The Digestive System and Body Metabolism Overview Of Digestion Chapter 14 The Digestive System and Body Metabolism http://discovermagazine.com/2009/dec/20-things-you-didn.t-know-about-digestion 20 Cool Things You Don’t Know About the Digestive System

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Digestive System Takes in food, breaks it down into nutrient molecules and absorbs them into the bloodstream, then rids the body of indigestible remains

Anatomy of Digestive System Alimentary canal – digests food and absorbs digested fragments through its lining into the blood GI, tract - continuous hollow tube: mouth, pharynx, esophagus, stomach, small and large intestine Accessory digestive organs - assist: teeth, tongue, glands

Mouth (Oral Cavity) Food enters Mucus membrane-lined cavity lips, cheeks, hard palate (anterior roof), soft palate (posterior roof) uvula - fingerlike projection of soft palate

Mouth Tongue - attached to hyoid bone and styloid processes of skull papillae containing taste buds on surface Frenulum - secures tongue and limits its posterior movements As food enters, it is mixed w/ saliva by tongue and chewed and swallowed Taste

Salivary Glands - 3 pair Parotid glands - anterior to ears mumps is inflammation of parotid glands Submandibular and sublingual glands - empty secretions into mouth through ducts

Saliva Product of salivary glands, mixture of mucus and serous fluids mucus moistens and binds food together into a mass (bolus) serous part contains salivary amylase (enzyme for starch digestion) Polls Everywhere

Teeth Masticate (chew) Deciduous (baby or milk) teeth - first set; formed from 6 months to 2 years Permanent teeth - cause baby teeth to fall out b/t 6 and 12 32 permanent teeth 3rd molars (wisdom teeth) form b/t 17 and 25; sometimes absent or impacted in jawbone and must be surgically removed

Teeth by shape/function Incisors - chisel-shaped, cutting Canines - fanglike, tearing/piercing Premolars (bicuspids) Molars - broad crowns w/ rounded tips, grinding

Pharynx Nasopharynx (respiratory), oropharynx (potesterior to oral cavity), and laryngopharynx (continuous w/ esophagus) Peristalsis: Alternating contraction of muscles propel food into esophagus Peristalsis

Esophagus Conducts food from pharynx through diaphragm to stomach 25 cm long

Walls of Alimentary Canal Mucosa - innermost layer; moist membrane Submucosa - blood vessels, nerve endings, lymph Muscularis externa - inner circular, outer longitudinal smooth muscle Serosa - outermost layer

Stomach C-shaped, left side, nearly hidden by liver and diaphragm Peristalsis C-shaped, left side, nearly hidden by liver and diaphragm cardioesophageal sphincter - food enters from esophagus fundus - expanded part body – midportion 3rd oblique layer in muscularis externa to move, churn, mix, and pummel food chemically breakdown proteins

Stomach Pylorus - funnel-shaped, terminal Pyloric sphincter - goes to small intestine 25 cm long when full, holds 4 liters of food empty - collapses into folds (rugae) Rugae on Dog Stomach

Stomach Mucosa has gastric pits which lead into gastric glands that secrete gastric juice chief cells - produce protein-digesting enzymes (pepsionogen) parietal cells - produce HCl Chyme is produced

Stomach - Food Breakdown Secretion of gastric juice by sight, smell, and taste of food presence of food and falling pH stimulate release of hormone gastrin that makes stomach produce enzymes, mucus, & HCl 2-3 liters gastric juice per day

Stomach: Food Propulsion Peristalsis in lower half, and contractions squirt 3 ml of chyme into small intestine takes 4 hrs for stomach to empty Irritation (food poisoning) may activate vomiting

Small Intestine Major digestive organ Muscular tube extending from pyloric sphincter to ileocecal valve average length: 2 m (6 feet) Hangs from coils suspended by mesentery Large intestine encircles and frames it

