Calcium Metabolism Flashcards
__ and ___ are the major minerals of bones
calcium and phosphate
where is total body calcium located
99% of total body calcium is bone, 1% of total body Ca is etracellular to act as a co-factor for many extracellular enzymatic reactions, coagulation, muscle contraction, neurotransmitter release, endocrine/exocreine secretion
1% of total body calcium is extracellular.
50% of that 1% circulates ___ bound. When it is ___, it is biolgoically active.
50% of that 1% circulates PROTEIN bound. When it is IONIZED, it is biolgoically active.
*beware disorders of serum protein fraction
location of total body PO4
85% of total body PO4 is in bone.
15% exist as organicc form part of biological moecules like nucleic acids, phospholipids, carbohydrates etc.
- extracellular Pi almost completely ionized (H2PO4 or HPO4)
T/F most of the extracellular phosphate is protein bound
false. minimal protein binding, minimally complexed with other cations
___ hormone is responsible for extraordinarily tight control of serum calcium. It is syntheized in the parathyroid gland, specifically from its __ cells.
PARATHYROID hormone is responsible for extraordinarily tight control of serum calcium. It is syntheized in the parathyroid gland, specifically from its CHIEF cells.
immediate and long term response of parathyroid glands
immediate ersponse is rapid secretion of PTH
mid term response; increases synthesis and storage of PTH
long-term response; hypertrophy and hyperplasia with chronic stimulation
On the chief cells, Calcium activates the ____ receptor, opens plasma membrane Ca Channels, and leads to an influx of Ca2+. Increased intracellular [Ca} leads to ____ function of PTH
On the chief cells, Calcium activates the CALCIUM SENSING RECEPTOR (CASR) receptor, opens plasma membrane Ca Channels, and leads to an influx of Ca2+. Increased intracellular [Ca} leads to DECREASED function of PTH
high serum PO4 ____ PTH.
high vitamin D ___ PTH
high serum PO4 STIMUALTES PTH.
high vitamin D DECREASES PTH
Calcium negative feedback loop to PTH
PTH ___ serum calcium
• And low calcium __ PTH
- PTH ___ serum phosphate
- And high phosphate ___ PTH
PTH raises serum calcium
• And low calcium stimulates PTH
- PTH lowers serum phosphate
- And high phosphate stimulates PTH
active vitamine D ____ serum calcium levels and __ serum PTH
active vitamine D INCREASES serum calcium levels and DECREASES serum PTH
actions of PTH on the bone, kidneys, and small intestine
bone; release calcium from bone to incresae levels of serum calcium
kidneys; conserve calcium in kidneys
GI: absorb Ca2+ and PO4 in small intestine.
all in attempt to maintain/raise serum calcium.
what specific organ system does active vitamin D act on?
acts on GI small intestine to absorb Ca2+ and phosphate in small intestine
PTH binds to the ___ receptor, which is a ___ type of receptor. Outline the mechanism
PTH binds to the PTH receptor, which is a type of G protein receptor. dissociation of GDP from the Gs-alpha initiates a cascade of events reusulting in an increase in intacellular [Ca] and activation of target enzymes, channels, leading to physiologic response.
PTH triggers the release of calcium from bone, how does this happen?
it increase bone resorbption, and has in indirect effect on osteoclasts. release of bone-stored calcium and PO4
calcium resorption in the kidenys:
65% of calcium is resorbed at the ___ with ___ ion.
- inceases distal calcium reabsorption.
- blocks ___ reabsorption in the proximal and distal tubules (endocytosis of ___ co-transporter)
65% of calcium is resorbed at the PCT with Na ion.
- inceases distal calcium reabsorption.
- blocks PO4 reabsorption in the proximal and distal tubules (endocytosis of NaPi co-transporter)
PTH ____ the renal enzyme that convers inactive to ACTIVE vitamin D
stimulates active vitamin D production in the kdiney. allows for absorbption of Ca and PO4 on the small intestine to raise the serum calcium
active vitamin D (via ____ process) acts on the GI system for calcium absorption. it induces the ___ ____, a calcium transporter on luminal and basolateal enterocytes.
active vitamin D (via Di-HYDROXYLATION process) acts on the GI system for calcium absorption. it induces the DUODENAL CALBINDIN, a calcium transporter on luminal and basolateal enterocytes.
Outline the general production of vitamin D.
- pro vitamin D is a very inert moleucle. when exposed to ___, it converts to pre vit D3 in the sun.
- pre vit D3 moves to small intestine, where it exists as ____.
- ____ moves to the liver, where it gets metabolized to the inactivated form of vitamin D, ___.
____ acts on the kidneys, where it can get activated to 1,2,5OH2VitD Active form, aka ___.
Outline the general production of vitamin D.
- pro vitamin D is a very inert moleucle. when exposed to SUN, it converts to pre vit D3 in the sun.
- pre vit D3 moves to small intestine, where it exists as CHOLESCALCIFEROL.
- CHOLESCALCIFEROL moves to the liver, where it gets metabolized to the inactivated form of vitamin D, CALCIDIOL.
CALCIDIOL acts on the kidneys, where it can get activated to 1,2,5OH2VitD Active form, aka CALCITRIOL.
Actiev vitamin D heterodimerizes with other nuclear receptors (__), then bonds to DNA sequences (___) in the promotor region of vitamin D regaulted genes.
Actiev vitamin D heterodimerizes with other nuclear receptors (RXR), then bonds to DNA sequences (VDRE) in the promotor region of vitamin D regaulted genes.
KEY enzyme in the kidney that activates vitamin D
1-a- hydroxylase. this is improtant because it regulates the amount of inactive vitamin D gets turned on
two main types of bone
cortical and trabecular
3 major bone cells
osteoblasts, osteoclasts, osteocytes
a bone is wrapped in fibrous ____. The ___ layer is the outer, dense layer, and makes up 80% of bone. the ____ layer is the inner spongy component.
a bone is wrapped in fibrous PERIOSTEUM. The CORTICAL (COMPACT) layer is the outer, dense layer, and makes up 80% of bone. the CANCELLOUS (TRABECULAR) layer is the inner spongy component.
there are 4 intertwining feedback loops that are involved in vitamin D regulating pathways
T/F bone is mainly made up of organic material
false. 70% inorganic, and 30% organic.
the bone is a composite material that is 70% inorganic material. what are these materials?
CALCIUM HYDROXYAPATITE (Ca10PO496) (OH)2)
other minerals like Na+, K+, Cl-
organic components of bone
cells are 2% of the organic materal. Osteoblasts, clasts, and cytes.
matrx is 98%. Type I collagen, proteoglycans, glycoprotiens, phospholipids
recall that the two “main” layers of bone is cortical or trabecular. what type of bone is more responseible for bone turnover?
trabecular bone is involved in 80% of bone turnover
note; location of cortical and trabecular bone
bone remodeling is a ynamic process that allows for bone growth, fracture healing and liberation of calcium bone stores to ECF. Which type of bone is more readily remodeled?
20% of TRABECULAR (CANCELLOUS) bone remodeled yearly. 4% of cortical (COMPACT bone is remodeled)
