digestive physiology Flashcards
Label:
Organs of the digestive system
in order
- oral cavity
- pharynx
- esophagus
- stomach
- small intestine: duodenum, jejunum, ileum
- large intestine: ascending colon, transverse colon, descending, sigmoid
- rectum
- anus
Label:
Accessory organs of the digestive system
in order
- teeth = mechanical breakdown
- tongue = concerts to bolus
- Salivary glands
- liver
- gall bladder
- pancreas
What is the aim of control of the digestive system?
motility & secretion
How is the digestive system controlled?
- neural mechanisms
- hormonal mechanisms
What does the neuroendocrine control?
- salivary secretion
- gastric function (stomach)
Describe:
Control of salivary secretion
controlled by ANS (PNS)
activated by:
* thought, sight, smell of feed
* stimuli associated with food (sitting at the dining table)
* food in the mouth
Name:
The salivary glands
- Parotid
- Sublingual
- Submandibular
Name:
Phases of gastric stimulation
- Cephalic Phase
- Gastric Phase
- Intestinal Phase
In what phase is gastric juice released before food is in the stomach?
Cephalic phase
What triggers the cephalic phase?
explain what happens after
triggered by: sight, smell, taste, or thought of food
- olfactory & taste centres send message to hypothalmus
- hypothalamus sends message to brainstem/medulla
- medulla stimulates gastrin release (from stomach) into blood vessels via vagus nerve
- gastrin stimulates stomach to release gastric juices into the lumen of the stomach
purpose = prepare stoamch for incoming food
What makes up gastric juices?
- HCl
- enzymes: pepsinogen, mucus (protects lining)
In what phase is food in the stomach?
gastric phase
Describe:
Receptors in the stomach wall
gastric phase
Chemoreceptors = stimulated by chemicals in the food
Stretch receptors = stimulated by distention of the stoamch wall
What stimulates chemoreceptors?
- proteins
- low acidity of stomach (low H+ ions)
What happens in the:
Gastric phase
2 effects
direct local effect = secretion of gastric juices into the lumen of the stomach
indirect effect = via hypothalmus –> medulla –> vagus nerve
* secretion of gastrin into blood –> stimulates more secretion of gastric juices into lumen of the stomach
purpose = maintain digestion
In what phase does food enter the duodenum?
Intestinal phase
What are the 2 phases of the intestinal phase?
Excitatory phase = stimulates release of increase of digestive enzymes
Inhibitory phase = when too much digestion is occuring, it slows down digestion (negative feedback)
How does chyme stimulate the duodenum?
- chemical (partially digested food)
- pH (Acid)
- stretch
What happens in the:
Intestinal phase
Part 1: positive feedback
* stimulates gastric secretion and motility –> release intestinal gastrin (via vagus neve)
* stimulates pyloric sphincter relaxation
Part 2: negative feedback
* increases acid (low pH) and stretch of duodenum decreases gastric secretion & slow down motility
* chemicals initiate secretion of some hormones
How is gastric function inhibited?
two mechanisms
- neural = enterogastric reflex
- hormonal = enterogastrones
Describe:
enterogastric reflex
activated by: distension of duodenum & low pH
effects: slow down!
* inhibits gastric motility
* inhibit secretion
* constricts pyloric sphincter
Describe:
Enterogastrones
hormones? functions?
hormonal regulation
hormones: GIP, CCK, secretin
functions:
* inhibit secretion and motility
* cause contractions of accessory organs –> stimulate pancreatic juice and bile into intestines
Describe:
gastric inhibitory peptide (GIP)
trigger? effects?
released by: presence of fats or glucose in chyme in duodenum
effects: inhibits gastric phase of gastric function
* decreases motility and secretion in stomach
Describe
cholecystokinin (CKK)
trigger? effects?
released by: presence of fatty chyme in duodenum
effects:
* stomach: inhbits gastric secretion and motility
* pancreas: increase secretion
* gall bladder: stimulate contraction to eject bile into duodenum
