Pituitary Hormones and Axes Flashcards
What are tropic hormones?
Hormones can be classified as tropic or trophic based on the effects they produce on target organs… Tropic and effector hormones can be considered trophic hormones too
Regulatory hormones that act to affect the secretion of another hormone
What are trophic hormones?
Hormones can be classified as tropic or trophic based on the effects they produce on target organs… Tropic and effector hormones can be considered trophic hormones too
Hormones that stimulate cell division in its target cells
What kind of interaction is the following:
PTH increases reabsorption of Ca+ by kidney tubule cells, calcitonin suppresses reabsorption of the Ca2+ by the kidney tubule cells
Antagonistic interaction
What kind of interaction is the following:
PTH (indirectly) increases osteoclast activity, increasing Ca2+ release from bone while calcitriol enhances the absorption of Ca2+ from the digestive tract
Integrative interaction
- both contribute to the same function but do it in slightly different ways
What kind of interaction is the following:
Epinephrine and glucagon both enhance the release of glucose by liver cells
Additive interaction
What kind of interaction is the following:
Estrogen and progesterone stimulate the production of oxytocin receptors by cells in the mammary glands
Permissive interaction
- both hormones permit the action of another hormone
- stimulates another protein receptor
What is an effector hormone?
Hormones can be classified as tropic or trophic based on the effects they produce on target organs… Tropic and effector hormones can be considered trophic hormones too
A hormone that has direct physiological effects on its target cells
What is the pituitary gland?
Pituitary gland is an endocrine organ
- a stalk of tissue that dangles from the inferior side of the forebrain
- has 2 distinct components that each secrete hormones
What is the hypothalamus?
Hypothalamus is part of the diencephalon and also an endocrine organ
- has 5 main functions
- does not secrete hormones as its main/only function
Is the pituitary gland a primary or secondary endocrine organ?
Primary endocrine organ
Is the hypothalamus a primary or secondary endocrine organ?
Secondary endocrine organ
What are the five functions of the hypothalamus?
- Regulating alertness through the limbic system and basal forebrain
- Controlling behavioural “drives”
- Regulating circadian rhythms by affecting the release of melatonin from the pineal gland
- Regulating autonomic functions through the brainstem and ANS
- Secreting both regulatory and effector neurohormones through the pituitary gland
What are the two (three) distinct components of the pituitary that each secrete hormones?
Hypophysis
- Adenohypophysis - epithelial tissue (anterior lobe of the pituitary gland)
- Neurohypophysis - neural tissue (posterior lobe of the pituitary gland)
(Intermediate lobe of pituitary gland - does not usually secrete hormones in adult humans but does in other vertebrates)
What is hypophysis?
Refers to the pituitary (components of the pituitary that secrete hormones)
What is adenohypophysis?
Refers to the anterior lobe of the pituitary gland
- made of epithelial tissue
- secretes regulatory hormones
What is neurohypophysis?
Refers to the posterior lobe of the pituitary gland
- made of neural tissue
- secretes effector hormones
The hypothalamus has indirect control of the release of 7 ________________ hormones:
The hypothalamus has indirect control of the release of 7 REGULATORY hormones:
What are the 9 hormones that the hypothalamus releases?
REGULATORY HORMONES
1. Corticotropin-releasing hormone (CRH)
2. Thyrotropin-releasing hormone (TRH)
3. Growth-hormone releasing hormone (GH-RH)
4. Growth-hormone inhibiting hormone (GH-IH)
5. Prolactin-releasing hormone (PRH)
6. Prolactin-inhibiting hormone (PIH)
7. Gonadotropin-releasing hormone (GnRH)
EFFECTOR HORMONES
8. Vasopressin/ADH
9. Oxytocin/OT
Which two effector hormones are released directly from the hypothalamus into the systemic circulation through axon terminals in the posterior pituitary gland?
- Vasopressin/ADH
- Oxytocin/OT
Vasopressin and Oxytocin are both examples of _________ (which class) hormones?
Both are examples of 9-aa peptide hormones (class 2 hormones)
How do vasopressin and oxytocin reach the systemic circulation?
- there are two distinct hypothalamic neuron groups branching into the posterior pituitary lobe
- synapse onto the hypophyseal vein in the neurohypophysis
- hormones can be released directly into the systemic circulation through the hypophyseal vein
What is the function of vasopressin?
- is an antidiuretic
- plays a role in water conservation in the kidney (urination)
- acts in the kidney
What is the function of oxytocin?
- uterine contraction during labour
- milk letdown and ejection
- acts in the mammary glands and the uterus
How are the 7 regulatory hormones released by the hypothalamus released?
- the seven regulatory hormones act on the anterior pituitary gland through the PITUITARY PORTAL SYSTEM
- secreted into the capillaries at the median eminence
- median eminence sends blood only to the adenohypophysis
- median eminence is located at the bottom of the hypothalamus
- these hormones only get sent to the anterior pituitary lobe
- once the anterior pituitary releases these hormones, then they can be secreted into the blood
What is the median eminence?
An area located at the bottom of the hypothalamus containing capillaries
- regulatory hormones are secreted into the capillaries at the median eminence, which send blood only to the adenohypophysis
The hypothalamus releases 7 regulatory hormones into the anterior pituitary lobe, but what are the 6 different hormones that the anterior pituitary itself releases?
