Metabolism of sacharides, lipids and
proteins. Energy metabolism.
Introduction
At steady state, the energy input must correspond to the energy output
̶ Energy expenditure = external work + energy reserves + heat
̶ Intermediate: various chemical, mechanical and thermal reactions
̶ Saccharides, lipids, proteins
̶ Conversion of proteins and sugars into fats - efficient energy storage
̶ Conversion of proteins into sugars - the need for fast energy
̶ BUT: there is no significant conversion of fats into sugars
Nutrient pools and metabolism
Metabolism of saccharides
̶ Energy source
̶ Functions of saccharides:
̶ Part of glycoproteins and glycolipids
̶ Inevitable for nucleic acids and coenzyme synthesis
̶ Part of extracellular matter
̶ Saccharides:
̶ Monosaccharides
̶ Oligosaccharides
̶ Polysaccharides
̶ Digestion and absorption
̶ Saliva (salivary amylase)
̶ Pancreatic juice (a-amylase)
̶ Epithelium of duodenum and jejunum (isomaltase, maltase, saccharase, lactase)
Metabolism of saccharides
̶ The key substrate is glucose
̶ Postprandial plasma glucose level: 3.5 – 6.5 mmol/l
̶ Glycemia. Hypoglycemia, hyperglycemia
̶ Glycolysis, gluconeogenesis
̶ Glycogenolysis, glycogenesis
Metabolism of saccharides
̶ Morning glucose intake - 70% consumed by peripheral tissues (muscles), 30% - splanchnic organs (liver)
Metabolic disorders - saccharides
̶ Diabetes mellitus
̶ McArdle syndrom (glycogenesis from deficiency of myophosphorylase
accumulation of glycogen in muscles: muscle stiffness, rigor during
exercise, lower tolerance of load)
̶ Galactosemia(inherited deficiency of phosphogalactosauridyltransferase;
disorders of growths and development)
Metabolism of lipids
̶ Main and most profitable form of energy store
̶ Lipid functions:
̶ Part of biological membranes - fospholipids
̶ Energy storage
̶ Protective cover for organisms
̶ Precursors of some important substances
̶ Vitamin solvents (A, D, E, K)
̶ Lipids:
̶ Triglycerides
̶ Sterols
̶ Phospholipids
̶ Digestion and absorption
̶ Bile acids salts (emulsification)
̶ Pancreatic lipase, cholesterol-estherase, phospholipase a2, enteric lipase(deestherification)
Metabolism of lipids
Metabolic disorders - lipids
̶ Hyperlipidemia
̶ Hyperlipoproteinemia
̶ Infrequent disorders of lipid metabolis
Metabolism of proteins
̶ Total proteins in body: 10 kg
̶ Protein minimum: 0,5 g / kg of body mass
̶ Protein optimum: 0,7 g / kg of body mass
̶ Increased supply (growth, convalescence, pregnancy, lactation): 1,5 – 2,0
̶ Aminoacides
̶ Essential (not synthesised)
̶ Non-essential (from glucose metabolism – citrate cycle)
̶ Potřeba esenciálních AMK: 0,5 – 1,5 g / den
Metabolism of proteins
̶ Digestion and absorption
̶ Stomach (pepsin)
̶ Duodenum (trypsin, chymotrypsin, carboxypeptidase)
̶ Jejunum (membrane peptidases)
̶ Functions of proteines:
̶ Structural (collagen, elastin, …)
̶ Motoric (actin, myosin, …)
̶ Informational (protein hormones)
̶ Protective (immunoglobulins, complement, antigens, …)
̶ Transport (albumin)
Metabolic disorders – proteins
̶ Proteinemia = plasmatic level of proteins.
̶ Dysproteinemia = change in representation of particular proteins
(fractions shift) – nephrotic syndrome, cirrhosis, inflammatory reactions
̶ Paraproteinemia = presence of pathological imunoglobulines (with no
antibodies specificity) – monoclonal immunopathy
̶ Defect proteinemia = some components of plasma proteins are missing
or lowered – syndromes of immunodeficiency, polyclonal
hypergamaglobulinemia
Energy storage
Fat tissue
http://www.e-dmj.org/ViewImage.php?Type=F&aid=284781&id=F1&afn=2004_DMJ_37_1_22&fn=dmj-37-22-g001_2004DMJ
Metabolism
= summary of all chemical (and physical) processes included in:
̶ Production of energy from internal and external sources
̶ Synthesis and degradation of structural and functional tissue
components
̶ Excretion of waste products and toxins from body
Metabolic rate
̶ Physical work (oxygen debt compensation)
̶ Specific-dynamic effect of food (assimilation of nutrients in the body)
̶ External temperature
̶ Height, weight and body surface
̶ Gender
̶ Age
̶ Emotions
̶ Body temperature
̶ Thyroid hormone level (T4, T3)
̶ Adrenaline and norepinephrine levels
Bazal metabolic rate (BMR)
̶ Energy for maintaining all vital functions
̶ Thermoneutral environment
̶ 12 - 14 hours after a meal
̶ 24 hours without exhausting physical work
̶ Elimination of all negative physical and mental factors
Direct calorimetry
= measuring the energy released by burning food outside the body
(oxidation of compounds in a calorimeter )
̶ Calorimetry:
̶ adiabatic = heating of the calorimeter content
̶ isothermal = generated heat is dissipated
Direct calorimetry
Noooooooooooooo!!!!
Direct calorimetry
BMR. Calculation
Energy expenditure
ENERGY EQUIVALENT (EE):
̶ the amount of energy released when consuming 1 liter of O2
̶ The thermal oxygen coefficient of individual nutrients differs, so the
EE also differs
̶ EE saccharides 21.1 kJ = 5.05 kcal
̶ EE proteines 18.0 kJ = 4.31 kcal
̶ EE lipides 19.0 kJ = 4.55 kcal
̶ In a mixed diet (60% carbohydrates, 30% fat, 10% protein):
̶ EE = 20.1 kJ = 4.81 kcal
Indirect calorimetry
̶ The amount of consumed O2
̶ Influence of diet composition - energy equivalent = universal constant for
calculation of energy expenditure under the assumption of mixed diet intake
̶ Open system
̶ Close system
Indirect calorimetry
Barret, K.E., Boitano, S., Barman, S.M., Brooks, H.L. Ganong´s Review of Medical Physiology. 23rd Ed. McGraw-Hill Companies 2010
Respiratory quotient
̶ Saccharides (glu)
̶ C6H12O6 + 6O2 = 6CO2 + 6H20
̶ RQ = 6/6 = 1.00
̶ Lipides
̶ 2 C51H96O6 + 145 O2 = 102 CO2 + 98 H2O
̶ RQ = 102/145 = 0.703 (0.70)
RQ = VCO2 : VO2
Respiratory quotient
Substrate or metabolic process RQ
saccharides/glycogen 1
lipids 0.7
proteins 0.9
glucogenesis 0.4
lipolysis 0.7
lipogenesis 2.75
̶ Hyperventilation RQ decreasis
̶ Workload RQ increases
̶ Acidosis RQ increases
̶ Alkalosis RQ decriases
Thank you for your attention