Chapter 41: Animal Nutrition
41.1 Nutritional Requirements
- ==A carbohydrate, protein, or fat is an example of a nutrient: a substance that an organism needs to remain alive.==
- Food is any material that contains nutrients.
- Although all nutrients are necessary for the growth and survival of animals, essential nutrients are those that cannot be synthesized and must be obtained from the diet.
- Humans require four classes of essential nutrients:
- Essential amino acids are amino acids that an animal cannot synthesize from simpler building blocks.
- Essential fatty acids are fatty acids that an animal must obtain in its diet.
- Vitamins are organic, or carbon-containing compounds at are vital for health but are required in only minute amounts.
- Minerals are inorganic substances used as components of enzyme cofactors or structural materials.
41.2 Capturing Food: The Structure and Function of Mouthparts
- The cichlids that inhabit the Rift Lakes of East Africa a spectacular example of adaptive radiation-the diversification of a single ancestral lineage into many species, each of which lives in a different habitat or exhibits a distinct form.
41.3 The Structure and Function of Animal Digestive Tracts
- Salivary amylase, the enzyme responsible for carbohydrate digestion in the mouth, is one of 1e best-studied enzymes.
- Salivary glands in the mouth secrete amylase and also produce the slimy substance called mucus.
- Cells in the tongue synthesize and secrete another salivary enzyme, lingual lipase, which begins the digestion of lipids by breaking triglycerides, a common form of fat in the diet, into diglycerides and fatty acids.
- ==Lingual lipase plays only a minor role in digestion, mostly once it has been swallowed into the stomach.==
- Once a bolus of food is swallowed, it enters a muscular tube called the esophagus, which connects the mouth and stomach.
- In response to nerve signals, the smooth muscles in the esophagus con act and relax in a coordinated fashion called peristalsis.
- In an array of bird species, the esophagus has a prominent, widened segment called the crop where food can be stored and, in some cases, processed.
- The stomach is a tough, muscular pouch in the digestive tract, bracketed on both the superior and inferior ends by ringlike muscles called sphincters, which control the passage of material.
- In cattle, sheep, goats, deer, antelope, giraffe, and pronghorn-species that are collectively called ruminants-the stomach is specialized for digesting cellulose instead of proteins.
- The small intestine is a long tube 1at is folded into a compact space within the abdomen.
- ==In the small intestine, partially digested food mixes with secretions from the pancreas, liver, and gallbladder and begins a journey of about 6 m (20 ft).==
41.4 Nutritional Homeostasis-Glucose as a Case Study
- The illness of diabetes mellitus is a classic example of nutrient imbalance. People with diabetes mellitus have an abnormally high level of glucose in their blood because cells cannot import glucose.
- Insulin is a hormone that is secreted by cells in the pancreas when the blood glucose level is elevated.
- If the blood glucose level falls too low, as it does when an animal has not eaten for a while, other cells in the pancreas secrete a hormone called glucagon.
- In response to glucagon, liver cells catabolize stored glycogen and produce glucose via the process of gluconeogenesis, the synthesis of glucose from non-carbohydrate compounds.
- As a result, the glucose level in the blood rises.
- The researchers found a strong relationship between the incidence of type 2 diabetes mellitus and body mass index (BMI), a measure of obesity.
- ==BMI is calculated as body mass (in kilograms) divided by height (in meters) squared.==
- A person with a BMI of 30 or higher is considered obese and has a far greater risk of developing type 2 diabetes mellitus than people with lower BMIs.