Lecture 24 Flashcards
What do we extract and absorb from food? What is the purpose of each of these?
- Metabolites for the growth and energy needs of the body.
- Fluid and electrolytes to replace losses
The gastrointestinal system is (3):
- a long epithelium lined tube
- functional sections separated by sphincters
- connected to accessory exocrine glands
What are the three sections of the small intestine in order?
duodenum
jejunum
ilium
What are the names of the sphincters in the GI tract and where are they located?
- Upper oesophageal sphincter
- lower oesophageal sphincter
- pyloric sphincter
- sphincter of Oddi (helps move bile and juices from your pancreas into your small intestine)
- ileocecal valve
- anal sphincters
What is gastrilation?
This forms the tube with a whole in the middle - you fold on yourself during development
What are the names of the accessory exocrine glands?
- parotid salivary glands
- sublingual salivary glands
- submandibular salivary glands
- liver
- gall bladder
- pancreas
What are the four layers of the GI tract called (in order from lumen, outwards)?
Mucosa
Submucosa
Muscularis externa
Serosa
What three things make up the mucosal layer?
Epithelium
lamina propria
muscularis mucosa
What is the purpose of the epithelium in the mucosal layer?
This is for secretion and absorption
What is the lamina propria?
Thin layer of _______ tissue that forms part of the ________ linings known as the _________. It pushes into the ________. There are also _________ vessels going into the lamina propria for the transport of ___________
Thin layer of connective tissue that forms part of the moist linings known as the mucosa. It pushes into the microvilli. There are also lymphatic vessels going into the lamina propria for the transport of nutrients
What is the muscularis mucosa and what is its purpose?
It is part of the mucosa and its job is to move the villi to bring the chyme into contact with the absorptive surfaces
What are the two layers of the submucosa?
The major blood and lymphatic vessels and the submucosal nerve plexus
What is the purpose of the submucosa?
This is to support the mucosa and to transport hormones and nutrients
What is the purpose of the submucosal nerve plexus?
This is a network of interconnected neurons that will receive info about the goings on in the GI tact lumen from cells in the epithelial layer and can send regulatory messages to secretory cells in this layer
What is a plexus?
This is a network of ________ neurons that communicate with the _______ plexus and the __________ nervous system.
This is a network of interconnected neurons that communicate with the submucosal plexus and the autonomic nervous system.
What are the three layers of the muscularis externa?
- circular muscle
- myenteric plexus
- longitudinal muscle
What is the purpose of the muscularis externa?
This is for controlling large gut motility patterns.
What is the serosa?
This is the final layer of the GI tract
What four things must the gut do?
- ________ the size of the ______ to allow _______
- deliver material to the site of _________
- ________ necessary _______ and _________ the rest
- act as a ______ to ________ and _______
- reduce the size of the food to allow absorption
- deliver material to the site of absorption
- absorb necessary material and excrete the rest
- act as a barrier to pathogens and disease
What four mechanisms are involved in the function of the GI system?
- motility
- secretion
- digestion
- absorption
What direction is secretion?
This is movement from the inside, across the epithelium to the lumen
What direction is absorption?
This is from the lumen, across the epithelium to the inside of the body
Describe the GI motility function
This moves food along the tact from mouth to the anus. It is also mixing and circulating the chyme to perform mechanical and chemical digestion.
Describe the GI secretion function
eg. salt, water, enzymes
this is maintain an environment for digestive functions
Describe the GI digestion function
This is the mechanical and chemical process that breaks down food
Describe the GI absorption function
This is the uptake or re-uptake of nutrients, salts and water into the body
What do we want to regulate in the GI tract?
The composition of the lumen
There are control mechanisms that are governed by what? Describe this
They are governed by the volume and the composition of the intestinal lumen. We are trying to get the contents to a resting state.
There are control mechanisms that are governed by what? Describe this
They are governed by the volume and the composition of the intestinal lumen. We are trying to get the contents to a resting state.
Why is it important that we regulate the lumen of the GI tract?
So that we can have the right solutes and the right pH for the enzymes to do their job
What two things are the GI reflexes stimulated by?
stretch
the chemical composition of the luminal contents
Describe the GI relflexes
Most of the GI __________ can be reflexed as the ENS acts _______ and has receptors to detect certain ________ (chemical and ________). It can send signals that have a direct effect on _______ of the _______ tract to change the _________ environment
Most of the GI neuroregulation can be reflexed as the ENS acts independently and has receptors to detect certain stimuli (chemical and stretching). It can send signals that have a direct effect on effectors of the GI tract to change the luminal environment
What is meant by the chemical composition of luminal contents that initiates a Gi reflex?
- osmolarity of chyme
- pH of chyme
- concentration of products of digestion in the chyme eg. amino acids, fatty acids
What do the stimuli in the GI tract act on?
mechano-, osmo- and chemoreceptors
What are the chemo and osmo receptors?
These are cells in the epithelial layer that communicate with the ENS and secrete their own hormones
What are external sensors?
eg. emotional states