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Food ProcessingFood Processing
Module 22.2: Nutrient pool Module 22.2: Nutrient pool substratessubstrates Nutrient pool supplies molecules
for catabolism, anabolism, and to fuel ATP production
◦ ATP used for metabolic makeover inside cell
◦ Organic compounds used for 2-carbon substrate molecules for mitochondrial activities
Figure 22.2 Figure 22.2 11
Organic compoundsthat can beabsorbed by cellsare distributed tocells throughoutthe body by thebloodstream.
The centrality of the nutrientpool to both anabolism andcatabolism
KEY
= Catabolic pathway
= Anabolic pathway CO2
H2O
O2
ATP
Citricacidcycle
Coenzymes Electrontransportsystem
MITOCHONDRIA
Two-carbon chains
Three-carbon chains
Fatty acids Glucose Amino acids
ProteinsGlycogenTriglycerides
Nutrientpool
Structural, functional, and storage components
Module 22.2: Nutrient pool Module 22.2: Nutrient pool substratessubstrates
When nutrients absorbed from digestive tract are insufficient for cellular metabolism, energy reserves come from various cells
◦ Liver cells store triglycerides and glycogen
Fatty acids and glucose can be released
◦ Adipocytes store triglycerides Fatty acids can be released
◦ Skeletal muscle cells store glycogen Amino acids can be released
Figure 22.2 Figure 22.2 22
Nutrients obtained throughdigestion and absorption
The use of the body’s metabolicreserves to maintain normalnutrient levels in the blood
Nutrients distributedin the blood
Cells in most tissuescontinuouslyabsorb andcatabolize glucose.
Neural tissue requires acontinuous supply ofglucose. During starvation,other tissues shift to fattyacid or amino acidcatabolism, conservingglucose for neural tissue.
Liver cells store triglycerides andglycogen reserves. If absorption by thedigestive tract fails to maintain normalnutrient levels, the triglycerides andglycogen are broken down and thefatty acids and glucose are released.
Skeletal muscles at rest metabolize fattyacids and use glucose to build glycogenreserves. Amino acids are used toincrease the number of myofibrils. If thedigestive tract, adipocytes, and liver areunable to maintain normal nutrient levels,the contractile proteins can be brokendown and amino acids released into thecirculation for use by other tissues.
Adipocytes convert excess fatty acids totriglycerides for storage. If absorption bythe digestive tract and reserves in theliver fail to maintain normal nurtientlevels, the triglycerides are broken downand the fatty acids released.
Module 22.2: Nutrient pool Module 22.2: Nutrient pool substratessubstrates Cellular catabolic and anabolic
pathways◦ Cells must synthesize some organic
molecules Insufficient nutrients from nutrient pool and diet Nutrients are often used to create 2-carbon
chains for mitochondrial ATP production
◦ Oxygen required must be continuously provided by diffusion from ECF
◦ CO2 produced must diffuse out of cell to ECF
Module 22.2: Nutrient pool Module 22.2: Nutrient pool substratessubstrates
Cellular nutrient dynamics◦ Fatty acids
Can be stored as triglycerides Can be created from acetyl-CoA and
triglycerides◦ Glucose
Can be stored as glycogen (glycogenesis) Can be created from:
Glycogen catabolism (glycogenolysis) Smaller carbon chain anabolism
(gluconeogenesis) Can be used to make two 3-carbon chains for
ATP production (glycolysis)
Module 22.2: Nutrient pool Module 22.2: Nutrient pool substratessubstrates Cellular nutrient dynamics
(continued)◦ Amino acids
Can be stored as proteins Can be created from:
3-carbon chains Protein catabolism (only during starvation)
Figure 22.2 Figure 22.2 33
CO2
H2O
O2
ATP
Citricacidcycle
Coenzymes Electrontransportsystem
MITOCHONDRIA
Two-carbon chains
Three-carbon chains
Fatty acids Glucose Amino acids
ProteinsGlycogenTriglycerides
Nutrientpool
Fatty acid synthesisbegins with acetyl-CoA.Because this is thecommon intermediaryfor all aerobic catabolicpathways, fatty acidscan be synthesized fromexcess carbohydrates oramino acids.
KEY
= Catabolic pathway
= Anabolic pathway
A general overview of the catabolic and anabolic pathways of cells
CO2 must leave the cytosol bydiffusion into the ECF, and thebloodstream must continuouslyabsorb CO2 in peripheral tissuesand eliminate it at the lungs toprevent potentially dangerouschanges in body fluid pH.
O2 must becontinuouslyprovided bydiffusion from theECF. This requiresnormal respiratoryfunction andadequate tissueperfusion.
The primary use of aminoacids is the synthesis ofproteins. Amino acids areseldom broken down if otherenergy sources are available.However, in starvation theproteins of muscle tissuesare mobilized, releasingamino acids that can becatabolized by other tissues.
Glycolysis:glucose break-down into twothree-carbonmolecules/chains
Gluconeogen-esis: glucosesynthesis fromsmaller carbonchains.
The breakdownof a fatty acidreleases glyceroland acetyl-CoAsuitable for useby mitochondria.
In glycogenesis,glycogen issynthesized fromglucose.
The release ofglucose fromglycogen is calledglycogenolysis.
Storedtriglyceridescan be brokendown intofatty acids.
Fatty acidscan bestored astriglycerides.
Module 22.2 ReviewModule 22.2 Review
a. Define nutrient pool.
b. Why do cells engage in catabolism?
c. Why do cells make new compounds?