- Thyroid-stimulating hormone (TSH)
- Adreno-corticotropic hormone (ACTH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LSH)
- Growth hormone (GH)
- Prolactin (PRL)
What are the five distinct cell types in the anterior pituitary that releases hormones (6)?
- Somatotropes - growth hormone
- Lactotropes - prolactin
- Thyrotropes - thyroid-stimulating hormone
- Corticotropes - adreno-corticotropic hormone
- Gonadotropes - follice-stimulating/luteinizing hormones
Notice how all 5 cell types in the anterior pituitary that release hormones end in -trope, what does this indicate about the hormones being released?
-trope = tropic hormones
= regulatory hormones
These cells release the 6 types of regulatory (effector) hormones
5/6 of the hormones released by the anterior pituitary are regulatory hormones. Which one is the exception and is PURELY AN EFFECTOR HORMONE?
PROLACTIN - all the others act on something that will release another hormone
How do hypothalamic regulatory hormones act as releasing hormones?
They stimulate the secretion of their corresponding pituitary hormone
CRH -> Corticotropes -> ACTH
TRH -> Thyrotropes -> TSH
GnRH -> Gonadotropes -> FSH & LH
Which two hypothalamic regulatory hormones have antagonistic hormones?
- Growth-hormone releasing hormone
- growth-hormone inhibiting hormone (somatostatin) - Prolactin-releasing hormone
- prolactin-inhibiting hormone
(no proof that PRH actually exists)
Explain how prolactin-inhibiting hormone is actually dopamine
Prolactin-inhibiting hormone = dopamine because dopamine can act as an inhibitor
Dopamine inhibits/prevents the release of prolactin
This an example of _________ type of hormone interaction:
- Mammary glands do not respond to either PRL or OT unless they have been exposed to estrogen for a prolonged period of time
Permissive hormone interaction
This an example of ___________ type of hormone interaction:
- Prolactin increases milk production while oxytocin increases milk let-down (excretion)
Integrative hormone interaction
What is a hormone axis?
- used to describe a higher order system involving multiple regulatory hormones
Hormone 1 regulates secretion of
Hormone 2 regulates secretion of
Hormone 3
Hormone axes are typically named after the endocrine organs that they link together: Hypothalamic pituitary adrenal axis (HPA)
What are the three types of hormones involved in the hypothalamus, pituitary, effector endocrine organ axis
- Releasing hormone
- Pituitary hormone
- Effector hormone
Hypothalamic neurons, anterior pituitary cells, and their target organs form axes which are regulated by ______________________
Hypothalamic neurons, anterior pituitary cells, and their target organs form axes which are regulated by negative feedback
What are the three HPE axes regulated through negative feedback of their effector hormones on their regulatory hormones?
- HPT axis - hypothalamus/pituitary/thyroid
- HPA axis - hypothalamus/pituitary/adrenal
- HPG axis - hypothalamus/pituitary/gonadal
Trace the HPT axis:
HPT axis = hypothalamus/pituitary/thyroid
- releasing hormone = TRH
- hormone 1 (from pituitary) = TSH
- endocrine target organ = thyroid gland
- hormone 2 (from endocrine target organ) = thyroid hormones
hormones released from the endocrine target organs inhibit the release of TRH and TSH
Trace the HPA axis:
HPA axis - hypothalamus/pituitary/adrenal
- releasing hormone = CRH
- hormone 1 (from pituitary) = ACTH
- endocrine target organ = adrenal cortex
- hormone 2 (from endocrine target organ) = glucocorticoids
hormones released from the endocrine target organs inhibit the release of CRH and ACTH from pituitary
Trace the HPG axis:
HPG axis - hypothalamus/pituitary/gonadal
- releasing hormone = GnRH
- hormone 1 (from pituitary) = FSH/LH
- endocrine target organ = testes/ovaries
- hormone 2 (from endocrine target organ) = FSH(inhibin/inhibin estrogens) and LH(androgens/progesterone estrogens)
hormones released from the endocrine target organs inhibit the release of GnRH and FSH/LH
Trace the growth hormone axis (negative feedback from the anterior pituitary hormone)
- release of growth hormone stimulates the release of a second hormone
- release of second hormone causes the release of another third hormone
- third hormone performs negative feedback with the second hormone
- stops the effects after the second hormone
Trace the prolactin hormone axis (negative feedback from the anterior pituitary hormone)**
True or False:
Anterior pituitary hormones can be both tropic and trophic hormones
True!
Tropic and trophic are similar words that refer to different concepts
Tropic = regulatory hormone that acts to affect the secretion of another hormone
Trophic = a hormone that stimulates cell division in its target cells
Some anterior pituitary hormones are trophic as well as tropic hormones
Which anterior pituitary hormones are both tropic and trophic hormones?
ACTH
TSH
LH
FSH
What causes endocrine disorders
Either overproduction or underproduction of hormones
What are the four main causes of hormone hyposecretion?
- Tumour (especially on the optic nerve) can compress the axons and/or blood vessels at the the median eminence
- tumour could stay and grow in the pituitary, squishing the axons and blocking/preventing the release of hormones into the anterior/posterior lobes of the pituitary - Physical damage to the pituitary gland can destroy some or all tropes (cells)
- Damage to target organ (often by antibodies created by autoimmune disease) can destroy effector producing cells
- Stroke or other causes of brain damage can destroy hypothalamic neurons (physical damage)
What is hyposecretion?
Under secretion of a hormone
What is hypersecretion?
Over secretion of a hormone
