Biology 221 Anatomy Physiology II TOPIC 9 Nutrition

Biology 221 Anatomy & Physiology II TOPIC 9 Nutrition, Metabolism & Body Temperature Regulation Chapter 25 pp. 949 -997 E. Lathrop-Davis / E. Gorski / S. Kabrhel

Definitions • A “Calorie” (kilocalorie) is “amount of heat energy needed to raise the temperature of 1 kilogram of water 1 o. C” (Marieb, 2001) • Nutrients are substances that are used to promote normal growth, body maintenance and tissue repair. – Major nutrients are needed in large amounts. – Minor nutrients are needed in small amounts.

Nutrients • Major nutrients include protein [amino acids], carbohydrate, and lipids. – Water is also a major nutrient. ° Ingested water comes in food and drink ° Metabolic water is a product of aerobic respiration. • Minor nutrients include: – vitamins, which are organic (Vit. B, Vit. C, Vit. D, etc. ); and – minerals, which are inorganic (e. g, iron, calcium, iodine).

Major Food Groups • The six major food groups are: – Grains – Fruits – Vegetables – Protein – Dairy – Fats, oils, sweets • The food pyramid (http: //www. nal. usda. gov: 8001/py/pmap. htm) suggests ratios of how much of each should be eaten. Fig. 25. 1, p. 949 See also http: //www. vegsource. com/nutrition/pyramid. htm (vegetarian food pyramid)

Carbohydrates: Sources & Uses • Dietary sources of carbohydrates are mostly from plants (lactose comes from milk). • Carbohydrates are used in the body as: – an energy source: ° glucose (which is a six-carbon sugar or hexose) is the primary sugar used to make ATP; ° fructose and galactose (also hexose sugars) are isomers of glucose and can be converted to glucose;

Carbohydrates: Sources & Uses • Uses also include: – providing structure for example, sugars (ribose and deoxribose) form the backbone of nucleic acids; and – cell recognition when they are joined to proteins to form glycoproteins and incorporated into the plasma membrane of the cell.

Carbohydrates: Miscellaneous • Carbohydrates are stored as: – glycogen in the liver, and skeletal and cardiac muscle (medium-term storage); or – fat in adipose cells after conversion to neutral fats (triglycerides; long-term storage). • Cellulose (a polymer of glucose) is not digested because we lack the enzymes necessary but provides bulk to feces, which is important to colon health.

Hormonal Control of Blood Glucose • See A&P I “Unit 11 – Endocrine System” – for more information. • Hypoglycemic hormones decrease blood sugar. Insulin is the only hypoglycemic hormone. • Hyperglycemic hormones increase blood sugar. Hyperglycemic hormones include: – glucagon – glucocorticoids (cortisol) – epinephrine – growth hormone http: //www. wikipedia. org/wiki/Insulin

Lipids: Sources • Most lipids are neutral fats, which are also called triglycerides, include fats & oils. • Neutral fats may be saturated or unsaturated. – Saturated fats are ones in which the fatty acid chains contain no double bonds. ° Saturated fats are found in animal products and a few plant products (e. g. , coconut and palm kernel oil). ° Saturated fats are generally solid at room temperature.

Lipids: Sources • Unsaturated fats come mainly from plants and are generally liquid at room temp. – Monounsaturated fats are ones in which the fatty acid chains have one double bond. – Polyunsaturated fats are ones in which the fatty acid chains have more than one double bond. • Cholesterol comes from animal products. – Cholesterol is carried in the blood by lipoproteins made by the liver.

Lipids: Sources: Essential Fatty Acids • Essential fatty acids must be in the diet because the liver lacks enzymes to synthesize them. • The two essential fatty acids are found in plants. – Linoleic acid is a fatty acid component of lecithen, a membrane lipid. – Linolenic acid may be “essential”, but the research is not clear.

Lipids: Uses in the Body Lipids are used in the body as: • components of adipose, which is used: – for long-term energy storage; – to cushions organs; and – to insulate the body to keep heat in. • components of plasma membranes (phospholipids; cholesterol). – Unsaturated fats and cholesterol help prevent the cell membrane from crystallizing at low temperatures.

