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Biology - Nutrition and Digestion

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    Study Guide Biology – Nutrition and Digestion 1. Introduction to Nutrition and Digestion Nutrition includes all the activities by which living organisms obtain materials from their environment and move them into their cells. Once inside the cells, these materials are metabolized , meaning they are chemically processed to build important substances such as: • structural components of the body • enzymes • energy - rich compounds • other materials needed for life All of the elements and compounds taken into an organism for these purposes are called nutrients . 1.1 Nutrition in Animals Animals, including humans, are heterotrophs . This means they cannot make their own food and must obtain nutrients by eating other organisms. The nutrients animals consume are already formed organic molecules . However, these molecules usually cannot be used right away. They are often too large or complex to be absorbed directly by the body. 1.2 Digestion To make nutrients usable, animals must break food down into simpler forms that can be absorbed into the bloodstream and transported to cells. This process is called digestion . Digestion allows the body to: • absorb nutrients efficiently • deliver them to cells • use them for energy, growth, repair, and maintenance

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    Study Guide 2. The Human Digestive System: A Clear and Friendly Guide The human digestive system helps the body turn food into energy and building materials. Large, complex food molecules are broken down into smaller pieces that the body can absorb and use. This process takes teamwork. Many organs and enzymes work together t o digest food efficiently. The main parts involved in digestion are the mouth, esophagus, stomach, small intestine, large intestine, and liver . 2.1 Mouth: Where Digestion Begins The mouth , also called the oral cavity, is the starting point of digestion. Its job is to receive food and begin breaking it down. 2.1.1 Teeth and Mechanical Digestion Digestion in the mouth begins with chewing , which breaks food into smaller pieces. Humans have four types of teeth, each with a special role: • Incisors : Flat, chisel - shaped teeth used for cutting and biting food • Canines : Pointed teeth used for tearing food • Premolars and molars : Broad, ridged teeth used for grinding and crushing food 2.1.2 Saliva and Chemical Digestion As you chew, food mixes with saliva , a sticky fluid that softens food and helps hold it together. Saliva is produced by three pairs of salivary glands: • Parotid • Submaxillary • Sublingual Saliva contains an enzyme called amylase , which begins chemical digestion by breaking starch into smaller sugar molecules called maltose .

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    Study Guide 2.1.3 Forming the Bolus The tongue moves food around and shapes it into a soft mass called a bolus . Once ready, the bolus is pushed into the pharynx (throat) and then into the esophagus. 2.2. Esophagus: Moving Food to the Stomach The esophagus is a muscular tube located behind the windpipe. It connects the mouth to the stomach. Food travels through the esophagus by peristalsis , which is a series of wave - like muscle contractions. These contractions push the bolus downward, and gravity also helps move the food toward the stomach. 2.3 Stomach: Mixing and Protein Digestion The esophagus connects to the stomach just below the diaphragm. A ring of muscle called the cardiac sphincter controls the opening. It relaxes to let food in and then closes to keep food from moving backward. 2.3.1 Structure and Function The stomach is a stretchy, pouch - like organ in the upper abdomen. Its muscles churn food and mix it with gastric juices , turning it into a soupy mixture called chyme . The stomach has several important jobs: • Stores food temporarily • Mixes food with digestive juices • Begins the digestion of proteins 2.3.2 Enzymes and Acids Special cells in the stomach lining release digestive substances: • Chief cells secrete pepsinogen , an inactive enzyme • Parietal cells release hydrochloric acid (HCl)

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    Study Guide The acid changes pepsinogen into pepsin , an enzyme that breaks large protein molecules into smaller pieces called peptides . 2.3.3 Protection of the Stomach Another type of cell secretes mucus , which coats the stomach lining and protects it from acid. If this mucus layer fails and too much acid damages the lining, an ulcer can form. 2.4 Small Intestine: Digestion and Absorption The chyme leaves the stomach through a sphincter and enters the small intestine , where most digestion and absorption occur. 2.4.1 Structure The adult small intestine is about 23 feet long and has three sections: • Duodenum : First 10 – 12 inches • Jejunum : Next 10 feet • Ileum : Final 12 feet The inner lining has tiny fingerlike projections called villi , and each villus has even smaller structures called microvilli . These greatly increase surface area, allowing more nutrients to be absorbed. 2.4.2 Chemical Digestion in the Duodenum Most chemical digestion happens in the duodenum . Enzymes from the small intestine and pancreas work together here. In addition, bile enters from the gallbladder to help digest fats. 2.4.3 Carbohydrate Digestion Different enzymes break down different sugars: • Amylase : Starch • Maltase : Maltose

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    Study Guide • Sucrase : Sucrose • Lactase : Lactose 2.4.4 Fat Digestion • Bile breaks large fat globules into smaller droplets • Lipase then digests fats into smaller molecules Bile is made in the liver and stored in the gallbladder , a small sac under the liver. 2.4.5 Protein Digestion Proteins are broken down by several enzymes: • Trypsin and chymotrypsin (from the pancreas) break peptides into smaller peptides • Peptidases turn peptides into amino acids 2.4.6 Nucleic Acid Digestion Nucleases break nucleic acids into nucleotides . 2.5 Absorption in the Jejunum and Ileum Most absorption occurs in the jejunum . Digested nutrients enter the cells of the villi and then move into: • Capillaries (for sugars, amino acids, and other nutrients) • Lacteals (for fats, which enter the lymphatic system) Some nutrients move by diffusion , while glucose and amino acids use facilitated diffusion . The ileum completes absorption. Any material that is not digested or absorbed moves on to the large intestine.

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    Study Guide 2.6 Large Intestine: Water Recovery and Waste Removal The small intestine connects to the large intestine in the lower - right abdomen at a pouch called the cecum . Attached to the cecum is the appendix , which is believed to be a leftover structure from human ancestors. 2.6.1 Structure and Function The large intestine, also called the colon , has three main sections: • Ascending colon • Transverse colon • Descending colon Each section is about one foot long. The main functions of the large intestine are: • Absorbing water • Storing and processing waste • Eliminating solid waste from the body 2.6.2 Feces Formation After water is absorbed, the remaining material becomes feces , which include: • Undigested food (such as cellulose) • Billions of mostly harmless bacteria • Bile pigments and other waste materials Feces are stored in the rectum and leave the body through the anus , completing digestion. 2.7 Liver: Processing and Regulation The liver plays a major role after digestion by processing nutrients absorbed into the bloodstream.

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