Small Intestine - 3 subdivisions Duodenum - curves around head of pancreas Jejunum - extends from duodenum to ileum ileum - terminal part that joins large intestine at ileocecal valve

Small Intestine Chemical digestion begins Small amount of food processed at a time - controlled by pyloric sphincter Pancreatic enzymes from pancreatic duct and bile from bile duct enter duodenum

Small Intestine - 3 structures that increase absorption Microvilli - tiny projections that give fuzzy look (brush border) Villi - fingerlike projections that give velvety appearance Circular folds - deep folds of both mucosa and submucosa

Small Intestine: Food Breakdown and Absorption Takes 3-6 hours By end, digestion is complete and most absorption has occurred Microvilli have brush border enzymes to break down sugars and complete protein digestion

Food Breakdown and Absorption Pancreatic juice digests starch, proteins, fats, and nucleic acids; contains bicarbonate to neutralize chyme When chyme enters, it stimulates hormones secretin and cholecystokinin to release bile

Food Breakdown and Absorption Bile is necessary for absorption of fats and fat-soluble vitamins K,D,A At end, all that remains is water, indigestible food and bacteria which enters large intestine Food propulsion - peristalsis

Large Intestine Larger in diameter, shorter in length (1.5 m) Extends from ileocecal valve to anus Dries out indigestible food by absorbing water, eliminates residue as feces

Large Intestine Subdivisions Cecum - saclike, first part Appendix - wormlike structure hanging from cecum; ideal bacteria location - appendicitis Colon - ascending, transverse, descending, and sigmoid Rectum Anal canal - ends in anus which opens to exterior; has external voluntary sphincter and internal involuntary sphincter

Large Intestine Lots of goblet cells to produce mucus to act as lubricant to ease passage of feces

Large Intestine: Food Breakdown and Absorption Residue is there 12-24 hours Bacteria metabolize nutrients and release gases (methane, hydrogen sulfide) 500 ml of gas produced each day

Food Breakdown and Absorption Absorption limited to vitamins, some ions, and most of remaining water Feces - solid product delivered to rectum; undigested food residue, mucus, bacteria, and some water

Large Intestine: Propulsion and Defecation Peristalsis and mass movements (long, slow-moving, powerful contractile waves that move over colon 3-4 times daily to push contents toward rectum) occur after eating; fiber increases strength of contraction

Propulsion and Defecation When feces in rectum, defecation reflex causes rectum to contract and anal sphincters to relax Diarrhea - food rushes through before water is absorbed, can result in dehydration and electrolyte imbalance How fast food Travels thorough.

Propulsion and Defecation Constipation - food residue remains too long and too much water is absorbed; due to lack of fiber, poor bowel habits, or laxative abuse A constipated body

Other Accessory Digestive Organs – Pancreas Soft, pink, triangular gland extending from spleen to duodenum produces enzymes that break down food and neutralize acidic chyme from stomach, produces hormones insulin, glucagon

Liver Liver - largest gland in body; under diaphragm on right 4 lobes produces bile which leaves liver through common hepatic duct

Gallbladder Small, thin-walled green sac in the inferior surface of liver When digestion is not occurring, bile is stored and concentrated by removal of water bile stored too long, it crystallizes forming gallstones Yellow-green, watery solution of bile salts, bile pigments (bilirubin), cholesterol, phospholipids, and electrolytes bile salts emulsify fats to provide more surface area

Disease: Jaundice Bile pigments enter bloodstream Can result from hepatitis (inflammation of liver from viral infection of contaminated water or blood transfusion) or cirrhosis (severe damage from drinking excess alcoholic beverages)

Nutrition and Metabolism Most foods used as metabolic fuels (transformed into ATP); some nutrients build cellular molecules Energy value measured in kilocalories (kcal) or Calories (C)

Nutrition Nutrient - substance in food used to promote normal growth, maintenance and repair Carbohydrates, lipids, proteins - bulk of food; vitamins, and minerals in minute amounts

. Water - 60% of volume of food Most foods are combination of nutrients from 5 food groups (grains, fruits, vegetables, meats, and milk products)

Obesity Rates in the US.

