Reproduction in Animals and Plants

• Two Types of Reproduction

  • Asexual reproduction
  • Sexual reproduction
• Sexual

  • Requires 2 parent organisms
  • Has 2 variations internal (mammals, reptiles, and insects) and external fertilization (fish, amphibians, and some invertebrates).
  • Used by humans, other animals and plants.
• Asexual

  • Requires 1 parent organisms
  • Has 3 types: Binary fission, budding and parthenogenesis
  • Used by yeast, sponges and bacteria.
• Binary Fission and Budding

  
• Parthenogenesis

  • Aka Virgin Birth, the females produces eggs, but these develop into young without ever being fertilized.
  • Occurs in some fishes, several kinds of insects and a few species of lizards.
• Hermaphroditism

  • Refers to organisms that have both male and female reproductive organs. These organs may be fully functional or partially functional. In the animal kingdom, true hermaphroditism is uncommon.
  • Ex: tape worms, liver flukes and Earthworms
• Simultaneous hermaphroditism

  • An individual has both functional male and female sex organs at the same time and can produce sperm and eggs concurrently. This means they can potentially fertilize their own eggs (self-fertilization) or exchange sperm or eggs with other individuals (cross-fertilization).
• Sequential hermaphroditism,

  also known as dichogamy in plants, the individual changes sex at some point in its life cycle.
• Protandry

  • One of the two types of sequential hermaphroditism
  • Refers to changing of the sex of an organism from male to female.
  • Production of mature sperms prior to egg
  • Rare when compared to protogyny
  • Ex: Clownfish, earthworms, ivy, salvia, rosebay and willowherb
• Progyny

  • One on two types of Sequential Hermaphroditism
  • Refers to changing of sex from female to male
  • Production of egg prior to sperms
  • Very Common type of sequential hermaphroditism
  • Ex: Labridae, Pomacanthidae, Apples, fig warts, pears and Schley.
• Variations of Embryonic Development

  Oviparity

  Ovoviviparity

  Viviparity
• 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

  • The HPO axis stands for Hypothalamic-Pituitary-Ovarian Axis.
  • It's a complex communication system in the female body that regulates the menstrual cycle, ovulation, and other reproductive functions.
  • 3 main players are hypothalamus, pituitary gland, and ovaries
• Hypothalamus: This is a region located at the base of the brain that functions as the body's control center. It produces gonadotropin-releasing hormone (GnRH), which plays a key role in regulating the HPO axis
• Pituitary gland: Nicknamed the "master gland", the pituitary gland is located just beneath the hypothalamus. It receives GnRH signals from the hypothalamus and then releases two hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Ovaries: The ovaries are the female reproductive organs that produce eggs and sex hormones, including estrogen and progesterone. These hormones regulate the development of the uterine lining and play a role in preparing the body for pregnancy
• The HPO axis functions through a feedback loop:

  1.The hypothalamus releases gonadotropin-releasing hormone (GnRH)in a pulsatile manner.

  2. GnRH stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

  3. FSH travels through the bloodstream to the ovaries and stimulates the development of follicles, which contain immature eggs. One follicle, called the Graafian follicle, becomes dominant.
• HPO Feedback Loop (Continuation)

  4. The theca interna, a layer within the Graafian follicle, produces androgens. These androgens diffuse into the surrounding granulosa cells of the follicle.

  5. Granulosa cells convert the androgens, with the help of an enzyme called aromatase, into estrogen. Estradiolis the main type of estrogen produced.

  6. Rising estrogen levels from the Graafian follicle trigger a surge in LH release from the pituitary gland.
• HPO Feedback Loop Continuation

  7. The LH surge triggers ovulation, which is the release of the mature egg from the Graafian follicle.

  8. After ovulation, the remaining follicular cells of the Graafian follicle transform into the corpus luteum.

  9. The corpus luteum produces progesterone in preparation for a possible pregnancy.
• HPO Feedback Continuation

  10. Progesterone prepares the uterine lining (endometrium) for implantation and nourishes an early embryo.

  11. If fertilization doesn't occur, progesterone levels drop from the corpus luteum. This drop signals the shedding of the uterine lining, leading to menstruation and the start of a new menstrual cycle.

