Get started: How do nutrients get from food to the blood stream? Today we will: • Intro to digestive system • Notes • Color/label diagram • The 1. alimentary canal (or gastrointestinal [GI] tract) is made of several organs that serve to break down and absorb nutrients from food and drink and remove the leftover material • It is a twisting, hollow tube that is open at both ends • It consists of the mouth, esophagus, stomach, small intestine, and large intestine • The mouth, or 2. oral cavity, is where food enters • It is lined with 3. mucous membranes • The anterior of the mouth is protected by the 4. lips, the lateral walls are formed by the 5. cheeks, the roof is formed by the 6. hard palate and 7. soft palate, and the bottom is filled primarily with the 8. tongue, which is secured to the bottom of the mouth by the 9. lingual frenulum • The space between the lips and cheeks is called the 10. vestibule • The teeth start the process of 11. mechanical digestion (physical breakdown of food) • 12. Saliva also serves to begin some 13. chemical digestion (chemical breakdown of food), but only of carbohydrates • The pharynx is also considered a digestive system organ (although the nasopharynx is only part of the respiratory system) • The walls of the pharynx contain 14. two layers of skeletal muscle: • The fibers of the internal layer are 15.longitudinal while the fibers of the external layer are 16. concentric. This arrangement allows for a special type of contraction called 17. peristalsis, which will be discussed later • The esophagus is a muscular tube that extends from the laryngopharynx through a hole in the diaphragm where it connects to the stomach • The wall of the esophagus (as well as the stomach and both intestines) consist of 4 layers: • 1) The 18. mucosa is the innermost layer that is made of epithelial cells (stratified squamous for esophagus to protect from friction, simple columnar for the rest). It also contains mucus-producing glands that secrete into the hollow cavity (lumen) of the alimentary canal • 2) The 19. submucosa is next. It contains blood vessels, nerves, lymph vessels and nodes, and additional mucosal glands • 3) The 20. muscularis externa layer contains two layers of smooth muscle (an inner circular layer and an outer longitudinal layer) that will assist with mechanical digestion and propulsion through the canal • 4) The 21. serosa is the outermost layer. It is a single layer of serous-producing cells and is also called the visceral peritoneum or adventitia. The visceral peritoneum is continuous with the parietal peritoneum, which lines the abdominopelvic cavity along with several membrane extensions called the 22. mesenteries. No digestion occurs in either the pharynx or the esophagus. They just move the food along. • The stomach is a J-shaped organ located in the upper left abdominal quadrant • The stomach has several portions: • a. The 23. cardiac region is named because of its proximity to the heart. It connects to the esophagus via a circular muscle called the 24. cardioesophageal sphincter. This muscle contracts to prevent food from moving back into the esophagus • b. The 25. fundus is the expanded portion lateral to the cardiac region • c. The 26. body is the mid-portion of the stomach • d. The funnel-shaped 27. pylorus is the terminal end and connects to the small intestine via another circular muscle called the pyloric sphincter • 28. The stomach is about 25 cm long, and when full can expand to hold about 1 gallon. • When empty it collapses inward into folds called 29. rugae. • The convex lateral surface is the greater curvature and the concave medial surface is the lesser curvature. • The muscularis externa of the stomach not only moves food along, but it mixes and churns it with several enzymes to turn it into a thick, creamlike substance called 30. chyme. • Thus, mechanical and chemical digestion 31. both occur in the stomach Digestive System, Part 1: Crash Course A&P #33 https://www.youtube.com/watch?v=yIoTRGfcMqM Digestive System, Part 2: Crash Course A&P #34 https://www.youtube.com/watch?v=pqgcEIaXGME Digestive System, Part 3: Crash Course A&P #35 https://www.youtube.com/watch?v=jGme7BRkpuQ • The small intestine is the 32.major digestive organ. Much of 33. chemical digestion and almost all 34. absorption occurs here. • It is a 2-4 m (7-13 ft) long twisting section of the alimentary canal that extends from the pyloric sphincter to the 35. ileocecal valve that connects it to the large intestine. • The coils are held together and anchored to the posterior abdominal wall by the mesenteric membranes • The small intestine has three sections: • 1) The 36. duodenum is about 25 cm (10 in) long and curves around the head of the pancreas • 2) The 37. jejunum is about 2.5 m(8 feet) long and extends from the duodenum to the ileum • 3) The 38. ileum is about 3.6m (12 feet) long and extends from the jejunum to the ileocecal valve, where it connects to the large intestine • Most chemical digestion occurs in the small intestine • The intestinal cells produce an important mucus, and the 39. pancreas and gall