Flashcards in 21. Nutritional biochemistry Deck (246):
What are the four proproteases secreted by the pancreas?
What are the active enzymes secreted by the pancreas?
What is the key ion secreted by the pancreas?
What are the three stages of pancreatic secretion?
What mediates pancreatic secretion in the cephalic phase?
What mediates pancreatic secretion in the gastric phase?
What mediates pancreatic secretion in the intestinal phase?
What is HCO3- secretion by pancreatic duct cells controlled by?
What are the three types of lipase?
Though lingual lipase and gastric lipase can act on their own, what does pancreatic lipase require for proper function?
What are the three types of enzymes responsible for the digestion of fat?
Lipase (lingual, gastric, pancreatic)
What components of fat can be taken up directly into an enterocyte?
Short chain fatty acids
Medium chain fatty acids
What components of fat are taken up in a mixed micelle?
Long chain fatty acids
What are the two main types of proteases?
Endopeptidases: cleaves in the center or proteins and peptides
Exopeptidates: cleaves from the N or C terminal ends of peptides and proteins
What is the endopeptidase in the stomach? What secretes it?
**activated by acid and auto-activation
What synthesizes and secretes the endopeptidases of the duodenum and jejunum?
Alpha cells of the pancreas
How is the endopeptidase trysinogen activated?
Activated by epithelial enteropeptidase/enterokinase
What is chymorypsinogen and proelastase activated by?
What are the two exopeptidases secreted into the duodenum?
What synthesizes the exopeptidase carboxypeptidase vs aminopeptidase?
Carboxypeptidase: alpha cells of the pancreas
Aminopeptidase: intestinal epithelial cells
What are the three types of protein transporters found in the duodenum and jejunum?
Amino acid class specific
What are the two kinds of epithelial cell peptidases?
What enzyme digests carbs and is active in the oral cavity, early in the stomach?
Salivary alpha amylase
What enzyme disgests carbs and is acitve in the lumen of the duodenum?
Pancreatic alpha amylase
Where are the di and trisacchridases located?
Intestinal epithelial cell membranes (brush borders)
Where are carbohydrates absorbed?
What are the two transporters for the absorption of carbohydrates?
What are the sx of lactase deficiency? Cause?
Bloating and diarrhea due to the bacterial degradation of lactose (upon delivery to the large intestine undigested)
What gets removed in a typical RNY bypass of the small intestine?
Part of the jejunum
What do calorie requirements depend on?
Energy expendature: BMR, thermal effect of food, physical activity
What are the two essential fatty acids?
Linoleic acid: w 3
Linolenic acid: w 6
What are the essential amino acids?
What has the highest calorie density of carbs, proteins, fat, alcohol
Alcohol 7 kcal/gm
What % of diet should carbs, proteins, and fat compose?
6 causes of malnutrition
Acute and chronic illness
Self-imposed dietary restriction
Other: GI disease, malabsorption syndrome, drugs, TPN
A malnourished child has a weight of less than __% normal
What are the two protein storing compartments?
Somatic protein: skeletal muscle stores
Visceral protein: visceral organ stores
What is marasmus?
Severe reduction in caloric intake leading to >60% reduction in body weight
What protein compartment is depleted in marasmus?
Somatic protein compartment
What is the presentation of marasmus?
Growth retardation and loss of muscle mass
Anemia and immunodeficiency
What protein stores are lost in Kwashiorkor?
Visceral protein stores
What causes Kwashiorkor?
Protein deprivation is greater than caloric deprivation
Chronic protein loss: protein losing enteropathies, nephrotic syndrome, chronic diarrhea
Is albumin abnormal in Kwashiorkor or masasmus?
What is the clinical presentation of Kwashiorkor?
Alternating hypo and hyperpigmented zones with desquamination
Hair color and texture changes
Immune deficiency, anemia
What are the patient populations that frequently show malnutrition?
Four complications of malnutrition:
Impaired wound healing
Death after surgery
How is the BMI calculated
BMI = weight (kg) / height (m2)
What are the key limitations to using BMI?
High muscle mass
High bone mass
Ranges change for children and teens
Two measurements for the % body fat?
What are the characteristics of metabolic syndrome?
What are the characteristic of type II diabetes?
Elevated blood sugars
How is type II diabetes controlled?
What are the key medical complications of obesity?
Type II diabetes
Obstructive sleep apnea
What are the 4 Fs of cholelithiasis?
What are the estrogen dependent cancers that are associated with obesity?
