8. Parathyroid & Parathyroid Hormone Flashcards by Ibby Khan

Total body CALCIUM

approx 1kg

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99% of body CALCIUM is stored where?

in BONES

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what is CALCIUM in BONES stored as and what is its purpose

stored as HYDROXYAPATITE

for SKELETAL STRENGTH
& RESEVOIR FOR CALCIUM

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remaining 1% of body CALCIUM is stored where… (3)

BLOOD, EXRRA-CELLULAR FLUID, SOFT TISSUES

Numerous important physiological functions:-
cell division, cell adhesion, glycogen metabolism, muscle contraction, neuronal excitability and coagulation

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NORMAL SERUM of CALCIUM ranges between…

2.18 - 2.62 mmol/L

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how are CALCIUM BLOOD LEVELS divided

45%- FREE or IONISED fraction and is BIOLOGICALLY FUNCTIONAL portion of total Ca.

45%- is BOUND to ALBUMIN in pH DEPENDENT manner.

10%- exists as a COMPLEX with ANIONS including
PHOSPHATE (PO4) and CITRATE.

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PHYSIOLOGICAL FUNCTIONS of CALCIUM

CELL DIVISION
CELL ADHESION
PLASMA MEMBRANE INTEGRITY
PROTEIN SECRETION
MUSCLE CONTRACTION including CARDIAC muscle
NEURONAL EXCITABILITY
GLYCOGEN METABOLISM
BLOOD COAGULATION (clotting)

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DAILY REQUIREMENTS of CALCIUM
INFANTS & CHILDREN:

350-550 mg/day

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DAILY REQUIREMENTS of CALCIUM
TEENAGE GIRLS & BOYS:

800-1000 mg/day

(need most)

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DAILY REQUIREMENTS of CALCIUM
ADULT MEN & WOMEN

700 mg/day

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CALCIUM SOURCES:

milk, cheese and other dairy foods

green leafy vegetables – such as broccoli, cabbage and okra,
but not spinach

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what play a major role in CALCIUM HOMEOSTASIS (3)

(Because of its physiological importance ECF concentration of Ca is
maintained within a narrow range.)

SKELETON
GUT
KIDNEYS

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what is stimulated when BLOOD CALCIUM levels DROP - LOW CALCIUM

release of PTH (parathyroid hormone) from PARATHYROID GLAND

INCREASES BLOOD CALCIUM

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effects of PTH on BONE to INCREASE CALCIUM

INHIBIT OSTEOBLASTS
STIMULATE OSTEOCLASTS

BREAKDOWN OF BONE, releasing calcium ions into bloodstream

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effects of PTH on KIDNEYS to INCREASE CALCIUM

STIMULATES KIDNEY TUBULE CELLS to:
- RECOVER WASTE CALCIUM from the URINE
- RELEASE CALCITROL

CALCITROL STIMULATES INTESTINES to ABSORB CALCIUM from DIGESTING FOOD

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what is the effect of CALCITROL on INTESTINES (released by kidney tubule cells, stimulated by PTH when calcium levels drop)

stimulate intestines to ABSORD CALCIUM from DIGESTING FOOD

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upon effects of PTH (when calcium levels drop) BLOOD CALCIUM LEVELS INCREASE. what is secreted to regulate this

CALCITONIN from THYROID

act on BONE
- STIMULATE OSTEOBLASTS
- INHIBIT OSTEOCLASTS
CALCIUM REMOVED from BLOOD and used to BUILD BONE

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80% of PHOSPHATE is STORED in… as…

stored in BONE as HYDROXYAPATITE

SKELETAL INTEGRITY
PRIMARY RESERVE

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20% of PHOSPHATE is stored in…

SOFT TISSUES both in inorganic or organic molecules

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PHYSIOLOGICAL FUNCTIONS of PHOSPHATE

Intracellular processes including
- NUCLEIC ACID SYNTHESIS
- ATP PRODUCTION (provides ENERGY at cellular level)
- KINASE and PHOSPHATASE ACTIVITY

DAILY REQUIREMENT of PHOSPHATE / PHOSPHORUS

ADULTS - 550 mg/day

PHOSPHATE SOURCES

Dairy
Red meat
Poultry
Bread

rice, oats

PHOSPHATE BLOOD LEVEL RANGE

0.8-1.5 mmol/L

systemic REGULATION of PHOSPHATE is maintained through…

PTH
VITAMIN D

INTESTINES
KIDNEY
BONES

possible CAUSES of HYPOPHOSPHATAEMIA (low phosphate levels)

