BIOL 2420 Lecture Notes - Lecture 6: Medulla Oblongata, Enteric Nervous System, Vagus Nerve
26 Apr 2018
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Unit 9 – Lecture 6
Integrated Function: The Cephalic Phase
- Digestive processes in the body begin before food enters the mouth
o Smelling, seeing, or thinking about food make our mouths water and our stomachs
rumble
- Cephalic phase of digestion
o A feedforward response created from the long reflexes beginning in the brain
- Anticipatory stimuli and the stimulus of food in the oral cavity activate neurons in the medulla
oblongata
o Medulla in turn sends an efferent signal though autonomic neurons to the salivary glands
o Through the vagus nerve to the enteric nervous system
o In response to these signals, the stomach, intestine, and accessory glandular organs begin
secretion and increase motility in anticipation of the food to come
Chemical and Mechanical Digestion Begins in the Mouth
- When food first enters the mouth it is met by saliva (a secretion)
- Saliva has 4 important functions
1. Soften and moisten food
▪ Water and mucus in saliva soften and lubricate food to make it easier to swallow
2. Digestion of starch
▪ Chemical digestion begins with the secretion of salivary amylase
• Amylase breaks starch into maltose after the enzyme is activated by Cl-
in saliva
3. Taste
▪ Saliva dissolves food so we can taste it
4. Defense
▪ Final function of saliva is defense
▪ Lysozyme – an antibacterial salivary enzyme
▪ Salivary immunoglobins and lysozyme disable bacteria and viruses
▪ Saliva helps wash the teeth and keep the tongue free of food particles
- Mechanical digestion of food
o Begins in the oral cavity with chewing
o Lips, tongue, and teeth all contribute to the mastication of food
▪ Creates softened, moistened mass (bolus) that can be easily swallowed
Saliva Is an Exocrine Secretion
- Saliva
o Complex hyposmotic fluid
o Contains water, ions, mucus, and proteins (enzymes and immunoglobins)
o 3 pairs of salivary glands produce <1.5L of saliva per day
▪ salivary glands are exocrine glands, with secretory epithelium arranged in grape-
like clusters of cells called acini
▪ each acinus surrounds a duct, and the individual ducts join to form larger and
larger ducts (like stems on a bunch of grapes)
▪ main excretory duct of each gland empties into the mouth
▪ secretions vary in composition from gland to gland
• parotid glands
o produce water solution of enzymes
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