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Questions and Answers

What is the primary purpose of glycogenolysis in the liver?

  • To synthesize new glycogen using glucose
  • To convert glucose into fatty acids
  • To produce amino acids from glucose
  • To break down glycogen into glucose (correct)

    • What role does gluconeogenesis play in metabolism during the fasted state?

  • It produces triglycerides from glucose
  • It breaks down glucose into pyruvate
  • It generates glucose from non-carbohydrate sources (correct)
  • It converts fatty acids into glucose

    • Which of the following best describes the energy production pathway involving muscle protein catabolism?

  • Muscle breakdown has no impact on energy production
  • Muscle proteins are converted to glucose exclusively
  • Some amino acids from muscle proteins are used for energy, others for gluconeogenesis (correct)
  • Muscle proteins are solely metabolized into triglycerides

    • During fasted-state metabolism, what happens to stored triglycerides in adipose cells?

    <p>They are broken down into free fatty acids and glycerol (A)</p> Signup and view all the answers

    Which of the following statements about glucose metabolism is accurate?

    <p>Glycogen serves as a main source of glucose during prolonged fasting (D)</p> Signup and view all the answers

    What is the primary process involved in breaking down glycogen into glucose?

    <p>Glycogenolysis (C)</p> Signup and view all the answers

    During the fasted state, how do cells primarily meet their energy needs?

    <p>By metabolizing stored molecules (C)</p> Signup and view all the answers

    Which metabolic pathway predominates after consuming a meal?

    <p>Anabolic pathways (C)</p> Signup and view all the answers

    What is the role of high-energy compounds like ATP in cellular metabolism?

    <p>To provide energy for cellular work (A)</p> Signup and view all the answers

    Which process involves the synthesis of glucose from non-carbohydrate precursors?

    <p>Gluconeogenesis (D)</p> Signup and view all the answers

    What is the result of catabolic metabolism during fasting?

    <p>Breakdown of storage molecules for energy (D)</p> Signup and view all the answers

    Which statement is true regarding the role of nutrients during the absorptive state?

    <p>Nutrients are utilized for energy and stored in various forms (D)</p> Signup and view all the answers

    Which of the following best describes protein catabolism?

    <p>The breakdown of proteins into smaller peptides or amino acids (C)</p> Signup and view all the answers

    Which of the following carbohydrates must be digested into monosaccharides before absorption?

    <p>Starch (A)</p> Signup and view all the answers

    What initiates the digestion of proteins in the stomach?

    <p>Pepsin (C)</p> Signup and view all the answers

    Which enzyme converts trypsinogen to trypsin?

    <p>Enteropeptidase (A)</p> Signup and view all the answers

    Which transport protein is involved in the absorption of glucose or galactose in the small intestine?

    <p>SGLT (B)</p> Signup and view all the answers

    What is the primary product of protein digestion that can be absorbed into the bloodstream?

    <p>Free amino acids, dipeptides, and tripeptides (B)</p> Signup and view all the answers

    Where does the digestion of dietary carbohydrates primarily take place?

    <p>Mouth and small intestine (B)</p> Signup and view all the answers

    What role does pancreas play in the digestion process?

    <p>Secretes digestive enzymes for carbohydrate and protein digestion (D)</p> Signup and view all the answers

    What is the function of salivary amylase in carbohydrate digestion?

    <p>Starts the digestion of starch into maltose (A)</p> Signup and view all the answers

    Flashcards

    Metabolic pathways

    Chains of chemical reactions in cells, extracting energy from nutrients and using it for work.

    Anabolic pathways

    Metabolic pathways that synthesize larger molecules from smaller ones.

    Catabolic pathways

    Metabolic pathways that break down large molecules into smaller ones.

    Fed state

    Metabolic state after a meal, where nutrient absorption and utilization happen.

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    Fasted state

    Metabolic state after the fed state, using stored nutrients for energy.

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    Energy use of nutrients

    Nutrient molecules that are metabolized and their energy is converted into high-energy compounds (ATP).

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    Nutrient molecule fate

    Absorbed nutrients are used for energy, building cells (anabolism), or stored.

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    ATP

    High-energy compound, storing and transferring energy in cells to power reactions.

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    Liver's role in fasted state

    The liver becomes the main source of glucose for the body when food is not available, using stored glycogen and making new glucose through gluconeogenesis.

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    Glycogenolysis

    The breakdown of glycogen, a stored form of glucose in the liver, to release glucose into the bloodstream.

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    Gluconeogenesis

    The process of creating new glucose from non-carbohydrate sources, like amino acids or lactate, in the liver.

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    Free fatty acids in fasted state

    Stored triglycerides in adipose cells are broken down into free fatty acids and glycerol during fasting, which are released into the bloodstream for energy.

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    Amino acid breakdown in fasted state

    Some amino acids from muscle breakdown are used for energy production during fasting, while others are converted to pyruvate and released into the bloodstream to be converted into glucose.

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    What are the types of carbohydrates digested in the small intestine?

