Metabolic Fate of Nutrients Flashcards
Why is nutrition important?
to develop and maintain a state of health
What is nutrition?
the process by which a living organism received nutrients from its environment and uses them to promote vital activities
What is food?
A substance when eaten, digested and absorbed provides at least one nutrient
What is a nutrient?
a substance which is digested and absorbed to promote bodily function
Give examples of macromolecules
proteins, fats, carbs
Give example of micromolecules
minerals and vitamins
What do we use the energy released from food for?
- muscle activity
- secretion by glands
- maintenance of membrane potentials by nerves and muscles
- synthesis of molecules
- cell division
- thermoregulation
What is basal metabolic rate?
the number of calories needed at rest for normal bodily function (50%-70% of calories needed per day)
What is the thermic effect of food?
energy required for digestion and absorption of food (5-10% of energy expenditure)
What is the other process that uses energy?
physical activity
What are other factors that may require energy use?
- temp changes
- pregnancy
- growth
- age
- health
Why is glucose a preferential source of energy?
readily available primary source of energy for CNS and red blood cells and also used in other tissues
What happens to the glucose produced by glycogenolysis by the muscle and liver?
muscle- used in muscle
liver- for rest of the body
How is glucose metabolised?
by glycolysis
Why are fats a good source of energy?
- high amount of energy stored per gram
- used in tissue activity and maintenance of body temp
- not used by brain, spinal cord or RBCs
Why is it difficult to use fat?
- require large amounts of oxygen to metabolise
- insoluble in water so difficult to access
What other roles do fats have?
- used in body structures e.g cell membranes
- protection
- insulation
- some vitamins are fat soluble so carriers assist absorption from intestine
- satiety (inhibit gastric motility and prevents hunger feeling)
How is fat metabolised?
- triglycerides undergo lipolysis to form fatty acids and glycerol
- the fatty acids can either be converted into phospholipids or undergo beta-oxidation to form acetyl-CoA to be used in the Krebs cycle
- glycerol can be converted to glucose and be used in glycolysis
Why do we need protein?
- manufacture new proteins
- build new tissue
- can also be oxidised to produce energy (not a main function-usually in starvation)
What does nitrogen anabolism equal?
catabolism
When do you need a positive nitrogen balance?
- pregnancy
- growth
- recovery
When would you have a negative nitrogen balance?
- starvation
- trauma/infection/sepsis
- tissue destruction
Give some examples of insoluble fibre
cellulose wheat, rich leafy vegetables and pulses
what is the role of insoluble fibres?
provide bulk to the gut (prevents constipation)
Give some examples of soluble fibres
proteins, plant gums, mucilage
What is the role of soluble fibres?
- absorb water in intestine this often stools which help waste move along colon
- lowers cholesterol (binds to cholesterol and prevents absorption)
What other benefits do fibres have?
- slows gastric emptying
- retards glucose absorption
- fermentation releases SCFA
- reduces bowel cancer risk
What are the types of vitamins?
- water soluble
- fat soluble
Can water soluble vitamins be stored?
no (so need regular intake)
What is the role of the B complexes?
enzyme cofactors
What is the role of vit C?
- protein synthesis
- antioxidant
role of vit A?
used in:
- development
- immune system
- vision
role of E?
- antioxidant
- immune function
D?
calcium metabolism
K?
blood clotting
Where are fat soluble vitamins stored?
in the liver and adipose tissue
Give examples of fat soluble and water soluble vitamins
Water soluble= B complexes and C
Fat soluble=A,E,D,K
What is rickets a deficiency of?
vitamin D
What is rickets?
poor mineralisation of bone
What is scurvy a deficiency of?
Vit C
What can scurvy cause?
- destruction of collagen
- damage to myelin
- loss/bleeding of tooth sockets
- sunken eye sockets
- paralysis
- death
Why is water important?
- prevent dehydration
- solvent
- important for metabolism/excretion
- thermoregulation
- osmoregulation
How do we maintain a consistent weight?
- without conscious effort
- finely tuned regulatory system
- involves neuroendocrine regulation of the process of feeding (appetite and satiety)
Does the GIT regulate energy intake?
no
What is energy intake regulated by?
hypothalamus and brain stem
-hunger centre
-satiety centre
works through glucostatic (blood glucose) decreased glucose increases hunger
-adipostatic (fat storage) if there is an increase in the fat stored it will cause satiety
-GIT tract can slow down digestion to reduce hunger
What hormone stimulates hunger in the hypothalamus?
ghrelin
What inhibits appetite?
- stopping ghrelin
- PYY, CCK and GLP-1 release from intestine
- insulin released in pancreas
- leptin released from adipose tissue
What can override satiety?