Lipids: Uses in the Body • regulatory molecules. – Steroid hormones produced by the gonads & adrenal cortex (See A&P I Unit 11 – Endocrine System). – Prostaglandins are paracrines (locally acting hormones) that cause pain and sensitize blood vessels to inflammatory compounds (See Topic 6), among other things. (http: //www. rndsystems. com/asp/g_sitebuilder. asp? bo dy. Id=194#Prostaglandins).

Proteins: Dietary Sources • All-or-none rule means that all amino acids needed must be present for a protein to be synthesized (if any are lacking, the protein will not be made). • Complete proteins contain all essential amino acids. – Animal products (eggs, milk, meat) contain complete proteins. – Soybeans are the only plants with complete protein.

Proteins: Dietary Sources • Incomplete proteins are low amounts or lacking certain amino acids. – Plant proteins are incomplete. ° Vegetarians need to mix grains (like rice or corn) with legumes (peas or beans) to get all essential amino acids at the same time. Or they can eat soy products.

Proteins: Essential Amino Acids • Like essential lipids, essential amino acids cannot be made by the body (liver lacks the proper enzymes); therefore, must be in diet • Vegetarians can get all by combining grains (e. g. , corn, rice) with legumes (beans, peas). Fig. 25. 2, p. 952

Proteins: Uses in the Body Proteins are used in the body: • for structure; • as catalysts; • to transport and store molecules and ions; • in contraction; • for regulation; • for defense.

Proteins: Uses – Structure Proteins: • are important components of plasma membranes. • form collagen, reticular and elastin fibers of connective tissues. • form the cytoskeleton within the cell. • form cell junctions (tight, loose [desmosomes], and gap junctions) between cells.

Proteins: Uses – Catalysts Protein enzymes: • increase reaction rates in metabolic pathways so that they occur at rates necessary for life; and • allow the body to control metabolism. – Because their activity relies on shape, their activity can altered by changing their shape ° This allows enzymes to be “turned on” or “turned off”. ° For example, the pathway of gluconeogenesis is turned “on” by glucagon and “off” by insulin.

Proteins: Uses Transport & Storage Proteins: • provide intracellular transport (e. g. , axonal transport carries neurotransmitters from the cell body to the axon terminals); • serve as membrane transport proteins (e. g. , ion channels, pumps, facilitated transport carriers); • transport molecules and ions in the blood (e. g. , hemoglobin transport O 2, transferrin transports Fe; HDLs and LDLs transport cholesterol) • serve as storage proteins (e. g. , hemosiderin stores Fe, ferritin stores Fe, myoglobin stores O 2 in redtwitch skeletal and cardiac muscle, thyroglobulin stores thyroxine in the thyroid gland).

Proteins: Uses – Contraction See Unit 13 – Muscular System – A&P I • Myosin and actin interact for contraction in muscles. • Tropomyosin and troponin regulate muscle contraction in skeletal and cardiac muscle. • Calmodulin regulates muscle contraction in smooth muscle

Proteins: Uses – Regulation Proteins regulate cellular activity by acting as: • hormones. – Hormones control body functions. – All hormones, except those from the adrenal cortex and gonads, are based on amino acids. • intracellular regulators such as calmodulin. – Calmodulin regulates muscle activity in smooth muscle. – Calmodulin also regulates activity in response to hormones that use the PIP-Calcium mechanism to control the cell (See A&P I Unit XI).

Proteins: Uses - Defense • Immunoglobulins (antibodies) provide specific resistance to disease by attacking antigens. • Defensins, lysozyme, complement, and interferon provide nonspecific resistance against pathogens.

Proteins: Miscellaneous • Adequacy of caloric intake – The diet must include sufficient carbohydrates or fat for ATP production so that amino acids are used for protein synthesis instead of being burned for energy. • Nitrogen balance of the body occurs when intake (through diet) equals loss through urine and feces. – Transamination adds an amino (NH 3) group from one molecule to another to make a nonessential amino acid. – Deamination removes the amino group from an amino acid so that the carbon skeleton can be used for energy (the amino group is converted to ureaby the liver).

Proteins: Hormonal Control of Protein Synthesis • Anabolic hormones (e. g. , testosterone, GH, insulin) promote protein synthesis. • Catabolic hormones (e. g. , glucocorticoids) promote degradation.

