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The Digestive System Features of the Generalized Vertebrate Gut Oral Cavity - Origin 1. Origin Heterostomes - most of the invertebrate phyla Mouth originates from the blastopore 2. Deuterostomes - not formed early, but breaks through later in development; anus originates from the blastopore Teeth 1. Origin - dermal denticles 2. Structure Enamel - hardest substance in the body, Enamel Dentin occurs above the gum line Pulp • Cementum - continuation of enamel below the gum line Cementum • Dentin-matrix Blood vessels• Pulp-living portion of tooth • and nerves Glands of the mouth Salivary glands secrete saliva mucin - lubricant salivary amylase converts starch to glucose Esophagus 1. Length-short in fish, longer in tetrapods to bypass lungs 2. Muscles Upper end- striated Lower 2/3 - smooth 3. Modifications of the esophagus - crop in birds for storing food Stomach 1. Occurrence Present in invertebrates with complete digestive tract Absent in most lower chordates, even fish 2. Regions Functions of the stomach Little absorbtion by stomach water and alcohol secretes HCl - very acid pH mucin - lubricant pepsin - digests proteins to shorter peptides gastrin - hormone which regulates HCl secretion Specialized stomachs Muscular gizzard of ground birds 4 chambers of grazing mammals ruminants rumen is specialized for storing food to be chewed later Small Intestine Primary site of digestion Digested food absorbed here absorbtion Enzymes peptidases - peptides to amino acids lactase - lactose (milk sugar) to simple sugars maltase - maltose to glucose sucrase - sucrose to simple sugars Absorbtion in the Small Intestine Pancreas - enzymes for digestion lipase - fats to triglycerides trypsin - proteins to shorter peptides nucleases - DNA & RNA secretin - hormone which stimulates buffering of HCl Caecum large sac at junction of small and large intestines contains symbiotic bacteria that digest cellulose our appendix is a rudimentary caecum Colon no digestion reabsorbs H20 and ions contains bacteria that synthesize Vitamin K Fermentation of gases by bacteria Liver A. Development - outpocket of the gut - tube that remains is the common bile duct B. Digestive function - produces bile that emulsifies fats Bile is stored in the gall bladder for secretion into the small intestine Other function of the liver C. Other functions stores glycogen stores fats - cholesterol filters and stores toxic materials destroys red blood cells Circulation and the Liver Pancreas A. Origin - outpocket of the gut B. Functions 1. Exocrine - produces digestive enzymes 2. Endocrine - produces insulin that regulates blood glucose levels The fate of food NUTRITION Nutrient - specific substance that must be taken into the body in sufficient quantities to meet the body’s needs Essential Nutrient - required preformed; body cannot make it or cannot make enough to meet needs Nonessential nutrient - body can make IF raw materials are available Body needs BOTH to function Nutrient Classes Water (H2O) Carbohydrate (CHO) Protein (Pro) Lipid (Fat) Amount of energy?? calorie - energy needed to raise 1 gm of H2O 1 degree Centigrade Kilocalorie (kcal) - 1000 calories; energy needed to raise 1 liter of H2O 1 deg. C Direct Calorimetry - measuring the heat (energy) Indirect Calorimetry - measuring the CO2 & O2 and “deriving” the energy Energy from Nutrients Nutrient Class Calories/gram CHO 4 Pro 4 Fat 9 Alcohol 7 Phytochemicals (plant) Only few of 10,000’s studied associated with decrease CVD & cancer risk decrease infections increase immune function examples - flavonoids; carotenoids (> 600); isoflavones; plant sterols Best to get from food NOT supplements ** soy; tomatoes, garlic, onions, legumes, green tea; cruciferous vegetables, red wine, grapes I.e., EAT MORE AND WIDER VARIETY OF FRUITS & VEGETABLES Water & Micronutrients Functions Intake Sources Losses Dehydration Balance Maintaining Hydration Water Functions Regulates body temperature Environment for cells & chemical reactions Transport (blood) cools body temperature AND evens heat throughout body blood pressure fxn of volume of H2O secondary lubrication of joints takes part in chemical reactions Body Water (45 liters) INTERCELLULAR (12) BLOOD/LYMPH (3) intracellular intercellular blood/lymph INTRACELLULAR (30) Sources of Water Fluids Foods Metabolic H2O - Total 550 - 1500 ml 700 - 1000 ml 200 - 300 ml 1450 - 2800 ml Carbohydrates Introduction to CHO Terminology Simple/sugars Complex/Starch Digestion Metabolism Overview Carbohydrates.... First link in the food chain Photosynthesis - plants store some