Section 2: Digestion and Section 2: Digestion and Metabolism of Organic Metabolism of Organic NutrientsNutrients Overview of digestive process
◦ Oral cavity (mechanical processing and chemical digestion of carbohydrates and lipids)
◦ Stomach (acidic chemical digestion)◦ Duodenum (various enzymes catalyze catabolism of
all organic molecules needed by cells)◦ Jejunum and Ileum (nutrient absorption)
Nutrients stored and processed by liver◦ Large intestine (water reabsorbed, nutrients and
vitamins produced by bacteria, feces eliminated)
Figure 22 Section 2Figure 22 Section 2
Steps in the Process of Digestion
In the oral cavity, saliva dissolves some organicnutrients, and mechanical processing withthe teeth and tongue disrupts the physicalstructure of the material and provides accessfor digestive enzymes. Those enzymes beginthe digestion of complex carbohydrates(polysaccharides) and lipids.
In the stomach, the material is further brokendown physically and chemically by stomachacid and by enzymes that can operate at anextremely low pH.
In the duodenum, buffers from the pancreas andliver moderate the pH of the arriving chyme, andvarious digestive enzymes are secreted by thepancreas that catalyze the catabolism ofcarbohydrates, lipids, proteins, and nucleic acids.
Nutrient absorption then occurs in the smallintestine, primarily in the jejunum, and thenutrients enter the bloodstream.
Indigestible materials and wastes enter the largeintestine, where water is reabsorbed and bacterialaction generates both organic nutrients andvitamins. These organic products are absorbedbefore the residue is ejected at the anus.
Most of the nutrients absorbed by the digestivetract end up in a tributary of the hepatic portalvein that ends at the liver. The liver absorbsnutrients as needed to maintain normal levelsin the systemic circuit.
Within peripheral tissues, cells absorb thenutrients needed to maintain their nutrient pooland ongoing operations.
Module 22.3: Module 22.3: CarbohydratesCarbohydrates Carbohydrates are usually preferred
substrates for catabolism and ATP production when resting
Steps of carbohydrate digestion◦ In mouth, salivary amylase digests
complex carbohydrates into disaccharides and trisaccharides
Enzyme active only down to pH 4.5 and denatured in stomach
◦ At duodenum, pancreatic alpha-amylase continues carbohydrate digestion
Module 22.3: Module 22.3: CarbohydratesCarbohydrates
Steps of carbohydrate digestion (continued)
◦ In jejunum, brush border enzymes finish carbohydrate digestion down to simple sugars (monosaccharides)
Maltase (digests maltose: glucose + glucose) Sucrase (digests sucrose: glucose + fructose) Lactase (digests lactose: glucose + galactose)
◦ In large intestine, remaining indigestible carbohydrates (such as cellulose) are food source for colonic bacteria
Produce intestinal gas (flatus) during metabolic activities
Module 22.3: Module 22.3: CarbohydratesCarbohydrates
Carbohydrate absorption and transport
◦ Transported into small intestine epithelial cells
Leave cells by facilitated diffusion through basolateral surface
◦ Enter cardiovascular capillaries to transport to liver in hepatic portal vein
Processed by liver to maintain glucose levels (~90 mg/dL) Released as glucose or Stored as glycogen
Module 22.3: Module 22.3: CarbohydratesCarbohydrates
Cellular use of digested carbohydrates◦ Generally preferred for catabolism
Proteins and lipids more important for structural components of cells and tissues
◦ In skeletal muscle, stored as glycogen◦ In most tissues, transported into cell by
carrier molecule (regulated by insulin) May be converted to ribose May be converted to 2 pyruvate molecules in
glycolysis Produces 2 ATP Pyruvates used by mitochondria
Uses 3 O2, generates 3 CO2, 6 H2O, 34 ATP
Figure 22.3Figure 22.3
Citricacidcycle
Coenzymes
ATP
Electrontransportsystem
CO2
H2O
O2
ATP
CO2Coenzyme A
Other simple sugars
Pyruvate(3-carbon)
Pyruvate(3-carbon)
Insulin
(6-carbon)GLUCOSE
Carbohydrates (such as glucose) are generallypreferred for catabolism because proteins andlipids are more important as structuralcomponents of cells and tissues.
Inside the cell, the glucose may be converted toanother simple sugar, such as ribose, used tobuild glycoproteins, other structural materials,or nucleic acids. They may also be converted toglycerol for the synthesis of glycerides.
If needed to provide energy, the 6-carbon glucosemolecule is broken down into two 3-carbonmolecules of pyruvate. This anaerobic process,called glycolysis, yields a net gain of 2 ATP forevery glucose molecule broken down.
For each molecule of pyruvate processed bymitochondria, the cell gains 17 ATP, consumes3 molecules of O2, and generates 3 molecules ofCO2 and 6 molecules of water. Thus for each pairof pyruvate molecules catabolized, the cell gains34 ATP.
Each pyruvate molecule can then be used bymitochondria, after conversion to acetyl-CoA.
In most tissues, thetransport of glucose into thecell is dependent on thepresence of a carrier proteinstimulated by insulin.
The events in carbohydrate catabolism and ATP production from glucose
Acetyl-CoA(2-carbon)
Module 22.3 ReviewModule 22.3 Review
a. Describe the source of intestinal gas.
b. Explain the role of glycogen in cellular metabolism.
c. Explain why carbohydrates are preferred over proteins and fats as an energy source.
