Endocrine Flashcards
What are the endocrine glands?
- Pineal gland
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Thymus
- Adrenal glands
- Pancreas
- Ovary (female) or Testis (male)
What does the endocrine system do?
- Processes of reproduction
- Controlling growth & development
- Metabolism
- Maintenance of fluid & electrolyte balance
- Mobilisation of immune defences
- Stress response
How does hormone regulation work?
Endocrine glands are stimulated to synthesise and release hormones in response to one of three stimuli:
- Hormonal stimuli
- Neural stimuli
- Humoral stimuli
The production of many hormones is regulated by negative feedback
What is hormonal stimuli?
Hormones stimulate other endocrine organs to release their hormones
What are examples of hormonal stimuli?
- Hypothalamic hormones stimulate release of most anterior pituitary hormones
Anterior pituitary gland - Anterior pituitary hormones stimulate targets to secrete still more hormones
- Hypothalamic–pituitary–target endocrine organ feedback loop
- Hormones from final target organs inhibit release of anterior pituitary hormones
What is neural stimuli?
- Nerve fibers stimulate hormone release
Hormone release caused by neural input.
Example: Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines
What is an example of neural stimuli?
Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines
What is humoral stimuli?
Changing blood levels of ions and nutrients directly stimulate secretion of hormones
What are some examples of humoral stimuli?
- Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone)
- PTH causes Ca2+ concentrations to rise, and stimulus is removed
What three categories of hormones are there?
- Protein & peptide hormone
- Amines & amino acids
- Steroid hormones
What are some examples and characteristics of protein & peptide hormone?
Examples: Insulin, growth hormone
- Water soluble
- Travel freely in blood
- Bind to cell-surface receptor
What are some examples and characteristics of amines & amino acids?
Examples: Adrenaline, thyroxine
- Water soluble
- Travel freely in blood
- Bind to cell-surface receptor
What are some examples and characteristics of steroid hormones?
Examples: Oestrogen, testosterone, thyroid hormone
- Lipid soluble
- Travel in blood bound to carrier
- Bind to intracellular receptor
What are examples of negative feedback regulation?
- Releasing hormone from hypothalamus
- Trophic hormone from anterior pituitary
- Target gland hormone from target gland
What are causes of hypofunction?
- Congenital defects resulting in absence or impaired development of the gland
- Absence of an enzyme needed for hormone production
- Destruction of a gland due to decreased blood flow, infection, autoimmune responses and neoplastic growth
- Atrophy of the gland due to medication
- Defective receptor sites or responses to the hormone is diminished
What are causes of hyperfunction?
- Excessive hormone production due to over stimulation of the gland
- Hormone producing tumour
- Autoimmune disorder
What are some tests to examine endocrine function?
- Blood - level of hormone
- Stimulation for hypofunction
- Suppression for hyperfunction
- Imaging - Isotopic (ability for the thyroid gland to take up iodine) & non-isotopic (CT, MRI)
What is the stimulation test?
- Tests for hypofunction
- Tropic or stimulating hormone administered
- If there is no increase then there is hypofunction
e. g ACTH stimulation test
What is the suppression test?
- Tests for hyperfunction
- External stimulus that there is enough of a hormone. If there is no reduction of the hormone there is hyperfunction
e. g. Dexamethasone suppression test
What is the thyroid hormone (TH)?
- Body’s major metabolic hormone
- TH enters target cell and binds to intracellular receptors within nucleus. Triggers transcription of various metabolic gene
- Found in two forms:
1) T4 (thyroxine)
2) T3 (triiodothyronine)
What is T4 (thyroxine)?
Major form of thyroid hormone secreted by thyroid follicles (90%); consists of two tyrosine molecules with four bound iodine atoms
What is T3 (triiodothyronine)?
- Thought to be active form of the thyroid hormone; has two tyrosines with three bound iodine atoms
- Most T3 converted from T4 at tissue level
What are some thyroid function tests?
- TSH - gives an initial indication of thyroid function
Following an abnormal TSH result: - serum FT4 (and FT3) and/or
- Thyroid antibodies
What is hyperthyroidism and what are causes?
- Hypersecretion of TH
- Autoimmune disease: body makes abnormal antibodies directed against thyroid follicular cells
- Antibodies mimic TSH, stimulating TH release
- Common in Grave’s disease
What are symptoms of hyperthyroidism?
- Elevated metabolic rate, sweating, rapid and irregular heartbeats, nervousness, and weight loss despite adequate food
- Protruding eyes
What are hyperthyroidism treatments?
- Carbimazole tablets (a thionamide)
- Surgical removal of thyroid
- Radioactive iodine to destroy active thyroid cells
What is primary hypothyroidism?
- Hyposecretion of TH
- Autoimmune disease e.g. Hashimoto’s, thyroidectomy, ablation, iodine deficiency
- Subclinical hypothyroidism increases with age and affects more woman than men
What are symptoms of primary hypothyroidism?
Decreased metabolic rate, lethargy slow pulse, weight gain, cold intolerance, constipation, puffy face
What are primary hypothyroidism treatments?
Replacement therapy with synthetic preparations e.g. levothyroxine
