GI System Flashcards
What structures are apart of the tubular GI tract?
Mouth, pharynx, esophagus, stomach, small and large intestine
What are the accessory organs?
teeth, tongue, salivary glands, liver, gall bladder and pancreas
Describe what occurs in the mouth.
Tongue - tastes and guides food
Teeth - grind food
Saliva - mixes food
Describe what occurs during the swallowing reflex
- tongue pushed against soft pallet
- respiration inhibited by epiglottis blocking larynx
- food pushed into esophagus from pharynx
What is the esophagus and how does it perform its function?
A tube that moves food to the stomach by peristalsis
What is peristalsis?
muscular contractions of the digestive tract
Describe what occurs in the small intestine
- peristalsis
- digestion of all nutrients
- main site of nutrient absorption
What are the three parts of the small intestine?
- duodenum
- jejunum
- ileum
How do the liver and pancreas aid in digestion?
liver - provides bile salts and bilirubin via gall bladder
pancreas - provides bicarbonate and various enzymes
What occurs in the large intestine (colon)?
- mass movement
- absorption of water and electrolytes
- storage of fecal material for expulsion
What is the structure of the GI tract wall (4 layers)?
- Mucosa
- submucosa
- muscularis (contraction)
- serosa
networks of neurons - submucosal plexus and myenteric plexus
What are the specialized cell of the mucosa and what is their function?
TRANSPORT cells - secrete acid, bicarbonate, absorb nutrients, water and vitamins
ENTEROENDOCRINE cells - secrete hormones into blood
EXOCRINE cells - secrete enzymes, mucous etc.
- goblet cells: secrete mucous
- paneth cells: secrete antimicrobial compounds
Myenteric plexus
regulates motility (contraction)
Submucosal plexus
regulates secretion and absorption
How does the PNS control the digestive system?
vagus nerve synapses on enteric system neurons, postganglionic fibres release ACETYLCHOLINE
- increase gut muscle activity
- relax sphincters
- increase secretion
How does the SNS control the digestive system?
postganglionic neurons innervate entire GI tract, releasing NORADRENALINE
- inhibit gut movements
- constrict sphincters
- reduce secretion
How does the GI tract regulate its own activity?
- neural mechanisms
- hormonal mechanisms
- local mechanisms ie. pH, physical/chemical stimulation
What arteries supply the stomach, small and large intestine?
Stomach - celiac artery
Small - superior mesenteric artery
Large - superior and inferior mesenteric srteries
Describe blood flow from the GI tract and in the liver.
Blood from GI tract returns to the heart via the liver.
- hepatocytes clean blood of harmful substances
- hepatic portal vein and artery blood pools in sinusoids
- moves to central veins, drains into hepatic veins and returns to heart
How does the GI smooth muscle operate as a single unit?
cells are connected by gap junctions and action potentials travel in all directions
What causes contractions of GI smooth muscle?
slow waves must exceed threshold - determines frequency of APs
force and duration of contraction are directly related to the amplitude and frequency of APs
Interstitial cells of Cajal
- generate slow waves and action potentials
- located between nerve fibres and smooth muscle cells
What causes depolarization of Interstitial cells of Cajal and how often does it occur?
Ca2+ entry
depolarizes ~3/min in stomach and ~12/min in duodenum
