Chapter 34 BSC 1005 TidwellNutrition and Digestion- Nutrients are substances obtained from the environment that organisms need for their growth and survivalo Nutrients fall into 6 categories: Carbohydrates Lipids Proteins Minerals Vitamins Water- Most energy is provided by carbohydrates and lipids.o Nutrients that supply energy are lipids (fats and oils), carbohydrates (sugars and starches), and proteins.- A calorie is the amount of energy required to raise 1 gram of water 1 degree Celsius.o The average human burns 70 Calories per hour at rest, and up to 20 Calories per minute during exercise.- Starch is the principal energy-storage material of plants.- Glycogen is used by animals for short-term energy storage.- Fats and oils are the most concentrated energy source.- The body mass index (BMI) is a common tool for estimating a healthy weight.- Our cells can synthesize most of the molecules our bodies require, but they cannot synthesize certain raw materials, called essential nutrients, which must be supplied in the diet.o Essential nutrients for humans include certain fatty acids and amino acids, a variety of minerals and vitamins, and water.o Humans are unable to synthesize 9 (adults) or 10 (infants) of the 20 amino acids needed to make proteins. Those amino acids that cannot be synthesized must be obtained in the diet, and are called essential amino acids.- Minerals are elements that play many crucial roles in animal nutrition and can only be obtained in the diet or dissolved in drinking water.o Iron is a central component of hemoglobin which carries O2 in the blood, and iodine is found in hormones produced by the thyroid gland.Page 1 of 4Chapter 34 BSC 1005 Tidwell- Vitamins are organic molecules that animals require in small amounts for normal cell function, growth, and development.o Many vitamins are required for the proper functioning of enzymes that control metabolic reactions in the body.o Vitamins are essential nutrients that the body cannot synthesize and must be obtained in the diet.o They are grouped together into two categories: water soluble or fat soluble. Water Soluble: vitamin C, vitamin B Fat Soluble: vitamin A, vitamin D, vitamin E, vitamin K- Most animals have tubular digestive systems with specialized compartments. (Extracellular digestion)- Teeth accommodate different dietso Incisors are used for bitingo Canines are used for tearingo Premolars are used for grindingo Molars are used for crushing and chewing- Carnivores have enlarged canines for stabbing and tearing flesh, and molars and premolars with sharp edges for shearing through tendon and bone.- Ruminant herbivores (such as cows) are able to break down cellulose and extract nutrients from tough plant matter.o These animals have elaborate digestive systems that house microorganisms able to break down cellulose.o Ruminants have multiple stomach chambers that contribute to the digestion of plant cellulose.- Small intestine length is correlated by diet.o Because cell walls are difficult to digest, herbivore intestines are long, to allow more time for nutrients absorption.o Carnivore intestines are relatively short because proteins are easy to digest.o In frog development, the herbivorous tadpole has a long small intestine, but the carnivorous frog intestine shortens to 1/3 its tadpole lengtho The human digestive system, which processes a wide variety of foods, provides agood example of the mammalian digestive system.- Pepsinogen is the inactive form of pepsin, a type of protease (protein digesting enzyme).- Most chemical digestion occurs in the small intestine.o The main functions of the small intestine are to chemically digest food into small molecules and to absorb these molecules into the body.Page 2 of 4Chapter 34 BSC 1005 Tidwello Most fat and carbohydrate digestion occurs in the small intestine, and the protein digestion started in the stomach is completed here.o Three sources aide the small intestine in digestion. Liver- Stores fats and carbohydrates- Regulates blood glucose levels- Synthesizes blood proteins- Stores iron and certain vitamins- Produces bile (bile salts emulsify large fat globs into microscopic particles) Pancreas- Produces sodium bicarbonate and digestive juices Cells of the small intestine- Microvilli provide a surface area for absorption and bear enzymes that complete the digestion process.o Peptidases complete the breakdown of peptides into amino acids.o Disaccharidases break down disaccharides into monosaccharides.- Villi line the small intestine and look like small fingerlike projectionso Each villus cell has many microvilli that increase the surface area even more.- Nutrients (amino acids & monosaccharides) are absorbed into intestinal cells by diffusion or by active transport, and then diffuse into the blood stream.- Fats are absorbed into the lacteals as chylomicrons, which enter lymphatic capillaries that lead to the bloodstream.- The large intestine is about 5 feet long and 2.5 inches wide; most is called the colon, but the last 6 inches is called the rectum.o A mix of water, undigested nutrients, and fiber enters the large intestine.o The remaining semisolid material is called feces. The feces is transported by peristaltic contractions to the rectum, which expands and stimulates defecation.o The large intestine contains bacteria that consume unabsorbed nutrients and synthesize vitamins such as vitamin B12, thiamin, riboflavin, and vitamin K—the typical human diet would be deficient in vitamin K without the bacteria.o The large intestine absorbs vitamins, leftover water, and salts.- Digestion is controlled by the nervous system and hormones.o Hormones secreted by the digestive system enter the bloodstream and circulate through the body, acting on specific receptors within the digestive tract.o Like most hormones, they are regulated by negative feedback.Page 3 of 4Chapter 34 BSC 1005 Tidwell- The amino acids and peptides in chime stimulate cells in the stomach lining to release gastrin into the bloodstream.o Gastrin stimulates gastric juice secretion in the stomach which promotes protein digestion.o When the pH of the stomach reaches a high level of acidity, this inhibits gastrin secretion, which inhibits gastric juice production.- Two additional hormones are released by cells of the duodenum in response to the acidity and nutrients in chime, particularly peptides and fat.o Secretin