1. Chapter 34-ANIMAL NUTRITION AND DIGESTIVE SYSTEM
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General Biology II
BSC 2011
(credit: modification of work by Julie Rybarczyk)

2. Types of Digestive Systems
34.1
Types of Digestive Systems
Heterotrophs are divided into three groups based on their food sources
Herbivores are animals that eat plants exclusively
Carnivores are animals that eat other animals
Omnivores are animals that eat both plants and other animals

3. Figure 34.2
Herbivores, like this (a) mule deer and (b) monarch caterpillar, eat primarily plant material. (credit a: modification of work by Bill Ebbesen; credit b: modification of work by Doug Bowman)

4. Figure 34.3
Carnivores like the (a) lion eat primarily meat. The (b) ladybug is also a carnivore that consumes small insects called aphids. (credit a: modification of work by Kevin Pluck; credit b: modification of work by Jon Sullivan)

5. Figure 34.4
Omnivores like the (a) bear and (b) crayfish eat both plant and animal based food. (credit a: modification of work by Dave Menke; credit b: modification of work by Jon Sullivan)

6. Invertebrate Digestive Systems
Figure 34.5
Invertebrate Digestive Systems
A gastrovascular cavity has a single opening through which food is ingested and waste is excreted, as shown in this hydra and in this jellyfish medusa.
An alimentary canal (more advanced) has two openings: a mouth for ingesting food, and an anus for eliminating waste, as shown in this nematode.

7. Monogastric: Single chambered Stomach
Figure 34.6
(a) Humans and herbivores, such as the (b) rabbit, have a monogastric digestive system. However, in the rabbit the small intestine and cecum are enlarged to allow more time to digest plant material. The enlarged organ provides more surface area for absorption of nutrients. Rabbits digest their food twice: the first time food passes through the digestive system, it collects in the cecum, and then it passes as soft feces called cecotrophes. The rabbit re-ingests these cecotrophes to further digest them.

8. Vertebrate Digestive Systems
Monogastric stomach
Consists of a tubular gastrointestinal tract and accessory organs
Mouth and pharynx – entry
Esophagus – delivers food to stomach
Stomach – preliminary digestion
Small intestine – digestion and absorption
Large intestine – absorption of water and minerals
Cloaca or rectum – expel waste

9. Vertebrate Digestive Systems
Accessory organs
Liver
Produces bile
Gallbladder
Stores and concentrates bile
Pancreas
Produces pancreatic juice
Digestive enzymes and bicarbonate buffer

10. Vertebrate Digestive Systems-Avian
The avian esophagus has a pouch, called a crop, which stores food. Food passes from the crop to the first of two stomachs, called the proventriculus, which contains digestive juices that break down food. From the proventriculus, the food enters the second stomach, called the gizzard, which grinds food.
Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Birds do not have separate openings to excrete urine and feces. Instead, uric acid from the kidneys is secreted into the large intestine and combined with waste from the digestive process. This waste is excreted through an opening called the cloaca.
Figure 34.7

11. Vertebrate Digestive System -Ruminants
Figure 34.8
Ruminant animals, such as goats and cows, have four stomachs. The first two stomachs, the rumen and the reticulum, contain prokaryotes and protists that are able to digest cellulose fiber. The ruminant regurgitates cud from the reticulum, chews it, and swallows it into a third stomach, the omasum, which removes water. The cud then passes onto the fourth stomach, the abomasum, where it is digested by enzymes produced by the ruminant.

12. Parts of the Digestive System-Oral Cavity
Figure 34.9
Digestion of food begins in the (a) oral cavity. Food is masticated by teeth and moistened by saliva secreted from the (b) salivary glands. Enzymes in the saliva begin to digest starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work by the National Cancer Institute)

13. Parts of the Digestive System-Mouth and Teeth
Inside the mouth, the tongue mixes food with saliva
Moistens and lubricates the food
Contains salivary amylase, which initiates the breakdown of starch
Salivation is controlled by the nervous system
Tasting, smelling, and even thinking or talking about food stimulate increased salivation

14. Parts of the Digestive System-Mouth and Teeth
Swallowing
Starts as voluntary action
Continued under involuntary control
When food is ready to be swallowed, the tongue moves it to the back of the mouth
Soft palate seals off nasal cavity
Elevation of the larynx (voice box) pushes the glottis against the epiglottis
Keeps food out of respiratory tract

15. Parts of the Digestive System-Esophagus
Muscular tube connecting the mouth to the stomach
Actively transfers food (called a bolus)from the mouth to the stomach through peristaltic movements.
Figure 34.10