Module 22.4: Catabolism of Module 22.4: Catabolism of glucoseglucose Glycolysis
◦ Anaerobic process making two 3-carbon pyruvate from one 6-carbon glucose
◦ Occurs in cytosol◦ Produces a net gain of 2 ATP
Also produces hydrogen atoms that are transferred by NAD to mitochondria for ETS
Module 22.4: Catabolism of Module 22.4: Catabolism of glucoseglucose
Steps of glycolysis◦ Phosphate group attached to glucose in
cytosol◦ 2nd phosphate attached (cost of 2 ATP)◦ 6-carbon molecule split into two 3-carbon
molecules◦ Another phosphate attached to each molecule
and processed further 2 NADH generated 2 ATP generated 2 H2O released
◦ Further processing creates an additional 2 ATP
Figure 22.4 Figure 22.4 11
The steps in glycolysis, the breakdown of a six-carbonglucose molecule into two three-carbon pyruvate molecules
Steps in Glycolysis
As soon as a glucose moleculeenters the cytosol, a phosphategroup is attached to the molecule.
A second phosphate group isattached. Together, steps 1 and 2cost the cell 2 ATP.
The six-carbon chain is splitinto two three-carbon molecules,each of which then follows therest of this pathway.
Another phosphate group isattached to each molecule, andNAD•H is generated from NAD.
One ATP molecule is formed foreach molecule processed.
The atoms in each molecule arerearranged, releasing amolecule of water.
A second ATP molecule is formedfor each molecule processed.Step 7 produces 2 ATP molecules.
GlucoseINTERSTITIAL
FLUID
CYTOSOLATP
ADP
Glucose-6-phosphate
Fructose-1,6-biphosphate
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ADP
ADP
ADP
Glyceraldehyde3-phosphate
Dihydroxyacetonephosphate
NAD From mitochondria
To mitochondria
1,3-Bisphosphoglycerate
3-Phosphoglycerate
Phosphoenolpyruvate
NAD•H
H2O
Pyruvate
To mitochondria
2
2
2
2
2
2
–2
+2
+2
+2
Steps 1 & 2:
Step 5:
Step 7:
NET GAIN:
Energy Summary
22
Module 22.4: Catabolism of Module 22.4: Catabolism of glucoseglucose Summary of aerobic ATP production
◦ 4 ATP from NADH produced in glycolysis
◦ 24 ATP from NADH generated in citric acid cycle
◦ 4 ATP from FADH2 generated in citric acid cycle
◦ 2 ATP via GTP produced during enzymatic reactions
◦ 34 ATP total
Figure 22.4 Figure 22.4 22
Module 22.4 ReviewModule 22.4 Review
a. List the molecular products from a glucose molecule after glycolysis.
b. Identify when most of the CO2 is released during the complete catabolism of glucose.
c. Explain when glycolysis may be important in cellular metabolism.
Module 22.5: Lipids Module 22.5: Lipids
Steps of lipid digestion◦ In mouth, mechanical processing and
chemical digestion by lingual lipase◦ In stomach, lingual lipase continues to
function but can only access surface of lipid drops that have formed
◦ In duodenum Bile salts break up lipid drops into smaller
droplets (= emulsification) Pancreatic lipase digests triglycerides into
fatty acids, monoglycerides, and glycerol Forms micelles (lipid–bile salt complexes)
Module 22.5: LipidsModule 22.5: Lipids
Absorption and transport of digested lipids◦ Lipids diffuse from micelle into intestinal epithelial cell◦ Intracellular anabolic reactions synthesize new
triglycerides from digested lipids◦ New triglycerides packaged in chylomicrons (chylos,
milky lymph, mikros, small) and released via exocytosis
◦ Chylomicrons diffuse into intestinal lacteals due to their size
Transported through lymphatic vessels (including thoracic duct) to bloodstream
◦ Enzyme in capillaries (lipoprotein lipase) breaks down chylomicron and releases digested lipids to tissues
Module 22.5: LipidsModule 22.5: Lipids
Digested lipid distribution and processing
◦ Tissues that use or process digested lipids
Skeletal muscles Use fatty acids to generate ATP for contraction and
to convert glucose to glycogen
Adipose tissue Uses fatty acids and monoglycerides to synthesize
triglycerides for storage
Liver Absorbs intact chylomicrons and extracts
triglycerides and cholesterol from chylomicron
Module 22.5: Module 22.5: LipidsLipids
Cholesterol distribution◦ Released from liver attached to low-density
lipoproteins (LDL) for distribution to peripheral tissues
◦ LDLs absorbed and broken down by lysosomes in cells Cholesterol extracted and used Unused cholesterol released into bloodstream
◦ High-density lipoproteins (HDL) (plasma proteins from liver) absorb peripheral cholesterol and return to liver
Cholesterol released again with LDLs or excreted in bile Ratio of LDL/HDL and total cholesterol used
diagnostically for cardiovascular problems
Figure 22.5Figure 22.5
From the lacteals,the chylomicronsproceed along thelymphatic vesselsand into thethoracic duct.
The chylomicronsenter the bloodstreamat the left subclavianvein, then passthrough thepulmonary circuitbefore entering thesystemic circuit.
Capillary walls contain theenzyme lipoprotein lipase,which breaks down thechylomicrons and releasesfatty acids and monoglycer-ides that can diffuse into theinterstitial fluid.
The liver absorbs chylomicrons, removes thetriglycerides, combines the cholesterol from thechylomicron with synthesized or recycledcholesterol, and alters the surface proteins. It thenreleases low-density lipoproteins (LDLs) intothe circulation, which deliver cholesterol toperipheral tissues. Some of the cholesterol is usedby the liver to synthesize bile salts; excesscholesterol is excreted in the bile.
Lipoproteins and Lipid Transport and Distribution
The HDLs returnthe cholesterol tothe liver, where itis extracted andpackaged in newLDLs or excretedwith bile salts inbile.
