Endocrine Physiology Flashcards
Hormone
- chemical messenger
- secreted from ductless gland
- emptied directly into circulation
- transported by blood to alter target organ
- present in small concentrations
Endocrine system
Glands that release hormones into circulation
- helps establish systemic homeostasis
What 3 things does the endocrine system regulate?
- metabolism
- growth and development
- mood
Endocrine glands
- hypothalamus
- pituitary
- thyroid
- parathyroid
- adrenal
- pancreas
- repro (ovary, testicle, placenta, mammary)
- kidneys
- GIT
Hormone structure affects
- function
- transport
- interaction with target cell
Protein hormones
Mostly go to the brain
- dissolved in blood: hydrophilic, no carrier needed
- receptors on plasma membrane
Hypothalamic protein hormones
- TRH
- CRH
Pituitary protein hormones
- TSH, ACTH
- growth hormone
- vasopressin
- oxytocin
Amine hormones
Derived from tyrosine
- thyroid hormones
- transported bound to proteins (99%) –> lipophilic
- only free form is active
- bound protein isn’t excreted
- receptors: intracellular
Steroid hormones
Derived from cholesterol
- transported bound to proteins –> lipophilic
- only free form is active
- receptors: cytosolic, nuclear
- cortisol
- sex hormones
Feedback control
Regulation of hormonal secretion from an endocrine gland by an effect of the circulating hormone that the gland itself produces
Negative feedback
Increased hormone concentrations result in less production of the hormone, usually through an interaction with the hypothalamus or pituitary gland
Negative feedback example (thyroid)
Higher thyroid hormone concentrations decrease release of stimulatory and releasing hormones (TSH, TRH)
- decreased release of stimulatory and releasing hormones results in decreased synthesis of T4
_____ of hormone production results in increased release of ______
Lack; sitmulatory hormones
The hypothalamus is part of the _______
Diencephalon
- forms floor of 3rd ventricle
Anterior versus posterior pituitary
Anterior: adenohypophysis - glandular - pars distalis/tuberalis/intermedia Posterior: neurohypophysis - neural tissue
AP embryology
- Rathke’s pouch
- invagination of pharyngeal epithelium
- epithelioid cells
PP embryology
- neural outgrowth from hypothalamus
- neural tissue
Hypothalamic/pituitary relationship
- hypothalamus controls release of pituitary hormones
- AP: releases hormones/inhibitory hormones
- PP: neuronal control
How does the hypothalamus receive signals from the brain?
- break in BBB
- fenestrated capillaries allow sampling of chemicals in the blood
Median eminence
Lower-most portion of HT
- connects with pituitary stalk
- arteries penetrate ME
- HT blood flows thru ME directly to AP
- HT hormones released into ME
Magnocellular
“Large neurons”
- cell bodies of PP in HT
- supraoptic nuclei (ADH)
- paraventricular nuclei (oxytocin)
- axons terminate in PP
Hormones secreted from PP neurons
Transported down nerve fibers
- released into surrounding capillaries
Anterior pituitary hormones
- corticotropes (20%): ACTH
- thyrotropes (4%): TSH
- somatotropes (30-40%): growth hormones –> acidophils
- lactotropes (4%): prolactin
- gonadotropes (4%): FSH, LH
Antidiuretic hormone
Aka: vasopressin
- regulates free water excretion from kidneys
- blood pressure
Oxytocin
- milk expression
- birth
- orgasm
