Calcium Metabolism

Question 1

__ and ___ are the major minerals of bones

Answer 1

calcium and phosphate

Question 2

where is total body calcium located

Answer 2

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

Question 3

1% of total body calcium is extracellular.

50% of that 1% circulates ___ bound. When it is ___, it is biolgoically active.

Answer 3

50% of that 1% circulates PROTEIN bound. When it is IONIZED, it is biolgoically active.

*beware disorders of serum protein fraction

Question 4

location of total body PO4

Answer 4

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)

Question 5

T/F most of the extracellular phosphate is protein bound

Answer 5

false. minimal protein binding, minimally complexed with other cations

Question 6

___ hormone is responsible for extraordinarily tight control of serum calcium. It is syntheized in the parathyroid gland, specifically from its __ cells.

Answer 6

PARATHYROID hormone is responsible for extraordinarily tight control of serum calcium. It is syntheized in the parathyroid gland, specifically from its CHIEF cells.

Question 7

immediate and long term response of parathyroid glands

Answer 7

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

Question 8

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

Answer 8

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

Question 9

high serum PO4 ____ PTH.

high vitamin D ___ PTH

Answer 9

high serum PO4 STIMUALTES PTH.

high vitamin D DECREASES PTH

Question 10

Calcium negative feedback loop to PTH

Question 11

PTH ___ serum calcium
• And low calcium __ PTH

• PTH ___ serum phosphate
• And high phosphate ___ PTH

Answer 11

PTH raises serum calcium
• And low calcium stimulates PTH

• PTH lowers serum phosphate
• And high phosphate stimulates PTH

Question 12

active vitamine D ____ serum calcium levels and __ serum PTH

Answer 12

active vitamine D INCREASES serum calcium levels and DECREASES serum PTH

Question 13

actions of PTH on the bone, kidneys, and small intestine

Answer 13

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.

Question 14

what specific organ system does active vitamin D act on?

Answer 14

acts on GI small intestine to absorb Ca2+ and phosphate in small intestine

Question 15

PTH binds to the ___ receptor, which is a ___ type of receptor. Outline the mechanism

Answer 15

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.

Question 16

PTH triggers the release of calcium from bone, how does this happen?

Answer 16

it increase bone resorbption, and has in indirect effect on osteoclasts. release of bone-stored calcium and PO4

Question 17

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)

Answer 17

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)

Question 18

PTH ____ the renal enzyme that convers inactive to ACTIVE vitamin D

Answer 18

stimulates active vitamin D production in the kdiney. allows for absorbption of Ca and PO4 on the small intestine to raise the serum calcium

Question 19

active vitamin D (via ____ process) acts on the GI system for calcium absorption. it induces the ___ ____, a calcium transporter on luminal and basolateal enterocytes.

Answer 19

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.

Question 20

Outline the general production of vitamin D.

1. pro vitamin D is a very inert moleucle. when exposed to ___, it converts to pre vit D3 in the sun.
2. pre vit D3 moves to small intestine, where it exists as ____.
3. ____ 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 ___.

Answer 20

Outline the general production of vitamin D.

1. pro vitamin D is a very inert moleucle. when exposed to SUN, it converts to pre vit D3 in the sun.
2. pre vit D3 moves to small intestine, where it exists as CHOLESCALCIFEROL.
3. 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.

Question 21

Question 22

Actiev vitamin D heterodimerizes with other nuclear receptors (__), then bonds to DNA sequences (___) in the promotor region of vitamin D regaulted genes.

Answer 22

Actiev vitamin D heterodimerizes with other nuclear receptors (RXR), then bonds to DNA sequences (VDRE) in the promotor region of vitamin D regaulted genes.

Question 23

KEY enzyme in the kidney that activates vitamin D

Answer 23

1-a- hydroxylase. this is improtant because it regulates the amount of inactive vitamin D gets turned on

Question 24

Answer 24

Question 25

two main types of bone

Answer 25

cortical and trabecular

Question 26

3 major bone cells

Answer 26

osteoblasts, osteoclasts, osteocytes

Question 27

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.

Answer 27

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.

Question 28

there are 4 intertwining feedback loops that are involved in vitamin D regulating pathways

Question 29

T/F bone is mainly made up of organic material

Answer 29

false. 70% inorganic, and 30% organic.

Question 30

the bone is a composite material that is 70% inorganic material. what are these materials?

Answer 30

CALCIUM HYDROXYAPATITE (Ca10PO496) (OH)2)

other minerals like Na+, K+, Cl-

Question 31

organic components of bone

Answer 31

cells are 2% of the organic materal. Osteoblasts, clasts, and cytes.

matrx is 98%. Type I collagen, proteoglycans, glycoprotiens, phospholipids

Question 32

recall that the two “main” layers of bone is cortical or trabecular. what type of bone is more responseible for bone turnover?

Answer 32

trabecular bone is involved in 80% of bone turnover

Question 33

note; location of cortical and trabecular bone

Question 34

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?

Answer 34

20% of TRABECULAR (CANCELLOUS) bone remodeled yearly. 4% of cortical (COMPACT bone is remodeled)