Lecture 9 Flashcards
(25 cards)
What is the growth hormone responsible for?
There are two different 3’ splice sites in the gene for growth hormone? What is the result of this alternative splicing for the growth hormone transcript?
Growth hormone is responsible for making you big and strong. 2 different versions of growth hormone will have different binding affinities for different receptors and will have slightly different effects in different cells.
How is the secretion of growth hormone controlled, and what enables the secretion of growth hormone?
Hypothalamus decides what signal to send out (growth hormone releasing hormone vs somatostatin)
Growth hormone releasing hormone stimulation will stimulate the release of growth hormone form somatotrophs. It must travel from the hypothalamus to the anterior pituitary and the growth hormone releasing hormone will act on somatotrophs to release growth hormone.
What occurs when growth hormone is released? What inhibits the secretion of growth hormone from the anterior pituitary?
As soon as growth hormone is released, it will be transported to different tissues in the body. The liver responds to the energy needs of the body and will help increase the amount of sugar that is circulating, the amount of fat metabolism that is happening, the amount of toxins that your liver is trying to clear out.
Insulin-like growth factor (IGF-1) will be released from the liver and bind to other tissues and cells that cause cells to divide. IGF-1 will act as a negative inhibitor for the pituitary. It will tell the pituitary that it does not have to release any more growth hormone, since the liver has already responded to the growth hormone that was released
What is the role of somatostatin in growth?
Body releases somatostatin because we don’t need to grow anymore. The release stops the anterior pituitary from releasing growth hormone. Since there’s no more growth hormone, there’s not more IGF-1, so cells don’t divide
Explain the role of the hormone ghrelin on growth.
It has to do with digestion, hunger, and satiety. This hormone will affect the pituitary by helping it decide if there’s enough energy to grow or not.
Why does growth hormone tend to peak after midnight?
This is when they tend to be asleep. This peak is important for recovery and repair. Anything that needs to be repaired will be fixed most efficiently at night.
What kind of receptor does growth hormone bind to in order to exert its effects?
JAK/STAT pathway
What is the role of prolactin? To what other molecule is prolactin related in structure to, and what are the relative concentrations of each in the pituitary?
It’s structurally related to growth hormone, but the degree of homology between these 2 are very low. (3D structures are simular, not sequences) The pituitary contains much less prolactin than growth hormone, but the mean serum levels of the two are equal in adults.
It’s responsible for stimulating the syntehsis of milk. Prolactin gets high in women who just gave birth.
What hormone is similar to prolactin in effect, as well as structure? How are the two different?
Placental lactogen is similar to prolactin but it’s secreted by the placenta vs prolactin in the anterior pituitary.
The placenta is grown by the baby and releases hormones to help support the baby and the pregnancy. Once the leaves the womb, this triggers the production of milk to support the baby.
What hormones increases prolactin secretion on a long term basis? What physical stimulation increases the stimulation of prolactin? What inhibits prolactin release? What is the connection between this hormone concentration in the body vs prolactin?
Prolactin secretion is increased on a long-term basis by estrogens, which lead to higher mean serum levels of prolactin in females than males. In general, pregnant and lactating women tend to have higher levels of prolactin than men. Thyrotropin-Releasing Hormone (TRH) is known to stimulate prolactin secretion as well.
Suckling stimulates prolactin secretion through direct neural influence on the hypothalamus. There is a really good connection between oxytocin and prolactin.
Dopamine is a hypothalamic inhibitor of prolactin release. Therefore if you have higher levels of prolactin, you will tend to have much lower levels of dopamine.
What allows for the secretion of prolactin, and what happens when prolactin is secreted? How is prolactin secretion controlled?
The hypothalamus is going to get information from hormones and the hypothalamus releases something to activate the anterior pituitary. The release of these two hormones are going to activate the anterior pituitary, such that the pituitary is going to release prolactin. This process is going to be helped with E2, as well as by pregnancy such that the female body releases a lot more prolactin.
When prolactin is secreted, the prolactin will stimulate breast tissues to produce milk. However, as soon as prolactin is released, this will initiate a negative feedback loop, prolactin will travel to the hypothalamus and tell it to be released, and the stimulation of prolactin release can stop. As the baby gets older, dopamine will begin to kick in to help decrease milk production and help regulate its production. Dopamine will affect the anterior pituitary and will inhibit prolactin release.
What two hormones are circadian besides serotonin and melatonin? Why is this the case?
Growth hormone: as we sleep, repair can occur so cells can divide
Prolactin: increases in the early morning because it’s involved in a whole bunch of things for a normal body
What signaling pathway does prolactin act through? What hormone does prolactin promote the synthesis of and where does this occur?
