Reproductive Hormone Cycles

Summary

This lecture explores the role of reproductive hormones, focusing on their structure, functions, and regulation by the hypothalamus. Key hormone types include peptide, protein, steroid, and amino acid-derived hormones, with a particular emphasis on steroid hormones like testosterone, estrogen, and progesterone. The lecture delves into how these hormones affect cognition, behavior, and the menstrual cycle. Hormonal feedback loops are also explained, including the processes of ovulation in women and testosterone regulation in men. The impact of oral contraceptives and male contraception are briefly mentioned, setting the stage for further discussion on reproductive hormones and cognition in the next lecture.

Takeaways

• 😀 Peptide and protein hormones, steroid hormones, and amino acid-derived hormones are the three main types of hormones, each with distinct chemical structures and functions.
• 😀 Steroid hormones, synthesized from cholesterol, play a key role in human reproduction, development, aging, and cognitive functions like memory and visual-spatial abilities.
• 😀 Enzymes like 5 alpha reductase and 17 beta HSD are crucial in converting hormones like testosterone into more potent forms, influencing sexual development and reproductive health.
• 😀 Dehydroepiandrosterone (DHEA) is a precursor hormone that can be taken as a supplement but requires specific enzymes to be converted into active steroid hormones like testosterone or estradiol.
• 😀 Progesterone, closely related to cortisol, can have both positive and negative effects on brain function, particularly influencing cognition and memory.
• 😀 Steroid hormones bind to membrane receptors, activating proteins and gene expression, influencing behavior and brain development.
• 😀 The menstrual cycle, driven by hormones like follicle stimulating hormone (FSH) and estradiol, is divided into phases: follicular, peri-ovulatory, luteal, and menstrual, each affecting fertility and mood.
• 😀 The drop in hormone levels at the end of the luteal phase (pre-menstrual phase) is associated with behavioral and mood disruptions such as irritability and depression.
• 😀 Ovulation, the release of an ovum from the ovary, is the time of highest fertility during the menstrual cycle, occurring after a surge in luteinizing hormone (LH) and FSH.
• 😀 The negative feedback loop in the male testosterone cycle involves the hypothalamus, pituitary, and testes, maintaining stable testosterone levels through a feedback mechanism.
• 😀 Testosterone levels in younger men exhibit a diurnal pattern, peaking at night and in the early morning, which can result in nocturnal emissions (nighttime ejaculations).

Q & A

What are the main types of hormones discussed in the lecture?

The main types of hormones discussed are peptide and protein hormones, steroid hormones, and amino acid-derived hormones. Peptide and protein hormones, like insulin, are involved in metabolic functions. Steroid hormones, which include testosterone and estrogen, are crucial for reproduction and cognitive functions. Amino acid-derived hormones, such as epinephrine and thyroxine, have various physiological roles.

How do steroid hormones affect cognition?

Steroid hormones, such as testosterone and estrogen, influence cognition. Testosterone is linked to visual-spatial abilities, while estrogen may have a positive effect on memory. The ongoing research is exploring the extent and mechanisms of these cognitive effects.

What is the role of 5-alpha reductase in the body?

5-alpha reductase is an enzyme that converts testosterone into dihydrotestosterone (DHT), a potent form of testosterone that plays a significant role in male sexual development and functions.

Why is cholesterol important for hormone synthesis?

Cholesterol is the foundational molecule from which steroid hormones, such as testosterone, estrogen, and progesterone, are synthesized. These hormones are critical for reproductive functions and various other physiological processes.

What is the menstrual cycle, and how is it regulated?

The menstrual cycle is a periodic fluctuation of hormone levels that controls fertility in women. It is regulated by the hypothalamus, pituitary gland, and ovaries. Key hormones involved include follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, and progesterone.

What happens during the follicular phase of the menstrual cycle?

During the follicular phase, which occurs after menstruation, FSH stimulates the ovaries to produce follicles. These follicles develop receptors that absorb more FSH and begin producing increasing amounts of estradiol, which prepares the body for ovulation.

How does ovulation occur in the menstrual cycle?

Ovulation occurs when the follicle reaches full maturity, triggered by a peak in estradiol levels. This leads to a spike in luteinizing hormone (LH), which causes the follicle to release an ovum, the potential for fertilization.

What is the function of progesterone during the luteal phase?

During the luteal phase, after ovulation, the remaining follicle transforms into the corpus luteum and starts releasing progesterone. Progesterone prepares the uterus for the implantation of a fertilized egg and inhibits further ovulation by reducing LH levels.

What is the relationship between the hypothalamus, pituitary gland, and testes in male testosterone regulation?

In males, testosterone production is regulated by a negative feedback loop involving the hypothalamus, pituitary gland, and testes. The hypothalamus releases GnRH, which stimulates the pituitary to release LH and FSH. These hormones stimulate the testes to release testosterone. High testosterone levels then inhibit GnRH release, reducing LH and FSH production, which in turn lowers testosterone levels.

How do oral contraceptives affect the menstrual cycle?

Oral contraceptives disrupt the normal hormonal feedback loop by preventing ovulation. They typically contain synthetic versions of estrogen and progesterone, which prevent the release of FSH and LH, thus inhibiting the formation and release of eggs from the ovaries.