Chapter 24: Nutrition, and Metabolism.

Question 1

Nutrition:

Answer 1

o Nutrient: a substance in food that promotes normal growth, maintenance, and repair.
o Major nutrients: Carbohydrates, lipids (fats), and proteins.
o Other nutrients: Vitamins and minerals (and even water).

Question 2

Carbohydrates:

Answer 2

o Dietary sources:
o Starch (complex carbohydrates produced by plants) in potatoes, grains and vegetables.
o Sugars (simple = crystalline carbohyrate = sucrose, lactose, fructose) in fruits, sugarcane, sugar beets, honey and milk.
o Insoluble fiber: whole grains, wheat bran, cellulose in vegetables provide roughage.
o Soluble fiber: oats, barley, pectin in apples and citrus fruits; reduces blood cholesterol levels.
o Uses:
o Glucose is (a monosaccharide = simple carbohydrate) is the fuel used by cells to make ATP.
o Glucose is only energy source for Neurons and RBCs.
o Carbs are stored as glycogen primarily in the liver and muscle cells (all cells can store a limited amount of glycogen).
o Excess carbs can be converted to TG (Fat).
o Dietary requirements:
o Minimum 100 g/day to maintain adequate blood glucose levels…but not known for sure.
o Recommended minimum 130 g/day.
o Recommended intake: 45–65% of total calorie intake; mostly complex carbohydrates.

Question 3

Lipids:

Answer 3

o Dietary sources
o Triglycerides (fats):
o Saturated fatty acids in meat, dairy foods (cheese, cream, butter and tropical oils = contributes to cardio disease.
o Unsaturated fatty acids in seeds, nuts, canola oil, olive oil, most vegetable oils, avocados, rapeseed.
o Cholesterol fat that is from animal foods (egg yolk, meats, organ meats, shellfish, and milk products)
o Essential fatty acids (essential because the body can’t manufacture this stuff).
o Linoleic and linolenic acid, found in most vegetable oils.
o Must be ingested.
o Essential uses of lipids in the body:
o Help absorb fat-soluble vitamins.
o Major fuel of hepatocytes and skeletal muscle.
o Phospholipids = diglyceride + phosphate are essential in myelin sheaths and all cell membranes.
o Glycoproteins and glycolipids are part of cell membranes.
o Functions of fatty deposits (adipose tissue):
o Protective cushions around body organs.
o Temperature regulation = Insulating layer.
o Concentrated source of energy, oxidized (catabolized) to make ATP.
o Helps body absorb fat-soluble vitamins.
o Slows gastric emptying = satiety.
o Regulatory molecules (hormone like) that are derived from fatty acids are called prostaglandins and involved in:
o Smooth muscle contraction (thromboxanes, prostacyclins).
o Control of blood pressure.
o Inflammation.
o Functions of cholesterol: (not used as an energy source), made in the liver, cells of the small intestine.
o Stabilizes (or makes up) plasma membranes.
o Precursor of bile salts and steroid hormones.
o Precursor to Vitamin D.
o Nerve mylenation.
o Dietary requirements suggested by the American Heart Association:
o Fats should represent 30% or less of total caloric intake.
o Saturated fats should be limited to 10% or less of total fat intake.
o Daily cholesterol intake should be no more than 300 mg.

Question 4

Proteins:

Answer 4

o Dietary sources:
o Eggs, milk, fish, and most meats contain complete proteins (all amino acids present to sustain human life).
o Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids).
o Legumes and cereals together contain all essential amino acids (nine altogether).
o Essential Amino Acids are amino acids that the body cannot manufacture on its own, so they must be obtained through the diet = nine essential amino acids altogether.
o Uses:
o Structural materials: to make keratin, collagen, elastin, muscle proteins.
o Functional molecules = to make enzymes and some hormones.
o The use of amino acids in the body entails:
o All-or-none rule: All amino acids needed must be present for protein synthesis to occur.
o Adequacy of caloric intake: Protein will be used as fuel if there is insufficient carbohydrate or fat available.
o Need enough protein to keep us in nitrogen balance.
o Need nitrogen of amino acids to make nucleic acids, creatine, hemoglobin, myoglobin + other proteins.
o Nitrogen balance: = nitrogen input minus nitrogen output. In healthy persons the rate of protein synthesis equals the rate of breakdown and loss.
o Positive if protein synthesis (input) exceeds breakdown (normal in children and tissue repair).
o Negative if protein breakdown exceeds synthesis (e.g., stress, burns, infection, or injury, starvation) = NH3 release in the form of urea in liver.
o Hormonal controls: Anabolic hormones (pituitary growth hormone, sex hormones) causes protein synthesis to accelerate.
o Dietary requirements: Rule of thumb: daily intake of 0.8 g per kg body weight

