Review Flashcards
What are the 3 calcium absorption mechanism in the small intestine?
- Saturable, active transport
- Nonsaturable, passive transport (diffusion)
- Paracellular
Where does calcium absorption occur?
Occurs along small intestine, but mostly in duodenum and upper jejunum (early in digestive tract)
The saturable or active transport of calcium requires what?
- Require energy
- Vitamin D dependent
- Uses Ca binding protein calbindin
Where does the paracellular calcium absorption occur?
Through the tight junctions between mucosal cells
Some Ca absorption can occur in colon, from what?
Ca released from bacterial action on some fermentable fibers like pectin
Calcium is usually bound to … in the blood
protein
How is blood calcium regulated?
Tightly regulated by several endocrine factors (hormones)
What are blood calcium levels closely influenced by?
- PTH
- Vitamin D
- Calcitonin
Describe what happens when there is low blood calcium levels.
- Increased secretion of PTH by the parathyroid glands
- Increased activation of vitamin D
- Increased reabsorption of calcium by kidneys
- Increased release of calcium into the bloodstream due to increased breakdown of bone
- Increased absorption of calcium from the intestines
- Increased blood calcium levels
Describe what happens when there is high blood calcium levels.
- Increased calcitonin secretion by the thyroid gland
- Inhibited vitamin D action
- Decreased reabsorption of calcium by the kidneys
- Decreased absorption of calcium from the intestines
- Decreased breakdown of bone
- Decreased blood calcium levels
Refeeding Syndrome is also known as …
Hypophosphatemia
Upon re-feeding insulin is released which stimulates the uptake of what from the bloodstream for anabolic processes? (5)
glucose, amino acids, fatty acids, phosphorous, and potassium
Refeeding Syndrome occurs during starvation when there is low blood levels of all nutrients. What hormonal effect occurs upon re-feeding?
insulin is released
Re-feeding results in what being driven rapidly into cells?
glucose & phosphorous
What is the result of re-feeding a starving person incorrectly?
Hypophosphatemia &/or hypokalemia
What leads to cardiac dysfunction, depression of neuromuscular activity?
Hypophosphatemia
What leads to cardiac failure, GI abnormalities, etc.?
Hypokalemia
What can lead to death upon refeeding?
Hypophosphatemia & hypokalemia
What individuals are at risk for Refeeding Syndrome? (4)
- Anorexics
- Kwashiorkor (protein deficiency)
- Alcoholics
- Anyone after prolonged fasting
What are the steps in the treatment of refeeding? (6)
- Important to measure and correct electrolytes BEFORE refeeding
- Administer electrolytes, minerals & vitamins routinely
- Deliver calories gradually and slowly
- Begin with low kcals and carbohydrates
- Gradually increase kcals and carbohydrates
- TPN adds phosphorous to prevent RS
Long rod shaped protein that gives strength
Collagen
What is required to produce collagen?
- Iron
- Vitamin C
- Vitamin D
What is collagen is involved in?
bone healing
What binds both calcium and collagen?
Osteonectin
What binds hydroxyapatite and bone cells?
Osteopontin
What is Mg role in the bone?
- lattice around hydroxyapatite crystal
- surface of bone (magnesium pool)
Mg acts as a coenzyme in ~300 enzymatic reactions name 8 of them.
- Glycolysis
- Krebs cycle
- HMP Shunt
- Beta oxidation
- Cholesterol synthesis
- Vitamin D activation
- Creatine phosphate formation
- In synthesis of cAMP
What is Mg role in glycolysis?
glucose -> glucose-6-phosphate
Mg+2 & ATP required
enzymes: hexokinase (liver) & glucokinase (body cells)
What is Mg role in the Krebs cycle?
Oxidative decarboxylation
- 3 steps - NADH & CO2
What enzyme is Mg a coenzyme for in HMP Shunt?
transketolase
Where is Mg involved in vitamin D activation?
First 2 steps
What is Mg a coenzyme for in creatine phosphate formation?
creatine kinase
How does intracellular free Mg have a profound effect in cardiac physiology?
By regulating K movement in cardiac muscle cells
What is Mg associated with? (3)
- membranes of phospholipids
- proteins
- nucleic acids
Another function of Mg is in the formation and reactions of …?
ATP
How is Mg involved with the formation of ATP?
Mg+2 provides stability to ATP
7-dehydrocholesterol is converted to what via UVB rays?
Previtamin D3
Previtamin D3 in the skin is converted to Vitamin D3 by what?
heat
What happens when you get a sunburn?
