The Endocrine System Flashcards
What is endocrine communication
Messages are trasmitted by circulating body fluids and specificity depends on receptors
What is the classical definition of the endocrine system
Endocrine cells within endocrine glands release hormones which are convent by the bloodstream and act on distant cells
Why has the classical definition of the endocrine system been updated
Hormones produced by many tissues can have local effects as well as distant effects
What is the updated definition of the endocrine system
Specialised cells release hormones which are converted by the bloodstream and act via receptors in target tissues
What are hormones
Chemical messengers synthesised by specialised cells that are secreted into the bloodstream in small amounts which act on specific receptors in target organs to regulate cellular function
What are the non classical endocrine tissues
Kidney, heart muscle, endothelium, platelets, adipocytes and white blood cells
What are the 3 main classes of hormones based on chemical structure
Steroids, peptides and amino acids
What are steroid hormones
Synthesised from cholesterol
What are peptide hormones
Synthesised from amino acids
What are amino acid hormones
Synthesised from tyrosine (or tryptophan for melatonin)
What are the features of steroid hormones
- small and hydrophobic
- released immediately following synthesis
- circulate in bound form
- slow long lasting effects
How do steroid hormones regulate gene transcription
Act on intracellular receptors which bind to DNA and regulate gene transcription
How do steroid hormones act on intracellular receptors
Bind to hormone binding site, which opens up the hinge region and disassociates the inhibitory protein complex from the DNA binding site, leaving the DNA binding site exposed
How are peptide hormones synthesised
Synthesised as preprohormones and stored prior to release
How do peptide hormones cause effects in target cells
Act on cell surface receptors then via 2nd messenger systems to cause an effect
How are amino acid hormones synthesised
Mostly from tyrosine and stored for instant release
Describe how amino acid hormones cause an effects
Have different modes of action ( some act on intracellular receptors others on cell surfaces)
What mechanisms regulate hormone secretion
Feedback control
What is feedback control
Response to maintain homeostasis
Describe negative feedback control
Systematic effects are imputed to hypothalamus by other brain areas, hypothalamus releases releasing factors to anterior pituitary, anterior pituitary releases tropic hormone to endocrine tissue, endocrine tissue releases hormone have a systematic effect. All areas feedback changes to hypothalamus
What is the hypothalamus-pituitary axis
The site of interaction between the nervous and endrocrine systems that exerts control over several endocrine glands and physiological activities
What is the hypothalamus
The region of the brain that plays a key role of homeostasis
What is the pituitary gland
The hypophysis which consists of two lobes (posterior and anterior pituitary)
What is the posterior pituitary
The posterior lobe which is of neural origin (neurohypophysis) and consists id axons and nerve endings of neurones whose cell bodies reside in the hypothalamus
What is the anterior pituitary
The anterior lobe which originates from Rathke’s pouch and is known and the adenohypophysis and consists of endocrine tissue
Where are posterior pituitary hormones produced
The magnocellular neurones of the hypothalamus
What are the 2 posterior pituitary hormones
Oxytocin and ADH
What are hypothalamic hormones
Hypophysiotropic hormones that the hypothalamus releases into portal circulation to act upon the anterior pituitary
What are the 6 hypothalamic hormones
thyrotropin releasing hormone, Gonadotrophin releasing hormone, corticotrophin releasing hormone, growth hormone releasing hormone, growth hormone inhibiting hormone, dopamine
Which hypothalamic hormone targets thyrotroph tissue
Thyrotropin RH
Which hypothalamic hormone targets gonadotroph tissue
Gonadotrophin RH
Which hypothalamic hormone targets corticotrophs tissue
Corticotrophin RH
Which hypothalamic hormones targets somatotroph tissue
Growth hormone RH and growth hormone IH
Which hypothalamic hormone targets lactotroph tissue
Dopamine
What are anterior pituitary hormones
Hormones released into systematic circulation and controlled by hypothalamic hypophysiotropic hormones
What are the 6 anterior pituitary hormones
Thyroid stimulating hormone, follicle stimulating hormone, lutenising hormone, adrenocorticotropic hormone, growth hormone and prolactin
