Endocrine System: Thyroid Gland Flashcards
Thyroid Hormones:
- Have effects on = ?
- Thyroid hormones increase = ?
Thyroid Gland
Thyroid Hormones:
- Have effects on every organ system in the body.
- It increases metabolism and protein synthesis.
Notes:
- It’s necessary for growth and development in children, including mental development and attainment of sexual maturity.
- Disorders of thyroid deficiency and excess are among the most common of the endocrinopathies affecting 4% to 5% of the population in US.
Three thyroid hormones = ?
Thyroid Gland
Different Thyroid Hormones:
(a) T3 - triiodothyronine
- T3 more active
(b) T4 - tetraiodothyronine
- The more common product out by thyroid gland is T4.
- T4 is converted to T3 in the target tissues.
(c) Calcitonin
- Opposite to the action of parathyroid hormone.
- Decreases levels of calcium and phosphorus in blood.
- Inhibits activity of osteoclasts and stops bone resorption
Notes:
- Structure differs by only a single atom of iodine.
- Thyroid hormones contain large amount of iodine which must be adequately supplied in diet.
Thyroid Gland:
- Functional units of the thyroid = ?
- Material in the lumen of the follicle = ?
- Why is thyroglobulin important = ?
Thyroid Gland
Thyroid Gland:
(a) Follicles
- Functional units of the thyroid.
- Each follicle is formed by a single layer of epithelial (follicular) cells.
(b) Hormones are synthesized and secreted by epithelial cells of the thyroid gland.
(c) Material in the lumen of the follicle is colloid
- Colloid is composed of newly synthesized thyroid hormones attached to thyroglobulin (TG).
(d) When thyroid gland is stimulated, colloid thyroid hormone is absorbed into the follicular cells by endocytosis-hydrolysis.
- End result = T3 and T4 enter the circulation.
Thyroid Hormone in blood:
- Three forms = ?
- T4 is converted to T3 by = ?
- When T4 can be converted to “reverse T3”, the end result is active or inactive = ?
Thyroid Gland
Binding of Thyroid Hormone in blood:
(a) Thyroid hormones in the bloodstream in three forms:
- (1) Bound to thyroxine-binding globulin (TBG)
- (2) T4-binding pre-albumin and albumin
- (3) Free, unbound form = Active form
(b) In the target tissues T4 is converted to T3 by 5’-iodinase
(c) T4 can be converted to “reverse T3” which is physiologically inactive form= NOT ACTIVE
Regulation of Thyroid Stimulation
Thyroid Gland
Normal Regulation of Thyroid Stimulation:
(I) Hypothalamus:
- Releases Thyrotropin-releasing hormone (TRH).
(II) Anterior Pituitary:
- Responds to TRH by releasing Thyroid-stimulating hormone (TSH).
(III) Thyroid Gland:
- Responds to TSH by producing and releasing Thyroid hormones (T3 and T4).
(IV) Thyroid hormones:
- Increase basal metabolic rate, regulate body temperature, and influence various other functions.
(V) High thyroid hormone levels:
- Inhibit TRH and TSH release through negative feedback, maintaining balance.
Glycogenolysis = ?
vs.
Gluconeogenesis = ?
(a) Glycogenolysis:
- Breakdown of glycogen to glucose.
(b) Gluconeogenesis:
- Making of glucose from other products like amino acids, fats, protein.
Thyroid Gland Disorders:
- Disorders significant to PT practice = ?
Thyroid Gland
(a) Thyroid gland disorders:
- Hypofunction
- Hyperfunction
(b) Disorders significant to PT practice:
- Goiter
- Hyperthyroidism
- Hypothyroidism
- Cancer
- PT can recognize the symptoms early and make a referral
(c) Notes:
- Genetics play a role in thyroid disease, can also develop later
Increase in size of thyroid gland, occurs in hypothyroid and hyperthyroid = ?
Thyroid Gland
Goiter:
(a) Increase in size of thyroid gland, occurs in hypothyroid, hyperthyroid
(b) Causes:
- Graves disease
- TSH secreting tumor
- Iodine deficiency (less T3, T4)
- Occurs in areas of world where iodine is deficient in diet
(c) Significant compression can…
- Compress esophagus
- Trachea
- Difficulty swallowing
- Difficulty chewing
- Chocking sensation
- Difficulty breathing
- Hoarseness
When tissues are exposed to high levels of circulating thyroid hormones = ?