16. Parts of the Digestive System-Stomach
Figure 34.11
The human stomach has an extremely acidic environment where most of the protein gets digested. (credit: modification of work by Mariana Ruiz Villareal)

17. Parts of the Digestive System-Stomach
Saclike portion of tract
Convoluted surface allows expansion
Contains 3rd layer of smooth muscles for mixing food with gastric juice
3 kinds of secretory cells
Mucus-secreting cells
Parietal cells
Secrete HCl and intrinsic factor (for vitamin B12 absorption)
Chief cells
Secrete pepsinogen (inactive form of pepsin) for protein digestion

18. Parts of the Digestive System- The Small Intestine
About 4.5 m long – small diameter
Consists of duodenum, jejunum, and ileum
Receives
Chyme from stomach
Digestive enzymes and bicarbonate from pancreas
Bile from liver and gallbladder

19. Parts of the Digestive System- The Small Intestine
Figure 34.12
Villi are folds on the small intestine lining that increase the surface area to facilitate the absorption of nutrients.

20. Parts of the Digestive System- The Small Intestine-Accessory Organs
Pancreas
Pancreatic fluid is secreted into the duodenum through the pancreatic duct
Enzymes to break down proteins, carbs and fats
Bicarbonate neutralizes acidic chyme from stomach
Exocrine and endocrine gland
Liver
Body’s largest internal organ
Secretes bile
emulsifies fats
Gallbladder
Stores and concentrates bile
Arrival of fatty food in the duodenum triggers the gallbladder to contract, causing bile to be transported through the common bile duct and injected into the duodenum

21. Parts of the Digestive System- The Large Intestine
Figure 34.13
The large intestine reabsorbs water from undigested food and stores waste material until it is eliminated.

22. Parts of the Digestive System- The Large Intestine (Colon)
Much shorter than small intestine, but has larger diameter
Small intestine empties directly into the large intestine at a junction where two vestigial structures, cecum and appendix, remain
No digestion occurs
Function to reabsorb water and remaining electrolytes
Prepare waste for expulsion

23. Parts of the Digestive System- The Large Intestine (Colon)/Rectum/Anus
Many bacteria live and reproduce within the large intestine. Provide humans with Vitamin K
Feces compacted and passed to rectum
Feces exit anus
Smooth muscle sphincter (involuntary)
Striated muscle sphincter (voluntary)

24. Overview of Digestive Process
Mechanical and chemical digestion of food takes place in many steps, beginning in the mouth and ending in the rectum.
Figure 34.19

25. Nutrition and Energy Production
Figure 34.14
For humans, a balanced diet includes fruits, vegetables, grains, and protein. (credit: USDA)

26. Organic Precursors Carbohydrates –primary source of organic carbon
Broken down into glucose to provide energy for metabolic pathways
Excess converted to glycogen
Proteins- provides source of organic nitrogen
Needed for nucleotides, nucleic acids, glycoproteins, etc
Lipids
Needed for fat-soluble hormones and vitamins
Needed for cellular membranes

27. Figure 34.16
Digestion of carbohydrates is performed by several enzymes. Starch and glycogen are broken down into glucose by amylase and maltase. Sucrose (table sugar) and lactose (milk sugar) are broken down by sucrase and lactase, respectively.

28. Figure 34.17
Protein digestion is a multistep process that begins in the stomach and continues through the intestines.

29. Figure 34.18
Lipids are digested and absorbed in the small intestine.

30. Figure 34.15
A healthy diet should include a variety of foods to ensure that needs for essential nutrients are met. (credit: Keith Weller, USDA ARS)

31. Essential Nutrients
Animal cannot manufacture these for itself but are necessary for health and so must be obtained in the diet
Vitamins
Humans, apes, monkeys, and guinea pigs have lost the ability to synthesize ascorbic acid (vitamin C)
Amino acids – humans require 9
Long-chain unsaturated fatty acids
Vertebrates can synthesize cholesterol, a key component of steroid hormones, but some carnivorous insects cannot
Minerals

32. Digestive System Processes
Ingestion
Digestion and Absorption
Carbohydrates
Proteins
Lipids

33. Mechanical and chemical digestion of food takes place in many steps, beginning in the mouth and ending in the rectum.
Figure 34.19

34. Figure 34.20 Neural Responses to Food
Seeing a plate of food triggers the secretion of saliva in the mouth and the production of HCL in the stomach. (credit: Kelly Bailey)

35. Neural Responses to Food
3 phases of gastric control
Cephalic
Sensory input stimulates gastric and salivary secretion
Gastric
Presence of food stimulates gastric secretions and contraction
Intestinal
Presence of food stimulates accessory organs (e.g. gallbladder, pancreas, liver) and the intestinal cells to secrete digestive e enzymes