Question 5

Vitamins:

Answer 5

o Organic compounds.
o Crucial in helping the body use nutrients.
o Most function as coenzymes.
o Vitamins D (skin,liver), some B (intestine), and K (intestine) are synthesized in the body, the rest need to be taken in orally.
o Two types, based on solubility:
o 1) Water-soluble vitamins:
o B complex and C are absorbed with water.
o B12 absorption requires intrinsic factor.
o Not stored in the body.
o 2) Fat-soluble vitamins:
o A, D, E, and K are absorbed with lipid digestion products (fatty chyme).
o Stored in the body, except for vitamin K.
o Vitamins A, C, and E act as antioxidants.
o Free radicals = unpaired electrons are produced as a result of oxidation caused by oxygen and can lead to cell damage or cell death).

Question 6

Minerals:

Answer 6

o Seven required in moderate amounts: Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium (helps in Ca++ absorption).
o Others required in trace amounts.
o Work with nutrients to ensure proper body functioning = bone and teeth, neuron conductivity, heart rythym, acid-base, enzyme formation).
o Uptake and excretion must be balanced to prevent toxic overload.

Question 7

Metabolism:

Answer 7

o Metabolism: the sum of all the biochemical reactions that take place in the body.
o Two types of reactions:
o Anabolism: synthesis of large or complex molecules from small ones.
o Catabolism: breakdown of complex molecules to simpler ones.

Question 8

Stages of Metabolism:

Answer 8

o Processing of nutrients:
o 1) Digestion, absorption and transport to tissues.
o 2) Cellular processing (in cytoplasm). Anabolism or synthesis of lipids, proteins, and glycogen, or Catabolism (glycolysis) into intermediates pyruvic acid and acetyl CoA.
o 3) Oxidative (mitochondrial) breakdown of glucose into CO2, water, and ATP = catabolism.

Question 9

ATP Synthesis:

Answer 9

o Two mechanisms for ATP Synthesis:
o Substrate-level phosphorylation (glycolysis and Kreb’s cycle).
o Oxidative phosphorylation (yields the most ATP).

Question 10

Glycolysis:

Answer 10

o	Phosphorylation is where high-energy phosphate groups directly transferred to ADP to make ATP = substrate-level phosphorylation (quick energy and occurs in the cytoplasm of the cell). 
o	Glycolysis (catabolism of glucose): 
o	Breakdown of glucose when it enters the cell = an anaerobic process that occurs in the cytoplasm.  
o	Yields 2 ATP plus 2 pyruvic acid molecules.

Question 11

Kreb’s Cycle:

Answer 11

o Occurs in the mitochondria of the cell.
o Pyruvic Acid produced by glycolysis and also fat breakdown is converted through oxidation (decarboxylation) to form acetyl CoA.
o Acetyl CoA enters the Krebs Cycle (series of many chemical reactions = oxidation / reductions where CO2 and 2 ATP are made.

Question 12

Oxidative Phosphorylation:

Answer 12

o Makes most of the ATP (= 28) during cellular respiration by pushing H+ (protons) across membranes within the mitochondria through the electron transport chain.
o H+ (protons) then come back across the mitochondrial membranes due to a “proton gradient” which creates electrical current or much energy which is used to attach many PO4 groups to ADP to make many ATP.
o H20 is produced as well.

