Session 5.2e - Lecture 1 - Epithelial Tissues and Glands Flashcards
Slides 65 - 78
Glands can be made up of a single cell or a collection of cell. What are the terms used to describe these compositions?
Unicellular
Multicellular
What is the simplest type of gland?
Unicellular (as opposed to multicellular).
Give an example of a unicellular gland.
A goblet cell
What type of gland is a goblet cell?
A unicellular exocrine gland.
Give an example of a unicellular exocrine gland.
Goblet cell
What is a goblet cell?
A unicellular exocrine gland that produces mucus. It is so-named bc it appears as a goblet under the microscope (has a long thin stem).
Fig. 65
Identify the mucus.
All the pink stuff would be filled with mucus
What organelles in the goblet cell are making mucus?
Golgi apparatus
Rough endoplasmic reticulum
Nucleus
etc. etc.
What do goblet cells sit on?
The basement membrane
What happens to the mucus in goblet cells?
It is secreted
Where is the mucus from goblet cells secreted?
Onto the respiratory or gut surface, often
Where are goblet cells found?
Respiratory tract:
- trachea, bronchi, and larger bronchioles
Intestinal tract:
- small and large intestines
Eye:
- conjunctiva in the upper eyelid
How do goblet cells appear under a microscope?
Pale and goblet shaped
Goblet cells are little ____
Little exocrine glands in their own right
Fig. 65
Caption this diagram, explaining about glands and goblet cells.
Glands can be UNICELLULAR or MULTICELLULAR. This diagram shows a goblet cell (a unicellular exocrine gland).
This type of unicellular gland is important for producing mucus in the respiratory and intestinal tracts.
Fig. 65
Label this diagram
- Microvilli
- Mucinogen granules
- Golgi apparatus
- rER
- rER
- basal lamina
Draw a diagram of a Goblet cell and its associated organelles.
See Fig. 65
- Microvilli
- Mucinogen granules
- Golgi apparatus
- rER
- rER
- basal lamina
Fig. 66
Caption and label this image.
G G
Unicellular goblet cells (G) in the epithelium of the upper respiratory tract.
Draw how goblet cells would appear on a histology slide, from the respiratory tract.
See Fig. 66
G G
Unicellular goblet cells (G) in the epithelium of the upper respiratory tract.
What type of epithelial cell do goblet cells derive from?
Simple columnar cells.
Fig. 66
Distinguish between the goblet cells and other simple columnar cells,
The other simple columnar cells have cilia and a different morphology and they’re not producing mucus
How do goblet cells differ from the other simple columnar cells around it?
The other simple columnar cells have cilia (1) and a different morphology (1) and they’re not producing mucus (1)
Fig. 67
Identify the goblet cells.
The ones looking like goblets/wine glasses.
Fig. 67
What is the function of a goblet cell here?
To secrete mucus onto the surface of an intestinal villus
What are intestinal villi?
Intestinal villi (singular: villus) are small, finger-like projections that extend into the lumen of the small intestine
Fig. 67
Other than the goblet cells, what other type of cell is present here?
Simple columnar cells which sit on a basement membrane
Fig. 67
What do the simple columnar cells have?
Microvilli (brush border)
Microvilli on the surface of epithelial cells form what?
A brush border
What is a brush border?
Microvilli on the surface of epithelial cells
Fig. 67
What is found amongst the simple cuboidal cells which have microvilli?
Goblet cells, which produce mucus
Fig. 67
Caption this image.
Unicellular goblet cells in the epithelium of an intestinal villus
(Note: - goblet cells look like a wine glass
- other simple cuboidal cells have microvilli, a brush border
- sits on a basement membrane (top?))
Draw the epithelium of an intestinal villus as seen under a histology slide.
See Fig. 67
Unicellular goblet cells in the epithelium of an intestinal villus
What is the function of goblet cells in the intestine?
Produce mucus that’s needed by the intestinal lumen contents.
What produces the mucus that’s needed by intestinal lumen contents?
Goblet cells
What are colonic crypts?
Crypts of Lieberkühn (intestinal glands)
Explain the relationship between goblet cells and crypts of Lieberkühn?
Goblets cells are one of the types of cells that make up these crypts. The goblet cells secrete mucus.
Fig. 68
Caption this image.
Goblet cells in tubular colonic crypts
(Goblet cells are the light coloured cells
Colonic crypts = crypts of Lieberkühn = intestinal gland, made up of (+ others) goblet cells.
This is further down the intestine than where the intestinal villus lay).