Resting skeletal muscles absorb fattyacids and break them down, using theATP provided both to power thecontractions that maintain muscle tone and to convert glucose to glycogen.
Adipocytes absorbthe monoglyceridesand fatty acids,and use them tosynthesize triglycer-ides for storage.
The LDLs released by theliver leave the bloodstreamthrough capillary pores orcross the endothelium byvesicular transport.
Once in peripheral tissues,the LDLs are absorbed.
Chylomicrons
Excesscholesterol isexcreted withthe bile salts
LDL
Cholesterolrelease
Lysosomalbreakdown
Used in synthesisof membranes,hormones,other material
LDL
Triglyceridesremoved
Cholesterolextracted
Lowcholesterol
Highcholesterol
HDL
HDL
HDL
Thoracicduct
Module 22.5 ReviewModule 22.5 Review
a. What is the difference between a micelle and a chylomicron?
b. What does the liver do with the chylomicrons it receives?
c. Describe the roles of LDL and HDL.
Module 22.6: Lipid catabolism and Module 22.6: Lipid catabolism and synthesissynthesis Lipolysis (lipid catabolism)
◦ Triglycerides absorbed into cells through endocytosis
Lysosomal enzymes break down to glycerol and fatty acids Glycerol
Converted to pyruvate in glycolysis (+ 2 ATP) Fatty acids
Enzymes convert two carbons to acetyl-CoA directly (= beta-oxidation) used in mitochondria
More efficient than glucose catabolism (6-carbon glucose = 36 ATP; 6 carbons from FAs = 51 ATP)
Module 22.6: Lipid catabolism and Module 22.6: Lipid catabolism and synthesissynthesis Lipid synthesis (lipogenesis)
◦ Begins with acetyl-CoA Almost any organic substrate (lipids, amino acids,
carbohydrates) can be converted to acetyl-CoA
◦ Fatty acids synthesized from acetyl-CoA Series of enzymatic steps (different from beta-oxidation) Essential fatty acids
Cannot be synthesized and must be obtained from diet Examples: linolenic acid (omega-3 fatty acid) and
linoleic acid (omega-6 fatty acid)
◦ Structural and functional lipids created from fatty acids
Fatty acids + glycerol (from glycolysis) = triglycerides
Figure 22.6 Figure 22.6 22
The synthesis of most types of lipids, includingnonessential fatty acids and steroids, beginswith acetyl-CoA. Lipogenesis can use almostany organic substrate, because lipids, aminoacids, and carbohydrates can be converted toacetyl-CoA.
The major pathways for lipogenesis, the synthesis of lipids
Start
Fatty acid synthesis involves a reaction sequencequite distinct from that of beta-oxidation. As aresult, body cells cannot build every fatty acidthey can break down. For example, our cells lackthe enzymes to insert double bonds in the properlocations to synthesize two 18-carbon fatty acidssynthesized by plants: linolenic acid (anomega-3 fatty acid) or linoleic acid (anomega-6 fatty acid). However, these fatty acidsare needed to synthesize prostaglandins andsome of the phospholipids found in plasmamembranes throughout the body. They aretherefore called essential fatty acids, becausethey must be included in your diet.
All of the other structural and functionallipids can be synthesized from fatty acids.
The glycerol required for triglycerideproduction is synthesized from one of theintermediate products of glycolysis.
Prostaglandins
Acetyl-CoA
Glycolipids
Phospholipids
Cholesterol
Steroids Triglycerides
Fatty acids
Glycerol
Glucose
Pyruvate
Citricacidcycle
MITOCHONDRIA
ATP
ADP
Coenzyme A
CYTOSOL
CO2
Module 22.6: Lipid catabolism and Module 22.6: Lipid catabolism and synthesissynthesis
Lipids as energy reserves◦ Beta-oxidation is very efficient◦ Can be easily stored as triglycerides
Although water-soluble enzymes cannot access, so not used for quick energy but for long-term storage
Module 22.6 ReviewModule 22.6 Review
a. Define beta-oxidation.
b. What molecule plays a key reactant role in both ATP production from fatty acids and lipogenesis?
c. Identify the fates of fatty acids.
Module 22.7: Protein digestion Module 22.7: Protein digestion and amino acid metabolismand amino acid metabolism Steps of protein digestion
◦ In mouth, mechanical processing occurs◦ In stomach:
Mechanical processing due to churning Stomach acid denatures protein secondary
and tertiary structures Pepsin (from parietal cells) attacks certain
peptide bonds Digests proteins to polypeptide and peptide
chains
Module 22.7: Protein digestion and Module 22.7: Protein digestion and amino acid metabolismamino acid metabolism
Steps of protein digestion (continued)◦ In duodenum:
Enteropeptidase (from duodenal epithelium) converts trypsinogen (pancreatic proenzyme) to trypsin
Trypsin activates other pancreatic proenzymes Chymotrypsin, carboxypeptidase, and
elastase
Activated pancreatic enzymes digest specific peptide bonds producing short peptides and amino acids
Module 22.7: Protein digestion Module 22.7: Protein digestion and amino acid metabolismand amino acid metabolism
Digested protein absorption and transport
◦ Epithelial brush border enzymes (peptidases) finish protein digestion
◦ Amino acids absorbed through: Facilitated diffusion Cotransport
◦ Released from epithelial cell basal surface through same cell transport mechanisms
◦ Amino acids transported to liver through intestinal capillaries to hepatic portal vein
Module 22.7: Protein digestion and Module 22.7: Protein digestion and amino acid metabolismamino acid metabolism
Amino acid processing in liver◦ Control of plasma amino acid levels is
less precise than glucose Normal range: 35–65 mg/dL Can increase after protein-rich meal
◦ Liver amino acid use Synthesize plasma proteins Create 3-carbon molecules for
gluconeogenesis
Module 22.7: Protein digestion and Module 22.7: Protein digestion and amino acid metabolismamino acid metabolism
Amino acid processing in liver (continued)
◦ Amino acid catabolism Deamination (removal of amino group)
Ammonium ions released are toxic Liver enzymes convert to urea excreted
into urine = Urea cycle
Figure 22.7Figure 22.7
Organic acid 1 Organic acid 2 TyrosineGlutamic acid
Transaminase
Amino Acid Synthesis
In a transamination, the amino group of one amino acid gets transferredto another molecule, yielding a different amino acid. The remaining carbonchain can then be broken down or used in other ways.