Question 13

Glycogenesis and Glycogenolysis:

Answer 13

o Glycogenesis:
o Glycogen formation when glucose supplies exceed need for ATP synthesis.
o Occurs mostly in liver and skeletal muscle.
o Glycogenolysis:
o Glycogen breakdown in response to low blood glucose (ATP = body’s fuel).

Question 14

Gluconeogenesis:

Answer 14

o Glucose formation from noncarbohydrate (glycerol and amino acid) molecules.
o Occurs mainly in the liver.
o Protects against the damaging effects of hypoglycemia.

Question 15

Lipid Metabolism:

Answer 15

o Fat catabolism yields 9 kcal per gram (vs 4 kcal per gram of carbohydrate or protein).
o Most TG from digestion are transported as chylomicrons in blood (chylomicrons are produced by intestinal cells).
o Lipolysis in liver: Triglycerides (TG) turn into Fatty acids + glycerol.
o Beta oxidation: breaks down fatty acids into 2-carbon fragments to form acetyl CoA that can enter the Kreb’s cycle.

Question 16

Lipogenesis:

Making of TG

Answer 16

o Triglyceride synthesis occurs when cellular ATP and glucose levels are high = stimulated by insulin.
o Glucose becomes pyruvic acid through glycolysis.
o Pyruvic acid is converted into Acetyl-CoA.
o Acetyl-CoA molecules join together to form fatty acids.
o Glycerol forms as a result of high glucose and ATP present.
o Glycerol + fatty Acids turn into TG.

Question 17

Lipolysis:

Breakdown of TG

Answer 17

o TG (Fat) turn into Fatty acids + glycerol.
o Beta oxidation breaks down FA to acetyl CoA.
o Glycolysis of glycerol leads to formation of acetyl CoA.
o Oxaloacetic acid is necessary for complete oxidation of fat in the Krebs cycle (combines with acetyl CoA in Krebs cycle).
o If not enough carbs (starvation), oxaloacetic acid is converted to glucose to feed the brain.
o Without sufficient oxaloacetic acid, Krebs Cycle stops and acetyl CoA accumulates and is then converted by ketogenesis in the liver into ketone bodies (ketones = organic acids) and released into blood which leads to metabolic acidosis leads to blood pH drops fast (depresses the nervous system leads to coma leads to death).

Question 18

Catabolic-Anabolic Steady State:

Answer 18

o A dynamic state in which:
o Organic molecules (except DNA) are continuously broken down and rebuilt.
o Organs have different fuel preferences.

Question 19

Metabolism in Absorptive (Fed) State:

Answer 19

o Absorptive state = “fed” state = first few hours after eating = pack-it-away.
o General facts:
o Building processes (anabolism) exceeds the breaking down processes (catabolism):
• Storage of fuel is emphasized.
• Synthesis of important body compounds occurs (glycogen, TG, important proteins).
o Anabolic processes require ATP.
o Glucose is the major energy fuel to make ATP in the Fed state (glycolysis/Kreb’s Cycle).

Question 20

Protein Metabolism in Fed State:

Answer 20

o The liver receives dietary protein in the form of amino acids, dipeptides, tripeptides
o The liver has choices:
o 20% of amino acids are used to make protein = some proteins the liver uses (e.g. carnitine = escorts fatty acids into mitochondria).
o Plasma proteins in the blood.
o 23% is not taken up by the hepatocytes but sent on to other body cells.
o 57% are deaminated, forming alpha-keto acids, which are very versatile molecules.

Question 21

Deamination of Amino Acids:

Answer 21

o The deaminated amino groups (NH2) turn into toxic ammonia (NH3) à the liver converts NH3 to urea.
o The resulting alpha-keto acids (e.g. pyruvic acid) are versatile:
o Can enter glycolysis = used as fuel (ATP).
o Can enter the Kreb’s cycle = used for fuel (ATP).
o Can be converted to acetyl-CoA and used to make FA (TG) or cholesterol.
o Can be converted to Glucose.
o Can be used to make amino acids.

