Fundamentals of Human Nutrition PDF

b. Fundamentals of Human Nutrititon Topics (Study Guide): b. Fundamentals of Human Nutrition i. Energy & Nutrients: energy, macronutrients, micronutrients, alcohol, fluids and electrolytes, acid-base balance Human Nutrition: intake, digestion, absorption, metabolism, elimination Food and Nut F L. En...

b. Fundamentals of Human Nutrititon Topics (Study Guide): b. Fundamentals of Human Nutrition i. Energy & Nutrients: energy, macronutrients, micronutrients, alcohol, fluids and electrolytes, acid-base balance Human Nutrition: intake, digestion, absorption, metabolism, elimination Food and Nut F L. Energy & Nutrients Energy Brain uses glucose exclusively as energy source, uses ketone bodies during starvation Storage: Glycogen → muscles and liver Fat → adipose tissue Protein → cellular mass Gluconeogenesis: conversion of non-carbohydrate sources into glucose, from glycerol and amino acids Homeostasis: state of equilibrium of the internal environment of the body Cellular processes: involve various factors and mechanisms Enzymes → organic catalysts that control reactions (proteins) Coenzyme → enzyme activators, include some vitamins Pantothenic acid, thiamin, riboflavin, niacin (needed for E production)Substrate → substance upon which enzyme works Cofactor → assists enzymes (minerals) Hormones → chemical messengers that trigger enzymes Secreted by endocrine glands Thyroxine: regulates metabolism and rate of oxidation Influences physical and mental growth Energy reactions Stimulates liver glycogenolysis, gluconeogenesis, raises BG Anabolism: synthesis of a more complex substance Catabolism; breakdown, uses and releases energy creating a constant energy deficit which must be supplied by food Measures of Energy Total Energy Expenditure (TEE) Basal Energy Expenditure (BEE) : minimum amount of energy needed at rest when fasting Amount needed to carry out involuntary work of the body, activity of internal organs, inter temperature maintenance Affected by extremes in environmental temperatures Tropical climate → 5-20% increase Caeine, alcohol, nicotine stimulate metabolic rate → 7-15% increase Energy Expended in PA (EEPA): highly variable Based on activity thermogenesis (AT) Thermic Effect of Food (TEF) / Diet-Induced Thermogenesis (DIT): calorigenic effect of food → about 10% of total energy expenditure Energy needed to digest, absorb and assimilate nutrients Greater after consumption of carbohydrate and protein vs fat Basal Metabolic Rate (BMR) Measures oxygen consumed and CO2 produced Measured in morning when reclining, awake, relaxed, at normal body temp, at least 12hr after last meal and several hours after strenuous activity Affected primarily by: Sex → women have 5-10% lower BMR Age → highest at 0-2 yrs of age, decrease with age (less activity, less LBM, more body fat) Body composition and SA Endocrine glands → thyroid Protein bound iodine (PBI)→ measures BMR Measures activity of thyroid gland High BPI = high BMR Hormones → thyroxine (T4), triiodothyronine (T3) Measures energy metabolism, level of thyroxine produced Not a nutritional assessment parameter Increases with: Periods of growth, exercise Pregnancy, lactation Fever → 7% increase for each degree rise in temp Diseases that increase cell activity Basal Eneray Expenditure (BEE) → calculated by BMR Includes age, sex, body surface area (ht, wt) Resting Metabolic Rate (RMR) Energy expenditure measured under similar conditions After short rest and controlled intake of caffeine/alcohol Used more frequently than BMR, 10-20% higher than BMR Equations Mifflin St-Jeor (MSJ) → predicts within 10% of indirect calorimetry Use with normal weight and obese individuals Weight Control Use ABW for underweight, overweight, and obese Following changes in weight and trends is the most practical way of measuring energy balance Calorimetry Direct calorimetry: measures heat produced in respiration chamber Indirect calorimetry: measures oxygen consumed and CO2 excreted using a portable machine Measures which nutrients are being used for energy and caloric needs Useful in athletes, burn patients Respiratory quotients (RQ)= VCO2/ VO2 CO2 expired vs O2 