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