Pancreatic Islets在线视频

Hello, everyone!

Today we are going to discuss

the pancreatic islets.

In this picture,

according to organ's location and morphology,

we can easily identify the pancreas.

The pancreas

is a mixed exocrine-endocrine gland.

The pancreatic islets

compose the endocrine pancreas.

The reason why we call it islets is that

isolated island-like cells are dispersed

in the exocrine pancreas.

There are more than 1 million islets

in a pancreas,

and mostly in the tail region.

These islets can produce secretions,

but they have no ducts,

so they belong to the endocrine system.

After this session,

you should be able to describe

the structure of islets,

list their hormones,

and explain the associated clinical changes

with pancreatic islets.

Talking about the structure

and function of pancreatic islets,

we will start from two young scholars.

One is the German pathologist Paul Langerhans.

He was born in Germany in 1847

and studied medicine at the University

of Jena and Berlin.

In 1869,

22-year-old Langerhans

detailed the microstructure

of the pancreatic islets for the first time

in his graduation assay.

He described

several different types of cells,

including irregularly shaped

polygonal small cells.

These "zellhaufen" (Germany word)

in the entire gland

which literally means a cell stack

in diameter of 0.1 to 0.24 mm.

This is what we call pancreatic islet today.

As we can see in the picture,

they are lightly stained cell clusters

and scattered among the exocrine pancreas.

It was Paul Langerhans

who first discovered

and described this structure,

so in 1893,

the French histologist G.E. Languesse

named these structures

"islets of Langerhans".

Langerhans was just a medical student at 22.

He discovered a new structure of human body

through careful observation.

There are still many mysteries

in the human body.

So,

you also have chances

to explore them during your study!

However,

Paul Langerhans did not make any assumptions

about the function of the pancreatic islets

and the nature of the cells.

The discovery of important functions

of the islets

was by another young scholar,

Frederick Grant Banting.

Banting was born in Ontario,

Canada in 1891.

He started as an art student

at the University of Toronto,

but later switched his major to medicine.

After graduation in 1916,

he joined the Canadian Army Medical Corps,

and served in France

during the First World War.

When the war ended,

Banting returned to Canada

and tried to be a medical practitioner,

but there were not enough patients

for him to carry on.

Eventually,

he did part-time teaching

at the University of Western Ontario.

In 1920,

29-year-old Frederick Grant Banting

was preparing an experiment

on pancreas function

and glucose metabolism.

He found that from the late 19th century

to the early 20th century,

many scholars speculated that diabetes

was related to pancreatic hormone.

They called this hormone 'insulin'.

However,

eating animal pancreas didn't help

in treating diabetes.

Considering the functions

of the digestive tract,

he suspected that eating animal pancreas

might have caused its hormone

to be destroyed

by proteases in the GI tract.

Meanwhile,

a surgical journal article mentioned that

pancreatic tumors

could compress the secretion ducts

and cause atrophy of the exocrine glands.

He was greatly inspired

and made the following animal experiment plan.

He would ligate the pancreatic ducts

to make protease-producing cells

atrophy without affecting

insulin-producing cells.

Then,

injecting the pancreas extract

could lower blood sugar in diabetics.

Working in Professor Macleod's lab

in Toronto,

although Banting and another

collaborator named Best,

failed many times,

they gradually improved the experiment.

They ligated the pancreatic ducts in dogs

and got the pancreatic extract.

Then they injected it

into the experimental diabetic ones.

This experiment finally proved that

pancreatic extract

contained the function of

lowering blood sugar and treating diabetes.

After their success,

insulin was purified

and put into clinical use

not long after.

In 1923,

Banting and Macleod

were awarded the Nobel Prize

in Physiology & Medicine

for their contribution

to the discovery of insulin.

Banting raised the question at 29-year-old

and won the Nobel Prize three years later.

Their success was the result of

persistence and resilience.

But pancreatic islet is not just composed

of one type of cells.

It can do more than secreting insulin.

The conventional Hematoxylin & Eosin staining

could not distinguish various cells

in the pancreas.

With special staining,

we will find that

there are many types of cells

in the pancreatic islets.

Among them,

the 3 main types are A-cells,

B-cells, and D-cells.

A-cells surround the pancreatic islets

and account for about

20% of the total cells

in the islets.

They produce glucagon

to increase blood glucose

by accelerating hepatic glycogen degradation

and gluconeogenesis.

B-cells locate in the center of islets

and account for 70% of the total cells.

The substance produced by B-cells

is insulin.

The main function of insulin

is to decrease the blood glucose

by causing glucose entry into body cells.

If the activity of B-cells is decreased,

for example destroyed by pathological

autoimmune response,

the insulin will decrease,

and blood glucose cannot enter cells.

This condition will lead to high blood sugar

but insufficient glucose

for cellular functions.

Eventually,

it can cause

the clinical manifestation of diabetes.

The third main type of the cells

are called D-cells,

which make up about

5% of the total pancreatic cells.

They are scattered between A-cell and B-cell

and produce somatostatin.

D-cells are paracrine cells,

so its hormones

can affect the adjacent cells.

That is,

somatostatin could regulate the secretion

of A-cells and B-cells.

Above is the introduction about

the pancreatic islets.

Now,

do you understand the work

of the two young scholars

associated with our pancreatic islets?

Langerhans identified the pancreatic islets

in morphology.

Banting discovered the role of insulin,

also the most important function

of pancreatic islets.

For you,

my young medical students,

please summarize the structural features

and functions of pancreatic islets

based on this picture.

Here are the references.

Thank you!