Histology of GIT Flashcards
Lisst the four layers
- Mucosa
- Submucosa
- Muscularis propria
- Adventitia/Serosa
- Mucosal changes due to different functions of the various organs e.g. submucosa thickness varies
Describe the components of the mucosa
◼ epithelium
◼ lamina propria
◼ muscularis mucosae
Describe the contents of the submucosa
loose collagenous
tissue containing
blood vessels,
lymphatics, nerve
submucosal plexuses
(meissner’s) and
lymphoid aggregates
Describe the muscularis propria
generally two layers
of smooth muscle
(inner circular and
outer longitudinal) to
allow for peristalsis,
and nerve plexuses
(myenteric)
Describe the adventitia and serosa
Adventitia
loose supporting
tissue containing
blood vessels and
nerves
Serosa
Mesothelial lining
covering the outer
most aspect of
gastrointestinal
tract
Distinguish between adventitia and serosa
Adventitia – found all parts
of GIT, lies between
muscularis propria and
serosa (in some parts of
bowel minimal to non-
existent)
Serosa – outer most lining
of those parts of GIT found
within abdomen (similar to
pleura of lungs)
- intraperitoneal?
List the functions of GIT mucosa
- Protection - barrier to external environment
- Secretion - and synthesis of various substances
(e.g digestive enzymes, mucus, antibodies,
hormones) - Absorption - products of digestion, water,
electrolytes - Immunological functions - containing lymphoid tissue
Describe the histology of the oesophagus
- Lumen is lined by
protective stratified
squamous epithelium - Primary function is to
transfer ingested food
and fluids from mouth
to stomach - Thin lamina propria
contains lymphoid
tissue –> immune role
Describe the oesophageal submucosa
- Submucosa contains
- elastic fibres (to
allow distension by a
bolus of food) - mucous glands (to
aid in lubrication of
bolus)
Describe Barrett’s
- Barrett’s oesophagus / adenocarcinoma
- metaplasia (Squamous to glandular epithelium), goblet cells
- biggest RF is untreated chronic reflux
- can become dysplastic i.e. malignant potential, cytological features of malignancy, +/- BM invasion
- if resected – big section, implications for morbidity
Describe the gasto-oesophageal junction
stratified
squamous
epithelium
of
oesophagus
columnar
epithelium
of stomach
Describe the functions of the stomach
◼ Holds food it receives – Distensible
◼ Responsible for mechanical breakdown of
food - muscular strength (churning
movements)
◼ Produces various substances which make up
gastric juice - responsible for partial chemical
digestion of food
Describe the stomach mucosa
- Cardia: small area
around oesophageal
orifice, mainly mucus
secreting glands, some
neuroendocrine cells - Fundus/body: largest
part, different cells
secrete gastric acid,
mucus and hormones - Pylorus: small area at
base of stomach,
mucus secreting cells,
neuroendocrine cells
(secrete gastrin)
List the cell types foundin the stomach mucosa
- Fundus and body consist of
straight tubular glands
(formed by simple columnar
epithelium)- note surface cells are low columnar or cuboidal
- Contains large mucinogen
granules which maintain the
thick mucus sheet protecting
epithelium - Surface mucous cells
secrete bicarbonate, helps to
protect epithelium from
acidic gastric juices
List and describe the cell types of the gastric glands
- Parietal cells: secrete
gastric acid and
intrinsic factor
(needed to absorb
vitamin B12 in
terminal ileum), stain
pink (many
mitochondria) - Chief cells: secrete
pepsin, stain blue
(many ribosomes)
http://www.lab.anhb.uwa.edu.au/mb140/default.htm
Gastric glands – cell types
* Neuroendocrine cells
– secrete hormones
such as serotonin and
gastrin
* Stem cells – can
differentiate into any
of other cells as
required —> constant turnover of cells
Found in antrum
summarise the layers ofhte stimamch
- Lamina propria – very thin
- Submucosa – contains nerves and
ganglion cells which make up submucosal
plexus - Muscularis propria – distinguished in
stomach by addition of a third muscular
layer, inner oblique layer
**Why understand histology of
stomach?
