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04. Gastrointestinal > L7. Gastrointestinal Histology > Flashcards

L7. Gastrointestinal Histology Flashcards

1
Q

What are the contents/segments of the GIT?

A 
Oral cavity
Oesophagus
Stomach
Small intestine
Large intestine (colon)
Rectum
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2
Q

What are the related glands of the GIT?

A

Salivary glands
Pancreas
Liver

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3
Q

What are the major functions of the GIT? [4] briefly describe each one

A
  1. DIGESTION - break down complex molecules to simplest levels (aa, monosaccharides, FA etc)
  2. ABSORPTION - take up products of digestion, water, minerals and vitamins and electrolytes
  3. MOVEMENT - shifts digesta along the tube and eliminates waste
  4. PROTECTION - passive by pH and motility and active by immune system
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4
Q

What is the stereotyped layering of the GIT wall?

A

Mucosa (epithelium and underlying lamina propria)
Submucosa
Muscularis externa
Serosa

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5
Q

What are the major components of the GIT mucosa?

A

Epithelium (either columnar or stratified squamous epithelium)
Lamina propria (connective tissue with nerves and vessels)
Thin layer of smooth muscle called the muscularis mucosae

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6
Q

Describe the shape of the gastric mucosa and secretory contents of the gastric mucosa

A

The mucosa is thick due to folding of be surface with glands that invaginate and penetrate into the lamina propria. As they penetrate they form a mesh of glands

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7
Q

Describe the GIT submucosa

A

Lies immediately beneath the mucosa

It is a dense, irregular connective tissue with vessels and nerves (and some glands)

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8
Q

What is the major function of the GIT submucosa

A

Provides strength and elasticity. It is largely a mechanical layer in terms of function

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9
Q

What is the muscularis externa?

A

Usually 2 layers of smooth muscle:

  1. Inner circumferential cells concentrically ranged so contraction narrows the lumen
  2. Outer longitudinal muscle arranged so that contraction shortens the length of the tube
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10
Q

What is the function of the muscularis mucosa?

A

Responsible for gut movement and peristalsis (which is coordinated by the autonomic system)

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11
Q

What is the serosa of the gut wall?

A

A very thin surface of the gut with squamous epithelium with flat nuclei providing a nonstick surface
and a small layer of connective tissue that binds the gut tube to surrounding structures

You would really only see the flat nuclei in a section

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12
Q

What is the enteric nervous system?

A

A branch of the autonomic system with neurones in the gut wall that forms its own separate nervous entity.

It is responsible for actions of mixing, peristalsis and secretion.

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13
Q

Describe the enteric nerve plexuses

A

The enteric neurons form ganglia in the gut wall
2 layers
- MYENTERIC PLEXUS between the longitudinal and circular muscle layers
- SUBMUCOSAL PLEXUS in the submucosa

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14
Q

What is the function of the oesophagus?

A

Connects the oral cavity to the stomach

Purely transport of food to the stomach

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15
Q

Describe the epithelial lining of the oeophagus. What is the implication of this?

A

Stratified squamous non-keratinised epithelium

Thus it is a protective, thick and strong lining against abrasion by food

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16
Q

Where are the complex glands located in the oesophagus and what do they do?

A

Submucosa

Produce large amounts of mucous to help food boluses slide down (lubrication) and to protect the lining from damaging abrasion

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17
Q

What is special about the muscularis mucosa of the oeophagus? How does it differ along the length of the tube?

A

It is composed of a mix of skeletal muscle and smooth muscle

Superior- mainly skeletal muscles to initiate swallowing
Middle- mix
Inferior- mainly smooth muscle

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18
Q

What is the stomach and its parts?

A

A large muscular sac that connects the oeophagus to the small intestine

Cardiac, fundus, body, pyloric Antrum and pyloric canal with the pyloric sphincter

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19
Q

What is the function of the pyloric sphincter?

A

Control the release of material into the intestine

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20
Q

What is the function of the stomach?

A

Initiate digestion
Produces chyme by mechanical and chemical breakdown
Regulates the release of contents into the intestine
Minimal absorption

21
Q

Describe the microscopic structures of the wall of the stomach

A

Simple columnar secretory epithelium
Prominent muscularis mucosa
Thick submucosa for toughness
Thick muscularis externa

22
Q

What is special about the muscularis externa of the stomach?

A

There is an extra/third layer of smooth muscle that adds complexity cor the mixing and mechanical movement of the stomach for making chyme

23
Q

Is the lining of the stomach completely smooth or is there a specialised structure?

A

It has low folds called RUGAE that allow for It to expand

It has many openings called GASTRIC PITS that lead to gastric glands

24
Q

Describe the structure of the gastric pits and glands in the wall of the stomach

A

Each gastric pit gives rise to 3-5 gastric glands and the secretions of the glands exit via this common gastric pit.

