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Flashcards in Metabolism and Energy Balance Deck (53):


-Nutrient (and it's 2 types)

-Nutrient: A substance used in an organism's metabolism or physiology

-Essential nutrient: those that MUST be supplied in diet
-Non-essential nutrient: Those that can be synthesized de novo


Major Nutrients; Carbohydrates

-% constitute of our diet

-formula - most common one too

-3 groups

-approx 55-60% of total energy intake
-general formula CnH2nOn
-most common is glucose (C6H12O6)
3 groups;
i. Monosaccharides
ii. Disaccharides


3 types of carbohydrates - features

i. Monosaccharides; e.g. glucose
-single C ring
-Used as an energy source and can pass epithelial lining
ii. Disaccharides; e.g. lactose, maltose, sucrose
-two sugar rings - to break is a dehydration reaction
iii. Polysaccharides; e.g. starch glycogen, fibre
-are long chains of C rings


Major Nutrients; Proteins

-% of energy intake

-what is is

-no in animals and essential a.a.

-approx 10-20% of total energy intake
-Are large, complex organic molecules - are building blocks of all cells
-animals have 20 a.a. linked by peptide bonds
-8 essential a.a. (deficient diets in these = developmental defects and slower growth)
-Higher quality a.a. in animal tissue than plant tissue


4 types of protein folding

1. Primary structure: a.a./DNA code
2. Secondary structure: alpha helix or beta sheet - when sequence of a.a. linked by H bonds
3. Tertiary structure: Occurs by folding of proteins
4. Quaternary structure: protein consisting of more than one a.a. chain (e.g. Haemoglobin)


Major Nutrients; Lipids

-% of energy intake

-What they are
-What they do
-What stored as

-approx 25-30% of total energy intake
-large, organic, hydrophobic molecules - important form of energy storage
-provides barrier function
-Comprised of fatty acids; can have short, medium and long chain
-Stored as triacylglyceral in liver, muscle and adipose tissue


Essential Fatty acids (2)

- Omega - 3 and Omega - 6 (as animals cannot produce sufficient amounts
-Ingested as alpha linolenic acid (from plant seeds) or linoleic acid found in fish (respectively)


Major Nutrients; Vitamins

-what they are
-categories and e.g. from each

-Unrelated molecules with diverse functions
-Categorized based on solubility (water soluable or fat soluble)
Fat soluble;
-A (retinol - eyesight), D (Calcium and Phosphorous), E (antioxidant) and K (blood clotting)
Water soluble;
-B vitamins (are all coenzymes


Major Nutrients; Minerals


-E.g. of functions

-e.g. Calcium, Phosphorus, iron, copper, zinc
-variety of functions;
-Co-factors in enzyme-catalysed reactions
-Regulation of acid-base balance
-Nerve conduction
-Muscle contraction


Major Nutrients; Water

-energy value?

-% of what we consume

-approx 60% of what we consume
-no energy value - acts as solvent for other nutrients


Digestion - what is it?

-Hydrolysis defin.

-Digestion is the breakdown of large molecules into absorbable units, achieved by mechanical and chemical digestion
-Hydrolysis: chemical breakdown of feed via addition of water molecule to broken bond


Absorption - what is it and where does it occur mainly

-Absorption = uptake into the body
-most nutrient absorption occurs in the small intestine (additional absorption of water, ions and some acids in large intestine)


Digestive enzymes

-what they do

-4 types

-Convert complex macromolecules into forms that can be absorbed and processed

-Amylases: break down polysaccharides into oligosaccharides
-Proteases: break down proteins to shorter polypeptides
-Lipases: Release fatty acids from triglycerides and phospholipids
-Nucleases: break down DNA into nucleotides


Carbohydrate breakdown

-Glycogen -> glycogen and oligosaccharides (via salivary amylases in mouth)
-Glycogen and oligosaccharides -> disaccharides (via pancreatic amylase in small intestine)
-Disaccharides -> monosaccharides (via disaccharidases in small intestine)

*no breakdown in stomach


Protein breakdown

-Proteins -> large polypeptides (via pepsin in stomach)
-Large polypeptides -> Dipeptides (via trypsin, chymotrypsin and carboxypeptidases in small intestine)
-Dipeptides -> amino acids (via dipeptidases in small intestine)


Lipid Breakdown

-problem - how overcome

-Transportation of different types of lipids

-Complicated by hydrophobicity - Gi tract secretes bile that emulsify lipids into small droplets (micelles)
-transport of lipids depends on physical properties
-in blood w/out assistance = short chain fatty acids and glycerol
-In lymph as complexes called chylomicrons (larger chain) = triglycerides, cholestrol




-GI tract

-Elimination (Egestion)

-Assimilation: the sequential processes of nutrient breakdown and absorption

-GI tract: continguous w/ external enviro (molecules that cross epithelia are apart of our body)

-Elimination: expulsion of undigested food


Gastrointestinal Tracts involved in the breakdown of food

-where reclamation of water and release of indigestible materials occur

-Mechanical breakdown: mouth, pharynx, esophagus
-Acidic: stomach
-Most digestion and absorption: upper or small intestines
-Reclamation of water: lower or large intestines
-Release of indigestible material: anus


