Food, Energy, and Digestion

• What do we need - nutrition 

  • Nutritional requirements for energy for external activity: reproduction, seeking resources, and avoiding predation

  • For internal activity: Maintenance and growth, Energy requirements at different life stages

  • Quality and quantity of food: The impact of what is consumed and how much, the need for proteins (amino acids), the need for vitamins and minerals, and availability also have significant effects. 

• Food: energy expended, forms of food - proteins (provide amino acids), simple sugars (carbohydrates), Fatty acids (lipids), vitamins, and minerals

  • Consumed more energy than needed - decreases in metabolism (panda) 

  • Food obtaining - feeding, foraging, securing, and obtaining food) - targeted for most vertebrates - identified, located, subdued, and consumes adaptations

  • Need - depends on how food is obtained, quality, and quantity, and the energetic needs of both predator and prey

  • Ballen Feeding system - suspension feeding, the largest mammal and fish feed this way, a low-energy feeding system 

  • After consumption, digestion (the breakdown of food molecules by enzymes or microbes in smaller molecules capable of being absorbed by tissues. Breakdown- 

extracellular (requires specialized organs) - pancreas (secretes digestive enzymes), liver (creates bile, lipid digestion) 

Hydrolysis: uptake of water that causes breakdown of large molecules (most digestive breakdown) 

Enzymes: catalysts produced by the body to aid digestion (specific) (activity dependent on pH and temperature)

• Protein digestion - intake in the form of amino acids (requires enzymes), common enzymes found in vertebrates are pepsin (stomach - works to hydrolyze peptide bonds between amino acids) and trypsin (midgut, the small intestine - the second level of protein digestion)

• Nitrogen cycle - how does atmospheric nitrogen become available to living organisms? - recycling of nitrogen - bacteria, gut flora, and  plants absorb  - nitrogen fixation 

• Lipid digestion - (midgut - small intestine) breaks up lipids into small droplets - emulsification (similar to how soap and detergents work). Requires - emulsification by bile salt from live, breakdown by enzymes (primarily lipases) secreted by the pancreas. Results: free fatty acids that can be transferred across cell membranes 

Carbohydrate digestion  - goal (produce monosaccharides that can be absorbed), disaccharides (simple sugars)(targeted by specific enzymes like lactose by lactase, sucrose by surace and more), polysaccharides (require multiple enzymes combined for breakdown), starches (breakdown by amylase secreted in saliva and the pancreas), cellulose (require cellulase which is not produced by any vertebrate) (require symbiotic relationship with microbes, - Typical digestive tract structures include

- Headgut: mouth, sub-gingival plaque, supra-gingival plaque, throat, palate, tonsils, tongue, buccal mucosa, saliva, keratinized gingiva.

- Foregut - liver, gallbladder, stomach, esophagus, cardiac sphincter, pyloric sphincter, pancreas

- Midgut - small intestine, appendix, ascending colon

- Hindgut - transverse colon, descending colon, rectum

Herbivore digestion

Intestinal fermentation (zebra, rhino, elephant)

Large intestine and enlarged cecum (hindgut fermentation) (large intestine/enlarged cecum = primary fermentation center)

Some nutrients and microbes are lost in defecation

Ruminants (cows, sheep, deer)

Multi-chambered stomach (foregut fermentation)

Regurgitation and remastication (allow for survival on low-quality food)

Coprophagy - pros (excrement) phagein (to eat) - the goal is to gain microbes lost after excretion, critical for digestion

Carnivore digestion

Shortened digestive tract (increased nutrient content in meat)

The stomach makes up about 60 to 70% of the digestive tract (roughly 10 times the amount of hydrochloric acid in the stomach)

Omnivore digestion

Highly adaptable digestive system

The advantage of being able to consume and digest a variety of food resources (results in a wide variety of digestive structures among omnivorous taxa)

Absorption: transport of monosaccharides and free amino acids across the membrane.