1. Nutrition and Metabolism
Chapter 18
Nutrition and Metabolism

2. Objectives Define and contrast catabolism and anabolism
Describe the metabolic roles of carbohydrates, fats, proteins, vitamins, and minerals
Define basic metabolic rate and list some factors that affect it

3. Objectives
Describe three disorders associated with eating or metabolism
Discuss the physiological mechanisms that regulate body temperature

4. Definitions
Nutrition—food, vitamins, and minerals that are ingested and assimilated into the body
Metabolism—process of using food molecules as energy sources and as building blocks for our own molecules
The two aspects of metabolism are catabolism and anabolism.

5. Definitions
Catabolism—process that breaks food molecules down, releasing their stored energy; oxygen used in catabolism
Anabolism—process that builds food molecules into complex chemical compounds
How do nutrition and assimilation relate to metabolism? Foods have to be ingested and assimilated into the bloodstream to be available to the cells for metabolism.

6. Metabolic Function of the Liver
Processes blood immediately after it leaves the gastrointestinal tract
Helps maintain normal blood glucose level
Site of protein and fat metabolism
Removes toxins from the blood
Synthesizes several kinds of protein compounds
What is the significance of the hepatic portal vein? The hepatic portal vein delivers blood directly from the gastrointestinal tract to the liver (see Figure 14-9).
Why is it desirable for the liver to have the first access to blood that comes directly from the gastrointestinal tract? Blood that has just absorbed nutrients and other substances need to be processed by the liver before being distributed throughout the body. Thus excess nutrients and vitamins can be stored and toxins can be removed from the bloodstream.
What is the role of the liver in carbohydrate, fat, and protein metabolism? The liver plays a major role in the digestion of all three major nutrients. Liver cells help maintain a normal blood glucose concentration by carrying on complex and essential chemical reactions. Liver cells also carry out the first steps of protein and fat metabolism and synthesize several kinds of protein compounds.
What are the functions of prothrombin, fibrinogen, and albumin? These are proteins synthesized by the liver that function as blood proteins or plasma proteins. Prothrombin and fibrinogen play essential parts in blood clotting and albumin helps maintain normal blood volume.
What role does the liver play in drug metabolism? Liver cells detoxify various poisonous substances such as drugs.

7. Nutrient Metabolism Carbohydrate metabolism
Carbohydrates are the preferred energy food of the body
Three series of chemical reactions that occur in a precise sequence make up the process of glucose metabolism
Glycolysis—occurs in cytoplasm of the cell
Anaerobic process (uses no oxygen)
Changes glucose to pyruvic acid, which is then converted into acetyl CoA
Yields small amount of energy (transferred to ATP)
Carbohydrates are the body’s preferred source of energy.
Glucose catabolism occurs in a series of three chemical reactions: glycolysis, citric acid cycle, and electron transfer.
What occurs in each chemical reaction of glucose catabolism? Glycolysis (which takes place in the cell and is anaerobic), citric acid cycle, and electron transport system (both take place in the mitochondria and need oxygen). This is the precise sequence of glucose catabolism.
What are anaerobic and aerobic processes? How do they apply to glycolysis? Anaerobic means without oxygen; the process of glycolysis occurs without oxygen. Aerobic processes do need oxygen; both the citric acid cycle and electron transport processes require oxygen.

8. Nutrient Metabolism
Citric acid (Krebs) cycle—occurs in the mitochondria
Aerobic process (requires oxygen)
Changes acetyl CoA to carbon dioxide
Yields small amount of energy
Most energy leaving the citric acid cycle is in the form of high-energy electrons)
Electron transport system—occurs in the mitochondria
Transfers energy from high-energy electrons (from citric acid cycle) to ATP molecules
ATP serves as direct source of energy for cells

9. ATP. A, The structure of ATP
ATP. A, The structure of ATP. A single adenosine group (A) has three attached phosphate groups (P).The high-energy bonds between the phosphate groups can release chemical energy to do cellular work. B, ATP energy cycle. ATP stores energy in its last high-energy phosphate bond. When that bond is later broken, energy is released to do cellular work. The ADP and phosphate groups that result can be resynthesized into ATP, capturing additional energy from nutrient catabolism.

10. Nutrient Metabolism Carbohydrate metabolism (cont’d)
Energy transferred to ATP differs from energy in food molecules
Not stored; released almost instantly
Can be used directly to do cellular work
Carbohydrates primarily catabolized for energy, but small amounts anabolized by glycogenesis (series of chemical reactions that changes glucose to glycogen—occurs mainly in liver cells where glycogen is stored)

11. Metabolism of glucose. Glucose is liberated from glycogen stores in the body and is converted into pyruvic acid. Acetyl CoA is formed from the pyruvic acid generated during glycolysis and enters the citric acid cycle where high-energy electrons are released. These high-energy electrons enter the electron transport system where they are transferred to molecules of ATP.