Food quality on digestion

-high vs low quality diet

Digestive Limitation - definition

-High quality food:
-requires minimal energy to capture and eat
-higher rate of digestion
-releases lot of energy
-Low quality food:
-More energy to capture and eat
-lower rate of digestion
-yields less energy

-Digestive Limitation: the rate in which the stomach is working


Features of the GI Tract that assist in its function (2)

-Specialised compartments: increase efficiency of digestion (differ in vary in pH, enzyme comp, etc)
-Muscular valves (sphincters): control passage of food from one compartment to next

*complexity of gut morphology varies across taxa


4 layers of the stomach

1. Mucosa (innermost)
2. Submucosa
3. Circular (muscle)
4. Longitudinal (muscle)


Cells of the Mucosa surface of the stomach (5)

-what they secrete

-Composed of columnar epithelial cells

-Mucous Neck cells: Secrete mucus
-Parietal Cells: Secrete HCL acid
-Chief cells: Secrete pepsin
-Enteroendrocrine cells: Secrete hormones into blood (w/in microvilli)
-Paneth cells: secrete antimicrobial molecules

*mucus is important as it stops autodigestion


The Liver - things produced that assist with digestion (3)

-Bile: solution of digestive chemicals and liver waste products
-produced in liver and stored in gallbladder
-Phopholipids - aid in uptake of lipids
-Bile salts - emulsify fats


The Pancreas

-Pancreatic exocrine secretions: contain digestive enzymes
-protease, amylase, lipase, nuclease
-Pancreatic endocrine secretions: control blood glucose
-alpha cells secrete glucagon
-beta cells secrete insulin


Patterns of GI tract in different animals (4)

-Carnivores have a small small intestine, as they mainly rely on their stomach to break down proteins
-Ruminants have a large fore-stomach
-Horses have a large large intestine
-Birds have a crop (where they keep stones to break down food)


GI tract of Ruminants/Foregut fermenters


-Have fore-stomach w/ 4 chambers
-cellulose converted to Volatile Fatty acids (VFA) by bacteria, protozoa and fungi
-same with carbohydrate
-glucose requirements met by conversion to glucose in the liver


GI tract of Hindgut fermenters (e.g. horses)

-kangaroos, foregut or hindgut fermenters?

-Cellulose passes through large intestine
-Fermentation in large intestine - produces VFAs

*Kangaroos are foregut fermentors (have a v. large stomach)


Metabolism Definiton

-2 types of metabolism

-Collective term for huge no. of biochemical and physiological reactions that are necessary for life

-Anabolic: large molecules synthesised from smaller ones
-Catabolic: processes that break down complex structures to smaller, simpler ones

*release of energy not 100% efficient due to heat increment


Heat lost in Metabolism

-75% of energy from nutrients -> ATP -> cellular systems is lost as heat during transfer
-only 25% of nutrients available for work


Metabolism: Absorptive and Postabsorptive states (definition)

-type of fuel most important in both conditions

-Absorptive (Fed) state: the period of time following a meal where products of digestion are being absorbed, used and stored
-primarily anabolic - glucose is most important fuel (except in ruminants - use VFAs)
-v. llittle fat/a.a used immediately - get stored
-most cells used glucose first (except gut enterocytes - use a.a. as helps maintain conc. w/ glucose
-Post- absorptive (fasted) state: the period of time when nutrients from a meal are no longer available
-primarily catabolic - body reserves are fuel used


Post-Absorptive State

-Primary goal = spare glucose
-Endogenous energy stores (fat and glycogen) mobilised
-if starving, proteins are the next to be broken down


Starvation Response

-Reorganisation of metabolism to ensure long-term survival
-Preserve glucose to protect glucose-dependent tissues
-muscles shift to lipid metabolism
-Once lipid and glucose stores depleted, a.a. converted to FAs and carbs
-degradation occurs


Key tissues/organs in different states and their roles

-Liver, adipose tissue, muscle and brain

-Liver: maintain blood glucose levels; also stores glycogen
-Adipose tissue: main energy storage site
-Muscle: primary site of a.a. storage and major energy user
-Brain: relies primarily on glucose for fuel (uses ketone bodies after fatty acid oxidation in starvation)


Meal Frequency in humans



-Average meal absorbed within 4 hours
- 3 meals a day = intermittent fasting

-Herbivores: v. little fasting as continuously graze and have a full rumen
-Carnivores: Long fasting periods; gorge on only few prey per month


Change of state following metabolism - pythons

-Reduce energetic costs in between meals, seen in pythons that eat v. infrequently
-B/ween large meals, mucosa and submucosa degrade, gut becomes thinner and brush border decreases
-smooth muscles and nerves are maintained

-Following a meal, snake rebuilds GI tract just ahead of bolus of food
-Very high Specific dynamic activity (neg. energy associated with meal)


Role of Hormones in metabolism

-main 2

-Which one is involved in fed state and fasted state

-Insulin and Glucagon regulate metabolism

-Fed state: insulin is dominant hormone - net anabolism
-triggers GLUT 4 translocation to increase uptake of glucose
-Fasted state: glucagon dominant hormone - net catabolism
-involved in breaking down glycogen


