The Digestive System and Body Metabolism Ch 14 Part D

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The Digestive System and Body MetabolismCh 14
Part D
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Metabolism

• Chemical reactions necessary to maintain life
• Includes 2 phases
• Catabolism substances are broken down to
  simpler substances
• Energy within chemical bonds of food is released
  captured to make ATP
• Anabolism larger molecules are built from
  smaller ones
• Major nutrient catagories used for various
  cellular body needs
• Carbohydrates used for ATP
• Fats used for cell membranes, myelin
  insulation, to make ATP when no carbohydrates
• Proteins for structures

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Carbohydrate Metabolism

• Carbohydrates are the bodys preferred source to
  produce cellular energy (ATP)
• Glucose (blood sugar) is the major breakdown
  product and fuel to make ATP

Figure 14.17
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Cellular Respiration

• Oxygen-using events take place within the cell to
  create ATP from ADP
• Carbon leaves cells as carbon dioxide (CO2)
• Hydrogen atoms are combined with oxygen to form
  water
• Energy produced by these reactions adds a
  phosphorus to ADP to produce ATP
• ATP can be broken down to release energy for
  cellular use

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Carbohydrate Metabolism
Figure 14.18
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Stages of Cellular Respiration

• Cellular Respiration includes
• Glycolysis
• Krebs Cycle
• Electron Transport Chain

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Metabolic Pathways Involved in Cellular
Respiration

• Glycolysis energizes a glucose molecule so that
  it can be split into two pyruvic acid molecules
  and yield ATP
• Occurs in cytoplasm
• Citric Acid (Krebs) Cycle
• Produces virtually all the carbon dioxide and
  water resulting from cell respiration
• Yields a small amount of ATP
• Occurs in mitochondria

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Metabolic Pathways Involved in Cellular
Respiration

• Electron Transport Chain
• Hydrogen atoms removed during glycolysis and the
  Krebs cycle are delivered to protein carriers
• Hydrogen is split into hydrogen ions and
  electrons in the mitochondria
• Electrons give off energy in a series of steps to
  enable the production of ATP

Figure 14.19a
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Cellular Respiration
Figure 14.19
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Metabolic Pathways Involved in Cellular
Respiration
Figure 14.20a
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Metabolism of Carbohydrates

• Hyperglycemia
• Excessively high levels of blood glucose
• Excess glucose is stored in liver as glycogen
• If blood glucose levels are still too high,
  excesses are converted to fat

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Metabolism of Carbohydrates
Figure 14.21a
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Metabolism of Carbohydrates

• Hypoglycemia
• Low levels of glucose in the blood
• Liver breaks down stored glycogen and releases
  glucose into the blood

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Fat Metabolism

• Handled mostly by the liver
• Use some fats to make ATP
• Synthesize lipoproteins, thromboplastin (clotting
  factor), and cholesterol
• Release breakdown products to the blood
• Body cells remove fat and cholesterol to build
• membranes and steroid hormones
• Used for myelin sheaths of neurons

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Fat Metabolism
Figure 14.21b
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Use of Fats for ATP Synthesis

• Stored fats energy
• 9 kcal of energy in 1g of fat
• 4 kcal of energy in 1g carbohydrates or proteins
• Fats must first be broken down to acetic acid
• Within mitochondria, acetic acid is completely
  oxidized to produce water, carbon dioxide, and
  ATP
• When low glucose, use fat for ATP

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Use of Fats for ATP Synthesis

• Acidosis (ketoacidosis) results from incomplete
  fat oxidation in which acetoacetic acid and
  acetone accumulate in the blood
• Breath has a fruity odor
• Common with
• No carbohydrate diets Atkins diet
• Uncontrolled diabetes mellitus
• Starvation

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ATP Formation
Figure 14.21d
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Protein Metabolism