bladder both empty important enzymes into the duodenum to aid in the chemical breakdown of foods • The 40. pyloric sphincter controls the amount of food that enters the small intestine as it can only handle a small amount of food at a time • The small intestine is also where almost all absorption takes place, and the small intestine is well suited for that function • The wall has three structures that aid absorption: • 1) 41. Microvilli are tiny projections of the mucosal cells that give the surface a fuzzy appearance • 2) 42. Villi are fingerlike projections that give it a velvety appearance and feel. They also include a capillary bed that allow nutrients to get into the bloodstream • 3) 43. Circular folds are deep folds of the mucosal and submucosal layers • Unlike the rugae of the stomach, the circular folds do not disappear during distension • All three of those structures increase 44. surface area to improve absorption • The structures 45. decrease in number toward the end of the small intestine to help prevent absorption of bacteria from the leftover 46.waste at the end of the small intestine • The large intestine is much 47. larger in diameter than the small intestine, but 48. shorter in length • It extends from the ileocecal valve to the anus and frames the small intestine on three sides • Its major function is to dry out undigested food be reabsorbing 49. water, and eliminate waste as feces • It has several sections as well: • 1) The 50. cecum is a saclike section after the ileocecal valve • 2) The 51. appendix hangs from the cecum, and is a potential site for bacteria to accumulate and multiply, causing a condition called appendicitis • 3) The 52. colon is divided into 4 sub-sections: the ascending colon travels up the right side of the abdominal cavity; the transverse colon continues across the abdomen from right to left; the descending colon extends from the upper left to lower left of the abdomen; and the sigmoid colon is an S-shaped region that brings the colon back to the midline of the body Get started: What effect does gravity have on the propulsion of food through the digestive system? • Three pairs of salivary glands secrete saliva into the mouth. • 1) The 55. parotid glands are located anterior to the ears and secrete into the upper lateral portion of the mouth • 2) The 56. submandibular glands and • 3) the 57. sublingual glands secrete through tiny ducts into the floor of the mouth • Saliva is a mixture of serous and mucous fluid and has several functions • The saliva dissolves food so it can be tasted, as well as binds it together into a mass called a 58. bolus • It contains an enzyme called salivary 59. amylase that starts the chemical digestion of carbohydrates • It also contains a substance called lysozyme and antibodies that help to inhibit bacteria that was present on food • Teeth are responsible for 60. mastication, or chewing • They are aided by the tongue, which helps to move food between the teeth • They are responsible for beginning 61. mechanical digestion by tearing and grinding food into smaller pieces that are more easily digested later in the process • Humans produce two separate sets of teeth • The first set (deciduous teeth) begins to erupt from the gums around 6 months, and the full set (20 teeth) is there by age 2. • As the second set (permanent teeth) forms and develops, the deciduous teeth fall out. The new set has come in by the end of adolescence. There are 32 permanent teeth, although in many people the last set of molars (wisdom teeth) do not erupt or are absent altogether Why might they be absent all together? 62. Like vestigial structures – structures that disappear due to the evolution of species The teeth are classified into several groups: 1) The 63. incisors are chisel-shaped and are adapted for cutting (4 on top, 4 on bottom) 2) The fanglike 64. canines are for tearing and piercing (2 on top, 2 on bottom) 3) The 65. premolars (bicuspids) and 4) 66. molars have rounded crowns and flatter centers and are suited for grinding food Teeth have two main regions: the exposed 67.crown and the hidden 68.root • The crown is covered in 69. enamel, a hard smooth substance that protects the tooth • 70. Dentin, a bone-like substance, underlies the enamel and forms the bulk of the tooth • The dentin surrounds the pulp cavity, which contains blood vessels, connective tissue, and nerve fibers (collectively called 71. pulp). • Where the pulp extends into the root, it becomes the 72. root canal, which provides a route for the pulp structures to enter the tooth • The pancreas is a soft, pink, triangular organ extending from the spleen to the duodenum • Its endocrine function has already been covered, but it also produces a very important substance for digestion called 73. pancreatic juice (the details will be discussed later) • It secretes the pancreatic juice into the duodenum in an alkaline fluid (to counteract the acidity of the stomach) • The 74. liver is the largest gland in the body located under the diaphragm in the upper right quadrant of the abdomen • It has four lobes and is suspended from