Draw an image of goblet cells in tubular colonic crypts, as seen on a histology slide.
See Fig. 68
Goblet cells in tubular colonic crypts
(Goblet cells are the light coloured cells
Colonic crypts = crypts of Lieberkühn = intestinal gland, made up of (+ others) goblet cells.
This is further down the intestine than where the intestinal villus lay).
What secretes mucus in the crypts of Lieberkühn?
Goblet cells (a ty[e of cell which make up the crypt) secrete mucus in the crypts of Lieberkühn
Why is it important to know what a gland is in histology?
Normally, for about the last 20 years the histology of glands would be covered comprehensively: salivary glands, the adrenal gland, the parathyroid glands etc., but now - once you’ve got the hang of the basics of histology you can read about any gland and understand it
Where does the pancreas sit?
Not far from the stomach, with its head tucked into the curve of the duodenum.
Where does the head of the pancreas lie?
Tucked into the curve of the duodenum
What lies tucked into the curve of the duodenum?
The head of the pancreas
What is the duodenum?
The first part of the small intestine (preceding the jejunum and the ileum). It is the shortest part of the small intestine, and connects the stomach to the jejunum.
What is the first part of the small intestine called?
The duodenum
What connects the stomach to the jejunum?
Duodenum
What does the duodenum connect in the alimentary tract?
Stomach and jejunum
What type of gland is the vast majority of the pancreas?
An exocrine gland
What do the exocrine cells of the pancreas produce?
Digestive enzymes, together with bicarbonate
What produces digestive enzymes in the pancreas?
Its exocrine cells (ductal cells and acinar cells)
80% ductal adenocarcinomas for pancreatic cancer
Where does the pancreas secrete its digestive enzymes into?
The duodenum
The duodenum receives digestive enzymes secreted by ____
The pancreas
What does the duodenum receive from the pancreas?
Digestive enzymes secreted by it
What secretes the bicarbonate from the pancreas?
Duct cells (exocrine glands)
What do duct cells secrete?
- Aqueous component (isotonic)
- Bicarbonate
What is the function of the bicarbonate produced by the pancreas?
To neutralise the acid (chyme) produced from the stomach.
What neutralises the acid produced by the stomach?
Bicarbonate
What is chyme?
Chyme is the semi-fluid mass of partly digested food that is expelled by the stomach, through the pyloric valve, into the duodenum (the beginning of the small intestine).
What is the semi-fluid mass of partly digested food expelled by the stomach known as?
Chyme
What pH is chyme?
Acidic (~2)
Where is chyme produced?
The stomach
Where does chyme from the stomach go?
To the duodenum
What are the endocrine cells in the pancreas?
Islets (literally, islands) of Langerhans
What types of cells are the islets of Langerhan?
Endocrine cells of the pancreas
Where are islets of Langerhans found?
Particularly in the tail and outermost area of the pancreas
Name 3 peptide hormones secreted by the islets of Langerhans.
- Glucagon
- Somatostatin
- Insulin
Where is glucagon produced?
Islets of Langerhans in the pancreas
Where is somatostatin produced?
Islets of Langerhans in the pancreas
Where is insulin produced?
Islets of Langerhans in the pancreas
What forms of the pancreas?
Acini, but islets of Langerhans are also in there (and duct cells).
Explain how the pancreas is an endocrine and exocrine gland.
Exocrine
- head of pancreas tucked into curve of duodenum
- bulk of pancreas made up of duct cells and acinar cells (exocrine glands)
- these secrete digestive enzymes into the duodenum, and bicarbonate, which neutralises chyme from the stomach
Endocrine
- islets (literally, islands) of Langerhans are endocrine glands
- these are found mostly in the tail and outermost area of the pancreas
- the islets secrete peptide hormones including, glucagon, somatostatin and insulin directly into the bloodstream
Fig. 69 (top left)
What is this image highlighting?
The pancreas, an exocrine AND endocrine gland.
Fig. 69a
Label the image.
- Common bile duct
- Pancreatic duct
- Lobules
- Tail of pancreas
- Body of pancreas
- Head of pancreas
- accessory pancreatic duct
- Duodenal papilla
- Duodenum
Fig. 69b
Label the image.
- Ducts
- Connective tissue septum
- Exocrine cells in pancreatic acini
- Endocrine cells in pancreatic islet
Fig. 69c
Label the image.
- Pancreatic islet (endocrine)
- Pancreatic acini (exocrine)
- Duct
Draw the pancreas in relation to the other structures of the GI tract.