What are the estrogen independent cancers that are associated with obesity?
Why is PE/DVT associated with obesity?
Estrogen is a RF for thrombosis
What are the three hyperlipidemias that are associated with accelerated, premature atheroscleorosis of the coronary arteries
Familial combined hyperlipidemia
What is the "Recommended Dietary Allowance" (RDA)?
Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97-98%) of healthy individuals
What is the definition of adequate intake?
Established when evidence is insufficient to develop an RDA and is set as a level assumed to ensure nutritional adequacy
What is a tolerable upper intake level?
Maximum daily intake unlikely to cause adverse side effects
What are 'daily values' used for?
Food and dietary supplement labels to indicate the percent of the recommended daily amount of each nutrient that a serving provides
What are the two general types of water soluble vitamins
What is the non-B complex water soluble vitamin?
Ascorbate (Vitamin C)
What are the three types of B-complex, water soluble vitamins
Amino acid metabolism
What are the energy-releasing, B-complex, water soluble vitamins?
Pantothenic acid (B5)
What are the hematopoietic/1C metabolism, B-complex, water soluble viatmins?
Vitamin B12 (cobalamin)
What is the amino acid metabolism, B-complex, water soluble vitamin?
Vitamin B6 (pyridoxine, pyridoxamine)
What are the fat soluble vitamins?
Vitamin A (retinol, carotenes)
Vitamin D (cholecalciferol)
Vitamin E (tocopherols)
Vitamin K (phylloquinones)
Where are most B vitamins absorbed? What is the exception?
Duodenum and jejunum
B12 absorbed in the ileum and mircobiota-produced biotin in the large intestine
What are the sources of most B-vitamins
Whole grains and fortified breads/cereals
Green leaky vegetables
What are the sources of vitamin B12
Milk, cheese, yogurt
**not available in plant products
What vitamin is thiamine pyrophosphate dependent on?
What vitamin is flavin adenine dinucleotide dependent on?
What vitamin is nicotinamide adenine dinucleotide dependent on?
Where is thiamine (B1) absorbed?
How long does it take for thiamine (B1) storage to be depleted
What is the active from of thiamine (B1)?
What are three key functions of thiamine (B1)?
1. Cofactor for pyruvate dehydrogenase (decarboxylation)
2. Cofactor in the pentose phosphate pathway
3. Maintains neural membranes and normal nerve conduction
What are dietary sources of thiamine (B1)
Whole grains and fortified breads/cereals
Legumes and nuts
Who commonly gets thiamine (B1) deficiency?
What are the three clinical syndromes of thiamine (B1) deficiency
1. Polyneuropathy--dry beriberi
2. Dilated cardiomyopathy--wet beriberi
3. Wernicke-Korsakoff syndrome
What are two possible treatments for thiamine (B1) deficiency
Banana bag (IV Mg, K, thiamine, folate)
What is Wernicke-Korsakoff Syndrome?
Reversible encephalopathy with opthalmoplegia, confusion and disorientation, nystagmus, and ataxia
Cause: Thiamine (B1) deficiency
What is the chronic stage of Wernicke Korsakoff syndrome?
Korsakoff syndrome: irreversible memory disturbances and confabulation
What is seen in the brain with Wernicke-Korsakoff syndrome?
Periventricular and mammilary body hemorrhage and necrosis
Is thiamine (B1) toxic?
What vitamin is panthothenic acid
Where is panthothenic acid (B5) absorbed?
Storage of pantothenic acid
Excess excreted, very little stored
What is the active form of panthothenic acid (B5)
What is the function of pantothenic acid (B5)
Carbohydrate and fatty acid synthesis
**acyl carrier protein function
What are good sources of panthothenic acid?
Panthothenic acid deficiency ? Toxicity
What vitamin is riboflavin
Where is riboflavin (B2) absorbed?
What are the active forms of riboflavin
Flavin mononucleotide (FMN)
Flavin adenine dinucleotide (FAD)
What is the function of riboflavin (B2)
Electron carrier: complex dehydrogenases, citric acid cycle to the electron transport chain
What are good sources of riboflavin?
Milk and milk products
Whole grains and fortified breads/cereals
Nuts and legumes
Who gets riboflavin (B2) deficiency?
Rare, except in alcoholics
What are the s/s of riboflavin (B2) deficiency?
Cheilosis: scaling and fissures at the mouth corners
Angular stomatitis: inflammation at the corners of the mouth
Glossitis: inflammation of the tongue
Toxicity of riboflavin (B2)
What vitamin is niacin?
