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27 Cards in this Set
- Front
- Back
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Where is GnRH pulse generator in humans (be specific!)?
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The arcuate nucleus of the major basal hypothalamus
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The GnRH acts on the pituitary gland to promote the release of what? Does it act on the Anterior or Posterior pituitary?
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LH (luteinizing hormone) and FSH (follicle-stimulating hormone)
GnRH acts on the anterior pituitary |
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What is GAP?
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This is a cleavage product of the larger peptide that makes GnRH and GAP. GAP is secreted with GnRH but its function is unknown.
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What is the GnRH half life (is it long or short)?
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Very short – 2-3 minutes, so portal system is key to its success.
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True or false, pulsatile release is critical to GnRH function?
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True! Anterior pituitary only response to pulsatile release (~every 15-20 minutes). Continuous infusion desensitizes the receptor and shuts down the axis.
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True or false, GnRH release is pulsatile throughout life?
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False! GnRH pulse generator is inactive during infancy. It only gears up during puberty. Pulse rates vary during different phases of life (ex: during menstruation, etc.).
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What is the first and primary signal of puberty? When does it happen?
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Not hairy upper lip or acne → but NEURAL: activation of the GnRH pulse generator is the first true sign of puberty. This happens during DEEP SLEEP. (Levels are very low during waking hours.)
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True or false, the GnRH cycle from before birth to age 1 ½ is similar to the adult cycle?
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True. From 1 ½ to puberty it’s INACTIVE. From puberty to adulthood, it’s STRONG DURING SLEEP but low during waking hours.
But from before birth to age 1 ½ and in adulthood, pulse cycling occurs CONTINUOUSLY. |
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What is thought to be responsible for the onset of GnRH pulsatile release in adolescence? What peptide is thought in particular to play a significant role in this? What evidence supports this idea?
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Some sort of metabolic signal that indicates the body’s energy stores (since reproduction requires a lot of energy) is thought to reinitiate GnRH pulsatile release. Malnutrition delays puberty. Good nutrition advances puberty (puberty is occurring earlier in this society than previously).
LEPTIN probably plays a big role. Puberty is delayed in leptin deficient mice. Leptin normalizes time of puberty in diet-restricted mice. NOCTURNAL leptin levels increase during the 30 days preceding the onset of puberty (daytime leptin levels DO NOT increase). |
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True or false, sertoli cells begin proliferation at puberty?
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False. Remember that GnRH is “surprisingly” active in the pre- and early post-natal periods. Higher testosterone and estrodiol levels can be measured at this time. Sertoli cells proliferate in early infancy. The early GnRH also is responsible for descent of the testes.
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Describe the structure of FSH and LH.
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They are ENORMOUS glycoproteins with an α and β subunit. The α subunit is the COMMON SUBUNIT (shared by LH, FSH, hCH, and TSH). The β is hormone-specific. Both subunits are required for hormonal activity.
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What 4 hormones share a common subunit?
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(KNOW THIS!!!)
LH, FSH, hCH and TSH all share the same α subunit. |
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What are the main functions of FSH and LH?
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FSH: gametogenesis (i.e. spermatogenesis in male, folliculogenesis in female)
LH: steroidogenesis |
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How is one neurohormone able to release two gonadotropins with separate secretion profiles?
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The difference is in the pulse frequency.
FAST GnRH pulse frequency favors LH β subunit production while SLOW GnRH pulse frequency favors FSH β subunit production. (Fast for steroids, Slow for sperm) |
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What is responsible for homeostasis in the HPG axis?
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Negative feedback, like everything else.
Fast Negative Feedback: Estradiol and testosterone act on the hypothalamus and pituitary gland to stop release of GnRH and LH/FSH, respectively. Slow Negative Feedback: Inhibin, acts on the pituitary to inhibit FSH release. |
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What is Inhibin? Where is it secreted? What forms of Inhibin do males and females have?
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This is a hormone that controls secretion of FSH (SLOW, negative feedback). It is secreted by the ovaries and testes. Males have Inhibin B; Females have both Inhibin A and B. (KNOW THIS!!!)
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What is the storage site for sperm? What connects the sminiferous tubules to this site?
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Epididymis is storage site. Ejaculatory duct connects seminiferous tubules to epidiymis.
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What is the role of Sertoli cells? Leydig cells? Where are they located? Which ones have LH receptors, which ones have FSH receptors?
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Sertoli → nurture the maturing sperm. [located in the seminiferous tubules in testes] → FSH receptors.
Leydig → produce testosterone and dihydrotestosterone [located in interstitium in testes] → LH receptors. |
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What are the stages of spermatogenesis for least to most differentiated? What is happening in the progression of phases? How long does the entire cycle take?
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Spermatogonium (stem cell) → Primary Spermatocyte → Secondary Spermatocyte → Spermatid → Spermatozoan
Spermatogonia → spermatocyte = mitotic divisions Spermatocyte → spermatids = meiotic divisions Spermatids → spermatozoa = structural changes Cycle takes 64-74 days |
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What of the two hormones produced by the Leydig cells, which one is generally the active form? What enzyme is critical in this process?
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Testosterone is converted to Dihydrotestosterone (the active form) via 5α-reductase. (Like in Middlesex.)
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What produces seminiferous fluid? What it is it for?
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Sertoli cells.
Needed to transfer the spermatozoa from the seminiferous tubules to the epididymis. |
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What four functions do sertoli cells serve?
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1.) Structural scaffolding
2.) Compartmentalization 3.) Paracrine secretion (ex: LACTATE) 4.) Seminiferous fluid (for transport) |
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What paracrine secretion is made by the sertoli cells and needed for sperm production?
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Lactate
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What, specifically, secretes inhibin A in the male? What regulates its secretion?
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Sertoli cells → it’s a way to tell the pituitary gland how successful spermatogenesis is. The more sperm is produced, the more activity in the Sertoli cell, the more Inhibin is secreted, the less FSH is needed to further stimulate the cell. (And the reverse: less sperm = less inhibin = more FSH.)
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What is the role of testosterone on the Sertoli cells?
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Promotes the growth of sertoli cells. Thus, LH has an INDIRECT action in the pituitary control of the testes.
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What would you expect to find in the testes of someone with the following conditions: Hypophysectomy, Delayed puberty with only FSH increase, Delayed puberty with both FSH & LH increase, Damaged testes
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Hypophysectomy: only spermatogonia will be present.
Delayed puberty – only FSH (i.e. beginning of puberty): increase in # Sertoli cells, but no spermatogenesis (b/c no LH → no testosterone). Delayed puberty – both FSH and LH present: Spermatogenesis will take place Damage to testes: Spermatogenesis CAN be restored with testosterone treatment |
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What can cause a delay in puberty?
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High FSH, low LH. Caused by a GnRH pulse generator that is inherently too slow.
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