What is the function of thyroid stimulating hormone
Stimulates thyroid hormone release
What is the function of follicle stimulating hormone
Stimulates sex steroid production
What is the function of lutenising hormone
Stimulates sex steroid production
What is the function of adrencorticotropic hormone
Stimulates cortisol release
What is the function of growth hormone
Stimulates growth
What is the function of prolactin
Stimulates milk production
What hormones are secreted by thyrotrophs
Thyroid stimulating horome
What hormones are secreted by Gonadotrophs
Follicle stimulating hormone and lutenising hormone
What hormone is secreted by corticotrophs
Adrenocorticotrophic hormone
What hormone is secreted by somatotrophs
Growth hormone
What hormone is secreted by lactotrophs
Prolactin
What is growth hormone (somatotropin)
Peptide hormones synthesised by somatotrophs in the anterior pituitary to stimulate growth and cell reproduction and regeneration that are released in response to GHRH from the hypothalamus and realises is inhibited by GHIH (somatostatin) from the hypothalamus
What is an indirect function of growth hormone
Stimulates the production of insulin-like growth factor 1 (IGF-1)
What are the acute metabolic actions of GH (direct)
- fatty acid release from adipose tissue and conversion to acetyl coa (energy from fats)
- reduced glucose metabolism and uptake into cells
- increased gluconeogenesis in the liver
- Increased production of insulin-like growth factor-1
What are the long term effects of GH (indirect via IGF-1)
-growth promotion on bone, epiphyseal cartilage, soft tissue, gonads, viscera
- promotes amino acid uptake and protein synthesis
- insulin like effects on tissues
What is the thyroid
2 lobes with connecting isthmus, a rich blood supply and two pairs of parathyroids
What are the functional units of thyroid
Follicles
What are thyroid follicles
Functional unit of thyroid that consists of a pool of colloid surrounded by c cells
What is the colloid in the thyroid
Pool where thyroid hormones are are stored and produced
What are the c cells in the thyroid
Single layer of cells surrounding a pool of colloid that secrete calcitonin (involved in calcium homeostasis)
What are the thyroid hormones
Thyroxine (T4) and Triiodothyronine (T3)
What is the major thyroid product
T4
What is the most active thyroid hormone
T3
What are the physiological effects of the thyroid hormones
Increased cardiac output and systolic pressure
Increase BMR
Improved altertness, memory, reflexes and wakefulness (neurological)
Foetal neural development and bone growth after birth
What are the three major thyroid transporting proteins
Thyroxine binding globulin, thyroxine binding prealbumin and albumin
How is most plasma T3 derived
From peripheral metabolism of T4 by deiodination
What are the three enzymes controlling local control of thyroid hormones
Type 1 deiodinase, type 2 deiodinase and type 3 deiodinase
What does type 1 deiodinase result in
Active or inactive T3
What does type 2 deiodinase result in
Active T3
What does type 3 deiodinase result in
Inactive/reverse T3
What are the 2 main components of the adrenals
Medulla and cortex
What are the 3 distinct zones of the cortex of the adrenals
zona glomerulosa (outer), zona fasciulata (middle) and zona reticularis (inner)
What hormones does the zona glomerulosa produce
Aldosterone
What hormones does the zona fasciculata and zona reticularis produce
Cortisol and androgens
What is the medulla
Highly specialised part of sympathetic nervous system that has a major product of epinephrine
What is aldosterone
Major mineralocorticoid that is bound to albumin in plasma and acts on kidney, colon and salivary glands to maintain normal Na+ and extracellular fluid volume
What does aldosterone upregulate in the kidney to
ENaC (Na+ channel), Na+/K+ pump and ATPase
How does aldosterone cause an effect on the kidney
Binds to mineralocorticoid receptors within principle cells
What is cortisol
The stress hormone that is a major glucocorticoid that effects virtually all tissues by controlling gene transcription and is mostly bound to plasma protein
What are the effects of cortisol
Hepatic gluconeogenesis
Inhibits glucose uptake
Stimulates muscle catabolism
Inhibits bone formation
Leads to loss of collagen and connective tissue
Increases vascular sensitivity to epinephrine and norepinephrine
Modulate behaviour and cognitive function
Inhibits gonadal release of testosterone, oestrogen and progesterone
Inhibits cytokines production and T cell proliferation
Inhibits prostaglandin and leukotriene production
What is Cushing’s syndrome
Excess cortisol
