Chapter 41 Notes Animal Nutrition

Nutritional Requirements The flow of energy into and out of an animal can be viewed as a “budget” - most of the energy taken in is used to produce ATP to power resting metabolism and temperature regulation - excess ATP can be used for biosynthesis

Nutritional Requirements In humans, the liver and muscle cells store energy in the form of glycogen. If glycogen stores are full, the excess is usually stored as fat. When fewer calories are taken in than used, fuel is taken out of storage deposits and oxidized.

Nutritional Requirements

Feedback mechanisms regulate fat storage and use - an increase in adipose tissue increases leptin levels in the blood - high levels of leptin cue the brain to depress appetite and to increase muscular activity and body-heat production

Nutritional Requirements In addition to providing fuel for ATP, a diet must also supply the raw materials needed for biosynthesis. - organic precursors (carbon skeletons) - essential amino acids - essential fatty acids - vitamins and minerals

Nutritional Requirements

Food Types and Feeding Mechanisms Even though animals are classified as herbivores, carnivores, or omnivores, they are opportunistic feeders in that they eat foods outside of their main dietary categories

Food Types and Feeding Mechanisms There are four main groups that animals can be separated into based on the way they feed Suspension-feeders: animals that sift food particles from water Substrate-feeders: animals that live on their food source, eating their way through food

Food Types and Feeding Mechanisms Fluid-feeders: animals the survive by sucking nutrient-rich fluids from a living host Bulk-feeders: animals that eat relatively large pieces of food

Overview of Food Processing The four main stages of food processing are ingestion, digestion, absorption, and elimination Ingestion: the act of eating Digestion: the process of breaking food down into molecules small enough for the body to absorb - enzymatic hydrolysis

Overview of Food Processing Absorption: the animal’s cells take up small molecules such as amino acids and simple sugars Elimination: undigested material passes out of the digestive compartment

Overview of Food Processing Digestion occurs in specialized compartments to reduce the risk of self- digestion Intracellular digestion: use of food vacuoles where hydrolytic enzymes break down food without digesting the cell’s cytoplasm

Overview of Food Processing

Extracellular digestion: the breakdown of food outside cells Many animals with simple body plans have gastrovascular cavities - these function in both the digestion and distribution of nutrients throughout the body

Overview of Food Processing

Most animals have digestive tubes extending between two openings- complete digestive tracts or alimentary canals - the advantage is that animals can ingest additional food before earlier meals are completely digested

Overview of Food Processing

The Mammalian Digestive System The oral cavity, pharynx, and esophagus initiate food processing - the presence of food in the oral cavity triggers the release of saliva. -saliva contains amylase, the enzyme that hydrolyzes starch

The Mammalian Digestive System The stomach stores food and performs preliminary digestion - the stomach secretes gastric juices and mixes them with food by a churning motion - also present in the gastric juices is pepsin, an enzyme that begins the hydrolysis of proteins

The Mammalian Digestive System

The small intestine is the major organ of digestion and absorption - the first 25 cm of the small intestine is called the duodenum. Here chyme from the stomach is mixed with juices from the pancreas, liver, and gall bladder

The Mammalian Digestive System

- the pancreas produces hydrolytic enzymes and an alkaline solution that acts as a buffer to neutralize the low pH of the chyme from the stomach - the liver produces bile. Bile does not contain enzymes, but acts as detergents that aid in the digestion and absorption of fats

The Mammalian Digestive System Carbohydrate digestion: - begins with salivary amylase in the oral cavity - pancreatic amylase hydrolyzes starch, glycogen, and other polysaccharides into disaccharides

The Mammalian Digestive System Protein digestion: - enzymes in the duodenum break apart proteins into amino acids - trypsin and chymotrypsin break the peptide bonds

The Mammalian Digestive System Fat digestion: - hydrolysis of fat is a special problem because fat molecules are insoluble in water - bile salts work through emulsification so that lipase can break down fat molecules

The Mammalian Digestive System Most absorption occurs in the small intestine - s.i. has a large surface area due to the folding of the lining into villi - each villus has many microscopic appendages called microvilli which increase the rate of absorption

The Mammalian Digestive System - in the core of each villus is a net of capillaries and a small vessel of the lymphatic system called the lacteal - nutrients are absorbed across the intestinal epithelium and then across the epithelium of the capillaries or lacteals - nutrients then flow into the bloodstream

The Mammalian Digestive System