GI Flashcards
Where does the GI tract extend to
From the mouth to the anus
Whats its primary function
absorption of dietary nutrients, this is maximised by sections that convert larger molecules to smaller molecules ie, digestion
What is motility
Contents, including secretions, mixed and moved along tube by coordinated contraction/relaxation of tube walls
What are the other functions of the GI
storage and excretion
What is mucosa composed of
epithelium + lamina propria + muscularis mucosa
tell me some facts about the GI epithelium
shed and replaced every 2-3 days
apical side faces GI lumen , basolateral side faces interstitum and vasculature
lamina propria
loose CT made up of: elastin and collagen fibres Contains: sensory nerves blood and lymph vessels secretary glands
Muscularis mucosa
thin layer of smooth muscle
further increases surface area by creating ridges and folds
Tell me about the submucosa
thick layer
blood vessels and nerve bindles that form a submucosal plexus (messier plexus)
this is an integral part of the nervous system
Tell me about the Muscularis externa
this is composed of circular muscle + myenteric plexus + longitudal muscle
this is known as the Auerbach plexus
What is the function of the ENS
coordinates contractions to mix and move contents between compartments
What do spinchters
regulate flow from compartment to next
Tell me about the serosa
outmost layer of the connective tissue
layer of squamous epithelial cells
Some GI tract sections do not have this and connect straight to adventitia (outer layer of the blood vessels) e.g. abdominal or pelvic wall
What are the 3 divisions of the autonomic system that regulate GI function
parasympathetic
sympathetic
enteric
Tell me about the parasympathetic systems role in the GI
PSNS signals stimulate GI secretions and motility facilitating digestion and absorption of nutrients
What does the Sympathetic nervous system do to the GI
decreases GI secretions and motility
Tell me about the functions of the ENS
The PSNS and the SNS usually synapse with ENS components and modulate the ENS
This can however operate autonomously via intrinsic regulation and sensory reflexes
ENS nerves are organised into myenteric and submucosal plexus
Desribe to me the myenteric plexus
A dense parallel neuronal configuration
primary role in regulating intestinal smooth muscle
participates in tonic and rhythmic contractions
describe the submucosal plexus
primary regulates intestinal secretions and local absorptive environment
can also synapse on blood vessels, circular and longitudinal muscle, muscularis mucosa
What is the ENS supported by?
enteric glial cells which resemble brain astrocytes
Tell me about the reflexes of the ENS
neural circuits involving mechanoreceptor or chemoreceptor stimulation in the mucosa regulate many GI reflex actions
signal transmitted back to neurons in submucosal plexus which stimulate other neurones in submucosal or myenteric plexus that regulate endocrine or secretory cells
Tell me about the neurotransmitters of the ENS
Enkephalins: constrict circular muscle around sphincters
VIP, substance P, ACh, nitric oxide, serotonin (5-hydroxytryptamine)
Non-neuronal signalling molecules: give me some examples of hormones
CCK, gastrin, secretin
Paracrines
released and act locally
prostaglandis and somatostatin are more widespread in their release and actions than histamine
What are the digestive phases
Cephalic
Gastric
Intestinal
Tell me about the cephalic
triggered by thought of food, conditions suggestive of previous food intake
primarily neural and causes ACh and VIP release
-stimulates secretion by salivary glands, stomach, pancreas, intestines
GASTRIC PHASE
Begins when food and oral secretions enter the stomach
coincides with distension
Elicits neural, hormonal, paracrine GI responses
INTESTINAL PHASE
Begins when stomach contents reach duodenum
Initiates primary hormonal, but also paracrine and neural responses
What are the GI hormones
Cholecystokinin Gastrin Glucose-dependant insulinotrpoic peptide motion secretin
GI paracrines include
histamines
prostaglandis
Somatostatin
What do the phases of digestion prepare for?
they allow for preparation and timing and regulation feedback, the cephalic is primary a feed forward regulation
the gastric and intestinal phases are feedback mechanisms
What is the upper GI tracts role
transports and prepares food to be absorbed, breaking into smaller pieces, hydrating it to improve environment for enzymatic actions
What is the mouths role in GI
mechanical and chemical breakdown
mastication = chewing
teeth = cut, tear and pierce, grind and crush
jaw muscles provide force and movement
tongue = repositions food, tastes
What is the role of the salivary glands
watery fluid lubricates mouth, begins food digestions, is protective
hypotonic to plasma:
-composition determined by ductal modification of primary secretion
what is the oesophagus in the GI
afferent feedback to the swallowing centre
efferent responses through other nuclei
-muscle contracted proximal to distal
-coordinates other functions like speech and breathing
What is the oesophagus’s role in peristalsis
series of coordinated muscle contractions/relaxations causing waves
commences after upper oesophageal sphincter this takes 6-10 seconds
what are the functions of the stomach
accept and store food
mix food with secretions
digest food
deliver food to small intestine
tell me about the secretions of the stomach
derived from pits known as gastric invaginations
What are the three sections of the small intestine
- duodenum
- jejunum
- ileum
This is where most macronutrient vitamin, mineral absorption occurs
LARGE INTESTINE
Caecum
Asending, transverse, descending, sigmoid colon
rectum
anus
this is where significant water and ion absorption
mixing and propulsion (pushing forwards)