Relationship between Insulin and Glucagon

-Insulin rises with glucose, which leads to a decrease in circulatory glucose concentration (as being taken up by cells)
-Glucagon antagonistic to insulin; less glucose in system stimulates glucagon release to start breaking down stores

*Ratio of insulin:glucagon important for direction of metabolism


Out of control Hormones - what it can lead to (2 types)

i. Type 1 (juvenile onset): lack of insulin production
-often requires insulin injections
ii. Type 2 (adult onset): insulin insensitivity/hypersensitivity
-usually managed w/ diet and exercise


3 hormones involved in the control of appetite (how they all work)

1. Leptin: white adipose tissue
2. Ghrelin: Stomach
3. Peptide YY: Colon

*all work by binding to receptors in hypothalamus


Positive and negative energy balance

-Positive Energy Balance: when the rate of energy assimilation is greater than energy output (gain weight as fat)
-Negative energy balance: when the rate of energy assimilation is less than energy output (lose weight)


What energy that is not lost as heat is used for (3)

1. Transport: movement of molecules across membranes
2. Mechanical: use of intracellular fibres and filaments to create movement
3. Chemical: for growth, maintenance and storage of info and energy
i. Synthesis (tissues) or ii. Storage (fat and glycogen)


Barrel model of energy balance

-Stores contain amount of energy - amount we can store depends on the rate we absorb food, which is dependent on the rate of digestion, which is dependent on the rate of foraging.

*barrel of energy has 3 taps - heat, work and tissue (heat tap is constantly dripping)


Energy Expenditure

-4 stages

*4 stages
1. Gross Energy: total energy content of a food
2. Digestible energy: energy contained in nutrients absorbed from digestive tract
3. Metabolisable energy: Chemical energy available
4. Net energy: represents true amount of energy available for maintenance, work, growth and reporduction


Relationship of mass and metabolic rate

-Is non-proportional
-smaller animals usu. have higher metabolic rates per unit body mass than larger animals
-small animals have a large SA = more heat loss
*Mass specific metabolic rate declines w/ increasing body mass


Basal Metabolic Rate

BMR= amount of energy expended while at rest in a neutrally temperate environment in a post-absorptive state
-v. specific set of conditions required to measure, therefore resting MR used (is the energy our body needs to maintain barrel reserve)


Metabolisable energy requirement at maintenance (MEM) equation

a = constant (average of 525 - higher for carnivores, varies with climate)
W = Body mass (Kleiber's Law)

e.g. for 30 kg dog
525 x 30^0.75 = 6410kJ/d


Direct Calorimetry

-what it is

-Calorie definition
-Kilocalorie definition

-Is a direct measurement of a Food's energy content
-volume of water w/ crucible of food w/in
-food is burnt, and the heat produced heats up the water which can then be measured
-Amount of heat released can be used to measure the chemical energy of the food

Calorie: energy required to increase temperature of 1 gram of water by 1 deg.
Kilocalorie: energy required to increase temp of 1 kg water by 1 degree


Atwater factors for Carbs, protein, fat and alcohol (kJ/gram)

-How to work out energy

-Carbs: 17kJ/gram
-Protein: 23kJ/gram
-Fat: 39 kJ/gram
-Alcohol: 29kJ/gram

-Multiply total grams of each category by its Atwater factor


Indirect Calorimetry

-what it is
-figures for carbs, fat and protein and mixed diet

-Respiratory Quotient -> what is it?

-Indirect Calorimetry: consumption of O2 and/or production of CO2 being measured

-Consuming 1 L of O2 associated with releasing 21.1kJ carbs, 19.8 kJ fat and 18.6 kJ protein
-average for mixed diet = 20.2kJ

Respiratory quotient (RQ) = ration of CO2 produced and O2 consumed


What Respiratory Quotient is used for

-Used to determine the metabolic substrate used by an animal

RQ 1 = carbs
RQ 0.7 = fats
RQ 08-0.9 = proteins


Which body organs are using energy at rest

-Liver = 27%
-Brain = 19%
-Skeletal muscle = 18%
-Kidneys = 16%
-Heart = 7%


Factors affecting BMR/RMR (7)

-Usual value

*usually is 20-25kcal per kg body mass
1. Age and gender (higher in males - have more muscle/less fat); declines w/ age
2. Body composition (fat-free mass uses more energy)
3. Diet (diet induced thermogenesis associated w/ digestion and absorption - fat causes little)
-Specific dynamic action
4. Temperature
5.Growth and reproduction (pregnancy - higher)
6. Hormones and drugs (thyroid hormones increase metabolic rate; smoking, drugs, caffeine can increase BMR trhough increased thermogenesis
7. Physical activity


Maintenance Metabolic rate

Maintenance energy requirement

MMR: energy use of animal that is permitted to eat and digest food in amounts needed to maintain constant body mass and composition
-always higher than BMR because it includes SDA

MER: amount of energy animal needs from food during 'maintenance' conditions