Female Reproductive System

Female Reproductive System

• Ovaries produce estrogen, progesterone, and ova (eggs), which are female gametes
• The oviduct is a narrow tube that transports eggs from the ovary to the uterus
  • Cilia (hair-like structures) in the oviduct propel the egg towards the uterus
  • Fertilization occurs in the oviduct
• The uterus, also known as the womb, is a hollow, muscular, pear-shaped organ where a fetus develops during pregnancy
  • It has elastic muscles that can stretch to accommodate the growing fetus
  • The endometrium is the inner lining of the uterus, is rich in blood vessels, and nourishes the fetus
• The cervix consists of muscular rings that are located at the end of the uterus, next to the vagina
  • During pregnancy, it is closed with thick mucus to prevent pathogen entry to the fetus, and prevent premature expulsion
• The vagina is an elastic, muscular tube that connects the cervix to the exterior of the body
  • It’s also known as the birth canal
  • Elastic muscles allow the fetus to pass during childbirth
• The vulva is the external opening of the vagina and the urethra

Male Reproductive System

• Testes produce sperm and testosterone (male sex hormone)
• The epididymis is where sperm matures and develops motility
  • Mature sperm is stored here until ejaculation
• The sperm duct/Vas Deferens is a long tube that transports sperm from the testes to the urethra
• The seminal vesicle secretes an alkaline fluid that provides nutrients such as glucose to nourish sperm, and mucus to protect sperm
• The prostate gland secretes an alkaline fluid to neutralize vaginal acids, which is necessary for sperm viability
• Cowper's gland produces a clear mucus to clear the system before ejaculation
• Secretions from the prostate gland, seminal vesicle, and Cowper’s gland collectively form semen
• The urethra carries sperm/semen out of the body via the penis, and also conveys urine
• The penis consists of erectile tissues that transfer sperm into the female reproductive system during sexual intercourse

Fertilization

• Fertilization is the fusion of the nucleus of a sperm (male gamete) and an egg cell (female gamete)
• Each gamete has half the number of chromosomes; the resulting zygote has the full set (46 in human body cells)
• Fertilization is important because:
  • It causes genetic variation, which is advantageous for adaptation
  • It restores the diploid number of chromosomes

Sperm Cell Structure and Adaptations

• Sperm cells are made in the testes by meiosis
• Adaptations:
  • The head contains genetic information and enzymes to penetrate the egg membrane
  • The middle piece has many mitochondria to provide energy
  • A flagellum (tail) propels the cell

Egg Cell Structure

• Cells in the ovary divide by meiosis to produce haploid egg cells
• The egg contains a large cytoplasm to store nutrients for the developing zygote after fertilization

Stages in Sexual Reproduction

• There are four stages:
  • Production of gametes (sperm and egg cells)
  • Transfer of sperm to the female gamete, which, in humans, occurs via sexual intercourse where sperm in semen are deposited into the woman's vagina
  • Fertilization
  • Development of the zygote into a new individual

Fertilization Process

• During fertilization, the sperm releases enzymes from the acrosome in its head to digest the egg membrane and penetrate it
  • The sperm nucleus then fuses with the egg nucleus to form a zygote
  • A fertilization membrane forms to prevent additional sperm from entering
• The zygote divides by mitosis to form a ball of cells called a blastocyst
• The blastocyst is pushed by cilia to the uterus, where it attaches to the endometrium
  • At this point, it is called an embryo
  • This process of attachment is called implantation
• The embryo develops a placenta, where it attaches to the uterus
• After two months, the embryo is called a fetus

Placenta

• The placenta’s functions include:
  • Transporting water, glucose, amino acids, vitamins, fatty acids, and mineral salts from the mother to the fetus
  • Transporting oxygen, hormones, and antibodies from the mother to the fetus
  • Transporting excess water, carbon dioxide, and urea from the fetus to the mother
  • Secreting progesterone to maintain pregnancy
  • Anchoring the fetus in the uterus
  • Preventing the entry of harmful substances like alcohol and harmful drugs from the mother

Umbilical Cord and Amnion

• Substances pass to and from the fetus through the umbilical cord
• The amnion, a membrane, encloses the fetus, and it secretes amniotic fluid with 2 main functions:
  • To protect the embryo from sudden movements and bumps
  • The fluid mainly consists of water, which prevents the embryo from drying