See Fig. 69 (top left)
Draw the pancreas tucked into the head of the duodenum.
See Fig. 69a
- Common bile duct
- Pancreatic duct
- Lobules
- Tail of pancreas
- Body of pancreas
- Head of pancreas
- accessory pancreatic duct
- Duodenal papilla
- Duodenum
Draw the cells involved in pancreatic glands.
See Fig. 69b
- Ducts
- Connective tissue septum
- Exocrine cells in pancreatic acini
- Endocrine cells in pancreatic islet
(Acini connected to ducts, secrete onto epithelial cells, islets are drawn as islands with no ducts surrounding them - secrete directly into bloodstream).
Draw the pancreatic glands as would be seen on a histology slide.
See Fig. 69c
- Pancreatic islet (endocrine)
- Pancreatic acini (exocrine)
- Duct
Fig. 70
Identify an islet of Langerhans.
The lighter pink patches surrounded by acini (darker).
What is the structure of the islets of Langerhans?
Endocrine tissue with little capillaries going all through them
Why is it important the islets of Langerhans have capillaries?
Bc they are endocrine glands, so they need to be able to secrete hormones into the bloodstream
Fig. 70
Identify the acini.
The little dark pink circles
What shape is an acinus?
Roughly circular
How are the acini and islets of Langerhans identified on histology?
The acini are roughly circular and much smaller than the islets of Langerhans. These normally stain a lighter colour (depending on the dye).
What are pancreatic acini?
Exocrine components of the pancreas which produce digestive enzymes
What type of gland are acini?
Exocrine
What do acini secrete?
Digestive enymes
What are the exocrine glands of the pancreas?
Acinar cells and duct cells
How do pancreatic acini secrete their hormones?
They are exocrine glands, so they produce their hormones into little ducts which merge and merge and merge into bigger ducts
What happens to the ducts surrounding pancreatic acini?
They are initially little ducts which merge and merge and merge into bigger ducts
Fig. 70
Caption this image.
Three islets of Langerhans surrounded by exocrine pancreatic acini.
(Islets of Langerhans - big light pink patches
Exocrine pancreatic acini - small dark pink circles)
Draw some islets of Langerhans surrounded by pancreatic acini.
See Fig. 70
Three islets of Langerhans surrounded by exocrine pancreatic acini.
(Islets of Langerhans - big light pink patches
Exocrine pancreatic acini - small dark pink circles)
Where do the ducts surrounding the pancreatic acini eventually lead?
Eventually secrete into the small intestine
Fig. 71
What is this picture showing?
A close up of an islet of Langerhans, so here are the acini which are producing digestive enzymes which will go into the gut
What are the pancreatic acini doing?
Producing digestive enzymes which will go into the gut.
Fig. 71
What is the big pink blob in the centre?
An islet of Langerhans (close up)
Fig. 71
What is surrounding the islet of Langerhans (pink central circle)?
Exocrine pancreatic acini
What is the function of exocrine pancreatic acini?
To produce digestive enzymes which will go into the gut.
What are islets of Langerhans filled with?
Capillaries
What lines the capillaries in the islets of Langerhans?
Squamous cells
What do islets of Langerhans do?
Produce 3 major hormones (glucagon, somatostatin and insulin) necessary for the body.
Fig. 71
What is the larger dark pink circle towards the right?
It’s lined by simple squamous epithelium and it’s full of little reddish cells, or they’re stained red – that’s a little blood vessel
What lines blood vessels?
Endothelium (simple squamous epithelia)
What can we see in a blood vessel on a histology stain?
Packed full of little red blood cells which haven’t fallen out before they stained it
Fig. 71
Caption this image.
An islet of Langerhans surrounded by exocrine pancreatic acini (high power).
Draw an islet of Langerhans surrounded by acini.
See Fig. 71
An islet of Langerhans surrounded by exocrine pancreatic acini (high power).
Fig. 71
Annotate this image in detail
An islet of Langerhans surrounded by exocrine pancreatic acini (high power).
Islet of Langerhans if filled with blood capillaries that have simple squamous cells lining it.
Red blood vessel to the right, lined by endothelium (simple squamous epithelia) and packed full of little red blood cells which haven’t fallen out before they stained it.
(Acini surround central islet.)
What is the pathophysiology behind cystic fibrosis?
In cystic fibrosis insufficiently hydrated mucus is formed in the respiratory tract and gut, with resultant pathologies.
What disease results from insufficiently hydrated mucus formed in the respiratory tract and gut?
Cystic fibrosis
What happens to the mucus in cystic fibrosis?
