Outline-3, BIO 2320, Digestive System (through stomach)

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)

РLabial frenulum РMidline 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

Stomach function video