    The carbohydrates digested in the small intestine include starch (from breads and potatoes), maltose (a product of salivary amylase digestion), and dietary disaccharides like sucrose, lactose, and maltose.

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    What is the final product of carbohydrate digestion?

    Carbohydrates must be digested into monosaccharides (simple sugars) like glucose, fructose, and galactose before they can be absorbed.

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    Where does carbohydrate digestion start?

    Carbohydrate digestion begins in the mouth with salivary amylase, continues in the small intestine with pancreatic amylase and brush border enzymes.

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    What are the roles of Na+ and GLUT proteins in glucose absorption?

    Sodium-glucose linked transporter (SGLT) uses the Na+ gradient to transport glucose and galactose into intestinal epithelial cells. GLUT5 transports fructose, and GLUT2 facilitates glucose and galactose exit into blood.

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    What is the role of pepsin in protein digestion?

    Pepsin, activated by stomach acid, breaks down proteins into smaller peptides in the stomach.

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    Where does protein digestion continue after the stomach?

    Protein digestion continues in the small intestine with pancreatic enzymes like chymotrypsin, carboxypeptidase, and trypsin.

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    What is the role of trypsinogen and enteropeptidase in protein digestion?

    Trypsinogen is an inactive proenzyme secreted by the pancreas. It is activated by enteropeptidase in the small intestine, forming trypsin, which then activates other pancreatic enzymes.

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    What are the final products of protein digestion?

    Protein digestion results in free amino acids, dipeptides (two amino acids linked), and tripeptides (three amino acids linked).

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    Study Notes

    Digestive System

    • The average American diet includes carbohydrates (polysaccharides and disaccharides), proteins (amino acid chains), and fats (triglycerides, cholesterol, and long-chain fatty acids).
    • The primary function of the digestive system is to break down these complex molecules into smaller, absorbable units for use by the body's cells.
    • Digestion, motility, absorption, and secretion are the four basic physiological processes of the digestive system.
    • Digestion involves the mechanical and chemical breakdown of food.
    • Motility involves the movement of materials within the digestive tract, aided by smooth muscle.
    • Absorption involves the movement of molecules from the lumen of the digestive tract into the body's cells.
    • Secretion involves the movement of fluids, electrolytes, mucus, acid, and enzymes into the digestive tract for digestion.

    Digestive System Anatomy

    • The digestive system includes the mouth, oral cavity, esophagus, stomach, small intestine, large intestine, rectum, and anus.
    • Associated organs such as the salivary glands, pancreas, and liver, play a crucial role in digestive processes.
    • The stomach temporarily holds food, increasing surface area with rugae and mixing with acid, mucus, and enzymes to form chyme, and regulates passage to the small intestines via the pyloric valve.

    The Stomach

    • The stomach walls consist of folds called rugae.
    • It contains gastric glands that secrete mucus, hydrochloric acid (HCl), and inactive enzymes (e.g., pepsinogen).
    • HCl activates pepsinogen to pepsin, initiating protein digestion.
    • The stomach also secretes intrinsic factor, which aids Vitamin B-12 absorption.
    • The stomach's significant secretions are mucus, HCl, and intrinsic factor, pepsinogen, histamine, somatostatin, and gastrin.
    • Gastrin is essential for regulating HCl secretion.
    • The sight and presence of food stimulate gastric secretions.
    • HCl activates the chief cells to produce pepsinogen which is the precursor for the enzyme pepsin.
    • HCl in the stomach lumen stimulates the chief cells to secrete pepsinogen and gastric lipase.
    • HCl also stimulates D cells to secrete somatostatin, a negative feedback regulator of acid and enzyme secretion.
    • The stomach regulates chyme movement to the small intestine via the pyloric valve (sphincter).

    The Small Intestine

    • The small intestine, folded into plicae and villi, maximizes surface area for nutrient absorption.
    • The lining of the small intestine comprises specialized cells called enterocytes.
    • Microvilli on enterocytes form the brush border, increasing surface area further.
    • The small intestine contains specialized enzymes (e.g., sucrase, maltase, lactase) on the brush border, crucial for carbohydrate digestion.
    • The small intestine breaks down sugars and proteins (via various enzymes) into absorbable forms.

    Digestive System Functions: Secretion

    • 9 liters of fluid enters the digestive tract daily; 2 liters from ingested food/drink, and the remaining from accessory organs.
    • Secretion of ions and fluids (like salt, water, and enzymes) is crucial for digestive functions.
    • Bile is a non-enzyme solution secreted by liver cells (hepatocytes); secreted in the small intestine and stored in the gall bladder.
    • The majority of water, electrolytes, enzymes, acids, and mucus is secreted in the small intestine.

    Digestive System Functions: Digestion and Absorption

    • Digestion involves breaking down food into absorbable units via mechanical and chemical processes.
    • Mastication and mechanical mixing in the stomach and small intestine aid mechanical digestion.
    • Digestive enzymes catalyze chemical breakdown.
    • Absorption is the transfer of nutrient molecules from the lumen into the blood stream.

