Chapter 45 & 46
Digestive System
Key Concepts
- Animal nutrition
- general principles of digestion and absorption of food
- overview of vertebrate digestive systems
- mechanisms of digestion and absorption in vertebrates
Intro to nutrition
- nutrient
- any substance taken in by an organism that is needed for:
- survival
- growth
- development
- tissue repair
- or reproduction
- any substance taken in by an organism that is needed for:
- nutrition
- process of consuming and using food for nutrients
- animals receive nutrients by consuming food
Dietary categories
- basic similarities in organ system function lead to similarities in nutritional requirements
- different animal physiologies can have different nutrient demands
- Herbivores
- eat only plants
- digestive system contains micro-organisms that help digest cellulose
- Carnivores
- eat only animal flesh or fluid
- Omnivores
- eat both
Animals are heterotrophic
- Heterotrophs
- ingest feeders
- cannot manufacture more food
- require already synthesized organic compounds of plants of other animals to supply materials
- survival
- maintenance
- growth
- reproduction
Gut Tracts
Two types
- Blind Gut
- no cavity between gut and body wall
- one opening
- primitive form
- tube-within-a-tube
- flow through digestive tube
- body cavity between git and body wall
- separate opening (mostly)
Digestion
- the breakdown of large molecules into smaller ones
Digestive enzymes (hydrolases)
- carbohydrases
- proteases
- lipases
- nucleases
Food processing in animals
Occurs in Five phases
- Ingestion
- food is taken into the body and moves into a digestive
- digestion
- food is broken down into smaller molecules
- chemical and mechanical
- transport
- absorption
- ions, water, and small molecules are transported into the circulatory system
- egestion
- undigested materials and other waste are passed from the body
- elimination or exceretion
Alimentary canal
- digestive tract or tube
- Gastrointestinal tract
- Five regions of food processing
- Single tube with opening at each end
- contains smooth muscles in walls
- lined with epithelial cells
- synthesize and secrete digestive enzymes
- secrete hormones
- transport digestive materials
- several specialized regions
- different structures for different processes
- storage area
Structure of GI Tract
- some general structure from midpoint of esophagus, to the anus or cloaca
- lumen lined by epithelial and glandular cells
- secretory cells release a protective layer of mucus
- other cells release hormones
- glands release enzymes, acids, water, and ions
- Epithelial cells linked by tight junctions and surrounded by layers of tissue made of smooth muscle, neurons, connective tissues, and blood vessels
- neurons activated by sight and smell of food and presence of food in tract
Region of Reception
Buccal cavity
- mouth and accessory structures
- ingestion site and digestion site
- chemical and mechanical
- jaws, teeth, cheek muscles, tongue, and salivary glands (saliva)
Pharynx
- back of mouth cavity
- point that respiratory and digestive system cross paths
Region of Conduction
Esophagus
-
- tube carrying materials from mouth cavity to the rest of the alimentary canal
- forces/pushes good down
- conducts food from pharynx to stomach
- Peristalsis
- rhythmic wave-like contractions which propel food forward in the GI tract
- No new digestion here
- only chemical continuation from buccal cavity
Region of digestion and storage
Stomach (mostly)
-
- saclike organ evolved for storing food
- muscular nature helps break up food
- partial protein digestion
- regulates rate of emptying into small intestine
- Secretions
- hydrochloric acid
- kills microbes
- dissolves particulate matter
- secreted by parietal cells
- Pepsinogen
- converted to pepsin to begin protein digestion
- secreted by Chief cells
- hydrochloric acid
- Epithelium coated with an alkaline mucus
- carbohydrate digestion continues from mouth
- little lipid digestion happens
- lumen (cavity) stomach
- pepsinogen + HCL -> pepsin (for protein breakdown)
Region of terminal digestion and absorption
Small intestine
- near