consumed Depends on the fuel mixture being metabolized: CHO→1 Protein →0.82 Fat →0.7 Mixed → 0.85 Macronutrients Carbohydrates→ 4kcal/ g Carbohydrate Structure (CHO) Simple carbs: short chain sugars (mono, disaccharides).Monosaccharides → glucose, galactose, fructose Disaccharides → maltose, lactose, sucrose Hydrolysis (breaks bonds), condensation (forms bonds) Complex carbs: composed of monosaccharides in straight or branching chains Oligosaccharides → 3-10 units Polysaccharides → glycogen, starch, fibre Glycogen: highly branched chains of glucose Storage form of carbs in animals, chains allow easy breaking Stored in muscles (for muscle cells) and liver (for all cells)In body = 200-500g Carb loading / glycogen supercompensation → temporary increase in glycogen stores (for endurance) Starch: straight or branching chains of glucose → digestible Storage form of carbs in plants, accumulates in roots/grains 50% of CHO intake Amylose → long straight chains of glucose Amylopectin → branched chains of glucose Resistant starch: indigestible starch, due to structural grain protection or altered digestibility from cooking Legumes, unripe bananas, rice, pasta, cold potato Dextrin: intermediate product on starch breakdown Fiber: complex carbs (+ lignin) that cannot be digested Cellulose: resistant to digestive enzyme amylase, adds bulk Dietary fiber → found intact in plants Functional fiber → isolated from plant source Total fiber → sum of dietary + functional fibre Can bind to minerals and prevent absorption (Zn, Ca, Mg, Fe) Soluble fibre: absorbs water to form viscous mixture and can be broken down by intestinal microflora → Oats, apples, beans Pectin: non-digestible fiber found in fruits, thickening quality Draw water into intestine, slows Gl passage + absorption Can help regulate BG, reduces cholesterol by binding to it Broken down by bacteria into SCFAs → gas Insoluble fibre: does not dissolve in water and cannot be broken down by bacteria in LI → Wheat bran, rye bran, broccoli Stimulates GI motility by increasing volume / bulk E Food and Nut Carbohydrates in the Diet Sources: flour, cereals, fruits, vegetables, dairy products Unrefined carbohydrates: largely unprocessed sources of carbs Whole grain → entire kernel of grain (bran, germ, endosperm) 75% starch, partially complete protein, 2% fat (found in germ) Bran = protective outer layer, high in fiber and vitamins Germ = embryo of sprouting portion of the kernel, contains oils, protein, fiber and vitamins (E, B6, riboflavin, thiamin, phosphorus) Scutellum in germ → has most of thiamin Endosperm = largest part of kernel, starchy food supply for germ, protein Whole fruits, vegetables, milk etc Refined carbohydrates: processed sources of carbs resulting in nutrient losses - Milling results in removal of bran and germ Added sugars: sugars/syrups added to foods HFCS, sucrose (white sugar)→ empty calories Fortified / enriched grains: added thiamin, riboflavin, niacin, iron and folic acid - Do not add other nutrients lost (E, Mg, B6, etc)Function Energy source Protein-sparing action→ allows more protein to be used for tissue synthesis Regulation of fat metabolism → carbohydrate restriction leads to ketosis Protein → 4 kcal/g Protein Structure Made up of C, H, O, N(~6%), S (found in cysteine and methionine) Amino acids: (20) building blocks of protein - C+H+ amino group (NH2) + carboxyl group (COOH) + side chain Amino acid → dipeptide/tripeptide → polypeptide → protein (3D) Essential amino acids: cannot be made by body in sufficient amounts → get through diet 9 aas: threonine, valine, tryptophan, isoleucine, leucine, lysine, phenylalanine, methionine, histidine (TV TILL PMH) Tryptophan → precursor for serotonin and niacin Nonessential amino acids: can be made by body in sufficient amounts 11 aa: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine (GAGAG CAA PST) Transamination: transfer of amino group to form new aa Methionine converts to cysteine (M→ C) Phenylalanine converts to tyrosine (P→ T) Conditionally essential: essential in diet only under certain conditions or life stages Tyrosine can be made from phenylalanine → if not enough, cannot be made Premature infancy, metabolic