Anterior pituitary Flashcards
What are cell that have major features of neurons but release hormones into the blood to affect non-neural tissue?
Neuroendocrine cells
What is the endocrine system?
Hormones being secreted into the blood to affect cells at a distance
What is it called when there are receptors on presynaptic cells for the transmitter that the cell releases?
Autocrine
How are hormones classified?
By their chemical structure (e.g. peptide, proteins etc)
What are the 5 different categories of hormones?
- Polypeptides
- Proteins
- Steroids
- Amines
- Thyroid hormones
Thyroid hormones are largely proteinaceous molecules. Why are the classified separately? (hint–what else do they contain)
They contain iodine
What are neuroendocrine hormones?
Chemical released into the bloodstream from a neuron
What is the first step in the synthesis of polypeptide/protein hormones? Is the protein active at this stage?
Preprohormones made from DNA translation. This is not active
What is the next step in peptide hormone synthesis after preprohormone is synthesized?
Preprohormones are cleaved to form prohormones and transferred to the golgi.
What is the next step in peptide hormone synthesis after cleavage to a prohormone and sent to Golgi?
Prehormone is packaged into a vesicle with enzymes that turn it “on”
What is the next step in prohormone synthesis after the peptide hormone is activated in the vesicle from the Golgi?
Vesicle is released via exocytosis in response to some signal
Are peptide hormones soluble? Where in the target cell, generally, do they act?
They are soluble, and act on the cell via effector cells on the membrane
What is the precursor molecule for steroid hormones? Are these stored in vesicles like peptide hormones? What is the consequence of this?
Cholesterol–not water soluble, so not stored in vesicles–just diffuse out once synthesized
Are steroid hormones stored?
No, but their precursors can be
How do steroid circulate in the blood? (hint, they are hydrophilic)
Bound to plasma proteins
Why does it take a longer amount of time for steroid hormones to be filtered from the blood via the kidneys compared to peptide hormones?
Not water soluble, and are bound to proteins. Proteins are not secreted, thus takes longer to be secreted
What are the amine hormones? (hint they are all derived from Tyrosine). Where are they synthesized/secreted?
Dopamine, epinephrine, norepinephrine
Synthesized/secreted from the adrenal medulla
How are catecholamines (amine) stored? Released?
Stored in vesicles and released via exocytosis
Are catecholamines water soluble?
Yes
What is the histological characteristics of cells that synthesize hormones (2)?
Tubular mitochondria
Large lipid stores
How are hormones specific (how do they “know” which cells to go to)? Similarly, how can the same hormone have different effects in different places?
Based on the receptors
Where in the cell do lipid soluble hormones bind?
Receptors in the cytoplasm or the cell nucleus
What are the four major types of hormone receptors?
- Ion channels
- Enzyme linked
- G-coupled
- Intracellular receptors
Where does the thyroid hormone bind/where is its receptor? What does binding allow for?
The receptor is bound on DNA constitutively. Binding stimulates the transcription of genes
Where are the receptors for testosterone/estrogen? What does binding do?
Found in the cytoplasm, and allows for binding of hormone/receptor complex to DNA
What is the pathway that insulin uses to exert intracellular effects?
Binds to an extracellular receptor, a Tyrosine kinase, that phosphorylates other proteins in a cascade
What are the two major types of negative feedback?
Physiological response-driven negative feedback
Endocrine axis- driven negative feedback
What are the three majors loops of negative feedback found in the axis-driven system?
Ultrashort
Short
Long
What is the ultrashort loop of negative feedback in the axial system?
Hypothalamus shuts itself off via hypophysiotropic factor
What is the short loop of negative feedback in the axial system?
Anterior pituitary shuts off the hypothalamus by releasing tropic hormones
What is the long loop of negative feedback in the axial system?
The target organ shuts off the hypothalamus
What is the factor that is released from the hypothalamus that causes the anterior pituitary to release hormones? What is the name of these hormones that the anterior pituitary releases, and where do they go?
Hypothalamic releasing factor
Tropic hormones, go to the effector organ
What is the classic example of positive feedback?
Ovulation
What are the 5 ways that hormones can be cleared from the blood?
