Gastrointestinal Tract Flashcards
What is the primary function of the GI tract?
Absoprtion of dietary nutrients
What 3 things make up the mucosa?
Epithelium, lamina propria and muscularis mucosa
Describe the epithelium in the GI tract
Single cell layer, replaced every 2-3 days, apical side faces lumen, basolateral side faces interstitium
Describe the lamina propria
Loose connective tissue made up of elastin and collagen fibres, contains nerves, blood and lymph vessels, secretory glands
Describe the musclaris mucosa
Thin layer of smooth muscle, increases surface area by creating ridges and folds
What are the different layers of the GI tract?
Mucosa, submucosa, muscularis externa and serosa
Describe the submucosa
Thicker layer- similar to lamina propria
What can be found in the submucosa layer?
The submucosal plexus- blood vessels and nerve bundles- integral part of the enteric nervous system
What 3 things make up the muscularis externa?
Circular muscle, myenteric plexus, longitudinal muscle
Describe the muscularis externa layer
ENS co-ordinates contractions to mix and move between compartments, sphincters regulate flow
Describe the serosa layer?
Outermost layer of connective tissue + layer of squamous epithelial cells
What occurs when there is no serosa layer in certain parts of the GI tract?
They will directly connect to the adventitia
What 3 divisions of the autonomic nervous system regulate the GI system?
Parasympathetic
Sympathetic
Enteric
Where is the PNS controlled from?
Medulla oblongata
Pelvic-splanchnic nerves
What does the PNS respond to?
Stretch, pressure, temperature and osmolarity
What are the primary neurotransmitters of the PNS?
Acetylcholine, Gastric-releasing peptide
What does the PNS signals?
Stimulation of GI secretions and motility
Where do the nerves originate from in the SNS?
Thorathic (T5-T12) and lumbar (L1-L3) regions
Where is the upper Gi tract innervated from?
Superior cervial gaglion
What is the SNS’ function?
Generally decreases GI secretions and motility
What is the ENS usually synpased with and controlled by?
Both the PNS and SNS
What can you organise the ENS nerves into?
Myenteric and submucosal plexuses
How can the ENS operate autonomously?
Via intrinsic regulations and sensory reflexes
Describe the myenteric plexus
Dense parallel neruonal configuration
What is the function of the myenteric plexus?
Regulating intestinal smooth muscle by participating in tonic and rhythmic contraction
What is the function of the submuscosal plexus?
Regulates intestinal secretions and local absorptive environment
What are ENS neurons supported by?
Enteric glial cells
Describe ENS reflexes
Neural circuits involving mechanoreceptor or chemoreceptor simulation in the mucosa, signal transmitted back to neurons in submucosal plexus
Examples of neurotransmitters of the ENS
Enkephalins- constrict muscle around sphincter
VIP, substance P, ACh, nitric oxide, serotonin
What are the non-neuronal signalling molecules?
Hormones and paracrines
Give some example of GI hormones
Gastrin- increases gastric acid secretion
Secretin- Releases HCO3- and pepsin
Give some examples of GI paracrines
Histamine- increases gastric acid secretion
Somatostatin- Inhibits peptide hormones and gastric acid secretion
What are the 3 phases of digestion?
Cephalic, gastric and intestinal phase
Describe the Cephalic phase of digestion
Triggered by thought of food
Primarily neural and causes ACh and VIP release- stimulates secretion
Describe the Gastric phase of digestion
Begins when food and oral secretions enter stomach
Coincides with distension
Elicits neural, hormonal, paracrine GI responses
Describe the Intestinal phase of digestion
Begins when stomach contents reach duodenum
Initiates primarily hormonal, paracrine and neural responses
What is included in the upper GI tract?
Mouth, oesophagus and stomach
What is the function of the upper GI tract?
Transports and prepares food to be absorbed
What is the function of the mouth?
Mechanical + chemical breakdown
What does mastication mean?
Chewing
What is the order of the type of teeth working front to back?
Incisors, canine, premolar and molars
What are the four basic structures of a tooth?
Enamel, dentin, pulp cavity and root canal
Describe the function of the salivary glands?
Produces watery fluid which; lubricates mouth, digest
What produces saliva?
Sublingual, submandibular and parotid glands
Describe peristalsis
Series of co-ordinated muscle contractions/relaxations
What are the functions of the stomach?
Accept and store food
Mix food with secretions
Digest food
Deliver food to small intestines
What muscle allows food to enter the stomach?
Lower eophageal sphincter
What muscle allows food to enter the duodenum?
Pyloric sphincter
Where do secretions come from in the stomach?
Pits
What cells make up the pits in the stomach?
Within the neck- mucous neck cell, G and D cells
Within the base- chief cell and parietal cell
What are the three parts of the small intestines?
Duodenum, jejunum and ileum
What parts make up the large intestines?
Caecum
Ascending, transverse, descending, sigmoid colon
Rectum
Anus
What is the function of the large intestine?
Significant water and ion absorption, motility of contents