-visual, smell and taste signals
What is loss of appetite called?
anorexia
What are the physiological factors that can cause loss of appetite?
- anaemia
- forms of cancer
- depression
- intestinal disorders
- intestinal parasites
- liver disorders
- malabsorption
- mouth disorders
- taste loss
What are the physiological factors that can cause loss of appetite?
- stress
- anxiety
- sadness
- wedding
- falling in love
What are the environmental factors?
- altitude
- acute cold
Where is most energy stored?
in fats
What is the advantage of carbohydrates as an energy source?
more ATP can be generated per unit time compared to oxidation of fats
Why is glucose required by the red blood cells?
no mitochondria so beta oxidation of fats can’t occur
Why does the brain use glucose instead of fats?
blood brain barrier
What do the other organs use for energy?
- can use glucose
- prefer using fats
What is the blood brain barrier?
- a highly selective permeable barrier
- endothelial cells have tight junctions
- separates blood with the brain and the extracellular fluid of the CNS
Whats the disadvantages of using fats in the brain instead of glucose?
- ATP generated demands more O2 (Brain cells need lots of O2)
- beta-oxidation generates superoxide (which kills brain cells)
- rate ATP generation is slower than glucose (brain needs a fast energy supply)
What type of energy is required for intense high impact exercise?
- glucose
- anaerobic glycolysis
Low intensity exercise e.g marathon running?
-glycogen until it has been used up
-then fats
(different type of muscle´fibre being utilised)
What happens when insulin is released in the liver?
it causes the beta cells to:
- uptake AA and increase protein synthesis
- increase glycogen synthesis
- increase lipogenesis
- decrease gluconeogenesis
What happens when insulin is released in the muscles?
- glucose uptake
- AA uptake
- protein synthesis
- glycogen synthesis
What happens when insulin is released in the adipose tissue?
- decrease lipolysis
- increase glucose uptake
- increase lipogenesis
What hormones increase the breakdown of triglycerides?
- glucagon
- adrenaline
- glucocorticoids
What are the two origins for obesity?
- innate (inherited)
- acquired
How does inherited obesity occur?
- monogenic mutation in leptin
- polygenic Prader-Willi syndrome
How does acquired obesity occur?
- overeating
- inactivity
- ageing
- stress
- endocrine disrupters
- drugs
What complicating diseases can occur due to obesity?
- diabetes
- polycystic ovaries
- fertility problems
- hpertension
- stroke
What happens if you eat too much glucose?
- glucose is converted into acetyl CoA
- if you already have enough energy, the acetyl CoA will eb converted into fatty acids which will become triglycerides
Fructose is often used in low fat diets, why is it bad?
- sweeter than glucose
- fructose is not preferred energy source for muscle and brain
- fructose has a greater conversion than glucose into TGs
- fructose does not stimulate insulin secretion which increases food uptake (no leptin release)
How is obesity treated?
- drugs that alter appetite (some act on the brain, inhibit neurotransmitter and suppress appetite, block endocannabinoid system)
- drugs alter absorption of calories (e.g inhibit pancreatic lipase)
-restrict food intake
calorie restricted diet, bariatric surgery (gastric band)(full feeling quicker), gastric balloon
-exercise
Why does starvation occur?
- deprivation of calories
- a need to preserve plasma glucose to maintain brain and spinal cord which results in consumption of tissues to preserve energy production
What happens when you are in a state of starvation?
- breakdown of muscles releases amino acids to bolster blood glucose (muscle performance declines)
- breakdown of fat to provide glycerol
- ketone bodies production
How are ketone bodies produced?
- from the breakdown of fatty acids in the liver
- beta-oxidation
How do ketone bodies reach the brain?
- water soluble
- diffuses via con gradient to blood
- taken up from blood without transporters
- cross blood brain barrier
What happens in the first 6 hours of starvation?
glucose from the blood is used as the main fuel for the brain
What happens in 6-16 hours?
glycogen is broken down in the liver to provide glucose for the brain
What happened 16-72 hours?
1st metabolic shift (low levels of glycogen)
- increase gluconeogenesis (increase wasting of muscle)
- increase lipolysis of TG into FA (fuels other tissues and glycerol converted into glucose for brain)
2-3 days?
2nd metabolic shift.
- increase lipolysis of TG into FA
- liver converts FA into ketone bodies used as fuel for the brain
- decrease gluconeogenesis
After 24 days?
- fat stores used
- gluconeogenesis relyed on
- all cells in body break down proteins to provide glucose for the brain
- basal metabolic rate decreases up to 50%