- Metabolic destruction by the tissues or by enzymes in the blood
- Binding to the tissues
- Excretion by the liver into the bile
- Excretion by the kidneys in the urine
- If water soluble filtered at the kidney
Where is the hypothalamus located (besides the fact that it is beneath the thalamus)?
Floor and lateral walls of the third ventricle
The hypothalamus is a part of what part of the brain?
Diencephalon
What are the two capillary beds in the pituitary connected by?
Portal hypophysial vessel
What is the connecting structure of the hypothalamus to the pituitary?
Hypophysial stalk
The area of the hypothalamus where the portal vessels arise, and neurons from the hypothalamus secrete signals is called what?
The median eminence
What is the adenohypophysis? neurohypophysis?
Adenohypophysis = Anterior pituitary Neurohypophysis = posterior
What are the two nuclei that have their axons descend into the posterior pituitary?
Supraoptic and paraventricular nuclei
What is the hypothalamic-hypophysial tract?
Axon tracts of the paraventricular and supraoptic nuclei
Where are oxytocin and ADH synthesized? Released?
Synthesized by neurons in the hypothalamus, sent down hypothalamic-hypophysial tract, and released from the posterior pituitary
What is the Pars Intermedia?
Tissue between the anterior and posterior lobe. Poorly developed in humans
What is the connecting vessel between the hypothalamus and the anterior pituitary?
The primary plexus
How does the hypothalamus signal the anterior pituitary to release hormones?
Secretes various peptide inhibiting/releasing factors
What is the hormone the hypothalamus releases to signal the release of thyroid hormone from the anterior pituitary?
Thyrotropin releasing hormone
What is the hormone the hypothalamus releases to signal the release of ACTH from the anterior pituitary?
corticotropin-releasing hormone (CRH/ ACTH)
What is the hormone the hypothalamus releases to signal the release of FSH/LH from the anterior pituitary?
Gonadotropin-releasing hormone
What is the hormone the hypothalamus releases to signal the release of growth hormone from the anterior pituitary?
GHRH
What is the hormone the hypothalamus releases to inhibit the release of growth hormone from the anterior pituitary?
growth hormone-inhibiting hormone (somatostatin)
What is the hormone the hypothalamus releases to inhibit the release of prolactin from the anterior pituitary?
prolactin-inhibiting factor (dopamine)
What does ACTH do?
Causes secretion of corticoids from the adrenal glands
What does GH do?
Causes the secretion of somatomedins from the liver
What does TSH do?
Stimulates thyroxine from the thyroid
What does FSH do?
Stimulate estrogen release from the ovaries
What does LH do?
Stimulates ovary stuff
What does prolactin do? What type of hormone is it (steroid, peptide, protein etc)
Stimulates milk production from the breasts. It is a steroid hormone
What are the cells of the anterior pituitary that release GH?
Somatotrophs
What are the cells of the anterior pituitary that release prolactin?
Lactotrophs
What are the cells of the anterior pituitary that release Thyrotropin?
Thyrotrophs
What are the cells of the anterior pituitary that release LH?
Gonadotrophs
What are the cells of the anterior pituitary that release FSH?
Gonadotrophs
What are the cells of the anterior pituitary that release ACTH (corticotropin)?
Corticotrophs
What are the steps of corticotropin synthesis? (3)
- Preproopiomelanocortin synthesized.
- Signal protein removed, now POMC
- POMC hydrolyzed to ACTH and beta-lipotrophin
What are the five hormones that ACTH stimulates synthesis/secretion of from the adrenal cortex?
- Aldosterone
- DHEA-S
- Androstenedione
- Testosterone
- Estradiol
What is end product in the feedback mechanism for ACTH?
Cortisol
What are the steps of thyroid hormone synthesis?
- Hypothalamus secretes TRH
- Thyrotrophs secrete TSH
- TSH in thyroid causes T3 and T4 synthesis
What is the feedback mechanism for TSH?
Free T3 & T4 inhibit hypothalamus and anterior pituitary
What are the functions of FSH for guys and gals?
