular hyperplasia
  2. stomach
  3. omentum


this is a canine

  • What organ?
  1. what lesion is this?
  2. Why do they generally form?

  • liver
  1. Nodular hyperplasia

  2. Rapidly growing cells do form correctly, Will be more likely to take up lipid


this is a feline

  • what organ
  1. what is seen here?
  2. ?

  • liver
  1. Lipofuscin

  2. Atrophy of hepatocytes

    • Will see increased clear space in sinosoids


this is a rat

  • What organ
  1. What is seen here
  2. What is this?
  3. ?

  • Uterus
  1. Stratified squamous epithelium (metaplasia)

    • Should be cuboidal

  2. Keratin

  3. Neutrophils

    • They don’t like keratin


This is a horse

  • what organ is this
  1. What is seen here
  2. ?
  3. Why does this happen?


  • esophagus
  1. normal esophagus
  2. Hypertrophy of esophagus
  3. Idiopathic change in horses


What is the full name of this?

Equine idiopathic esophageal muscular hypertrophy