Digestive System and Nutrition Notes

Overview of Digestion

• The digestive system's organs are located within the gastrointestinal (GI) tract.

• The function of the digestive system is to hydrolyze, or break down, the macromolecules found in food.

• The subunit molecules (monosaccharides, amino acids, fatty acids, and glycerol) can cross plasma membranes using facilitated and active transport.

• The nutrients made available are transported by the blood to our cells.

Processes of Digestion

• Ingestion: Intake of food via the mouth.

• Digestion: Mechanically or chemically breaking down foods into their subunits.

  • Mechanical digestion: Chewing in the mouth and contractions of smooth muscles in the stomach.

  • Chemical digestion: Digestive enzymes hydrolyze macromolecules into subunits.

    • Begins in the mouth, continues in the stomach, and is completed in the small intestine.

Stages of Digestion

• Movement: Food is passed from one organ to the next, normally by contractions of smooth muscle called peristalsis; indigestible material must be expelled.

• Absorption: Movement of nutrients across the GI tract wall into the blood; they are then delivered to cells.

• Elimination: Removal of indigestible wastes via defecation.

Wall of the Digestive Tract

• Lumen: Open area of a hollow organ or vessel; in the GI tract, it contains food or feces.

• Layers of the digestive tract wall:

  • Mucosa: Innermost layer; produces mucus for protection; also produces digestive enzymes.

  • Submucosa: Loose connective tissue; contains blood vessels, lymphatic vessels, and nerves.

  • Muscularis: Made of two layers of smooth muscle (inner, circular layer, and an outer, longitudinal layer) that move food along the GI tract.

  • Serosa: Outer lining; is part of the peritoneum.

Diverticulosis and Diverticulitis

• Diverticulosis: A condition in which the mucosa of any part of the GI tract (usually the large intestine) pushes through the other layers and forms pouches where food collects.

• Diverticulitis: Occurs when the pouches become infected; happens in 10–25% of people with diverticulosis.

Bowel Diseases

• Inflammatory bowel disease (IBD): Chronic diarrhea, abdominal pain, fever, and weight loss.

• Irritable bowel syndrome (IBS): Contractions of the muscularis cause abdominal pain, constipation, and diarrhea. The underlying cause is not known.

The Mouth

• The mouth (oral cavity) receives food and begins mechanical and chemical digestion.

• The roof of the mouth separates the nasal cavity from the oral cavity and consists of two parts: a bony hard palate and a soft palate made of muscle that ends in the uvula.

• Tonsils are lymphatic tissue in the back of the mouth on either side of the tongue and help protect from disease. There is also a single pharyngeal tonsil in the nasopharynx, commonly called the adenoids.

• Three pairs of salivary glands secrete saliva that contains:

  • Salivary amylase: Begins carbohydrate digestion.

  • Lysozyme: Antibacterial enzyme.

• The tongue is covered in taste buds and assists in mechanical breakdown and movement of food, forming a bolus (mass of chewed food) and moves it toward the pharynx.

• Teeth mechanically digest food.

  • There are 20 smaller deciduous (baby) teeth and 32 adult teeth.

  • Two main divisions of teeth:

    • Crown: The part of the tooth above the gum line.

    • Root: The portion below the gum line.

  • Enamel: Extremely hard outer layer of teeth.

  • Dentin: A thick layer of bonelike material in teeth.

  • Pulp: Nerves and blood vessels in teeth.

  • Periodontal membranes: Anchor the tooth to the jawbone.

Dental Issues

• Dental caries: Tooth decay, cavities, occur when bacteria metabolize sugar and produce acids, which erode the teeth; can be painful when it reaches the nerves of the pulp.

• Gingivitis: Inflammation of the gums; can spread to the periodontal membrane, causing loosening of the teeth.

• Periodontitis: Loss of bone and loosening of the teeth.

The Pharynx and Esophagus

• The mouth and nasal passages lead to the pharynx, which opens into both the food passage (esophagus) and air passage (trachea, or windpipe).

  • These two tubes are parallel to each other; the trachea is in front of the esophagus.

