Midterm Review Important Concepts Flashcards
Describe the energy conversion flow chart
Components of energy expenditure
- BEE
- TEF
- EEPA
Direct vs. indirect measurements of energy
- Direct: measures changes in body temperature (heat production) - difficult, costly (complex equipment, chamber)
- Indirect: oxygen consumption as a marker of heat production
Premise for indirect measurements of energy
- body store of O2 is low, most aerobic reactions use oxidative substrates for heat production (energy) e.g. Glycolysis/ETC
- Every litre of O2 = avg 4.83 kcal energy (+/- 8% regardless of nutrient)
- Measures O2 consumed and CO2 released: Respiratory Quotient (RQ) = CO2 produced / O2 consumed
Factors influencing EE
- 80% of BEE accounted for by body size, thus, variance in TEE for people of the same size = change in EEPA (mostly NEAT)
- TEF is only about 5-15% and considered the same between people
What factors acount for variability in NEAT?
- environmental including egocentric and geocentric
- biological including hypo control and orexin activity
Concept of nutrient balance
essentially want EI = EE
* postive balance = overfed = gain weight
* negative balance = underfed = lose weight
What are the afferent signals controlling energy balance?
- Meal
- Adipose
- Pancreas
- Stomach
- SI
What are the efferent outputs for controlling energy balance?
- appetite
- energy expenditure
- growth
- hormones
- nutrient partitioning
- reproduction
What are the points of regulation for digestion and absorption?
- Digestion: gastric & pancreatic secretions, bile
- Absorption: surface area of smallintestine, motility, expression of transporters
What regulates digestion and absorption?
- Enteric nervous system: GI innervated by sympathetic (inhibitory) & parasympathetic (stimulatory) nerve fibres
- Hormones/regulatory peptides–can be endocrine, paracrine and/or neurocrine; most have multiple actions (mostly either inhibitory or stimulatory)
Gut hormones & major functions of the duodenum
- CCK
- Secretin
- GIP
- motilin
Gut hormones & major functions of the stomach
- ghrelin
- gastrin
Gut hormones & major functions of the pancreas
- insulin
- glucagon
- PP
- Amylin
Gut hormones & major functions of the LI
- GLP-1
- GLP-2
- oxyntomodulin
- PYY
How do insulin and leptin act on the brain to regulate food intake with energy surplus?
Increased hormone secretion converges at the Arc and inhibits food intake and increases EE
* inhibits NPY and AgRP neurons in ARC thus inhibiting orexigenic (LHA) neurons in stimulation from NPY and preventing anorexigenic (PVN) neuron inhibition from AgRP.
* Stimulates POMC neurons in the ARC which stimulates aMSH which stimulate anorexigenic neurons (PVN)
How do insulin and leptin act on the brain to regulate food intake with energy deficit?
Decreased hormone secretion converges at the Arc and stimualtes food intake and decreases EE
* NPY and AgRP neurons in ARC are stimulated thus orexigenic (LHA) neurons are stimulated from increased NPY and anorexigenic (PVN) neurons are inhibited from increased AgRP.
* Inhibites POMC neurons in the ARC which inhibits aMSH which cannot act on anorexigenic neurons (PVN), thus inhibting them
What factors contribute to obesity?
- physiology
- behaviour
- environment
EAR DRI for CHO
The amount of carbohydrates needed to fuel the central nervous system (CNS) without having to rely on partial replacement of glucose by ketoacids
* EAR = 100 g/day (increases during pregnancy and lactation)
RDA DRI for CHO
Based on the amount of carbohydrates (glucose) needed to sustain energy function in the brain
* RDA = 130g/day (100g = brain ; 20-30g = non-CNS use) for children and adults (increases during pregnancy and lactation)
AMDR DRI for CHO
Based on the kilocalories of carbohydrate needed to maintain body weight
* AMDR = 45-65% Calculate total carbohydrate requirements: kcal/day * 0.45/4, kcal/day * 0.65/4
CHO classification
What are the 2 steps of CHO digestion?
- Intraluminal hydrolysis (amylases)
- Membrane digestion (brush border glycohydrolases)
describe the bsorption of monosaccharides into circulation
- SGLT1 transports glucose and galactose (facilitated transport with Na+) into cell
- GLUT5 is specific to fructose transport into cell
- GLUT2 mediates the efflux of glucose, galactose and fructose from the enterocyte into the capillaries
- GLUT2 Transiently involved in sugar uptake following a high sugar meal
Integration of macronutrient metabolic pathways
Why is the integration of the macronutrient pathways regulated?
- Meet energy needs of the body
- Maintain cellular concentrations of specific metabolites (homeostasis)
What is the fate of glucose?
What does pyruvate entering the CAC depend on?
- availability of oxygen
- metabolic state of the cell
What are the major points of regulation in glycolysis and gluconeogenesis?
The RLS enzymes
* glycolysis: HK, PFK, PK
* gluconeogenesis: PC, PEPCK, F16P, G6P
What is the fate of post-prandial glucose?
glucose uptake in the
* liver
* skeletal muscle
* adipose tissue
* cardiac muscle
* other tissue
What are the differences in homeostasis Glc level in the liver vs. the pancreas?