Where is niacin absorbed?
What are the active forms of niacin (B3)
When is NADH generated? Function?
Generated during degradation of carbs, fats, amino acids, nucleic acids
Carried electrons from the TCA cycle to the electron transport chain
When is NADPH generated? Function?
Glucose-6-phosphate dehydrogenase in the pentose phosphate pathway
Used in synthesis reactions for carbohydrates, fats, amino acids, and nucleic acids
What are good dietary sources of niacin (B3)
Whole grains and fortified cereal/breads
Nuts and legumes
What is the name fore niacin or tryptophan deficiency?
Who gets pellagra (niacin or tryptophan deficiency)?
People living in poverty
What are the three key sx of pellagra?
Dermatitis (when exposed to the sun)
What is the toxicity of niacin (B3) when given at pharmacological levels for hypercholesterolemia?
What vitamin is biotin?
Where is biotin (B7) absorbed?
What is the active form of biotin (B7)?
Biotin bound to carboxylase
WHat is the function of biotin (B7)?
Carboxylase cofactor: pyruvate carboxylase and acetyl CoA carboxylase
What are dietary sources of biotin (B7)
Where in the body is biotin synthesized?
By intestinal bacteria
What can lead to biotin (B7) deficiency?
Rare, but more prevalent in the elderly
Can occur by binding of biotin to avidin in raw egg whites
What happens in a biotinidase deficiency?
Inability to convert dietary-derived biocytin to free biotin
What is the presentation of biotin deficiency in infants?
What is the presentation of biotin deficiency in infants and adults?
None--excess is excreted
What vitamin is pyridoxine?
Where is pyridoxine absorbed?
Jejunum and ileum
What is the active form of pyridoxine (B6)?
What is the function of pyridoxyl phosphate?
Coenzyme involved in:
1. Amino acid degradation: aminotransferases, decarboxylases, serine hydroxymethyltransferase, aldolase
2. Glycogen degradation: glycogen phosphorylase
3. Porphyrin synthesis
Dietary sources of pyridoxine (B6)
Beans, nuts, leugmes
Whole grains and fortified grains and cereals
Who gets pyridoxine (B6) deficiency?
People with kidney failure
People on Isoniazid for tuberculosis
What are the sx of pyridoxine deficiency?
Cheilosis: scaling at the corners of the mouth
Angular stomatitis: inflammation at mouth corners
Glossitis: inflammation of the tongue
Microcytic hypochromic anemia
Confusion and irritability
What is the toxicity of pyridoxine (B6)?
Peripheral sensory neuropathy
What are the two hematopoietic/1C metabolism vitamins?
Where is folate (B9) absorbed?
What is the active form of folate (B9)?
What is the function of folate (B9)
Carrier of 1C units for:
1. Purine synthesis
2. dTMP synthesis
3. Conversion of homocysteine to methionine for S-adenocylmethionine synthesis
Dietary sources of folate?
Beans and legumes
Dark, leafy green vegetables
Fortified grain and cereals
What are the 2 main causes of folate deficiency?
Antifolate treatment (methotrexate, 5-flurouracil)
What are the main sx of folate deficiency?
Fetal neural tube defects
What are the sx of spina bifida occulta, a neural tube defect that can occur with inadequate maternal folate intake?
Numbness in the legs and back
What is anencephaly?
Missing parts of the brain
How much supplementation of folate does the USPHS recommend?
400 ug dose daily
How is vitamin B12 (cobalamin) absorbed?
IF-B12 complex in the ileum
Storage of cobalamin (B12)
Storage lasts around 2 years
What are the only 2 biochemical rxns that require B12?
Methyl malonyl-conenzyme A mutase
What are good sources of B12?
Milk and yogurt and cheese
**NOT PLANT PRODUCTS
What are some causes of vitamin B12 deficiency?
1. Impaired absorption: IF deficiency or ilieal resection
2. Increased requirement
3. Decreased intake (vegan)
4. Tapeworm (Diphyllobothrium)
What are the clinical s/s of B12 deficiency? (3)
1. Megaloblastic anemia (pernicious anemia)
2. Neural tube defects
3. Subacute combined neural degeneration: dorsal and lateral tract demyelination, parasthesias, spastic paraparesis, sensory ataxia
What are the three antioxidant vitamins?
Beta carotene (provitamin A)
What are the post-translational modificaiton vitamins?
Where is ascorbate absorbed?