• The esophagus is a muscular tube that leads to the stomach.

Swallowing

• Swallowing starts off voluntary, but once food or drink is pushed back into the pharynx, it becomes an involuntary reflex.

• Food normally enters the esophagus because other possible avenues are blocked.

  • The soft palate moves back to close off the nasal passage, and the trachea moves up under the epiglottis to cover the glottis, the opening to the larynx.

Peristalsis

• Peristalsis: Contractions that push food through the digestive tract.

• Sphincter: A ring of muscle that acts as a valve.

  • When it contracts, it stops food from moving through; when it relaxes, it allows food through.

  • The lower esophageal sphincter is between the esophagus and the stomach.

Heartburn and Vomiting

• Heartburn: Failure of the lower esophageal sphincter; stomach contents move from the stomach into the esophagus.

• Vomiting: When strong contractions of the abdominal muscles and the diaphragm (the muscle separating the thoracic and abdominal cavities) force the contents of the stomach into the esophagus and oral cavity.

The Stomach

• The stomach stores food, starts digestion of proteins, and controls movement of food into the small intestine but does not absorb nutrients (except alcohol, because alcohol is fat- soluble and can pass through membranes easily).

  • There are three layers of muscle in the muscularis layer (instead of two) to help in mechanical digestion: circular, longitudinal, and third oblique layer.

Heartburn (GERD)

• Heartburn (GERD): The lining of the esophagus is thinner than the lining of the stomach; if chyme enters the esophagus, it produces a burning sensation.

  • Can be caused by pregnancy and excess fat pushing on the stomach.

  • Gastroesophageal reflux disease (GERD) is chronic heartburn.

• The mucosa has deep folds called rugae and also has gastric pits, which contain gastric glands.

  • The gastric glands produce gastric juice, which contains:

    • Pepsin: Digests proteins.

    • Hydrochloric acid (HCl): pH of 2; kills bacteria and activates pepsin.

    • Mucus.

• Normally, the stomach empties in 2–6 hours.

• Chyme: A mixture of food and gastric juice.

• Pyloric sphincter: Allows only a small amount of chyme to enter the small intestine at a time.

The Small Intestine

• The small intestine is named for its small diameter compared with the large intestine’s. The small intestine is very long, longer than the large intestine.

  • Averaging about 6 m (18 ft) in length, whereas the large intestine is about 1.5 m (4.5 ft).

  • It consists of three regions:

    • Duodenum.

    • Jejunum.

    • Ileum

• The Small Intestine Is the Main Digestive Organ

Pancreas

• Pancreas: Secretes digestive enzymes through a duct into the duodenum, the first portion of the small intestine.

• Another duct brings bile from the liver and gallbladder into the duodenum.

  • Bile emulsifies fat (mechanical digestion); causes fat droplets to disperse in water to expose more of it to lipase.

    • Produced by the pancreas, it hydrolyzes fats into glycerol and fatty acids.

  • Pancreatic amylase: Produced by the pancreas, secreted into the duodenum, digests carbohydrates.

  • Trypsin: Produced by the pancreas, secreted into the duodenum, digests proteins, so is a protease—a class of enzymes that digest proteins.

  • Pancreatic juice contains sodium bicarbonate, which neutralizes acidic chime.

Major Digestive Enzymes

• Carbohydrate Digestion

  • Salivary amylase: Produced by salivary glands, acts in the mouth, optimum pH is neutral, function is to begin the breakdown of starch to maltose.

  • Pancreatic amylase: Produced by the pancreas, acts in the small intestine, optimum pH is basic, function is to breakdown of starch to maltose.

  • Maltase: Produced by the small intestine, acts in the small intestine, optimum pH is basic, function is to breakdown of maltose to glucose.

  • Lactase: Produced by the small intestine, acts in the small intestine, optimum pH is basic, function is to breakdown of lactose to glucose and galactose.

• Protein Digestion

  • Pepsin: Produced by gastric glands, acts in the stomach, optimum pH is acidic, function is to breakdown of proteins to peptides and amino acids.

