II. DIGESTIVE SYSTEM
A. Overall digestive process
1. Ingestion– Eating
2. Movement
3. Digestion (mechanical & chemical)
4. Absorption
Digested food moves from GI tract to blood/lymph vessels
5. Elimination – defecation
Eliminate waste
B. Organization
1. Digestive tract, canal, G.I., Alimentary
Continuous tube, about 30 feet from mouth to anus
2. Accessory structures
Aid in digestion, but outside of GI tract
C. Microstructure
1. Mucosa (Villi, microvilli)
Inner lining, mucous membrane
2. Submucosa
Very vascular
3. Muscularis
Mixes and moves food
4. Serosa = Visceral peritoneum
“Watery” connective tissue
D. Peritoneum
1. Parietal peritoneum
Lines abdominal wall
2. Visceral peritoneum
Covers organs
3. Peritoneal cavity
4. Folds of peritoneum
Binds organs together, anchors them to body wall, suspends blood vessels/lymphatics
a. Mesentery proper (S.I.-Dorsal Body Wall)
b. Mesocolon (mesorectum) (L.I.-Dorsal B.W.)
c. Falciform ligament (Liver-Ventral B.W.)
d. Lesser omentum (Lesser curvature stomach
& duodenum to liver)
e. Greater omentum (Greater curvature stomach to dorsal B.W.)
E. Mouth = Oral Cavity
1. Lips (Labia)
– Labial frenulum – Midline fold of mucous membrane
2. Hard palate
Maxilla, palatine bones
3. Soft palate
– Uvula
F. Tongue(Accessory) (glosso-; lingu-)
1. Tissue
Skeletal muscle covered by mucous membrane
2. Lingual frenulum
Midline fold of mucous membrane under tongue
3. Papillae with Taste Buds
4. Function –Bolus
helps to shape a rounded mass of food to be swallowed
G. Salivary Glands(Accessory)
1. Parotid
2. Submandibular
3. Sublingual
4. Saliva [1-11/2 l/d]
a. Composition
1. Water [99%]
2. Mucins
Forms mucus and lubricates food
3. Amylase
Starch breakdown
4. Lysozyme
Anti-microbial
b. Controls of secretion
1. Nervous control; Medulla, pons
2. Autonomic Nervous System
3. Smell, sight, thought, irritation
Increases secretion
4. Dehydration, Fear
Decreases secretion
H. Teeth(Accessory)
1. Gingivae– Gums
2. Crown, Root, Neck
Above, below, at gum line
3. Structure of typical tooth
a. Periodontal ligament (Collagen)-Alveolar process
Anchors tooth root to socket
b. Dentin
Bone-like substance comprising bulk of tooth
c. Pulp / Pulp cavity
Blood vessels, nerves, lymphatics in cavity within dentin
d. Root canal
Extension of pulp cavity through tooth root
e. Apical foramen
At end of root canal for blood vessels/nerves to enter and exit
f. Enamel
Covers dentin on crown, hardest substance in body, calcium phosphate and calcium carbonate
g. Cementum
Bone-like material covering dentin on root of tooth
4. Deciduous [20] vs Permanent [32] teeth
FYI, Not on exam. Dentists count teeth starting with number 1 the farthest back on right upper jaw (wisdom tooth) across to upper left, then down to lower left, tooth 17, across to lower right, tooth 32.
5. Types according to shape & function
a. Incisor [2/2]
Chisel-shaped for cutting food
b. Canine [1/1]
Pointed for tearing food
c. Premolar [2/2]
Crushing and grinding surface
d. Molar [3/3]
Crushing and grinding surface
6. Dental terminology
a. Labial
Towards lips
b. Buccal
Towards cheeks
c. Lingual
Towards tongue
d. Palatal
Towards palate
e. Occlusal
Biting/chewing surface
I. Digestion In Mouth
1. Ingestion
Taking in food/liquid
2. Mastication
Chewing
3. Chemical digestion (salivary amylase)
4. Deglutition
Swallowing, voluntary and involuntary phases
Next structure is pharynx, but was already discussed in respiratory system.
J. Esophagus
1. Hiatus
Passageway through diaphragm
2. Sphincters
Circular muscle superior and inferior esophagus
3. Function
a. Peristalsis
b. Heartburn
K. Stomach(Gastric)
1. Anatomy
– Main areas
a. Cardia
Area where esophagus enters
b. Fundus
Storage area above and left of Cardia
c. Body
Central region
d. Pylorus (sphincter)
Inferior
e. Greater curvature
Convex border
f. Lesser curvature
Concave border
2. Digestion in the stomach
a. Stores food – Chyme
b. Motility & Mixing & Emptying
1. Peristalsis
2. Pyloric sphincter & Duodenum
3. “Pacemaker” Cells [depolarize about 3x/min]
4. Controls [2-6 hours to empty]
a. Volume, Distension
b. Gastrin
Hormone released by cells of pylorus in response to distention. It stimulates gastric motility. Caffeine stimulates gastrin release.
c. Enterogastric reflex
As duodenum distends, it inhibits gastric motility.
d. Secretin, cholecystokinin, gastric inhibitory peptide=glucose-dependent insulinotropic peptide
These intestinal hormones are released in response to duodenal distention with chyme and inhibit gastric motility.
c. Gastric glands & their secretions
1. Juice
a. Zymogenic Cells –Pepsinogen
Activates to Pepsin and breaks down proteins
b. Parietal Cells –HCl– Alkaline tide following a meal
Protein break down, anti-microbial
c. Mucus Cells –Mucus
Protects stomach wall
2. Enteroendocrine Cells (Gastrin)
a. Increased secretions
b. Increased motility
c. Caffeine increases gastrin
3. Controls
a. Cephalic = Reflex phase, Seeing, smelling tasting food
b. Gastric phase – Distension increases secretion
c. Intestinal phase
d. Enterogastric reflex
e. G.I.P., cholecystokinin, secretin– Inhibit gastric secretions
d. Absorption
Very little