abnormalities, physical stress etc 6 aa: arginine, cysteine, glutamine, glycine, proline, tyrosine Types of Protein Conditionally essential during catabolic stress → arginine, glutamine Complete: all essential amino acids in sufficient quantities and ratios to maintain body tissues and promote growth High biological value (HBV) If low protein in the diet, ensure mostly HBV Incomplete; deficient in one or more essential amino acids Classification: Simple → amino acids Conjugated → simple plus non-protein substance (lipoprotein)Derived → fragments from simple and conjugated (peptide)Sources → meat, poultry, fish, eggs, milk, legumes Diet requirements: 0.8 g/kg BW (10-15% total energy intake). Soybeans are low in methionine Soybean is equivalent in protein quality to animal protein Legumes are low in methionine, cysteine, tryptophan Gelatin is low in methionine and lysine, no tryptophan Protein Function Tissue synthesis → maintains growth Structure → skin, hair, muscle, tendons, ligaments - Collagen: most abundant body protein, contributes to structures Energy → inefficient source, N must be removed first (58% 0T PRO can be converted to glucose) Enzymes → in diet are denatured through cooking/digestion - Lactase remains functional in gut Transport → hemoglobin, lipoproteins etc Protection → skin, blood clotting, antibodies Muscle contractions → actin, myosin, heart muscles, GIT, arteries Hormones → peptide hormones (glucagon, insulin) Fluid balance → protein pumps, protein molecules in blood (hold fluid) Acid-base regulation → act as buffers Lipids → 9kcal/g Types of Lipids → made of c, H, o Triglycerides (simple): major form of lipid in food/body Consists of 3 fatty acids and a glycerol Fatty acids → straight hydrocarbon chains ending in carboxyl group (COOH) on one end and methyl group (CH3) on other end - Classified by number of C's in chain, number of double bonds, position of first double bond (counted from methyl end of FA) Short-chain FA → 4-7 carbons, liquid at cool temps Medium chain FA- 8-12 carbons, liquid at room temp, solid at cool (coconut oil) Long-chain FA→ 12+ carbons, solid at room temp (beef fat) Saturated FA: no carbon double bonds → found mostly in animals, solid at room temp Palmitic acid → 16C Stearic acid → 18C Plant sources: tropical oils (palm, coconut) Unsaturated FA: contains C double bond(s)→ more bonds = more liquid at room temp MUFAs → 1 double bond (oleic acid) PUFAs → more than 1 double bond (linoleic acid) Omega 3: double bond between 3rd and 4th C ALA→ alpha linolenic (in veg oil) Retinal function and brain development Deficiency → neuro changes (numb, blurred vision) Decreases hepatic production of TGs (inhibits VLDL synthesis) Little effect on total cholesterol levels EPA → eicosapentaenoic acid (fish oils) DHA → docosahexaenoic acid (fish ois, walnuts, flaxseed, canola) both can be made from alpha linolenic acid Omega 6: double bond between 6th and 7th C -Linoleic acid (corn, safflower) Lack leads to eczema, poor growth rate, petechiae (red, purple skin spots) If linolenic replaces CHO → LDL lowers, HDL rises If linolenic replaces sat fat → total chol lowers, HDL lowers Arachidonic acid (meat, fish)→ synthesized from linoleic Omega ratio important for bp regulation, clotting, immunity Hydrogenation: H atoms added to double bonds, making them more saturated and stable (reduction process) Trans fatty acids: unsaturated FA with H atoms on opposite sides of double bond Higher melting point than cis Cis fatty acids: H on same side as double bond, most natural fats and oils Phospholipids (compound): phosphorus containing lipids, found in cell membranes Control passage of compounds in and out of the cell Most are lecithins which contain choline (lipotropic factor) Helps prevent fat accumulation in liver Functons in the transport and utilization of FAs and cholesterol through the enzyme LCAT (lecithin-cholesterol acyltransferase) Phosphoglycerides: glycerol + 2 fatty acids + phosphate group (most common) Results in water soluble and fat soluble ends Emulsifiers: allow water and fat to mix Lipid bilayer: form due to solubility differences Sterols: lipid with structure made of multiple