Gastrointestinal Histology

Question 1

What are the major subdivisions of the GI tract?

Answer 1

1 - Oral cavity, teeth, tongue

2 - Pharynx

3 - Esophagus

4 - Stomach

5 - Small intestine

6 - Large intestine

Question 2

What are the accessory organs of the digestive system?

Answer 2

Salivary glands, liver, gallbladder, pancreas

Question 3

Describe the general structure of the GI tract.

Answer 3

Tunics:

1 - Tunica Mucosa (epithelium, lamina propria and underlying muscularis mucosa)

2 - Tunica Submucosa

3 - Tunica Muscularis

4 - Tunica Adevntitia/serosa

Question 4

Describe the general structure of the Mucosa.

Answer 4

Innermost layer that surrounds the lumen. Divided into 3 layers.

Question 5

What are the 3 layers that make up the Tunica Mucosa?

Answer 5

1 - a layer of epithelium that lines the lumen with underlying basement

2 - lamina propria (loose layer of connective tissue) that supplies nutrients to the epithelium and contains immune cells

3 - muscularis mucosa (smooth muscle)

Question 6

Describe the general structure of the submucosa.

Answer 6

layer of connective tissue that contains fat, small blood vessels and nerves.

Question 7

Describe the general structure of the muscularis.

Answer 7

comprises of 2-3 layers of smooth muscle. contraction of the smooth muscles propels substances through the organs.

Question 8

Describe the general structure of the adventitia/serosa.

Answer 8

outermost layer, determined by the location of the organ.

adventitia is the connective tissue layer that surrounds organs without an epithelial membrane

serosa is composed of connective tissue covered by a simple squamous epithelium that is continuous with the lining of the body cavities.

Question 9

What is the main purpose/function of the connective tissue?

Answer 9

Supporting/connective tissue provides general structure, mechanical strength, space filling and physical support for more specialised tissues.

Question 10

What are the three structural properties of connective tissues?

Answer 10

1 - high tensile strength, collagen

2 - elasticity, elastin

3 - volume, glycoproteins and complex carbs with water binding ability

Question 11

What makes up the extracellular matrix and how is it produced?

Answer 11

Fibres + ground substance = ECM, produced and assembled by support cells mainly fibroblasts.

Question 12

What are the 2 types of fibres in connective tissue?

Answer 12

1 - collagen, secreted by connective tissue cells i.e. fibroblasts

2 - elastin, synthesised by fibroblasts as precursor

Question 13

What are the properties of the basement membrane?

Answer 13

1 - bind epithelium to underlying tissue

2 - control epithelial growth

3 - provide nutrients and metabolites to the epithelium

4 - regulate permeability

Question 14

Explain the role of the oesophagus.

Answer 14

Muscular tube which food is carried from the pharynx to the stomach.

Question 15

State the way in which the structure of the oesophagus is related to its function.

Answer 15

At the junction with the stomach, there is a sphincter which prevents reflux or regurgitation.

Lumen is usually compressed unless processing a large bolus of food.

Question 16

Within the mucosa of the oesophagus, what kind of epithelium are present?

Answer 16

Stratified squamous epithelium, with secretory glands under which lies a layer of irregular smooth muscle.

Question 17

What is the sub-mucosa, muscularis externa and adventitia within the oesophagus made of?

Answer 17

1 - Submucosa made of coarse connective tissue and glands

2 - Muscularis Externa:

• • top 1/3: skeletal
• • middle 1/3: mixed
• • bottom 1/3: smooth

3 - Adventitia made of dense connective tissue which becomes serosa following passage through diaphragm

Question 18

What is the role of the stomach?

Answer 18

Food is digested and absorbed

Digestion is limited to water, alcohol and some drugs

Question 19

What is gastric juice secreted by and what does it contain?

Answer 19

Secreted by gastric mucosal glands and contains hydrochloric acid, mucus and proteolytic enzymes pepsin and lipase.

Question 20

Describe the structure of the mucosa within the stomach.

Answer 20

Simple columnar epithelium with goblet cells and a thin layer of smooth muscle. Highly vascularised.

Folded to form gastric pits with glands that secret HCl and intrinsic factor (parietal cells), hormones (G cells) and pepsinogen

Question 21

Describe the structure of the muscularis externae within the stomach.

Answer 21

Three poorly defined layers

1 - inner oblique

2 - middle circular

3 - outer longitudinal

Question 22

Describe the structure of the Serosa within the stomach.

Answer 22

Irregular dense connective tissue with mesothelium (simple squamous)

Question 23

What makes up the small intestine?

Answer 23

Duodenum, jejunum, ileum

Question 24

Describe the structure of the mucosa within the duodenum.

Answer 24

villous forms covered in columnar epithelium with brush border

• plicae circulares - mucosal/submucosal folding
• villi - projections from the mucosa with blood vessels
• microvilli - projections from absorptive cells

Question 25

Describe the structure of the submucosa, muscularis externa and serosa within the duodenum.

Answer 25

submucosa - occupied by brunners glands (secrete alkaline mucin) which mepty into the mucosal crypts

muscularis externa - two layers of smooth muscle

serosa - irregular dense connective tissue with mesothelium

Question 26

What is the function of the large intestine?

Answer 26

absorb water from undigested food, structurally distinct from the small intestine

Question 27

Describe the structure of the mucosa, sub mucosa, muscularis externae and serosa within the large intestine.

Answer 27

1 - muscosa:

• • columnar epithelium
• • no plicae circulares
• • no villi and microvilli
• -deep crypts present

2 - submucosa: course fibroelastic

3 - muscularis externa: 2 layers of smooth muscle

4 - serosa: irregular dense connective tissue with mesothelium (simple squamous)