Gastrointestinal Tract Flashcards
What is the overall function of the GI Tract
Digestion and absorption of nutrients
What are the major organs of the GI Tract
Oral Cavity (mouth) Pharynx (throat) Oesophagus Stomach Small Intestine Large Intestine rectum lol
What is the mucosa
The luminal lining of the trac
What are the 4 layers of the GI tract from inside to out
Mucosa
Submucosa
Muscularis
Serosa - squamous epithelial cells, separated from muscularis by loose CT.
What are the 3 layers of the mucosa
Epithelium
Lamina Propria - loose CT
Muscularis Mucosae - thin layer of smooth muscle that supports the mucosa and provides it with the ability to move and fold.
What are the roles of the epithelium in the mucosa
Mainly protective in the mouth, oesophagus and anal canal
Secretion and Absorption in the stomach/intestines
What is the role of the lamina propria
Contains blood and lymphatic vessels - loose CT between muscualris mucosae and epithelium
What is the muscularis mucosae and what is its role
Thin layer of smooth muscle fibres pull mucosa into folds to increase the absorptive surface area
Describe the neuronal networks in the highly vascular submucosa
Has a submucosal plexus AKA Meissner’s plexus - part of the enteric nervous system
What do the neuronal networks of the highly vascular submucosa control
Primarily secretions but also the smooth muscle and blood vessel tone
What parts of the muscularis are skeletal muscle and under voluntary control
Muscularis of the mouth, upper oesophagus and external anal sphincter - these are skeletal muscles
What is the rest of the muscularis, that is not under voluntary control controlled by
Contains intrinsic nerve supply - myenteric plexus AKA auerbach’s plexus
This part is smooth muscle btw
What does the intrinsic nerve supply in the muscularis control
Controls the GI tract motility
What is the serosa
It is the superficial layer of those portions of the GI tract suspended in the abdominopelvic cavity
What are the 2 distinct nervous systems that control GI tract activity
Autonomic nervous system
Enteric/internal nervous system
What effect do the SNS and PNS have on GI tract activity
SNS - inhibitory action on GI tract activity
PNS - excitatory
What plexuses make up the enteric nervous system
Myenteric plexus (Auerbach's) Submucosal plexus (Meissner's)
Describe the myenteric plexus and what it mainly controls
Situated between the longitudinal and circular muscle of the muscularis. Consists of a linear chain of interconnecting neurones and extends the full length of the GI tract.
Mainly controls motor activity along length of GI tract.
Where is the submucosal plexus and what does it mainly control
Lies in the submucosa
Mainly controls secretions and local absorption function within the inner wall of each segment of the gut.
What is mastication
The breakdown of food mechanically and initial enzymatic digestion of ptyalin (alpha-amylase)
What is another word for swallowing
Deglutition
What are the stages of swallowing
- Oral stage - bolus to the back of the oral cavity
- Pharyngeal stage (involuntary)
- Oesophageal phase (involuntary)
What are the main muscles involved in chewing
Masseter
Temporalis
Pterygoids
What innervates the main muscle of mastication
The mandibular division of the trigeminal nerve
What innervates the tongue
Hypoglossal nerve
What nerve mainly supplies the buccinator and orbicularis iris muscles
Facial
What does the bolus pass through in the pharyngeal stage
Oropharynx
Cricopharynx
Into the upper oesophagus
What prevents nasal regurgitation of masticated food
The nasopharynx is shut off from the oropharynx in the pharyngeal stage by the contraction of muscles of the soft palate and posterior pharyngeal wall.
Where does food pass to in the oesophageal stage
Propels food bolus down the oesophagus.
What nerves mediate the oesophageal stage
The vagus nerve and sympathetic nerves
What is the primary peristaltic wave
The positive pressure peristaltic wave that coincides with the entry of the bolus into the oesophagus
What is the stripping wave
This is the smaller positive wave that clears the left over food material from the oesophagus.
What are secondary peristaltic waves
Waves generated in the oesophagus in response to dilation of the oesophagus
Describe tertiary peristaltic waves
Irregular, non-propulsive contractions involving large segments of oesophagus, that occur during emotional stress
How does the rate of progression of peristaltic wave vary in different portions of the oesophagus
- upper part of oesophagus, the peristaltic wave progresses rapidly
- Waves are more sluggish in the lower third of the oesophagus
Why is there a difference in the rate of progression of peristaltic waves in different portions of the oesophagus
Due to the musculature being striated in the upper portion of the oesophagus and smooth at the lower 1/3 of the oesophagus
What are the 3 layers of the smooth muscle in the muscularis
- Outer longitudinal
- Middle circular
- inner oblique
What are the 3 types of exocrine gland cells in the gastric glands
Mucous Neck cells
Chief (zymogenic) cells
Parietal (oxyntic) cells
What do mucous neck cells secrete
Mucus and HCO3-
What do chief (zymogenic) cells secrete
The principal gastric enzyme precursor - pepsinogen
What do parietal (oxyntic) cells secrete
HCl and an intrinsic factor involved in the absorption of Vit. B12
What is gastric juice
This is the combined secretions of the 3 types of exocrine gland cells
What are G cells (enteroendocrine) and what do they do
In mucosa, secrete gastrin
What are the 4 major digestive secreted by enteroendocrine cells
Gastrin
Secretin
Choleocystokinin (CCK)
Gastric Inhibitory Peptide (GIP)
What does gastrin do
stimulates G cells of stomach to secrete gastric juice, a mix of HCl and pepsinogen
What does CCK act on and what reaction does it cause
Acts on gall bladder
Simulates it to contract and release bile
Acts on pancreas to release pancreatic digestive enzymes into the pancreatic fluid
When is secretin released
Secreted by cells in the duodenum when exposed to acidic contents of the emptying stomach
(causes bicarbonate release to neutralise acid)
What does secretin stimulate
Stimulates the pancreas to secrete bicarbonate into the pancreatic fluid (neutralising the acidity of the intestinal contents)
What are the phases of gastric secretion
Cephalic
Gastric
Intestinal
What is the cephalic phase of gastric secretion
Sight/sound/smell initiates reface via medulla, hypothalamus and vagal output to stimulate submucosa plexus to increase gastrin release, gastric peristalsis and HCl release
What is the gastric phase of gastric secretion
Food stretches stomach wall, stretch receptors and chemoreceptors increase submucosal plexus activity that increases gastric juice secretion
Increased myenteric plexus activity increases stomach peristalsis.
Increased parasympathetic = release of gastrin by enteroendocrine cells
What is the intestinal phase of gastric secretion
Activation of receptors in duodenum results in hormonal/neuronal reflexes that are inhibitory on gastric motility and gastric acid secretion.
3 hormones, Secretin inhibits gastric juice secretion,
CCK inhibits motility and GIP inhibits both.
What is the submucosa
The submucosa is a thick connective tissue layer that contains arteries, veins, lymphatics, and nerves.
