Download Thyroid and Parathyroid Glands

Thyroid and Parathyroid Glands
Thyroid Gland
• This gland is located at the
front of the neck, below the
larynx.
• Follicular cells secrete
thyroxine (T4) and
triiodothyronine (T3),
collectively termed “thyroid
hormone” (TH)
• Other Thyroid cells produce
a second hormone
“calcitonin”
Thyroid-Stimulating Hormone
• Produced by the anterior pituitary
• Stimulates the normal development
and secretory activity of the thyroid
• Regulation of TSH release
⟶ Stimulated by thyrotropinreleasing hormone (TRH)
⟶ Inhibited by rising blood levels of
thyroid hormones that act on the
pituitary and hypothalamus
Direct Links to Other Endocrine Axes
TRH also help control PRL & GH
Indirect Links to Other Systems
Glucocorticoid
Excess  ↓ TSH, TBG, TTR, T3, T4, ↑rT3
Deficiency  ↑ TSH
Estrogens
 T4 requirement in hypothyroidism
↑ TSH in postmenopausal women
Androgens
 TBG
↓ T4 turnover in women
 T4 requirement in hypothyroidism
Functions of the Thyroid
• Metabolic rate
• Regulate protein, carbs
and fat metabolism
• Increase RBC
production
• Increase bone
formation, decrease
bone resorption of Ca+
Regulation of Metabolism
• Hormones T3 & T4 increase BMR
• Secretion controlled by hypothalamic-pituitarythyroid gland axis
• TRH » TSH » T3 & T4 (neg feedback)
• Protein and Iodine very important for T3 & T4
production
Calcium and Phosphorus
Balance
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Calcitonin (thyrocalcitonin, or TCT)
Reduces bone resorption, lowers serum Ca+
Low serum Ca+ suppress TCT:
Elevated serum Ca+ trigger TCT
Thyroid Hormone
• Major metabolic hormone
• The effects of TH are:
⟶ stimulation of growth (in conjunction with growth hormone)
⟶ development of the nervous system in the foetus and infant
⟶ increased basal metabolic rate and increased heat production
⟶ increased alertness, reflexes
Thyroid Hormone
Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroid
hormones
Target cells
Negative feedback
regulation of TH release
Rising TH levels provide
negative feedback
inhibition on release of TSH
Stimulates
Inhibits
Pregnancy & the Thyroid Axis
Pregnancy Causes:
 TBG
Maternal Thyroid Axis
Impacts:
 Plasma volume
 T4 production
 hCG
 Total [ T4 ] & [ T3 ]
fetal T4 synthesis in 2nd &
3rd trimester
 O2 consumption by fetus,
placenta, uterus & mother
 T4 & T3 pool
 cardiac output
 Free T4
 Basal TSH
 I2 requirements
 BMR
Calcitonin
• Produced by parafollicular cells of the
thyroid gland
• Antagonist to parathyroid hormone
(PTH)
• Inhibits osteoclast activity and release
of Ca2+ from bone matrix
• Stimulates Ca2+ uptake and
incorporation into bone matrix
Remember:Thyroid also
secretes Calcitonin
• Calcitonin helps-->
• keep Calcium in bones
• maintain balance of
Calcium and
Phosphorus
Calcium -- 8.8 - 10.5
Phosphorus - 3 - 4.5
Parathyroid Glands
• Four to eight tiny glands embedded in the posterior aspect of the
thyroid gland
• secrete parathyroid hormone (PTH), a peptide hormone
• PTH—most important hormone in Ca2+ homeostasis
• Functions
⟶ Stimulates osteoclasts to digest
bone matrix
⟶ Enhances reabsorption of Ca2+ and
secretion of phosphate by the kidneys
⟶ Promotes activation of vitamin D
(by the kidneys); increases absorption
of Ca2+ by intestinal mucosa
Causes of Hyperthyroidism
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Graves’ disease (Autoimmune)
Toxic multinodular goiter
Thyroid adenoma (benign tumor)
Pituitary hyperthyroidism
Excessive use of thyroid hormone
Goiter and Exophthalmos in
Graves' Disease
Hyperthyroidism
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More common in women
Lab assessment p.1485: T3, T4
 TSH (Graves’)
Thyroid Scan (RAIU) = increased
Interventions
• Nonsurgical: monitor V/S, rest, cool
environment
• Medications: PTU (propylthiouracil), SSKI, beta
blockers
• Radioactive Iodine Therapy
• Remember eye care
Interventions
• Surgical: total or subtotal thyroidectomy
• Preop = antithyroid meds, SSKI
• Postop = very important
– Monitor for Bleeding, respiratory distress, tetany,
weak voice, thyroid storm
Causes of Hypothyroidism
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Removal or destruction of thyroid
Autoimmune (Hashimoto’s Disease)
Iodine deficiency
Medications (ex.Lithium)
Hypothyroidism
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More common in women
Lab assessment:  T3, T4
 TSH
Monitor for depression
Interventions
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Levothyroxine sodium (Synthroid)
Avoid sedatives & narcotics
Monitor vital signs
Monitor for S&S of hyperthyroidism
Family teaching re: mental status
Myxedema Coma
• Hypothyroid Crisis --> rare but serious
• Etiology:
– acute illness/ trauma
– * rapid withdrawal of thyroid meds.
– use of sedatives / narcotics
– surgery
– exposure to cold
Myxedema Coma
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 temp / BP
 Na+
 blood glucose
Lactic acidosis
Coma
Thyroiditis

Acute
– Bacterial
 Pain
  Temp.
 Malaise
 Dysphagia
– TX
 Antibiotics

Subacute
– Viral
  Temp.
 Chills
 Pain in jaw and/or
ear
– TX
 ASA and steroids
Thyroid Cancer
• Painless nodule in thyroid
• Treatment :
–RAI
–Surgery
Hyperparathyroidism
Pathophysiology
•
PTH secretion = Ca+  Phos
– increased reabsorption of calcium by kidneys =
• increased excretion of Phosphate
• Causes
–tumors
–hyperplasia of parathyroid gland
Data Collection :
•  PTH
– renal calculi
– nephrocalcinosis
– bone decalcification
•  serum Ca
– GI: anorexia, N&V, epigastric pain, constipation,
– M/S: fatigue & lethargy
– [serum Ca] > 12 mg/dl =  mental status
Complications:
• Renal Failure
• Fractures
• Collapse of vertebra
Collaborative Management :
focuses to decrease serum calcium
• Diuretic & Fluid Therapy
– Lasix /0.9% Na Cl
• Drug therapy
– Phosphates
– Calcitonin -miacalin spray Skel. Release
Renal clearance
– Calcium Chelators - binds with Ca. -< dec.
Levels of free calcium
• Parathyroidectomy
Hypoparathyroidism
•  PTH
• Etiology (rare)
– thyroid / parathyroid
surgery
– Hypomagnesemia
– Idiopathic