Previtamin D3 and Vitamin D3 are exposed to excess UVB rays and converted into inactive photoproducts.
What are the 2 places Vitamin D can go?
Liver or Adipose Tissue
*Adipose tissue vitamin D can go to Liver also
In the liver Vitamin D is converted to what?
25(OH)D
Enzyme: Vitamin D-25-hyroxylase
What is the inactive and measurable form of Vitamin D?
25(OH)D
25(OH)D goes to … where it is converted to 1,25(OH)2D by 1a-hydroxylase.
Kidney and other tissues/cells
What stimulates 1a-hydroxylase?
PTH
What inhibits 1a-hydroxylase?
Phosphorous, Calcium, FGF-23
Vitamin D receptor is expressed on …
immune cells (B cells, T cells, & antigen presenting cells)
What is capable of converting the circulating form of vitamin D in to the active vitamin D metabolite?
All of the immune cells
*Kidney is the main organ that does this, however the fact that these specific immune cells have the capacity to do it as well means “big” things about the relationship of vitamin D with immune function.
Vitamin D can modulate …
the innate and adaptive immune responses
“non-specific” immune system, where immune cells will attack any foreign invader, regardless of whether it has come in contact with it before or not.
Innate Immune System
the “specific” immune system, where cells like B & T cells, or “memory” cells will develop a memory, providing immunity for life
Adaptive Immune System
What is vitamin D deficiency associated with? (2)
- Increased autoimmunity
- Increased susceptibility to infection
Autoimmune disease cells are responsive to the ameliorative (making it better) effects of vitamin D such as in?
Type 1 diabetes
Iron must first be released from food components via … before it can be absorbed.
- HCl from stomach
- Proteases from small intestine
When … is low, iron absorption is low.
gastric acid
Iron absorption occurs mostly in the …
upper duodenum
Most people absorb what percent of iron intake?
5-15%
Heme Fe is hydrolyzed from … and absorbed (metalloporphyrin)
globin
Non-heme must be released from … before iron absorption can occur.
food components
*(plants/fortified foods)
Non-heme iron when released from food components is primarily in what form?
oxidized, Fe3+ or ferric form
What is the poorly soluble and difficult to absorb form of Fe?
ferric form
The ferric form is difficult to absorb, so most is …
excreted in feces
Free heme is absorbed intact by …, located primarily in the proximal small intestine.
heme carrier protein (hcp) 1
Within the enterocyte, heme is catabolized by heme oxygenase to what?
Protoporphyrin and Fe2+
What on the brush border membrane converts Fe3+ -> Fe2+?
Reductase
What carries Fe2+ across the brush border membrane into the cytosol of the enterocyte?
Divalent metal transporter (DMT) 1
What protein does Fe2+ bind to for transport in the cytosol?
Ceruloplasmin
Iron may be used within the cell or …
stored as part of ferritin
What transports iron across the basolateral membrane?
Ferroportin
Iron transport into the blood via Ferroportin is coupled with?
Irons oxidation to Fe3+ by Hephaestin and its reduction of -Cu+ to -Cu2+
What does Fe3+ attach to for transport in the blood?
Transferrin
List 3 factors that increase iron absorption by keeping it in its ferrous form (Fe2+), or more readily absorbable form.
- Vitamin C (by far the strongest factor)
- Organic acids: including amino acids, citric acid, & lactic acid
- Meat Fish Poultry Factor (MFP factor): refers to beef, chicken, fish, lamb, pork and cysteine content of the meats
List 4 other factors that will increase iron absorption.
- Peptides from the digestion of myosin and actin
- Enhanced erythropoesis
- Iron deficient person will absorb 10-20%
- Pregnancy (particularly the last half)
Why does being iron deficient increase iron absorption?
Low body stores of iron will increase # of iron receptors on enterocyte.
What causes enhanced erythropoesis to increase iron absorption?
Due to: blood loss, hemolysis, hemorrhage, hypoxia
List 12 factors that decrease iron absorption.
- Achlorhydria
- Antacid use
- Acid blockers
- Rapid GI transit time
- Malabsorption syndromes
- Phytic Acid, Oxalic Acid
- Tea: tannins (60%)
- Coffee: polyphenols (40%)
- Iron overload
- Infection
- Inflammation
- Calcium, Zinc
Why does antacid use decrease iron absorption?
It precipitates iron into phosphates and carbonates
5-10mg of phytic acid can reduce iron absorption by what percentage?