- liver: energy storage and regulation of blood Glc
- pancreas: glucose sensor and insulin release
Purpose of the glucose sensor mechanisms in liver and pancreas
adjusts glycolytic flux to plasma [glucose] in β-cells and hepatocytes
* liver: energy storage
* pancreas: insulin secretion
2 glucokinase system
‘senses’ blood glucose levels
Liver and pancreas via combined action of GLUT2 transport of glucose and rate of glycolysis (glucokinase)
How does glucagon promote the mobilization of stored energy?
It is released from the pancreas in responce to declining blood glucose levels and promotes breakdown of liver glycogen, adipose tissue, and muscle protein, and the synthesis of ketones and glucose from noncarbohydrate sources.
How does insulin promote energy storage?
Insulin is released from plancreas is response to rising blood Glc levels and stimulate glucose transport into cells. Insulin also promotes energy storage , glycogen synthesis, protein synthesis (muscle), and fat synthesis (adipose tissue)
* Anabolic effects
What is amylin?
AA peptide that is stored in pancreatic beta cells and is co-secreted with insulin. Amylin and insulin levels rise and fall in a synchronous manner and have complementary actions in regulating nutrient levels in the circulation
* suppressing glucagon release in response to caloric intake, delaying the rate of gastric emptying, and stimulating the satiety center in the brain to limit caloric intake.
Postprandial levels of glucose, insulin and glucagon
What is the normal range for blood glucose levels?
4-6 mmol/L (average ~6 mmol/L)
Postabsorptive vs postmeal?
- postabsorptive: fasted state; food has been digested, absorbed, and stored so energy reserves are used (no absorption of nutrients is occuring) OR period when the nutrients are digested, absorbed, utilized and stored in the designated tissues?
- postprandial: fed state; embodies the digestion and absorption of nutrients
Define
Dietary fibre
Plant-derived non-starch polysaccharides indigestible by human enzymes
Commonly accepted factors about dietary fibre
- naturally occuring in food
- obtained from food material and have a physiological benefit to health
- synthetic carbohydrate polymers that have a physiological benefit to health
Content of fibre in foods
- Large variation
- Usually a mix of different types
How are fibres classified?
- composition: monosaccharides, β-bonds
- physical properties: water solubility, fermentability, viscositiy
Summary of fibre functionality
Fibre DRIs
RDA/ AI for total fibre
What are the AAs?
Acronym for remembering the essential AAs
Cascade of zymogen activation
AA transport during absorption
portal AA concentrations when absorbed into circulation
describe transamination reactions
Involves the transfer of an amino group to an 𝝰-keto acid to form a new amino acid.
* different enzymes and differnt substrates but the reaction is the same
* essentially amino acid with an ammonia group and keto acid with no ammonia group and the reaction causes a switch
What are the enzymes called that catalyze transamination?
aminotransferases
* pyridoxal 5’-phosphate [PLP] dependant
What AAs do not participate in transamination reactions?
- Lys
- Thr
- Pro
What AAs are actively transaminated in human tissue?
Ala
Asp
Glu
Ser
Val
Ile
Leu
What 𝝰-keto acid is used widely as the acceptor in transamination reactions?
𝝰-ketoglutarate
* 𝝰-amino group of many AAs are funneled through Glu during AA catabolism
What are the most common aminotransferase enzymes for transamination?
- ALT: alanine amino transferase
- AST: Aspartate amino transferase
both are widespread in tissues and allow movement of amino groups between glutamate/𝝰-ketoglutarate & aspartate/oxaloacetate or alanine/pyruvate
Describe the deamination reaction
Is the liberation of free ammonia from the amino acid coupled with oxidation
* main mechanism for how we get rid of ammonia
* takes place mainly in the mito of liver and kidneys
* provide NH3 for urea synthesis and alpha keto acids for a variety of reactions including energy production when needed
* Substantial amounts of ammonia are generated in the liver from glutamate and in the kidney by deamidation of glutamine.
What AAs are ketogenic, glucogenic, and partially keto and glucogenic?
Describe the glucose-alanine cycle
- Alanine forms in muscle from transamination with glutamate (generated from leucine transamination) and from pyruvate (generated from glucose oxidation via glycolysis)
- alanine travels in the blood to the liver
- In the liver, alanine is transaminated with 𝝰-ketoglutatrate to form pyruvate and glutamate (essentially opposite from muscle)
- pyruvate can be converted back to glucose through gluconeogenesis
- the glucose is released from the liver back into circulation to be used for energy
- the glutamate goes through deamination reaction to release NH4 which is then excreted in the urea cycle.
What are the major pathways of protein degradation?
- Ubiquitin-proteasome system (UPS): 80-90% of protein degradation; Ubiquitin: A universal garbage tag
- ER-associated degradation (ERAD)
- Autophagy-lysosomal pathway (ALP)
- Calcium/calpain-dependent system
Define
protein turnover
The process of continuous degradation & re-synthesis (Homeostasis)
DRIs for protein
- EAR: 0.66g protein/kg body weight
- RDA: 0.8 g/kg/d
- AMDR: 10-35% of total E intake
true digestibility of protein vs. apparent digestibility
Da is fraction of amino acid intake that is absorbed and accounts for ingested and fecal excretion of N
* Da= (Intake - Fecal Excretion) /Intake
* Dt is Da corrected for endogenous protein losses Da < Dt
