ENDO - Endocrine Systems and Receptors Flashcards
Compare and contrast endocrine and exocrine glands.
- ENDOCRINE - Substances released into bloodstream
- EXOCRINE - Substances released into duct e.g mammary, sweat
Give examples of endocrine glands.
- Pituitary and hypothalamus
- Thyroid and parathyroid
- Thymus
- Stomach
- Pancreas
- Adrenals
- Intestines - GLP-1
- Gonads
Heart, placenta, kidneys, skin, adipose tissue
Describe endocrine signalling.
Cell releases hormone into systemic circulation, which has an effect on a distal tissue
Describe paracrine signalling.
Cell releases hormone which has an effect on neighbouring different cell types
Describe autocrine signalling.
Chemical released from cell which then acts on itself
Describe intracrine signalling.
- Signalling chemical acts on intracellular receptors within same cell
- Receptors may alter DNA transcription or initiate intracellular signalling cascades
Where is the pituitary gland located?
Pituitary fossa
Compare and contrast the anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis).
- ANTERIOR - made up of glandular tissue
- POSTERIOR - made up of neural tissue
Describe the HPA axis in terms of its hypothalamic releasing hormone, anterior pituitary hormone and target organ.
- TRH - TSH and prolactin - thyroid and mammary gland/testes
- GnRH - FSH and LH - Ovaries/testes
- GHRH - GH - various targets including bone, muscle and liver
- CRH - ACTH - Adrenal gland
Describe what happens at the posterior pituitary gland.
- Hormones synthesised by hypothalamic magnocellular neurons e.g oxytocin and vasopressin (as opposed to anterior pituitary which does synthesise its own)
- Synthesised in cell bodies within hypothalamus, transported down axons and stored in pre-snaptic terminals in posterior pituitary
- Terminals secrete hormone into circulation in response to physiological stimuli
Using the hypothalamic-pituitary-adrenal axis, a patient presents with general fatigue, weight loss, nausea and vomiting. You take a blood test, which reveals low cortisol, low ACTH and normal CRH levels.
At which point of the axis is there an issue?
Issue at level of pituitary – possible pituitary adenoma or trauma/infection.
Using the hypothalamic-pituitary-adrenal axis, you refer your patient to an endocrinologist, who performs a CRH and ACTH test. During the CRH test, the patient is administered exogenous CRH. During the ACTH test, the patient is administered ACTH.
What effect on cortisol levels do you expect in this patient following the two tests?
CRH test = no rise in ACTH or cortisol (already normal - increases won’t affect)
ACTH test = rise in cortisol
Describe positive feedback, using oxytocin as an example.
- Uterine contractions stimulate the hypothalamus to release oxytocin from nerve endings in the posterior pituitary
- Oxytocin travels in the systemic circulation where it stimulates the uterus to contract, leading to further oxytocin release
- This feedback loop stops when the baby is born
Describe the blood brain barrier.
- Protects the brain from the entry of anything that may harm it.
- Composed of astrocytes which wrap feet like processes around blood vessels, creating tight interactions which prevent the diffusion of most larger substances in the blood
Describe the behaviour of hormones at the blood brain barrier. PART 1
- Steroid hormones are lipid soluble - freely diffuse across the membrane into the brain
- Peptide hormones cannot freely diffuse across and as such require saturable transport mechanisms – usually in the form of specific channels.
