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AP0510 Medical Biochemistry > Nutrient Uptake and Metabolism > Flashcards

Nutrient Uptake and Metabolism Flashcards

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USMLE® Step 1 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)
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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
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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
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4
Q

Amino acid and monosaccharide uptake

A
  • hydrophilic nutrients require specialist proteins to cross cell membranes: monosaccharides, amino acids, ions
  • transport stages
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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
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6
Q

Lipid uptake

A
  • amino acids –> apolipoproteins
  • cholesterol + fatty acids –> cholesterol esters
  • fatty acids + monoglycerides –> triacylglycerol
  • form chylomicrons, which go into lymphatic system
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7
Q

Metabolism

A
  • energy-balancing act between catabolic reactions and anabolic reactions
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8
Q

Catabolism

A
  • Oxidative breakdown of foodstuffs is an exergonic process releasing free energy (ATP & NADH) & reducing power (NADPH)
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9
Q

Anabolism

A
  • endergonic & use chemical energy stored as ATP & NADPH
  • Synthesis of macromolecules from smaller precursors
  • ADP + Pi, NAD+, NADP+
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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
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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)
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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
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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
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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
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15
Q

Biotin (vitamin B7)

A
  • eggs and milk
  • produced by intestinal bacteria
  • involved in carboxylation reactions
  • deficiency: dermatitis, glossitis, nausea
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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
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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
Q

Absorption of vitamins

A
  • 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
Q

Minerals

A
  • 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
Q

Dietary intake of iron

A
  • Animal products (haem iron; tends to be easily absorbed).
  • Plant products is non-haem iron (less accessible)
  • or even iron cookware
28
Q

Functions of iron

A
  • Component of haem in haemoglobin and myoglobin (O2 transport and utilisation)
  • Component of cytochromes, cofactor for some enzymes
29
Q

Where iron is stored

A
  • in liver and other cells

- e.g. enterocytes, bound to protein ferritin

30
Q

Iron deficiencies

A
  • iron deficiency anaemia, impaired immunity
  • most common micronutrient deficiency issue worldwide
  • toxic in excess or in unbound state – can induce free radical formation
31
Q

Iodine

A
  • 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
Q

Iodine deficiency

A
  • Goitre (swollen thyroid gland)
  • Foetal/developmental issues
  • Inadequate iodine intake appears highly prevalent globally
33
Q

Pancreatic orchestration of energy utilisation

A
  • 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
Q

Hormonal regulation of fuel metabolism - metabolic effects of insulin and glucagon

A
  • 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
Q

Insulin

A
  • 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
Q

Effects of insulin in carbohydrate metabolism

A
  • 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
Q

Effects of insulin in lipid metabolism

A
  • decrease in triglyceride degradation

- increased uptake of glucose

38
Q

Effects of insulin in protein metabolism

A
  • Stimulate increase uptake of amino acids, increase in protein synthesis
39
Q

Role of glucagon

A
  • 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
Q

Fate of other sugars absorbed by intestine

A
  • 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
Q

Cholesterol metabolism

A
  • 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
Q

Hormones in food intake regulation

A
  • hunger signals: ghrelin

- Satiety signals: cholecystokinin (CCK), PYY-3-36, leptin, adiponectin, insulin, amylin

AP0510 Medical Biochemistry (21 decks)

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