the diaphragm and the abdominal wall by the 75. falciform ligament • Its digestive function is to produce 76. bile • 77. Bile is a yellow-green solution containing bile salts, pigments (primarily bilirubin), cholesterol, phospholipids, and electrolytes • The bile salts will 78. emulsify fats by breaking large fat globules into smaller ones, allowing fatdigesting enzymes to work better • The liver secretes the bile through the 79. common hepatic duct and it enters the 80. duodenum through the bile duct • If food digestion is not occurring, the bile backs up through the cystic duct into the 81. gallbladder, a small pouched organ located under the liver • If the bile is stored too long in the gallbladder, the cholesterol can crystallize into 82. gallstones, which can cause tremendous pain • If the gallstones block the ducts leading to the small intestine, the bile accumulates and backs up into the liver, which then causes the bile salts to enter the blood stream • The end result is a condition that yellows the tissues of the body called 83. jaundice, which can also be a symptom of hepatitis or cirrhosis of the liver • The activities of the GI tract include six processes: • 1) Ingestion – an active, voluntary process of food entering the mouth • 2) Propulsion – the moving of food from one organ to the next. The main process is a wavelike contractive process called peristalsis. A second movement pattern called segmentation moves food back and forth within the walls of the digestive system • 3) Mechanical digestion – mixing of food in the mouth, chewing, churning in the stomach, and segmentation in the small intestine all serve to physically break down food into smaller pieces • 4) Chemical digestion – the sequence of steps in which large food particles are broken into smaller ones by enzymes • 5) Absorption – transport of digested food particles into the bloodstream • 6) Defecation – the elimination of undigested substances from the body • Control of digestive functions occurs primarily in response to change. The stimuli involved include: • 1) the stretch of an organ caused by food • 2) the pH of the contents • 3) the presence of breakdown chemicals (like saliva) • When the stimuli occur, they activate or inhibit 1) the glands that secrete digestive juices or 2) the smooth muscles involved in mixing and propulsion 1) Ingestion – clearly ingestion of food occurs in the mouth 2) Mechanical digestion – the teeth are involved in breaking food into smaller pieces The tongue also mixes the food with saliva 3) Chemical digestion – salivary amylase is involved in breaking down carbohydrates 4) Propulsion – swallowing occurs to move food from the oral cavity down the pharynx and esophagus • Swallowing involves several reflexes: • 1) the soft palate raises to seal off the nasopharynx, 2) the tongue seals off the oral cavity to force food down the pharynx, 3) the epiglottis seals the trachea, and 4) the walls of the pharynx and esophagus contract to force food downward • Peristalsis continues to move the food toward the cardioesophageal sphincter 1) Mechanical digestion – the smooth muscles in the wall of the stomach will mix and churn food to break it down 2) Chemical digestion – stomach glands produce gastric juice. In addition, the presence of food causes the release of the hormone gastrin, which stimulates even more release of mucus, hydrochloric acid, and enzymes. The hydrochloric acid is needed to activate the enzyme pepsin, which is a major enzyme for protein digestion. • The alkaline mucus produced helps protect the stomach itself from being digested by the acidic environment and enzymes • The start of protein digestion is the only chemical digestion that occurs in the stomach, and virtually no absorption takes place (except for aspirin and alcohol) • 3) Propulsion – once the food has been mixed, peristalsis begins in the lower half of the stomach. The pylorus acts to regulate the amount of chyme that enters the small intestine • Each contraction of the pylorus only squirts about 3 ml of chyme into the duodenum, so the rest is pushed back into stomach for more mixing • It usually takes about 4 hours for the stomach to empty completely (up to 6 hours for a high-fat meal) • If the stomach is irritated (or overdistended) and contracts prematurely, some of the high acid chyme can move back into the esophagus where mucus does not protect the wall and cause a burning sensation (heartburn) • If the stomach has severe irritation, it may activate the emetic center of the brain located in the medulla. This causes forceful contraction of the stomach (and even the small intestine), as well as contraction of the abdominal muscles and diaphragm. The result is a reverse peristalsis called vomiting. • The emetic center can also be activated by problems with equilibrium (see: motion sickness) • 1) Chemical Digestion – the majority of chemical digestion occurs in the small intestine, although intestinal juice itself does not contain many enzymes (although the mucus it secretes helps in protection) • Pancreatic juice contains several important enzymes that go