• Proteins are conserved by body cells because they
  are used for most cellular structures
• Ingested proteins are broken down to amino acids
• Cells remove amino acids to build proteins
• Need 20 amino acids 9 are essential (cannot be
  made by body)
• Synthesized proteins are actively transported
  across cell membranes
• Amino acids are used to make ATP only when
  proteins are overabundant or there is a shortage
  of other sources

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Production of ATP from Protein

• Amine groups are removed from proteins as ammonia
• The rest of the protein molecule enters the Krebs
  cycle in mitochondria
• The liver converts harmful ammonia to urea which
  can be eliminated in urine

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Protein Metabolism
Figure 14.21c
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Role of the Liver in Metabolism

• Several roles in digestion
• Manufacturers bile
• Detoxifies drugs and alcohol
• Degrades hormones
• Produce cholesterol, blood proteins (albumin and
  clotting proteins), lipoproteins
• Albumin maintains osmotic pressure of blood
  keeps fluids in the blood
• Plays a central role in metabolism
• Process all nutrients
• Removes amino acids, fatty acids glucose for
  later use
• Removes bacteria
• A person will die within 24 hours of liver loss!!

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Role of the Liver in Metabolism

• Humans have excess liver tissue it also
  regenerates if part of it is damaged or removed
• Hepatic portal circulation-
• Brings nutrient-rich blood from digestive system
  to liver so liver can process it

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Metabolic Functions of the Liver

• Glycogenesis glycogen formation
• Glucose molecules are converted to glycogen
• Glycogen molecules are stored in the liver
• Glycogenolysis glucose splitting
• Glucose is released from the liver after
  conversion from glycogen
• Gluconeogenesis formation of new sugar
• Glucose is produced from fats and proteins

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Metabolic Functions of the Liver
Figure 14.22
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Metabolic Functions of the Liver

• Fats and fatty acids are picked up by the liver
• Some are oxidized to provide energy for liver
  cells
• The rest are broken down into simpler compounds
  and released into the blood
• Acetic acid acetoacetic acid
• Makes cholesterol, which is used to strengthen
  cell membranes

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Cholesterol Metabolism

• Cholesterol is not used to make ATP (not used for
  energy)
• Functions of cholesterol
• Serves as a structural basis of steroid hormones
  and vitamin D
• Is a major building block of plasma membranes
• In bile salts
• Most cholesterol is produced in the liver (85)
  and is not from diet (15)

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Cholesterol Transport

• Cholesterol and fatty acids cannot freely
  circulate in the bloodstream
• Not water soluble
• They are transported by lipoproteins (made in
  liver) (lipid-protein complexes)
• Low-density lipoproteins (LDLs) transport to body
  cells
• Bad cholesterol since they can lead to
  artherosclerosis
• High-density lipoproteins (HDLs) transport from
  body cells to the liver
• good cholesterol

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Body Energy Balance

• Energy intake total energy output
• (heat work energy storage)
• Energy intake is liberated during food oxidation
• Glycolysis, Krebs cycle, electron transport
• Energy output
• Heat is usually about 60 of total
• Storage energy is in the form of fat or glycogen

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Regulation of Food Intake

• Body weight is usually relatively stable
• Energy intake and output remain about equal
• Mechanisms that may regulate food intake
• Levels of nutrients in the blood
• Glucose, amino acids
• Hormones
• Insulin, glucagon, leptin
• Body temperature
• Psychological factors

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Metabolic Rate and Body Heat Production

• Basic metabolic rate (BMR) amount of heat
  produced by the body per unit of time at rest
• energy needed for essential life activities
• Average BMR is about 60 72 kcal/hour
• Kilocalorie (kcal) is the unit of measure for the
  energy value of foods and the amount of energy
  used by the body

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Metabolic Rate and Body Heat Production

• Factors that influence BMR
• Surface area small body usually has higher BMR
• Gender males tend to have higher BMR
• 70kg adult has BMR of 60-72 kcal/hr
• Age children and adolescents have a higher BMR
• The amount of thyroxin (from thyroid) produced is
  the most important control factor
• More thyroxin means higher metabolic rate
• Hyperthyroidism- lose weight
• Hypothyroidism- gain weight