Dietary Sources of Major Nutrients - Carbohydrates From plants except lactose and glycogen in meats sugar - fruit, sugar cane, milk starch - grains, legumes, root vegetables cellulose - most vegetables

Lipids Neutral fats: saturated in animal products, unsaturated in seeds, nuts, vegetable oils Cholesterol - egg yolk, meats, and milk Phospholipids

Proteins Animal products, eggs, milk Amino acid polymers legumes, nuts, and cereals are low in one or more essential amino acids

Vitamins Organic nutrients, small amounts No one food contains all required vitamins, need balanced diet Most function as coenzymes: act w/ enzymes for task

Minerals Requires adequate supplies of 7: Ca, P, K, S, Na, Cl, and Mg; trace amounts of others Fats/sugars have none, cereals and grains poor sources In veggies, legumes, milk, meats

Metabolism All chemical reactions necessary to maintain life Catabolism - substances broken down, energy released and captured to make ATP Anabolism - larger molecules built from smaller ones

Metabolism Carbohydrates (glucose) - broken down to make ATP Fats - build cell membranes, myelin sheaths, insulate, ATP Proteins - structural materials hoarded by body cells

Carbohydrate Metabolism Carbs - preferred fuel to produce ATP from glucose (blood sugar): energy from bonds broken binds phosphate to ADP to make ATP Carbon atoms leave as CO2 and hydrogen combines w/ oxygen to make water

Carbohydrate Metabolism - Homeostasis of blood glucose Hyperglycemia - high levels; excess stored as glycogen and converted to fats Hypoglycemia - low levels; liver breaks down stored glycogen and releases glucose to blood

Fat Metabolism Liver - make ATP, synthesize lipoproteins, clotting protein and cholesterol for membranes or steroid hormones Form myelin sheaths and fatty cushions around organs Most concentrated form of enegy

Fat Metabolism To be used for ATP synthesis, it must be broken down into acetic acid; when not enough glucose, acetone accumulates in blood making it acidic (acidosis/ketosis) no carb diets, diabetes, and starvation

Protein Metabolism Proteins - bulk of cell structures; broken down into amino acids for enzymes, membranes Cells use ATP to actively transport amino acids (8 of the 20 are not made by cells - essential amino acids)

Protein Metabolism Amino acids make ATP when protein is in excess or no fats or carbs amine groups are removed as ammonia which is toxic so it combines w/ CO2 to form urea

Central Role of Liver Manufactures bile, detoxifies drugs and alcohol, degrades hormones, makes substances vital to body, metabolism We have more liver tissue than needed, so if damaged, it regenerates rapidly and easily

General Metabolic Functions Liver maintains blood glucose levels After high carb meal, glucose is removed from blood and converted to glycogen (glycogenesis) and stored in liver

General Metabolic Functions As body cells remove glucose from blood, liver breaks down stored glycogen (glycogenolysis) gluconeogenesis - make glucose from fat and protein

General Metabolic Functions Hormones insulin, thyroxin, and glucagon control blood sugar Fats are oxidized for energy, broken down into acetic acid or stored as fat reserves Makes cholesterol and secretes its breakdown products as bile

General Metabolic Function Albumin - most abundant protein; holds fluids in bloodstream insufficient albumin causes fluid to go from blood to tissues (edema) Synthesize amino acids and detoxify ammonia

Cholesterol Metabolism and Transport Cholesterol - structural base for steroid hormones and vitamin D; major building block of plasma membranes 15% from diet, 85% made by liver Broken down and secreted in bile salts, which leave as feces

Cholesterol Metabolism Insoluble in water, so transported bound to lipid-protein complexes - lipoproteins Low-density lipoproteins (LDLs) - transport cholesterol/lipids to body cells; if too much deposited on arteries - “bad lipoproteins”

