Gastro-Intestinal System Flashcards
List the layers of the GI tract
Serosa
Muscularis Externa
- Longitudinal plexus - Myenteric plexus - Circular muscle
Submucosa
Mucosa
- Eptihelium - Lamina propria - Muscularis mucosa
List the three divisions of autonomic neural systems (NS) that regulate GI functions and their functions
PSNS - parasympathetic:
- S2-S4
- stimulates GI secretions and motility
SNS - sympathetic:
- T5-T12, L1-L3
- decreases GI secretions and motility
ENS - enteric:
- myenteric plexus - regulates intestinal smooth muscle
- submucosal plexus - regulates intestinal secretions and local absorptive environment
Give two examples of two non-neuronal signalling molecules and give examples of each
Hormones - endocrine cells; eg.: CCK, gastrin, secretin
Paracrines - prostaglandins and somatostatin
What is prostaglandin responsible for?
Increases blood flow, mucus, and HCO3- secretions
What is somatostatin responsible for?
Inhibits peptide hormones and gastric acid secretions
What are the three digestive phases?
Describe them and their responses/secreted molecules
Cephalic phase
- triggered by thought of food
- releases ACh and VIP
- responsible for 25% of overall secretions by salivary glands, stomach, pancreas, intestines
Gastric phase
- begins when food and oral secretions enter stomach
- responsible for 10% of overall secretions
- causes neural, hormonal, paracrine GI responses
Intestinal phase
- begins when stomach content reach duodenum
- causes mainly hormonal, but paracrine and neural responses too
Talk about ENS reflexes and neurotransmitters
Reflexes:
- Neural circuits that involve mechanoreceptor or chemoreceptor stimulation in the mucosa
Neurotransmitters:
- Enkaphalins: constrict circular muscle around sphincters
- VIP, substance P, ACh, nitric oxide, serotonin
Give 5 examples of GI hormones and explain their function
Cholecystokinin (CCK) - increases enzyme secretions
Gastrin - increases gastric acid secretions
Glucose-dependent insulinotropic peptide - releases insulin; inhibits acid secretions
Motilin - increases contractions and migrating motor complexes
Secretin - releases HCO3- and pepsin
Give 3 examples of GI paracrines and explain their function
Histamine - increases gastric acid secretions
Prostaglandins - increases blood flow, mucus, and HCO3- secretion; decreases gastric acid secretions
Somatostatin - inhibits peptide and gastric acid secretions
Describe the roles of the mouth and its salivary glands in the GI system
Mouth:
- mechanical and chemical breakdown
- tongue repositions food
Salivary glands:
- Sublingual gland
- Submandibular gland
- Parotid gland
Describe the role of the oesophagus
Swallowing - parasympathetic process:
- Afferent feedback to swallowing centre
- Efferent responses through other nuclei (causing muscle contraction)
Peristalsis
- Series of co-ordinated muscle contractions/relaxations that create a wave that pushes food down
- Sphincter relaxes to allow food enter the stomach
Describe the functions, and locations and contents of secretions of the stomach
Functions:
- Accept and store food
- Mix food with secretion
- Digest food
- Deliver food to small intestine
Secretions:
- secretion occurs at gastric vaginations/pits, which are devided into the neck and base
- they contain different types of cells, eg.: Mucous neck cells, G cells, D cells, Chief cells, Parietal cells
- Pits near sphinctors have more mucus cell for protective secretions
Secretions include:
- ions and water;
- mucus from mucous neck cells;
- pepsinogen from chief cells;
- intrinsic factor and H+ from parietal cells
What molecules increase and decrease gastric acid secretion?
Increases:
- ACh (from nerves)
- Gastrin (from G cells)
- Histamine (from enterochromaffin-like cells)
Decreases:
- Somatostatin (from D cells)
- Prostaglandin
Describe the small intestine and list the three sections of the small intestine
- Most macronutient, vitamin and mineral absorption occurs here
- Facilitated by large surface area due to villi and microvilli
- Mixing via segmentation (can slow movement of chyme), and propulsion via peristalsis
Parts:
Duodenum - C-shape around pancreas; function is to neutralise gastric acid and continue digestion (especially fat digestion via bile salts)
Jejunum - suspended on mesentries;
Ileum - suspended on mesentries; enters the first part of the colon (cecum) in the right iliac fossa;
Describe the parts of the large intestine
Cecum (ileocecal sphincter)
Ascending, transverse, descending, sigmoid colon
Rectum
Anus
Function of the ileocecal sphincter
Regulates the amount if chyme entering the large intestine
