2.2 Histology of the GI tract

Question 1

List the 4 histological layers of the GI tract and describe what is in each

Answer 1

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)

Question 2

List the functions of the following:

oesophagus, stomach, small intestine, large intetsine

Answer 2

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

Question 3

List the 3 salivary glands and what each secretes

Answer 3

Sublingual: mucus

Parotid: serous

Submandibular: both

Question 4

Which parts of the esophagus are voluntary and involuntary?

Answer 4

Upper 1/3: Voluntary (also contains skeletal muscle)
Lower 2/:3: Involuntary, purely peristalsis (smooth muscle)

Question 5

Name the epithelia and their functions

Mouth and Oesophagus
Stomach and Intestines
Rectum

Answer 5

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

Question 6

Below is a histolgical section of an oesophagus

Lable the black arrow + list 2 cell types that would also be found here

Answer 6

GALT (gut associated lymphoid tissue) (the mucosa is associated with regions of GALT).

Dendritic antigen presenting and Langerhan cells can also be found here

Question 7

What is the lower part of the oesophagus that connects to the stomach called?

Answer 7

The gastro-oesophageal junction

Question 8

The stomach contains an additonal layer of what?

Answer 8

Olique smooth muscle

Question 9

Within the stomach, the mucosa and submucose are arranged into fold known as ____ the purpose of these is to _____

Answer 9

Rugae

Flatten with distention to increase volume of stomach

Question 10

What are the four regions of the stomach

Answer 10

1) Cardia- continuous with the oesophagus
2) Fundas
3) Body
4) Pylorus- leads to duodenum

Question 11

What are both the cardia and fundas of the stomach covered in? What is the purpose of these?

Answer 11

Covered in gastric pits that leads to gastric glands.

These secrete hydrochloric acid, mucus and digestive enzymes

Question 12

What is the sphincter at which the stomach opens into the duodenum called?

Answer 12

Pyloric Sphincter

Question 13

What epithelium type lines the gastric pits?

Answer 13

Simple columnar

Question 14

Label the regions and cells on the image below and state what each cell secretes

Answer 14

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

Question 15

Lable the cell types found in the gastric glands

Answer 15

Question 16

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.

Answer 16

mucus neck, crypts, high, 5-7

Question 17

In which region of the glands are common progenitor cells found

Answer 17

Isthmus/ Neck

Question 18

In what part of the GIT are plicae circularis most abdundant

Answer 18

Jejunum

Question 19

Brunner’s gland are compound tubular glands that secrete _________ to counteract ___________.

This protects the mucous membrane and creates the optimal _______ for enzymatic digestion.

Answer 19

alkaline mucus, acidic chyme, pH

Question 20

In what part of the small intestine are Peyers patches and Brunner glands ABSENT

Answer 20

Jejunum

Question 21

Describe the location and characteristics of a Paneth cell

Answer 21

Located in crypts

Contain characteristic red cytoplasmic granules that produce immunoglobulins, glycoprotein and lysozyme

Question 22

Describe the location and function of enterendocrine cells (K cells)

Answer 22

Located in the duodenum and jejunum and function to produce gastric inhibitory peptide (GIP) ➞ suppresses acid secretion

Question 23

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)

Answer 23

serous membrane, mesothelium, mesothelium, peritoneal cavity, mesentery

Question 24

Name the lymphoid follicles indicated below and in which part of the GIT these are most abundant?

What is their function?

Answer 24

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.

Question 25

What special cell is found in the epithelium of peyer patches within the ileum

Answer 25

Specialised M-cells These trancytose antigens from the lumen to a reservoir of immune cells enclosed by the basal aspect of the cell.

Question 26

Decribe the function of M-Cells in the Ileum

Answer 26

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.

Question 27

What is Crohns disease and which part of the GI is most commonly affected? Crohns is commonly associated with the formation of what?

Answer 27

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

Question 28

What are the 5 regions of the large intestine?

Answer 28

Caecum, apendix, colon, rectum and anal canal

Question 29

What is the main function of the large intestine?

Answer 29

The recovery of water and electrolytes, and the formation of faeces.

Question 30

What are Taeniae coli and where are they found?

Answer 30

Three longitudinal bands formed by the outer muscular layer of the colon

Question 31

At the lower region of the colon the epithelium changes, describe this change

Answer 31

Simple columnar to stratified squamous non-keratinised at the recto-anal junction AND Serosa is replaced by adventitia

Question 32

Which nerve plexus is located in the submucosa and where is it derived from? Lists 3 things it controls

Answer 32

Meissner's plexus ➞ derived from the Myenteric nerve plexus Controls: * Glandular secretions * Regulates local blood flow * Alters electrolyte and water transport

Question 33

What nerve plexus is located in the muscularis externa and what is it derived from? What does it control?

Answer 33

Auerbach's plexus (b/w circular and longitudinal muscle), which is derived from plexus of PNS nerves around SMA Controls GI tract motility/peristalsis

Question 34

Name the 7 accessory digestive organs (TTSSGLP)

Answer 34

Teeth, tongue, gall bladder, salivary glands (parotid, submandibular, sublingual), spleen, liver and pancreas

Question 35

What is the effect of the SNS and PNS nervous innervation on salivary secretions?

Answer 35

SNS: produces thicker secretions, as well as reducing blood flow to glands. PNS: innervation stimulates release of fluid secretions and increased blood flow.

Question 36

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.

Answer 36

Stratified squamous non- keratinised, dorsal papillae, multiple, Intrinsic

Question 37

What is the function of myoepithelial cells and where are they found? What other cell type is found here and what is its function?

Answer 37

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.

Question 38

Describe the structure and secretion type of the following salivary glands: * Submandibular * Sublingual * Parotid

Answer 38

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)

Question 39

Decribe the structure of the ENDOCRINE pancreas

Answer 39

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

Question 40

Describe the stucture of the EXOCRINE pancreas

Answer 40

The exocrine pancreas releases proteases, amylases, lipases and DNAses as zymogens into the duodenum via the major duodenal papilla

Question 41

What is the main digestive function of the liver and what is the purpose of this?

Answer 41

Production of bile to emulsify fats

Question 42

How are nutrients recieved from the digestive system to liver?

Answer 42

Via the portal vein

Question 43

What supplies oxygenated blood to the liver

Answer 43

Hepatic artery

Question 44

Describe the structure of a liver lobe

Answer 44

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

Question 45

Where is the bile produced by the hepatocytes stored? How does it get there and how is it concentrated

Answer 45

Stored in the gallbladder Arrives via the cystic duct and concentrated by recovery of water

Question 46

What hormone stimulates the contraction of the gall bladder? How is the bile transported to the duodenum?

Answer 46

Cholecystokinin. Bile is transferred to the duodenum via the common bile duct and the major duodenal papilla

Question 47

What stimulates CCK?

Answer 47

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

Question 48

What cell lines the ducts of the biliary tract and what are their role?

Answer 48

Cholangiocytes ➞ modify the bile

Question 49

What 2 ducts fuse to form the common bile duct?

Answer 49

The cystic duct and the common hepatic duct