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Description : Chapter 17 in anatomy and physiology ppt

Tags : Body Temperature,Metabolism,anatomy,physiology

Published on : Mar 06, 2021 | Views : 2042 | Downloads : 0

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Slide 1-

Chapter 17 Body Temperature and Metabolism
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Metabolism—the total of all reactions that take place within the body These reactions include the energy-requiring ones, such as synthesis of proteins or DNA for mitosis, and the energy-releasing ones such as those in cell respiration. Many of these reactions release energy in the form of heat, which gives human beings a body temperature.
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Body Temperature The normal range of human body temperature is 96.6o to 99.6oF (36o to 38oC), with an average oral temperature of 98.6oF (37oC). Within a 24-hour period:fluctuates 1 to 2 degrees Lowest temperature:occurs during sleep The elderly and very young:likely to loose more heat rapidly
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Heat Production—heat is released as an energy product of cell respiration; many factors affect the rate. 1. The hormone thyroxine (and T3) increases the rate of cell respiration. Thyroxine is secreted when the metabolic rate decreases. Question: What kind of mechanism regulates the secretion of thyroxine, and what other glands are involved?
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Answer The secretion of thyroxine is regulated by a negative feedback mechanism that includes hormones from the anterior pituitary gland (TSH) and the hypothalamus (TRH).
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Heat Production (continued) 2. In stressful situations: sympathetic impulses and epinephrine:increases metabolic activity of many organs;increases ATP & heat production 3. Active organs continuously produce heat: Skeletal muscle tone:requires ATP; heat produces is about 25% of total body heat at rest Liver:always metabollicaly active;produces 20% of body heat at rest 4. Food intake:increases activity of GI tract,ATP & heat production 5. Changes in body temperature: as body temperature rises, metabolic rate increases 
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Heat Loss—most heat is lost through the skin Blood flow through the dermis determines the amount of heat lost by: Radiation:heat from body is transferred to cooler objects not touching skin. Conduction:loss of heat to cooler air or objects that touch the skin. Convection:air moves the warm air away from skin & facilitate the loss of heat. Vasodilation in the dermis increases blood flow— Vasoconstriction in the dermis decreases blood flow— Question: In what type of environment would radiation and conduction be ineffective?
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Answer Radiation and conduction would be ineffective heat loss mechanisms when the environmental temperature is very high, close to, or exceeding human body temperature.
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Heat Loss (continued) Sweating is a very effective heat loss mechanism, because water has a very high heat of vaporization Sweating does have a potentially serious disadvantage in that it requires the loss of water in order to also loose heat (could cause dehydration) Question: In what type of environment would sweating be an ineffective mechanism of heat loss, and why?
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Answer Sweating would be ineffective in an environment where the humidity is very high. High humidity means that the air is nearly saturated with water vapor and cannot hold more.
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Heat Loss (continued) (see Table 17–2 for summary) Minor pathways of heat loss: urinary,digestive & respiratory tracts Loss from the respiratory tract:evaporation (water vapor is exhaled) Loss from the urinary and digestive tracts: urination and defacation
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Regulation of Body Temperature Hypothalamus—the thermostat; balances heat production and heat loss Information for changes:neurons detect change in temp. of blood flow through brain.receptors in skin provide info about external temps. Mechanisms to increase heat loss:vasodilation,sweating& decrease of muscle tone To decrease heat production:vasodilation brings warm blood closer to skin. Mechanisms to conserve heat:vasoconstriction,sweating & increased muscle tone To increase heat production:vasoconstriction brings blood away from the skin. Sweating decreases. Increased muscle tone=shivering (increase heat production)
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Fever—an abnormally elevated body temperature Pyrogens—substances that may cause a fever: Endogenous pyrogens:inflammatory chemicals that “raise the setting” of the hypothalamic thermostat Fever cycle: pyrogen resets the hypothalamic thermostat upward. Responses by the body:raise body tempature When the pyrogen has been eliminated, the hypothalamic thermostat drops. Responses by the body:sweating & vasodilation
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Fever (continued) Benefits of a fever:shortens the duration of an infection by accelerating the destruction of pathogens(WBCs increase) Serious consequences of a very high fever:proteins of cells become damaged causing cells to die. Cellular death is the cause of brain damage Antipyretic:medication that lowers fevers
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Metabolism—all of the reactions that take place within the body Anabolism—synthesis reactions:bonding together of smaller molecules to form larger ones Examples: synthesis of glycogen by liver cells Catabolism—decomposition reactions:breaking of bonds from larger molecules forming smaller ones: Examples: cell respiratiom Most reactions are catalyzed by enzymes; the human body has thousands of enzymes. Question: Explain the active site theory of enzyme functioning.
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Answer The active site theory states that the function of an enzyme is determined by the shape of the enzyme and the shapes of the substrates that will “fit” the enzyme.
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Cell Respiration—the breakdown of food molecules to release their potential energy and synthesize ATP Summary equation: Glucose + O2  CO2 + H2O + ATP + heat The breakdown of glucose has three stages: Glycolysis The Krebs (citric acid) cycle The cytochrome (electron) transport system Question: Where does the oxygen for cell respiration come from, and what happens to each of the products of cell respiration?
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Answer The oxygen for cell respiration comes from breathing. Products: The water formed becomes part of intracellular fluid. The CO2 is exhaled. The ATP is used for cellular processes that require energy. The heat gives us a body temperature.
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Glycolysis—takes place in the cytoplasm, does not require oxygen (anaerobic). (see Table 17–3) Glucose (6 carbon), with 2 ATP as energy of activation, is broken down to 2 molecules of pyruvic acid (3 carbon). 4 ATP are formed, a net gain of 2. 2 NADH2 are formed—the hydrogens from glucose will be taken to the cytochrome transport system.
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Krebs Citric Acid Cycle—takes place in the mitochondria, requires oxygen (aerobic) (see Table 17–3) Pyruvic acid is broken down, first to an acetyl group (2 carbon): CO2 is formed. ATP is formed (two per glucose). NADH2 and FADH2 take hydrogens from pyruvic acid to the cytochrome transport system. A four-carbon molecule is regenerated for the next cycle.
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Cytochrome (Electron) Transport System— takes place in the mitochondria, requires oxygen (aerobic) (see Table 17–3) NADH2 and FADH2 bring hydrogens (from glucose) to the cytochromes. The electrons of the hydrogens are passed to oxygen. The protons (H+) of the hydrogens combine with this oxygen to form metabolic water. Enough energy is released to form 25 ATP molecules.
Slide 22-

