Endocrine System Flashcards
Thyroid Hormones- T3
virtually affects every cell
triiodothyronine- 2 tyrosines with 3 bound iodines
-4x more potent than T4
-present in lower concentrations than T4
-shorter half-life than T4 (T1/2= 1.5 days)
iodine must be present in diet approx= 100 mcg/day
Thyroid Hormones- T4
affects every cell in the body
thyroxine (2 tyrosines and 4 bound iodine)
serves as a precursor to T3
must be present in the diet at approx = 100 mcg/day
Thyroid Disorders
more common between ages 20-40, females>males
- hyperthyroidism: elevated levels of thyroid hormone in blood- T3 and T4: HIGH and TSH: LOW
- hypothyroidism: decreased levels of thyroid hormone in blood- T3 and T4: LOW and TSH: HIGH
Effects of Thyroid Stimulating Hormone (TSH) on Thyroid Follicular Cells
- growth of thyroid follicular cells
- increased iodide uptake and thyroglobulin iodination, and thyroid hormone synthesis
- thyroid hormone release into blood
Physiological Effects of Thyroid Hormone
- fetal growth and brain development
- increased oxygen consumption and heat production
- increased rate and force of heart contraction
- increased beta adrenergic receptor
- increased red blood cell production
- increased bowel motility
- increased bone turnover
- increased speed of muscle contraction and relaxation
- maintain normal CNS function
Endocrine System
major organ system by which cells and tissue communicate- hormones are secreted directly into circulation and exert their effects by binding in or on target cells
Hormones
secreted from glands, bind to receptor, and initiate action
-homeostatic regulation of: growth, reproduction, metabolism, energy, fluid and water balance
negative feedback!
Hormone Receptors
proteins that bind hormones with high affinity and specificity- each receptor has a domain that recognizes a specific hormone and a domain that generates a signal once a hormone binds
-cells have a mechanism for release to stop physiological response
Endocrine Glands include…
- hypothalamus
- pituitary
- thyroid
- parathyroid
- pancreas
- adrenal
- ovary
- testis
- placenta
Hypothalamus
“central relay system”!
- gather signals from the central nervous system to send information via hormones and neurotransmitters
- influence many vital functions, such as: arterial pressure, thirst, temperature regulation, body weight, emotions, sleep, instinct
- hypothalamic-pituitary axis: controls action of thyroid gland, adrenal glands, gonads, growth hormone, prolactin, oxytocin, vasopressin (ADH)
Endocrine Homeostasis
goal= maintain homeostasis
- excess hormone downregulates number of receptors, decreased receptor availability diminishes tissue response to excess hormone
- hormone depletion upregulates receptors, enhance receptor availability increase tissue response
What leads to hormone excess/deficiency and possible outcome?
CONTROL MECHANISM FAIL= excess/deficiency leads to: -abnormal metabolism -water imbalance -blood pressure abnormalities -growth and reproductive issues
Anterior Pituitary Adenomas
excess hormone secretion impacts hormone axis (mostly in adults), most common: lactotroph adenoma, excess prolactin (PRL)
classified as:
-microadenomas are <10mm
-macroadenomas are >10mm
What is Hyperprolactinemia/Lactotroph Adenoma?
increased prolactin (PRL) secretion, caused by prolactinoma or in some cases medication (antipsychotics, antidepressants, or metoclopramide), which results in gonadal dysfunction (decreased bone mineral density and also, excess prolactin inhibits normal secretion of LH and FSH, lack of ovulation, estrogen deficiency)
Result of Hyperprolactinemia in males and females and treatment options
-Females: amenorrhea, galactorrhea (increased/abnormal milk production), infertility
-Males: decrease libido, impotence
treatment includes:
-microadenoma: dopamine agonist (cabergoline)
-macroadenoma: surgery, radiotherapy
Somatotroph adenoma/Excess GH- difference in children and adults
excess GH secretion
- children/adolescent: anti-insulin, long bone and muscle growth, gigantism
- adults: anti-insulin, acromegaly
Acromegaly
signs/symptoms: cardiomegaly(hypertension), barrel chest, male sexual dysfunction/female menstrual disorders, increase size in hands and feet, degenerative arthritis
treatment: somatostatin analog (inhibits GH secretion) or surgery
Corticotroph Adenoma
overproduction of adrenocorticotropic hormone (ACTH) which functions to stimulate adrenal cortex to produce cortisol (stress hormone)
Cushing Syndrome
- adrenal gland excess: too much cortisol, caused by: iatrogenic (corticosteroids), ACTH producing pituitary adenoma, adrenocortical tumor
- clinical findings: central obesity, purple striae, weight gain, moon facies, cervical fat pad (“buffalo hump”), acne, thinned skin, bruises easily, muscle weakness, fatigue, hypertension, neurological disturbances
- diagnosis: 24-hour urinary free cortisol, salivary cortisol, overnight dexamethasone suppression test, serum ACTH
Diabetes Insipidus (DI)
- inadequate release of antidiuretic hormone (ADH/vasopressin)
- polyuria, polydipsia, dilute urine (but normal glucose)
- causes: genetics (mutation in vasopressin II, vasopressin V2 receptor, or aquaporin genes), brain tumors which compress posterior pituitary, or idiopathic (unknown cause)
What is the hormone involved in Diabetes Insipidus and treatment options
ANTIDIURETIC HORMONE (ADH deficiency)
ADH normal functions, include:
-secreted in response to high solute concentration in blood
-causes aquaporin water channels to increase in renal collecting duct
-increases renal water reabsorption, more water in blood
Treatment: ADH/vasopressin
Hypothyroidism- types, signs/symptoms, diagnostic, treatment
- primary: most common! failure of the thyroid gland
- secondary: failure of the pituitary or hypothalamus
- Hashimoto’s thyroiditis (with or without goiter (enlarged thyroid gland)- depends on stage of disease): autoimmune disease, CHRONIC INFLAMMATION, antibodies to thyroid peroxidase, thyroglobulin and TSH receptors
- signs/symptoms: decreased/absent T3 and T4, slow pulse, decreased cardiac output, hypotension, lowered body temperature, cold intolerance, dry skin, weight loss, hair loss, muscle cramps, edema of face and eyelids, constipation, menstrual irregularities
- diagnostic tests: measure FT4 and TSH in blood
- treatment: daily thyroid hormones
Hyperthyroidism (Graves Disease): Signs/Symptoms
-signs/symptoms: palpitations, tachycardia, nervousness, tremor, hyperkinesia, diarrhea, excessive sweating, intolerance to heat, weight loss, lack of appetite, ophthalmopathy, profound muscle weakness, goiter (enlarged thyroid gland)
Pathophysiology of Graves Disease and Treatment
- IgG antibodies bind to TSH receptor on plasma membrane of thyroid follicular cells- antibodies are TSH AGONIST= increase thyroid hormone secretion and proliferation of thyroid follicular cells- goiter (enlarged thyroid gland)
- increased FT4 and decreased TSH
- treatment: anti-thyroid medication, destruction of thyroid tissue with radioactive iodine