of sun’s energy (0.1%) in chemical bonds of CHO CO2 + H2O -----> CHO ALL PLANT foods have CHO Only significant animal sources of CHO are milk and some milk products Energy source for man - 8% Eskimos; >70% some non-industrialized countries CHO Functions Energy - all cells use Some cells (RBC, brain) can use only CHO until starvation sets in Needed for effective burning of fat Spares protein from use for energy Fiber, alternative forms of CHO, provides a number of benefits CHO Terminology Saccharide = building block Simple CHO = “sugars” Complex CHO = Starch or Amylose (1-3 saccharides) mono (1), di (2), tri (3) (many saccharides) - poly Complex CHO = Fiber Different bonding than starches Monosaccharides Glucose (Glu) - most abundant CHO; part of table sugar; “blood” sugar Fructose (Fru) - found in fruit & honey; part of table sugar Galactose (Gal) - part of milk sugar; generally not found free in nature Disaccharides Sucrose = Glu + Fru Maltose = Glu + Glu Table sugar product of amylase digestion; beer; sprouts Lactose = Glu + Gal Milk sugar Polysaccharides multiple glucose (usually) units bound together Starch/Amylose = many Glu Storage form of energy in plants Fiber - # different kinds; some are multiple Glu units but different chemical bonding from Amylose examples - cellulose; pectin Fiber (cont.) - often the structural CHO in plants ONLY FOUND IN PLANTS Glycogen = storage form of CHO in animals (many Glu units) very highly branched to aid release Major Hormones of Digestion Insulin - made in pancreas; lowers Glucagon - made in pancreas; raises Epinephrine (adrenaline) - made in blood glu; increases all energy stores blood glu; decreases adipose fat & liver glycogen stores adrenal glands; raises blood glu; decreases all energy stores CHO Health Issues Fiber Abnormal CHO Metabolism Lactose Intolerance Hypoglycemia Diabetes Mellitus Type 1 diabetes Results from the body's failure to produce insulin, the hormone that "unlocks" the cells of the body, allowing glucose to enter and fuel them. It is estimated that 5-10% of Americans who are diagnosed with diabetes have type 1 diabetes. Type 2 diabetes Results from insulin resistance (a condition in which the body fails to properly use insulin), combined with relative insulin deficiency. Most Americans who are diagnosed with diabetes have type 2 diabetes. Gestational diabetes Gestational diabetes affects about 4% of all pregnant women - about 135,000 cases in the United States each year. Pre-diabetes Pre-diabetes is a condition that occurs when a person's blood glucose levels are higher than normal but not high enough for a diagnosis of type 2 diabetes. There are 41 million Americans who have pre-diabetes, in addition to the 20.8 million with diabetes. Syndrome X – insulin resistance (the inability to properly deal with dietary carbohydrates and sugars), abnormal blood fats (such as elevated cholesterol and triglycerides), overweight, and high blood pressure. Sources of Sugar Processed 45% Beverages 29% Home Use 26% Beverages Home Use Processed Take 12 oz H2O add 10 tsp sugar drink ~ 160 empty calories, i.e., A soda Proteins Structure Digestion Absorption Roles in Body Tissue maintenance & Growth Regulation & Control Energy Distribution of Body Proteins Skin 10% Other 20% Muscle Bone Skin Other Bone 20% Muscle 50% Protein Structure Made up of carbon, oxygen, hydrogen & nitrogen (C, O, H, N) Amino acids (aa) are building blocks 9 essential 11 nonessential (can be made from other aa or carbon skelton (“glucose”) if N available AA differ by side chain (R group) Regulation & Control Functions Enzymes Hormones (some) Antibodies; immune system Transport Acid-base balance (buffers in blood) Fluid & electrolyte balance Protein Sources (US) Vegs 7% Grains 19% Meats Legumes Dairy Vegs Grains Dairy 21% Legumes 5% Meats 48% Protein in Foods “Food” M Meat M Dairy Vegetable Grain Legume Serving 3 oz 1cup or 1 oz 1/2 cup gm Pro 21 gm 8 gm 2 gm 1 sl or 1/2 cup 3 gm 1/2 cup 7-8 gm Lipids Classes Triglycerides (TG) Phospholipids (PL) Sterols Class Functions Terminology Digestion Transport - Lipoproteins Lipid Classes Triglycerides Phospholipids made of 3 fatty acids (fa) & 1 glycerol fa 4-22 Carbons long; mostly 16-20 95% of dietary lipids (fats & oils) 1 fa replaced by a phosphate group Sterols complex ringed structures; noncaloric ex. cholesterol & Vit D TG Functions Concentrated energy (diet and main storage form) Provides essential fatty acids (linoleic; linolenic) Carrier of Fat Soluble Vits (A,D,E,K) Body Insulation & padding around organs Cell membranes Adds flavor & texture to foods Contributes to satiety