Prolactin actions are mediated through the JAK/STAT pathway and will lead to changes in gene expression such that the body is able to produce more milk. Prolactin acts on the liver to promote the synthesis of IGF-1 which stimulates the immune system/lymphoid cells to promote proliferation/rapid increase of lymphoid cells.
What hormones fall under the category glycoprotein hormones? What similarities do these hormones share and what differences do they have as well?
Follicle stimulating hormone (FSH), luteinizing hormone (LH), thyroid stimulating hormone (TSH), and human chorionic gonadotropin (hcG)
- similar in structure but act by different receptors
- act by G-protein linked receptors and through the activation of adenylyl cyclase
- They have a common alpha-subunit but unique beta-subunit
Explain why TSH, FSH, and LH are pituitary basophils.
Explain why FSH, LH, and hCG are gonadotropins.
Explain why FSH and LH are both.
It depends on the location of hormone production and the function of the hormone. Pituitary cells produce TSH, FSH, and LH. Since FSH and LH stimulate the gonads and TSH doesn’t, this gives them the classification of gonadotropins as well. hCG is produced by the placenta, so it’s only a gonadotropin and not classified as pituitary basophils.
What is measured in over-the-counter pregnancy tests to determine if someone is pregnant or not?
They measure hCG levels because this is produced by the placenta and not under any other circumstances.
What are the roles of follicle stimulating hormone (FSH)? What are the roles of luteinizing hormone (LH)?
Follicle stimulating hormone will act on specific cells in the ovaries to promote estrogen synthesis as follicle development. In males, follicle stimulating hormone acts on the serotonin cells in the testis to stimulate spermatogenesis.
Luteinizing hormone stimulates the actual ovulation of the follicle and to promote the formation of the corpus luteum. In men, LH stimulates testosterone production in the leydig cells.
What hormone is human chorionic gonadotropin most similar to in terms of its effects and structure? What is hCG a sensitive indicator for?
It’s similar to luteinizing hormone (LH), but it exhibits more prolonged actions. The structures of LH and hCG are extremely similar. hCG exhibits more prolonged action and its presence is an indicator of the development of the placenta.
What does thyroid stimulating hormone do?
It acts on the thyroid follicle cells to stimulate uptake of iodide and synthesis of thyroglobulin.
What hormones regulate the secretion of thyroid stimulating hormone? How is secretion of thyroid stimulating hormone controlled? Where are thyroid stimulating hormones released from, and from what cells?
Thyroid releasing hormone (TRH) and somatostatin (SST)
The secretion of thyroid stimulating hormone is controlled by a long feedback loop which is based on the amount of circulating thyroid hormones in the body which go back and affect the pituitary to activate/inhibit these processes. They are released from the anterior pituitary by thyrotrope cells.
What common precursor molecule do all the adrenocorticotropic hormone-related peptides come from? How do we obtain these related corticotropic hormones from this precursor molecule?
All the ACTH peptides are formed from proopiomelanocortin (POMC).
A series of cleavages occur using specific proteases that cleave regions on the peptide chain that contain paired basic residues. ACTH requires both proconvertase 1 to cleave around it and proconvertase 2 to modify it.
What does adrenocorticotropic hormone do? How is ACTH secretion triggered?
There are certain amounts of cortisol at any given time and it can increase/decrease depending on the bodily situation. If something stressful is received by your CNS, a signal will be sent to your hypothalamus which tells it to secrete the corticotropin-releasing hormone (CRH) to affect the anterior pituitary. It then secretes ACTCH in microgram doses to affect the adrenal gland. The adrenal gland will be stimulated to secrete cortisol such that this stress hormone will circulate the rest of the body and affect muscles, liver, adipose tissue, metabolism, and ability to function.
How does adrenocorticotropic hormone secretion become inhibited? Why is inhibition of the secretion of this hormone important?
After adrenocorticotropic hormone is released, cortisol will initiate a negative feedback loop. Cortisol will target the anterior pituitary and the hypothalamus to inhibit the secretion of both adrenocorticotropic hormone and corticotropin-releasing hormone. This will help stop us from getting to extremely high levels of cortisol.
How are the effects of adrenocorticotropic hormone mediated, and in what cells does this response occur?
The effects of adrenocorticotropic hormones are mediated through G protein linked receptors in adrenal cortex cells. Adenylyl cyclase makes cAMP, cAMP activates phospholipase C, which cleaves PIP2 into IP3 and DAG. IP3 will open calcium channels on the endoplasmic reticulum, causing an increase in intracellular calcium. As a response, the adrenal cells synthesize steroids at a higher rate. (Adrenal cell RNA and protein levels are increased.)
