Basic structure of GI system Flashcards
Roles of GI system
Motility: transport food into and through the body, mixing luminal content and transport waste out
Secretion: synthesis and release enzymes, mucus and serous fluid into the lumen
Digestion: break nutrients into smaller pieces
Absorption: bring nutrients/water from the lumen to internal environments
Key structures of GI system
Long tube running through body with outgrowths
Spinchters close off ends and separate sections of tube, thick rings of muscle that when constrict close off tube, dilate to open
Different environments within different organs (e.g. stomach very acidic environment)
Lined by epithelium, reflects function of what is happening in the body
Organs in GI system
Major organs: oral cavity, pharynx, oesophagus, stomach, small intestine and large intestine
Accessory organs: teeth, tongue, salivary glands, liver, gall bladder and pancreas
Epithelia in the GI system
In the mouth/oral cavity, pharynx and oesophagus there is stratified squamous epithelium to protect from abrasion from food
In the stomach, small intestine and large intestine there is simple columnar epithelium for secretion and absorption
In the anus there is stratified squamous epithelium to protect from abrasion from faeces
What are goblet cells?
Goblet cells are unicellular glands which have a basal nucleus and are columnar epithelium. Helps move things along and forms barrier between cells and lumen
What are multicellular glands?
Surface epithelium invaginates to form glands, simple glands have a single duct (e.g. stomach and small intestine) and compound glands have 2 or more ducts which increases surface area and secretion (e.g. salivary glands)
What are the 4 layers of the gut tube?
Mucosa (inner most)
Submucosa
Muscularis
Adventitia (outermost)
What is the mucosa?
Mucosa is epithelial cells attached via a basement membrane to the underlying lamina propria (made up of FCT), amongst this there are blood vessels and lymphatics. Sometimes there are also glands found. Muscularis mucosae is smooth muscle which moves mucosa
What is the submucosa?
Found below the mucosa, predominantly FCT, also contains glands, blood vessels and lymphatics. Secretion of glands is regulated by the submucosal nerve plexus (network of nervous tissue), part of the enteric nervous system, ENS, which controls GI system and regulates secretion
What is the muscularis?
The muscularis consists of smooth muscle and has two main layers: inner circular (circularly arranged) and outer longitudinal
It is innervated by the myenteric plexus which is located between muscle layers and regulates motility
What is the adventitia?
The adventitia is the outermost connective tissue layer consisting of FCT, supports organ and anchors neighbouring structures
Mouth and oral cavity
Digestion begins in the mouth and oral cavity. Mechanical (chewing-teeth)and chemical (requires enzymes-amylase), lubrication needed. Goes through faucets, into oropharynx and laryngopharynx then into oesophagus
Salivary glands
3 pairs connected to oral cavity via ducts. Parotid are located behind the ear and secrete serous fluid with amylase, sublingual are located below the tongue and secrete mucus only and submandibular are located below your mandible and secrete serous fluid and mucus
Histology of salivary glands
Compound secretory glands (want lots of secretions), multiple ducts/cells in clusters - acinus. Acinar cells can secrete serious fluid, enzymes (amylase) and mucus. Duct cells secrete bicarbonate (useful for pH buffering)
What is the oesophagus?
The oesophagus is a long tube ~ 25cm, located posterior to trachea, extending from pharynx to stomach. Epiglottis ensures that food enters oesophagus and not trachea