Gestation and Placental Blood Exchange

• The gestation period in humans is 38-40 weeks, after which the fetus sends a hormonal signal to the mother to initiate childbirth
• The placenta connects to the mother through the umbilical cord, which contains arteries and veins
  • The placenta has blood capillaries with fetal blood in the walls of the uterus
  • The placental wall separates the mother's blood from the fetus's blood
• The mother's blood does not mix with the fetus's blood because:
  • The mother's pressure being too high may damage the fetus's delicate blood vessels
  • If the blood groups differ, agglutination may occur, potentially causing death

Umbilical Blood Vessels

• The umbilical artery carries deoxygenated blood and waste substances (like urea) from the fetus to the placenta
• The umbilical vein carries oxygenated blood and soluble nutrients (glucose, amino acids) from the placenta to the fetus

Placental Adaptations for Diffusion

• Exchange of substances occurs by diffusion across the membranes separating maternal and fetal blood
• Adaptations of the placenta for efficient exchange:
  • Numerous villi increase surface area for diffusion
  • Numerous blood capillaries increase the diffusion gradient
  • Very thin walls to reduce diffusion distance

Childbirth stages

• Dilation, delivery, afterbirth
• Dilation of the Cervix
  • The cervix widens to allow the baby to pass through
  • Strong uterine contractions cause the amnion to rupture, releasing amniotic fluid ("breaking of waters")
• Delivery of the Baby
  • Strong uterine contractions push the baby’s head through the cervix and vagina to the outside
• Delivery of Afterbirth
  • The uterus continues to contract and expel the placenta, along with the surrounding membrane (afterbirth)

Hormones Controlling Reproduction

• At birth, the sex of a baby is determined by its sex organs (primary sex characteristics)
• Humans become sexually mature during their teens, in a process that is called seconday sexual characteristics
• These events are triggered by hormones released from the pituitary gland (follicle stimulating hormone and luteinizing hormone)
• In boys
  • FSH stimulates sperm production
  • LH stimulates the testes to produce testosterone
  • Testosterone controls secondary sexual characteristics
    • These include; growth of the penis and testes, growth of facial and body hair, muscle development, and deepening of the voice
• In girls, pituitary hormones control the release of estrogen from the ovaries
  • Estrogen drives female secondary sexual characteristics
    • These include; breast development, widening of hips, and the beginning of menstruation

Secondary Sexual Characteristics During Puberty

Menstrual cycle

• The menstruation cycle is a periodic discharge of blood and tissue from the uterus in females
• It occurs in 3 stages: Maturation, Ovulation, and Menstruation
• Four hormones control this cycle
  • FSH, estrogen, LH, and progesterone

Function of the Menstrual Cycle

• One function of the cycle is to control the development of the lining of the uterus so that if the egg is fertilized, the lining will be ready to receive it Menstruation
  • The first day of menstruation is usually called day 1
  • Just after menstruation the pituitary gland releases FSH (follicle stimulating hormone) which performs the following
    • Stimulates the growth of the graafian follicle. An ovum matures inside a follicle
    • Stimulates the ovaries to release oestrogen
  • Oestrogen
    • Repairs the endometrium wall which is destroyed during menstruation
    • Slows down production of FSH
    • Increased level of oestrogen in the blood stimulates the pituitary gland to secrete luteinisng hormone
  • LH
    • Stimulates the graafian follicle to mature
    • Stimulates the graafian follicle to release an ovum into the oviduct. Called ovulation
• After the egg travels to the oviduct, fertilization may occur if sexual intercourse has taken place
• The graafian follicle then changes into a yellow body which starts to secrete the hormone progesterone
  • Progesterone - Thickens and maintains the uterus lining, preparing the uterus for implantation - It prevents the release of FSH and LH and stops ovulation
• If the egg is not fertilized corpus luteum breaks down and stops making progesterone, hence menstruation starts
• If the egg is fertilized, the corpus luteum continues making progesterone, the uterus lining is not shed, and menstruation does not occur
  • Later during pregnancy the placenta secretes progesterone