The menstrual cycle includes a critical component known as the ovarian cycle, which undergoes two main phases each month—the follicular phase and the luteal phase. The follicular phase is variable and averaging around 14 days. Ovulation, triggered by a surge in luteinizing hormone (LH), marks the transition between the two phases. The second phase, the luteal phase, is relatively consistent, lasting approximately 14 days, and is marked by the activity of the corpus luteum. While a cycle...

The gonads, namely the testes in males and the ovaries in females, are pivotal in producing gonadal hormones that orchestrate the intricate processes of sexual development and reproduction.
In males, testosterone is the primary gonadal androgen. It plays a central role in the maturation of male reproductive organs — the penis and testes. Additionally, testosterone is instrumental in the development of secondary sexual characteristics — a deep voice as well as facial and pubic hair...

The ovarian cycle is meticulously regulated by the hypothalamic-pituitary-gonadal axis. This cycle orchestrates the release of a mature oocyte, essential for reproduction.
Before puberty, the hypothalamus releases GnRH in a low frequency, low amplitude pulsatile manner. This along with the immature hypothalamic-pituitary-gonadal axis activity, results in low estrogen levels and the absence of a fully functional ovarian cycle.  At puberty, GnRH secretion increases in both frequency and...

The ovarian cycle regulates endometrial changes throughout a single menstrual cycle via the coordinated action of gonadotrophin-releasing hormone (GnRH) and gonadotrophins.
At puberty, GnRH begins a pulsatile release pattern, which triggers the anterior pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The frequency and amplitude of GnRH pulses vary across the menstrual cycle, with faster pulses favoring LH release and slower pulses favoring FSH...

Transcytosis is the process in which molecules are internalized by endocytosis, transported across the cell, and released through exocytosis from the opposite end of the cell. Molecules such as insulin, immunoglobulins, and certain nutrients are transferred through the recycling endosomes by recycling and transcytosis.
IgG molecules from a mother undergo transcytosis starting around 13 weeks of gestation. The amount of IgG transferred and entering the fetal blood circulation increases with...

Regulation of hormone secretion is a finely tuned orchestration driven by various types of stimuli, encompassing neural, humoral, and hormonal signals. Environmental cues instigate neural stimuli, where action potentials traverse nerve fibers to reach their designated targets. An illustrative scenario is the body's response to stress, wherein the sympathetic nervous system releases epinephrine from the adrenal glands, inducing the well-known 'fight or flight' reaction.
Humoral...