Question 22

What Happens to Carbs in Your Meal (Fed State):

Answer 22

o 50% is oxidized by your body cells to make ATP via glycolysis/Kreb’s cycle/oxidative phosphorylation.
o 40% is converted to TG and stored either inside body cells or in the TG of adipose cells.
o 10% is stored as glycogen in liver and in muscle tissues.
o 100 grams stored in liver.
o 325 grams stored in muscle.

Question 23

Lipid Metabolism in Fed State:

Answer 23

o Lipids are sent to liver as chylomicrons made by intestinal cells.
o As chylomicrons travel in the blood capillaries, they are broken down by an enzyme called lipoprotein lipase: releases fatty acids to adipose cells where TG is made.
o The liver easily makes TG and transports it to other body cells via VLDLs (very low density lipoproteins).

Question 24

Lipoproteins:

Answer 24

o Lipoproteins are transport vehicles for fatty substances that otherwise are not soluble in blood.
o Lipids do not dissolve in water (plasma)….so lipoproteins carry or escort lipids in blood plasma.
o Lipoproteins carry TG, cholesterol, phospholipids, and some protein.
o Each type of lipoprotein has a different structure and a very specific function!
o Chylomicrons.
o VLDL = transport fat from liver to adipose cells.
o LDL = bad cholesterol (deposits fats into cells).
o HDL = good cholesterol (sends fat back to liver).

Question 25

Functions of Lipoproteins:

Answer 25

o Chylomicrons deliver absorbed fat to adipose cells and liver from the small intestine.
o VLDL’s deliver fat the liver has made to other body cells.
o LDL’s deliver cholesterol to body cells: if LDL is high, cholesterol will be delivered to smooth muscle of blood vessels (less is better).
o HDL’s pick up excess cholesterol from body cells and return it to the liver (the more the better).

Question 26

Non-Dietary Factors Affecting Cholesterol:

Answer 26

o Stress, cigarette smoking, and coffee lower HDL levels.

o Aerobic exercise and estrogen increase HDL levels and decrease LDL levels.

Question 27

Hormones in the Fed State:

Answer 27

o	Primary hormone in the FED state is INSULIN.
o	Released by beta cells of pancreas.
o	Stimulus for release of insulin:
o	Vagus nerve.
o	Food hitting duodenum (incretins).
o	Hyperglycemia (sensed by the beta cells).
•	Blood glucose > 100 mg/dL.
o	Elevated amino acids in the blood.

Question 28

Actions of Insulin:

Answer 28

o Insulin targets most body cells.
o Insulin is an ANABOLIC HORMONE (helps cells “make stuff”).
o Drives glucose into cells.
o Drives amino acids into cells.
o Drives F.A. into cells.
o Insulin promotes many anabolic pathways:
o Glycogenesis (synthesis of glycogen).
o Protein synthesis.
o Lipogenesis (synthesis of TG).
o Insulin decreases many catabolic pathways, including lipolysis.
o Insulin Promotes Glucose entry into cells.
o Insulin interacts with a receptor on cell membrane of target tissues (does not enter the body cell).
o Activates a SIGNAL CASCADE that results in the synthesis of glucose transporters (“taxi’s” that pull glucose into the cell).
o Several types of glucose transporters (GLUT1, GLUT2, GLUT3, GLUT4, etc.).

Question 29

Disorders of Fed State:

Answer 29

o	Diabetes Mellitus:
o	Type I DM
o	Usual onset is in childhood.
o	Autoimmune disorder… heredity component.
o	Beta cells of pancreas are destroyed.
o	Insulin levels are non-existent.
o	Type II DM
o	Insulin-resistant diabetes.
o	Onset in adults… now being seen in kids!
o	Several causes possible… at least 10 genes implicated!!!
o	Associated with obesity.
o	Obesity

Question 30

Diabetes Mellitus:

Answer 30

o Glucose is unavailable to most body cells (exceptions: brain cells, liver, RBC).
o Blood glucose cannot get into cell and stays very high = hyperglycemia.
o Body tries to compensate by breaking down body fat from cells to use to make ATP.
o If this gets out of hand, then too many 2-carbon fragments (acetyl-CoA), ketones (e.g. acetone), metabolic acidosis.

