HUMB1000 Lecture Notes - Lecture 3: Salivary Gland, Anal Canal, Mouth

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Digestion
Enzymes
A protein catalyst that increases the rate at which a chemical
reaction proceeds, without the enzyme being permanently
changed.
Highly specific active site on an enzyme can only bind to
specific reactant.
Many different enzymes needed in the body for different
chemical reactions.
Often named by adding ‘ASE’ as a suffix to their reactant.
Lipase enzyme that breaks down lipids
Protease breaks down proteins
Anatomy of the Digestive System
Digestive tract: also called alimentary tract.
Accessory organs: Primarily glands, secrete fluids
into tract
Oral cavity (mouth) with salivary glands
Pharynx (throat)
Esophagus
Stomach
Small intestine (duodenum, ileum, jejunum) with
liver, gallbladder and pancreas as accessory organs
Large intestine including cecum, colon, rectum and anal canal
Anus
Functions of the Digestive System
Ingestion: introduction of food into stomach (via mouth)
Mastication: chewing. Chemical digestion requires large surface area so breaking
down large particles mechanically facilitates chemical digestion
Secretion: lubricate, liquefy, digest (e.g. Mucus: secreted along entire digestive tract,
lubricates food, coats and protects lining)
Digestion: Mechanical and chemical digestion of food into nutrients
Absorption: Movement of nutrients out of digestive tract into cells
Elimination: Waste products removed from body; faeces. Defecation
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Histology of the Digestive Tract
1. Mucosa: innermost layer, secrets mucus.
2. Submucosa: connective tissue layer, contains blood vessels, nerves etc.
3. Muscularis: 2/3 muscle layers, movement & secretion.
4. Serosa / Adventitia: outermost layer, connective tissue, stability
Peritoneum
The walls & organs of the abdominal cavity are lined with serous membranes.
o Visceral peritoneum: Covers organs
o Parietal peritoneum: Covers interior surface of body wall
o Mesenteries: peritoneum (epithelial tissue) which connects organs together. Routes
by which vessels and nerves pass from body wall to organs.
Greater omentum: connects stomach to transverse colon
Lesser omentum: connects stomach to liver & diaphragm
Oral Cavity
Digestion begins in the oral cavity (mouth).
Hard Palate: Hard bone, anterior.
Soft palate: Soft muscle, posterior.
Tongue
Teeth
Masticate (chew) food and turn it into a bolus.
Teeth
Two sets: Primary, milk: Childhood
Permanent or secondary: Adult (32)
Types: Incisors, canines, premolars and molars
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Oral Cavity Salivary Glands
Salivary glands (green) produce & secret saliva into the oral cavity.
Saliva protects oral cavity, moistens, lubricates and digests food.
Amylase enzyme found in saliva that breaks down carbohydrates into smaller
sugars.
Lysozyme antibacterial enzyme
Pharynx & Esophagus
Pharynx (throat) connects oral cavity to the esophagus.
Uvula (soft palate) prevents food/drink from entering the nasopharynx.
Esophagus tube that connects pharynx to stomach. 25cm long, lies posteriorly to
the trachea.
Epiglottis prevents food/drink from entering the trachea.
Swallowing
~ organs of digestion ~
1. Voluntary phase: Tongue pushes bolus to back of oral cavity towards pharynx
(oropharynx).
2. Pharyngeal phase: Soft palate (Uvula) close off the nasopharynx. Bolus touches
receptors on oropharynx and swallowing reflex moves bolus down pharynx and into
esophagus. Epiglottis covers trachea.
3. Esophageal phase: bolus is moved down esophagus towards stomach by peristalsis.
Peristalsis
Process by which food moves through the gut. Waves of smooth muscle relaxations
& contractions.
Stomach
Located in abdomen. ‘holding point’ for
food.
Food comes from the esophagus and the
stomach mixes it (churns) into chyme
(thick liquid).
Produces mucus, hydrochloric acid,
protein digesting enzymes (pepsin).
Contains a thick mucus layer that
lubricates and protects epithelial cells on
stomach wall from acid pH 2-3
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