Anatomy & Physiology

Anatomy & Physiology Study Guide

The Ovarian Cycle Ovarian follicles are specialized structures in the cortex of the ovaries where both oocyte growth and meiosis I occur. Primary oocytes are located in the outer portion of the ovarian cortex in clusters called egg nests. A single squamous layer of follicle cells surrounds each primary oocyte. The primary oocyte and its follicle cells form a primordial follicle. Beginning at puberty, primordial follicles are continuously activated to join other follicles already in development. The activated primordial follicle will either mature and be released as a secondary oocyte or degenerate (atresia). This monthly process is known as the ovarian cycle. The ovarian cycle can be divided into a follicular phase, or preovulatory phase, and a luteal phase, or postovulatory phase. During ovulation , the mature follicle releases the secondary oocyte. The distended follicular wall suddenly ruptures, ejecting the follicular contents, including the secondary oocyte, into the pelvic cavity. The empty tertiary follicle collapses. An endocrine structure known as the corpus luteum (named for its yellow color) forms from the remaining granulosa cells. This process occurs under LH stimulation. The cholesterol contained in the corpus luteum is used tomanufacture steroid hormones known as progestins (progesterone literally means a steroid). Although, moderate amounts of estrogens are also secreted, levels are not as high as they were at ovulation, and progesterone is the principal hormone in the luteal phase. Roughly 12 days after ovulation, the corpus luteum begins to degenerate, unless fertilization occurs. 25.6 The Uterus The uterus provides mechanical protection, nutritional support, and waste removal for the developing embryo (weeks 1–8) and fetus (week nine through delivery). In addition, the muscular wall of the uterus contracts in order to eject the fetus at birth. The uterus covers the superior and posterior surfaces of the urinary bladder. If the uterus bends backward the condition is termed retroflexion . The uterosacral ligaments extend from the lateral surfaces of the uterus to the anterior face of the sacrum. This support prevents the body of the uterus from shifting anteriorly and inferiorly. The cardinal (lateral) ligaments extend from the base of the uterus and vagina to the lateral walls of the pelvis. The uterus can be divided into two anatomical regions: the body and the cervix. The uterine body, or corpus, is the largest portion of the uterus. The body ends at a constriction known as the isthmus of the uterus. The cervix extends from the isthmus to the vagina and is the inferior portion of the uterus. The tubular cervix projects into the vagina. The uterus leads into the cervical canal, a constricted passageway that opens into the uterine cavity. The uterine wall has a thick, outer, muscular myometrium and a thin, inner, endometrium . The glandular and vascular tissues of the endometrium support the physiological demands of the growing fetus.

©2018

Achieve Page 346

of 368