Animal Reproduction and STIs

ANIMAL REPRODUCTION

Female Reproductive Organs

• Ovary: Produces ova (female gametes) that mature and develop when hormones are released.

• Oviduct: Connects the ovary to the uterus; lined with ciliated cells to push the ovum down; fertilization occurs here.

• Uterus: Muscular bag with a soft lining where the fertilized egg (zygote) implants to develop into a fetus.

• Cervix: Ring of muscle at the lower end of the uterus to keep the developing fetus in place during pregnancy.

• Vagina: Muscular tube leading inside the woman's body, where the male's penis enters during sexual intercourse, and sperm are deposited.

Male Reproductive Organs

• Testis: Contained within the scrotum, produces sperm (male gamete) and testosterone hormone.

• Scrotum: Sac supporting the testes outside the body to maintain sperm at a temperature slightly lower than body temperature.

• Prostate Gland: Produces fluid called semen, providing sperm cells with nutrients.

• Sperm Duct: Transports sperm to be mixed with fluids from glands before entering the urethra for ejaculation.

• Urethra: Tube running down the center of the penis, carrying urine or semen; a ring of muscle prevents urine and semen from mixing.

• Penis: Passes urine out of the body and allows semen to pass into the vagina during sexual intercourse.

Sperm Cells

• Streamlined Shape: Reduces resistance as they swim through fluids.

• Flagellum (Tail): Enables movement, propelling the sperm toward the egg.

• Acrosome: Contains enzymes to break down the outer layers of the egg, facilitating entry.

• Mitochondria: Supply energy for movement, helping the sperm travel long distances.

• Condensed Nucleus: Contains densely packed DNA for efficient delivery of genetic material.

• Receptors: Help navigate chemical signals from the egg, guiding them to their target.

Egg Cells

• Large Size: Contains plenty of cytoplasm to support early embryonic development.

• Nutrient-Rich Cytoplasm: Packed with nutrients and organelles to nourish the fertilized egg.

• Egg Jelly: Layer of fats and proteins surrounding the egg cell to prevent multiple sperms from fusing with the egg cell.

• Haploid Nucleus: Contains half the genetic material (23 chromosomes in humans).

• Receptive Membrane: Designed to bind with a sperm cell and facilitate the merging of genetic material.

Why Are Sex Cells Haploid?

• Fertilization: Sperm cell and egg cell fuse to form a diploid zygote; diploid gametes would result in excessive chromosome count.

• Genetic Diversity: Haploid cells formed through meiosis, a process that shuffles genetic material, leading to genetic diversity.

Importance of Meiosis in Making Gametes

• Reduction of Chromosome Number: Meiosis reduces the chromosome number by half, creating haploid gametes to produces sex cells.

• Introduction of Genetic Variation:

  • Crossing Over: Parental chromosomes exchange genetic material, creating new combinations of genes.

• Prevention of Chromosome Abnormalities: Meiosis ensures each gamete receives the correct number of chromosomes.

  • Errors can lead to conditions like Down syndrome (extra chromosome 21).

Fertilization Process

• Multiple sperm swim toward the egg, attracted by chemical signals released by the egg.

• When a sperm contacts the egg jelly, the acrosome releases enzymes.

• These enzymes digest the egg jelly, allowing the sperm to reach the egg's surface.

• The sperm and egg membranes fuse, and the sperm's nucleus enters the egg.

• The egg undergoes changes to prevent additional sperm from penetrating.

• The haploid nucleus of the sperm combines with the haploid nucleus of the egg, forming a diploid zygote.

Implantation

• The fertilized egg (zygote) forms after the fusion of the sperm and egg nuclei, creating a diploid cell.

• The zygote undergoes multiple rounds of mitosis, forming a ball of cells called a embryo.

• The embryo travels down the fallopian tube toward the uterus, aided by cilia and muscular contractions.

• Upon reaching the uterus, the embryo (or blastocyst) embeds itself into the thick, nutrient-rich lining of the uterus (endometrium).

• This step is crucial for establishing a connection between the embryo and the mother's blood supply.

• After implantation, the placenta begins to develop, facilitating nutrient and oxygen exchange while removing waste products.

• The implanted embryo continues to grow and differentiate into various tissues and organs.

The Placenta

• Forms early in pregnancy when the fertilized egg implants into the uterine wall.

• Structure:

  • A disc-shaped organ, rich in blood vessels, contains chorionic villi.

