Stoelting Chapter 33 Metabolism Flashcards
Flood (Stoelting) → Chapter 33 → METABOLISM
Carbohydrate metabolism
- Carbohydrates comprise a group of compounds that include:
- Sugars and starches
- In addition to carbon, contains hydrogen and oxygen
- 3 disaccharides are important in human biology:
- Sucrose → (1) and fructose
- Lactose → (2) and galactose
- Maltose → (3) and glucose
- Starch
- Found in grains such as wheat, rice, barley, and other plants, including potatoes and corn
- Consists of many units of glucose joined by (4) bonds
- Glucose
- Monosaccharide
- An important energy source for the body and the sole source of energy for the brain
- Glucose levels are tightly controlled in the body by the enzyme (5)
- Ingested sugars and starches are digested in the small intestine to the monosaccharides glucose, fructose, and galactose
- In the liver, glucose can be stored as glycogen or released into the systemic circulation depending on blood glucose concentrations.
- The fetus derives almost all its energy from glucose obtained from maternal circulation
- The neonate is vulnerable to hypoglycemia if feeding is not initiated
- glucose
- glucose
- glucose
- glycosidic
- glucokinase*
Glycogen
- After entering cells, glucose can be used immediately for release of energy to cells or it can serve as a substrate for glycogen synthase
- Glycogen synthase is activated when dephosphorylated by protein phosphatase 1
- Regulated by _______(1) and glucagon
- The liver and skeletal muscles are particularly capable of storing large amounts of glycogen, but all cells can store at least some glucose as glycogen, and the glycogen in these cells is increasingly recognized as having important roles in both health and disease.
- The liver stores glycogen for release of glucose during fasting
- Muscle, which can store as much as 90% of the glucose contained in a meal, catabolizes glycogen during strenuous exercise.
Gluconeogenesis
- Gluconeogenesis is the formation of glucose from _______(2) and the glycerol portion of fat.
- This process occurs when body stores of glycogen decrease below normal levels.
- Gluconeogenesis is stimulated by _______(3).
- Particularly in the liver, simultaneous release of cortisol mobilizes proteins, making them available for breakdown to amino acids used in gluconeogenesis.
- Thyroxine is also capable of increasing the rate of gluconeogenesis.
- insulin
- amino acids
- hypoglycemia
Energy release from Glucose
- Glucose is progressively broken down into two molecules of _______(1), both of which can enter the citric acid cycle, and the resulting energy is used to form ATP.
- The most important means by which energy is released from the glucose molecule is by _______(2) and the subsequent oxidation of the end products of glycolysis.
- Glycolysis is the splitting of the glucose molecule into two molecules of pyruvate, which enter the mitochondria where the pyruvate is converted to acetyl-coenzyme A (acetyl-CoA), which enters the citric acid cycle and is converted to carbon dioxide and hydrogen ions with the formation of ATP (oxidative phosphorylation).
Anaerobic glycolysis
- In the absence of adequate amounts of oxygen, a small amount of energy can be released by anaerobic glycolysis, also known as fermentation in plants, fungi, and bacteria because conversion of glucose to pyruvate does not require oxygen.
- Glucose is the only nutrient that can serve as a substrate for the formation of ATP without _______(3).
- This release of energy to cells can be lifesaving for a few minutes should oxygen become unavailable
- During anaerobic glycolysis, most pyruvic acid is converted to _______(4), which diffuses rapidly out of cells into extracellular fluid.
- When oxygen is again available, lactic acid can be reconverted to glucose, predominantly in the liver.
- Severe liver disease may interfere with the ability of the liver to convert lactic acid to glucose, leading to metabolic _______(5).
- pyruvate
- glycolysis
- oxygen
- lactic acid
- acidosis
Lipid metabolism
- Lipids are hydrophobic organic molecules that include _______(1), sterols, fat-soluble vitamins, triglycerides (fats), phospholipids, and other substances.
- Lipids contain a high amount of potential energy but are also important as structural components of cell membranes, in signaling pathways, and as precursors to a number of cytokines.
- Twenty carbon chain fatty acids are stored in the second position of phospholipids and, when released, serve as substrates for a group of very important cytokines, the eicosanoids
- Eicosanoids → Prostaglandins, Thromboxanes, and Leukotrienes.
- Arachidonic acid, a 20–carbon chain of fatty acid, is a precursor for prostaglandins and thromboxanes of the two series and leukotrienes of the four series, whereas eicosapentaenoic acid, is a precursor for prostaglandins and thromboxanes of the three series and leukotrienes of the five series.