  • Trypsin: Produced by the pancreas, acts in the small intestine, optimum pH is basic, function is to breakdown of proteins to peptides and amino acids.

  • Peptidases: Produced by the small intestine, acts in the small intestine, optimum pH is basic, function is to breakdown of peptides to amino acids.

• Nucleic Acid Digestion

  • Nuclease: Produced by the pancreas, acts in the small intestine, optimum pH is basic, function is to breakdown of nucleic acids to nucleotides.

  • Nucleosidases: Produced by the small intestine, acts in the small intestine, optimum pH is basic, function is to breakdown of nucleotides to phosphates, bases, and sugars.

• Fat Digestion

  • Salivary lipase: Produced by salivary glands, acts in the mouth, optimum pH is neutral, function is to begin the breakdown of triglycerides into fatty acids.

  • Lipase: Produced by the pancreas, acts in the small intestine, optimum pH is basic, function is to breakdown of lipids to glycerol and fatty acids.

Nutrient Absorption in the Small Intestine

• The mucosa contains fingerlike projections called villi (sing., villus).

• The cells that cover the villi have microvilli.

  • Give the villi a fuzzy “brush border.”

  • Contain brush border enzymes that complete digestion.

• These two structures greatly increase the surface area of the small intestine for absorption of nutrients.

• Nutrients are absorbed into the villi, which contain blood capillaries and a small lymphatic capillary called a lacteal.

  • Monosaccharides and amino acids enter the blood capillaries of a villus.

  • Glycerol and fatty acids form lipoprotein droplets called chylomicrons, which then enter a lacteal.

• After nutrients are absorbed, they are eventually carried to all the cells of the body by the blood.

Lactose Intolerance and Celiac Disease

• Lactose Intolerance: Lactose is the primary sugar in milk.

  • Lactase is the brush border enzyme that digests lactose.

  • Characterized by diarrhea, gas, bloating, and abdominal cramps after ingesting milk and other dairy products.

    • Diarrhea occurs because the undigested lactose causes fluid retention in the small intestine.

    • Gas, bloating, and cramps occur when bacteria break down the lactose anaerobically.

• Celiac Disease

  • Autoimmune response against a protein called gluten, which is naturally found in grains such as wheat, barley, and rye.

  • The presence of gluten in the small intestine results in an inflammatory response, which damages the villi and microvilli of the small intestine.

  • Can lead to abdominal pain, diarrhea, and malnutrition.

Accessory Organs

• Pancreas

  • Located behind the stomach.

  • Most pancreatic cells produce pancreatic juice, which enters the duodenum via the pancreatic duct; contains sodium bicarbonate and digestive enzymes.

  • Also an endocrine gland; secretes the hormone insulin when the blood glucose levels rise.

    • Type 1 diabetes: not enough insulin; normally diagnosed in childhood.

    • Type 2 diabetes: the body’s cells are insulin- resistant; normally occurs in adulthood; risk factors: obesity, inactivity, family history.

• Liver

  • The largest gland in the body.

  • Lies mainly in the upper right abdominal cavity, under the diaphragm.

  • Lobules: structural and functional units.

  • The hepatic portal vein brings blood to the liver from the GI tract.

    • The lobules filter this blood, removing poisonous substances.

  • Functions of the Liver:

    • Destroys old red blood cells; excretes bilirubin, a breakdown product of hemoglobin in bile, a liver product

    • Detoxifies blood by removing and metabolizing poisonous substances

    • Stores iron (Fe^{2+}), the water-soluble vitamin B12, and the fat-soluble vitamins A, D, E, and K

    • Makes plasma proteins, such as albumins and fibrinogen, from amino acids

    • Stores glucose as glycogen after a meal; breaks down glycogen to glucose to maintain the glucose concentration of blood between eating periods

    • Produces urea after breaking down amino acids

    • Helps regulate blood cholesterol level, converting some to bile salts

  • Stores vitamins.

  • Involved in blood glucose homeostasis

    • Stores glucose as glycogen; when blood glucose is low, it releases glucose by breaking down glycogen.

    • Converts glycerol and amino acids to glucose.