Proteins and Fats as Energy Sources (see Table 17–4 for hormonal regulation) To be used for energy, other nutrients must be changed to molecules that can enter the Krebs cycle. Excess amino acids  pyruvic acid Glycerol, a three-carbon molecule  Fatty acids are split by the process of beta-oxidation into acetyl groups. Ketones are formed from fatty acids or excess amino acids. Question: In what organ does most beta-oxidation take place?
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Answer Most beta-oxidation takes place in the liver.
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Energy Available from Food—energy in food is measured in kilocalories. With respect to food, kilocalories may be called calories. One gram of carbohydrate = 4 cal. One gram of protein = 4 cal. One gram of fat = 9 cal. Question: A nutty ice cream sundae has 70 grams of fat, 30 grams of protein, and 40 grams of carbohydrate. How many calories does it provide?
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Answer Fat: 70 x 9 = 630 Protein: 30 x 4 = 120 Carbohydrates: 40 x 4 = 160 This ice cream sundae has 910 calories.
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Synthesis Uses of Foods Glucose  pentose sugars: nucleic acids turned into glycogen in liver  glycogen: used for energy,increases conversion of glycogen to glucose Amino acids  non-essential amino acids synthesized by liver &used in the synthesis of proteins in all tissues Fatty acids and glycerol  phospholipids—  triglycerides—  cholesterol—
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Synthesis Uses of Foods (continued) Any food type eaten in excess will be changed to fat and stored. Vitamins—organic molecules needed by the body in very small amounts (see Table 17–5). Minerals—inorganics (trace elements, electrolytes) needed by the body in relatively small amounts (see Table 17–6). Question: In what tissue is fat stored, and where in the body is most of it found?
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Answer Fat is stored in adipose tissue. Most adipose tissue is subcutaneous.
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Metabolic Rate—a measure of heat production by the body; measured in kilocalories Basal metabolic rate (BMR)—the energy required to remain alive, to maintain the body at rest (an average of 55 to 70 kcal per hour) Many factors contribute: 1. Age: highest in young children decreases with age by about 2% per decade 2. Body configuration—more surface area proportional to weight = a higher BMR:
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Metabolic Rate (continued) 3. Sex hormones:testosterone increases metabolic activity to a greater rate then estrogen,men tend to have more active tissue as women tend to have more fat 4. Sympathetic activity:in stress situations the metabolic rate of many body cells is increased 5. Decreased food intake:causes metabolic rate to decrease 6. Climate:people who live in colder climates have a 10-20% higher metabolic rate
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Wrap-Up Question Name the part or aspect of temperature or metabolism described. 1. Causes a fever 2. Response of dermis arterioles to cold 3. Units of heat energy 4. Heat loss involving evaporation 5. A breeze cools the skin 6. Food type with the most cal/gram 7. Muscular heat-generating mechanism 8. CNS temperature-regulating center
Slide 32-

Answers 1. Causes a fever—pyrogen 2. Response of dermis arterioles to cold—vasoconstriction 3. Units of heat energy—calories 4. Heat loss involving evaporation—sweating 5. A breeze cools the skin—convection 6. Food type with the most cal/gram—fats 7. Muscular heat-generating mechanism—shivering 8. CNS temperature-regulating center—hypothalamus