- Females causes growth of follicles
2. Males causes sperm maturation
FSH is a gonadotropin. Its release is under control of what hormone from the hypothalamus?
gonadotropin-releasing hormone (GnRH)
LH is synthesized by what cells of the anterior pituitary?
gonadotropes
LH secretion from gonadotrophs is under the control of what hormone from the hypothalamus?
GnRH
What is the function of LH for guys and gals?
Guys = Testosterone synthesis Gals = Stimulation of ovulation
Growth hormone (GH) is made by what cells of the anterior pituitary?
somatotropes
GH release is controlled by what two opposing hypothalamus hormones?
Hypothalamic growth hormone-releasing hormone (GHRH)
Somatostatin inhibits the action of GHRH
GH has what effect on the liver?
Causes the release of IGF-I (insulin like growth factor I)
Increases insulin secretion and glucose synthesis
What is the overall function of GH?
stimulates protein synthesis and overall growth of most cells and tissues
What is the feedback mechanism for GH?
IGF-I can inhibit GH release
What is Ghrelin, where, and what does it do?
Secreted from the stomach, and stimulates GH secretion
What happens to GH secretion with increasing age?
Decreases
What is the function of GH in adipose tissue?
Increase lipolysis
Decrease glucose uptake
What is the function of GH in muscle tissue?
Increase protein synthesis
Decrease glucose uptake
What is the function of GH in the liver?
Stimulates gluconeogenesis
somatomedins = ?
IGF
What is the function of prolactin?
Promotes the development of female breast and milk production
Release of prolactin is predominantly under tonic inhibition by what hormone?
Prolactin-inhibiting hormone (PIH)
What are the two major hormones secreted by the posterior pituitary?
Oxytocin and vasopressin
Hormones released from the posterior pituitary are synthesized as pre-prohormones in (BLANK) neurons located in the (BLANK) nuclei of the hypothalamus.
magnocellular
supraoptic and paraventricular
Where does the processing of posterior pituitary hormones occur?
Occurs as the neurosecretory vesicles are transported down the hypothalamic-hypophysial tract
What causes the release of posterior pituitary hormones?
in response to depolarization of the neuron terminals.
What can cause nephrogenic DI?
The patient might have a mutation that affects the V2 receptor for ADH on the collecting duct cells.
Less commonly the patient could have a mutation that affects the production and insertion of the aquaporins needed to produce concentrated urine.
Patients on what treatments can develop acquired diabetes insipidus?
lithium
What is Syndrome of Inappropriate Antidiuretic Hormone (SIADH)? What significant problem does it cause?
Increased secretion of ADH for some reason
Can cause hyponatremia since too much water is held
The two main target organs for oxytocin are what?
The lactating breast and the uterus during pregnancy
The release of oxytocin is stimulated during what?
breastfeeding and childbirth
What causes the milk-let down reflex, and causes the myoepithelial cells in the breast to contract to expel milk?
Afferent signals from the nipples of the mother’s breast when an infant suckles
What happens to the number of oxytocin receptors throughout pregnancy? Where is this change most prominent?
Goes up in the breasts and uterus
What causes labor?
Increase afferent signals from the uterus, causing increase in oxytocin release from the pituitary
What are the very general effects of GH?
a. promotes increased size of cells
b. promotes increased numbers of cells through increased mitosis
What are the three main metabolic effects of GH?
- Increased rate of protein synthesis in most body cells
- Increased release of fatty acid from adipose tissue with increased amounts of fatty acid in the blood which allows increased use of fatty acids for energy
- Decreased use of glucose throughout the body “insulin resistance”
What are the four ways the protein synthesis is increased via GH?
- Enhances amino acid transport through cell membranes into cells
- Enhances RNA translation
- Stimulates transcription of DNA
- Decreases breakdown of cell protein
What is the effect of GH on long bone growth?
Stimulate osteoblasts = thickness
Can increase bone length iff epiphyseal plates have not closed
Strenuous exercise increases or decreases GH secretion?
Increases
When is GH highest during sleep?
First two hours
What is the effect of starvation on GH release?
Increases
Acromegaly = ?
Increased GH synthesis for some reason