Question 31

Diabetic Symptoms:

Answer 31

o	Type I DM:
o	Polyuria (excessive urination).
o	Polydipsia (excessive thirst).
o	Polyphagia (excessive hunger/eating).
o	Type II DM:
o	Fatigue.
o	High blood insulin levels (until burnout).
o	Weight gain.
o	Occasionally polyuria & polydipsia.

Question 32

Chronic Problems Associated with Hyperglycemia (Uncontrolled DM):

Answer 32

o Peripheral neuropathy (pain and ↓ sensation):
o Poor wound healing:
o Gangrene
o Amputation of extremities
o Microvascular disease:
o Retinal blood vessel disease leads to blindness.
o Kidney disease leads to renal failure.
o Macrovascular disease:
o Atherosclerosis leads to CAD leads to MI.
o Atherosclerosis leads to carotid arteries leads to CVA.

Question 33

Events Making Glucose Available to Blood:

Answer 33

o Glycogenolysis:
o In Liver is a rapid responder and can maintain sugar levels for about 4 hours during the postabsorptive state.
o In Skeletal muscle has as much stored glycogen as the liver (must first must be converted to pyruvic acid and made to glucose in liver).
o Gluconeogenesis:
o Liver (glucose made from amino acids + glycerol).
o Lipolysis by adipose tissue and liver cells (only glycerol portion of TG can be converted to glucose in the liver).
o F.A. can NOT be converted to glucose!
o Catabolism of cellular proteins (muscle).

Question 34

Events that Spare Glucose:

Answer 34

o Lipolysis: TG leads to glycerol + F.A.
o F.A. can be used by most cells to make ATP which leaves glucose for the brain.
o Skeletal muscle cells switch to burning an even greater amount of F.A. to make ATP.
o Ketosis: Liver oxidizes its stored fats to KETONES and releases ketones into blood for cells to use to make ATP.

Question 35

Neuronal and Hormonal Controls in the Post-Absorptive State:

Answer 35

o The major stimulus for regulatory mechanisms is LOW blood glucose.
o Hypothalamus detects low glucose and increases ANS sympathetic output.
o Stimulates adrenal medulla to release Ep and NE.
o Stimulates adipose tissue to mobilize F.A.
o Dropping blood glucose also stimulates ALPHA CELLS of pancreas to release GLUCAGON.
o Glucagon targets primarily the liver & adipose tissue.
o Glucagon: Puts the brakes on insulin, insulin antagonist.
o Targets liver cells:
o Promotes glycogenolysis.
o Stimulates gluconeogenesis.
o Targets adipose tissue:
o Stimulates lipolysis of TG leads to F.A. + glycerol.
o Glycerol travels back to liver for conversion to glucose.

Question 36

Cortisol (Hydrocortisone):

Answer 36

o Released from the adrenal cortex when stressed and a “fight or flight” hormone.
o Suppresses immune system and increased abdominal fat is chronic stress.
o Targets liver cells:
o Stimulates gluconeogenesis.
o Targets skeletal muscle cells:
o Stimulates protein catabolism resulting amino acids are sent on to liver for gluconeogenesis.
o Targets adipose cells:
o Stimulates lipolysis.

Question 37

Thermoregulation:

Answer 37

o	Hypothalamus = thermostat.
o	Hypothalamic heat-losing center:
o	Receives signals from peripheral thermoreceptors.
o	Affected by cytokinesHypothalamic heat-losing center.
o	Cutaneous vasodilation.
o	Sweating.
o	Hypothalamic heat-promoting center:
o	Cutaneous vasoconstriction.
o	Shivering thermogenesis.
o	Non-shivering thermogenesis.
o	Thyroid hormone.
o	Sympathetic nervous system.

Question 38

Metabolic Role of the Liver:

Answer 38

o Hepatocytes:
o Process nearly every class of nutrient.
o Play a major role in regulating plasma cholesterol levels.
o Store vitamins and minerals.
o Metabolize alcohol, drugs, hormones, and bilirubin.