  12. The corpus luteum, deprived of LH support, degenerates into a scar-like tissue called the corpus albicans.
• The Uterine or Menstrual Cycle

  • Phase 1: Menstruation (Days 1-5)
  • Phase 2: Follicular Phase (Days 6-14)
  • Phase 3: Ovulation (Day 14, approximately)
  • Phase 4: Luteal Phase (Days 15-28)
• Phase 1: Menstruation (Days 1-5)

  • This is the period you likely know best -it's when you experience vaginal bleeding as the lining of your uterus (endometrium) sheds.
  • The shedding is triggered by a drop in progesterone and estrogen levels at the end of the previous cycle.
  • Menstruation typically lasts 3-5 days but can range from 2-8 days.
• Phase 2: Follicular Phase (Days 6-14)

  1.This phase is marked by the growth and development of follicles in your ovaries.

  2. Each follicle contains an immature egg.

  3. Follicle-stimulating hormone (FSH) from the pituitary gland stimulates multiple follicles to begin maturing.

  4. As the follicles grow, they produce increasing amounts of estrogen, particularly estradiol.
• Phase 2: Follicular Phase (Days 6-14)(Continuation)

  5. Estrogen plays a key role in thickening the lining of your uterus (endometrium) in preparation for a possible pregnancy.

  6. It also stimulates the growth of the cervical mucus, making it thinner and more slippery to allow sperm to pass through more easily during ovulation.

  7. Towards the end of this phase, one follicle becomes dominant and continues to grow, while the others stop developing and eventually die off.
• Phase 3: Ovulation (Day 14, approximately)

  • This is the short window (around 24-48 hours) when ovulation occurs.
  • A surge in luteinizing hormone (LH) from the pituitary gland triggers the release of the mature egg from the dominant follicle.
  • The egg travels down the fallopian tube towards the uterus.
  • This is the time during your cycle when you're most fertile and have the highest chance of getting pregnant if you have unprotected sex.
• Phase 4: Luteal Phase (Days 15-28)

  1.The remaining follicular cells left behind after ovulation form the corpus luteum.

  2. The corpus luteum produces progesterone, another essential hormone for pregnancy.

  3. Progesterone further stimulates the growth and thickening of the uterine lining, preparing it to receive a fertilized egg.
• Phase 4: Luteal Phase (Days 15-28)(Continuation)

  4. If fertilization doesn't occur, the corpus luteum starts to degenerate around day 24.

  5. This drop in progesterone levels triggers the shedding of the uterine lining during menstruation, marking the beginning of a new menstrual cycle.
• Menstrual cycle


  Can vary in length from woman to woman and even cycle to cycle for the same woman
• Factors influencing cycle length

  • Stress
  • Illness
  • Medications
  • Exercise
• Ovulation doesn't always occur exactly on day 14
• Ovulation can vary depending on your cycle length
• Premenstrual symptoms (PMS)


  Physical symptoms like cramps, bloating, and breast tenderness during certain phases of the menstrual cycle
• Menstrual cycle regulation


  1. Hypothalamus

  2. Pituitary gland

  3. Ovaries (HPO axis)
• Menopause

  It occurs because of the unresponsiveness of ovarian follicles to stimulation by the FSH, thus, the levels of estrogen remain low despite increased FSH levels.
• Male Reproductive System Regulation

  • Hypothalamus (of the Nervous System)
  • Pituitary Gland (of the Endocrine System)
  • Leydig Cells and Sertoli Cells (in the Testes)
• Hypothalamus (Male Reproductive): This region at the base of the brain acts as the control center, releasing Gonadotropin-Releasing Hormone (GnRH) in a pulsatile manner.
• Pituitary Gland (Male Reproductive): Often referred to as the "master gland," the pituitary gland receives GnRH signals from the hypothalamus. In response, it releases two crucial hormones
• Follicle-Stimulating Hormone (FSH): FSH travels through the bloodstream to the testes, stimulating the production of sperm cells(spermatogenesis).