**
* Gastritis – H. pylori
Gastric ulcer
H. Pylori organisms
- tend to hang out in crypts or in mucin on antral surface
- ulcer —> adenocarcinoma and lymphoma risk
Describe the gasto-duodenal junction
Cell types are the same but the structure of the epithelium changes.
Simple
columnar
epithelium
of stomach
vs
villous
mucosa
lined by
columnar
mucosa with
goblet cells
of duodenum
Broadly describe the anatomy and function of small intestine, and hwo the histology facilitates this
- Three anatomic components:
duodenum, jejunum and ileum - Main functions:
- digest food
- absorb the products of digestion
- Specialised cells increase surface area (plicae
circulares, villi, and microvilli) to enhance absorption - Velvety, undulating appearance
Describe SI mucosa
- Villi- finger-like
projections of mucosa - increase surface
area for absorption - longest in
duodenum, shorter
towards ileum - Crypts of Lieberkuhn -
between villi - Peyer’s patches -
lymphatic tissue within
lamina propria (in ileum)
Describe the epithelium of the small intestine
- Simple columnar
epithelium aka Enterocytes:
absorptive cells with
microvilli, cover villi
and crypts - Goblet cells:
scattered along
epithelium and
produce mucus - Paneth cells: base of crypts,
contain secretory granules of
lysozymes, can phagocytose
some bacteria and protozoa - Neuroendocrine cells:
produce hormones such as
secretin (important for
digestion- regulates pH) - Stem cells: at base of crypts – regeneration and high cell turnover
- Intraepithelial lymphocytes:
mainly T cells
What are the features of duodenal submucosa
submucosal mucus
producing glands,
Brunner’s glands
lymphoid tissue
Describe histology of Crohn’s
**
* Crohn’s disease – transmural inflammation
- occurs along length of GIT
- characterised by loss of villi in addition to transmural inflammation
- macro: fissuring ulcers, pseudoulcers
Describe the ileo-caecal junction
lined by
columnar
mucosa with
goblet cells and
Paneth cells of
ileum
vs
Mucosa with
crypts lined by
columnar mucosa
with goblet cells
of large intestine
Overview: anatomy and function large intestine
- Anatomical components:
Caecum, appendix, ascending colon,
transverse colon, descending colon, sigmoid
colon and rectum - Main functions:
- absorb water and electrolytes from bowel
contents - to move contents distally for elimination
- Smooth lumen (no plicae circulares
or villi) – dd. Haustra- caused by
taenia coli
Describe the mucosa of the large intestine
- Simple columnar
epithelium which forms
tubular glands (crypts) - Enterocyte, - absorptive
cell - microvilli (most
common cell type) - Goblet cells produce
mucus, needed to
lubricate intestine and
allow for passage of
bowel contents - Stem cells found at base
of crypts
What is a key differentiator between small and large intestine?
finger-like villi and crypts vs
deep crypts without villi
List macro and micro features of the large intestine
- Teniae coli -
longitudinal bands,
seen macroscopically
are formed by outer
longitudinal layer of
muscularis propria
* Thick muscularis propria
seen microscopically
Also seen microscopically:
lymphoid tissue,
deep crypts with goblet
cells and enterocytes
Describe the appendix
*Appendix arises from the
caecum and is lined by large
intestine mucosa
* Abundant lymphoid tissue
in lamina propria and
submucosa
**Why understand histology of large
intestine?
**
* Colorectal cancer - staging
- need to know layers of colon to know extent of invasion
- T4 tends to be unresectable
Describe the recto-anal junction
glandular mucosa of rectum
vs
stratified
squamous
epithelium
of anus
- a gradual transition zone
Describe anatomy and function of anus
- Main functions:
- Protection (squamous
mucosa through to skin
containing sebaceous
glands and apocrine
sweat glands) - some lubrication - Outlet for passage of
faeces
**Why understand histology of the
anus?
**
* Squamous carcinoma, linked to HPV, high morbidity
