2. INTRODUCTION
DIVISIONS OF CA+ IN OUR BODY :
BODY CONTENT = 1300GMS
BONE = 99%
INTRACELLULAR = 1%
EXTRACELLULAR = 0.1%
CALCIUM IN BLOOD IS VERY
TIGHTLY CONTROLLED.
3. FUNCTIONS OF CALCIUM :
1.MUSCLE FUNCTIONS - DECREASED
EXTRACELLULAR CALCIUM INCREASES THE
EXCITABILITY OF EXCITABLE CELLS & HENCE,
CAUSING TINGLING AD NUMBNESS (SENSORY) AND
SPONTANEOUS MUSCLE TWITCHES (MOTOR
NEURONS AND MUSCLES).
2.INCREASE IN INTRACELLULAR CA2+
CONCENTRATION CA2+ BINDS TO TROPONIN C
CONFORMATIONAL CHANGE IN THE TROPONIN
COMPLEX MOVES TROPOMYOSIN OUT OF THE
WAY PERMITTING THE BINDING OF ACTIN TO THE
MYOSIN HEADS LEADING CROSS-BRIDGE
FORMATION AND THE MUSCLE CONTRACTS AS A
WHOLE
4. FUNCTIONS :
3.HOMEOSTASIS.
4.NEUROTRANSMITTER RELEASE - DIRECTLY
PROPORTIONAL TO THE CALCIUM LEVEL - ARRIVAL
OF ACTION POTENTIAL TO AXONAL TERMINAL
OPENING OF VOLTAGE GATED CALCIUM
CHANNELS CALCIUM INFLUX INTO THE
TERMINAL TRANSMITTER VESICLE FUSE WITH
THE RELEASE SITES EXOCYTOSIS-RELEASE OF
TRANSMITTERS INTO THE CLEFT
5.ESSENTIAL COMPONENT IN THE PRODUCTION
OF ENZYME AND HORMONES THAT REGULATE
DIGESTION, ENERGY, AND FAT METABOLISM.
5. CALCIUM HOMEOSTASIS :
BLOOD CALCIUM IS TIGHTLY
REGULATED BY:
1) PRINCIPLE ORGAN SYSTEMS:
INTESTINE
BONE
KIDNEY
2) HORMONES:
PARATHYROID HORMONE (PTH)
VITAMIN D
6. PARATHYROID HORMONE (PTH) :
THERE ARE 4 PARATHYROID GLANDS, ON DORSAL SIDE OF THYROID & BLOOD IS
SUPPLIES BY THYROID ARTERIES.
CHIEF CELLS SECRETE PTH & OXYPHIL CELLS FUNCTION IS UNKNOWN PROBABLY
DEGENERATED CHIEF CELL .
7. MECHANISM :
INCREASE IN EXTRACELLULAR CALCIUM
CONCENTRATION THEN, CA2+ BINDS TO THE
RECEPTOR AND ACTIVATES PHOSPHOLIPASE C
THEN, INCREASED LEVELS OF IP4 /CA2+ THEN,
WHICH INHIBITS PTH SECRETION.
WHEN EXTRACELLULAR CA2+ IS DECREASED,
THERE IS DECREASED CA2+ BINDING TO THE
RECEPTOR, WHICH STIMULATES PTH SECRETION.
ACTIONS OF PTH ON BONE, KIDNEY AND SMALL
INTESTINE •
DIRECT VS INDIRECT
1) ACTIONS ON BONE - PTH RECEPTORS ON
OSTEOBLASTS – INITIAL BONE FORMATION
(DIRECT ACTION).
2)LATER ON – BONE RESORPTION (INDIRECT
ACTION) VIA CYTOKINES FROM OSTEOBLAST.
3)OVERALL EFFECT : PROMOTE BONE
RESORPTION AND INCREASE CALCIUM
CONCENTRATION
8. A) PTH INHIBITS PO4 REABSORPTION (INHIBITS NA-PO4 COTRANSPORT IN PCT) –
PHOSPHATURIA – LESS COMPLEXED CA-PO4 – INCREASE PLASMA CALCIUM.
B) STIMULATES CALCIUM REABSORPTION (ON DCT) PHOSPHATURIA + CA2+ REABSORPTION
= INCREASE IN CA2+ CONCENTRATION
9. VITAMIN D :
Action Of Vitamin D on Bone, Kidney, Intestine.
10. Common diseases related to vitamin D :
1) Rickets - insufficient amounts of calcium and phosphate to
mineralize the growing bones then, growth failure and
skeletal deformities.
2) Osteomalacia – new bone fails to mineralize then, bending
and softening of weight bearing bones
11. HYPOCALCEMIA :. SIGNS AND
SYMPTOMS :
"CATS GO NUMB"- CONVULSIONS,
ARRYTHMIAS, TETANY AND
NUMBNESS/PARESTHESIA IN HANDS, FEET,
AROUND MOUTH AND LIPS. • TROUSSEAU
SIGN OF LATENT TETANY (ELICITING CARPAL
SPASM BY INFLATING THE BLOOD PRESSURE
CUFF AND MAINTAINING THE CUFF
PRESSURE ABOVE SYSTOLIC) • CHVOSTEK'S
SIGN (TAPPING OF THE INFERIOR PORTION
OF THE ZYGOMA WILL PRODUCE FACIAL
SPASMS)
13. Summary :
Calcium is crucial for body physiological function It must be
tightly regulated to maintain physiological stability, by the
interaction between the major organs (Intestine, kidney, bone) and
hormones ( PTH, Calcitonin, Vitamin D)
A decrease in calcium level – stimulate PTH release – increase
bone reabsorption, increase Ca2+ reabsorption from kidney (DCT),
decrease PO4 reabsorption from kidney (PCT), and increase
calcium uptake from GI (indirect) Vitamin D – same action but
increase PO4 reabsorption from kidney Calcium imbalance must
be recognized and treated early to prevent any catastrophe.