    • As amino acids are converted to glucose, urea is formed.

  • Produces plasma proteins.

  • Regulates blood cholesterol levels.

  • Produces bile, which contains bile salts, water, cholesterol, and bicarbonate.

    • Contains bilirubin, a green pigment formed from the breakdown of hemoglobin.

• Gallbladder

  • Pear-shaped organ just below the liver.

  • Stores bile.

  • Gallstones: Made of a stone-like material.

Liver Disorders

• Liver disorders: hepatitis and cirrhosis.

• Liver disease can cause bile pigments to leak into the blood, causing jaundice; yellowish tint to the whites of the eyes and the skin.

• Hepatitis

  • Inflammation of the liver.

  • Has different forms.

    • Hepatitis A: Usually acquired from sewage- contaminated drinking water and food.

    • Hepatitis B: Usually from sexual contact, but also from blood transfusions or contaminated needles; more contagious than the AIDS virus and is spread in the same way; vaccines are available for hepatitis A and B.

    • Hepatitis C: Usually acquired by infected blood; can lead to chronic hepatitis, liver cancer, and death.

• Cirrhosis

  • Chronic disease; first, liver becomes fatty, and then filled with fibrous scar tissue.

  • Often seen in people with obesity and alcohol use disorder, due to malnutrition and the excessive alcohol (a toxin) the liver is forced to break down.

  • The liver can regenerate and recover if the rate of regeneration exceeds the rate of damage.

  • During liver failure there may not be enough time to let the liver heal so will need a liver transplantation.

Regulation of Digestive Secretions

• Secretion of digestive juices is controlled by the nervous system and digestive hormones.

• When you look at or smell food, the parasympathetic nervous system stimulates gastric secretion.

• A meal rich in protein causes the stomach to produce the hormone gastrin; increases the secretory activity of gastric glands.

• Secretin: Secreted by the duodenum; release is stimulated by HCl (present in chyme).

• Cholecystokinin (CCK): Released by the duodenum when proteins and fat are present.

  • Causes the liver to increase production of bile and causes the gallbladder to contract and release stored bile.

  • These hormones increase the production of pancreatic juice.

The Large Intestine

• The large intestine includes the cecum, the colon, the rectum, and the anal canal; larger in diameter than the small intestine, but it is shorter in length.

• Cecum: The first portion.

  • Vermiform appendix: Projection off of the cecum; fights infections.

  • Appendicitis: Inflamed appendix; can cause peritonitis, a life-threatening infection of the peritoneum.

• Colon: includes the ascending colon, which goes up the right side of the body; transverse colon, which crosses the abdominal cavity; descending colon, which passes down the left side; and the sigmoid colon, which enters the rectum, the last portion of the large intestine.

  • The rectum opens at the anus, where defecation, the expulsion of feces, occurs.

• Functions of the large intestine:

  • Does not produce digestive enzymes.

  • Does not absorb nutrients except certain vitamins.

  • Absorbs water from feces to prevent dehydration.

  • Absorbs vitamins produced by intestinal flora, the bacteria that inhabit the intestine.

    • Bacteria break down indigestible material and produce B- complex vitamins and vitamin K.

  • Forms feces

    • \frac{3}{4} water, \frac{1}{4} solid wastes.

    • Bacteria and dietary fiber (indigestible remains) make up the solid wastes.

    • Bacteria digesting the indigestible materials causes the odor of feces and accounts for the gas.

    • Stercobilin, a breakdown product of bilirubin, and oxidized iron cause the brown color of feces.

  • Defecation: ridding the body of feces.

    • Peristalsis forces feces into the rectum.

    • Stretching of the rectal wall initiates nerve impulses to the spinal cord.

    • Then the rectal muscles contract and the anal sphincters relax, allowing the feces to exit the body through the anus.

    • Can inhibit defecation by contracting the external anal sphincter, which is made of skeletal muscle.

Disorders of the Colon and Rectum

• Diarrhea: Increased peristalsis and failure to absorb water from feces, due to either an infection or nervous stimulation.

• Constipation: Dry, hard feces; may be controlled with water and fiber.

