ch 27 Flashcards
Mitosis purpose and outcome
- Purpose: Cell division for growth, tissue repair, and asexual reproduction.
- Outcome: Produces two genetically identical diploid daughter cells (same number
Stages of the mitosis
- Prophase: Chromosomes condense, spindle fibers form, and the nuclear envelope breaks down.
- Metaphase: Chromosomes align at the cell’s equatorial plate.
- Anaphase: Sister chromatids separate and move to opposite poles.
- Telophase: Nuclear envelopes reform around each set of chromosomes, which decondense, and the cell begins to divide.
- Cytokinesis: Cytoplasm divides, resulting in two separate cells.
Meiosis purpose and outcome
- Purpose: Production of gametes (sperm and eggs) for sexual reproduction.
- Outcome: Produces four genetically unique haploid cells (half the chromosome number of the original cell).
Stages of the meiosis 1
- Prophase I: Chromosomes pair up in homologous pairs and exchange segments (crossing over), increasing genetic diversity.
- Metaphase I: Homologous chromosome pairs align at the cell equator.
- Anaphase I: Homologous chromosomes (not sister chromatids) are separated to opposite poles.
- Telophase I and Cytokinesis: Two haploid cells form, each with half the number of chromosomes, but each chromosome still consists of two sister chromatids.
Stages of the meiosis 2
- Prophase II: Chromosomes condense again in each haploid cell.
- Metaphase II: Chromosomes align at the equator in both cells.
- Anaphase II: Sister chromatids separate and move to opposite poles.
- Telophase II and Cytokinesis: Results in four genetically unique haploid cells.
Key Differences Between Mitosis and Meiosis
- Chromosome Number: Mitosis maintains the diploid number, while meiosis reduces it to haploid.
- Genetic Variation: Mitosis produces identical cells; meiosis introduces genetic diversity through crossing over and independent assortment.
- Divisions: Mitosis has one division, while meiosis includes two rounds (Meiosis I and Meiosis II).
Oogenesis location
Ovaries in females.
Oogenesis Process:
- Begins before birth: In the fetal stage, oogonia (diploid stem cells) undergo mitosis to form primary oocytes, which begin meiosis I but pause at prophase I.
- After puberty: Each month, one primary oocyte resumes meiosis I in response to hormonal signals. This oocyte divides into two cells—a large secondary oocyte and a smaller first polar body (which typically degenerates).
- Ovulation: The secondary oocyte is released during ovulation. It begins meiosis II but pauses at metaphase II unless fertilization occurs.
- If fertilized: The secondary oocyte completes meiosis II, forming a mature ovum and a second polar body. The mature ovum then combines with sperm to form a zygote.
Spermatogenesis Location
Seminiferous tubules in the testes of males.
Spermatogenesis Process
- Begins at puberty: Spermatogonia (diploid stem cells) divide by mitosis, creating two cell types—Type A cells (maintain the germ line) and Type B cells (develop into sperm).
- Meiosis I: Type B cells (now primary spermatocytes) undergo meiosis I to form two haploid secondary spermatocytes.
- Meiosis II: Each secondary spermatocyte quickly undergoes meiosis II, resulting in four haploid spermatids.
- Spermiogenesis: Spermatids undergo further maturation, developing a flagellum, acrosome (enzyme cap), and losing excess cytoplasm to become fully formed spermatozoa (sperm).
* End Result: Four functional sperm cells per spermatogonium, optimized for mobility and fertilization.
Key Differences of oogenesis and spermatogenesis
- Timing: Oogenesis largely completes in the fetal period with pauses, while spermatogenesis is a continuous process from puberty onward.
- Output: Oogenesis produces one egg with ample cytoplasm per cycle; spermatogenesis produces four motile sperm per cycle.
Gonadotropin-Releasing Hormone (GnRH):
o Secreted by the hypothalamus.
o Stimulates the anterior pituitary gland to release FSH and LH.
Follicle-Stimulating Hormone (FSH):
o Released by the anterior pituitary.
o Stimulates the growth and maturation of ovarian follicles in the ovaries.
o Supports granulosa cells in the follicles to produce estrogen.
Luteinizing Hormone (LH):
o Also released by the anterior pituitary.
o Triggers ovulation by causing the mature follicle to release the secondary oocyte.
o LH surge leads to the formation of the corpus luteum, which produces progesterone.
Estrogen
o Produced by granulosa cells in the follicles.
o Regulates the development of the female reproductive system, secondary sexual characteristics, and helps prepare the endometrium for potential implantation.
o High levels trigger the LH surge.
Progesterone:
o Secreted mainly by the corpus luteum after ovulation.
o Maintains the endometrial lining of the uterus, essential for supporting early pregnancy.
o Inhibits further release of FSH and LH during the luteal phase.
Inhibin
o Secreted by the granulosa cells.
o Inhibits FSH release, preventing the maturation of additional follicles during the cycle.
Testes
o Male gonads located in the scrotum.
o Produce sperm through spermatogenesis and secrete testosterone.
Epididymis
o A coiled duct on the testis where sperm mature and gain motility.
o Stores sperm until ejaculation.