to work in the small intestine. They include pancreatic amylase (carbohydrate), trypsin, chymotrypsin, and carboxypeptidase (protein), lipases (fats), and nucleases (nucleic acids) • Pancreatic juice also contains bicarbonate, which helps neutralize the acidic chyme • The small intestine mucosal cells also produce two hormones (secretin and cholecystokinin), when chyme enters which will stimulate pancreatic juice release as well as bile production • The bile salts are important to chemically emulsify large fat molecules so the lipases from pancreatic juice can work more effectively • 2) Absorption – almost all absorption occurs in the small intestine as nutrients are moved through active transport or diffusion into the capillary beds that surround the villi. At the end of the ileum, all that remains is some water, indigestible food (like cellulose), and bacteria • 3) Propulsion – peristalsis moves the food through the long small intestine (which needs to be long to allow time for all the digestion and absorption). The process takes 3-6 hours on average. • The residue that arrives at the large intestine still has about 12-24 hours to spend there • 1) Chemical Digestion – Although the large intestine does not contain any digestive enzymes, the bacteria that live there play a role in chemical digestion as they break down the waste and produce vitamin K and some B vitamins • 2) Absorption – absorption is limited to the vitamins produced as well as most of the remaining water • 3) Propulsion – two types of movements occur in the large intestine. • The first is a sluggish form of peristalsis, which contributes little to propulsion but does help pack the feces more tightly. • The second is called mass movements, which are long, slow, powerful contracting waves that force the contents toward the rectum. They occur 3 or 4 times daily, usually during or just after a meal. • 4) Defecation – the elimination of solid waste only occurs in the large intestine • Defecation is stimulated by the presence of feces in the rectum, and consists of a reflex that contracts the sigmoid colon and rectum as well a relaxation of the anal sphincters • Fiber in the diet helps to soften the stool and increase contraction strength to make defecation easier • Diarrhea occurs when irritation causes the mass movements to occur too frequently before enough water has been absorbed • Constipation is the opposite condition, when too much water is absorbed and feces become dry and difficult to eliminate • A nutrient is a substance used by the body to promote normal growth, maintenance, and repair • There are six categories of nutrients: carbohydrates, proteins, lipids, vitamins, minerals, and water • Water is important as a solvent and for many body functions (such as transport and temperature maintenance) • Almost all carbohydrates we consume are from plants (except for lactose in milk and a small amount of glycogen in meat) • Sugars come mainly from fruits, sugar cane, and milk • Starches are found in grains, legumes, and root vegetables (beets, potatoes, etc.) • Cellulose from plants is not a digestible carbohydrate for humans, but provides fiber that aids in waste removal • Carbohydrates are the preferred source of energy for body cells because they are easily broken down into glucose, which is the main fuel used in the formation of ATP in cellular respiration • If blood glucose levels are high because of too much carbohydrate consumption, some of it is stored as glycogen in the liver and in muscle cells • If it is still too high, the remainder is stored as fat • Most dietary fats are triglycerides (saturated and unsaturated fats) • Saturated fats come from animal products such as meat, dairy, and eggs (some are from plants like coconuts and avocados) • Unsaturated fats are mainly from plants like seeds, nuts, and most vegetable oils • The liver produces all the cholesterol we need, but we consume it like saturated fats in animal foods • The liver metabolizes most fat that goes into the body. It uses some to make ATP, some to make thromboplastin (for clotting), and some to make cholesterol; however, it releases the rest into the bloodstream in the form of small fat-breakdown products • The cells use those products to build cell membranes, create steroid hormones, and build myelin sheaths around neurons • The rest is stored in the body. Although some subcutaneous fat is important for temperature maintenance, excess storage inhibits the cardiovascular system Proteins come in two forms: complete and incomplete • Complete proteins contain all of the essential amino acids needed to for tissue maintenance and growth. They are found in eggs, milk, and most meat products • Incomplete proteins – such as those found in legumes, nuts, and starches – are incomplete because they lack one or more of the essential amino acids needed. Different types of incomplete proteins must be consumed to meet nutritional demands • Proteins are broken down into their amino acids which are transported via the bloodstream to the cells to absorb and use for protein synthesis to make body