The Endocrine System Flashcards
What does the endocrine system regulate?
Development, growth, reproduction, parturition, lactation, metabolism, BP, blood ion conc, behaviour
What is endocrine signalling?
Signalling mediators are released into the bloodstream from endocrine cells
- Enables cell signalling across long distances to target tissues
- Slow
- Specific to receptors but not tissues
- Endocrine glands do not have ducts
Where are endocrine cells located?
- Close proximity to capillary beds
- Found in endocrine tissues or glands
What are hormones?
Signalling mediators
Can be:
- Protein e.g. insulin
- Amino acid derived e.g. adrenaline
- Steroid e.g. estradiol
What does the type of hormone influence?
Its cells membrane permeability
How are peptide hormones synthesised?
From amino acids
How are AA derived hormones synthesised?
Derivatives of tyrosine
Requires specific enzymes
How are steroid hormones synthesised?
Metabolites of cholesterol
Requires specific enzymes
How are peptide hormones released?
Secretory granules by exocytosis
How are AA derived hormones released?
Vesicles via exocytosis
(except thyroid hormone)
How are steroid hormones released?
Lipid soluble so can cross membranes directly
Where do peptide and AA derived hormones bind to receptors?
On cell surface membrane
(except thyroid)
Where do steroid hormones bind to receptors?
Diffuse into cells and bind to intracellular/nuclear receptors
What is the response time of peptide and AA derived hormones?
Seconds to minutes
(except thyroid)
What is the response time of steroid hormones?
Hours to days
What are the 7 classic endocrine glands?
Anterior and posterior pituitary
Thyroid
Parathyroids
Adrenals (cortex and medulla)
Ovaries
Testes
Endocrine pancreas
What are the endocrine tissues?
Hypothalamus
Kidneys
GI tract
Heart
liver
Adipose tissue
What could locally acting hormones be classed as?
Paracrine factors or neuropeptides
What is the adenohypophysis?
Anterior lobe of pituitary gland
Develops from an upward projection of the pharynx
What is the neurohypophysis?
Posterior lobe of pituitary gland
Develops from a downward projection of the brain
How are hormones released from adenohypophysis?
- Neurohormones released into portal system
- Releasing hormones move in bloodstream into anterior pituitary
- Stimulates troph cells within anterior pituitary
- Depending on the releasing hormone - acts on different troph cells to release different tropic hormones - go round body in systemic circulation
What is the structure of the adenohypophysis?
Smaller diameter hypothalamic neurones with shorter axons that terminate on blood vessels around pituitary stalk
What is the structure of the neurohypophysis?
- Hypothalamus has lots of different nuclei within it
- Cell bodies sit in the hypothalamus in the different nuclei
- They send axonal projections down through the pituitary stalk and into posterior pituitary
How are hormones released from the neurohypophysis?
Neural hormones released from the large diameter neurones directly into systemic circulation
What hormones are released by the neurohypophysis?
ADH, Oxytocin
What hormones are released by adenohypophysis?
In response to releasing hormones:
- Growth hormone
- TSH
- FSH, LH
- Prolactin
What does the thyroid gland release?
T3 and T4 AA derived hormones
What is required for the synthesis and release of thyroid hormones?
Hypothalamic pituitary hormones
Iodine
How are thyroid hormones transported?
Facilitated diffusion
What does thyroid hormone bind to?
Nuclear receptors - bind to DNA and regulate transcription
What does thyroid hormone regulate?
Metabolism
Development and growth
What hormone does the parathyroid gland secrete?
Parathyroid hormone (PTH) (peptide hormone)
What does PTH regulate
Vital parameters of plasma calcium and phosphate
Targets - bone, kidneys, intestines
What is the plasma calcium -ve feedback loop?
Plasma [Ca2+] sensed by chief cells
- Increased [Ca2+]
Causes decreased PTH release
- Decreases kidney tubule reabsorption (so more Ca2+ excreted)
- Decreases bone Ca2+ resorption
- Decreases intestinal Ca2+ absorption
Eventually lowers plasma [Ca2+]
What are the parts of the adrenal gland?
Adrenal medulla
Adrenal cortex
What does the adrenal medulla secrete?
Chromaffin cells release adrenaline by exocytosis in vesicles
What is the adrenal medulla a target of?
The ANS
What does the adrenal cortex secrete?
Steroid hormones
Glucocorticoids e.g. cortisol (from zona glomerulosa)
Mineralocorticoids e.g. aldosterone (from zona fasciculata)
What do beta cells release?
Insulin
What do alpha cells release?
Glucagon
What hormones do the ovaries release?
Steroid hormones - oestrogen and progesterone from cells within the developing follicles
- Can switch between +ve and -ve feedback
Which cells produce testosterone?
Leydig cells in the testes
- Testosterone stimulates protein synthesis - can lead to development and growth
