2.2 Histology of the GI tract Flashcards
List the 4 histological layers of the GI tract and describe what is in each
Mucosa: epithelia, lamina propria, muscularis mucosae (smooth muscle)
Submucosa: connective tissue, blood, lymph vessels, fat and Meissner’s nerve plexus
Muscularis Externa: inner circular and outer longituidnal layers with Auerbach’s nerve plexus located between layers
Serosa: connective tissue with mesothelial covering (adventitia on retroperitoneal regions)
List the functions of the following:
oesophagus, stomach, small intestine, large intetsine
oesophagus: transport of chewed food
stomach: secretion of acid, mucus, pepsinogen
small intestine: digestion and absorption
large intetsine: absorption of H2O and passage of bowel contents
List the 3 salivary glands and what each secretes
Sublingual: mucus
Parotid: serous
Submandibular: both
Which parts of the esophagus are voluntary and involuntary?
Upper 1/3: Voluntary (also contains skeletal muscle)
Lower 2/:3: Involuntary, purely peristalsis (smooth muscle)
Name the epithelia and their functions
Mouth and Oesophagus
Stomach and Intestines
Rectum
Mouth and Oesophagus - stratified squamous non- keratinised provides protection from abrasion and acid reflux
Stomach and Intestines - simple columnar to aid in secretion and absorption
Rectum - stratified squamous non- keratinised for protection and to resist abrasion
Below is a histolgical section of an oesophagus
Lable the black arrow + list 2 cell types that would also be found here
GALT (gut associated lymphoid tissue) (the mucosa is associated with regions of GALT).
Dendritic antigen presenting and Langerhan cells can also be found here
What is the lower part of the oesophagus that connects to the stomach called?
The gastro-oesophageal junction
The stomach contains an additonal layer of what?
Olique smooth muscle
Within the stomach, the mucosa and submucose are arranged into fold known as ____ the purpose of these is to _____
Rugae
Flatten with distention to increase volume of stomach
What are the four regions of the stomach
1) Cardia- continuous with the oesophagus
2) Fundas
3) Body
4) Pylorus- leads to duodenum
What are both the cardia and fundas of the stomach covered in? What is the purpose of these?
Covered in gastric pits that leads to gastric glands.
These secrete hydrochloric acid, mucus and digestive enzymes
What is the sphincter at which the stomach opens into the duodenum called?
Pyloric Sphincter
What epithelium type lines the gastric pits?
Simple columnar
Label the regions and cells on the image below and state what each cell secretes
Surface mucous cells: alklaine fluid containing mucin
Mucus neck cell: acid fluid containing mucin
Parietal cell: intrinsic factor (B12 absorption) and HCl
Cheif cell: pepsinogen and gastric lipase
G cells/eneteroendocrine cells: secrete gastrin into the blood
Lable the cell types found in the gastric glands
Stem cells of the gastric epithelium are interspersed among the _________ cells and Intestinal stem cells are found in _______.
They have a _______ proliferative rate, some cells are replaced every ____-___ days.
mucus neck, crypts, high, 5-7
In which region of the glands are common progenitor cells found
Isthmus/ Neck
In what part of the GIT are plicae circularis most abdundant
Jejunum
Brunner’s gland are compound tubular glands that secrete _________ to counteract ___________.
This protects the mucous membrane and creates the optimal _______ for enzymatic digestion.
alkaline mucus, acidic chyme, pH
In what part of the small intestine are Peyers patches and Brunner glands ABSENT
Jejunum
Describe the location and characteristics of a Paneth cell
Located in crypts
Contain characteristic red cytoplasmic granules that produce immunoglobulins, glycoprotein and lysozyme
Describe the location and function of enterendocrine cells (K cells)
Located in the duodenum and jejunum and function to produce gastric inhibitory peptide (GIP) ➞ suppresses acid secretion
Most of the small intestine is covered with a ________, (the visceral peritoneum) comprised of a thin layer of connective tissue and a ________.
The ________ produces a lubricating fluid to allow movement within the ___________, and is continuous with the ________,(an infolding of the parietal peritoneum)
serous membrane, mesothelium, mesothelium, peritoneal cavity, mesentery
Name the lymphoid follicles indicated below and in which part of the GIT these are most abundant?
What is their function?
Peyer’s patches
Large aggregations of lymphoid follicles (MALT) found in the ileum (esp distal region) which project into the mucosa. They are covered with a layer of epithelium + relatively few goblet cells.
They function to provide immune surveillance.
What special cell is found in the epithelium of peyer patches within the ileum
Specialised M-cells
These trancytose antigens from the lumen to a reservoir of immune cells enclosed by the basal aspect of the cell.
