Endocrinology Flashcards
Endocrine Signaling
- Involves hormone secretion into the blood by an endocrine gland.
- The hormone is transported by the blood to a distant target site
e.g. Anterior Pituitary gland –> blood vessels –> Gonads (target site) –> Cells of ovary and testis –> or steroid hormones , Estrogens(female) and Androgens (male).
Neuroendocrine Signaling
-cell type that releases the hormone is a nerve. In this case it is the hypothalamus
Paracrine Signaling
Long distance signaling
Autocrine Signaling
cell releases hormone that acts on self
Communication by hormones (or neurohormones) can involves six steps
- Synthesis: of the hormone by endocrine cells (or neurons in case of neurohormone
- Release: of the hormone by the endocrine cells (or the neurohormones by the neurons)
- Transport: of the hormone or neurohormone to the target site by the blood stream
- Detection of the hormone or neurohormone by a specific receptor protein on the target cells
- A change in cellular metabolism triggered by the hormone receptor interactions
- Removal of the hormone, which often terminates the cellular response
*each step has a regulatory aspect to it
How most hormones are transported?
Transported via binding protein
The “Classical” endocrine organs
- Brain: Hypothalamus w/ Anterior and Posterior Pituitary Gland
- Thyroid and parathyroid glands
- Heart: Atrial natriuretic peptides (ANP)
- Adrenal glands: Cortex and medulla
- Pancreas: islets of Langerhans
- ovaries and testis
Hypothalamic-Pituitary Signaling
- via blood vessels of the pituitary stalk
- hypothalamic-Hypophyseal Portal System- from the hypothalamus to the adenohypophysis (anterior pituitary)
- hypothalamic neurohormones either activate or inhibit activity of one of the six types of hormone-producing celling in the anterior pituitary
- called either releasing hormones (releasing factors) or inhibiting hormones (inhibiting factors).
- hypothalamus and pituitary are almost continuos tissues.
- hypothalamus hormones have two functions: inhibit the release of something, or tell the pituitary to release something.
Classes of Hormones Based on Structure
Glycoproteins -FSH -LH -TSH Polypeptides -GH -Insulin -Glucagon Steroids -Aldosterone -cortisol -progesterone Amines -epinephrine -melatonin
Synthesis of Protein Hormones
-by definition, if its secreted it’s a hormone.
- Synthesis on ribosomes: preprohormones
- Rough endoplasmic reticulum –> prohormones
- Golgi Apparatus: prehormones packaged into secretory vesicles: prehormone –> hormone + other peptide
- Vesicles: storage of hormone
- Co-release of hormone + other peptides.
Structures of some steroid hormones
-common four carbon ring structure
“lock and key” mechanism for a hypothetical membrane receptor
- the hormone acts as a key for a lock
- the lock being the receptor that is a chemical and physically specialized for the hormone
- Receptor hormone reaction are very specific
Properties of Hormone Receptors
a. Specificity: recognition of single hormone or hormone family
b. Affinity: binding hormone at its physiological conc.
c. Should show saturability; i.e. a finite number of receptors
d. Measurable biological effect: a measurable biological response due to interaction of hormone with its receptor
Receptor Regulation
a. Receptors can be upregulated either by increasing their activity in response to hormone or their synthesis
b. Receptors can be down-regulated either by decreasing their activity or their synthesis
* it makes no physiological sense for a receptor with a micromolar conc. to have affinity for a hormone at a nanomolar conc. Same goes vice versa
3 mechanisms by which a hormone can exert effects on target cells
- Direct effects on function at the cell membrane
- Intracellular effects mediated by second messenger systems
- Intracellular effects mediated by genomic or nuclear action
Direct effect
Hormone acts on a receptor –> receptor directly attach to a regulatory protein –> result is seen in the effect on what happens to the protein
Signaling via an intracellular second messenger
- a lot of second messengers are kinases
Hormone interacts with receptor –> changes the activity of a protein –> protein released into cytoplasm –> can influence the function on other proteins
Intracellular genomic signaling
e.x. Estrogen stimulate the transcription of certain genes –> more certain proteins are made, oppresses other genes –> more of wanted genes and less of unwanted genes.
TO be clear
Estrogen is a steroid. Steroid is very lipophilic meaning it can cross the membrane. Hormone goes directly into the nucleus of the cell and binds with a receptor. Receptor will change the way gene translation is regulated in the target cell. Ultimately changes the protein content of the cell
Feedback Control of Hormone Secretion
- Hormone secretion is precisely regulated by feedback mechanisms
- an excess of hormone, or excess hormonal activity, leads to a diminution of hormone secretion
- conversely, a deficiency of hormone leads to an increase in hormone secretion
e.x. of Feedback control of hormone secretion
- plasma Ca conc. goes down –> parathyroid glands are stimulated –> the synthesis and release of the parathyroid hormone will increase –> secretion will increase –> kidney will filtrate less Ca –> Ca will be saved from the bone and more will be taken out of the Gut
- Ca conc. will go up –> when there is enough, Ca will bind to the Ca receptor to tell the parathyroid gland to stop stimulation
Need to Know about endocrine glands and their secretions
- Anatomic Location
- Hormones secreted
- Chemical Nature of Hormones
- Effects
- Mechanism of Action
- Control of Release
- Problems
- Treatment
Pituitary Gland
Anatomy: two distinctly different tissues
- Adenohypophysis (aka Anterior pituitary) - endocrine tissue
- Neurohypophysis (aka posterior pituitary) - neural tissue
Hormones that the Hypothalamus releases
- Gonadotropin releasing hormone (GnRH)
- Growth Hormone releasing Hormone (GHRH)
- Somatostatin (SS)
- Thyrotropin releasing hormone (TRH)
- Prolactin release inhibiting Hormone (PIH)
- Prolactin releasing hormone (PRH)
- Corticotropin releasing Hormone (CRH)
Hormones that Anterior Pituitary Hormones releases:
- FSH and LH (+ affected by GnRH)
- Growth hormone (+ by GHRH and - by SS)
- TSH (+ TRH and - by SS)
- Prolactin (+ by TRH and PRH and - by PIH)
- ACTH (+ by CRH)