Reproductive System Animals and Plants

• Asexual reproduction


  Has 3 types: binary fission, budding, and parthenogenesis (a female produces offspring from an unfertilized egg)

  
• Sexual reproduction


  Has 2 variations: internal (mammals, reptiles, and insects) and external fertilization (fish, amphibians, and some invertebrates)
• Hermaphroditism


  Organisms that have both male and female reproductive organs, which may be fully or partially functional

  
• Hermaphroditic organisms


  • Tapeworms and liver flukes (capable of self-fertilization)
  • Earthworms (incapable of self-fertilization)
• Simultaneous hermaphroditism


  An individual has both functional male and female sex organs at the same time and can produce sperm and eggs concurrently
• Sequential hermaphroditism


  The individual changes sex at some point in its life cycle, including protandry and protogyny

  
• Variations of embryonic development

  • Oviparity (eggs are fertilized internally and are deposited outside, e.g., all birds)
  • Ovoviviparity (fertilized eggs are retained inside the mother to complete development, but the embryo obtains nourishment from the yolk, e.g., bony fishes)
  • Viviparity (the young develops inside the mother and obtains nourishment directly from the blood through the umbilical cord, e.g., all mammals except monotremes)

  
• HPO axis


  Hypothalamic-Pituitary-Ovarian Axis, a complex communication system in the female body that regulates the menstrual cycle, ovulation, and other reproductive functions

  
• Hypothalamus


  A region located at the base of the brain that functions as the body's control center, producing gonadotropin-releasing hormone (GnRH) to regulate the HPO axis
• Pituitary gland


  The "master gland" located just beneath the hypothalamus, receiving GnRH signals and releasing follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Ovaries


  The female reproductive organs that produce eggs and sex hormones, including estrogen and progesterone, which regulate the development of the uterine lining and prepare the body for pregnancy

  
• Regulation of the female reproductive system

  1. Hypothalamus releases GnRH

  2. GnRH stimulates pituitary gland to release FSH and LH

  3. FSH stimulates follicle development in ovaries

  4. Follicles produce estrogen

  5. Estrogen triggers LH surge

  6. LH surge causes ovulation

  7. Corpus luteum produces progesterone

  8. Progesterone prepares uterine lining

  9. If no fertilization, progesterone drops, leading to menstruation

  
• Phases of the uterine/menstrual cycle

  • Menstruation (Days 1-5)
  • Follicular Phase (Days 6-14)
  • Ovulation (Day 14, approximately)
  • Luteal Phase (Days 15-28)

  
• Menopause


  Occurs due to the unresponsiveness of ovarian follicles to stimulation by FSH, leading to low estrogen levels despite increased FSH
• Hypothalamus (in male reproductive system regulation)

  Acts as the control center, releasing Gonadotropin-Releasing Hormone (GnRH) in a pulsatile manner
• Pituitary Gland (in male reproductive system regulation)


  Receives GnRH signals from the hypothalamus and releases Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH)
• Leydig Cells


  Located in the testes, they are the target of LH and are responsible for producing testosterone
• Sertoli Cells


  Found within the seminiferous tubules, they nurture developing sperm cells and are influenced by both FSH and testosterone
• GnRH (Gonadotropin-Releasing Hormone)


  Produced by the hypothalamus, it stimulates the pituitary gland to release FSH and LH
• FSH (Follicle-Stimulating Hormone)


  Released by the pituitary gland, it travels to the testes and stimulates the Sertoli cells to support sperm cell development (spermatogenesis)
• LH (Luteinizing Hormone)


  Released by the pituitary gland, it targets the Leydig cells in the testes, prompting them to produce testosterone
• Testosterone


  The primary male sex hormone, it promotes sperm production, supports the development of male secondary sexual characteristics, contributes to bone health and red blood cell production, and influences sex drive
• Feedback loop in the male reproductive system

  1. Low testosterone levels increase GnRH production

  2. Increased GnRH stimulates pituitary to release more FSH and LH

  3. FSH and LH stimulate sperm and testosterone production

  4. Rising testosterone levels inhibit the hypothalamus and pituitary gland
• Inhibin, a hormone produced by Sertoli cells, also plays a role in regulating FSH production
• The male reproductive system matures during puberty, and testosterone levels typically peak in early adulthood, gradually declining with age
• Males should have at least 20 million sperm per mL to be considered fertile
• Reproductive system operates through a negative feedback loop


  1. Testosterone levels low

  2. Hypothalamus increases GnRH production

  3. Increased GnRH stimulates pituitary gland to release more FSH and LH

  4. FSH stimulates sperm production, LH stimulates testosterone production

  5. As testosterone levels rise, they send inhibitory signal back to hypothalamus and pituitary gland

  6. Feedback loop ensures hormone levels are maintained within healthy range
• Inhibin


  Hormone produced by Sertoli cells, plays role in regulating FSH production
• Sperm production is high

  Inhibin levels rise, providing another layer of control
• Male reproductive system


  • Matures during puberty, testosterone levels typically peak in early adulthood, gradually declining with age
• Males should have at least 20 million sperm per mL to be considered fertile, at least 75% of sperm must be alive, and at least 25% should be swimming with rapid forward movement
• Sperm head


  Oval-shaped front part containing genetic material, houses nucleus with tightly packed chromosomes, acrosome covering head contains enzymes to help penetrate egg

  
• Sperm midpiece


  Connecting head to tail, powerhouse containing numerous mitochondria that convert oxygen and nutrients into ATP to fuel sperm's swimming
• Sperm tail


  Long, whip-like structure that propels sperm forward with undulating movements to navigate female reproductive tract
• Contraceptive methods


  • Combined Oral Contraceptive Pill
  • Progestin-Only Pill
  • IUD
  • Implant
  • Patch
  • Vaginal Ring
  • Spermicide
  • Withdrawal
  • Barriers/condoms
  • Diaphragm & Cervical Cap
  • Sterilization
• Typical use success rate

  Ranges from 72% to 99% depending on method
• Perfect use success rate

  Ranges from 78% to 99.90% depending on method
• Mammalian development - first 4 stages

  1. Fertilization

  2. Cleavage

  3. Gastrulation

  4. Organogenesis

  
• Pregnancy in humans usually lasts 9 months or 38 to 42 weeks
• At 8 weeks fetal heartbeat can be heard, at 19 weeks mother can feel baby's movements, at 28 weeks lungs can perform gas exchange, at 30 weeks progressive growth and organ development