rings, do not dissolve well in water Cholesterol: sterol found in animals → made by the liver Necessary for the body → cell membranes, nerve cell myelin Needed to synthesize → vit D from skin, cholic acid (bile), hormones (sex). cortisol (glucose syn in liver) - Plant sterols: reduce cholesterol levels by decreasing cholesterol absorption in diet Derived: fat substance derived from a simple or compound fat by hydrolysis or enzymatic breakdown (e.g. FA, glycerol, steroid) Winterized oils: will not crystallize when cold, remain clear (not cloudy) Corn, soy, cottonseed oils are winterized; used for salad dressings Sources & Function In order of predominance Saturated →coconut oil, palm kernel, cocoa butter, butter, palm oil, canola - MCT are SFAs between 6-12 carbons Naturally found in milk fat, coconut oil, palm kernel oil Monounsaturated → olive, canola, peanut, sunflower, coconut Polyunsaturated → safflower, corn, soybean, cottonseed, palm kernel Butter → SAT, MUFA, PUFA Margarine →PUFA, MUFA, SAT Food sources: butter, oils, nuts, bacon Most heart healthy lipids → 0g trans fat, not partially hydrogenated, are liquid plant oils Diet requirements → less than 30% of kcals Function: Energy, insulation, padding, depresses gastric secretions and delays emptying Has less O2 and more CO2 than carbs thus provides more energy - More carbons for oxidation Lipid Regulation Essential FAs: cannot be made by body or in sufficient quantities Must be consumed in diet to meet needs Omega 3 (alpha linolenic acid) → inefficient conversion to EPA/DHA (must eat) -Walnuts, flaxseed, leafy greens, canola oil Omega 6 (linoleic acid) → growth, skin, fertility, RBC structure (plentiful in diet)Eicosanoids: regulatory molecules made from omega fatty acids Omega 6: Omega 3 = 5:1-10:1 From omega 6 →→ increases blood clotting, promote inflammation From omega 3→ decreases blood clotting, anti inflammatory Help CV health, autoimmune disease (rheumatoid arthritis, IBD, MS) Micronutrients Vitamins Vitamins: organic compounds essential in the diet in small amounts Water soluble vitamins: B vitamins + vitamin C B1 (thiamine), B2 (riboflavin), B3 (niacin), biotin, pantothenic acid, vitamin B6, folate, vitamin B12 Fat soluble vitamins: vitamin A, D, E, K Supplementation - appropriate for: Dieters → calorie-restricted diets, avoid deficiency Vegans / no-dairy → B12, also vitamin D and Ca Infants / children → fluoride, vit D, Fe sometimes recommended Young women / pregnant → 400 ug folic acid; Fe + folic acid Older adults → B12 (atrophic gastritis), vit D Dark skin / covered → vit D Restricted diets / malabsorption → bariatric surgery, CF, etc Medications → can interfere Smokers / alcohol → higher vit C; B vitamins Bioavailability: how well nutrients can be absorbed and used by the body 40-90% of vitamins in foods are absorbed, primarily in SI Fat soluble vitamins → require fat in diet for absorption Water soluble vitamins → may require active transport or specific molecules Active transport → thiamin, vit C Carrier proteins → riboflavin, niacin Binding molecule → B12 (intrinsic factor) Provitamin: inactive form of vitamin that must be converted to active form Excretion → water soluble vitamins easily excreted in urine (except B12) Rapidly depleted, must be consumed regularly Function: promote and regulate body activities B vitamins → coenzymes used in metabolism B6, folate, B12→ carbon metabolism (support fetal development, RBC formation, nerve tissue health Vitamin C + E → vit C = coenzyme; works with vit E to protect from oxidative damage Anemia-related = B6, B12, F, K, E, Cu, Fe Minerals Mineral: inorganic elements needed in small amounts for structure and regulation of body processes Maior minerals: need >100 mg/d or present in >0.01% of body wt Electrolytes (Na, K, CI), Ca, P, Mg, Sulfur Trace elements/minerals: need carbs Small Intestine (SI) Food is forced into SI through pyloric sphincter of stomach - Complete digestion of food takes place in SI (duodenum, jejunum, ileum)Structure: narrow tube 6m, 3-5 hour transit time. Duodenum: first 30cm (receives bile from gallbladder) Jejunum: next 2.4m Ileum: last 3.3m Villi: line the SI and aid in