Human Digestion and Absorption Digestive Anatomy Overview Copyright

Human Digestion and Absorption

Digestive Anatomy: Overview Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Human digestive system

Phases of Digestion: Overview Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin

The Process…. . • Ingestion- the process of taking food in. • Digestion - The process of changing food into simple components which the body can absorb. • Egestion- ridding the body of solid waste. • Route- Mouth->esophagus->stomach>small intestine->large intestine

Ingestion Mouth- food enters • mechanical digestion (mastication) o Teeth- break up food • Bolus of food forms- semi solid • chemical digestion o Saliva- secretion of enzymes – amylase » enzyme digests starch (breaks down into smaller molecules) – mucin » slippery protein (mucus) » protects soft lining of digestive system » lubricates food for easier swallowing – buffers » neutralizes acid to prevent tooth decay – anti-bacterial chemicals » protect » kill bacteria that enter mouth with food » Lysosomes and immunoglobulins kill viruses and bacteria.

Secretions of Digestion

mouth break up food digest starch kill germs moisten food

Swallowing reflex: Soft Palate & Esophagus Figure 21 -13: The swallowing reflex Copyright ©

Which type of digestion is the following? 1. Chewing a saltine? 2. Saliva breaking the saltine down into molecules of glucose? 3. Your tongue breaking pieces of a hamburger apart? 4. Pepsin (an enzyme) in your stomach breaking the hamburger into amino acids?

Pharynx • The back of the throat. • Larynxpassage for air, closes when we swallow. • Is approximately 15 cm long.

Digestion • Esophagus – connects mouth to stomach 1. Epiglottis – closes airway 2. Bolus moved along by peristalsis 3. Cardiac sphincter – keeps food from backing up into esophagus

Digestion • Stomach – collecting & churning (mechanical and chemical digestion) 1. Gastric glands secrete: gastric juice (water, enzymes, hydrochloric acid) that kills most bacteria and begins protein digestion and mucus to protect lining 2. Chyme – semi-liquid mass of partially digested food 3. Pyloric sphincter – regulates passage of chyme into small intestine

Secretions of Digestion

Digestion • Small Intestine – 3 segments: 1. Duodenum – opening from common bile duct secretes fluids from: a. Liver & Gallbladder – bile emulsifies fat b. Pancreas – amylase break down carbohydrate, sodium bicarbonate neutralizes the acidic chyme and lipase 2. Jejunum 3. Ileum a. Ileocecal valve – sphincter that regulates passage of chyme into large intestine

Digestion • Large intestine (colon) - reabsorbing & eliminating 1. Fermentation of undigested residues by bacteria occurs (e. coli) 2. Terminates at rectum, where water some minerals are absorbed 3. Anus – sphincter that controls defecation (excretion of fiber residue, wastes and some water)

The Final Stage

Digestion Muscular action helps to propel liquefied food through the G. I. tract by: 1. Peristalsis – muscular contractions that push contents forward 2. Segmentation – inward squeezing for greater mixing of secretions 3. Sphincter contractions

Peristalsis

Sphincter Contractions

Stomach • Functions – food storage • can stretch to fit ~2 L food – disinfect food • HCl = p. H 2 – kills bacteria – chemical digestion • pepsin – enzyme breaks down proteins But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food sphincter

Gastric Juices • Secreted by the stomach. • Acidic (p. H 1. 5 -2. 5) (HCl). • Pepsin- an enzyme that breaks down large proteins into amino acids. • Food is further broken down into a thin liquid called chyme.

Digestive Glands • Groups of specialized secretory cells. • Found in the lining of the alimentary canal or accessory organs.

Accessory Organs • Pancreas • Gall Bladder • Spleen

Gall bladder • Pouch structure located near the liver which concentrates and stores bile • Bile duct – a long tube that carries BILE. The top half of the common bile duct is associated with the liver, while the bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.

BILE • Bile emulsifies lipids (physically breaks apart FATS) • Bile is a bitter, greenish-yellow alkaline fluid, stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion.

Pancreas • An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine) • ** Pancreatic juice digests all major nutrient types. • Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

Pancreas • Digestive enzymes – digest proteins • trypsin, chymotrypsin – digest starch • amylase • Buffers – neutralizes acid from stomach

Liver • Function – produces bile • bile stored in gallbladder until needed • breaks up fats – act like detergents to breakup fats bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

mouth break up food digest starch kill germs moisten food liver produces bile - stored in gall bladder break up fats pancreas produces enzymes to digest proteins & starch stomach kills germs break up food digest proteins store food

Small Intestine • Most chemical digestion takes place here. • Simple sugars and proteins are absorbed into the inner lining. • Fatty acids and glycerol go to lymphatic system. • Lined with villi, which increase surface area for absorption, one cell thick.

