Examples of follicle in the following topics:
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- Follicle development signals the beginning of the menstrual cycle.
- At the start of the menstrual cycle, some 12-20 primary follicles begin to develop under the influence of elevated levels of follicle-stimulating hormone (FSH) to form secondary follicles.
- The primary follicles form from primordial follicles, which develop in the ovary as a fetus during conception and are arrested in the prophase state of the cellular cycle.
- The remaining follicle, called the dominant follicle, is responsible for producing large amounts of estrogen during the late follicular phase.
- This causes the secondary follicle to develop into a tertiary follicle, which then leaves the ovary 24–36 hours later.
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- Follicle cells produce the hormone inhibin, which inhibits FSH production.
- As the follicles grow, they begin releasing estrogens and a low level of progesterone.
- The follicles that did not rupture degenerate and their eggs are lost.
- The level of estrogen decreases when the extra follicles degenerate.
- The luteal and secretory phases refer to changes in the ruptured follicle.
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- During the follicular phase, follicle-stimulating hormone (FSH) is secreted by the anterior pituitary gland.
- The rise in FSH levels recruits five to seven tertiary-stage ovarian follicles (also known as Graafian or antral follicles) for entry into the menstrual cycle.
- These follicles compete with each other for dominance.
- This slowdown in LH and FSH production leads to the atresia (death) of most of the recruited follicles, though the dominant follicle continues to mature.
- This in turn causes increased levels of FSH, leading to recruitment of follicles for the next cycle.
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- The rise in FSH recruits tertiary-stage ovarian follicles (antral follicles) for entry into the menstrual cycle.
- Follicle-stimulating hormone induces the proliferation of granulosa cells in the developing follicles and the expression of luteinizing hormone (LH) receptors on these cells.
- Many endocrinologists believe that the estrogen secretion of the dominant follicle lowers the levels of LH and FSH, leading to the atresia (death) of most of the other recruited follicles.
- The ovum then leaves the follicle through the formed stigma.
- Increased levels of FSH start recruiting follicles for the next cycle.
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- Acne, clinically known as acne vulgaris, is a common human skin disease affecting skin with the densest population of sebaceous follicles such as the face, upper parts of the chest, and back.
- Acne develops as a result of blockages in hair follicles.
- Bacteria becomes trapped in these clogged follicles, producing pus and inflammation as the immune system attempts to destroy the bacteria.
- The sebaceous gland produces oily secretions that can block the follicle, resulting in a pimple.
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- The root is part of the
hair enclosed by the hair follicle, which is itself a tube-like involution of
the skin.
- In the deepest portion of
the each hair follicle lies the hair bulb.
- Attached to a hair follicle is a bundle of
muscle fibers.
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- The thyroid gland is made up of many spherical thyroid follicles which are lined with a simple cuboidal epithelium.
- These follicles contain a viscous fluid, called colloid, which stores the glycoprotein thyroglobulin.
- The follicles produce hormones that can be stored in the colloid or released into the surrounding capillary network for transport to the rest of the body via the circulatory system.
- Follicle cells are stimulated to release stored T3 and T4 by thyroid-stimulating hormone (TSH), which is produced by the anterior pituitary.
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- If the pituitary gland is removed, spermatogenesis can still be initiated by follicle-stimulating hormone (FSH) and testosterone.
- Follicle-stimulating hormone (FSH) is released by the anterior pituitary gland.
- Follicle-stimulating hormone stimulates both the production of androgen-binding protein by Sertoli cells and the formation of the blood-testis barrier.
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- Male baldness is the result of genetic sensitivity of hair follicles to dihydrotestosterone that causes hair follicles to atrophy.
- Male pattern baldness is caused by a genetic sensitivity of hair follicles to dihydrotestosterone (DHT).
- 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.
- In time, hair becomes thinner and its overall volume is reduced, resembling fragile vellus hair or "peach fuzz" until, finally, the follicle falls dormant and ceases producing hair completely.
- Recent research suggests that elevated levels of the enzyme prostaglandin D2 synthase and its product prostaglandin D2 (PGD2) in hair follicles contribute to androgenetic alopecia.
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- Chemotherapy causes hair loss by killing cells that divide rapidly, one of the main properties of most cancer cells and hair follicles.
- Chemotherapy also harms cells that divide rapidly under normal circumstances, such as cells in the bone marrow, mouth, nail beds, and hair follicles.