1. Human Anatomy and Physiology The Digestive System

2. Organization Gastrointestinal tract (alimentary canal)
Tube open at both ends for the transit of food during processing.
Functional segments include the mouth, esophagus, stomach, small intestine, and large intestine.
Accessory structures
Contribute to the food processing.
Teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

3. Figure 24.1 Organs of the Digestive System
Accessory organs are highlighted in pink

4. Six Basic Digestive Processes
Ingestion
Secretion
Mixing and propulsion
Digestion
Mechanical digestion
Chemical digestion
Absorption
Defecation

5. Catabolism
Breaking down complex substances into simpler ones with the release of energy (ATP).

6. LAYERS OF THE GI TRACT

7. Four Layers of the GI tract
Mucosa - innermost
Submucosa
Muscularis
Serosa - outermost

8. Mucosa Composed of three layers: Epithelium
Lamina Propria (contains MALT)
Muscularis mucosa
Plays an important role in digestion and absorption
Muscularis
mucosae
Mucosa-associated lymphatic tissue (MALT)
MUCOSA:
Epithelium
Lamina propria

9. Mucosa Epithelium Mucus and enteroendocrine cells
Nonkeratinized stratified squamous epithelium
Simple columnar epithelium
Mouth
Pharynx
Esophagus
Anal canal
FNC: Protection
Stomach
Intestines
FNC: Secretion and Absorption
Mucosa
Epithelium
Mucus and enteroendocrine cells

10. Mucosa 2. Lamina Propria Areolar connective tissue
Blood and lymphatic vessels
Nerves and sensors
Mucosa-associated lymphatic tissues (MALT)
immune system cells
All throughout G.I tract
Prominently tonsils, S.I., appendix and L.I.
Supports epithelium, binds to muscularis mucosa

11. Mucosa 3. Muscularis mucosa Smooth muscle
Creates folds in stomach and S.I
Increases surface area

12. Submucosa Composed of: Areolar connective tissue (highly vascular)
Submucosal plexus (part of the ENS)
Binds mucosa to muscularis
Regulates chemical digestion
Glands in submucosa
Submucosal plexus (plexus of Meissner)
SUBMUCOSA

13. Muscularis
Skeletal muscle in mouth, pharynx, superior esophagus, and external anal sphincter
Rest of GI tract is composed of smooth muscle:
Inner circular muscle
Outer longitudinal muscle
Contains myenteric plexus between (part of ENS)
Plays an important role in mixing and propulsion
MUSCULARIS:
Circular muscle
Longitudinal muscle
Myenteric plexus (plexus of Auerbach)

14. Serosa
Serous membrane of areolar connective tissue and simple squamous epithelium
Secretes serous fluid
Also called the visceral peritoneum
Esophagus lacks a serosa – replaced with adventitia (single layer of loose areolar CT)

15. Figure 24.2 Layers of the GI tract

16. NEURAL INNERVATION OF THE GI TRACT

17. Enteric Nervous System
Second brain  “Brain of the gut.”
Consists of 100 million motor neurons, interneurons, and sensory neurons that extend from the esophagus to the anus.
Located in sheaths of tissue lining the esophagus, stomach, S.I and colon
Neurons arranged into the myenteric plexus and the submucosal plexus.

18. Enteric Nervous System
Myenteric neurons control gastric motility.
Submucosal neurons control the secretory cells.
Can function independently of the CNS.

19. Figure 24.3 Organization of the Enteric Nervous System

20. Autonomic Nervous System
Vagus nerve (X) supplies parasympathetic fibers that stimulate ENS neurons.
Stimulate GI secretion and motility
Sympathetic nerves (from thoracic and upper lumber regions of the spinal cord) inhibit synapse of ENS neurons.
Anger, fear and anxiety slow digestion

21. Gastrointestinal Reflex Pathways
Regulate secretions and motility in response to stimuli present in the lumen.
Reflexes begin with receptors associated with sensory neurons of the ENS.
ENS, CNS, and ANS can modulate reflexes.

22. Sensory Receptors in G.I Tract
Chemoreceptors – respond to chemicals in food in the lumen.
Mechanoreceptors – stretch receptors that are activated when food distends the wall of a GI organ.
Controls of the digestive activity are both extrinsic and intrinsic (nervous and hormonal)

23. PERITONEUM

24. Key Terms
Serous Membrane - Smooth, transparent, two-layered membrane that lines internal cavities of the body, lubricated by a fluid derived from serum. Mesothelium.
Peritoneum – body’s largest serous membrane
Parietal peritoneum – lines abdominal wall
Visceral peritoneum - covers most abdominal organs (serosa); some organs (kidneys, pancreas) are retroperitoneal
Peritoneal cavity - potential space between parietal and visceral peritoneum; contains serous fluid.

25. Figure Relationship of the peritoneal folds to one another and to organs of the digestive system

26. Main extensions of the peritoneum
Greater omentum
Falciform ligament
Lesser omentum
Mesentery
Mesocolon

27. Greater Omentum
Arises from stomach and duodenum, covers small intestine, and attaches to transverse colon. Adipose tissue

28. Falciform Ligament
Attaches liver to abdominal wall and diaphragm.

29. Lesser Omentum
Suspends stomach and small intestine from liver.

30. Mesentery
Largest fold. Binds small intestine to posterior abdominal wall

31. Mesocolon
Binds large intestine to posterior abdominal wall. Works with mesentery to keep the intestines in place.

32. MOUTH

33. Mouth (oral or buccal cavity)
Formed by cheeks, hard and soft palate, lips, and tongue.
Covered externally by skin.
Covered internally by mucous membrane.

34. Mouth (oral or buccal cavity)
Divided into:
Vestibule - bounded externally by cheeks and lips and internally by gums and teeth.
Oral cavity proper - extends from gums and teeth to fauces (the opening between oral cavity and pharynx)

35. Cheeks – contain buccinator muscles
Lips (labia) – contain orbicularis oris muscles; attached to gum by labial frenulum
Lips and cheeks keep food between teeth and assist in speech.
Uvula – the hangy-thing in the back of the throat; blocks nasopharyngeal opening during swallowing