Endo 2 Flashcards
What are the two different tissues present in the pituitary gland? what are their functions?
Anterior pituitary: Endocrine tissue
Posterior pituitary: Neural tissue (extension of the hypothalamus)
What are the two types of hormones released by the posterior pituitary?
Posterior pituitary hormones:
Released by the post. pit. and will release directly into the circulation
Hypophyseotropic hormones:
hormones that are used to regulate the anterior pituitary
Name examples of Post. pit and hypophyseotropic hormones
Post pit:
ADH (arginine vasopressin)
Oxytocin
Hypophys:
TRH (thyrotropin)
GnRH (gonadotropin)
GRH
CRH
PIH (prolactin, dopamine)
T or F
Dopamine is only a neurotransmitter un human physiology.
False, dopamine can be both a neurotransmitter and a hormone depending on the context in which it is released
T or F
Oxytocin and ADH are released from the same nucleus in the posterior pituitary gland.
False, they are released by separate nuclei in the hypothalamus before travelling down to the p. gland, close to the capillaries
What is the circulating half-life of oxytocin and ADH?
1-3 minutes
It is a biochemically expensive process
Explain the effects of oxytocin on females (3)
(i) Parturition: dilation because of the head causes the release of Oxy –> uterine contractions to assist expulsion
(ii) Milk ejection: response to suckling is contraction of milk-filled ducts (lactating women only)
(iii) Behavioural effects: local release of oxy to the brain reduces anxiety and enhances bonding
Explain the effects of oxytocin on males (2)
(i) Ejaculation: Oxy surge during sex assists passage of sperm
(ii) Behavioural effects: local release of oxy to the brain reduces anxiety and enhances bonding
how are the thyroid hormones stored?
The colloid is a fluid-filled space with thyroglobulin inside. The thyroglobulin is used to store T4 and T3 until they are released into the plasma by attaching to proteins
T or F
The thyroid gland is larger in males
False, it is larger in females, but the size depends on sex, age, diet, etc
Where can iodine be found in the body?
It is trapped in the thyroid follicular cells to be transported across cells against the iodine’s gradient
What are the steps of thyroid hormone synthesis?
- Iodine (I2) is used for iodination of the tyrosine residue of the thyroglobulin to form MIT (monoiodothyrosine) and DIT
- Oxidative coupling of 2 DIT forms T4 and coupling of a MIT and DIT forms T3
- Both hormones are stored attached to the thyroglobulin
What controls the rate of T3 and T4 production? Where does that hormone come from and what stimulates it’s release?
TSH is released from the anterior pituitary after stimulation from the TRH
When T3 and T4 are circulating in the bloodstream, what effects does it have on thyroid activity?
The control of the hormones is done with a negative feedback loop, meaning that circulating T3 and T4 will decrease release of TSH and TRH
What happens in the presence of iodine deficiency?
- Synthesis of T3 and T4 decreases and hormones decrease in circulation
- This stimulates TSH release so the thyroid follicular cells are stimulated to grow (colloid and thyroglobulin accumulation) without making T# because of the lack of iodine
- Thyroid enlarges and may form a goitre
What type of goitre is present in iodine deficiency
Since the enlarged thyroid is not capable of synthesizing hormones due to the iodine deficiency, the goitre is considered non-toxic
What are the effects of thyroid hormones?
Controls basal metabolism of carbohydrates, lipids, and proteins, as well as growth of bone (stimulates GH) and the nervous system
When is thyroid deficiency most dangerous? Why?
at a young age because it could impede NS development and lead to irreversible mental delays in growth
What is the mechanism of action of the thyroid hormone when interacting with target cells?
- T# enters target cells to bind to the nuclear receptors
- Hormones alter the transcription of a specific gene and lead to thyroid-specific protein levels
Classic pathway: Nuclear receptor binding
What is the mechanism of action of the thyroid hormone when interacting with the plasma membrane and mitochondria?
(i) The hormone can bind to the mitochondria to increase ATP prod. and metabolism (too fast for gene transcription and so not dependent on protein synthesis)
(ii) the hormone can also bind to the plasma membrane and increase the uptake of amino acids (too fast for gene transcription and so not dependent on protein synthesis)
What is primary hypothyroidism? Where does it occur more often?
occurs at the level of the thyroid hormone:
Inability to produce the thyroid hormone
Seen more often in women and appears at about 40-60 years old
What are the different causes of primary hypothyroidism? (3)
(i) Atrophy of the thyroid
(ii) Autoimmune thyroiditis: Destruction by antibodies against cellular components of the thyroid (Hashimoto)
(iii) Goitrous hypothyroidism: non-toxic goitre formed by a blocked T4 and T3 synthesis
What is secondary hypothyroidism?
Occurs at the level of the pituitary, where there is little or no TSH
What is tertiary hypothyroidism?
Occurs at the level of the hypothalamus, where there is little or no TRH
What is infantile hypothyroidism?
The absence of the thyroid gland or incomplete development
What can happen if infantile hypothyroidism is not treated early enough?
it can cause dwarfism or cretinism
How can all types of hypothyroidism be treated?
administration of thyroid hormone
What is primary hyperthyroidism? (2)
(i) Graves disease:
Autoimmune disease where LATS mimics the action of TSH and stimulates the release of T#. This forms a toxic goitre: enlarged thyroid that synthesizes T#
(ii) Thyroid cancer
synthesis of thyroid hormone independently of TSH stimulation
What is secondary hyperthyroidism?
At the level of the pituitary gland, there is no negative feedback from increased T# (TSH keeps getting synthesized autonomously)
Often, because of a pituitary tumour
What is tertiary hyperthyroidism?
At the level of the hypothalamus, there is no negative feedback to decrease TRH
Often, because of a hypothalamic tumour
Depending on the severity of the hyperthyroidism, what are the different treatment options?
(i) Surgery with replacement therapy
(ii) Administration of radioactive iodine to destroy thyroid follicles (replacement if needed)
(iii) Administration of antithyroid drugs to block the addition of iodine to thyroglobulin (have to be careful not to inhibit synthesis of hormone to a great extent and cause hypothyroidism
How can calcium be efficiently stored?
in bone
What are the 3 hormones important in calcium level control?
PTH (parathyroid): increases circulating Ca
Calcitonin: decreases circulating Ca
Vitamin D: increases circulating Ca