Water-soluble Vitamins • Vit. C and B-complex vit. are absorbed along with water in the small intestine. • Absorption of Vit. B 12 requires the presence of intrinsic factor produced by stomach. – Pernicious anemia is caused by inadequate intake of vit. B 12 due to lack of intrinsic factor. • Some B vitamins are produced by gut bacteria. • Excesses are usually eliminated in the urine so there are seldom problems with excessive doses.

Fat-soluble Vitamins • Vit. A, D, E and K absorption is aided by micelles in small intestine • Vit. K is produced by bacteria in the large colon. • Vit. D is made by the body (starting in the skin after exposure to UV radiation and completed in the kidney under control by PTH; See A&P I Unit III Integumentary System and Unit II Endocrine System) – Dietary sources include egg yolk, some fish oils and some plants. • Excesses of Vit. A, D, and E stored in fat (megadoses may cause problems).

Functions of Vitamins • Coenzymes are molecules that help enzymes perform their functions. – Riboflavin and niacin form part of the electron carriers FAD and NAD+, respectively, that carry electrons during catabolism of glucose. • Antioxidants (Vit. A, C and E) interact with free radicals in cells to prevent damage to cell. • Vit. A is precursor to visual pigments in the retina.

Minerals: Miscellaneous & Sources • Dietary sources of minerals include vegetables, legumes, milk, and some meats. • Some minerals are required in large amounts, including: – calcium (Ca 2+), potassium (K+), phosphorus (P), sulfur (S), sodium (Na+), chloride (Cl-), and magnesium (Mg+). • Others are required in small amounts = trace minerals, including – iron (Fe), zinc (Zn) and iodine (I).

Minerals: Uses in Body Minerals are used: • for structure (especially Ca 2+ and Mg 2+ / PO 4= salts in bones and teeth); • as enzyme cofactors that form part of the active sites of enzymes (Mg 2+); • for oxygen transport by hemoglobin (Fe) and storage by myoglobin (Fe); • to maintain ionic and osmotic balances (especially Na+, Cl-, and K+). – These also affect blood pressure as a result of water retention (especially Na+).

Minerals: Uses in Body Minerals are: • essential to action potentials and impulses (Na+, K+, Ca 2+); • essential to contraction (Na+, K+, Ca 2+); • an essential part of Thyroid hormones (I-); • essential to clotting (Ca 2+ = clotting factor IV) • used in energy transfers (PO 4=).

Metabolism: Definitions • Metabolism is the sum of all the chemical processes occurring in the body. • Anabolism refers to reactions in which larger molecules manufactured from smaller ones. – Anabolic reactions usually require energy (ATP) input from the cell. – The production of peptides (proteins) from amino acids is an example.

Metabolism: Definitions • Catabolism refers to reactions in which larger molecules are broken into smaller ones. – This includes breakdown of food in GI tract. – Catabolism as part of cellular respiration releases energy, some of which is used to make ATP. – An example is glucose oxidation during glycolysis.

Metabolism: Phosphorylation • ATP is made from ADP by phosphorylation. • There are two major types of phosphorylation: – Substrate-level phosphorylation occurs as a phosphate group is passed from a phosphorylated (energized) molecule to ADP to make ATP. ° This occurs during glycolysis and the Kreb’s cycle. ° This also is how ATP is made in skeletal muscle by the transfer of phosphate from phosphocreatine to ADP. Fig. 25. 4 p. 964

Metabolism: Phosphorylation – Oxidative phosphorlyation occurs in mitochondria under aerobic conditions ° ATP is synthesized by addition of phosphate to ADP using energy of H+ gradient as they pass through the membrane-bound enzyme ATP synthase. ° Most of cell’s ATP is made this way. Fig. 25. 4 p. 964

Glucose Oxidation: Overview Glucose oxidation occurs in three main stages: • Glycolysis • Krebs cycle • Electron transport chain with oxidative phosphorylation See animations of aerobic and anaerobic metabolism - Metabolism Review Fig. 25. 5 p. 965

Glucose Oxidation: Glycolysis • Glycolysis produces pyruvate (a 3 -carbon sugar) as glucose (a 6 -carbon sugar) is broken down. • A net of 2 ATP are made by substrate-level phosphorylation. • Glycolysis occurs in cytoplasm • Glycolysis is an anaerobic process, meaning it does not require oxygen to occur. • Glycolysis is the initial series of reaction for both aerobic and anaerobic catabolism of glucose. Fig. 25. 6, p. 966