• Hemorrhoids: Enlarged, inflamed blood vessels of the anus due to chronic constipation, pregnancy, aging, anal intercourse.

• Diverticulosis: Pouches; weak spots in the muscularis layer.

• Irritable bowel syndrome (IBS), or spastic colon: the muscularis contracts powerfully but without normal coordination; symptoms: abdominal cramps, gas, constipation, and urgent, explosive stools.

• Inflammatory bowel disease (IBD) includes:

  • Ulcerative colitis: Affects the large intestine and rectum; results in diarrhea, rectal bleeding, abdominal cramps, and urgency to defecate.

  • Crohn’s disease: Usually in the small intestine; ulcers in the intestinal wall; they are painful and bleed as they erode the submucosal layer, where there are nerves and blood vessels; can’t absorb nutrients in the affected areas; symptoms: diarrhea, weight loss, abdominal cramping, anemia, bleeding, and malnutrition.

• Polyps and cancer

  • Polyps: Small growths in the colon lining; can be benign or cancerous; if colon cancer is detected while still confined to a polyp, the expected outcome is a complete cure.

  • Increased dietary fat raises the risk of colon cancer.

  • Fiber in the diet inhibits colon cancer, and regular elimination reduces the time that the colon wall is exposed to cancer-promoting agents in the feces.

Nutrition and Weight Control

• Obesity: Significantly overweight; one of the greatest health problems in the United States; almost 42% of adults and 18.5% of children are obese; excess body fat is associated with a higher risk for premature death, type 2 diabetes, hypertension, cardiovascular disease, stroke, osteoarthritis, and certain types of cancer.

• Defining obesity: Having a body mass index (BMI) of 30 or greater; weight in kilograms (kg) is divided by the height in meters squared (kg/m^2).

• BMI Values

  • Healthy: 18.5 to 24.9

  • Overweight: 25.0 to 29.9

  • Obese: 30.0 to 39.9

  • Extremely (morbid) obese: 40.0 and higher

Classes of Nutrients

• Nutrient: A required component of food that performs a physiological function in the body; provides energy, promotes growth and development, and regulates cellular metabolism; includes carbohydrates, proteins, lipids, minerals, and vitamins.

Carbohydrates

• Carbohydrates are either simple or complex.

• Glucose is a simple sugar.

• Complex carbohydrates are digested to glucose.

• Although body cells can use fatty acids as an energy source, brain cells require glucose.

• Any product made from refined grains, such as white bread, cake, and cookies, should be minimized in the diet because, during refinement of grains, fiber is removed, along with vitamins and minerals.

• Sources of complex carbohydrates, such as beans, peas, nuts, fruits, and whole-grain products, are good sources of vitamins, minerals, and fiber.

  • Insoluble fiber adds bulk to the feces and stimulates movements of the large intestine, preventing constipation.

  • Soluble fiber combines with bile salts and cholesterol in the small intestine and prevents them from being absorbed.

• Can carbohydrates be harmful?

  • High intake of refined carbohydrates and fructose sweeteners contribute to obesity; in addition, they have a high glycemic index, because they quickly increase blood glucose.

  • When blood glucose levels rise rapidly, the pancreas produces a lot of insulin to bring the level down.

  • Chronically high insulin levels may lead to insulin resistance, type 2 diabetes, and increased fat deposition.

• Reducing High-Glycemic-Index Carbohydrates

  • To Reduce Dietary Sugar

    • Eat fewer sweets, such as candy, soft drinks, ice cream, and pastries.

    • Eat fresh or frozen fruits or fruits canned without heavy syrup. Avoid artificial fruit juices.

    • Use less sugar—white, brown, or raw—and less honey and syrups.

    • Avoid sweetened breakfast cereals.

    • Eat less jelly, jam, and preserves.

    • When cooking, use spices, such as cinnamon, instead of sugar to flavor foods.

    • Do not put sugar in tea or coffee.

    • Avoid processed foods made from refined carbohydrates, such as white bread, rice, and pasta, and limit potato intake.

Proteins

• Proteins are made of 20 different amino acids.

