I. Chapter 25: Digestive System

A. Components (Fig 25.1)

1. Gastrointestinal (GI) Tract ‑ alimentary canal

2. Accessory Organs

3. Digestive processes

a) Ingestion

b) Propulsion (& segmentation)

c) Mechanical digestion

d) Chemical digestion

e) Secretion

f) Absorption

g) Defecation

B. Histology ‑ recurring, from esophagus to anus. Some variation, but generally:

1. Four Layers (from inside → outside; Fig 25.2)

a) Mucosa

b) Submucosa

c) Muscularis

(1) Propulsion & segmentation (Fig 25.3)

d) Serosa

C. Peritoneum (Fig 25.4a, 25.4b, 25.4c, 25.4d)

1. Largest serous membrane in body.

2. Parietal peritoneum ‑ lines walls of abdominal cavity.

3. Visceral peritoneum ‑ covers some of organs.

4. Peritoneal Cavity ‑ contains serous fluid (ascites fluid).

5. Peritoneum has large folds or extensions that connect organs.

6. The Mesenteries

a) Structures

(1) falciform ligament

(2) greater omentum

(3) lesser omentum

(4) mesentery (proper)

(5) mesocolon (transverse & sigmoid; rest is retroperitoneal)

D. Organs of Digestion

1. Oral (Buccal) Cavity (Fig 25.5a, 25.5b)

a) Cheeks ‑ form lateral walls. Epithelium is stratified squamous.

b) Lips ‑ ant terminations of cheeks ‑ inferior, superior. Transparent epidermis

c) Roof

d) Floor ‑ tongue and associated muscles (intrinsic, extrinsic)

e) Lingual tonsils ‑ at base of tongue.

f) Palatine tonsils ‑ between glossopalatine arch and pharyngopalatine arch on each

g) Frenula (lingual, upper lip, lower lip)

h) Uvula

i) Salivary glands ‑ produce saliva ‑ lie outside actual GI tract (Fig 25.6)

j) Teeth ‑ mechanical digestion (Fig 25.7a, 25.7b, 25.7c, 25.7d, 25.7e)

k) Teeth (mechanical) and saliva (chemical) begin the digestive process

2. Esophagus (Fig 25.1, 25.8)

a) Muscular/collapsible tube 10" long.

b) Lies behind trachea, in front of spine.

c) Extends thru the diaphragm via the esophageal hiatus.

d) Terminates in upper stomach.

e) Layers (Fig 25.9)

(1) Mucosa/submucosa as described

(2) Muscularis

(3) Peristalisis: pusching and squeezing of food bolus down the esophagus.

(4) Tunica adventitia: outer layer (no serosa)

3. Stomach ‑ J‑shaped enlargement/mixing/processing area of GI tract (Fig 25.10, 25.11a, 25.11b)

a) Areas

(1) Cardia ‑ around lower esophageal sphincter

(2) Fundus ‑ rounded portion above, left of cardia

(3) Body ‑ large central portion

(4) Pylorus ‑ inferior portion, connects to small intestine, contains pyloric

b) Curvatures (Fig 25.11a)

c) Layers (Fig 25.13L, 25.13)

(1) Mucosa ‑ has large folds, rugae (ROO-gē) allow stomach to distend, increase surf area.

(a) Gastric glands

(i) Parietal cells: HCl & intrinsic factor (absorp. of vit B₁₂ in duodenum)

(ii) Chief cells: pepsinogen

(iii) Goblet cells: mucus

(iv) Enteroendocrine cells: gastrin (↑ smooth muscle contraction in muscularis, ↑ HCL & pepsinogen secretion)

(2) Submucosa ‑ loose & areolar (adipose) CT

(3) Muscularis ‑ extra layer

(4) Serosa ‑ part of visceral peritoneum

4. Small Intestine (Fig 25.14)

a) Three portions: duodenum, jejunum, ileum

b) Histology (Fig 25.15)

(1) Layers of small intestine same as in other GI area, but specialized for absorption

(2) Mucosa

(a) Plicae circularis, villi, microvilli, intestinal crypts

(b) Lamina propria: vessels, lacteals, Peyer’s patches

(c) Regional differences (Fig 25.16)

5. Large Intestine (Fig 25.17a, 25.17b)

a) Function

(1) Completion of absorption

(2) Production of vitamins

(3) Formation of feces

(4) Expulsion of feces

b) Regions: ascending, transverse, descending, & sigmoid colon (rectum/anus)

c) Flexures: hepatic & splenic

d) Histology (Fig 25.19a)

(1) Mucosa

(2) Muscularis ‑ longitudinal muscles; taenia coli, three bands of muscle running

6. Liver (Fig 25.20a, 25.20b, 25.20c, 25.20d)

a) Anatomy

b) Histology

(1) Functional units: lobules (Fig 25.21)

c) Functions

7. Gallbladder (Fig 25.22)

8. Pancreas ‑ Produces digestive juices containing many enzymes. bicarbonate (Fig 25.23)