GI System Flashcards
What is the mucosa layer of the GI made up of?
epithelium
lamina propria
muscularis mucosa
Properties of epithelium in GI?
continuous lining in GI tract
shed and replaced every 2-3 days
apical side faces GI lumen, basolateral side faces interstitium and vasculature
extent of vili and crypts depend on the section function of GI
What is the lamina propria?
Loose connective tissue made up of elastic and collagen fibres
contains sensory nerves, lymph vessels and secretory glands
What is the muscularis mucosa?
thin layer of smooth muscle that increases surface area by creating ridges and folds
What is the submucosa?
Thicker layer with similar composition to lamina propria
incorporates blood vessels and nerve bundles that form a submucosal plexus- it is an integral part of enteric nervous system
What is the Meissner Plexus?
Submucosal plexus
What is the muscularis externa made up of?
circular muscle
myenteric plexus
longitudinal muscle
What is the Auerbach plexus?
Myenteric plexus
Properties of muscularis externa
ENS coordinates contractions to mix and move contents between compartments, sphincters regulate this flow.
What makes up the serosa?
Outermost layer of connective tissue and squamous epithelial cells
What do sections of the GI tract have if they do not have a serosal layer?
They connect directly with adventitia
What divisions of the autonomic nervous system regulate the GI?
parasympathetic
sympathetic
enteric
Where is GI innervation from the parasympathetic nervous system derived from?
Vagus in the medulla oblongata
Pelvic splanchnic nerves in S2-S4
What stimulates the sensory and motor components of the parasympathetic NS?
stretch
pressure
temperature
osmolarity
What are the primary transmitters of the parasympathetic NS in the GI?
acetylcholine ACh
gastric-releasing peptide
substance P
What processes does the parasympathetic nervous system facilitate in GI system? *
digestion and absorption of nutrients
Where does the nerves of the sympathetic nervous system originate and synapse?
Originate: thoracic region T5-T12 lumbar region L1-L3 celiac ganglion Synapse: superior mesenteric ganglion inferior mesenteric ganglion
What innverates the upper GI region? (sympathetic NS)
Nerves that synapse in superior cervical ganglion
decreases GI secretions and motility
Organisation of ENS nerves?
myenteric and submucosal plexuses
Operation of ENS?
Autonomously by intrinsic regulation and sensory reflexes
Properties of myenteric plexus?
dense parallel neuronal configuration
regulates intestinal smooth muscle
tonic and rhythmic contractions
Properties of submucosal plexus?
regulates intestinal secretion and local absorptive environment
can synapse on blood vessels, circular muscle and longitudinal muscle, and muscularis mucosa
What supports ENS neurons?
enteric glial cells that resemble brain astrocytes
What regulates ENS reflexes?
Neural circuits involving mechanoreceptor or chemoreceptor stimulation in mucosa
Explain how a signal is transmitted in ENS?
Signal transmitted to neurons in submucosal plexus, which stimulate other neurons in submucosal or myenteric plexus that regulate endocrine or secretory cells
What neurotransmitters are used by ENS?
enkephalins: constrict circular muscle around sphincters
VIP, substance P, ACh, nitric oxide and seratonin
Explain cephalic phase of digestion*
triggered by the thought of food
Neural and causes release of ACh and VIP which stimulates secretion by salivary glands, stomach, pancreas, intestines
Explain the gastric phase of digestion*
begins when food or oral secretions enter stomach
coincides with distension
neural, hormonal and paracrine GI responses
Explain intestinal phase of digestion*
begins when stomach contents reaches duodenum
hormone, paracrine and neural responses
GI hormones
cholecystokinin gastrin glucose dependent insulinotropic peptide motilin sectretin
GI paracrines
histamine (increases secretion)
somatostatin (decrease secretion)
prostagladins (decrease secretion)
What is the role of the upper GI tract?
transports and prepares food for absorption- breaking food down and hydrating to improve environment for enzymatic action
Role of mouth*
mechanical and chemical breakdown with mastication (chewing)
Role of salivary glands
Produces saliva by sublingual and submandibular and parotid glands
lubricates mouth, begins food digestion and is protective
What type of process is swallowing?*
A parasympathetic process
provides afferent feedback to swallowing centre and efferent responses through other nuclei
Describe the process of swallowing*
tongue forces food back to initiate voluntary process
soft palate pulled upward to close access to nasopharynx
larynx and hyoid bone pulled upwards and epiglottis closes off access to larynx
upper esophageal sphincter relaxes to allow food to enter esophagus
What is peristalsis? *
A series of coordinated muscle contractions/relaxations that commence after the upper esophageal sphincter and propels food down oesophagus
What are the functions of the stomach?
accept and store food
mix food with secretions
digest food
deliver food to small intestine
How are salivary secretions controlled?
by sympathetic and parasympathetic processes in 2 steps
- Na+ and Cl- transported into duct lumen
- ductal cells modify them by reabsorbing Na+ and Cl- and secreting HCO3 and K+
Gastric secretions
ions water mucus from mucus neck cells pepsinogen from chief cells intrinsic factor and H+ from paritetal cells
Properties of small intestine *
longest section where most macronutrient, vitamin and mineral absorption occurs
mixing by segmentation and propulsion by peristalsis of contents
made up of duodenum, then jejunum, then ileum (longest)
Properties of large intestine *
consist of caecum, ascending, transverse and descending, sigmoid colon, rectum and anus
where water and ion absorption take place
segmentation, peristalsis and mass movement occur
What does the ileocecal sphincter do?
regulates amount of chyme entering large intestine
Function of sympathetic nervous system in relation to GI system? *
Sympathetic stimulation causes inhibition of gastrointestinal secretion and motor activity, and contraction of gastrointestinal sphincters and blood vessels.
Function of enteric nervous system in relation to GI system? *
It contains full reflex circuits for control of intestinal motility, fluid transport, blood flow and nutrient handling.
Role of oesophagus? *
Transports food from mouth to stomach
What are the different parts of the stomach from top to bottom?
Fundus
Body
Antrum
Pyloric sphincter
What are the layers of the GI from inside to out?
Mucosa
Submucosa
Muscularis externa
Serosa