digestion and absorption Microvilli:(brush border) projection on mucosa cell membrane that increase absorptive surface area of Sl Lacteal: tubular-like lymph vessels in intestine that transport large particles (fat)Segmentation: rhythmic constrictions of SI that mix food with juices and speed absorption by repeatedly moving food mass over intestinal walls Secretions: SI cells → some secretions (enzymes, intestinal juice) Hepatic duct from liver and cystic duct from gallbladder join together to release substances into the SI Liver: hepatic duct Produces bile that is stored in gallbladder Stores glycogen and synthesizes glucose Gallbladder: cystic duct Stores bile produced by liver and secretes it to aid in fat digestion Secretin stimulates liver to secrete bile into gallbladder Bile → emulsifies fat, breaks it into small droplets, allows lipase to work more efficiently Also helps form small droplets of digested fat which can then be absorbed more easily Pancreas: CCK→ stimulates contraction to release bile into duodenum Lies between duodenum and stomach Pancreatic juice → bicarb ions (neutralize acid) and digestive enzymes Secretin stimulate bicarbs, CCK stimulates enzymes Pancreatic amylase: starch → dextrin → maltose Lipase: TGs → FFA + glycerol Cholesterol enterase: cholesterol → cholesterol esters Phospholipase: phospholipids →lysolecithin + FFA Trypsin: protein + proteose + peptone → polypeptides Chymotrypsin: proteose + peptone → poly and dipeptides Intestinal: Carboxypeptidase: polypeptide → dipeptides + aas Sucrase: sucrose → glucose + fructose Maltase maltose → glucose + glucose Lactase: lactose → glucose + galactose Aminopeptidase: polypeptide → peptide + aas. Nutrient Absorption Dipeptidase: dipeptides → aas Simple diffusion → vit E, FAs Osmosis → water Facilitated diffusion → fructose Large Intestine (LI) Active transport → glucose (use energy to move to area of high concentration) Undigested food and water pass through ileocecal valve into LI (colon) Colon → largest portion of LI Water + some vitamin and mineral absorption Peristalsis slower than in SI, may spend 24 hrs Favors growth of bacteria Intestinal microflora: microorganisms that inhabit LI Act on unabsorbed foods to produce nutrients that bacteria or the body can use E.g. fiber Microflora synthesizes small amounts of FAs, some B vitamins, vitamin K Produce gas as a byproduct (200-2,000L of gas daily) Unabsorbed materials are excreted as waste in feces through anus Rectum→ connects colon to anus Hold feces prior to defecation → voluntary sphincter Absorption & Metabolism Mechanisms of Absorption Active transport: requires energy to move molecules against gradient Used for most nutrients → glucose, aas, Na, K, Mg, Ca, Fe Sodium pump → pumps from lower to higher concentration across membrane Simple diffusion: moves from-higher to lower concentration Used for water and electrolytes E.g. intestine to blood to lymph Passive diffusion: moves from higher to lower concentration facilitated by a carrier Carbohydrates Used for water-soluble nutrients Glucose Simple sugars converted to glucose + glycogen in small intestine Glucose sources → dietary glucose, liver glycogen, intermediary products of CHO metabolism (i.e. reconversion of lactic acid and pyruvic acid) CHO=100% Protein = 58% → via gluconeogenesis Synthesis of glucose from simple non-carb molecules (amino acids) Glucogenic aas yield glucose after deamination Uccurs in liver and kidney Alanine is most glucogenic aa (alanine-glucose cycle) Helps meet energy needs when carbs are low (carbs = protein sparing) Catabolized to pyruvate or to krebs cycle intermediates Fat = 10% → glycerol can be converted to glucose FAs and muscle glycogen do not contribute to body's supply of glucose Liver glycogen releases glucose to blood to maintain normal BG levels in a process that requires glucose-6-phosphatase → muscle cells do not have this enzyme thus glycogen in muscle is only used by that muscle Glucose uses → mainly for energy Storage → glycogenesis (in muscle and liver), lipogenesis Small amount converted into other CHO compounds - Ribose→ needed to form RNA and DNA Hormones → control blood glucose levels Insulin → lowers BG Increases cell permeability to glucose; fosters glycogenesis, lipogenesis Made by beta cells in pancreas Glucagon → increases BG Induces glycogenolysis (glycogen → glucose) Made by alpha cells in pancreas - Glucocorticoids → increases BG - Induces gluconeogenesis (protein → glucose)Epinephrine → increases BG Stimulates sympathetic nervous system (adrenal medulla) Stimulates liver and muscle glycogenolysis (glycogen → glucose) Decreases release of insulin from pancreas during catabolic stress Growth hormone + adrenocorticotropic hormone (ACTH)→ insulin antagonists Glucose Energy Metabolism Glucose in cell is oxidized to produce energy + CO2 and H20 (end products) Glycolysis → goal is to break down glucose to produce pyruvate to feed into Krebs cycle Aerobic glycolysis: end product is pyruvate Anaerobic alycolysis: end product is lactic acid 1. Glucose → glucose-6-phosphate a. Glucose enters cells (insulin) and combines with P in presence of Mg 2. G6P → pyruvic acid a. G6P can also go through pentose shunt (side channeling of glucose) i. Does not require ATP ii. Produces ribose (part of RNA) i. Produces NADPH (essential for FAs synthesis, has niacin) 3. Pyruvic acid → acetyl CoA OR lactic acid Acetyl CoA as first substrate of Kreb's cycle Requires thiamin (TDP), niacin (NAD), riboflavin (FAD), pantothenic acid (CoA), Mg, lipoic acid Most pyruvic acid is converted to acetyl CoA (active acetate) Irreversible reaction Lactic acid via Cori cycle To be used for muscle contractions when energy needs exceed 02 supply (02 debt) Only produces small amount of lactic acid Cori cycle can reconvert lactate back to pyruvate → lactate released from tissues, transported to liver and then converted back to pyruvate Kreb's Cycle → aka TCA cycle (tricarboxylic acid cycle), citric acid cycle Produces 90% of body's energy as ATP + H20 and CO2 Takes place in mitochondria Full oxidation of 1 molecule of glucose yields 38 ATP Acetyl CoA → intermediate breakdown product of CHO, protein and fat CHO → pyruvic acid that is converted to acetyl CoA Fat → oxidation of FAs (2 carbon) resulting in acetyl CoA Protein → degradation of carbon skeleton of certain aas Requires constant supply of CHO to maintain cycle 1. Oxaloacetate reacts with acetyl CoA to form citric acid (start of cycle) a. Main CHO fuel; formed from pyruvic acid and some aas b. If not enough oxaloacetate from CHO, acetyl CoA from fat cannot be handled properly and is diverted to form ketone bodies c. Alpha ketoglutaric acid (from aas via gluconeogenesis) needs thiamin for decarboxylation Protein Amino Acids Absorbed by intestinal vili into vili capillaries→ bloodstream → tissues Pyridoxine → needed for transport of aas Branched chain aas → valine, leucine, isoleucine Exercise → releases alanine from muscle protein which is then transported to liver, deaminated, and converted tó glucose Oxidation of leucine also increases (branched chain aa / BCAA)Tyrosine → can be synthesized from phenylalanine Cysteine → can be synthesized from methionine Nitrogen balance Measures body's equilibrium of protein Compares intake of N to output of N→ N in - N out (total daily protein intake (g) / 6.25)-(UUN + 4) Nitrogen-to-protein conversion factor = 6.25 (i.e. 6.25g of PRO has 1g N) 0.16g N/g PRO UUN → urinary urea nitrogen (g of N excreted x 24h) +4 → insensible losses of N via skin and GI 0→ N equilibrium, maintenance +→ net gain in body protein (infancy, growth, pregnancy, healing) - → net loss in body protein (erosion, inadequate intake) Protein Digestion & Absorption Denaturation: alteration of protein 3D structure Protein-digesting enzymes: breaks protein into polypeptides and aas Pepsin (stomach), trypsin, chymotrypsin From pancreas and brush border of SI - Absorption → via active transport, shared by similar aas → compete for absorption Only a concern with supplements Protein Quality. Arginine supplement can lead to lysine deficiency Biologis Value (BVI: uses N balance techniques to determine fraction of absorbed N retained for growth and maintenance Eggs have BV of 100 (i.e. 100% of N absorbed is retained) Net Protein Utilization (NPU): measures amount of protein actually used