It is insufficiently hydrates
The affected mucus in cystic fibrosis affects which systems?
Respiratory and intestinal tract (due to the production of mucus in those areas).
How can we classify glands, other than by secretions?
By structure (of their secretory part)
How can we classify glands by structure?
- Acinar
- Tubular
How are glands sorted into acinar and tubular?
This is whether the secretory part of the gland is tubular or acinar.
How can we classify glands?
By SECRETION:
- EXOCRINE (glands with ducts, secrete onto epithelial cells)
- ENDOCRINE (ductless, secrete directly into the bloodstream)
By STRUCTURE:
- ACINAR (a swelling that performs exocrine secretion)
- TUBULAR (tube that’s coiled at its end - can be eccrine, apocrine etc.)
What is a tubular gland?
A secretory gland that is very coiled at its end (blind-ended), e.g. a sweat gland.
What is an acinus?
The secretory unit of many exocrine glands.
It is a swelling of cells which are pumping out a secretory product (enzymes normally), which go off along a duct, and the ducts get bigger and bigger and merge and merge - so an acinus is really a round swelling which is to do with exocrine secretion.
What type of gland is a round swelling associated with exocrine secretion?
Acinus (acinar gland)
What does an acinus secrete?
Any secretory products; enzymes normally.
What type of cell normally secretes enzymes?
Acinus glands (exocrine glands)
Fig. 74
Label this image.
An acinus (the secretory unit of many exocrine glands)
(You need not learn anything from this diagram other than what an acinus is.
Extra info:
- Mucous cell
- Myoepithelial cell
- Serous demilune
- Lumen of acinus
- Intercalated ducts
- Striated ducts
- Excretory duct)
Draw some acini converging into their respecting ducts.
See Fig. 74
An acinus (the secretory unit of many exocrine glands)
(You need not learn anything from this diagram other than what an acinus is.
Extra labels:
- Mucous cell
- Myoepithelial cell
- Serous demilune
- Lumen of acinus
- Intercalated ducts
- Striated ducts
- Excretory duct)
What are acini analogous to?
A bunch of grapes, where each grape is an acinus and the stalks are the ducts that merge into bigger ducts, in which enzymes travel
What is different about the grape analogy to acini?
In acini, enzymes travel down the little ducts which get to be bigger ducts and finally get secreted somewhere.
The grape analogy breaks down ofc bc in this case, sugars and water and nutrients are travelling this way, but in a gland, it’s the enzymes and so on which travel the other way
What is the grape analogy to acini?
The analogy really is like a bunch of grapes, so each of these grapes could be an acinus, producing its enzymes which go down little ducts which get to be bigger ducts and finally get secreted somewhere. The analogy breaks down ofc bc in this case, sugars and water and nutrients are travelling this way, but in a gland, it’s the enzymes and so on which travel the other way.
Fig. 75
Caption this image.
In some ways ACINI and their ducts in an exocrine gland are analogous to grapes and their stalks in a bunch of grapes
Draw grapes as an analogy to acini, and explain how this represents the acini.
See Fig. 75
In some ways acini and their ducts in an exocrine gland are analogous to grapes
and their stalks in a bunch of grapes
What happens to the ducts/stalks in acini/grapes?
They start off little and get bigger and bigger
What is normally secreted from acini?
Enzymes
What do glands develop from?
Mostly, from epithelium (basically, many many glands, not every one of them, many glands, are epithelially derived)
What are glands derived from?
Invagination of epithelium (little downgrowths) as we develop
What is derived as invaginations of epithelium?
Glands (many many glands, not every one of them, many glands, are epithelially derived)
(Remember: adenocarcinomas are malignant tumours from glandular structures of epithelial origin).
Why is it important to know that glands are mostly derived from epithelial origin?
Adenocarcinomas are malignant tumours from glandular structures of epithelial origin).
What do epithelia invaginate into?
Connective tissue down below
Why does some epithelia invaginates into connective tissue down below?
To form glands of all sorts of different shapes, sometimes v big glands.
Fig. 76
Explain what this figure is showing.
You do not have to learn the above detail, but it would be helpful for you to realise that many glands are in fact invaginations of epithelium, specialised for secretion
What are most glands?
