Chapter 34 BSC 1005 Tidwell are substances obtained from the environment that organisms need for their Nutrition and Digestion Nutrients growth and survival o 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 obtained in the diet or dissolved in drinking water are elements that play many crucial roles in animal nutrition and can only be 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 4 Chapter 34 BSC 1005 Tidwell Vitamins function growth and development are organic molecules that animals require in small amounts for normal cell o Many vitamins are required for the proper functioning of enzymes that control o Vitamins are essential nutrients that the body cannot synthesize and must be metabolic reactions in the body 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 diets o Incisors o Canines o Premolars o Molars are used for biting are used for tearing are used for grinding 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 nutrients from tough plant matter such as cows are able to break down cellulose and extract o These animals have elaborate digestive systems that house microorganisms able o Ruminants have multiple stomach chambers that contribute to the digestion of to break down cellulose 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 length o The human digestive system which processes a wide variety of foods provides a good 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 4 Chapter 34 BSC 1005 Tidwell o 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 Cells of the small intestine Produces sodium bicarbonate and digestive juices Microvilli digestion process provide a surface area for absorption and bear enzymes that complete the 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 projections o 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 4 Chapter 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 stimulates bicarbonate production by the pancreas and stimulates bile stimulates the pancreas to release digestive enzymes and the o Secretin production by the liver gallbladder to release bile o Cholecystokinin