Thyroid Gland
Hyperthyroidism:
(a) When tissues are exposed to high levels of circulating thyroid hormones.
(b) Etiology:
- Graves disease (most common)
- Adenoma of thyroid
- Excessive production of TSH by pituitary adenoma
- Hashimoto Thyroiditis (autoimmune disorder)
Graves Disease:
- What is it = ?
- Triggering factors = ?
- Gender most affected = ?
Thyroid Gland
(a) Graves Disease:
- Autoimmune condition, excessive stimulation of thyroid gland by TSH.
(b) Triggering factors
- Often unknown
- Genetic
- Family history
- Gender
- Environmental
- Stress
- Smoking
(c) Notes:
- Women 7-10 times more likely to develop than men.
- Affects 0.5%-1% of population under the age of 40 years.
- State of hyperthyroidism, goiter and opthalmopathy (involvement of optic nerve with visual loss, diplopia).
Graves Disease:
- Pathophysiology = ?
Thyroid Gland
Graves Disease:
(a) Pathophysiology:
- IgG antibodies bind to TSH receptors on thyroid cells, and stimulate excessive thyroid hormone secretion.
Graves Disease:
- Clinical Manifestations = ?
Thyroid Gland
Graves Disease - Clinical Manifestations:
Symptoms related to:
(a) Enlargement of thyroid gland:
- Goiter: Enlargement of thyroid gland.
- Hyperplasia of follicular epithelial cells.
(b) Excessive metabolic rate:
- Increased DTRs
- Increase oxygen consumption, and use of metabolic fuels.
- Excessive sympathetic system activity.
- Increased respiratory rate
- Diarrhea
(c) Exophthalmos:
- Bulging / protruding eyes
(d) Chronic periarthritis:
- Inflammation of periarticular structures (tendons, ligaments, joint capsule)
- Pain
- Reduced ROM
- Most often shoulder (unilateral/ bilateral)
- Can develop into frozen shoulder
- Acute calcific tendinitis of the wrist
- Myopathy in 70% of people
- Proximal weakness (pelvic girdle and thigh) with atrophy
(e) Thyroid storm or thyrotoxic crisis:
- Sudden, severe worsening of hyperthyroidism.
- Extreme and life threatening form of thyrotoxicosis (rare).
- Seen in people not adequately treated.
- High fever (105 F)
- Severe tachycardia
- Chest pain
- Heart failure
- Agitation
- Restlessness
- Irritability
- Abdominal pain
- Vomiting
- Coma
(f.1) Precipitating factors:
- Trauma
- Infection
- Surgery
- Stress
(f.2) Important for PT:
- Recognize
- Immediate referral required to prevent the CV collapse
- Look at the history of precipitating factors mentioned
Graves Disease:
- Diagnosis = ?
Thyroid Gland
Graves Disease - Diagnosis:
- History / physical exam
- Family history
- (Autoimmune disease / thyroid disease)
- Enlarged / firm thyroid gland
- Protrusion of eyes
- TSH levels:
- Reduced in graves disease
- Increased with increased secretion of TRH/TSH
- Elevated serum T3 / T4 levels
- Antithyroid antibodies
- Radioactive iodine uptake
Graves Disease:
- Treatment = ?
Thyroid Gland
Graves Disease - Treatment:
(a) Reducing thyroid hormone levels
- Medication that block thyroid hormone reproduction.
- Propylthiouracil
- Methimazole
- Surgical removal of all or part of gland
Hypothyroidism:
- What is it = ?
- Etiology = ?
Thyroid Gland
Hypothyroidism: Thyroid gland doesn’t make enough thyroid hormone.
(a) Deficient thyroid hormone
- Creates a generalized depression of body metabolism.
- More common in women.
(b) Etiology:
- Congenital
- In utero, hormones are supplied by mother
- If untreated after birth, mental retardation, intellectual disability and impaired physical growth (cretinism).
- Thyroid hormone replacement
(c) Acquired:
- Destruction (surgical removal, radiation) of thyroid gland.
- Impaired pituitary function
- Impaired hypothalamic function
- Iodine deficiency
- Uncommon in US
- Hashimoto Thyroiditis
- Autoimmunity that block TSH or TSH receptors.
