4Digestive SystemDigestion is the mechanical and chemical breakdown of foods and the absorption of the resulting nutrients.Mechanical digestion breaks large pieces into smaller ones without altering their chemical composition.Chemical digestion breaks food into simpler chemicals.
5Digestive SystemThe digestive system consists of the alimentary canal, which extends about 8 m from the mouth to the anus, and the accessory organs which secrete substances used in the process of digestion.
6Alimentary CanalThe alimentary canal includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.The accessory organs of the digestive system include the salivary glands, the liver, gallbladder, and pancreas.Overall, the digestive system has a surface area of over 186 square meters.
7Alimentary CanalMuscular tube that passes through body’s ventral cavity.Wall has four distinct layers:Mucosa: carries out secretion and absorption.Submucosa: carries away absorbed materials.Muscular layer: produces movements of the tubeSerosa: outer covering.
8Alimentary Canal Two movements: Mixing – rhythmic contractions. Mix food with digestive juices that mucosa secretes.Propelling – peristalsis wave pushes tubular contents ahead.
9MouthMouth – receives food and begins digestion by mechanically reducing size of food.Oral cavity – chamber between palate and tongueVestibule – space between teeth, cheeks, and lips.C. megalodon, extinct shark
10MouthCheeks –pads of subcutaneous fat, muscles associated with expression and chewingLips –surround the mouth opening.Tongue – Nearly fills oral cavity. Frenulum connects tongue to floor of mouth. Mixes food particles with saliva during chewing and moves food to pharynx during swallowing.
11Mouth Papillae on tongue provide friction and bare tastes buds. Palate forms the roof of the mouth. Consists of hard and soft palate.Soft palate to back of mouth and forms uvula.During swallowing, muscles draw soft palate and uvula upward, allowing closure of nasal cavity and pharynx.Why?
12MouthPalatine tonsils are masses of lymphatic tissue located at the back of the mouth.Pharyngeal tonsils, or adenoids, are also in the back of the mouth.Why are all of these lymphatic tissues in the mouth?Have any of you had a tonsillectomy? What could possible consequences be later in life?
13MouthTwo different sets of teeth form during development: primary (deciduous) and secondary (permanent) teeth.Teeth begin mechanical digestion by breaking pieces of food into smaller pieces.Why?Increases surface area of food particles, allowing digestive enzymes to react more effectively.
14Salivary Glands The salivary glands secrete saliva. Saliva moistens food particles, binds them, and begins chemical digestion.Amylase, a digestive enzyme splits starch and glycogen down into disaccharides.Mucus is secreted by mucosa cells that bind food and lubricates during swallowing.
15Salivary GlandsWhat happens if your body quits making saliva (xerostomia)?“Meth Mouth” is the result of no spit, poor dental hygiene, tooth grinding, and clenching.Want to kiss this?Didn’t think so
16Pharynx (throat) [Look familiar?] Made of muscle and mucous lining into 3 divisionsNasopharynx – posterior nares to soft palateOropharynx – soft palate to hyoid bone; adenoid tonsilsLaryngopharynx – hyoid bone to esophagus; palatine and lingual tonsils
17Esophagus A straight, collapsible tube about 25 cm long Food passageway from pharynx to stomachSecretions moisten and lubricate tubeThe cardiac sphincter (lower esophageal sphincter) remains contracting, closing the entrance to the stomach.Why is this important?To keep the stomach contents from regurgitating into esophagus.When peristaltic waves hit stomach, these fibers relax and allow food to enter.
18Stomach The stomach is an organ that: receives food from the esophagus mixes the food with gastric juicesbegins chemical digestionmoves food on to the small intestine.The pH of the stomach, due to gastric acids, can go as low as 1, and ranges up to 3-4 when food enters.Why do you think it’s important to have such a low pH in the stomach?
19StomachGastric glands in the stomach excrete digestive enzymes such as:Pepsin, formed from pepsinogen upon contact with HCl from parietal cells. Pepsin begins digestion of proteins.Intrinsic factor which helps the small intestine absorb vitamin B12.When a person tastes, smells or sees appetizing food, the brain releases Ach, which stimulates gastric glands to secrete gastric juices.
20StomachAfter a meal, the mixing movements of the stomach wall and a mix of gastric juice and food particles form chyme.Chyme is what leaves the stomach and moves into the duodenum (the first part of the small intestine), where secretions from other organs are added.
21PancreasThe pancreas has both endocrine and exocrine functions. It secretes a digestive juice – pancreatic juice.What are the differences between endocrine and exocrine glands?Endocrine glands secrete hormones or other chemicals into the local environment, while exocrine glands secrete their products into ducts which lead to other parts of the body.
22Pancreas Pancreatic juice has several enzymes including: Pancreatic amylase – splits molecules of srach or glycogen into disaccharides.Pancreatic lipase – breaks down triglycerides into fatty acids.Nucleases – break down nucleic acids into nucleotides.Proteolytic enzymes – break down proteins.
23The Liver The liver is divided into lobes – left and right. The liver functions in many ways including with carbohydrate, lipid, and protein metabolism, storage, blood filtering, detoxification, and the secretion of bile.
24The LiverThe most vital function of the liver is its work in protein metabolism.This protein metabolism involves deaminating amino acids, forming urea, and synthesizing plasma proteins (such as clotting factors).The liver also stores iron, glycogen, vitamins, and breaks down fats that can be stored in adipose tissue throughout the body.
25The LiverBile – yellowish-green liquid secreted from hepatic cells in the liver. Bile contains water, salts, bile pigments (bilirubin and biliveridin), cholesterol, and electrolytes.
26Gallbladder The gallbladder is a sac located on the liver’s surface. It stores bile between meals, reabsorbs water to concentrate the bile, and contracts to release bile.