Glutamic acidα–Ketoglutarate
In an aminationreaction, an ammoniumion (NH4
+) is used toform an amino groupthat is attached to amolecule, yielding anamino acid.
Liver cells and other body cells can readily synthesize the carbonframeworks of roughly half of the amino acids needed to synthesize proteins.There are 10 essential amino acids that the body either cannot synthesizeor that cannot be produced in amounts sufficient for growing children.
The liver does not control circulating levelsof amino acids as precisely as it doesglucose concentrations. Plasma amino acidlevels normally range between 35 and 65mg/dL, but they may become elevated aftera protein-rich meal. The liver itself usesmany amino acids for synthesizing plasmaproteins, and it has all of the enzymesneeded to synthesize, convert, or catabolizeamino acids. In addition, amino acids thatcan be broken down to 3-carbon moleculescan be used for gluconeogenesis whenother sources of glucose are unavailable.
NH4+
H+
H2O
Module 22.7 ReviewModule 22.7 Review
a. Name the enzyme secreted by parietal cells that is necessary for protein digestion.
b. Identify the processes by which the amino group is removed.
c. What happens to the ammonium ions that are removed from amino acids during deamination?
Module 22.8: Absorptive and Module 22.8: Absorptive and postabsorptive statespostabsorptive states
Absorptive state◦ Period following a meal, when nutrient
absorption is occurring◦ Commonly continues for ~4 hours◦ Insulin is primary regulating hormone by
stimulating:1. Glucose uptake and glycogenesis2. Amino acid uptake and protein synthesis
Others can be involved (GH, androgens, estrogens)
3. Triglyceride synthesis◦ ATP can be produced from nutrient pool
Figure 22.8 Figure 22.8 11
KEY
The activities during the absorptive state following a meal
= Catabolic pathway= Anabolic pathway= StimulationGlucoselevels elevated
Insulin
Triglycerides Glycogen Proteins
Glucose
Lipid levelselevated
Fatty acids Glycerol Amino acids Amino acidselevated
Pyruvate
Insulin
InsulinInsulinAndrogensEstrogensGrowth hormone
Insulin
Insulin,Growth hormone
LIPIDS CARBOHYDRATES PROTEINS
ATP
ATP
In the absorptive state:• Insulin stimulates (1) glucose uptake and glycogenesis, (2) amino acid uptake and protein synthesis, and (3) triglyceride synthesis.
• Androgens, estrogens, and growth hormone also stimulate protein synthesis.
• Glycolysis and aerobic metabolism provide the ATP needed to power cellular activities as well as the synthesis of lipids and proteins.
CO2
CO2
H2O
Acetyl-CoA
Citricacidcycle
CoenzymesElectrontransportsystem
MITOCHONDRIA
O2 O2
GlycolysIs
Module 22.8: Absorptive and Module 22.8: Absorptive and postabsorptive statespostabsorptive states
Postabsorptive state◦ Period when nutrient absorption in not occurring and
body relies on energy reserves (~12 hours/day)◦ Metabolic activity focused on mobilizing energy
reserves and maintaining blood glucose Lipid levels decrease = fatty acids released by
adipocytes Amino acid levels decrease = amino acids released by
liver Glucose levels decrease = glucose released by liver
◦ Coordinated by several hormones Glucagon, epinephrine, glucocorticoids, growth hormone
Module 22.8: Absorptive and Module 22.8: Absorptive and postabsorptive statespostabsorptive states
Postabsorptive state (continued)
◦ Catabolism of lipids and amino acids in liver produce acetyl-CoA
Leads to formation of ketone bodies Diffuse into blood and are used by other cells
as energy source
Module 22.8: Absorptive and Module 22.8: Absorptive and postabsorptive statespostabsorptive states
Postabsorptive state (continued)◦ Hormone effects
Glucocorticoids Stimulate mobilization of lipid and protein reserves
Enhanced by growth hormone Glucagon
Stimulates glycogenolysis and gluconeogenesis Mainly in liver
Epinephrine Glycogenolysis in skeletal and cardiac muscle Lipolysis in adipocytes
Module 22.8 ReviewModule 22.8 Review
a. Define absorptive state and postabsorptive state.
b. When and how do ketone bodies form?
c. How do the absorptive and postabsorptive states maintain normal blood glucose levels?