Phospholipid Functions Cell membranes Help transport other fats in blood Precursor for some neural transmitters Lecithin ----> Acetyl Choline emulsifier in foods Cholesterol Functions Cell membranes Precursor for Vit D & some hormones (estrogen, testosterone) Major component of bile ONLY FOUND IN ANIMALS; NEVER FOUND IN PLANTS not an essential nutrient since man makes Saturated Fats maximum # of Hydrogen atoms usually solid at room temp. mostly from animal sources Exceptions - tropical oils (palm, coconut) are very saturated raise blood cholesterol Unsaturated Fats fewer H atoms; double bonds b/t Carbons usually liquid at room temp. mostly plant and fish sources more chemically active (turn rancid faster) lower blood cholesterol Monounsaturated fat acid (MUFA) - 1 double bond (minus 2 H) Polyunsaturated fat acid (PUFA) - 2 or more double bonds Dietary fats (TG) really mix of saturated and unsaturated fats Classified by predominate type Fatty acids can differ by 1) degree of saturation or 2) length (# carbons) BUT NOT by calories (all 9 kcals/g) Essential Fatty Acids Linoleic (Omega 6/n-6) - found mostly in plant oils Linolenic – (n-3) found mostly in cold-water fish and some plant oils (canola oil, nuts, seeds) Deficiency leads to poor growth, liver problems, dermatitis O-6 to O-3 ratio MUCH higher than in Hunter Gatherers - inc risk # diseases or adverse outcomes (CVD, pregnancy, learning, bone health) Lipoproteins Transport lipids mixture of protein and lipids packaged so water soluble cpds on outside and insoluble cpds on inside Pro & phospholipids are water soluble like homogenized milk LP have different forms, functions, & effects on CVD risk Low Density LP (LDL) remnant of VLDL after most TG removed very HIGH in Cholesterol not always effectively cleared by liver so other tissues remove including artery walls major component of total blood cholesterol esp when cholesterol has been modified risk of “high blood cholesterol” is from LDL, i.e., increases risk of CVD High Density LP (HDL) made by liver & intestine & then altered in blood carries cholesterol from tissues (including arteries) & other LP to Liver Reduces risk of CVD Ratio of LDL/HDL may be better predictor of CVD risk than any single LP or total blood cholesterol level Levels of LP & CVD Risk HDL > 60mg/dl = Low risk HDL < 35 mg/dl = High risk LDL/HDL ratio < 4 = Low risk men’s HDL run from high 30’s to high 40’s women’s from low 50’s to low 60’s (estrogen effect) Sources of Fat Grains 10% Sweets/Frt 10% Vegetables 6% Dairy 18% Meats 22% Fats/oils 34% Meats Fats/oils Dairy Grains Sweets/Frt Vegetables ~50% fat from animal sources ~ 75% Saturated fat from animal sources 6 foods foods provide 1/2 sat. fat cheese; beef (esp ground), milk, baked goods, margarine, butter Trend towards less animal & more plant fat lower % of fat 42% (60’s) -> 36% (80’s) -> 34% now BUT > amount of fat Excretory System Among vertebrates the #1 Apparatus in the Excretory System is the KIDNEY Filters 2000L of blood/day 3 Functions Filtration – Blood Filter Reabsorption – Selective – take back the good stuff – leave the waste Secretion and Excretion– secretion of foreign molecules and waste across membranes of capillaries and kidney tubules – opposite of reabsorption Excretion of waste - Urine Basic Structure of Kidney Units The Mammalian Kidney Route of waste In the nephron tubule, filtration occurs from glomeruli into Bowman's capsule The filtrate passes from Bowman's capsule through the PCT (proximal convoluted tubule), the loop of the nephron (loop of Henle), the DCT (distal convoluted tubule), before reaching a collecting duct. Now, just dumping out the filtrate would be a waste (literally) and would not address issues of osmoregulation. Functional Unit of Kidney Nephron Glomerulus Bowman’s capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct 2 types – Juxtamedullary and cortical Nephron - Filtration •Filter is non-selective except for size ( <70,000 MW; 7 nm in diameter). •Blood cells and proteins do not pass through the filter. •Fluid in Bowman's capsule much like plasma without the proteins. Large amounts of water are necessary for filtration. Most of this water is reabsorbed back into the circulation through the tubules - proximal & distal conv. tubules and Henle’s loop. Reabsorption Need to reabsorb stuff (H20, ions, nutrients) or animal literally urinate itself to death 180L of water leave the blood in filtrate Water, selected ions, glucose, and other items must be reabsorbed This reabsorption most typically involves the use of energy to reclaim sodium (and other items tagging along with it)