50%
300mg of … will decrease iron absorption by 70%
Calcium citrate
How is Transferrin absorbed into body cells?
endocytosis (receptor mediated)
List 18 symptoms of Iron deficiency.
- Nonspecific glossitis
- Anorexia
- Slight pallor
- Night cramps
- Tinnitis & Vertigo
- Faintness
- Increased cold sensitivity
- Headache, Nausea, Constipation, Diarrhea
- Low grade fever
- Menstrual irregularity
- Loss of libido
- Urinary frequency
- Koilonychia (spoon shaped nails)
- Achlorhydria
Who is at risk for iron deficiency? (5)
- Decreased absorption states: bariatric surgery, renal disease, hookworm infestation, H. Pvlori infection, ulcer disease
- Rapid growth spurts
- Menstruation
- Pregnancy
- Infants (low iron formulas)
Iron deficiency might have a decrease in: (2)
- transferrin saturation
- serum ferritin
*However, HGB is still normal
Kidneys detect Hypoxia (decreased O2 due to decreased RBC) which stimulates what hormone to be released?
Increase in EPO production
What does the increase in EPO stimulate?
Erythropoesis in Bone Marrow
RBCs from bone marrow erythropoesis are released into the bloodstream, which causes what?
Blood O2 to return to normal, and decreased EPO production
Zinc - even amounts slightly over the RDA might impair what absorption?
Copper
Zinc induces synthesis of …for which copper has a stronger affinity for, displacing zinc and trapping copper.
metallothionein
Metallothionein can act as … when Cu intake is excessive.
detoxifying agent
What does excess zinc cause?
Hypocupremia
What exerts a negative feedback to the hypothalamus with normal iodine levels?
T3 & T4
Negative feedback mechanism to the hypothalamus, slows pituitary which in turn slows thyroid tissue function, resulting in…
Decrease production of T3 & T4
What happens when the is low T3 & T4 levels due to iodine deficiency?
T3 & T4 fail to exert negative feedback, causing pituitary to continue to stimulate the thyroid gland with TSH to produce T3 & T4.
What results when the thyroid gland is continually stimulated?
It grows larger and larger and the result is classic goiter growth in neck area.
List 8 results of Hypothyroidism.
- Overall slowing of metabolism
- Lower body temperature
- Mental & physical sluggishness
- Constipation
- Dry skin
- High levels of TSH
- Low levels of T4
What does Glutatione Peroxidase do?
Destroys hydrogen peroxides and hydroperoxides (turns into water)
Glutathione Peroxidases functions as an … in cytosol, also spares vitamin E.
antioxidant
Glutathione Peroxidase requires what coenzyme?
Selenium
Glutathione Peroxidase uses … to catabolize hydrogen peroxide; into water and oxidized glutathione (GSSG)
glutathione molecule (GSH)
Oxidized Glutathione (GSSG) is reduced to glutathione (2 GSH) via?
Glutathione reductase
*Coenzyme: Riboflavin (FAD)
What trace mineral is involved in insulin signaling?
Chromium
Chromium forms a complex with amino acids (3) to form …
Glucose Tolerance Factor (GTF)
What does GTF initiate between insulin and the insulin receptor?
disulfide bridge
What effect does the disulfide bridge between insulin and the insulin receptor have?
Potentiates the effect of insulin (creates an action potential)
What does chromium do to insulin?
Doubles the actions of insulin; increases its effectiveness
What must occur for arsenicals to be excreted in urine?
must be methylated
What is the primary methylating enzyme?
S-adenosylmethionine (SAM)
After methylating arsenic SAM becomes …
Homocysteine
Homocysteine can do what 2 things?
- Cysteine metabolism (B6)
- Synthesize methionine to synthesize SAM
What are the methyl donors in the conversion of Homocysteine to Methionine?
Folate (MTHF) & Vitamin B12
*Can be B12 deficient because folic acid will compensate
Vitamin E (a-tocopherol) is regenerated from a-tocopherol radical via …
Ascorbic acid -> dehydroascorbic acid
Dehydroascorbic acid can be reduced to ascorbic acid by …
Glutathione (2GSH) oxidized to GSSG
GSSG is reduced back to GSH via…
NADPH -> NADP+
What medication is used to thin blood, keep vitamin K from forming Gla proteins, and reduce risk of thrombosis?
Warfarin
What are the 2 sites of Warfarin action on the Vitamin K Cycle?
- Quinone (VItamin K) reductase
- Epoxide reductase