Glucose Oxidation: Krebs cycle • The Krebs cycle produces 2 ATP by substrate-level phosphorylation. • The Krebs cycle occurs in the mitochondria. • The Krebs cycle is aerobic (requires oxygen), although it does not use it directly. • The Krebs cycle requires an intermediate step in which pyruvate (from glycolysis) is made into acetyl-Co. A. • The Krebs cycle produces: – reduced energy carriers (NADH+H+; FADH 2) that will be used during the ETC. – CO 2. Fig. 25. 7, p. 968

Glucose Oxidation: Electron Transport and Oxidative Phosphorlyation • Most ATP is made by oxidative phosphorylation • Oxidative phosphorylation occurs in the mitochondria. • Reduced electron carriers (FADH 2 and NADH + H+) produced during the Krebs cycle pass electrons to proteins in the inner mitochondrial membrane, which regenerates the oxidized forms. • Energy associated with the transfer of electrons is used to pump H+ into intermembrane space between the inner and outer mitochondrial membranes. Fig. 25. 8, p. 969

Glucose Oxidation: Electron Transport and Oxidative Phosphorlyation • The energy of the H+ gradient is used by the enzyme ATP synthase to make ATP. • The process is aerobic in that it requires oxygen as final acceptor of the electrons passed through the electron transport chain. – If oxygen is not available, electrons can’t be passed to it and the FADH 2 and NADH + H+ and the Krebs cycle stops as well. – Metabolic water is produced as H+ combine with reduced oxygen. Fig. 25. 9, p. 971 Fig. 25. 8, p. 969

Summary of ATP Production • Glycolysis produces a net of 2 ATP • Krebs cycle produces a net of 2 ATP • Oxidative phosphorylation produces 32 (most cells) or 34 (liver) ATP • Total net ATP produced = 36 or 38 ATP Fig. 25. 10, p. 965

Liver Functions • The liver performs many functions (see also Topic 8). • These functions include: – fat metabolism – protein metabolism – carbohydrate metabolism – storage of various nutrients

Role of the Liver: Fat Metabolism The liver: • Packages fatty acids into forms that can be stored or transported • Stores fat • Synthesizes cholesterol (from which it can synthesize bile salts) • Forms lipoproteins for transport of fats, fatty acids and cholesterol to and from other tissues

Role of the Liver: Lipoproteins The liver makes proteins for lipid transport. • VLDLs (very low density lipoproteins) carry triglycerides from the liver to peripheral tissues (mostly adipose). • LDLs (low density lipoproteins) are cholesterolrich lipoproteins transporting cholesterol from adipose to peripheral tissues for incorporation into plasma membrane. – These may deposit cholesterol in the arteries leading to atherosclerosis (see Topic 3). – LDL cholesterol is sometimes referred to as “bad cholesterol”. Return to Lipid Sources

Role of the Liver: Lipoproteins • HDLs (high density lipoproteins) transport cholesterol from peripheral tissues to the liver for removal. – HDLs pick up cholesterol from tissues and from arterial walls. – HDLs transport cholesterol to the gonads and adrenal cortex where it is used to make steroid hormones. – HDL cholesterol is sometimes called “good cholesterol”.

Role of the Liver: Protein Metabolism The liver: • Synthesizes plasma proteins – including clotting proteins – albumins (osmotic balance) • Synthesizes nonessential amino acids by transamination (transferring amino group (NH 2) from one molecule to another) • Converts ammonia formed by deamination of amino acids into urea, which is less toxic than ammonia. – The carbon skeleton “burned” aerobically as fuel. See Fig. 25. 14, p. 976

Role of the Liver: Carbohydrate Metabolism The liver: • Stores glucose as glycogen, a process called glycogenesis, when blood levels are high. – This is stimulated by insulin. • Releases glucose when blood sugar is low. – This is stimulated by hyperglycemic hormones when blood sugar is low (glucagon) or under stress (GH, epinephrine, cortisol)

Role of the Liver: Carbohydrate Metabolism The liver: • Forms new glucose from noncarbohydrate sources (e. g. , fats or amino acids) in a process called gluconeogenesis under the influence of hyperglycemic hormones. • Breaks down glycogen, a process called glycogenolysis, under the influence of hyperglycemic hormones.