Module 22.9: Module 22.9: VitaminsVitamins Nutrition
◦ Absorption of nutrients from food Vitamins
◦ Organic compounds required in very small quantities for essential metabolic activities
◦ Two classes1. Fat-soluble vitamins (A, D3, E, and K)
2. Water-soluble vitamins (B vitamins and C)
Module 22.9: Module 22.9: VitaminsVitamins
Fat-soluble vitamins◦ Absorbed primarily from digestive tract with micelles◦ Vegetables are potential sources
Vitamin D3 produced in skin
Vitamin K produced by intestinal bacteria
◦ Stored in lipid deposits Gives large bodily reserves
Avitaminosis (vitamin deficiency) rarely occurs with fat-soluble vitamins
Hypervitaminosis can occur as metabolism from lipid reserves takes time
Figure 22.9 Figure 22.9 22
Figure 22.9 Figure 22.9 22
Module 22.9: VitaminsModule 22.9: Vitamins
Water-soluble vitamins◦ Most are components of coenzymes◦ Nutritional sources
B vitamins are found in meat, eggs, and dairy products
Vitamin C is found in citrus fruits
◦ Significant stores of only vitamins B12 and C
◦ Intestinal bacteria produce four of nine B vitamins
Module 22.9: VitaminsModule 22.9: Vitamins
Water-soluble vitamins (continued)◦ Readily exchanged between body fluid
compartments◦ Most easily absorbed across intestinal wall
B12 requires transport with intrinsic factor
◦ Excess amounts excreted in urine Hypervitaminosis rarely occurs with water-
soluble vitamins
Figure 22.9 Figure 22.9 44
Figure 22.9 Figure 22.9 44
Figure 22.9 Figure 22.9 44
Module 22.9 ReviewModule 22.9 Review
a. Define nutrition.
b. Identify the two classes of vitamins.
c. If vitamins do not provide a source of energy, what is their role in nutrition?
StopStop
Module 22.10: Nutrition and Module 22.10: Nutrition and dietdiet
Balanced diet◦Contains all ingredients required for
homeostasis Substrates for ATP production Essential amino acids Fatty acids Vitamins Electrolytes Water
◦Malnutrition Unhealthy state from inadequate or excessive
nutrient absorption
Module 22.10: Nutrition and Module 22.10: Nutrition and dietdiet
MyPyramid.gov Steps to a Healthier You◦U.S. Dept. of Agriculture personalized
eating plans based on current Dietary Guidelines for Americans
◦Color-coded vertical food groups indicate recommended proportions Grains (orange) Vegetables (green) Fruits (red) Milk products (blue) Meat and beans (purple) Oils (yellow)
Figure 22.10 Figure 22.10 11
The MyPyramid.gov Steps to a Healthier You
Activity
GRAINS VEGETABLES FRUITSOILS
MILK MEAT & BEANSMake half your grains wholeVary your veggies Focus on fruits Get your calcium-rich foodsGo lean with proteins
Figure 22.10 Figure 22.10 11
Figure 22.10 Figure 22.10 11
Module 22.10: Nutrition Module 22.10: Nutrition and dietand dietFood energy content
◦ Common units are calories or joules (0.239 calories) 1 calorie = energy to raise temperature of 1 g of water by
1°C
◦ Kilocalories (kcal or Calorie) or kilojoule (kJ) are used for whole-body metabolism 1 kCal = energy to raise temperature of 1 kg of water by
1°C
◦ Energy yield of different nutrients varies Carbohydrates: 4.18 Cal/g Proteins: 4.32 Cal/g Lipids: 9.46 Cal/g
◦ Average adult needs 2000–3000 Cal daily
Figure 22.10 Figure 22.10 22
Figure 22.10 Figure 22.10 33
Module 22.10: Nutrition and Module 22.10: Nutrition and dietdietDifferent nutritional proteins
◦Complete proteins Provide all essential amino acids From beef, fish, poultry, eggs, and milk
◦Incomplete proteins Deficient in one or more essential amino acids Mostly from plant sources Vegetarians and vegans must closely monitor
sufficient combination of plant protein sources
Module 22.10 ReviewModule 22.10 Review
a. Define balanced diet.
b. Distinguish between a complete protein and an incomplete protein.
c. Of these three—carbohydrates, lipids, or proteins—which one releases the greatest number of Calories per gram during catabolism?
CLINICAL MODULE 22.11: CLINICAL MODULE 22.11: Metabolic disordersMetabolic disorders
Disorders related to diet and digestion◦ Eating disorders (psychological problems
resulting in abnormal eating habits) Anorexia nervosa
Self-induced starvation or lack/loss of appetite Weights commonly 30% below normal
Most common in adolescent Caucasian females Patients convinced they are too fat
Bulimia Binge eating followed by vomiting, or use of
laxatives or diuretics More common than anorexia
CLINICAL MODULE 22.11: CLINICAL MODULE 22.11: Metabolic disordersMetabolic disorders Disorders related to diet and digestion
(continued)◦ Obesity
Condition of being >20% over ideal weight Due to energy input > energy output
U.S. Centers for Disease Control (CDC) estimate: 32% of men and 35% of women are obese
Two major categories1. Regulatory obesity (failure to regulate food input)
Most common form2. Metabolic obesity (secondary to underlying
malfunction in cell/tissue metabolism)
CLINICAL MODULE 22.11: CLINICAL MODULE 22.11: Metabolic disordersMetabolic disorders
Disorders related to diet and digestion (continued)
◦ Elevated cholesterol levels May cause development of atherosclerosis
and coronary artery disease Recommended <300 mg/day High LDL levels can lead to deposits in
peripheral tissues such as blood vessels
CLINICAL MODULE 22.11: CLINICAL MODULE 22.11: Metabolic disordersMetabolic disorders
Nutritional/metabolic disorders◦ Phenylketonuria (PKU)
Inability to convert phenylalanine to tyrosine Essential to synthesis of:
Norepinephrine Epinephrine Dopamine Melanin
◦ Protein deficiency disease Liver unable to produce plasma proteins leading to
edema Example: kwashiorkor
CLINICAL MODULE 22.11: CLINICAL MODULE 22.11: Metabolic disordersMetabolic disorders Nutritional/metabolic disorders
(continued)◦ Ketoacidosis
Acidification of blood due to ketone body production Leads to ketosis
Occurs when glucose supplies are limited Fatty acid and amino acid catabolism in liver leads
to acetyl-CoA production and generation of ketones In extreme cases, may cause coma, cardiac
arrhythmias, and death◦ Gout (insoluble urea crystal formation)
Commonly in joints (gouty arthritis)
CLINICAL MODULE 22.11 CLINICAL MODULE 22.11 ReviewReviewa. Identify and briefly
define two eating disorders.
b. Define protein deficiency disease and cite an example.
c. Briefly describe phenylketonuria (PKU).
