1. Fueling Body Activities: Digestion
Chapter 43

2. Outline
I. Types of Digestive Systems
II. Vertebrate Digestive Systems
The Mouth and Teeth
Esophagus and Stomach
The Small Intestine
The Large Intestine
Accessory Organs
III. Neural and Hormonal Regulation of Digestion
IV. Food Energy and Energy Expenditure

3. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Types of Digestion
Intracellular digestion: organisms that digest their food within the cell.
Ex: Single-celled organisms and Sponges
Ameoba

4. Extracellular Digestion: within a digestive cavity.
Fig (TE Art)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Extracellular Digestion: within a digestive cavity.
*digestive enzymes released into a
cavity.
Food
Wastes
Mouth
Tentacle
Gastrovascular
cavity
Body stalk

5. Specialization occurs when the digestive tract, or alimentary canal, has a separate mouth and anus=
One way digestive tract

6. Fig. 43.03(TE Art) Nematode Earthworm Salamander Pharynx Mouth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nematode
Pharynx
Mouth
Intestine
Anus
Crop
Gizzard
Earthworm
Pharynx
Mouth
Intestine
Anus
Intestine
Stomach
Cloaca
Salamander
Anus
Liver
Mouth
Pancreas
Esophagus

7. *Food Ingested
*Food stored or first subjected to physical fragmentation.
*Chemical digestion occurs next.
Hydrolysis reactions liberate subunit molecules.
*Molecules absorbed: pass through
epithelial lining.
*Waste excreted

8. Vertebrate Digestive Systems
Consists of tubular gastrointestinal tract and
accessory digestive organs.
*Tubular gastrointestinal tract:
mouth and pharynx
esophagus - delivers food to stomach
stomach - preliminary digestion
small intestine - absorption
large intestine - water absorption
cloaca or rectum - waste storage

9. Fig. 43.04(TE Art) Pharynx Esophagus Stomach Small intestine Colon
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Pharynx
Esophagus
Stomach
Large intestine
Small intestine
Colon
Rectum/Cloaca
Anus

10. *Accessory digestive organs include:
liver : produces bile
gallbladder : stores and concentrates bile
pancreas : produces pancreatic juice
Salivary glands

12. Tubular gastrointestinal tract
Tubular gastrointestinal tract has a characteristic layered structure.
mucosa – epithelium that lines the inside of tract
submucosa - connective tissue, also contain
plexuses: nerves that regulate activity
muscularis - double layer of smooth muscle
circular layer than longitudinal layer
serosa - connective tissue covering the external surface of tract.

13. Gastrointestinal Tract Layers

14. The Mouth and Teeth
Vertebrate teeth
Carnivorous mammals have pointed teeth that lack flat grinding surfaces.
Herbivores must pulverize cellulose of cell walls of plant tissue before digestion and have large, flat teeth suited to grinding
Humans are essentially carnivores in the front, and herbivores in the back.

16. Birds lack teeth and have a two chambered stomach
Fig (TE Art)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Vertebrates that lack teeth break up food in a two chambered stomach (gizzard). Birds must ingest pebbles to help breakdown.
Esophagus
Stomach
Mouth
Gizzard
Intestine
Crop
Anus
Birds lack teeth and have a two chambered stomach
(gizzard) and ingest pebbles to help break down.

17. The Mouth and Teeth
Mouth
*The tongue mixes food with saliva.
moistens and lubricates food
secretions controlled by nervous system
Taste-sensitive neurons in the mouth send impulses to the brain, which responds by stimulating the salivary glands.

18. The Mouth and Teeth
When food is ready to be swallowed, the tongue moves it to the back of the mouth.
elevated by soft palate
pressure against pharynx triggers an automatic, involuntary reflex
larynx contracted and raised
glottis pushed against epiglottis that keeps food out of respiratory tract.

19. Human Pharynx, Palate, and Larynx

20. Esophagus and Stomach Structure and function of the esophagus
Swallowing center stimulates successive waves of contraction that moves food along esophagus to stomach, controlled by ring of smooth muscle (sphincter)
Structure and function of the stomach
Surface is highly convoluted, enabling it to fold when empty and expand as it fills with food.
50 mls when empty, 2-4 liters when full!

21. Secretory systems
Exocrine glands contain two cell types:
parietal cells - secrete hydrochloric acid
chief cells - secrete pepsinogen( weak or inactive protease enzyme) which is stimulated to break down into pepsin (active enzyme) by
the HCl.

22. Fig. 43.11(TE Art) Gastric pits Esophagus Mucous cell Stomach Pyloric
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Esophagus
Gastric pits
Mucous
cell
Stomach
Pyloric
sphincter
Mucosa
Chief
cell
Epithelium
Parietal
cell
Mucosa
Villi
Gastric glands
Submucosa
Duodenum

23. Action of acid
Human stomach produces about 2 liters of HCl and other gastric juices everyday.
helps denature food proteins (chyme)
Note: Proteins digested a small amount in stomach, carbohydrates and fats are not at all.