tissues, antibodies, enzymes, hormones, spindle fibers, and mucus • Of the 20 amino acids, cells can produce 12 of them. The other 8 essential amino acids must be consumed in the diet. Amino acids are only used to make ATP if there is an overabundance of them • The liver is important in protein metabolism because it detoxifies ammonia (a by-product of protein metabolism) by combining it with carbon dioxide to make urea. Urea is not toxic and is flushed out of the body as a component of urine • Why would a urine test show if you are positive for drug use? • In addition to this (and maintaining sugar balance in the blood), the liver also detoxifies all medicines and alcohol in a similar manner • It also synthesizes the non-essential amino acids that are used by the cells • The synthesis of cholesterol in the liver is important because cholesterol is the basis of steroid hormone production and vitamin D synthesis • The liver is also responsible for making bile which, as was discussed earlier, is responsible for emulsifying large fat molecules in the small intestine to begin chemical digestion of fats • The basal metabolic rate (BMR) is the amount of heat produced by the body per unit of time when it is at rest • Put another way, it is the amount of energy used by a person to perform life-supporting activities like breathing, heartbeat, and kidney function BMR can be influenced by several factors: • 1) Surface area to volume ratio – the higher the ratio, the higher the BMR • 2) Gender – males typically have a higher BMR • 3) Thyroxine production – thyroxine produced by the thyroid influences oxygen consumption and ATP use, increasing BMR • 4) Age – BMR typically gets lower as humans age • 5) Strong emotions – high stress, fear, anger, and also infections increase BMR • Outside of BMR, a person’s activity level requires different amounts of fuel • Total metabolic rate (TMR) is the amount of kilocalories the body must consume to meet the fuel demands of all activities • In a well-conditioned person, the TMR jumps significantly with just a few minutes of vigorous activity (and stays elevated for hours afterward) • Weight is controlled using a simple formula: Calories Consumed vs. Calories Needed • Vitamins are small organic molecules produced by living things that assist in many body functions • They come in two categories: water-soluble and fat-soluble • Fat-soluble vitamins include vitamins A, D, E, and K. • Water-soluble vitamins include vitamin C and the B vitamins • One difference is that fat-soluble vitamins can be stored, while water-soluble vitamins must be consumed daily to as they are flushed out through urine • The other difference is in their ability to resist heat; water-soluble vitamins are destroyed in high temperatures, so cooked fruits and vegetables lose those benefits. • Vitamin A - maintaining healthy eyes, skin, and bones; hormone synthesis • The B vitamins have a range of functions but most center on aiding metabolism • Vitamin C is important in helping the body absorb iron for hemoglobin and in synthesis of collagen (for healthy skin and gums) • Vitamin D helps the body absorb calcium and phosphorus to maintain strong bones and teeth. • Vitamin E is an antioxidant that helps maintain cell membranes • Vitamin K is essential in the process of coagulation during wound healing • Minerals are also small molecules needed for body process, but they are NOT made by living organisms and are instead found in nature • The main important minerals include calcium, phosphorus, potassium, iron, sulfur, sodium, chloride, iodine, and magnesium • Calcium – bone and teeth formation; needed for muscle contraction • Phosphorus – bone and teeth formation • Potassium – involved in nervous system function and muscle contraction • Sodium – maintains fluid balance and is involved in nerve impulse propagation • Chloride – involved in acid-base balance and formation of gastric juice • Iron – main component of hemoglobin in red blood cells • Sulfur – component of cartilage, tendons, and most proteins • Magnesium – component of enzymes • Iodine – needed for thyroid hormones Resources: Medline Plus – Health Topics https://medlineplus.gov/healthtopics.html Web MD Health Line Clear Health from NIH Presentation: 1 – Share your patient’s scenario with the class 2 – Explain your hypotheses and why you ruled out first guesses 3 – Give your final diagnosis or opinion (may be more than one) and the advice/information you would give this patient/next of kin At the Clinic 1. (29) Mary Maroon – vegetarian diet 2. (30) Mr. Ashe – heartburn 3. (33) A woman – severe pain left iliac 4. (36) Zena - body fat, crash diets, lack of exercise 5. (38) A 21 year old man – result of untreated appendicitis 6. (32) Bert – heat 7. Dairy issues You should have completed this: Copy this list: Protein, saturated fat, carbohydrates/sugars, calcium, iron, Vitamin A, Vitamin C, Vitamin D, Vitamin E, Potassium Research these nutrients (macronutrient, vitamin, or mineral) and how deficiencies and excesses of that nutrient would impact the body in terms of disease or diminished quality of life.