Nutrition and Digestion

Ways animals ingest their food Omnivores – ingest both plants and animals Herbivores – ingest plants Carnivores – ingest other animals Mechanisms of ingestion 1. suspension feeders – extract food particles suspended in the surrounding water 2. substrate feeders – live in or on their food source and eat their way through it 3. Fluid feeders – suck nutrient-rich fluids from a living host 4. Bulk feeders – ingest large pieces of food

Stages of food processing

Specialized compartments for digestion

Peristalsis – rhythmic waves of contraction of smooth muscles in the walls of the digestive tract

Digestion begins in the oral cavity Mechanical digestion – chewing makes it easier to swallow and exposes more food surface to digestive enzymes 1 L saliva per day Buffers neutralize food acids, antibacterial agents kill bacteria, salivary amylase begins digesting starch

Ulcers Formerly thought to be caused by too much pepsin or acid or too little mucus in the stomach lining We now know a spiral-shaped prokaryote, Helicobacter pylori causes ulcers Attaches to the stomach lining and neutralizes the acids. It leads to loss of protective mucus and damage to the stomach lining White blood cells come to fight the infection and produce inflammation called gastritis About 50% of people are infected with H. pylori. The stomach wall can degrade until it has a hole in it which can lead to infection and internal bleeding. Can also lead to some kinds of stomach cancer. The first section of the small intestine can also get ulcers

Small intestine – major organ of chemical digestion and nutrient absorption Starch digestion begins in the mouth, protein breakdown in the stomach, all other chemical digestion occurs in the small intestine Also absorbs nutrients into the blood Pancreas – produces digestive enzymes and neutralizes the acid Liver makes bile which dissolves in fats to make them more easily digested

Large intestine (colon) reclaims water

A healthful diet satisfies three needs Fuel to power all of the bodies activities Organic raw materials needed to make the bodies own molecules Essential nutrients, or substances the animal cannot make for itself but needs

Basal metabolic rate (BMR)- the number of kc an animal requires to fuel essential processes

Ketosis/ketogenesis/ketoacidosis Ketogenesis is part of fatty acid digestion where too many fats are being broken down, and ketones build up Ketogenesis is normally activated in starvation to provide an important fuel for the peripheral tissues and brain. When insulin is totally lacking, overproduction of ketones leads to the life-threatening syndrome of diabetic ketoacidosis In the last trimester of pregnancy insulin action can be impaired as part of the process of diverting nutrients to the fetus. In an extreme insulin-resistant state diabetic ketoacidosis and coma occurs. Always in the 6 th to 8 th month of pregnancy.