Ductus (Vas) Deferens:
o A tube that transports mature sperm from the epididymis to the ejaculatory duct during ejaculation
Ejaculatory Duct:
o Formed by the union of the ductus deferens and seminal vesicle.
o Passes through the prostate and empties into the urethra.
Urethra
o Carries both urine and semen out of the body through the penis (but never simultaneously).
Penis
o Male copulatory organ.
o Contains erectile tissues (corpora cavernosa and corpus spongiosum) that fill with blood to produce an erection.
Seminal Vesicles:
o Glands that produce a yellowish fluid rich in fructose, which provides energy for sperm and makes up a large portion of semen.
Prostate Gland:
o Surrounds the urethra below the bladder.
o Secretes a milky, slightly acidic fluid that activates sperm and is part of semen.
Bulbourethral (Cowper’s) Glands:
o Produce a clear mucus that lubricates and neutralizes acidic urine in the urethra before ejaculation
Ovaries
o Female gonads that produce oocytes (eggs) and secrete estrogen and progesterone.
o Located in the pelvic cavity.
Uterine (Fallopian) Tubes:
o Extend from the ovaries to the uterus.
o The site of fertilization, where the egg and sperm meet.
o Contains fimbriae (finger-like projections) that help guide the released egg into the tube.
Uterus
o A muscular, hollow organ where a fertilized egg implants and develops into a fetus.
o Composed of three layers: the perimetrium (outer), myometrium (muscular middle), and endometrium (inner lining that sheds during menstruation).
Cervix
o The lower part of the uterus that opens into the vagina.
o Produces mucus that changes consistency during the menstrual cycle to facilitate or inhibit sperm passage.
Vagina
o A muscular canal that connects the cervix to the external body.
o Serves as the birth canal, the exit for menstrual flow, and the female organ of copulation.
- External Genitalia (Vulva):
o Includes structures such as the labia majora and labia minora (protective folds of skin), clitoris (erectile tissue and sensory organ), and vestibule (area surrounding the vaginal and urethral openings).
Mammary Glands
o Present in both males and females but functional only in females.
o Produce milk to nourish the newborn, consisting of lobules containing alveoli that produce milk when stimulated by hormones after childbirth.
Hormones Involved in Ovulation
Gonadotropin-Releasing Hormone (GnRH)
Follicle-Stimulating Hormone
Luteinizing Hormone (LH)
Hormones Regulating Pregnancy
-Progesterone
-Human Chorionic Gonadotropin (hCG):
-Estrogen
Progesterone for pregnacy
o Initially produced by the corpus luteum and later by the placenta.
o Maintains the endometrial lining to support the developing embryo, inhibits uterine contractions, and prepares the uterus for potential implantation.
- Human Chorionic Gonadotropin (hCG):
o Produced by the developing embryo shortly after implantation and later by the placenta.
o Maintains the corpus luteum, ensuring continued progesterone production in early pregnancy.
Hormones Regulating the Menstrual Cycle
- FSH and LH:
- Estrogen
- Progesterone
- FSH and LH:
o FSH promotes follicle growth, and LH is essential for triggering ovulation and the formation of the corpus luteum.
o Fluctuations in FSH and LH levels drive the follicular phase, ovulation, and luteal phase of the menstrual cycle.
Know the three stages of the endometrial cycle
- Menstrual Phase (Days 1–5)
- Proliferative (Pre-Ovulatory) Phase (Days 6–14)
- Secretory (Post-Ovulatory) Phase (Days 15–28)
- Menstrual Phase (Days 1–5)
- What Happens: The functional layer of the endometrium, which built up in the previous cycle, is shed.
- Hormones: Estrogen and progesterone levels are at their lowest, causing the shedding.
- Result: Menstrual bleeding occurs as the endometrial lining is sloughed off.
- Proliferative (Pre-Ovulatory) Phase (Days 6–14)
- What Happens: The endometrium begins to regenerate and thicken.
- Hormones: Rising estrogen levels from the developing ovarian follicles stimulate the growth of the endometrium.
- Result: The endometrium rebuilds, glands enlarge, and spiral arteries proliferate, preparing the uterus for potential implantation. This phase ends with ovulation around day 14.
- Secretory (Post-Ovulatory) Phase (Days 15–28)
- What Happens: The endometrium continues to thicken and becomes more glandular and vascularized to support a fertilized egg if implantation occurs.
- Hormones: Progesterone, produced by the corpus luteum, maintains and further develops the endometrial lining.
- Result: The endometrium is primed for embryo implantation. If fertilization does not occur, progesterone and estrogen levels drop, leading to the breakdown of the endometrium and the start of a new menstrual cycle.
Know the purpose of the corpus luteum
hormone production, support early pregnancy, degeneration in no pregnacy
- Hormone Production:
o After ovulation, the ruptured follicle transforms into the corpus luteum.
o It secretes progesterone and some estrogen.
o Progesterone is crucial for maintaining the thickened endometrial lining, creating a supportive environment for a potential fertilized egg.
- Support for Early Pregnancy:
o If fertilization occurs, the corpus luteum continues to produce progesterone, which sustains the endometrial lining and prevents menstruation.
o This support continues until the placenta develops enough (around the 10th to 12th week of pregnancy) to take over hormone production.