- DECREASED INTESTINAL ABSORPTION (due to low dietary intake or condition affecting absorption) - INREASED RENAL WASTING (increased excretion, phosphate wasted) - REDISTRIBUTION FROM ECF INTO CELLS (common)

clinical consequences of HYPOPHOSPHATAEMIA

poor growth in children fatigue, weakness, loss of appetite bone pain and fragile bones - 5% of hospitalised patients (30% in alcoholics)

causes of HYPERPHOSPHATAEMIA (high phosphate levels)

DECREASED RENAL EXCRETION ACUTE EXOGENOUS PHOSPHATE LOAD REDISTRIBUTION of INTRACELLULAR PHOSPHATE to EXTRACELLULAR SPACE

clinical consequences of HYPERPHOSPHATAEMIA

HYPOCALCAEMIA SOFT TISSUE CALCIFICATION CALCIFICATION of ARTERIES and HEART VALVES

PARATHYROID GLANDS contain 2 main types of CELL:

CHEIF CELLS OXYPHIL CELLS (no recognised physiological function)

CHEIF CELLS of PARATHYROID GLANDS FUNCTION

FUNCTIONAL CELL - responsible for SYNTHESISING & SECRETING PARATHYROID HORMONES

PARATHYROID GLANDS develop from ENDODERM of which PHARYNGEAL ARCHES

3 and 4

PARATHYROID GLANDS are functional during GESTATION to..

control CALCIUM BALANCE in FETUS

INITIAL state of PTH is as... with how many amino acids?

PRE-PRO-PTH - 115 amino acids polypeptide

PRE-PRO-PTH is CLEAVED to form... with how many amino acids?

PRO-PTH - 90 amino acids polypeptide

PRO-PTH is further CLEAVED to form...

active PTH - 84 AMINO ACIDS

how many amino acids in PTH

CALCITRIOL is the end product of .... metabolism

VITAMIN D METABOLISM

EFFECTS of PTH

INCREASE CALCIUM LEVELS BONE: stimulates osteoclasts to breakdown bone, Ca2+ released into bloodstream KIDNEY: reabsorption of calcium from urine Calcitriol secretion by ACTIVATION OF VITAMIN D Calcitriol acts on INTESTINES for reabsorption of calcium from foodb

what is the effect of PTH on BONES that causes stimulation of Osteoclasts and Reabsorption of Bones to release Ca2+

- STIMULATES OSTEOBLASTS - STIMULATES RANK LIGAND SYSTEM - allows for CHANGE from OSTEOBLASTS TO OSTEOCLASTS

PTH action on KIDNEYS besides increased Ca Reabsorption and Activation of Vitamin D

DECREASED PHOSPHATE REABSORPTION

the effect of PTH on INTESTINES is due to

INCREASE IN ACTIVE VITAMIN D - increases absorption of CALCIUM and PHOSPHATE

HYPERPARATHYROIDISM (HPTH): PRIMARY (PHPT)

ABNORMALITY of the GLAND ITSELF caused by Adenoma, Hyperplasia, rarely carcinoma

HYPERPARATHYROIDISM (HPTH): SECONDARY (SHPT)

compensatory OVER-SECRETION (too much PTH secreted when Ca low) can be due to.. CKD - chronic kidney diseas Vitamin deficiency (D) malabsorption

HYPERPARATHYROIDISM (HPTH): TERTIARY (THPT)

after SECONDARY HYPERTHYROIDISM is TREATED (still secreting high levels) RARE

Clinical features of HPTH - HYPERPARATHYROIDISM usually due to HYPERCALCAEMIA

Nausea and vomiting Constipation ECG changes – short QT interval Kidney stones Bone pain Osteoporosis Psychosis Altered mental status

HYPOPARATHYROIDISM means

LOW PTH & LOW CALCIUM

HYPOPARATHYROIDISM causes:

- Surgical removal or damage - Auto-immune disorders

what is PSEUDOHYPOPARATHYROIDISM

HIGH PTH target organ RESISTANCE to PTH (developmental disorder)

CLINICAL FEATURS of HYPOPARATHYROIDISM and HYPOCALCAEMIA

Muscles: WEAKNESS MUSCLE CRAMPS Nerve Function: PERORAL (mouth) NUMBNESS, TINGLING CHVOSTEK'S SIGN (twitch of facial muscles/spasm when tap) TROUSSEAU' SIGN (arm spasm with high pressure eg BP machine) TENTAY (involuntary muscle contractions and overly stimulated peripheral nerves)