The Menstrual Cycle: Structures

The Structures

Welcome to Part 1 of the Menstrual Cycle Series.

Before delving into the whole cycle, we first need to understand the major players-the physical structures and chemical substances involved.

Brain Structures

• Hypothalamus: The neuro-endocrine highway. Small but mighty, not much bigger than an almond. It's part of the limbic system (instinct, drives, memory, emotions, behavior), releases certain hormones, and regulates essential nervous system functions, including:

  • Hunger

  • Thirst

  • Sleep

  • Body temperature

  • Bonding

  • Attachment

• Pituitary: The endocrine part of the neuro endocrine highway-even smaller than the hypothalamus. Receives messages from the hypothalamus in the form of hormones, which direct it to release its own hormones and chemical messengers to other body structures. Consists of Anterior and Posterior pituitary.

The hypothalamus and the pituitary operate within a complex feedback loop known as the HPO-Axis- The Hypothalamic Pituitary Axis. Conversations between these structures causes the release and/or inhibition of hormones and other chemical compounds.

Reproductive Structures

• Ovaries: Female reproductive glands where eggs are produced, stored, and released. The ovaries are responsible for producing estrogen and progesterone, which influence ovarian follicle growth, ovulation, and uterine lining growth with the assistance of some other hormone messengers.

• Uterus: Female reproductive organ composed of muscle. Houses the fetus during pregnancy. Grows and sheds it's lining, causing menstruation (a "period") if pregnancy does not occur.

To Recap:

Hypothalamus: Director and coordinator, sends messages to the pituitary gland, receives feedback messages.

Pituitary: Receives messages from from Hypothalamus. Receives feedback messages.

Ovaries: Receives messages from the pituitary. Sends feedback messages.

Uterus: Receives messages.

In Part 2, we will go through the main hormones involved in the menstrual cycle. Stay Tuned!

Pictured Below: An illustration of the HPO Axis and sending/receiving of messages between structures.