Organisation varies throughout the stomach but They are simple tubular glands that penetrate into the lamina propria

25
Q

Describe the cells that make up the gastric glands

A
  1. Gastric surface lining cells - at the top of the glands and produce mucous
  2. Neck cells - at the neck of the glands and produce mucous
  3. Regenerative cells - short lived stem cells in the neck of the gland
  4. Parietal cells - produce hydrochloric acid (pH 2)
  5. Chief cells - at the base of the glands the release pepsinogen (inert form of an enzyme)
26
Q

Describe the release of pepsinogen and its activation. What is the role of pepsin in the stomach?

A

Pepsinogen is released as an inactive precursor that is activated only in low pH levels. In the stomach the HCl produces this low pH environment to activate it into pepsin. Pepsin is able to autocleave pepsinogen (cycle)

Pepsin breaks down proteins into peptides and another acids and thus aids food break down into chyme

27
Q

How is the stomach lining protected from the enzymatic cleavage and breakdown action of pepsinogen?

A

The mucosa is protected by a layer of mucus (1-2mm thick) so that the digestive process doesn’t occur directly against the wall

The mucous is constantly being released - loss of this mucous layer leads to peptic ulcer formation.

28
Q

What is the major function of the small intestine?

A

Duodenum, Jejunum and Ileum

Function is to complete digestion and to absorb products of digestion

29
Q

Describe the three organisations of layers of the epithelium that increase the surface area of the small intestine exponentially

A

Transverse folds of mucosa called the plica circularaes
Villi which are prominent extensions of the epithelium
Microvilli which are microscopic, finger like projections off the top of individual epithelial cells (brush border)

30
Q

what kind of epithelium lines the small intestine?

A

Simple columnar epithelium with microvilli

31
Q

What is the structure and function of microvilli?

A

All columnar epithelial cells have microvilli
They are subcellular projections of the epithelial cells
They are non-motile. They simply increase the surface area

32
Q

What are the tubular glands in the small intestine called? Where do they arise?

A

Crypts of Leiberkuhn

They arise at the Bae of the villi and penetrate into the lamina propria

33
Q

What is the function of the crypts of Leiberkuhn?

A

Glandular cells

They secrete fluid and mucous (intake plus secretion)
(Note that mucous is also secreted from goblet cells on the villi)

The crypts also contain stem cells to renew the epithelium (thus epithelial cells are ‘born’ in these crypts and move upwards with ageing to the surface until they die and Slough off.

34
Q

Describe the lamina propria of the small intestine

A

It is both a layer underlying the epithelium but it also extends up to fill the core of each villus

Contains smooth muscle (muscularis mucosa), blood vessels, lymphatics and immune cells

Lymphocytes in the villi are very close proximity to the edge

35
Q

What is the purpose of having a muscularis mucosa that extends to fill the core of the villus?

A

Can move the villus to mix the contents and prevent any unstirred layers

36
Q

What are some defining features of the duodenum?

A

Has low plica circularaes

Fewer goblet cells

37
Q

The duodenum receives additional secretions from accessory organs. What are these?

A

Digestive enzymes from the pancreas
Bile from the gall bladder - surfactant for breakdown of fat

These enter from the major (and minor) duodenal papilla

38
Q

The duodenum receives acidic chyme including active pepsin from the stomach. How does it deal with this?

A

It has glands in the submucosa called BRUNNER’S GLANDS that secrete alkaline mucous raising the pH to about 7.3

This inactive area the pepsin enzyme back to pepsinogen

39
Q

What is the tend of goblet cells in the small intestine?

A

Tends to be more appearing as you move down the gut

40
Q

What is the site of the most intestinal flora growth? What does this mean about this area?

A

The ileum

Thus there are aggregates of lymphocytes and immune cells highly prevalent in the area

41
Q

Define some microscopic features that distinguish the Jejunum and ileum

A

Jejunum
More plicae circularis but have shorter villi
Lots of goblet cells

Ileum
Smallest villi
Have payers patches (immune cells)

42
Q

What is the function of the small intestine?

A

To complete digestion using enzymes form the pancreas and bile from the gall bladder
Secretes fluid to enable for balanced osmotic effects for efficient digestion
Absorbs amino acids, monosaccharides, fatty acids, minerals, electrolytes, water and vitamins

43
Q

How much fluid does the small intestine absorb per day?

A

About 8.5 litres

44
Q

What is the function of the colon?

A

Compacts faeces and recovers water and electrolytes

45
Q

What is special about the muscular externa of the colon?

A

The outer longitudinal Muscle is discontinuous

It forms three distinct bands of longitudinal muscle called the tinea coli

46
Q

Describe the surface of the colon

A

Similar structure to the rest of the gut
no villi

Has many tubular glands (crypts of Leiberkuhn) with the dominant cell type here being the mucous cell

47
Q

What is the faeces made up of?

A

Leftovers of digestion
Mucous - glues contents together and protects the mucosa
Bicarbonate - neutralises the bacterial acid as poo is largely made up of bacteria
Only about 100mL per day of fluid is in the poo

48
Q

How long is the GIT, what orifices does it connect?

A

9m long

It connects the oral cavity to the anus

04. Gastrointestinal (25 decks)

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