Invaginations of epithelium, specialised for secretion
Fig. 76
Label the image
(!Do not need to learn)
SIMPLE GLANDS
- Gland cells
SIMPLE TUBULAR
Examples:
Intestinal glands - Duct
SIMPLE COILED TUBULAR
Examples:
Merocrine glands
SIMPLE BRANCHED TUBULAR
Examples:
Gastric glands
Mucous glands of oesophagus, tongue, duodenum
SIMPLE ALVEOLAR (ACINAR)
Examples:
Not found in adult; a stage in development of simple branched glands
SIMPLE BRANCHED ALVEOLAR
Examples:
Sebaceous (oil) glands
Draw an image of simple glands.
! Do not need to know
See Fig. 76
SIMPLE GLANDS
- Gland cells
SIMPLE TUBULAR
Examples:
Intestinal glands - Duct
SIMPLE COILED TUBULAR
Examples:
Merocrine glands
SIMPLE BRANCHED TUBULAR
Examples:
Gastric glands
Mucous glands of oesophagus, tongue, duodenum
SIMPLE ALVEOLAR (ACINAR)
Examples:
Not found in adult; a stage in development of simple branched glands
SIMPLE BRANCHED ALVEOLAR
Examples:
Sebaceous (oil) glands
What is an obvious example of an exocrine gland that’s full of acini?
The human breast
What is the human breast full of (in relation to glands)?
It is an exocrine gland full of acini
What is the structure of acini?
Like bunches of grapes
What do the acini in the breast produce?
Milk
How does milk travel to the nipple?
It is produced in acini and carried into bigger and bigger ducts until the ducts of the nipple
What are acini surrounded by?
Little myoepithelial cells
What are myoepithelial cells?
Like little smooth muscle cells which contract when they relieve the right stimulus, to help expel the secretions of exocrine glands
What is the function of myoepithelial cells in the breast?
They contract when they receive the right stimulate, to help secrete the milk
How do myoepithelial cells help secrete milk?
They contract, squashing the acini so the contents of the acini (luminal contents) are forced along
As well as in the breast, where are myoepithelial cells located?
Sweat glands.
What is the ‘let-down’ experience felt in breastfeeding?
A definite feeling, almost painful, of when a baby starts sucking on the nipple, as 100s of 1000s of myoepithelial cells contract to help the acini produce milk for the baby
Sometimes women feel an almost painful experience as a baby starts sucking on the nipple. What is this called?
‘Let-down’
What is the physiology behind the ‘let-down’ reflex in breastfeeding?
Myoepithelial cells around each acinus can constrict simultaneously to assist secretion of milk from the lumens of the acini, and therefore from the breast.
Their contraction is experienced as ‘let-down’.
Fig. 77
Label this image.
- Adipose tissue
- Connective tissue
- Lobules of tubuloalveolar glands
- Lactiferous sinus
- Lactiferous duct
Fig. 77
Caption this image.
Diagram of human breast as seen during lactation.
Draw a human breast showing the cells involved during lactation.
See Fig. 77
- Adipose tissue
- Connective tissue
- Lobules of tubuloalveolar glands
- Lactiferous sinus
- Lactiferous duct
Fig. 78
What section of the eccrine sweat gland is this showing?
A section through the highly coiled end of an eccrine sweat gland
Fig. 78
Where does the duct portion go?
Towards the surface of the skin
What do myoepithelial cells resemble?
Almost like little smooth muscle cells
What happens to the acinus when myoepithelial cells contract?
It gets squashed, and the secretions from the acinus get released.
How do eccrine sweat glands and myoepithelial cells secrete sweat?
Myoepithelial cells surround the acinus and its lumen, acting almost like smooth muscle cells, and when they contract, the acinar lumen gets squashed, essentially squeezing that tube to squeeze the sweat out when it’s needed.
How do myoepithelial cells faciliate the transport of sweat?
The myoepithelial cells contract in order to facilitate the transport of luminal contents (unmodified sweat) towards the duct.
What is released from the acinus in sweat glands?
Unmodified sweat
Where does unmodified sweat travel?
Released from the acinus towards the duct
Fig. 78
Caption this image.
Photomicrograph of eccrine sweat glands (in dermis of skin) showing secretory portion and duct.
Fig. 78
Label this image.
- adipose tissue
- duct
- myoepithelial cells
- lumen
- secretory component
Draw an eccrine sweat gland as seen on a histology slide.
See Fig. 78
Photomicrograph of eccrine sweat glands (in dermis of skin) showing secretory portion and duct.
- adipose tissue
- duct
- myoepithelial cells
- lumen
- secretory component
Summarise what we have covered in this lecture.
Mucous membranes
Serous membranes
Epithelia
- Simple
- Stratified
Exocrine glands
- secretory invaginations of epithelium
