Endocrine system Flashcards
define hormone
A chemical messenger produced and secreted by a specialized endocrine gland that is transported in the bloodstream to a distant target organ/cell where it elicits a physiological response.
functions of the endocrine system and nervous system
Monitor and coordinate internal environment and make appropriate adaptive changes (homeostasis!);
Regulate growth, development, reproduction, senescence;
Enable you to respond and adapt to changes in external environment (eg: food intake, water availability, temperature change, “stressors” etc)
what do Hormone actions affect?
what do hormones act on?
Affect growth, development, metabolic activity and function of tissues
May act on several tissues or just one specific target tissue
what are Circulating Hormone Levels Influenced by?
Rate of secretion - by endocrine gland
Rate of metabolism - by target tissue, blood, liver, kidney
Regulation of Hormone Secretion
1. By physiological changes e.g. …
Blood glucose regulates insulin & glucagon release from pancreas
‘Stress’ regulates adrenaline release from adrenal medulla
Blood calcium regulates parathyroid hormone release from parathyroids
2. By endogenous rhythms e.g. …
Ultradian - cycles in minutes. GnRH pulses (90-120 min.)
Circadian - daily cycles. testosterone (24 hr.) Cortisol (24h.)
Infradian cycles- monthly. LH in females (~28 day menstrual cycle)
3. By Feedback Mechanisms:
Mostly Negative (“closed-loop” feedback) - maintains homeostasis
Some Positive feedback - e.g. milk-ejection reflex - involving oxytocin pre-ovulatory LH surge - involving oestrogen.
Types of Endocrine Dysfunction
Hyposecretion
Hypersecretion
Ectopic hormone secretion - hormone made outside normal endocrine gland (eg: Tumour)
End Organ Insensitivity/Resistance
causes of Hyposecretion
Genetic - e.g. Congenital Adrenal Hyperplasia; defect in cortisol production
Dietary - e.g. Iodine deficiency => thyroid malfunction
Immunological (auto-immune disease) - e.g Destruction of thyroid tissue in Hashimoto’s Disease. e.g. destruction of adrenal cortex in Addison’s Disease.
Cancer/Tuberculosis - e.g.Addison’s Disease, destruction of adrenal cortex
Iatrogenic (=doctor-caused) - e.g. removal of parathyroid glands during thyroidectomy.
Idiopathic - unknown cause
Hyposecretion: treatment
Hormone Replacement:
Steroids or Thyroid Hormone
- Straightforward
- Absorbed in GI. Tract
- High Success
Protein Hormones
- Difficult
- Must be injected
- Species specific
Human GH only for humans
causes of Hypersecretion
Functional tumour - e.g. Prolactin secreting pituitary adenoma
Ectopic hormone-secreting tumour - e.g. Oat cell carcinoma of lung secreting ACTH => cortisol excess (Cushing’s Disease).
Immunological - Grave’s Disease, antibodies that bind and activate TSH receptor on thyroid
Also, consider excess hormones due to … Substance abuse: Anabolic steroid use, exogenous source of high hormone levels.
Hypersecretion: treatment
Surgical removal of the gland that is hyper-secreting. (but will then need replacement therapy!) - e.g. Hyperthyroidism
Irradiation of Gland – reduce function (but will then need replacement therapy!) - e.g. Hyperthyroidism
Antagonists of the hypersecreted hormone - e.g. ß blocker for pheochromocytoma. (NorAd/Adrenaline-secreting tumour of adrenal medulla).
causes of End Organ Insensitivity / Resistance
Genetic defect
- e.g. Laron Syndrome
- GH receptor mutation=> non-functional
- normal/raised GH levels
- Very low IGF
Acquired Defect
- e.g. Type 2 Diabetes Mellitus
- impaired insulin receptor signalling
- Normal insulin levels, but compromised physiological response
Hypothalamic-pituitary system functions
Organizes appropriate hormonal responses to stimuli from higher centres of brain in response to:
- changes in external environment (e.g. photoperiod, temperature, food availability, mate availability, stress)
- changes in internal environment (e.g. hormonal feedback signals from target organs, nutritional status, water balance, salt balance, BP, heart rate, pregnancy, trauma, disease etc.)
which 2 lobes does the Pituitary gland comprise?
posterior and anterior lobes