Role of the Liver in Metabolism: Miscellaneous The liver: • Stores vitamins A, D, B 12; • Removes worn-out blood cells from circulation (See Topic 1); • Stores iron from the recycling of worn-out red blood cells; • Degrades hormones; • Detoxifies toxic substances (e. g. , drugs, alcohol). – Prolonged substance abuse or exposure to toxins/toxics damages the liver.

Body Temperature • Normal body temperature is 96 -100 o. F (35. 6 -37. 8 o. C) – Temperature varies with activity and time of day. – Temperature averages around 98. 2 o. F (36. 6 o. C). – Temperature represents a balance between heat production and heat loss • Core temperature refers to the temperature of organs within the skull (cranial cavity), thoracic and abdominal cavities (ventral body cavity). – It is more critical than shell temp. • Shell temperature is the temperature of skin and appendages. • Increased temperature increases chemical reaction rates.

Heat Exchange Mechanisms There are 4 main heat exchange mechanisms: • Radiation is the loss or gain of heat in the form of infrared radiation. We lose heat to the environment but also gain heat from the sun by radiation. • Conduction is the transfer of heat from one object to another by touch (e. g. , touching a warm radiator or a cold cement bench). • Convection is loss to air moving over body surface • Evaporation is loss of body heat to water as it evaporates from the body surface. See Fig. 25

Heat Producing Mechanisms • Basal metabolism is the amount of energy needed to maintain body at rest without activity from digestion. – The higher the metabolic rate, the more heat is produced. – Most heat is generated by activity in the brain, liver, endocrine organs, and heart. – Inactive skeletal muscle accounts for 20 -30%. • Muscular activity includes shivering and uses more ATP so increases metabolism. • Thyroxine and epinephrine stimulate metabolic rates in cells.

Role of the Hypothalamus • Thermoreceptors in the hypothalamus respond to changes in temperature • There are 2 thermoregulatory centers – The heat-loss center ° is activated when core temperature rises above normal range; and ° promotes heat loss to cool the body. – The heat-promoting center ° is activated when core temperature falls below the normal range; and ° promotes production of heat to warm the body.

Keeping the Body Warm Fast-acting Mechanisms • Vasocontriction of cutaneous blood vessels keeps warm blood closer to core (away from surface where heat is lost). • Increased metabolic rate occurs by: – non-shivering thermogenesis, which is increased metabolic rate in response to norepinephrine secreted by sympathetic nervous system; and – Shivering, wherein the brain alternately stimulates small contractions in antagonistic muscles.

Keeping the Body Warm Fast-acting Mechanisms • Behavioral modifications include: – adding more clothing; – rubbing to produce friction; and – increasing activity.

Keeping the Body Warm Slow-acting mechanism • Thyroxine is not very important in adult, but does work in children. • Decreased body temperature in response to seasonal cooling causes: ®the hypothalamus to releases more thyrotropin releasing hormone (TRH), which causes: ®the Adenohypophysis to release more thyroidstimulating hormone (TSH), which causes: ®the Thyroid to enhanced thyroxine release, which ®increases basal metabolic rate (BMR), which ®increases heat production.

Cooling the Body When Core Becomes Too Hot The body can be cooled by: • Vasodilation of cutaneous blood vessels, which brings warm blood to the surface where it loses each by radiation. • Enhanced sweating, which causes evaporative cooling; • Behavioral changes, such as: – decreased activity; and – removing insulating layers of clothing.

Imbalances of Thermoregulation Hyperthermia is excessive body heat. • Heat exhaustion occurs when elevated body temperature causes mental confusion or fainting due to dehydration. • Heat stroke results from loss of ability to regulate body heat due to increased body temperature (a rather nasty form of positive feedback). • Fever is a controlled hyperthermia in response to infection and release of pyrogens (see Topic 6) – Fever may also be caused by cancer, allergic reactions, CNS injuries. – Fever promotes function of white blood cells.

Imbalances of Thermoregulation Hypothermia is decreased body temperature due to excessive loss of body heat • The core temperature may drop so low that CNS function stops (chemical reaction rates decrease to level that does not support life). • Hypothermia lowers oxygen requirement and improves chances of survival during drowning.