Small intestine • Function – chemical digestion • major organ of digestion & absorption – absorption through lining • over 6 meters! • small intestine has huge surface area = 300 m 2 (~size of tennis court) • Structure – 3 sections • duodenum = most digestion • jejunum = absorption of nutrients & water • ileum = absorption of nutrients & water

Duodenum • 1 st section of small intestines – acid food from stomach – mixes with digestive juices from: § pancreas § liver § gall bladder

mouth break up food digest starch kill germs moisten food pancreas produces enzymes to digest proteins & starch stomach kills germs break up food digest proteins store food

Absorption in the SI • Much absorption is thought to occur directly through the wall without the need for special adaptations • Almost 90% of our daily fluid intake is absorbed in the small intestine. • Villi - increase the surface area of the small intestines, thus providing better absorption of materials

Absorption by Small Intestines • Absorption through villi & microvilli – finger-like projections – increase surface area for absorption

Absorption & Transport • End-products of digestion: 1. CHO >>> Monosaccharides 2. Fats >>> Glycerol + fatty acids 3. Proteins >>> Amino acids 4. Vitamins, minerals & water – no digestion

Absorption

Absorption & Transport • Absorption occurs in the small intestine 1. Wall of small intestine covered with 100 s of folds 2. Each fold covered with 1000 s of villi 3. Each villi contains 100 s of microvilli

The Small Intestine Villi

Absorption & Transport • Absorbed nutrients enter either the: 1. Vascular system – water-soluble nutrients (monosaccharides, amino acids, water-soluble vitamins, minerals, water) enter the blood via the portal vein for transport to the liver

Absorption & Transport 2. Lymph system – fat-soluble nutrients (lipids, fat-soluble vitamins) enter here, eventually entering the blood near the heart 3. Transport of lipids – since fats are insoluble in water, they must be packaged for transport as lipoproteins (triglyceride, phospholipid, protein,

Absorption & Transport 4 basic types of lipoprotein: 1. Chylomicrons – very, very low density (85% triglyceride); absorbed from small intestine into lymph & circulated to cells where some of lipid material is picked off & remnants return to liver 2. VLDL – very low density lipoprotein (50% triglyceride); made by liver & travels to cells

Absorption & Transport 3. LDL – low density lipoprotein (50% cholesterol); remains of VLDL; high levels increase risk of heart attack 4. HDL – high density lipoprotein (50% protein); removes cholesterol from blood for return to liver; high levels decrease risk of heart attack

VILLI

Absorption • once digested, absorption needs to take place – most takes place in small intestine • small intestine – 10 feet long – area = to tennis court – engulfs and absorbs nutrients – blood carries nutrients to live and other parts of body

Small Intestine Anatomy • inner surface – wrinkled and folded – each fold has 1, 000’s of projections • villa – made up of 100’s of cells, each covered with hairs: microvilli – constantly wave, squirm, and wiggle – traps nutrient molecules

Small Intestine Villi Stomach Small intestine Circular muscles Longitudinal muscles Folds with villi on them

Lymphatic vessel (lacteal) Capillaries A villus Goblet cells Crypts Artery Vein Lymphatic vessel

Microvilli

Villi Cells • recognize and absorb nutrients the body needs – the microvilli have enzymes and “pumps” – can handle all types and any combinations of food

Absorption of Nutrients Carrier loads nutrient on outside of cell. . . Outside cell Cell membrane Inside cell Carrier loads nutrient on outside of cell. . . Energy SIMPLE DIFFUSION . . . and then releases it on inside of cell. FACILITATED DIFFUSION . . . and then releases it on inside of cell. ACTIVE TRANSPORT Absorption of nutrients into intestinal cells typically occurs by simple diffusion or active transport.

Specialization • ready early, absorbed near the top – sugars, white bread, bananas • slower to digest, absorbed farther down – whole grain bread, fats, protein

Large intestines (colon) • Function – re-absorb water • use ~9 liters of water every day in digestive juices • > 90% of water reabsorbed – not enough water absorbed » diarrhea – too much water absorbed » constipation

Large Intestine • Solid materials pass through the large intestine. • These are undigestible solids (fibers). • Water is absorbed. • Vitamins K and B are reabsorbed with the water. • Rectum- solid wastes exit the body.