12. Nutrient Metabolism Carbohydrate metabolism (cont’d)
Blood glucose (imprecisely, blood sugar)—amount of glucose in blood
Normally stays between about 80 and 110 mg per 100 mL of blood during fasting
Insulin accelerates the movement of glucose out of the blood into cells, therefore decreases blood glucose and increases glucose catabolism
How are blood glucose levels measured? Blood glucose is measured as mg per ml of blood. About 80 to 110 mg in 100 mg of blood is usual.
Describe hyperglycemia and hypoglycemia. Hyperglycemia means elevated blood glucose – above normal levels. Hypoglycemia means lowered blood glucose – below normal levels.
Discuss medical conditions in which elevated blood glucose levels are found. Absence or a low level of insulin will elevate the blood glucose level. Problems with endocrine glands that secrete other hormones that will elevate blood glucose (such as growth hormone, hydrocortisone, epinephrine, and glucagon) will also elevate blood glucose.

13. Nutrient Metabolism Fat metabolism Protein metabolism
Fats are primarily an energy food
Converted to glucose by catabolism
Excess fat is anabolized to form adipose tissue
Protein metabolism
Proteins are catabolized for energy only after carbohydrate and fat stores are depleted
Gluconeogenesis breaks apart amino acids to convert them to glucose
ATP is the powerhouse molecule.
If ATP’s components are no longer needed for energy requirements, they can be resynthesized later into ATP by adding energy from carbohydrate catabolism.
If insufficient carbohydrate is available, fats will be broken down to yield energy.
In what situations are proteins catabolized? If no other source of energy is available to the body, proteins can be catabolized to release energy. This may occur in the case of starvation when fat supplies are low. When vital proteins in the muscles and nerves are catabolized, death may occur quickly (as in anorexia nervosa).
What types of cellular processes are fueled by energy from ATP? ATP is one of the most important biological compounds to serve as a direct source of energy for cellular work. Energy from food molecules must be changed to ATP to do cellular work. New ATP is being constantly made and used for all cellular processes.

14. Catabolism of nutrients
Catabolism of nutrients. Fats, carbohydrates, and proteins can be converted to products that enter the citric acid cycle to yield energy.

15. Vitamins and Minerals
Vitamins—organic molecules that are needed in small amounts for normal metabolism (Table 18-2)
Avitaminosis—deficiency of a vitamin
Can lead to severe metabolic problems
Avitaminosis C can lead to scurvy
Hypervitaminosis—excess of a vitamin
Can be just as serious as avitaminosis
May be chronic or acute
What functions do vitamins perform? Most vitamins attach to enzymes or coenzymes to help them work properly. Many enzymes are totally useless without the appropriate vitamins to activate them. Vitamin A plays an important role in detecting light in the sensory cells of the retina. Vitamin D can be converted to a hormone that helps regulate calcium homeostasis in the body. Vitamin E acts as an antioxidant that prevents highly reactive molecules called free radicals from damaging DNA and molecules in cell membranes.
What are the dangers of avitaminosis and hypervitaminosis? Avitaminosis (vitamin deficiency) can lead to severe metabolic problems. Avitaminosis C can lead to scurvy. Hypervitaminosis can be just as serious. Hypervitaminosis A can lead to dry skin, hair loss, anorexia, vomiting, severe headaches, mental disturbances, liver enlargement, and cirrhosis. An excess of fat-soluble vitamins is usually more serious than an excess of water-soluble vitamins because fat-soluble vitamins are stored in the body (A,D,E,K).
Why is folic acid recommended for pregnant women and for women before they become pregnant? Folic acid is critical for development of the neural tube (brain and spinal cord) in the fetus.
Does vitamin C really prevent colds? Or does it merely diminish the adverse effects of colds? Vitamin C helps in the manufacture of collagen factors – it is useful only in this way.
Which minerals have deleterious effects if an overdose is consumed? Too much potassium can adversely affect the heart. Too much iron can result in a “poisoning.”
What mineral might be effective for leg cramps during physical exertion? Calcium is important for proper skeletal functioning. During exertion, excess sodium may be lost. Potassium is also important.

16. Vitamins and Minerals
Minerals—inorganic molecules found naturally in the earth
Required by the body for normal function, including nerve conduction (Table 18-3)
Can attach to enzymes to facilitate their work

17. Metabolic Rates
Basal metabolic rate (BMR)—rate of metabolism when a person is lying down, is awake, is not digesting food, and the environment is comfortably warm
Total metabolic rate (TMR)—the total amounts of energy, expressed in calories, used by the body per day
Higher activity = higher metabolic rate.
What is a calorie? A measure of the energy contained in food. A kilocalorie? This term applies to what we usually think of as a calorie, as in the calories listed on a food product label. How many excess calories would you have to consume to gain a pound of weight? A pound of body weight is equal to 3500 calories, so an extra 500 calories/day for 1 week results in 1 pound of weight gain.
What mechanism generally protects the body from rapid weight loss or gain? Metabolic rate changes to try to maintain homeostasis.
If a person’s TMR is 3100 kcal, how many calories would he have to consume daily to maintain his weight at its current level? 3100
What happens when your food intake supplies more calories than your TMR? Weight gain

18. Factors that determine the basal and total metabolic rates.

19. Metabolic and Eating Disorders
Disruption or imbalance of metabolism caused by several different factors
Inborn errors of metabolism—genetic conditions involving deficient or abnormal metabolic enzymes
Some metabolic disorders are complications of other conditions
Hormonal imbalances
Compare and contrast anorexia nervosa and bulimia. Anorexia nervosa is a behavioral disorder characterized by refusal to eat because of a fear of becoming fat. Bulimia is a behavioral disorder characterized by an insatiable craving for food alternating with periods of self-deprivation.