- A glycerol stem to which three fatty acid molecules are bound is known as a _______(2)
- A triglyceride molecule to which one of the terminal fatty acids is replaced with a phosphate ion is known as a phospholipid
- Phospholipids are the building blocks of cell membranes, form myelin, and, because of their unique structure and functions, are being used in other scientific applications.
- Triglycerides, after absorption from the gastrointestinal tract, are transported in the lymph and then, by way of the thoracic duct, into the circulation in droplets known as _______(3).
- Chylomicrons are rapidly removed from the circulation and stored as they pass through capillaries of adipose tissue and skeletal muscles.
- Triglycerides are used in the body mainly to provide energy for metabolic processes similar to those fueled by carbohydrates.
- waxes
- triglyceride
- chylomicrons
Lipid metabolism
- Cholesterol does not contain fatty acids, but it is a lipid because it is composed of carbon and hydrogen, not as aliphatic chains of carbon but with four rings made up of carbon
- _______(1) of cholesterol is produced in the liver in a synthetic process that involves 37 steps; the other _______(2) of cholesterol is ingested in the diet.
- Molecules that are part lipid and part protein, lipoproteins, are also synthesized primarily in the liver
- The presumed function of lipoproteins is to provide a mechanism of transport for lipids throughout the body
- All the cholesterol in plasma is found in lipoprotein complexes, with low density lipoproteins (LDLs) representing the major cholesterol component in plasma.
- These LDLs provide cholesterol to tissues, where it is an essential component of cell membranes and is used in the synthesis of corticosteroids and sex hormones.
- Drugs that selectively inhibit hydroxymethylglutaryl CoA are known as _______(3).
- Statins effectively lower plasma LDL cholesterol concentrations and may provide protection against acute cardiac events, perhaps reflecting antiinflammatory effects.
- In addition, statins lower plasma triglyceride concentrations and modestly _______(4) high-density lipoprotein cholesterol concentrations.
- In contrast to glycogen, large amounts of lipids can be stored in adipose tissue and in the liver.
- A major function of adipose tissue is to store triglycerides until they are needed for energy.
- _______(5) and norepinephrine activate triglyceride lipase in cells, leading to mobilization of fatty acids.
- 75%
- 25%
- statins
- increase
- Epinephrine
Protein metabolism
- Approximately 75% of the solid constituents of the body are proteins
- All proteins are composed of the same 20 amino acids, and several of these must be supplied in the diet because they cannot be formed endogenously (essential amino acids)
- Protein Metabolism
- The process begins in the stomach where pepsinogen is converted to pepsin in the acidic pH.
- The process continues in the small intestine into which the pancreas secretes trypsin and chymotrypsin and carboxypeptidases.
- Table 33.4 → AMINO ACIDS| ESSENTIAL AMINO ACIDS | NONESSENTIAL AMINO ACIDS |
|———————-|————————-|
| _______(1) | Alanine |
| Histidine | Asparagine |
| Isoleucine | Aspartic Acid |
| Leucine | Cysteine |
| Lysine | Glutamic Acid |
| Methionine | Glutamine |
| Phenylalanine | Glycine |
| Threonine | Proline |
| Tryptophan | Serine |
| Valine | Tyrosine |
- Arginine
Protein metabolism
- Nonessential amino acids can be synthesized from the appropriate α-keto acid.
- Each amino acid has an _______(1) group (COOH) and an amino group (NH3R)
- Amino acids are relatively strong acids and exist in the blood principally in the ionized form.
- In the normal person, however, loss of amino acids in the urine each day is negligible.
- Failure to transport amino acids into the blood is indicative of renal disease.
Storage of Amino Acids
- Immediately after entry into cells, amino acids are conjugated under the influence of intracellular enzymes into cellular proteins.
- Tissues can synthesize new proteins from amino acids in blood.
- This response is especially apparent in relation to protein synthesis in cancer cells.
- Cancer cells are prolific users of amino acids, and, simultaneously, the proteins of other tissues become markedly depleted, contributing to cachexia
Plasma Proteins: Albumin and Coagulation Factors
- Plasma proteins are represented by
- (1) _______(2) → which provides colloid osmotic pressure
- (2) _______(3) → necessary for innate and acquired immunity
- (3) _______(4) → which polymerizes into long fibrin threads during coagulation of blood.
- Essentially, all plasma albumin and fibrinogen, and 60% to 80% of the globulins are formed in the liver
- The rate of plasma protein formation by the liver can be greatly increased in situations, such as severe burns, in which there is loss of large amounts of fluid and protein.