  • Fetal side: Connected to the fetus via the umbilical cord.

  • Maternal side: Attached to the uterine wall.

• Functions:

  • Exchange of Materials: Transfers oxygen and nutrients (glucose, amino acids) from the mother’s blood to the fetus; Removes waste products.

  • Barrier: Acts as a selective barrier to prevent certain harmful substances from reaching the fetus.

  • Hormonal Support: Produces hormones (HCG, progesterone, estrogen) to maintain pregnancy.

  • Immune Protection: Transports maternal antibodies to provide passive immunity to the fetus.

Amniotic Sac

• Formation: Begins forming in the second week of pregnancy.

  • Consists of two membranes:

    • Amnion: The inner layer enclosing the amniotic fluid.

    • Chorion: The outer layer, which also contributes to placenta formation.

• Structure:

  • A thin, tough, and elastic sac filled with amniotic fluid.

• Functions:

  • Protection: Cushions the fetus against physical shocks and trauma.

  • Temperature Regulation: Maintains a consistent temperature around the fetus.

  • Movement: Allows the fetus to move freely, promoting muscular and skeletal development.

  • Prevention of Adhesion: Prevents the fetus from sticking to the amniotic sac walls.

  • Support for Lung Development: Facilitates fetal breathing movements and lung development.

Umbilical Cord

• Structure Composition:

  • Contains two arteries and one vein, surrounded by Wharton's jelly.

  • Arteries carry deoxygenated blood and waste products from the fetus to the placenta.

  • Vein carries oxygenated blood and nutrients from the placenta to the fetus.

  • Protection: Wharton's jelly protects the blood vessels, preventing compression.

• Function:

  • Transport of Nutrients and Oxygen: The umbilical vein delivers oxygen and essential nutrients from the mother to the fetus for growth and development.

  • Removal of Waste: The umbilical arteries carry waste products from the fetus to the placenta for elimination through the mother's blood.

  • Connection to the Placenta: Facilitates the exchange of gases, nutrients, and waste via the placenta.

The Menstrual Cycle

• Definition: Recurring series of events in the female reproductive system, controlled by hormones, that prepares the body for potential pregnancy.

• Purpose:

  • To mature and release an egg (ovum) for possible fertilization.

  • To prepare the uterine lining for implantation of a fertilized egg.

  • To reset the cycle if fertilization does not occur.

Process of The Menstrual Cycle

• Pituitary Gland releases FSH which stimulates the development of follicles in the ovaries.

• One matures into the Graafian follicle, which contains the egg and secretes estrogen to rebuild the uterine lining.

• A surge in LH, triggers ovulation, the follicle ruptures and releases the mature egg.

• Estrogen levels peak just before ovulation, contributing to the LH surge.

• The ruptured Graafian follicle becomes the corpus luteum which secretes progesterone and small amounts of estrogen to maintains the uterine lining (thickened), preparing it for implantation.

• If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone and estrogen levels, which causes the uterine lining to break down, menstruation occurs, and the cycle restarts.

Stages of The Menstrual Cycle

• DAY 1-5: Menstruation as estrogen and progesterone levels plummet

• DAY 6-14 : Follicular development

• DAY 14: Ovulation

• DAY 20-28: Progesterone and estrogen maintain the uterine lining

Sexually Transmitted Infections (HIV)

• HIV (Human Immunodeficiency Virus): Attacks the immune system, specifically targeting T-Lymphocytes.

  • These cells are essential for defending the body against infections, weakening the immune system over time.

• HIV and AIDS:

  • HIV: The virus that causes the infection.

  • AIDS (Acquired Immunodeficiency Syndrome): If HIV is not treated, it can progress to AIDS, where the immune system is too weak to fight off diseases.

• How is HIV Transmitted?

  • Unprotected Sexual Contact: Direct contact with infected blood, semen, or vaginal fluids during intercourse.

  • Blood Contact: Sharing needles or syringes or receiving contaminated blood products.

  • Mother-to-Child Transmission: During pregnancy, childbirth, or breastfeeding.

Preventions or Treatments

• Safe Practices: Use condoms during sexual activity. Avoid sharing needles or syringes. Avoid multiple sexual partners

• Testing and Treatment: Regular HIV testing. Antiretroviral therapy (ART) for those diagnosed with HIV to suppress the virus and prevent transmission. Protect Yourself and Others!