Metabolism and Energy Balance Flashcards
Definitions;
-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
iii.Polysaccharides
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
- Primary structure: a.a./DNA code
- Secondary structure: alpha helix or beta sheet - when sequence of a.a. linked by H bonds
- Tertiary structure: Occurs by folding of proteins
- 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.
- 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
- structure
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
- in blood w/out assistance = short chain fatty acids and glycerol
- transport of lipids depends on physical properties
Definitions;
- Assimilation
- 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
- Mucosa (innermost)
- Submucosa
- Circular (muscle)
- 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
-features
- 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
- Herbivores
- Carnivores
- 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)
- Diabetes;
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)
- Leptin: white adipose tissue
- Ghrelin: Stomach
- 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)
- Transport: movement of molecules across membranes
- Mechanical: use of intracellular fibres and filaments to create movement
- 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
- smaller animals usu. have higher metabolic rates per unit body mass than larger animals
- 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
aW^0.75
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
- Process
- 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
- Temperature
- Growth and reproduction (pregnancy - higher)
- Hormones and drugs (thyroid hormones increase metabolic rate; smoking, drugs, caffeine can increase BMR trhough increased thermogenesis
- Physical activity
- Specific dynamic action
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