You’ve got company! • Living in the large intestine is a community of helpful bacteria – Escherichia coli (E. coli) • produce vitamins – vitamin K; B vitamins • generate gases – by-product of bacterial metabolism – methane, hydrogen sulfide

Appendix Vestigial organ

Rectum • Last section of colon (large intestines) – eliminate feces • undigested materials – extracellular waste » mainly cellulose from plants » roughage or fiber – masses of bacteria

Digestive Homeostasis Disorders • ULCERS – erosion of the surface of the alimentary canal generally associated with some kind of irritant

Digestive Homeostasis Disorders • CONSTIPATION – a condition in which the large intestine is emptied with difficulty. • Too much water is reabsorbed • and the solid waste hardens

Digestive Homeostasis Disorders • DIARRHEA – a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine. • This results in increased, multiple, watery feces. • This condition may result in severe dehydration, especially in infants

Digestive Homeostasis Disorders • APPENDICITIS – an inflammation of the appendix due to infection • Common treatment is removal of the appendix via surgery

Upper GI Problems Dysphagia – difficulty swallowing with tendency to choke/aspirate 1. Foods that are soft texture & smooth consistency critical to avoid aspiration (i. e. pudding consistency or pureed) 2. Thickened liquids using commercial thickeners are easier to swallow 3. Tube feeding into duodenum may be indicated

Upper GI Problems Reflux esophagitis (“heartburn”) which often occurs due to a hiatal hernia and Gastritis (inflammation of stomach lining) and Peptic Ulcers (erosions of the lining of stomach or duodenum) require a bland diet to reduce gastric secretions and eliminate foods that cause pain or discomfort 1. Avoid chocolate, garlic/onions, caffeine, spicy & fatty foods, mint, alcohol 2. Small meals with fluids between meals 3. Antacids & acid controllers

Gastroesophageal Reflux

Digestive Problems Delayed Gastric Emptying – may be delayed temporarily following surgery or chronically due to Diabetes Mellitus 1. Low fiber, low fat speeds gastric emptying & prevents bezoars that may form a blockage Constipation – prevent with a high fiber diet and treat by drinking plenty of fluids including prune juice, get regular exercise & add laxatives (hydrophilic colloids), as needed

Digestive Problems Diarrhea/dehydration – treat underlying cause and replace fluids & electrolytes to prevent dehydration 1. Mild cases use juices, sports drinks, caffeine-free sodas, tea, broth, oral rehydration formulas (e. g. Pedialyte) Diverticular Disease 1. Avoid nuts, seeds, hulls (e. g. okra, strawberries, popcorn) which may get trapped & cause diverticulitis

Diverticula in the Colon

Malabsorption Syndromes Dumping Syndrome Carbohydrate malabsorption that occurs due to removal of pyloric sphincter from partial gastrectomy causing osmotic diarrhea 1. Symptoms include weakness, dizziness, rapid heartbeat, diarrhea, abdominal pain 2. Avoid concentrated sweets, drink fluids between meals, eat small, frequent meals

Malabsorption Syndromes Lactose Intolerance Carbohydrate malabsorption due to a lack of the enzyme lactase that splits lactose into glucose + galactose 1. Incidence assoc. with aging, certain ethnic groups, and G. I. disease or surgery 2. Symptoms include cramping, distention, diarrhea after consuming products containing milk or lactose 3. Lactose-Restricted Diet or enzyme tablets & treated milk are also available

Malabsorption Syndromes Fat Malabsorption – caused by disorders of the stomach, intestine, pancreas & liver 1. Steatorrhea (fatty, loose, foamy, foul smelling stools) with subsequent loss of energy, essential fatty acids, and fat-soluble vitamins 2. Limit fat intake to 35 -40 gms/day 3. Supplementation with fat-soluble vitamins (water-miscible forms available) 4. Enzyme replacement to aid digestion & absorption

Malabsorption Syndromes Pancreatitis – inflammation of the pancreas, resulting in impaired digestion/absorption 1. Symptoms include severe abdominal pain, and nausea & vomiting 2. Initially, N. P. O. (nothing by mouth) to rest the pancreas using I. V. fluids to maintain fluid & electrolyte balance 3. Avoiding alcohol is imperative as diet progresses 4. Chronic pancreatitis may lead maldigestion of fats, chronic abdominal pain, weight loss & diabetes

Malabsorption Syndromes Cystic Fibrosis – hereditary disease characterized by thick mucus affecting many body organs, including lungs & pancreas, and abnormally high electrolyte concentration in sweat 1. Energy & nutrient needs 120 -150% of normal 2. Fat needed to meet high energy needs so enzyme replacements used to control steatorrhea 3. Liberal use of fluids & salt

Malabsorption Syndromes Celiac Disease (Gluten-sensitive enteropathy) – sensitivity to gliadin, part of the protein gluten, found in wheat, rye, barley & oats 1. Symptoms include weight loss, diarrhea, fatigue, anemia (iron, folate, Vit. B 12), generalized malabsorption, bone disease 2. Avoiding foods containing gluten requires reading labels!

Digestive Homeostasis Disorders • GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder • Can either be “passed” (OUCH!!) or surgically removed

Digestive Homeostasis Disorders • • • ANOREXIA NERVOSA - a psychological condition where an individual thinks they appear overweight and refuses to eat. Weighs 85% or less than what is developmentally expected for age and height Young girls do not begin to menstruate at the appropriate age.

Digestive Homeostasis Disorders • HEART BURN – ACID from the stomach backs up into the esophagus.

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Digestive System Cadaver

Travel Through the Digestive System