Nutrient Uptake and Metabolism Flashcards
1
Q
Types of nutrients we consume
A
- Essential nutrients (vitamins, minerals, essential fatty acids and essential amino acids that body can’t synthesize)
- Conditionally-essential nutrients (factors that can’t be synthesized fast enough to support growth/maintenance)
- “Non-essential” nutrients (factors that can be produced by the body/do not have defined issues resulting from deficiency)
2
Q
Nutrients from gut into bloodstream
A
- can’t passively diffuse
- Must first be released from the food matrix in which they exist
- Specialist transport systems required to absorb them
3
Q
Nutrient distribution around the body
A
- For storage
- For active function (nutritional bioavailability)
- Potentially site-/organ-specific or a general cellular requirement
- specialist transport systems required for bodily distribution
4
Q
Amino acid and monosaccharide uptake
A
- hydrophilic nutrients require specialist proteins to cross cell membranes: monosaccharides, amino acids, ions
- transport stages
5
Q
Transport stages of amino acid and monosaccharide uptake
A
- Apical transport (lumen to enterocyte)
- Basolateral (enterocyte towards bloodstream)
- Often against concentration gradient (so require energy input/co-transport)
- Further transporters required to move from bloodstream into cells
6
Q
Lipid uptake
A
- amino acids –> apolipoproteins
- cholesterol + fatty acids –> cholesterol esters
- fatty acids + monoglycerides –> triacylglycerol
- form chylomicrons, which go into lymphatic system
7
Q
Metabolism
A
- energy-balancing act between catabolic reactions and anabolic reactions
8
Q
Catabolism
A
- Oxidative breakdown of foodstuffs is an exergonic process releasing free energy (ATP & NADH) & reducing power (NADPH)
9
Q
Anabolism
A
- endergonic & use chemical energy stored as ATP & NADPH
- Synthesis of macromolecules from smaller precursors
- ADP + Pi, NAD+, NADP+
10
Q
Vitamins
A
- Organic compounds that are required in small amounts for the normal functioning of the body and maintenance of metabolic integrity
- Essential for life health and well-being
- mostly can’t be synthesised by the human body
- Deficiency results in specific symptoms which can be cured by addition of the vitamin to the diet
11
Q
Water-soluble vitamins
A
- Vitamin B Group: B1 (thiamine), B2 (riboflavin), Niacin (B3), Biotin (B7), Pantothenic acid (B5), B6 (pyridoxine), Folic acid (B9), B12 (cobalamin)
- Vitamin C (ascorbic acid, dehydroascorbic acid)
12
Q
Thiamine (vitamin B1)
A
- found in meat, yeast and unpolished meals
- thiamine pyrophosphate: coenzyme in carb metabolism
- deficiency: peripheral neuropathy, dementia
- water soluble, easily excreted
13
Q
Riboflavin (vitamin B2)
A
- eggs, dairy, high protein diets
- cellular respiration in oxidation/reduction reactions
- deficiency is rare, non severe symptoms, cracked lips, tongue inflammation
- water soluble, easily excreted
14
Q
Niacin (vitamin B3)
A
- meat, yeast, dairy
- cellular respiration in oxidation/reduction reactions
- deficiency: pellagra - dermatitis of skin, diarrhoea and dementia
- easily excreted
15
Q
Biotin (vitamin B7)
A
- eggs and milk
- produced by intestinal bacteria
- involved in carboxylation reactions
- deficiency: dermatitis, glossitis, nausea
16
Q
Folic acid (vitamin B9)
A
- green leafy veg and in liver
- involved in 1-carbon transfer reactions, amino acid and purine and pyrimidine synthesis
- deficiency: megaloblastic anaemia. Spina bifida in pregnancy
17
Q
Cobalamin (vitamin B12)
A
- meat and animal products
- involved in methionine synthesis and in purine and pyrimidine metabolism
- deficiency: pernicious anaemia
18
Q
Pantothenic acid (vitamin B5)
A
- widely available
- forms part of coenzyme A and functions as acyl group carrier
- deficiency is rare and toxicity isn’t known
19
Q
Vitamin C
A
- forms ascorbic acid, dehydroascorbic acid
- human sources: green vegetables, citrus fruits, potatoes, berries
- animal requirements: most animals can synthesise vitamin C
- roles: collagen formation, formation of adrenaline/noradrenaline, iron absorption, antioxidant defence
20
Q
Fat soluble vitamins
A
- alongside vitamin B12, are stored in the liver
- must be absorbed and transported alongside dietary lipids
- vitamin A (retinol, retinal, retinoic acid)
- vitamin D (ergosterol, cholecalciferol)
- vitamin E (tocopherol, tocotrienol)
- vitamin K (phylloquinone, menaquinone)
21
Q
Roles of vitamin A
A
- vision pigment
- epithelial differentiation
- reproduction
- possible antioxidant roles
22
Q
Roles of vitamin D
A
- bone maintenance/calcium homeostasis
- proposed roles in immune/inflammatory response
23
Q
Role of vitamin E
A
- Membrane-bound protection against oxidative stress
24
Q
Roles of vitamin K
A
- blood-clotting
- post-translation protein modification
- bone development and health
25
Absorption of vitamins
- approx. 40-90% absorbed in the small intestine
- fat-soluble vitamins require fat in diet to be absorbed
- water-soluble vitamins require transport molecules or specific uptake co-factors in the gut
- Some are absorbed in inactive provitamin or vitamin precursor forms that must be converted into active forms by the body
- e.g. carotenoids converted to active vitamin A analogues
26
Minerals
- elements needed by the body in small amounts for health and maintenance
- major minerals are needed in the diet in amounts >100 mg/day or are present in the body in amounts >0.01% of body weight
- amounts available in foods can be greatly affected by soil conditions or other growing medium
- trace minerals are required in diet in amounts <100 mg/day or are present in the body in amounts <0.01% of body weight.
