Gastrointestinal Histology Flashcards
What are the major subdivisions of the GI tract?
1 - Oral cavity, teeth, tongue
2 - Pharynx
3 - Esophagus
4 - Stomach
5 - Small intestine
6 - Large intestine
What are the accessory organs of the digestive system?
Salivary glands, liver, gallbladder, pancreas
Describe the general structure of the GI tract.
Tunics:
1 - Tunica Mucosa (epithelium, lamina propria and underlying muscularis mucosa)
2 - Tunica Submucosa
3 - Tunica Muscularis
4 - Tunica Adevntitia/serosa
Describe the general structure of the Mucosa.
Innermost layer that surrounds the lumen. Divided into 3 layers.
What are the 3 layers that make up the Tunica Mucosa?
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)
Describe the general structure of the submucosa.
layer of connective tissue that contains fat, small blood vessels and nerves.
Describe the general structure of the muscularis.
comprises of 2-3 layers of smooth muscle. contraction of the smooth muscles propels substances through the organs.
Describe the general structure of the adventitia/serosa.
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.
What is the main purpose/function of the connective tissue?
Supporting/connective tissue provides general structure, mechanical strength, space filling and physical support for more specialised tissues.
What are the three structural properties of connective tissues?
1 - high tensile strength, collagen
2 - elasticity, elastin
3 - volume, glycoproteins and complex carbs with water binding ability
What makes up the extracellular matrix and how is it produced?
Fibres + ground substance = ECM, produced and assembled by support cells mainly fibroblasts.
What are the 2 types of fibres in connective tissue?
1 - collagen, secreted by connective tissue cells i.e. fibroblasts
2 - elastin, synthesised by fibroblasts as precursor
What are the properties of the basement membrane?
1 - bind epithelium to underlying tissue
2 - control epithelial growth
3 - provide nutrients and metabolites to the epithelium
4 - regulate permeability
Explain the role of the oesophagus.
Muscular tube which food is carried from the pharynx to the stomach.
State the way in which the structure of the oesophagus is related to its function.
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.
Within the mucosa of the oesophagus, what kind of epithelium are present?
Stratified squamous epithelium, with secretory glands under which lies a layer of irregular smooth muscle.
What is the sub-mucosa, muscularis externa and adventitia within the oesophagus made of?
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
What is the role of the stomach?
Food is digested and absorbed
Digestion is limited to water, alcohol and some drugs
What is gastric juice secreted by and what does it contain?
Secreted by gastric mucosal glands and contains hydrochloric acid, mucus and proteolytic enzymes pepsin and lipase.
Describe the structure of the mucosa within the stomach.
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
Describe the structure of the muscularis externae within the stomach.
Three poorly defined layers
1 - inner oblique
2 - middle circular
3 - outer longitudinal
Describe the structure of the Serosa within the stomach.
Irregular dense connective tissue with mesothelium (simple squamous)
What makes up the small intestine?
Duodenum, jejunum, ileum
Describe the structure of the mucosa within the duodenum.
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
Describe the structure of the submucosa, muscularis externa and serosa within the duodenum.
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
What is the function of the large intestine?
absorb water from undigested food, structurally distinct from the small intestine
Describe the structure of the mucosa, sub mucosa, muscularis externae and serosa within the large intestine.
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)
