Science Q3

• The menstrual cycle is controlled by female sex hormones and includes the ovarian and uterine cycle
• Puberty in females is marked by the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) by the pituitary gland
• The menstrual cycle prepares a woman for pregnancy through hormonal changes initiated by the pituitary gland
• The typical menstrual cycle is about 28 days long, involving changes in both the ovary and the uterus
• At the start of the ovarian cycle, the pituitary gland secretes FSH, allowing an ovarian follicle to mature and estrogen to be secreted
• Luteinizing hormone (LH) and FSH bring about the maturation of the follicle, leading to ovulation on the 14th day of the cycle
• During ovulation, the egg is released and is ready for fertilization within 24 hours
• The ruptured follicle develops into the corpus luteum, producing estrogen and progesterone to prepare the uterine wall for a possible implantation
• The rise in estrogen and progesterone levels inhibits the secretion of LH and FSH, leading to the degeneration of the corpus luteum
• In the uterine cycle, low levels of progesterone cause the endometrium to disintegrate, leading to menstruation
• After menstruation, the endometrium builds up due to increasing estrogen levels, leading to the proliferative phase of the uterine cycle
• The secretory phase of the uterine cycle involves the formation of the corpus luteum, secretion of progesterone, and preparation of the endometrium for a developing embryo
• The uterine cycle may be interrupted by stress, health concerns, or pregnancy, but if pregnancy doesn't occur, the cycle begins anew
• Menarche is the first menstrual discharge of blood from the vagina, marking the onset of puberty in females
• Oocytes that were unripe or untouched become active during menarche, initiating cyclic changes in the ovary
• The human ovaries usually produce only one egg during a 28-day cycle, controlled by FSH (Follicle-Stimulating Hormone) from the pituitary gland
• FSH stimulates follicle maturation and estrogen production, leading to the formation of a fluid-filled follicle containing estrogen when the egg reaches maturity
• The corpus luteum, formed after ovulation, produces progesterone which maintains the growth of the mucus lining of the uterus and causes effects on secondary characteristics like breast enlargement
• Important female hormones:

  • Estrogen: responsible for secondary female characteristics, thickens endometrium, inhibits facial hair growth
  • Progesterone: stimulates endometrium, inhibits uterine contractions and ovulation
  • LH (Luteinizing Hormone): develops and maintains the corpus luteum, stimulates ovulation
  • FSH: stimulates the formation of follicles in the ovaries
• Menstrual cramps are caused by the strong contractions of the uterine wall before and during menstruation, often due to the excessive secretion of prostaglandins
• The menstrual cycle involves:

  1. Pituitary gland releasing hormones for egg maturation

  2. Ovary releasing estrogen and egg on day 14

  3. Egg moving to the uterus, which thickens

  4. If no fertilization, thickened uterus breaks apart, leading to menstruation

  5. Cycle restarts after menstruation
• Feedback mechanism in the menstrual cycle:

  • Negative feedback affects hormone production
  • High estrogen levels inhibit FSH production
  • Estrogen stimulates LH release, controlling progesterone production
  • High progesterone levels inhibit further LH release
• A zygote or fertilized egg is formed when a sperm successfully penetrates the egg's nucleus, and a fertilization membrane develops to prevent other sperms from further penetration
• Fertilization occurs while the egg is traveling along the oviduct or fallopian tube, taking about 7 to 10 days for the egg to reach the uterus
• Implantation is when the fertilized egg attaches itself to the wall of the uterus, remaining there for nine months as it develops into a baby
• Ectopic pregnancy occurs if implantation happens anywhere other than the uterine cavity, with the most common site being the fallopian tube, which can be fatal and cause rupture
• Ovulation refers to the release of a mature egg from the ovary, usually on the 14th day of a 28-day cycle from the first day of menstruation
• Implantation happens before the end of the first week, where the zygote attaches to the uterine lining and develops into an embryonic disc
• Birth or Parturition takes place about 39 weeks after fertilization, starting with uterine contractions and ending with the newborn's delivery and placenta expulsion
• The male reproductive system includes the testes, scrotum, penis, vas deferens, urethra, and glands like the seminal vesicle, prostate gland, and Cowper’s gland
• The scrotum holds the testes, which produce sperm cells, requiring a slightly lower temperature than the human body
• The epididymis is a tightly coiled series of tubules where sperm cells mature
• The vas deferens carries sperm from the testes to the urethra, emerging from the epididymis and ascending along the posterior side of the testes
• The ejaculatory duct connects to the prostate gland and ends by joining the urethra within the prostate gland
• The urethra is a pathway for both urine and male reproductive fluids, but they do not exit the urethra at the same time
• The penis functions in the transfer of sperm cells from the male to the female vagina, composed of erectile tissues that enlarge during erection
• The seminal vesicles, prostate gland, and Cowper’s gland contribute fluids to the traveling sperm cells, forming semen
• Testosterone, the main male sex hormone secreted by the testis, is responsible for the normal development of male reproductive organs and secondary male characteristics
• True or False statements about the male reproductive system:

  • A. True: In cold temperatures, the scrotum becomes firm and wrinkled, reducing its overall size
  • B. False: The penis is composed of epithelial tissues and engorgement of erectile tissue with blood causes it to enlarge and become firm
  • A. True: The vas deferens emerges from the epididymis and ascends along the posterior side of the testes to become associated with blood vessels and nerves
  • A. True: Testosterone brings about the changes experienced during puberty in males
  • A. True: The ejaculatory duct extends into the prostate gland and ends by joining the urethra within the prostate gland
  • A. True: The urethra is a pathway for both urine and male reproductive fluids
  • A. True: A man’s testes produce sperm cells which are ejected through ducts during ejaculation
  • A. True: Each testis contains two to three highly coiled tubes, the seminiferous tubules, where sperms develop

  
• • A. True: The sperm cells continue to mature along the epididymis