follicular phase

Examples of follicular phase in the following topics:

• Ovarian Cycle

  • The menstrual cycle is the scientific term for the physiological changes that occur in fertile women for the purpose of sexual reproduction.The menstrual cycle is controlled by the endocrine system and commonly divided into three phases: the follicular phase, ovulation, and the luteal phase.
  • However, some sources define these phases as menstruation, proliferative phase, and secretory phase.
  • The follicular phase (or proliferative phase) is the phase of the menstrual cycle in humans and great apes during which follicles in the ovary mature, ending with ovulation.
  • During the follicular phase, follicle-stimulating hormone (FSH) is secreted by the anterior pituitary gland.
  • FSH levels begin to rise in the last few days of the previous menstrual cycle and peak during the first week of the follicular phase.

• Hormonal Regulation of the Female Reproductive Cycle

  • The menstrual cycle is divided into three stages: follicular phase, ovulation, and the luteal phase.
  • During the follicular phase (or proliferative phase), follicles in the ovary mature under the control of estradiol.
  • Levels of FSH peak during the first week of the follicular phase.
  • Throughout the entire follicular phase, rising estrogen levels in the blood stimulate growth of the endometrium and myometrium of the uterus.
  • This also causes endometrial cells to produce receptors for progesterone, which helps prime the endometrium to the late proliferative phase and the luteal phase.

• Oogenesis

  • The remaining follicle, called the dominant follicle, is responsible for producing large amounts of estrogen during the late follicular phase.

• Female Hormones

  • The first half of the ovarian cycle is the follicular phase.
  • After about five days, estrogen levels rise and the menstrual cycle enters the proliferative phase.
  • Following ovulation, the ovarian cycle enters its luteal phase and the menstrual cycle enters its secretory phase, both of which run from about day 15 to 28.
  • The luteal and secretory phases refer to changes in the ruptured follicle.
  • The pattern of activation and inhibition of these hormones varies between phases of the reproductive cycle.

• Premenstrual Syndrome and Premenstrual Dysphoric Disorder

  • While most women of child-bearing age (up to 85%) report having experienced physical symptoms related to normal ovulatory function, such as bloating or breast tenderness, medical definitions of PMS are limited to a consistent pattern of emotional and physical symptoms occurring only during the luteal phase of the menstrual cycle that are of sufficient severity to interfere with some aspects of life.
  • It is a diagnosis associated primarily with the luteal phase of the menstrual cycle.
  • Up to one-third of women diagnosed with premenstrual dysphoric disorder (PMDD) report residual symptoms into the first two or three days of the follicular phase.
  • Symptoms begin in the late luteal phase of the menstrual cycle (after ovulation) and end shortly after menstruation begins.

• Uterine (Menstrual) Cycle

  • The levels of estrogen gradually rise, signalling the start of the follicular, or proliferation, phase of the menstrual cycle.
  • Follicular development may start but not be completed although estrogen will still stimulate the uterine lining.

• Hair and Hormones

  • In genetically-prone scalps, i.e. those experiencing male or female pattern baldness, DHT initiates a process of follicular miniaturization in which the hair follicle begins to deteriorate.
  • As a consequence, the hair's growth phase (anagen) is shortened and young, unpigmented vellus hair is prevented from growing and maturing into the deeply-rooted and pigmented terminal hair that makes up 90 percent of the hair on our heads.

• Formation, Storage, and Release of Thyroid Hormones

  • Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and regulated by thyroid-stimulating hormone (TSH).
  • The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are produced from thyroid follicular cells within the thyroid gland, a process regulated by the thyroid-stimulating hormone secreted by the anterior pituitary gland.
  • Thyroglobulin, the pre-cursor of T4 and T3, is produced by the thyroid follicular cells before being secreted and stored in the follicular lumen.

• Hormonal Methods

  • They inhibit follicular development and prevent ovulation as their primary mechanism of action.
  • Decreased levels of FSH inhibit follicular development, preventing an increase in estrogenl levels.
  • Inhibition of follicular development and the absence of a LH surge prevent ovulation.
  • Estrogen negative feedback on the anterior pituitary greatly decreases the release of FSH, which inhibits follicular development and helps prevent ovulation.
  • High dose progesterone only contraceptives, such as the injectables Depo-Provera and Noristerat, completely inhibit follicular development and ovulation.

• Interpreting Phase Diagrams

  • The lines that separate these single phase regions are known as phase boundaries.
  • By focusing attention on distinct single phase regions, phase diagrams help us to understand the range over which a particular pure sample of matter exists as a particular phase.
  • When evaluating the phase diagram, it is worth noting that the solid-liquid phase boundary in the phase diagram of most substances has a positive slope.
  • With a knowledge of the major components of phase diagrams and the features of phase plots, a phase diagram can be used to understand how altering thermodynamic parameters influences the states/phases of matter a sample of a substance is in.
  • A typical phase diagram illustrating the major components of a phase diagram as well as the critical point.