Decribe the function of M-Cells in the Ileum
M (microfold) cells form a pocket that encloses T and B lymphocytes and dendritic cells.
Transcytosed antigens are taken up by dendritic cells and presented to Th-cells.
These, in turn, activate B-lymphocytes which mature and secrete IgA molecules.
IgAs are transported into the gut to neutralise invaders.
What is Crohns disease and which part of the GI is most commonly affected?
Crohns is commonly associated with the formation of what?
A disease that causes transmural inflammation that leads to deep ulceration (unknown cause)
It can affect any part of the GIT but most commonly the distil Ileum or colon
Often associated with granuloma formation
What are the 5 regions of the large intestine?
Caecum, apendix, colon, rectum and anal canal
What is the main function of the large intestine?
The recovery of water and electrolytes, and the formation of faeces.
What are Taeniae coli and where are they found?
Three longitudinal bands formed by the outer muscular layer of the colon
At the lower region of the colon the epithelium changes, describe this change
Simple columnar to stratified squamous non-keratinised at the recto-anal junction AND Serosa is replaced by adventitia
Which nerve plexus is located in the submucosa and where is it derived from?
Lists 3 things it controls
Meissner’s plexus ➞ derived from the Myenteric nerve plexus
Controls:
- Glandular secretions
- Regulates local blood flow
- Alters electrolyte and water transport
What nerve plexus is located in the muscularis externa and what is it derived from?
What does it control?
Auerbach’s plexus (b/w circular and longitudinal muscle), which is derived from plexus of PNS nerves around SMA
Controls GI tract motility/peristalsis
Name the 7 accessory digestive organs (TTSSGLP)
Teeth, tongue, gall bladder, salivary glands (parotid, submandibular, sublingual), spleen, liver and pancreas
What is the effect of the SNS and PNS nervous innervation on salivary secretions?
SNS: produces thicker secretions, as well as reducing blood flow to glands.
PNS: innervation stimulates release of fluid secretions and increased blood flow.
The tongue is comprised of ________ epithelium, bearing ________ (some of which bear taste buds).
It contains skeletal muscle, with fibres orientated in ______ planes.
_______ muscles interdigitate directly with CT of tongue.
Stratified squamous non- keratinised, dorsal papillae, multiple, Intrinsic
What is the function of myoepithelial cells and where are they found?
What other cell type is found here and what is its function?
Found in the oral cavity surrounding acini, tubules and
small ducts. Contraction of these cells helps move saliva towards the oral cavity.
Resident plasma cells are also found in the oral cavity and produce IgA.
Describe the structure and secretion type of the following salivary glands:
- Submandibular
- Sublingual
- Parotid
Submandibular: mixed serous/ mucous tubule-acinar glands that secrete various enzymes, including α−amylase and lysozyme. (2/3 volume)
Sublingual: branched tubule-acinar glands producing mainly
lubricating mucus
Parotid: mainly serous branched acinar glands that secrete α-
amylase (stored as zymogen granules)
Decribe the structure of the ENDOCRINE pancreas
Contains islets of Langerhans with the following cell types
β-cells produces insulin
α-cells produce glucagon
γ-cells produce somatostatin
PP cells produce pancreatic polypeptide
Describe the stucture of the EXOCRINE pancreas
The exocrine pancreas releases proteases, amylases, lipases and DNAses as zymogens into the duodenum via the major duodenal papilla
What is the main digestive function of the liver and what is the purpose of this?
Production of bile to emulsify fats
How are nutrients recieved from the digestive system to liver?
Via the portal vein
What supplies oxygenated blood to the liver
Hepatic artery
Describe the structure of a liver lobe
Sinusoids arise from branches of the portal vein and hepatic
artery, bathing hepatocytes in mixed venous and arterial blood.
Sinusoids merge to form the central veins of each lobe
These join to form the hepatic veins that drain into the inferior vena cava
Where is the bile produced by the hepatocytes stored?
How does it get there and how is it concentrated
Stored in the gallbladder
Arrives via the cystic duct and concentrated by recovery of water
What hormone stimulates the contraction of the gall bladder?
How is the bile transported to the duodenum?
Cholecystokinin.
Bile is transferred to the duodenum via the common bile duct and the major duodenal papilla
What stimulates CCK?
Cholecystokinin is stimulated by the introduction of HCl, amino acids or fatty acids in the stomach or duodenum
It is secreted from duodenal APUD cells - it then triggers contraction of the gall bladder so bile is released into the duodenum via the cystic duct
What cell lines the ducts of the biliary tract and what are their role?
Cholangiocytes ➞ modify the bile
What 2 ducts fuse to form the common bile duct?
The cystic duct and the common hepatic duct
