Lecture 30 Flashcards
Which types of papillae are taste buds present on?
taste buds are present on fungiform, foliate and circumvallate papillae
Overview of the parts of the Digestive System
Gastrointestinal (GI) tract:
• Esophagus
• Stomach
- Cardiac region
- Body region
- Pyloric region
• Small intestine
- Duodenum
- Jejunum
- Ileum
• Large intestine
Accessory Organs:
• Liver
• Pancreas
• Gallbladder
Organization of the Gastrointestinal Tract
Epithelium differs based on specific functions that the region of the GI tract has. The epithelium of the mucosa functions as a barrier, it separates lumen of GI tract from rest of the body.
Main layers (innermost (next to gut lumen) to outermost layer)
- mucosa (ep lining, lamina propria of LCT, muscularis mucosa of smooth muscle)
- submucosa (DICT)
- muscularis externa (formed by 2 layers of smooth muscle) (inner circular smooth muscle layer) (outer longitudinal smooth muscle layer)
- CT adventitia in esophagus section and simple squamous epithelium where the GI tract of non-esophagus sections is suspended in the body cavity
Functions of Gastrointestinal tract
Main functions include protection, absorption, secretion and motility (specific structures help transport the substances
we absorb).
Esophagus functions in absorption by allowing movement of nutrients into blood and lymph vessels for further processing
Secretory component helps the liver: digestive enzymes, hormones and
antibodies into the GI tract; several glands carry out this function
Plexuses in the Gastrointestinal Tract
Auerbach’s plexus (myenteric plexus): located between the 2 layers of muscularis externa
Meissner’s plexus (submucosal plexus): located submucosa, innervating mucosa layer, and allows lumen of GI tract to expand or contract
Muscularis externa contractions
Muscularis externa formed by 2 layers of smooth muscle (inner circular and outer longitudinal)
In GI tract, there is contraction of inner circular smooth muscle layer that will mix the contents by constricting the lumen. Contraction of the outer longitudinal smooth muscle layer will cause shortening of the tube. The enteric nervous system controls
the contraction of these 2 things, which makes peristalsis (waves of
contraction). Peristalsis is constriction and shortening of tube, allowing food to
move together in GI tract
Esophagus layers
Upper 1/3 – Predominantly skeletal muscle
Middle 1/3 – Both skeletal and smooth muscle
Lower 1/3 – Predominantly smooth muscle
Skeletal muscle is striated
Irregularly shaped lumen
Stratified Squamous Non-Keratinized Epithelium: provides protection from abrasion from the food we eat
Submucosa (DICT) has excretory duct that delivers mucus to the surface and submucosal mucous gland
Parts of the stomach
Esophagus
Esophageal sphincter
- circular smooth muscle layers
Cardia region
Fundus region
Body region with rugae
- largest stomach region
- rugae are folds within stomach that increase SA
Pyloric sphincter
- circular smooth muscle layers
Pylorus region
Duodenum
Gastroesophageal Junction
Stomach
- Simple Columnar Epithelium
- cardiac glands producing mucous secretions
- in first part of stomach, the cardiac section, it has cardiac glands rich in bicarbonate ions to help with acidity of stomach and it prevents stomach acidity from damaging the tissue
- glands formed by epithelial indentations (there are glands specific to each region of stomach)
Esophagus
- Stratified Squamous Non- Keratinized Epithelium
Layers of stomach
Mucosa
- Gastric pits and gastric glands located within mucosa of stomach
- gastric pits open up to gastric glands
Muscularis mucosa
Submucosa
Musculares externa
Mucosa of the Stomach
Mucosa is composed of epithelial indentations, called gastric pits
Gastric pits open up to gastric glands, which are tubular glands and the gastric glands are sometimes coiled up
Gastric gland has NECK (top of gland where it opens up to gastric pit; located on the top of the epithelium) and BASE (towards the bottom)
The surface epithelium and ep lining of
gastric pit are all the same cell type. But, when we reach the gastric gland, we can differentiate b/w diff cell types in the stomach
3 regions of the stomach
Cardia region
- where food enters stomach via esophagus
- pits and glands of same length
- function is to make mucous
Body region
- short pits and long glands
Pylorus region
- long pits and short glands
Different Cell Types found in the Stomach
Cells lining surface epithelium of stomach and gastral pit are the same cell type called surface mucous cells; These cells are lighter in colour and produce mucus/mucin to protect surface epithelium from stomach acidity; surface mucus cells also make bicarbonate.
The neck region has mucous neck cells that produce mucous/mucin
Further down the neck there is parietal cell (very eosinophilic staining); it makes intrinsic factor and hydrochloric acid.
Even further down is endocrine cells that make gastrin; eating or seeing food stimulates gastrin
Even even further down is chief cells in abundance at base of gastric gland; They make pepsinogen (inactive precursor of pepsin) and lipase. Pepsin is first made by chief cells from the inactive precursor
pepsinogen. Pepsinogen needs HCl in order to become pepsin
NOTE: HCL produced by Parietal Cells is made in response to gastrin. Pepsinogen produced by Chief Cells requires HCL to become active as Pepsin.
There is also isthmus, which is “around” the gastric pit
How is pepsin made
HCL produced by Parietal Cells is made in response to gastrin. Enteroendocrine cells make gastrin.
Pepsinogen produced by Chief Cells requires HCL to become active as Pepsin.
Parietal Cells of the Gastric Gland
Parietal Cells appear very eosinophilic because lots of protein in cytoplasm
Has a central nucleus
Parietal cells also form a little canal system called intracellular canaliculis, which increases SA for hydrogen and chloride pumps. Hydrogen and chloride combine to make HCl
They also contain abundant mitochondria in their cytoplasm since lots of energy needed to carry out these processes