Cholesterol Metabolism High-density lipoproteins (HDLs) - transport cholesterol from tissue cells to liver for disposal in bile; high levels are good Both types necessary; ratio determines whether cholesterol will go to arterial walls

Body Energy Balance When fuel is burned, it consumes O2 and generates heat Energy intake = total energy output (heat + work + energy storage)

Body Energy Balance Energy intake - liberated during food oxidation Energy output - lost as heat (60%) + used to do work (driven by ATP) + stored as fat or glycogen

Regulation of Food Intake When energy intake and energy outflow are balanced, body weight is stable Food intake controlled by rising or falling blood levels of nutrients, hormones, body temp. and psychological factors

Basal Metabolic Rate Carbs & proteins yield 4 kcal/g, fats yield 9 kcal/g Basal metabolic rate (BMR) - amount of heat produced by body per unit time at rest; energy supply for breathing, heartbeat, and kidney function

Basal Metabolic Rate Avg. adult has BMR of 60-72 kcal/hr; influenced by surface area, gender, age, and thyroxin production (more thyroxin produced by thyroid gland, higher O2 consumption and ATP use and metabolic rate)

Basal Metabolic Rate Hyperthyroidism - excessive rate, lose weight despite increased hunger and food intake, bones and muscles weaken Hypothyroidism - slow rate, obesity, diminished thought process

Total Metabolic Rate When active, more glucose must be oxidized to provide more energy for activities Total Metabolic Rate (TMR) - total amount of kcal body must consume to fuel all activities

Total Metabolic Rate When total calories = TMR, weight is constant If eat more, excess calories appear as fat deposits If active w/o enough food, break down fat reserves and even tissues to satisfy TMR

Body Temp Regulation Heat warms tissues and blood keeping them at homeostatic temps Reflects balance b/t heat production and heat loss, controlled by hypothalamus, regulated b/t 96-100ºF

Heat-Promoting Mechanisms When cold, heat is conserved by vasoconstriction of blood vessels and shivering makes blood route to vital body organs causing temp of skin to drop if extended, skin cells w/o O2 die leading to frostbite

Heat-Promoting Mechanisms Hypothermia - extremely low body temp from prolonged exposure to cold; vital signs decrease, person becomes drowsy and can progress to coma and death as metabolic rate stops

Heat Loss Mechanisms Most loss occurs through skin by radiation (when body temp increases, blood vessels dilate and heat radiates off surface) or evaporation (too hot - perspiration off skin’s surface; effective unless humid)

Heat Loss Mechanisms Hyperthermia (elevated body temp) depresses hypothalamus and positive-feedback cycle occurs: soaring body temp increases metabolic rate, which increases heat production

Heat Loss Mechanisms Heat stroke - skin hot and dry - fatal unless immersed in cool water and given fluids Heat exhaustion - collapse during vigorous activity due to excessive loss of fluids (dehydration), causing low blood pressure, fast heart rate and cool, clammy skin

Heat Loss Mechanisms Fever - controlled hyperthermia - results from infection, cancer, or allergies; pyrogens are released to hypothalamus that set thermostat at higher level chills - reset lower - sweat too high - protein denatures

Developmental Aspects 5th week - alimentary canal forms cleft palate/lip - child unable to suck properly tracheoesophageal fistula - connection b/t esophagus and trachea - causes drool, cyanosis during feedings

Development Aspect Cystic fibrosis - blockage of pancreatic ducts so that fats and fat-soluble vitamins are not digested or absorbed PKU - inability of tissue cells to use phenylalanine (amino acid) causes brain damage

Developmental Aspects Newborn: rooting & sucking reflex Appetite decreases in elementary age and increases in adolescence Gastroenteritis - inflammation of GI tract due to contaminated food Appendicitis - common in teens

Developmental Aspects Middle age - metabolic rate decreases 5-8% every 10 yrs ulcers & gallbladder problems Old age - activity of GI tract declines, taste and smell decrease cancer of stomach and colon