PHYL2001 Study Guide - Final Guide: Glut5, Ileum, Vagus Nerve
Gastrointestinal Physiology
Functions of the Gastrointestinal System:
• Secretion
• Mixing and metering
o Motility to mix and deliver food to appropriate sites at appropriate
rates
▪ Propulsive to deliver
▪ Non-propulsive to mix
• Absorption
o Requires digestion in appropriate sites because most food is too
big to be absorbed intact
• Excretion
o Biliary system
o Non-absorbed materials
o Dead cells, bacteria
Nerves and Hormones:
• Both coordinate motility to deliver food to absorptive sites at a rate
readily handled by small intestine
• Stimulate secretion when food is present in right place
• Turn off secretion when food is no longer present
• Relies on pacemaker activity → modulated by parasympathetic and
sympathetic nervous systems
• Effector systems
o Muscles
o Secretory epithelium
o Endocrine and exocrine cells
• Sensory systems
o Stretch receptors
o Chemoreceptors
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Phases of Digestion:
• Interdigestive → little activity
• Cephalic → nerves
• Gastric → nerves and hormones
• Intestinal → largely hormones
Organs of the Gastrointestinal System:
• Mouth
o Teeth → mechanical breakdown
o Salivary glands → secrete mucous, amylase and lysozyme
o Secretion mainly activated by parasympathetic nerves and
chewing
o Sympathetic nervous system can modify saliva composition
• Oseophagus
o Peristalsis to move food bolus down into stomach
o Start of gastric phase
• Stomach
o Muscular dilation of GIT
o Role → digestion, mixing,
metering
o Produces
▪ HCl
• Activates
pepsinogen for
protein
breakdown
• Gastric germicidal
barrier
• Denatures protein,
assisting digestion
• Solubizes Fe3+,
assisting
absorption
▪ Pepsinogen
• Converted to pepsin → active form
• Begins protein digestion
• Reduces gastric contents to chime (with acid)
▪ Mucous with bicarbonate to protect against acids
▪ Intrinsic factor → binds vitamin B12 (for absorption)
o Irritations to digestive tract can lead to retropulsion → food
material ejected out of stomach/intestine via osepophagus
o 3 parts
▪ Fundus
▪ Body → contains mucous cells, parietal cells, chief cells
▪ Antrum → closest to duodenum
• Large intestine
o Digestion of dietary fiber
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