CHAPTER 4 HUMAN DIGESTION AND ABSORPTION

ORGANIZATION OF THE HUMAN BODY Chemical Level Atoms combine to form molecules Cell Level Molecules form organelles Use ATP Tissue Level Similar cells make up tissues

ORGANIZATION OF THE HUMAN BODY Organ Level Different tissues combine to form organs Organ System Level Organs make up an organ system Organism Level Organ systems make up an organism

DIGESTIVE ORGAN SYSTEM GI tract Mouth, esophagus, stomach, small intestine, large intestine Accessory organs: Liver, pancreas and gall bladder

DIGESTIVE ORGAN SYSTEM

DIGESTIVE SYSTEM OVERVIEW Digestion Process of breaking down foods into a form the body can use Absorption Uptake of nutrients from the GI tract into the blood or lymph

ANATOMY OF THE GI TRACT GI tract Long hollow muscular canal. Nutrients pass through the wall of the canal to be absorbed Four layers (listed from inner most layer to outermost layer) Mucosa Submucosa Muscle Serosa

GI MOTILITY Peristalsis Contractions of the GI tract, mainly in esophagus, stomach, and small intestine Segmentation Back and forth movement-happens in small intestine so there is mixing with digestive juices Mass movements Slow peristalsis over widespread area- in large intestine to help propel fecal matter to rectum Elimination

Sphincters: Ring like muscles along the GI tract that control the flow of contents ONE WAY STREET

MOUTH (ORAL CAVITY) Chewing breaks up food and increases surface area. These smaller food particles are mixed with saliva and forms a bolus. Saliva Lysozyme Break down bacteria Amylase Break down starch Mucus Lubricate and hold bolus together

TASTE AND SMELL Taste buds on the tongue and soft palate Salty (from metal ions) Sour (from acids) Sweet (from organic compounds) Bitter (many diverse compounds like phytochemicals) Umami or savory (from amino acids) Olfactory glands Sense of smell (enhances sense of taste)

ESOPHAGUS Swallowing Moves bolus from the mouth to the esophagus Epiglottis Prevents food from lodging in the trachea Covers the larynx

STOMACH Bolus goes through lower esophageal sphincter into stomach Mixed with stomach secretions becomes chyme Pyloric sphincter allows chyme into the small intestine Gastric inhibitory peptide (hormone) slows release of chyme into the small intestine to allow time for acid neutralization and digestion (only one teaspoon is allowed into the SI at a time).

STOMACH SECRETIONS Chief cells produce: Pepsinogen (an inactive protein-digesting enzyme) Other secretions include, Gastric lipase Gastrin Hormone stimulated when food is in stomach; controls release of HCl and pepsinogen and stimulates motility Mucus Protects the stomach from being digested

STOMACH SECRETIONS Parietal cells produce hydrochloric acid which: Inactivates proteins Destroys bacteria and viruses Aids in mineral absorption (dissolves them) Converts pepsinogen (protein digesting enzyme) into pepsin (active form)

SMALL INTESTINE Most digestion and absorption occurs here Sections: Duodenum, Jejunum Ileum

SMALL INTESTINE Villi (finger like projections on interior of SI) that are lined with: Goblet cells make mucus Endocrine cells produce hormones Cells (enterocytes) that produce enzymes for absorption

HORMONES OF THE SMALL INTESTINE Gastrin Also released by stomach, stimulates intestinal motility Cholecystokinin (CCK) Stimulated by dietary fat in chyme, stimulates release of pancreatic enzymes and bile Secretin Stimulated by acidic chyme, stimulates release of pancreatic bicarbonate Gastric Inhibitory peptide Stimulates stomach to limit gastric juices, slows motility

ACCESSORY ORGANS: LIVER, GALLBLADDER AND PANCREAS Liver Provides bile Needed to emulsify fat (disperse into droplets and suspend in water) so it can be absorbed Gallbladder Bile storage Pancreas Produces sodium bicarbonate, lipases, proteases and pancreatic amylase

ACCESSORY ORGANS: LIVER, GALLBLADDER AND PANCREAS

LARGE INTESTINE Functions: Absorption of water and electrolytes, house bacterial flora, and form and expel feces. Colon Cecum, ascending colon, transverse colon, descending colon and sigmoid colon Rectum Anus

LARGE INTESTINE

ABSORPTION

Passive (fat, water, some minerals) High concentration to low Facilitated (ex. fructose) High concentration to low + carrier protein Active (amino acids, glucose) Low concentration to higher + energy Endocytosis (large proteins like immune factors) Engulfment

ABSORPTION

MOVING NUTRIENTS Cardiovascular System Includes heart, blood vessels and blood Water-soluble nutrients transported via capillaries in villi to portal vein, which leads to liver Allows liver to process nutrients before entering general circulation Lymphatic System Includes lymph Fat-soluble nutrients and large particles transported via lacteals into the lymph vessels to thoracic duct, where it connects to the blood stream.

BACTERIAL FLORA Beneficial bacterial flora Controls pathogenic bacteria Synthesize Vitamin K and Biotin Aid lactose digestion and fermentation Pro-biotic Live bacteria Pre-biotic Non digestible carbohydrates that promote the growth of beneficial bacteria

PUTTING IT ALL TOGETHER Be able to trace the pathway of food from when you first eat it until it is eliminated or absorbed Know the major function of each organ and if it secretes any major enzymes or hormones

DIGESTION GONE AWRY Heartburn and Gastroesphogeal reflux (GERD) Causes Overweight, alcohol, smoking, pregnancy Foods that increase reflux Citrus, caffeine, chocolate, fatty foods, spicy foods, onion, garlic and tomato based foods Medications include H2 blockers (blocks histamine formation) and proton pump inhibitors

DIGESTION GONE AWRY Heartburn and Gastroesphogeal reflux (GERD)

DIGESTION GONE AWRY Ulcers Causes: H pylori, alcohol, aspirin and smoking (not stress) Treatment: Medications (abx, same as GERD) Avoid foods that increase symptoms

DIGESTION GONE AWRY Gallstones Food Intolerances Lactose, gluten, MSG Intestinal Gas Flatulence Air and undigested CHO in large intestine

DIGESTION GONE AWRY

Constipation Fiber, fluid and exercise Laxative use (bulk, osmotic, stimulants, softeners, and lubricants) Diarrhea Replace fluid and electrolytes Irritable bowel Cause unknown, examine dietary factors Hemorrhoids