Jejunum and ileum
What are the functions of ascorbate (vitamin C)
Antioxidant: reduces ROS
Cofactor of enzymes that reduce metal ions
Post-translational modification of proteins (collagens), lysyl and proyl hydroxylase
Synthesis of neurotransmitters and hormones
What are sources of ascorbic acid?
Fruits and vegetables
Highest in citrus fruits, strawberries, green peppers, broccoli, green leafy vegetables, tomatoes, potatoes
What happens with vitamin C defiency?
Impaired collagen formation: poor vessel support results in bleeding tendency, impaired wound healing, easy bruising, corkscrew hairs, and petechial hemorrhage
What are the fat-soluble vitamins?
Vitamin A (Retinol, Carotenes)
Vitamin D (Cholecalciferol)
Vitamin E (Tocopherols)
Vitamin K (Phylloquinones)
Where are fat soluble vitamins absorbed?
Where is vitamin D absorbed?
Duodenum and jejunum
ALSO the ileum
Where is vitamin K produced in the body?
Produced by microbiota in the large intestine
What vitamin is tocopherol?
What is the most active form of vitamin E?
How is tocopherol (vitE) absorbed?
From micelles in the duo and jej
How is vitE, or tocopherol distributed in the body?
Where is tocopherol (vitE) stored?
What is the function of vitamin E/tocopherol?
Antioxidant--scavengers free radicals
What are dietary sources of vitaminE/tocopherol?
Incidence of vitamin E / tocopherol deficiency?
Uncommon, except for with malabsorption syndromes, TPN, and premature infants
What are the sx of tocopherol/vit E deficiency
What is a pharmacological use of tocopherol/vitamin E
Alzheimer's disease progression inhibitor
What vitamin is phylloquinones?
How is vitamin K absorbed?
From micelles into the duo, jej, ileum
How is vitamin K distributed in the body?
Where is vitamin K stored?
What is the active form of vitamin K?
What are the functions of vitamin K?
- Cofactor for vit K dependent gamma carboxylase (needed for factors II, VII, IX, X, S, C)
--> modified Gla residue binds Ca and localizes coagulation proteins on activated platelets
What are the dietary sources of vitamin K?
Green vegetables, spinach, kale
Cauliflower and cabbage
Synthesized by bacteria in the intestine
Though vitamin K deficiency is rare, what can cause it?
Broad spectrum antibiotics (kills flora)
Lack of gut flora in neonates
Chronic liver disease
What are the sx of vitamin K deficiency?
->Easy bruising and hematomas
->Hemorrhagic disease of the newborn
What is seen in vitamin K toxicity?
Shortened bleeding time
**no toxicity with food as a source of the vitK
What vitamin are cerotenes and retinoids?
Where is vitamin A stored?
Liver stellate (ito) cells
What is the function of beta carotene?
Vitamin A precursor
What is the major transport form of vitamin A?
What form of vitamin A is important for vision?
11-cis retinal (retinaldehyde)
What form of vitamin A is involved in the regulation of retinoid responsive gene expression--epithelilal cells function, mucous cell function, immunity, reproduction
Retinoic acid (all-trans, 9-cis)
How is 11-cis-retinal involved in vision?
Binds rhodopsin in rods and to cone pigments in cones: difference in binding to the three cone pigments results in absorption of different wavelengths of light
Light converts 11-cis retinal to all-trans-retinal
What happens with the conversion of 11-cis to all-trans retinal by light?
-The GPCR transducin in the rod and cone membranes changes conformation and activates the G-protein, activating a phosphodiesterase
-Cleavage of cGMP closes cGMP coupled ion channel, signal to brain
What are good sources of beta carotene?
Green leafy vegetables
Intensely colored vegetables like carrots, sweet potatoes, and red peppers
What are good sources of rentinyl esters?
When is vitamin A deficiency seen in the US?
Poor intake with serious viral infections
What is the clinical presentation of vitamin A deficiency?
Impaired vision--night blindness
Squamous metaplasia--mucus and epithelial cells
Renal, urinary calculi
Predisposition to pulmonary infections, diarrhea
What are some of the consquences of squamous metaplasia with retinoic acid deficinecy?
Bitot's spots (keritin debris)
Corneal ulceration, keratomalacia
Toxicity of beta carotene?
Non-toxic, but yellow skin due to fat deposition
**sclera not yellow
Toxicity of retinol
Toxic at high levels: blurred vision, abdominal pain, peeling of the skin, hair loss, headache, dizziness, vomiting, bone pain and deformities
Death if levels are high enough
Toxicity of retinal?
