1. Digestive System
Chapter 22 – Day 1
3/24/08

2. Digestive system Respiratory System Cardiovascular System
Brings O2 to the body
Cardiovascular System
Brings O2 to the cells
In tissues O2 is used for cellular respiration, BUT…
O2 is only one of the ingredients – you also need
Glucose
Digestive System
Brings glucose to the body
Other sources of nutrients
And other building blocks to make cells
3/24/08

3. Digestive system Food is broken down & processed
Nutrients are absorbed
Waste products are eliminated
All of this happens in the digestive tract
A.K.A. alimentary canal or GI tract
The digestive tracts is a long, continuous muscular tube starting at the esophagus
3/24/08

4. Digestive system
Fig
3/24/08

5. Digestive system - Processes
In order for nutrients to reach cells the digestive system carries out several processes
Ingestion = food in the mouth
Mechanical processing = physically breaking food into bits
Digestion = enzymes and hormones
Absorption = organic molecules enter interstitial fluid
Excretion = elimination of unwanted materials
3/24/08

6. Digestive system – Cell/Tissue layers
The digestive system has a distinct system of tissue layers
There is an “open” surface inside the GI tract – epithelial tissue covering on outside
4 layers – from inside to outside
These are there ALL ALONG the GI tract
Mucosa
innermost layer
Submucosa
Muscularis externa
Serosa
outermost layer
Fig. 22.3
3/24/08

7. Cell/Tissue layers - MUCOSA
Digestive epithelium
Connective tissue – lamina propria
(smooth) muscle tissue – muscularis mucosa
Type of epithelium varies along the GI tract
Pharynx & esophagus handle large masses of food = stratified epithelium
In the stomach – food becomes liquid & passes to intestines
A great deal of absorption happens in the intestines
Simple columnar epithelium
Secrete mucous
Highly folded epithelial surface (small intestine)
Lamina propria – areolar connective tissue right below basement membrane of epithelium
Contains blood vessels, nerves, mucous glands (in the intestines this is where you find the Peyer’s patches)
Muscularis mucosa = smooth muscle – helps movement in the GI tract
3/24/08

8. Cell/Tissue layers - SUBMUCOSA
Dense connective tissue
Nerve network
Submucosal plexus
Communication with the nervous system – helps muscle movement
3/24/08

9. Cell/Tissue layers – MUSCULARIS EXTERNA
Smooth Muscle Tissue
Nerve network
Mysenteric plexus
More forceful contractions for movement
2 layers of muscle
Longitudinal
Circular
Allows 2 types of movement
Rocking motion
Forward movement
3/24/08

10. Cell/Tissue layers – SEROSA
Fibrous tissue on outside
Protective covering which helps in attachment to abdominal wall
Fig. 22.3
3/24/08

11. Other important general features
Membranes
Perotineal cavity
2 membrane layers
Encloses abdominal portion of digestive tract
Serosa = visceral peritoneum (inner layer)
Parietal peritoneum = lines abdominal wall (outer layer)
Additional serous membrane connects serosa/visceral to parietal peritoneum
The space between the 2 layers if filled with fluid
Peritoneal fluid
Secreted by cells of the peritoneum
3/24/08

12. Other important general features
Mesenteries
Sheets of serous membrane allow blood vessels, nerves, and lymph vessels to pass through & network
Stabilize the position of the GI tract
Prevents “flopping around”
OMENTUS – associated with the stomach (Fig )
Lesser omentum & greater omentum
Contains adipose tissue (fat around the belly)
Mesentery proper
Within small intestine, between loops
Mesocolon
Stabilizes large intestine
Areas without mesentaries = pancreas & duodenum – which are attached to the abdominal wall for stability
3/24/08

13. Secretions
Within the digestive tract – secretions are evident throughout
Mucus
To lubricate food & “walls”
Digestive enzymes
Break chemical bonds
Electrolytes
Buffers pH
Cofactor for enzymes
Parts of digestive system & direction of food…
Explore important structures, secretions, absorption, digestion process, movement of food
3/24/08

14. Alvioli – Capillary Interface
Fig
3/24/08

15. ld
3/24/08

16. Movement of Bolus Forward movement
Waves of contraction in muscularis externa
Along length of tube
Process of peristalsis
Circular muscles contract behind bolus
Longitudinal muscles contract at cardiac sphincter
Wave of relaxation opens entrance to stomach
3/24/08

17. Movement of Food (bolus)
Fig. 22.4
3/24/08

18. Movement of Bolus Forward movement Side to side movement
Waves of contraction in muscularis externa
Along length of tube
Process of peristalsis
Circular muscles contract behind bolus
Longitudinal muscles contract at cardiac sphincter
Wave of relaxation opens entrance to stomach
Side to side movement
No set direction
Helps to mix bolus with mucus for more lubrication
Contraction in muscles → segmentation
Mostly in large & small intestine – helps to fragment bolus
3/24/08

19. Stomach Anatomy Shape Sphincters Folds = rugae Mucosa Cardiac Pyloric
Deep muscular folds
Mucosa
Fig
3/24/08

20. Stomach Anatomy Mucosa 4 types of secretory cells: Cell Secretion
Gastric pits with gastric glands
Secretory cells
4 types of secretory cells:
Cell Secretion
Chief cells → Pepsinogen
Parietal cells → HCl (acid)
Mucus cells → Mucus
Enteroendocrine cells → Gastrin (hormone)
3/24/08

21. Stomach Processes What happens to food when it enters the stomach?
Digestion & Secretion – almost no absorption
3 phases of secretion in the stomach
Cephalic
Begins at the sight of food
Gastrin is secreted
Stimulates HCl & pepsinogen
Food enters the stomach
3/24/08

22. Phases of Gastric Secretion in Stomach
Gastric Phase
Secretion
Mucus is secreted to protect stomach lining
More gastrin, more pepsinogen
Acidic environment – pH drops (pepsinogen → pepsin at low pH)
Secretions stop when pH reaches 2.0
Digestion
Proteins in food →pepsin →amino acids
Milk proteins →gastric lipase → amino acids & renin
3/24/08

23. Phases of Gastric Secretion in Stomach
Intestinal Phase
Mixing
Rugae become stretched – stomach is distended
Muscular contractions mix food for several hours
Food becomes watery mixture
Chyme (acidic)
After several hours of mixing waves of contractions (peristalsis) reach the lower end/base of the stomach – near the pyloric sphincter
Sphincter opens & closes with each wave
Squirts chyme into the duodenum
The Duodenum secretes enteric gastrin
starts next phase
3/24/08

24. Phases of Gastric Secretion in Stomach
Gastric Phase
Mixing
Rugae become stretched – stomach is distended
Muscular contractions mix food for several hours
Food becomes watery mixture
Chyme (acidic)
After several hours of mixing waves of contractions (peristalsis) reach the lower end/base of the stomach – near the pyloric sphincter
Sphincter opens & closes with each wave
Squirts chyme into the duodenum
The Duodenum secretes enteric gastrin
starts next phase
3/24/08