Section 3: Energetics and Section 3: Energetics and ThermoregulationThermoregulation
Energetics◦ Study of energy flow and energy conversion◦ Basal metabolic rate (BMR)
Minimum resting energy expenditure of awake, alert person Various factors can affect BMR
Person’s size or weight Level of physical activity
Common benchmark for energetics studies Direct measurement method
Measuring respiratory activity and assuming 4.825 Cal/L oxygen consumed
Average is 70 Cal/hr
Figure 22 Section 3 Figure 22 Section 3 22
The approximate number ofCalories expended per hourat various levels of physicalexertion
Estimated Calories expendedby a 70-kg individual
Resting Slowwalking
Speedwalking
Climbingstairs
Jogging Competitiveswimming
Calo
ries p
er
hou
r
1000
800
600
400
200
0
Section 3: Energetics and Section 3: Energetics and ThermoregulationThermoregulation
Thermoregulation◦Homeostatic control of body temperature
Maintaining food intake adequate to support body activities
◦Catabolic reactions generating ATP 40% of energy used to form ATP 60% released as heat
◦Many enzymes and metabolic activities require a specific temperature range
Module 22.12: Appetite Module 22.12: Appetite regulationregulation Appetite is controlled by two areas of
hypothalamus1. Feeding center2. Satiety center
Causes inhibition of feeding center
Regulation of appetite can occur on two levels1. Short-term regulation2. Long-term regulation
Module 22.12: Appetite Module 22.12: Appetite regulationregulation
Short-term regulation of appetite◦Stimulation of satiety center
Elevation of blood glucose levels Hormones of digestive tract (like CCK) Digestive tract wall stretching
◦Stimulation of feeding center Neurotransmitters
Example: neuropeptide Y or NPY from hypothalamus
Ghrelin Hormone secreted by gastric mucosa when stomach is
empty
Module 22.12: Appetite Module 22.12: Appetite regulationregulationLong-term regulation of appetite
Leptin Peptide hormone secreted by adipocytes Stimulates satiety center and suppresses appetite Effects are gradual
Figure 22.12Figure 22.12
Short-Term Regulation of Appetite
Stimulation of Satiety Center
Elevated bood glucose levels depressappetite, and low blood glucosestimulates appetite. The likelymechanism is glucose entry stimulatingthe neurons of the satiety center.
Several hormones of the digestive tract,including CCK, suppress appetiteduring the absorptive state.
Stimulation of stretch receptors alongthe digestive tract, especially in thestomach, causes a sense of satiationand suppresses appetite.
Stimulation of Feeding Center
Several neurotransmitters havebeen linked to appetite regulation.Neuropeptide Y (NPY), for example,is a hypothalamic neurotransmitter that(among other effects) stimulates thefeeding center and increases appetite.
The hormone ghrelin (GREL-in),secreted by the gastric mucosa,stimulates appetite. Ghrelin levels arehigh when the stomach is empty, anddecline as the stomach fills.
Mechanisms in the controlof appetite
Hypothalamus
Satiety center
Feeding center
Long-Term Regulation of Appetite
When appetite outpaces energy usage,excess calories are stored as fat inadipose tissue. Leptin is a peptidehormone released by adipose tissuesas they synthesize triglycerides. In theCNS it stimulates the satiety centerand suppresses appetite. The effectsare gradual, and it is probably involvedin long-term regulation of food intake.
Module 22.12 ReviewModule 22.12 Review
a. What hormone inhibits the satiety center and stimulates appetite in the short-term?
b. Describe leptin and its effect on appetite.
c. How might a lack of Neuropeptide Y in the hypothalamus affect the control of appetite?
Module 22.13: Module 22.13: ThermodynamicsThermodynamicsThermodynamics
◦About 40% of energy from catabolism is captured as ATP Rest is heat that warms surrounding tissues
◦To maintain body temperature, heat loss and heat production must be in balance Varying activities and environmental
conditions affect heat balance
Module 22.13: Module 22.13: ThermodynamicsThermodynamicsPrimary heat transfer mechanisms
1. Radiation (infrared radiation from warm objects)
~50% of body heat lost by radiation2. Convection (conductive heat loss due to
air movement)3. Evaporation (water loss from moist
areas) Insensible perspiration (from alveoli and skin) Sensible perspiration (from sweat glands)
4. Conduction (direct transfer through physical contact)
Figure 22.13 Figure 22.13 11
The primarymechanisms ofheat transferbetween the bodyand the surroundingenvironment
Primary Mechanisms of Heat Transfer
Radiation: Warm objects lose heat energy as infraredradiation. More than 50 percent of the heat you loseindoors is attributable to radiation.
Convection: This process results from conductive heatloss to the air that overlies the surface of the body.Convection accounts for roughly 15 percent of thebody’s heat loss indoors
Evaporation: When water changes from a liquid to avapor, evaporation absorbs energy and cools thesurface where it occurs. Insensible perspiration—theevaporation of water across epithelia, from alveolarsurfaces, and from the skin—accounts for roughly 20percent of heat loss indoors. The water in sweat istermed sensible perspiration.
