Food Processing. Module 22.2: Nutrient pool substrates Nutrient pool supplies molecules for...

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


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)


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


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


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)


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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

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


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)


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

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

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


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)


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


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


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.


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)


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.


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


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


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


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


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.

Food Processing. Module 22.2: Nutrient pool substrates Nutrient pool supplies molecules for...

Documents

Transcript of Food Processing. Module 22.2: Nutrient pool substrates Nutrient pool supplies molecules for...