Toxic at high levels, esp to the retina
Toxicity of retinoic acid
Toxic at levels used to treat acne: teratogenic and peeling of the skin
What vitamin is calciferol?
What are the two dietary forms of vitamin D?
Animals: D3, cholecalciferol
Plants: D2, ergocalciferol
What form of vitamin D can be synthesized in the skin
What is the active form of vitamin D?
1,25 dihydrovitamin D (cholecalciferal)
Absorption of vitamin D?
Micelles to epithelial cells
Duodenum, jejunum, ileum
Where is vitamin D stored?
WHat is the function of vitamin D?
Controls the expression of vitamin D responsive genes
Maintains normal calcium and phosphate levels
Controls: cell cycle arrest, apoptosis, immune suppression, anti-inf, differentiation
What is the effect of vitamin D when calcium or phosphate is low
Increases absorption in the intestines
Decreases excretion by the kidney
Increases release by the bones
Sources of vitamin D/calciferols
Butter and margarine
What causes vitamin D deficiency?
Inadequate sunlight/dietary deficiency
End organ resistance
What is the result of vitamin D deficiency in children
- bowed legs
- frontal bossing
- pigeon breast
What is the result of vitamin D deficiency in adults
- soft, painful, bendable
- osteoporosis: loss of bone density, fragile bone
- Dowager's humb
What are s/s of vitamin D toxicity?
Calcification of soft tissue
Decalcificaiton of bones
Where are ions absorbed?
What form is iron absorbed in?
How is iron stored?
Ferritin and hemosiderin
In the liver, spleen, and bone marrow
Sources of iron
Function of iron
In heme as part of hemoglobin or myoglobin
Iron sulfer complexes in the TCA cycle, ETC
What is the most common nutritional deficiency?
Causes of iron deficiency
Inadequate diet, milk fed infants
Blood loss--GI and menstrual
What are the sx of iron defiicency?
Hypochromic, microcytic anemia
Impaired cognition and work capacity
What is the toxicity of iron?
Abnormal deposition in the liver, pancreas, heart, and skin
Where is zinc absorbed?
What are sources of zinc?
Oysters and other shellfish
What are the functions of zinc
Component of enzymes involved in metabolism (oxidases, metalloproteinases)
Gene expression--Zn finger protein
Skin maintenance and wound healing
Though incidence of zinc deficiency is rare, in what cases is it relatively common?
Malabsorption syndromes and chronic diarrhea
Renal disease and dialysis
Major burn patients
Inborn error of zinc absorption
What are the sx of zinc deficiency?
Depressed wound healing and immune response
Infertility due to inhibition of testosterone syn
What happens in zinc toxicity?
Inhibits copper absorption, leading to a copper deficiency
Where is iodine absorbed?
What are sources of iodine?
Salt water fish and shellfish
What is the main function of iodine?
Component of thyroid hormones
What are the sx of iodine deficiency?
Cretinism: children with dwarfism, retardation, bone deformation, subnormal BMR)
Myxedema: adults with dry skin, swelling of the skin around nose and lips, mental deterioration, subnormal BMR
What ate sx of iodine tox?
Where is copper absorbed?
What are the sources of copper?
Functions of copper
1. Oxidation rxns including e- transport: cyt C oxidase, tyrosinase
2. Neurotransmitter reg: dopamine beta oxidase
3. Antioxidants: superoxide dismutase
4. Collagen crosslinking enzymes: lysyl oxidase
5. Development of vascular and skeleton structures and the CNS
Though copper deficiency is rare, when do you see it?
Excess zinc intake
Genetic diseases like Menke's syndrome
What are the sx of copper def?
Microcytic hypochromic anemia
Abnormal collagen crosslinks leading to bleeding
When do you get copper toxicity?
What are the sx of copper tox?
Kaiser Fleischer rings
Where is fluoride absorbed?
What are the sources of fluoride?
Water (natural or supplemented)
Functions of fluoride
Required by teeth
What happens with fluoride deficiency?
When does fluorine tox occur?
Kids eating fluorinated toothpaste
What are the sx of fluoride tox?
Mottled tooth enamel
Where is selenium absorbed?
Sources of selenium
Plants grown in selenium containing soil
Fish and shellfish
What are the functions of selenium
Component of glutathione peroxidase
Antioxidant with vitamin E
Regulates thyroid hormone action
Effects of selenium def
Hair and hail damage