    Digestion of Dietary Food Molecules: Carbohydrates

    • Digestion of carbohydrates begins in the mouth with salivary amylase, breaking down starch into disaccharides.
    • Salivary amylase is inactive in the stomach due to the acidic environment.
    • Brush border enzymes (sucrase, maltase, lactase) digest disaccharides into monosaccharides.
    • Pancreatic amylase participates in carbohydrate digestion in the small intestine.

    Digestion of Dietary Food Molecules: Proteins

    • Protein digestion starts in the stomach with pepsin, activated by HCl.
    • Further protein digestion occurs in the small intestine, with enzymes like trypsin, chymotrypsin, and carboxypeptidase.
    • Enteropeptidase activates trypsinogen into trypsin.
    • Endopeptidases and exopeptidases work together to break down peptides into single amino acids and small peptides.
    • Amino acids, dipeptides, and tripeptides are absorbed into the bloodstream.

    Digestion of Dietary Food Molecules: Fats

    • Lipases break down triglycerides into monoglycerides and free fatty acids.
    • Bile salts emulsify fats into smaller droplets, increasing the surface area for lipase action.
    • Monoglycerides and free fatty acids are absorbed, reassembled into triglycerides, and packaged into chylomicrons.
    • Chylomicrons are transported via the lymphatic system.

    Digestive System Functions: Peptide Absorption

    • Individual amino acids are absorbed via Na+ symporters and moved into interstitial fluid with Na+-amino acid antiporter.
    • Di- and tripeptides are absorbed via H+ symporters, and are then either moved into the interstitial fluid via another H+ antiporter or digested into amino acids.

    Regulation of Digestion in the Small Intestine

    • Chyme entering the small intestine stimulates local reflexes, slowing gastric motility and secretion, and allowing for more efficient digestion.
    • Hormones such as secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP), and glucagon-like peptide-1 (GLP-1) regulate digestion.
    • Bile salts are important for fat digestion and are reabsorbed by the liver.
    • These hormones regulate secretion and motility in the small intestine and influence pancreatic and other secretions, as well as blood glucose.

    Large Intestine Functions

    • Chyme enters the large intestine through the ileocecal valve.
    • Mass movements (segmental contractions) mix and move contents.
    • The large intestine absorbs water and electrolytes.
    • Bacteria in the large intestine ferment undigested materials, producing vitamins and short-chain fatty acids.
    • Feces are formed and eliminated through defecation.

    Chapter 22: Metabolism

    • Metabolism is the sum of all chemical reactions in the body.
    • Nutrient molecules are the source of energy for maintaining body structure and function.
    • Energy is extracted from nutrients such as glucose and stored in ATP.
    • Metabolism is controlled by various physiological mechanisms including hormone and enzyme regulation.

    Metabolism and Energy Balance

    • Metabolic state determines the fate of digested nutrients.
    • Energy from nutrients can generate heat, build structures, and be stored.
    • The body's metabolic state balances energy input (digestion) against energy use (maintenance, activity, etc).

    Metabolic Pathways

    • Metabolic pathways are sequences of chemical reactions.
    • Anabolic pathways synthesize larger molecules.
    • Catabolic pathways break down large molecules.
    • These pathways use energy from various nutrient molecules to synthesize ATP or store energy in other molecule forms.
    • These processes of metabolic pathways help regulate various processes in the human body such as cellular respiration to convert chemical energy from various nutrients into ATP.

    Overall Body Metabolism: Fed vs Fasted States

    • Fed state metabolism: Occurs after a meal and involves nutrient absorption and use.
    • Fasted state metabolism: Occurs between meals and involves breaking down stored nutrients for energy.

    Fate of Absorbed Nutrient Molecules

    • Nutrient molecules are used for energy, synthesis, or storage.
    • The fate of the molecules depends on the metabolic state of the body.
    • Monosaccharides are used for energy, stored as glycogen, or converted to triglycerides.
    • Amino acids are used for protein synthesis or converted to glucose.
    • Fats are stored as triglycerides or used for energy.

    Fate of Biomolecules during Fed vs. Fasted States

    • Glycogen reserves are used to provide glucose during the fasted state.
    • These various nutrient molecules are utilized by various cell groups in the body such as the adipose, liver, muscle, and intestinal cells.
    • Fasted state metabolism is driven by release of various hormones such as glucagon which stimulates glycogenolysis or gluconeogenesis to maintain the body's glucose levels.

    Homeostatic Control of Metabolism

    • The endocrine system regulates metabolism via hormones like insulin and glucagon to maintain homeostasis.

    • Insulin and glucagon act on various target tissues including the liver, adipose, and muscle tissues to regulate the metabolic state in the various bodily systems.

    • Insulin and glucagon are the primary regulators of various metabolic enzymes in the various tissues in the body.

    • Insulin effects:

    • Increase glucose transport

    • Enhance cellular utilization of glucose

    • Enhance amino acid utilization

    • Enhance fat synthesis

    • Glucagon effects:

    • Increase blood glucose levels

    • Stimulate glycogenolysis and gluconeogenesis

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