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Factors Determining BMR
Table 14.3
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Total Metabolic Rate (TMR)

• Total amount of kilocalories the body must
  consume to fuel ongoing activities
• TMR increases with an increase in body activity
• TMR must equal calories consumed to maintain
  homeostasis and maintain a constant weight
• ? TMR leads to ? weight gain

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Body Temperature Regulation

• Most energy is released as foods are oxidized
• Most energy escapes as heat
• Less than 40 of food energy forms ATP

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Body Temperature Regulation

• The body has a narrow range of homeostatic
  temperature
• Must remain between 35.6 to 37.8C (96 to 100
  F)
• The bodys thermostat is in the hypothalamus
• Initiates heat-loss or heat-promoting mechanisms

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Heat Promoting Mechanisms

• When cold
• Vasoconstriction of blood vessels
• Blood is rerouted to deeper, more vital body
  organs
• Skin becomes cold
• Shivering contraction of muscles produces heat
• Hypothermia
• ? respiration rate, BP, heart rate, metabolism
  comes to a halt

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Mechanisms of Body Temperature Regulation
Figure 14.23
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Mechanisms of Body Temperature Regulation
Figure 14.23, step 3
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Mechanisms of Body Temperature Regulation
Figure 14.23, step 4
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Mechanisms of Body Temperature Regulation
Figure 14.23, step 6
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Heat Loss Mechanisms

• When hot
• Heat loss from the skin via radiation and
  evaporation
• Skin blood vessels and capillaries are flushed
  with warm blood
• Evaporation of perspiration cools the skin
• Less evaporation if humidity is high

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Mechanisms of Body Temperature Regulation
Figure 14.23, step 7
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Mechanisms of Body Temperature Regulation
Figure 14.23, step 12
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Mechanisms of Body Temperature Regulation
Figure 14.23, step 13
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• Hyperthermia
• ? T depresses hypothalamus ? positive feedback
  causing ? metabolism ? ? T ? brain damage
• heat stroke heat loss mechanism NOT working
• Heat exhaustion
• From dehydration ? BP, ? heart rate cool,
  clammy skin, heat loss mechanisms still work

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Body Temperature Regulation

• Fever controlled hyperthermia
• Results from infection, cancer, allergic
  reactions, CNS injuries
• Body T reset high heat promoting mechanisms
  vasoconstriction, shivering (the chills), ?
  metabolic rate inhibits bacterial growth
• Too high a fever can lead to body proteins being
  denatured and permanent brain damage

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Developmental Aspects of the Digestive System

• The alimentary canal is a continuous tube by the
  fifth week of development
• Digestive glands bud from the mucosa of the
  alimentary tube
• The developing fetus receives all nutrients
  through the placenta
• In newborns, feeding must be frequent (small
  stomach), peristalsis is inefficient, and
  vomiting is common

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Developmental Aspects of the Digestive System

• Newborn reflexes
• Rooting reflex help the infant find the nipple
• Sucking reflex helps the infant hold on to the
  nipple and swallow
• Teething begins around age six months

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• Congenital defects
• Cleft lip/palate
• Tracheoesophageal fistula
• Inborn errors of metabolism
• Cystic fibrosis pancreatic duct blocked
• No fat digestion
• PKU brain damage

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Cleft lip
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Cleft lip
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Cleft lip palate
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Tracheoesophageal fistula
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Developmental Aspects of the Digestive System

• Problems of the digestive system
• Gastroenteritis inflammation of the
  gastrointestinal tract
• Appendicitis inflammation of the appendix
• Metabolism decreases with old age
• Metabolic rate ? by 5-8/10 years
• Middle age digestive problems
• Ulcers
• Gall bladder problems

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Developmental Aspects of the Digestive System

• Activity of digestive tract in old age
• Fewer digestive juices
• GI activity slows
• Peristalsis slows
• Diverticulosis and cancer (stomach colon) are
  more common