• There are eight essential amino acids—must be attained through the diet.

• Complete proteins: Contain all essential amino acids; usually derived from animal sources; non-animal sources of complete proteins are tofu, soymilk, and other processed food from soybeans.

• Incomplete proteins: Plant sources; need to combine them to get all essential amino acids.

• Must ingest essential amino acids every day; they are not stored in the body.

• Can proteins be harmful?

  • An overabundance of protein intake can result in dehydration during exercise.

  • Can also lead to calcium loss in urine, which can lead to kidney stones.

  • Eating red meat can lead to cardiovascular disease since it is high in saturated fats.

Lipids

• Lipids include fats, oils, and cholesterol.

  • Saturated fats. Usually of animal origin; solid at room temperature (unsaturated fats are usually liquid at room temperature); that is, butter, fat in meat, coconut oil, and palm oil.

  • Unsaturated fats. Don’t promote cardiovascular disease; that is, corn oil and safflower oil are high in polyunsaturated fatty acids.

  • Polyunsaturated oils contain the essential fatty acids linoleic acid and linolenic acid.

  • Olive oil and canola oil have more monounsaturated fatty acids than others.

  • Omega-3 fatty acids preserve brain function and protect against heart disease; flaxseed and cold-water fish are excellent sources.

• Can lipids be harmful?

  • The risk for cardiovascular disease is increased by a diet high in saturated fats and cholesterol.

  • Saturated fats contribute to the formation of atherosclerotic plaques that limit blood flow.

  • Cholesterol is carried in the blood by two transport proteins: high-density lipoprotein (HDL) and low-density lipoprotein (LDL).

    • HDL (the “good” lipoprotein) ends up in the liver, where the cholesterol is metabolized.

    • LDL (the “bad” lipoprotein) ends up being deposited in the tissues.

  • Trans fatty acids (trans fats) arise when unsaturated fatty acids are hydrogenated to produce a solid fat; found in commercially packaged goods, such as cookies and crackers; if something contains partially hydrogenated vegetable oil, it contains trans fats.

Reducing Lipids in the Diet

• To Reduce Saturated Fats and Trans Fats in the Diet

  • Choose poultry, fish, or dry beans and peas as a protein source.

  • Remove skin from poultry, and trim fat from red meats before cooking; place on a rack, so that fat drains off.

  • Broil, boil, or bake rather than fry.

  • Limit your intake of butter, cream, trans fats, shortenings, and tropical oils (coconut and palm oils).

  • Use herbs and spices to season vegetables instead of butter, margarine, or sauces. Use lemon juice instead of salad dressing.

  • Drink skim milk instead of whole milk and use skim milk in cooking and baking.

• To Reduce Dietary Cholesterol

  • Avoid cheese, egg yolks, liver, and certain shellfish (shrimp and lobster). Preferably, eat white fish and poultry.

  • Substitute egg whites for egg yolks in both cooking and eating.

  • Include soluble fiber in the diet. Oat bran, oatmeal, beans, corn, and fruits, such as apples, citrus fruits, and cranberries, are high in soluble fiber.

Minerals

• Minerals are divided into major minerals and trace minerals.

• Major minerals are needed at quantities greater than 100 mg per day; trace, less than 100 mg.

• Major minerals are in cells and body fluids and are structural components of tissues.

• Trace minerals are often part of larger molecules; that is, iron is present in hemoglobin, and iodine is a part of thyroid hormones; that is, zinc, copper, and manganese are present in enzymes.

• Minerals: Major (More than 100 mg/Day Needed)

  • Calcium (Ca^{2+}): Strong bones and teeth, nerve conduction, muscle contraction, blood clotting; food sources include dairy products and leafy green vegetables; deficiency leads to stunted growth in children and low bone density in adults; toxicity leads to kidney stones and interferes with iron and zinc absorption.

  • Phosphorus (PO_4^{3-}): Bone and soft tissue growth; part of phospholipids, ATP, and nucleic acids; food sources include meat, dairy products, sunflower seeds, and food additives; deficiency leads to weakness, confusion, and pain in bones and joints; toxicity leads to low blood and bone calcium levels.

