THE DIGESTIVE SYSTEM D. C. Mikulecky Faculty Mentoring Program Virginia Commonwealth University.
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Transcript of THE DIGESTIVE SYSTEM D. C. Mikulecky Faculty Mentoring Program Virginia Commonwealth University.
Motility
The digestive tract is surrounded by layers of smooth muscle
These muscles enable mixing and propulsive movement to be carried out by the digestive tract
Secretion
Digestion requires that enzymes be secreted by the pancreas and other organs
Mucous secretions protect the digestive tract
Acid is secreted in the stomachThere are other secretions of
importance
DIGESTION
Breaking down complex foodstuffs into absorbable units by enzymes produced in the digestive system
Involves the breakdown of carbohydrates, proteins fats, and other foods
Absorption
All other functions support this one
This is how we obtain the necessary fuel for our cells
THE DIGESTIVE TRACT
Lumen
Mucosa
SubmucosalPlexus
CircularMuscle
Myenteric Plexus
Logitudinal Muscle
ExtrinsicNerves
CONTROL OF DIGESTIVE SYSTEM
ExternalInfluences
LocalInfluences
Receptors in Digestive Tract
IntrinsicNervePlexuses
Extrinsic Autonomic Nerves
GIHormones
Smooth muscleExocrine Gland CellsEndocrine Gland Cells
Chewing
Chewing is the first step in the digestive process
Food is mixed with saliva and broken up into smaller pieces
Taste buds are stimulated
Salivary secretion
Salivary amylase: digests carbohydrateMoistening and lubricating agentAntibacterial action: lysozyme and
rinsingSolvent for taste stimuliSpeech facilitationOral hygeneBicarbonate buffers neutralize acids
Swallowing A programmed all-or-none reflex Chewing and moving the bolus of food back is manly
voluntary (striated muscle) Pressure of bolus on pharynx triggers involuntary
reflex (smooth muscle) Tongue prevents food from moving back Uvula elevated, sealing nasal passage Larynx elevates and closure of glottis Respiration briefly inhibited Pharyngeal muscles force bolus back Peristaltic waves move bolus through esophagus
THE STOMACH
Esophagus
Body
Antrum
GastroesophagealSphincter
Pyloric
Sphincter
OxynticMucosa
PyloricGlandArea
Fundus
THE STOMACH
Mixing and storage organHas its own pacemaker: sets frequency
of rhythmic peristaltic contractionsPeristalsis becomes stronger in antrumMotility is highly controlledNo absorption of food, only aspirin and
alcohol
FACTORS INFLUENCING GASTRIC MOTILITY
Distension of stomach: increasesFeedback from the small intestine:
decreasesControl from CNSGastrin: increases
FACTORS CONTROLLING STOMAC EMPTYING
Gastric MotilityEnterogastric reflex: Via intrinsic and
autonomic nervesEnterogastrones: secretin,
cholecystokinin (CCK), gastric inhibitory peptide
GASTRIC SECRETIONS
Mucous: Surface Cells Mucous: Mucous Neck
Cells Hydrochloric Acid: Parietal
cells Intrinsic Factor: Parietal
Cells Pepsinogen: Chief Cells Gastrin: Only in the Pyloric
Gland Area
STIMULATION OF GASTRIC SECRETION: Cephalic Phase
Seeing,Smelling,TastingFood
Vagus Intrinsic Nerves
Pyloric Area
Parietal& ChiefCells
GastrinIncreasedGastricSecretion
STIMULATION OF GASTRIC SECRETION: Gastric Phase
Stimuliin Stomach:protein, distension,caffeine,alcohol
VagusIntrinsic Nerves
Pyloric Area
Parietal& ChiefCells
GastrinIncreasedGastricSecretion
THE GASTRIC MUCOSAL BARRIER
Protects the cells from contents of stomach
Luminal membranes of cells are impermeable to protons
Cells are tightly adjoinedRapid turnoverIf broken, peptic ulcer may result:
positive feedback involving histamine