- Bioaccessibility is very important eg phytates can limit the body’s ability to absorb calcium, zinc and iron
- Minerals from intact plant foods may be more difficult to release/absorb
27
Dietary intake of iron
- Animal products (haem iron; tends to be easily absorbed).
- Plant products is non-haem iron (less accessible)
- or even iron cookware
28
Functions of iron
- Component of haem in haemoglobin and myoglobin (O2 transport and utilisation)
- Component of cytochromes, cofactor for some enzymes
29
Where iron is stored
- in liver and other cells
| - e.g. enterocytes, bound to protein ferritin
30
Iron deficiencies
- iron deficiency anaemia, impaired immunity
- most common micronutrient deficiency issue worldwide
- toxic in excess or in unbound state – can induce free radical formation
31
Iodine
- component of thyroid hormones T3 (tri- iodothyronine) and T4 (thyroxine)
- Thyroxine may be an important factor affecting basal metabolic rate
- A lot of global iodine consumption is from iodised salt
- Seafood and dairy foods may be other major sources
32
Iodine deficiency
- Goitre (swollen thyroid gland)
- Foetal/developmental issues
- Inadequate iodine intake appears highly prevalent globally
33
Pancreatic orchestration of energy utilisation
- Exocrine pancreas: major role in digestion of macronutrients
- Endocrine pancreas helps utilise absorbed macronutrients: via insulin and glucagon, control blood glucose homeostasis (usually >2.5 to <5.5 mM), absorption of glucose and amino acids by tissues around the body
34
Hormonal regulation of fuel metabolism - metabolic effects of insulin and glucagon
- Changes in levels of Insulin and Glucagon allow the body to store energy when food is available in abundance
- Or to make energy available
35
Insulin
- secreted in response to postprandial glucose and amino acid spikes in the bloodstream
- Inhibited as a result of starvation, stress, trauma & extreme exercise by adrenalin (epinephrine), cortisol and sympathetic innervation
36
Effects of insulin in carbohydrate metabolism
- increased glycogen synthesis
- decreased glucose production by inhibiting glycogenolysis
- increased glucose uptake by increasing number of glucose transporters in membrane
- overall causes decrease in blood glucose concentration
37
Effects of insulin in lipid metabolism
- decrease in triglyceride degradation
| - increased uptake of glucose
38
Effects of insulin in protein metabolism
- Stimulate increase uptake of amino acids, increase in protein synthesis
39
Role of glucagon
- increase blood glucose levels
- glycogenolysis (glycogen conversion to glucose in liver and skeletal muscle)
- gluconeogenesis (formation of new sugar from protein)
- lipolysis (release of stored TGs for use as metabolic fuel)
- stimulation of secretion: low blood glucose levels, exercise
- diminished secretion: somatostatin, insulin
40
Fate of other sugars absorbed by intestine
- Others are absorbed into the hepatic portal bloodstream, from the intestinal lumen: e.g. galactose (from milk), fructose (from sucrose)
- Fructose is converted into phosphorylated compounds that enter the glycolytic pathway
- Galactose is converted to phosphorylated glucose
- Deficiencies in the enzymes involved in galactose metabolism give rise to (hyper) galactosaemias
41
Cholesterol metabolism
- not used as fuel source
- structural basis of bile salts, steroid hormones, vitamin D & plasma membranes
- component of chylomicrons
- component of VLDLs & LDLs
- component of HDL’s - but HDLs are involved in removal of cholesterol from the tissues to the liver
42
Hormones in food intake regulation
- hunger signals: ghrelin
| - Satiety signals: cholecystokinin (CCK), PYY-3-36, leptin, adiponectin, insulin, amylin