  • Potassium (K^+): Nerve conduction, muscle contraction; food sources include many fruits and vegetables, bran; deficiency leads to paralysis, irregular heartbeat, and eventual death; toxicity leads to vomiting, heart attack, and death.

  • Sulfur (S^{2-}): Stabilizes protein shape, neutralizes toxic substances; food sources include meat, dairy products, and legumes; deficiency is not likely; toxicity in animals depresses growth.

  • Sodium (Na^+): Nerve conduction, pH and water balance; food source is table salt; deficiency leads to lethargy, muscle cramps, loss of appetite; toxicity leads to edema and high blood pressure.

  • Chloride (Cl^-): Water balance; food source is table salt; deficiency is not likely, toxicity leads to vomiting and dehydration.

  • Magnesium (Mg^{2+}): Part of various enzymes for nerve and muscle contraction, protein synthesis; food sources include whole grains and leafy green vegetables; deficiency leads to muscle spasm, irregular heartbeat, convulsions, confusion, and personality changes; toxicity leads to diarrhea.

• Minerals: Trace (Less than 100 mg/Day Needed)

  • Zinc (Zn^{2+}): Protein synthesis, wound healing, fetal development and growth, immune function; food sources include meats, legumes, and whole grains; deficiency leads to delayed wound healing, stunted growth, diarrhea, and mental lethargy; toxicity leads to anemia, diarrhea, vomiting, renal failure, and abnormal cholesterol levels.

  • Iron (Fe^{2+}): Hemoglobin synthesis; food sources include whole grains, meats, and prune juice; deficiency leads to anemia, physical and mental sluggishness; toxicity leads to iron toxicity disease, organ failure, and eventual death.

  • Copper (Cu^{2+}): Hemoglobin synthesis; food sources include meat, nuts, and legumes; deficiency leads to anemia and stunted growth in children; toxicity leads to damage to internal organs if not excreted.

  • Iodine (I^-): Thyroid hormone synthesis; food sources include iodized table salt and seafood; deficiency leads to thyroid deficiency; toxicity leads to depressed thyroid function and anxiety.

  • Selenium (SeO_4^{3-}): Part of antioxidant enzyme; food sources include seafood, meats, and eggs; deficiency leads to vascular collapse and possible cancer development; toxicity leads to hair and fingernail loss and discolored skin.

  • Manganese (Mn^{2+}): Part of enzymes; food sources include nuts, legumes, and green vegetables; deficiency leads to weakness and confusion; toxicity leads to confusion, coma, and death.

• Occasionally individuals do not receive enough iron, calcium, magnesium, or zinc in their diets.

• Adult females need more iron in their diet than males because they lose hemoglobin each month during menstruation.

• A varied and complete diet usually supplies enough of each type of mineral.

• Calcium

  • In bones, teeth.

  • Needed for nerve impulse conduction, muscle contraction and blood clotting.

  • Calcium supplements prevent osteoporosis—a degenerative bone disease common in the elderly.

  • Vitamin D is needed with calcium to prevent bone loss.

• Sodium

  • Regulates water balance.

  • Important in the movement of materials across the plasma membrane as well as the conduction of a nerve impulse.

  • The recommended amount of sodium intake per day is 1,500 mg, but the average American takes in more than 3,400 mg.

  • Excess sodium can worsen hypertension.

• Reducing Dietary Sodium

  • Use spices instead of salt to flavor foods.

  • Add little or no salt to foods at the table, and add only small amounts of salt when you cook.

  • Eat unsalted crackers, pretzels, potato chips, nuts, and popcorn.

  • Avoid hot dogs, ham, bacon, luncheon meats, smoked salmon, sardines, and anchovies.

  • Avoid processed cheese and canned or dehydrated soups.

  • Avoid brine-soaked foods, such as pickles and olives.

  • Read nutrition labels to avoid high-salt products.

Vitamins

• Vitamins: Organic compounds; used for metabolism; need to ingest, since they are not produced in high enough quantities by the body; are often parts of coenzymes.

