Biology 107

Lecture Notes: Animal Nutrition II.

Reading: Chapter 41 in text.

The mammalian digestive system

• The digestive system in mammals includes the alimentary canal and accessory glands that secrete digestive juices into the canal through ducts

· The oral cavity, pharynx, and esophagus initiate food processing

o The oral cavity

o The esophagus

· The stomach stores food and performs preliminary digestion

o Food storage

· Rugae:

o Churning

· Product is acid chyme:

o Secretion

· The stomach epithelium contains three types of secretory cells.

· Mucous cells

o Secrete mucin:

o Gastrin:

· Chief cells

o Secrete pepsinogen:

· Parietal cells

o Secrete HCl

· Protein digestion

· Both components of gastric juice, HCl and pepsin, are involved with protein digestion

• The small intestine is the major organ of digestion and absorption
• Accessory organs secrete products into small intestine to aid in digestion
• The pancreas:

• The liver
• Secretes bile:

• Enzymatic action in the small intestine
• Carbohydrate digestion

• Protein digestion

• Nucleic acid digestion

• Fat digestion

• Macromolecules are completely hydrolyzed as peristalsis moves the mixture through the duodenum
• The remaining areas of the small intestine, the jejunum and ileum are specialized for absorption of nutrients
• Absorption of nutrients
• Nutrients must cross the digestive tract epithelium to enter the body. Most absorption occurs in the small intestine
• Large folds in the walls are covered with projections called villi, which in turn have many microscopic microvilli; this results in a surface area for absorption of about 300 m².
• brush border:
• Lacteal:

• Hormones help regulate digestion
• Gastrin:

• Secretin:

• Cholecystokinin (CCK):

• Enterogastrone :

· Reclaiming water is a major function of the large intestine