Conduction: This process, which is the direct transferof energy through physical contact, is generally not aneffective mechanism for gaining or losing heat. Whenyou are standing, conductive losses are negligible.
Figure 22.13 Figure 22.13 22
The effects of afailure to controlbody temperature
Underlying physical orenvironmental condition
Thermoregulatorycapabilities
Majorphysiological effects
Normal range (oral)
CNS damageHeat stroke
Active childrenSevere exercise
Disease-related fevers
Early mornings incold weather
Severe exposure
Hypothermiafor open heart
surgery
Severely impaired
Impaired
Effective
Impaired
Severely impaired
Lost
DeathProteins denature
ConvulsionsCell damage
Disorientation
Systems normal
DisorientationLoss of
muscle controlLoss of
consciousnessCardiac arrest
Death
°F °C
114
110
106
102
98
94
90
86
82
78
74
44
42
40
38
3634
32
30
28
26
24
Module 22.13 ReviewModule 22.13 Review
a. Define insensible perspiration.
b. What heat transfer process accounts for about one-half of an individual’s heat loss when indoors?
c. How is heat loss different between conduction and convection?
Module 22.14: Module 22.14: ThermoregulationThermoregulation Thermoregulation
◦ Heat loss and heat gain involve many systems
◦ Coordinated by two centers in hypothalamus preoptic area 1. Heat-loss center2. Heat-gain center
Module 22.14: Module 22.14: ThermoregulationThermoregulation
Responses to high body temperature◦ Behavioral changes (moving to shade,
pool, etc.)◦ Vasodilation and shunting of blood to
skin surface Radiational and convective heat loss
increases
◦ Sweat production Increases evaporative heat loss
◦ Respiratory heat loss Depth of respiration increases to increase
evaporative heat loss from lungs
Figure 22.14Figure 22.14
Responses Coordinated by the Heat-LossCenter When Body Temperature Rises
Behavioral Changes: A senseof discomfort leads to behavioralresponses—getting into the shade, goinginto the water, or taking other steps thatreduce body temperature.
Vasodilation and Shunting of Blood toSkin Surface: The inhibition of thevasomotor center causes peripheralvasodilation, and warm blood flows to thesurface of the body. The skin takes on a reddish color, skin temperatures rise, andradiational and convective losses increase.
Sweat Production: As blood flow to theskin increases, sweat glands are stimulatedto increase their secretory output. Theperspiration flows across the body surface,and evaporative heat losses accelerate.Maximal secretion, if completely evaporated,would remove 2320 Cal per hour.
Respiratory Heat Loss: The respiratorycenters are stimulated, and the depth ofrespiration increases. Often, the individualbegins respiring through an open mouthrather than through the nasal passageways,increasing evaporative heat losses throughthe lungs.
Convection
Radiation
Preoptic area
Heat-loss center
Heat-gain center
Module 22.14: Module 22.14: ThermoregulationThermoregulation
Responses to low body temperature◦ Increased generation of body heat
Nonshivering thermogenesis Release of hormones that increase metabolic rate
Shivering thermogenesis Increased muscle tone leading to brief contractions
◦ Conservation of body heat Vasoconstriction of vessels near body surface Countercurrent exchange of heat
Transfer of heat from deep arteries to deep veins
Figure 22.14Figure 22.14
Convection
Radiation
Warmblood from
trunk
Warm bloodreturnsto trunk
Cooled bloodto distal
capillaries
Cool bloodreturnsto trunk
23°C24°C
37°C
37°C36.5°–
H e
a t
t
r a
n s
f e
r
The deep veins lie alongside the deep arteries, and heatis conducted from the warm blood flowing outward to thelimbs to the cooler blood returning from the periphery.This arrangement traps the heat close to the body coreand dramatically reduces heat loss. The transfer of heat,water, or solutes between fluids moving in oppositedirections is called countercurrent exchange.
The vasomotor center decreases blood flow to the dermis,thereby reducing losses by radiation and convection. Theskin cools, and with blood flow restricted, it may take on abluish or pale color. The epithelial cells are not damaged,because they can tolerate extended periods at temperaturesas low as 25°C (77°F) or as high as 49°C (120°F).
Conservation of Body Heat
In shivering thermogenesis, a gradual increase inmuscle tone increases the energy consumption ofskeletal muscle tissue throughout your body. Bothagonists and antagonists are involved, and muscle tonegradually increases to the point at which stretch receptorstimulation will produce brief, oscillatory contractionsof antagonistic muscles. In other words, you begin toshiver. Shivering can elevate body temperature quiteeffectively, increasing the rate of heat generation by asmuch as 400 percent.
Nonshivering thermogenesis (ther-mō-JEN-e-sis)involves the release of hormones that increase themetabolic activity of all tissues. Sympathetic stimulationof the adrenal medullae releases epinephrine, whichquickly increases the rates of glycogenolysis in liver andskeletal muscle and the metabolic rate of most tissues.
Increased Generation of Body Heat
The heat-gain center responds to low bodytemperature in two ways:
Responses Coordinated by the Heat-Gain CenterWhen Body Temperature Falls
Module 22.14 ReviewModule 22.14 Review
a. Name the heat conservation mechanism that results in the conduction of heat from deep arteries to adjacent deep veins in the limbs.
b. Describe the role of nonshivering thermogenesis in regulating body temperature.
c. Predict the effect of peripheral vasodilation on an individual’s body temperature.
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