Protein Digestibility Corrected AA Score (PDCAAS): method of evaluating the quality of a protein based on aa requirements and ability to digest it Protein coefficient of digestibility → estimates % of protein in each food category that is actually digested Animal protein 97% Protein Metabolism Plant protein 70-90% Amino acid pool: all aas in body tissues and fluid available for use Protein turnover: continuous synthesis and breakdown of body proteins High rate → chemical signals, hormones with close regulation (insulin) Slow rate → structural proteins (collagen) Protein synthesis: DNA gene instructions used to build proteins (anabolism) Involves aa synthesis, transcription, translation, post-translational modifications, and protein folding Dictated by DNA DNA forms RNA on ribosomes, RNA forms template (mold) which carries the protein plan to the cytoplasm for synthesis Amount of DNA in cell indicates the number of cells per organ, thus helps determine stages of growth Hormones → pituitary growth hormone, thyroid hormone, insulin, testosterone Limiting aa: essential aa in lowest concentration in relation to needs Regulation of gene expressions helps regulate protein quantities Synthesis of non-protein molecules → that use N (neurotransmitters)Excess aas → convert to FAs → stored as TG in adipose tissue Protein breakdown → catabolism If low glucose supply, aa can be used for gluconeogenesis (for energy) 1. Deamination → removal of amino group (NH2) from aa by hydrolysis in liver (aa → NH2 + C-chain) a. NH2 →NH3 (ammonia) which is toxic b. NH3 + CO2 (in liver)→ urea (excreted by kidneys) i. Some NH3 → purines i. Some NH3→ used to make non-essential aas via transamination 2. Oxidation → remaining carbon chain is a ketoacid, can be oxidized for energy a. See steps below b. 58% of protein converts to glucose (10% of fat)Hormones → adrenal steroids (glucocorticoids) Stimulate protein catabolism and gluconeogenesis Fat Metabolism & Absorption Lipase → breaks TGs into FAs + glycerol for absorption Enzyme produced by pancreas and released into SI Usually very little fat lost in stool Certain fat molecules are absorbed directly into portal blood → glycerol (water sol), SCFAs (< 12C), some phospholipids Bile acid → surrounds fat molecules in SI to form a micelle Facilitates absorption of fat Bile produced by liver, stored in gallbladder, released in SI Absorption of fat-soluble vitamins occurs through micelles → requires fat Absorption Short and medium chain FAs = water soluble → through blood Long chain FA + cholesterol = insoluble → need lipoproteins Chylomicrons: lipoprotein that transports lipids from mucosal cells of SI Long FAs reassembled into TGs + cholesterol + phospholipid + some protein to form chylomicron →TGs later broken down into FAs (via lipoprotein lipase) Transferred into lymphatic system then enters bloodstream (bypasses liver) Then penetrate intestinal mucosa and travel through lymph into thoracic duct and then into blood Cholesterol → most absorbed with cholesterol enterase Converted into cholesterol esters and excreted by the liver as bile Metabolic Activities Some absorbed with bile salts Transport to/from Liver TGs in liver incorporated into lipoproteins: Chylomicron → largest lipoprotein, mostly TGs, low protein - Derived from diet, aids in lipid absorption in SI VLDL: larger, half protein half TGs carries lipids from liver, delivers TGs to body cells LDL: smaller, mostly cholesterol transport cholesterol to cells (and some TGs) - HDL: smallest, protein rich pick up cholesterol from cells to transport to liver for elimination or other cells High HDL in blood prevents cholesterol from depositing in artery walls Lipogenesis → synthesis, deposition of fat Excess FA (from fat or carb/protein excess) transported to adipose cells for storage Insulin = anabolic hormone Adipose tissue is most active site of lipogenesis (FA + glycerol → TG) Needs NADPH from pentose shunt- Liver synthesizes fat but should not store it To prevent fat accumulation → lipotropic factors (choline) produce lipoproteins which transfer FAs out of liver Lipolysis → breakdown of fat via beta oxidation Oxidation of FAs → acetyl CoA → which