27Small IntestineThe small intestine receives secretions from the pancreas and liver and completes the digestion of the nutrients in chyme, absorbs products of digestion and transports remains to the large intestine.
28Small IntestineIntestinal villi are tiny projections that greatly increase the surface area of the intestine.Why would this be important in this organ?Aids the absorption of digestive products.Digestive enzymes are released from these villi:Peptidase – breaks down peptides into amino acidsSucrase – breaks down sucroseMaltase – breaks down maltoseLactase – breaks down lactosePeople who are lactose intolerant lack lactase in intestine
29Small IntestineSmall intestine is the most important absorbing organ of the alimentary canal.Nutrients are absorbed into the villi and transported through the blood to various body parts.Example: cholesterol transported to liver.
30Main SqueezeIn snakes that feed as constrictors, the small intestine stretches after meals to increase its mass by over 40%, therefore increasing surface area to help with the absorption of nutrients.Green Anaconda (Eunectus murinus) constricting a Caiman
31Large IntestineThe large intestine is so named because it has a larger diameter than the small intestine.The cecum is the beginning of the large intestine.From the cecum hangs the veriform appendix.The appendix is a vestigial organ.What do you think the appendix might have been used for in our ancestors?
32Large IntestineThe large intestine absorbs water and electrolytes from chyme remaining the alimentary canal.It also forms and stores feces.1 - cecum2 - ascending colon3 - transverse colon4 - descending colon5 - Sigmoid colon6 - rectum
33Large Intestine The large intestine wall lacks villi. The large intestine does not secrete enzymes.Only secretion is mucus.Instead, large intestine absorbs water and electrolytes and remainder becomes feces.Intestinal flora, the bacteria that inhabit the large intestine, break down molecules in food, such as cellulose.
34Large Intestine The human colon is home to over 100 trillion bacteria. Flatus, intestinal gas, is the result of bacterial actions in the large intestine.Escherichia coli in human large intestine
35Large IntestinePeristaltic waves and mixing motions produce mass movements in the large intestine forcing the contents towards the rectum.Feces include material that were not digested or absorbed, plus water, electrolytes, mucus, and bacteria. Feces are usually about 75% water.…Or if you ask the girl in Donnie Darko, “What are feces?”“Baby mice.”
36Nutrition Four Basic Food Groups Nutrition is the study of nutrients and how the body uses them.Nutrients include carbohydrates, lipids, proteins, vitamins, minerals, and water.Macronutrients – proteins, lipids, carbohydrates. Required in large amounts.Micronutrients – vitamins and minerals.
37NutritionMacronutrients provide potential energy that can be expressed in calories (unit of heat).Calorie – the amount of heat required to raise the temperature of a gram of water by 1° C.The “calorie” used to measure food energy is actually the kilocalorie, but is often written Calorie.1 gram of carbohydrate or 1 gram of protein yields about 4 calories.1 gram of fat yields about 9 calories.Nutrients that human cells cannot synthesize, such as some amino acids, are called essential nutrients.
38NutritionCarbohydrates are organic compounds used to supply energy for cellular processes.Starch, mono- and disaccharides, glycogen, and cellulose are all carbohydrates.What is an example of a cellular process in which a carbohydrate is being used?
39CarbohydratesMonosaccharides absorbed from the digestive tract such as fructose, galactose and glucose are broken down and used in cellular respiration.Excess glucose is stored as glycogen in liver. Glycogen can be converted to glucose when needed. Some excess glucose is stored as fat.Ribose and deoxyribose are required for the production of these…Nucleic acids RNA and DNA
40LipidsLipids are organic compounds that include fats, oil, waxes, and cholesterol.Main function is to supply energy.Saturated fats are found mainly in meat, eggs, milk but also in coconut and palm oil.Unsaturated fats are in seeds, nuts, and plant oils.
41LipidsSaturated fats are “saturated” with hydrogen atoms because they lack double bonds.Unsaturated fats have a cis double bond.Trans fats are unsaturated but have a trans double bond. This adds a kink to the chain.Often this occurs due to hydrogenation, a process that adds hydrogen atoms and results in the trans bond. This allows the unsaturated fat to remain solid at room temperature, thus acting as a saturated fat and being able to be preserved longer.
42Lipids So what? Trans fats are not essential to the diet. Also, they can raise LDL cholesterol levels and lower HDL cholesterol, causing problems.
43Protein Proteins are polymers of amino acids. Proteins have a variety of functions. Many are enzymes. These and other proteins function in:Metabolic rateClottingKertain in skin and hairElastin and collagen of connective tissueWater balanceMuscle components (actin, myosin)HormonesAntibodies
44Protein Food sources of protein: Meat Fish Cheese Milk Nuts Eggs CerealLegumes
45ProteinAmino acids that the body can synthesize are called nonessential.Those that it cannot synthesize are called essential amino acids.Complete proteins supply all of the essential amino acids. These include: milk, eggs, meat. Eggs are the only 100% complete protein.Incomplete proteins must be combined.Example: rice and beans.
46Vitamins and MineralsVitamins are organic compounds that are required in small amounts and which the cells cannot synthesize in adequate amounts.Fat-soluble vitamins: A, D, E, KWater-soluble vitamins: B, CMinerals are elements other than carbon that are essential in human metabolism.
47Stomach Stomach is divided into four parts: Cardiac – near heart/esophagusFundic – balloons upBody – main partPyloric – near small intestineTaste, smell, or see food, Ach stimulates gastric glands to secrete gastric juice (HCl, pepsin, etc).Gastrin also released which aids gastric juiceChurning of food produces chyme.
48PancreasAs chyme enters duodenum, hormone secretin released, pancreatic juice excreted.Pancreatic juice includes:Pancreatic amylasePancreatic lipaseNucleasesProteolytic enzymes