• There are 13 vitamins, two types: fat soluble and water soluble.

Fat-Soluble Vitamins

• Vitamin A

  • Functions: Antioxidant synthesized from beta-carotene; needed for healthy eyes, skin, hair, and mucous membranes and for proper bone growth

  • Food Sources: Deep yellow/orange and leafy, dark green vegetables; fruits; cheese; whole milk; butter; eggs

  • Deficiency: Night blindness, impaired growth of bones and teeth

  • Toxicity: Headache, dizziness, nausea, hair loss, abnormal development of fetus

• Vitamin D

  • Functions: Group of steroids needed for development and maintenance of bones and teeth and for absorption of calcium

  • Food Sources: Milk fortified with vitamin D, fish liver oil; also made in the skin when exposed to sunlight

  • Deficiency: Rickets, decalcification and weakening of bones

  • Toxicity: Calcification of soft tissues, diarrhea, possible renal damage

• Vitamin E

  • Functions: Antioxidant that prevents oxidation of vitamin A and polyunsaturated fatty acids

  • Food Sources: Leafy green vegetables, fruits, vegetable oils, nuts, whole-grain breads and cereals

  • Deficiency: Unknown

  • Toxicity: Diarrhea, nausea, headaches, fatigue, muscle weakness

• Vitamin K

  • Functions: Needed for synthesis of substances active in clotting of blood

  • Food Sources: Leafy green vegetables, cabbage, cauliflower

  • Deficiency: Easy bruising and bleeding

  • Toxicity: Can interfere with anticoagulant medication

Water-Soluble Vitamins

• Vitamin C

  • Functions: Antioxidant; needed for forming collagen; helps maintain capillaries, bones, and teeth

  • Food Sources: Citrus fruits, leafy green vegetables, tomatoes, potatoes, cabbage

  • Deficiency: Scurvy, delayed wound healing, infections

  • Toxicity: Gout, kidney stones, diarrhea, decreased copper

• Thiamine (vitamin B1)

  • Functions: Part of coenzyme needed for cellular respiration; also promotes activity of the nervous system

  • Food Sources: Whole-grain cereals, dried beans and peas, sunflower seeds, nuts

  • Deficiency: Beriberi, muscular weakness, enlarged heart

  • Toxicity: Can interfere with absorption of other vitamins

• Riboflavin (vitamin B2)

  • Functions: Part of coenzymes, such as FAD; aids cellular respiration, including oxidation of protein and fat

  • Food Sources: Nuts, dairy products, whole- grain cereals, poultry, leafy green vegetables

  • Deficiency: Dermatitis, blurred vision, growth failure

  • Toxicity: Unknown

• Niacin (nicotinic acid)

  • Functions: Part of coenzyme NAD; needed for cellular respiration, including oxidation of protein and fat

  • Food Sources: Peanuts, poultry, whole-grain cereals, leafy green vegetables, beans

  • Deficiency: Pellagra, diarrhea, mental disorders

  • Toxicity: High blood sugar and uric acid, vasodilation, etc.

• Folacin (folic acid)

  • Functions: Coenzyme needed for production of hemoglobin and formation of DNA

  • Food Sources: Dark, leafy green vegetables; nuts; beans; whole-grain cereals

  • Deficiency: Megaloblastic anemia, spina bifida

  • Toxicity: May mask B12 deficiency

• Vitamin B6

  • Functions: Coenzyme needed for synthesis of hormones and hemoglobin; CNS control

  • Food Sources: Whole-grain cereals, bananas, beans, poultry, nuts, leafy green vegetables

  • Deficiency: Rarely, convulsions, vomiting, seborrhea, muscular weakness

  • Toxicity: Insomnia, neuropathy

• Pantothenic acid

  • Functions: Part of coenzyme A needed for oxidation of carbohydrates and fats; aids in the formation of hormones and certain neurotransmitters

  • Food Sources: Nuts, beans, dark green vegetables, poultry, fruits, milk

  • Deficiency: Rarely, loss of appetite, mental depression, numbness

  • Toxicity: Unknown