24. Esophagus and Stomach
Ulcers
Gastric ulcers are rare because epithelial cells in the mucosa are protected by a layer of alkaline mucus.
Susceptibility increased when mucosal barriers are weakened by Helicobacter pylori.
Chyme leaves the stomach through the pyloric sphincter.

25. The Small Intestine
Digestion
approximately 4.5 m long, and divided into duodenum, jejunum and ileum
epithelial wall covered with villi
covered by microvilli
greatly increase surface area

26. Small Intestine

27. Accessory Organs
Secretions of the pancreas
Pancreatic fluid is secreted into duodenum through the pancreatic duct.
host of enzymes: trypsin, chymotrypsin, pancreatic amylase, and lipase
Digest proteins into smaller polypeptides, polysaccharides into shorter sugar chains, and fat into free fatty acids.

28. Pancreas
Pancreas also functions as endocrine gland, secreting hormones to control blood glucose.
produced in islets of Langerhans

29. Accessory Organs
Liver and gallbladder
Liver is largest internal organ of the body.
Main secretion is bile, a fluid mixture of bile pigments and bile salts delivered into the duodenum during digestion.
Bile pigments are waste products.
Bile salts act as detergents.
emulsification of fat
stored in gallbladder

30. The Small Intestine
Absorption
Glucose and amino acids enter the bloodstream via the hepatic portal vein.
Fat enters the lymphatic system.
Approximately 9 liters of fluid passes through the small intestine daily.
Only about 50 g of solids and 100 ml of liquid leave the body as feces.

31. The Large Intestine
Small intestine empties directly into the large intestine at a junction where two vestigial structures, cecum and appendix, remain.
no digestion takes place, and only about 4% of absorption occurs there
undigested material, primarily bacterial fragments and cellulose, compacted and stored
compacted feces driven by peristaltic contractions pass into rectum

32. Variations in Vertebrate Digestive Systems
Digestive tracts of some animals contain bacteria and protists that convert cellulose into substances the host can digest.
Ruminants have large, divided stomachs.
rumen and reticulum
omassum and abomasum
rumination
Rodents and lagomorphs practice coprophagy.

33. Four-Chambered Ruminant Stomach

34. Variations in Vertebrate Digestive Systems
All mammals rely on intestinal bacteria to synthesize vitamin K.
necessary for blood clotting
prolonged treatment with antibiotics greatly reduces bacterial populations in the body

35. Neural and Hormonal Regulation of Digestion
Gastrointestinal activities are coordinated by the nervous system and endocrine system.
Stomach secretions are regulated by food and gastrin.
The passage of chyme into the duodenum inhibits stomach contractions.
Duodenum secretes other hormones that inhibit stomach emptying and promote bile release and bicarbonate secretion.
enterogastrones

36. Hormonal Control of Gastrointestinal Tract

37. Accessory Organs
Liver regulatory functions
Liver chemically modifies substances absorbed in the gastrointestinal tract before they reach the rest of the body.
also removes toxins and poisons, and converts them into less toxic forms
Liver regulates many compounds such as steroid hormones, and produces most proteins found in blood plasma.

38. Accessory Organs
Regulation of blood glucose concentration
After a carbohydrate-rich meal, the liver and skeletal muscles remove excess glucose from blood and store it as glycogen.
stimulated by insulin
When glucose levels decrease, the liver secretes glucose in the blood.
breakdown of glycogen
gluconeogenesis - process of converting other molecules into glucose

39. Actions of Insulin and Glucagon

40. Food Energy and Energy Expenditure
Ingestion of food serves two primary functions:
provides source of energy
provides raw materials that cannot be manufactured by the organism
Basal metabolic rate (BMR) refers to the minimum rate of energy consumption under defined resting conditions.

41. Food Energy and Energy Expenditure
If the amount of food energy taken in is greater than the energy consumed per day, the excess energy will be stored in glycogen and fat.
As glycogen reserves are limited, ingestion of excess food energy results primarily in the accumulation of fat.

42. Food Energy and Energy Expenditure
Regulation of food intake
Recent human studies show activity of ob gene and blood concentrations of leptin (satiety factor) are higher in obese people than in lean people.
Leptin produced by obese people appears to be normal.
Most cases of human obesity may result from reduced sensitivity to action of leptin in the brain.

43. Essential Nutrients
Essential nutrients are substances an animal cannot manufacture for itself but which are necessary for health must be obtained in the diet.
essential amino acids
unsaturated fatty acids
Essential minerals
trace elements

44. Summary
Types of Digestive Systems
Vertebrate Digestive Systems
The Mouth and Teeth
Esophagus and Stomach
The Small Intestine
The Large Intestine
Accessory Organs
Neural and Hormonal Regulation of Digestion
Food Energy and Energy Expenditure