- Even during starvation or severe debilitating diseases, the ratio of total tissue proteins to total plasma proteins in the body remains relatively constant at approximately _______(5).
- Albumin is the most abundant plasma protein and is principally responsible for maintaining plasma osmotic pressure and as a transporter of plasma-bound substances, often including exogenously administered drugs.
Within hours of the onset of a critical illness or injury, albumin levels decrease by as much as 33% due to changes in the distribution between intravascular and extravascular compartments and rates of synthesis and degradation of protein.
- acidic carboxyl
- albumin
- globulins
- fibrinogen
- 33:1
Use of Protein for Energy
- Once cells contain a maximum amount of amino acids, any additional amino acids are deaminated (oxidative deamination) to keto acids that can enter the citric acid cycle to become ATP or the keto acids are released into the bloodstream, taken up by adipocytes, and converted to and stored as triglycerides.
- The conversion of amino acids to glucose or glycogen is _______(1).
- The conversion of amino acids into fatty acids is _______(2).
- Growth hormone and insulin promote the synthetic rate of cellular proteins, possibly by facilitating the transfer of amino acids into cells.
- Glucocorticoids increase the breakdown rate of extrahepatic proteins, thereby making increased amino acids available to the liver.
- Testosterone increases protein deposition in tissues, particularly the contractile proteins of skeletal muscles.
Obesity and Pharmacologic Treatment
- TABLE 33.5 → DRUGS COMMONLY ASSOCIATED WITH WEIGHT GAIN
CLASSIFICATION | DRUG | ALTERNATIVE DRUG |
|——————|——————————–|—————————————-|
| Antidepressants | Tricyclic antidepressants | Selective serotonin reuptake inhibitors|
| | Monoamine oxidase inhibitors | |
| Antidiabetics | Insulin | Metformin |
| | Sulfonylureas | Acarbose |
| | Thiazolidinedione | |
| Antiepileptics | Gabapentin | Lamotrigine |
| | Valproic acid | Topiramate |
| Antipsychotics | Clozapine | Haloperidol |
| Steroids | Glucocorticoids | |
- gluconeogenesis
- ketogenesis
Obesity and Pharmacologic Treatment
- Obesity is the most common and costly nutritional problem in the United States.
- Based on body mass index (BMI) (weight in kilograms divided by the square of the height in meters), 67% of adult males and 62% of adult females are overweight
- The prevalence of obesity peaks between 60 and 69 years of age, but greater numbers of children are increasingly found to be obese for their age
- Central adiposity, that is, increased _______(1), correlates with cardiometabolic risk, independent of the BMI.
- In this regard, an overweight person with a predominant abdominal fat distribution (common in elderly males with impaired glucose tolerance) may be at high risk for these diseases even if not considered obese by BMI criteria.
- The increased risk for morbidity and mortality extend beyond measurements of BMI and fat distribution, as reflected by the diagnosis of metabolic syndrome, which is present if a patient has three of the following five risk factors:
- Increased waist circumference (as described previously),
- Low levels of high-density lipoprotein cholesterol
- Increased triglycerides
- Hypertension
- Glucose intolerance
- TABLE 33.6 → CRITERIA FOR DIAGNOSIS OF METABOLIC SYNDROME
- ANY 3 OF THE FOLLOWING:
|———————————–|————————————-|
| Increased Waist circumference | Males > 102 cm (40 in) |
| | Females > 88 cm (35 in) |
| Blood glucose concentration | > 110 mg/dL |
| (fasting) | |
| Increased systemic blood pressure | Systolic > 130 mmHg |
| | Diastolic > 85 mmHg |
| High Serum triglyceride | > 150 mg/dL |
| concentration | |
| Low levels of high-density | Males < 40 mg/dL |
| lipoprotein cholesterol | Females < 50 mg/dL |
| concentration | |
- waist circumference
Pharmacologic Treatment
- Phentermine
- A sympathomimetic amine, is an appetite _______(1) that is used for short-term (a few weeks) therapy intended to induce weight loss.
- It is the most commonly prescribed weight loss drug in the United States
- Combination drug with _______(2)
- Orlistat
- Inhibits _______(3) in the gastrointestinal lumen, thus antagonizing triglyceride hydrolysis and decreasing fat absorption by about 30%.
- Gastrointestinal side effects (abdominal discomfort, flatus, fecal urgency) reflecting the increased fat content in stool are dose limiting and occur in the majority of patients treated with orlistat
- Lorcaserin
- A selective 5-HT2C agonist, which activates proopiomelanocortin production and promotes weight loss through satiety
- suppressant
- topiramate
- lipases