20. Metabolic and Eating Disorders
Anorexia nervosa—characterized by chronic refusal to eat
Bulimia—an alternating pattern of craving of food followed by a period of self-denial; in bulimarexia, the self-denial triggers self-induced vomiting
Obesity—abnormally high proportion of fat in the body; may be a symptom of an eating disorder
Protein-calorie malnutrition (PCM)—results from a deficiency of calories in general and proteins in particular

21. Metabolic and Eating Disorders
Protein-calorie malnutrition (PCM)—results from a deficiency of calories in general and proteins in particular
May be a complication of a preexisting condition
Marasmus—type of advanced PCM caused by an overall lack of calories and protein, characterized by tissue wasting and fluid and electrolyte imbalances
Kwashiorkor—type of advanced PCM caused by a lack of protein in the presence of sufficient calories; similar to marasmus but distinguished by ascites and flaking dermatitis
Protein-calorie malnutrition (PCM) is an abnormal condition resulting from a deficiency of calories in general and, specifically, protein.
What might be the causes of PCM? Increased nutrient loss, increased use of nutrients by the body, deficiency of calories
What are some advanced forms of PCM? Marasmus occurs in parts of the world where there is not enough food; kwashiorkor occurs when there is sufficient calorie intake but not sufficient protein intake.

22. Protein-calorie malnutrition (PCM). A, Marasmus results from starvation. B, Kwashiorkor results from a diet sufficient in calories but deficient in protein. Note the abdominal bloating typical in kwashiorkor. (A, B, From Zitelli BJ, Davis HW: Atlas of pediatric physical diagnosis, ed 5, Philadelphia, 2007, Mosby.)

23. Body Temperature
Hypothalamus—regulates the homeostasis of body temperature through a variety of processes
Blood flow to the skin increases when body is overheated
Heat is lost through the skin by radiation, conduction, convection, evaporation
What factors affect a person’s basal metabolic rate? Activity, intake, inborn errors of metabolism
Can an individual’s basal metabolic rate be altered? How? Hyperthyroidism and hypothyroidism affect BMR.
Can an individual’s total metabolic rate be altered? How? By increasing or decreasing activity.
Why are the elderly and infants more susceptible to temperature-related illnesses? The negative feedback loop is less effective in the very young and the very old. Changes in skin, capillaries in the skin, and subcutaneous fat affect it.
Why does your body sweat when you perform heavy physical activity? The body is using evaporation to try to cool the body.

24. The skin as a thermoregulatory organ
The skin as a thermoregulatory organ. When homeostasis requires that the body conserve heat, blood flow in the warm organs of the body’s core increases (left). When heat must be lost to maintain the stability of the internal environment, flow of warm blood to the skin increases (right). Heat can be lost from the blood and skin by means of radiation, conduction, convection, and evaporation.

25. Body Temperature
Abnormal body temperature can have serious physiological consequences
Fever (febrile state)—unusually high body temperature associated with systemic inflammation response
Malignant hyperthermia (MH)—inherited condition that causes increased body temperature (hyperthermia) and muscle rigidity when exposed to certain anesthetics
Discuss the body’s survival mechanism for preserving normal body temperature of vital organs. Homeostasis will maintain the body temperature within a narrow range for normal functioning of the body.
Discuss vasoconstriction vs. vasodilation. Vasoconstriction makes capillaries smaller and preserves the heat of the body; vasodilation makes the capillaries larger and lets heat dissipate from the body.
Why do chills often accompany a fever? The body is trying to “warm” to the new fever temperature and shivering is a way to increase body temperature.

26. Body Temperature
Heat exhaustion—results from loss of fluid as the body tries to cool itself; may be accompanied by heat cramps
Heat stroke (sunstroke)—overheating of body resulting from failure of thermoregulatory mechanisms in a warm environment
Why is heat stroke more likely when the weather is hot and humid, as opposed to hot and dry? Heat does not dissipate from the body as quickly when the air is hot and humid. Evaporation occurs more quickly with dry air.

27. Body Temperature
Hypothermia—reduced body temperature resulting from failure of thermoregulatory mechanisms in a cold environment
Frostbite—local tissue damage caused by extreme cold; may result in necrosis or gangrene
How does the body protect itself against hypothermia? What are signs of hypothermia? What is happening in the body? As the body temperature lowers, respirations become shallow and slow and the pulse becomes faint and slow; this conserves energy that the body can use to try to maintain the core body temperature.
What is frostbite? What are the signs? Frostbite is local damage to tissues caused by ice formations accompanied by a reduction in local blood flow. Necrosis (tissue death) and even gangrene (decay of dead tissue) can result.