SLE211 Lecture Notes - Salivary Gland, Esophagus, Small Intestine
13 Jun 2018
School
Course
Professor
Digestive System
Functional Processes:
1. Motility: Mixes and moves food throughout the GI system
• Smooth muscle maintaining constant level of tone
Tone: Maintains steady pressure on the contents of DS and prevents the wall from remaining
stretched for too long
2. Secretion: Enzymes (break down food) and hormones (regulation/communication)
• Product emptied into duct where it can be modified
3. Digestion: Mechanical and chemical breakdown of food into smaller absorbable portions
• Hydrolysis
4. Absorption: Movement of digested end products from GI tract into blood or lymph to be
transported around the body
• Most occurs in the small intestine
• Electrolytes
• Organic constituents
Digestive tract -
• Mouth
• Pharynx
• Oesophagus
• Stomach
• Intestines
Accessory Organs -
• Teeth
• Tongue
• Salivary glands
• Liver
• Gallbladder
• Pancreas
Contents of the GI tract are outside the body:
• pH - Highly acidic
• Enzymes are only activated in the lumen (proteases)
• Intestine inhabited by millions of microorganisms
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Basic Structure:
Lumen - Central inside space of a tubular structure, such as an artery or intestine
4 Major Tissue Layers: (innermost)
1. Mucosa (3 layers)
2. Submucosa (Think layer of smooth muscle)
3. Muscularis externa (Longitudinal and inner circular muscle layers)
4. Serosa (Outer connective tissue covering)
Regulation of digestive function:
Autonomous smooth muscle function:
• Smooth muscles do not have constant resting membrane potential
• Intestinal cells of Cajal – Gut Pacemaker cells produce slow-wave potentials
• Slow-wave potentials – wave life fluctuations in membrane potential that if reach threshold,
produce a burst of action potentials
• Basic Electrical Rhythm (BER)
Stimuli Triggers: Food
• When digestive tract is stretched by food, it produces excitatory stimuli
• Resting membrane potential is closer to threshold
Intrinsic Nerve Plexuses (Enteric NS):
• Two major networks of nerves provide GI tract with self-regulation
Myeteri Auerah’s – Located between two muscle layers
Suuous Meisser’s – Located in the submucosa
Primary Afferent Neurons – Respond to local stimuli
Efferent Neurons – Innervate smooth muscles and endocrine/exocrine glands
Excitatory (Ach) – Cause contraction
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Inhibitory (Nitric oxide, vasoactive intestinal peptide) – Cause relation
Extrinsic Nerves:
• Innervate digestive organs (autonomic system)
• Modifies activity of enteric plexus
Gastrointestinal Hormones:
Mouth/Oral Cavity
Functions of mastication: Mostly involuntary
• Mixing food with saliva
• Stimulation of taste buds
Tongue
• Large skeletal muscle
• Repositions food
• Rolls food into a bolus ready for swallowing
• Taste perception
Salivary Glands:
Salivary Proteins:
Amylase - Breakdown of polysaccharides into disaccharides via hydrolysis (Breakdown product =
maltose 2X)
• Most digestion occurs in the stomach
• NO ABSORPTION of food in the mouth
Functions:
1. Lysozyme - Destroys certain bacteria (gram +ve)
2. Solvent for molecules that stimulate taste buds
3. Aids speech – lips and mouth moist
4. Oral hygiene – Flushes mouth
5. Bicarbonate buffers - Neutralises acids to reduce
dental cavities
Mucus - Facilitates swallowing by providing lubrication and holds particles together
Mumps -
• Inflammation of the parotoid glands caused by mumps virus (myxovirus)
• Mainly affects children and males
• May lead to encephalitis (invades the brain)
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