then enters Kreb's cycle for ATP Insulin antagonists → growth hormone, glucagon Hormones that increase rate of fat mobilization → glucocorticoids, thyroxine, epinephrine, ACTH Gluconeogenesis → glycerol used to form glucose (very small amount) Using Stored Fat Hormone sensitive lipase: enzyme in adipose cells that breaks down TGs into free FAs due to hormonal signals (fat loss) Insulin → stimulates enzyme lipoprotein lipase → promotes uptake of TG from chylomicrons by adipose tissue → fat gain Also suppresses hormone sensitive lipase → lower release of TGs from fat cells = Glucose fatty acid cycle Ketosis - Normal fat metabolism → requires adequate CHO for complete fat oxidation CHO CHO CHO FA---> acetyl CoA ---> Krebs ---->ATP, CO2, HzO acetyl CoA C ketone bodies: acetoacetic acid, acetone beta-hydroxybutyric acid Acetoacetic acid and beta-hydroxybutyric acid enter the blood and are taken to peripheral tissues and converted back to acetyl CoA and oxidized as fuel Abnormal fat metabolism → inadequate CHO results in incomplete fat oxidation A response to starvation or uncontrolled DM (lack of CHO) Acetyl CoA cannot enter Krebs cycle and make ATP→ ends up being broken down into ketones instead Acetyl CoA cannot enter Krebs cycle and make ATP→ ends up being broken down into ketones instead Ketones can then be used as energy source to fuel muscles and brain Occurs in liver; excess ketones excreted by kidneys in urine Ketosis → inadequate water to remove ketones causing build up in blood disturbing acid-base balance Headaches, dry mouth, foul breath, loss of appetite Metabolism of Nutrients - Summary ATP Production Cellular respiration: reactions that break down carbs, fats, and proteins in the presence of O3 to produce CO2, water and ATP (energy) Carbs → glucose -(glycolysis)→ acetyl CoA Fats → fatty acids -(deamination)→ acetyl CoA Protein → amino acids -(B-oxidation)→ acetyl CoA Without O2, only glucose can be used for energy Citric acid cycle: acetyl CoA used to generate ATP Forms CO2, electrons, and some atp Electron transport chain: uses O2 and electrons produced from above to make ATP + water Oxidation: compound loses electron (LEO) Reduction: compound gains electron (GER) Synthesis of New Molecules Glucose → glycogen Glucose → fatty acids (if excess glycogen) Fatty acids → triglycerides → body fat Amino acids → protein Amino acids → fatty acids (if excess amino acids) Vitamin/Mineral Absorption Factors affecting absorption: Vit A→ bile salts, pancreatic lipase, fat Vit D→bile salts, chyme acidity - Hydroxylated in liver then kidney Accompanies absorption of Ca and P Fe→HCI, Ca(binds oxalates) B12→ileum/stomach secretions (HCI, intrinsic factor) Folate → zinc dependent - Cleaves polyglutamate to monoglutamate. Folic acid fortified food and supplms → use monoglutamate Riboflavin → phosphorus Transporting Nutrients Cardiovascular System After large meal, greater proportion of blood flow will go to intestines to support digestion, absorption and transport Exercise = 85% of blood flow to skeletal muscles for respiration → food = cramps Hepatic Portal Circulation System of blood vessels that collects nutrient laden blood from digestive organs to liver Hepatic portal vein; vein that transports blood from GIT to liver In SI, water soluble molecules cross mucosal cells of villi and enter capillaries → venules → eventually to portal vein → liver - Liver processes nutrients before entering general circulation (gatekeeper) Some stored, broken down, allowed to pass through unchanged Maintains blood glucose concentration Synthesis and breakdown of amino acids, protein, fat Modifies end products of protein breakdown for safe transport to kidney Lymphatic System for excretion System of vessels, organs, and tissues that drain excess fluid from interstitial spaces, transports fat-soluble substances from GIT and contributes to immune function Substances absorbed via lymphatic system do not pass through liver Elimination of Waste Lungs + skin → CO2, water, protein breakdown products, minerals Kidneys → primary site for water, N waste, excess mineral, metabolic waste excretion Glomerulus: filters blood Tubules: reabsorb molecules