Nutrition 3 Flashcards
What do macrominerals include?
What do trace minerals include?
Macrominerals include calcium, phosphorus, magnesium and iron
Trace minerals include zinc, copper, iodine, selenium & chromium
Describe Calcium and its homeostatic regulation.
How is plasma calcium regulated?
Where are Ca-sensing receptors found?
In hypocalcemia, What will occur?
Homeostatic Regulation
Plasma calcium tightly regulated at about 2.5 mM (9-10 mg/dL)
Ca2+-sensing receptors found on surface of parathyroid, clear cells of thyroid glands, kidney, intestine & bone marrow
Hypocalcemia: plasma Ca2+ concentration decrease and increase PTH gene expression and secretion activates vitamin D to
enhance intestinal calcium absorption
increase renal reabsorption of Ca2+
activate bone resorption & augment osteoclast activity
Bone resorption is the process by which osteoclasts break down bone and release the minerals, resulting in a transfer of calcium from bone fluid to the blood. The osteoclasts are multi-nucleated cells that contain numerous mitochondria and lysosomes. These are the cells responsible for the resorption of bone
Describe the Regulation of Calcium Balance by Vitamin D and Parathyroid Hormone (PTH) in a flow diagram.
Slide 3
How is Ca absorbed in the gut?
Describe active absorption.
Passive absorption.
How is Ca absorption inhibited?
(paracellular and transcellular)
Active absorption - Ca2+ enters calcium channel, binds to calbindin, transported across cytosol; released into circulation via Ca-ATPase & Na+-Ca2+ exchanger
- Passive absorption – between intestinal cells along calcium gradient
- Calcium absorption generally poor; 30% calcium in dairy products absorbed, only approx5% in vegetables
- Oxalic acid potent inhibitor – binds calcium in gut & forms indigestible salt
- Phytate – plant storage form of phosphorus also forms salts & inhibits absorption
Describe factors that enhance and decrease Ca absorption.
Factors enhancing absorption: vitamin D adequacy, calcium deficiency, pregnancy, postweaning status and mucosal permeability
Factors decreasing absorption: vitamin D deficiency, menopause, decreased stomach acid, rapid intestinal transit time and estrogen deficiency (including drug-induced, eg, tamoxifen)
What diets will increase Ca excretion?
High dietary sodium increases urinary calcium excretion – sodium & calcium share a transporter in kidney
High protein diets increase calcium excretion
What are the main functions of Ca?
Component of hydroxyapatite [Ca10(PO4)6(OH)2]; skeleton and dentition
Activation of catalytic & mechanical properties of cellular proteins
Intracellular messenger – ionized Ca2+ most common signal transduction element
Cofactor for several
proteases & blood clotting enzymes
What is the main mineral present in hydroxyapatite?
Calcium [Ca10(PO4)6(OH)2]
