Fertilization and Reproduction

• Sexual reproduction in animals involves the fusion of male and female gametes, a process known as fertilization.
• In lower vertebrates, fertilization usually happens outside the female body (external fertilization).
• Internal fertilization occurs inside the female body in some animals and humans.
• Oviparous animals lay eggs because embryonic development happens outside the mother.
• Viviparous animals have embryos that grow inside the mother.
• Fertilization restores the diploid (2n) number of chromosomes, with the zygote developing into an embryo and eventually a young organism.
• Fertilization involves the fusion of a sperm and an ovum, resulting in a diploid (2n) zygote.
• Fertilization can be internal or external.

Internal Fertilization

• Fusion of male and female gametes happens inside the female's body.
• Fewer sperm are released.
• Sperm are deposited inside the female body.
• Only male gametes are released into the female genital tract.
• Development (syngamy) happens inside the body.
• Examples include mammals, reptiles, and birds.
• Offers higher chances of offspring survival due to parental care and successful fertilization rates.
• Survival chances of offspring are higher, even in harsh conditions.
• Fewer offspring are produced.

External Fertilization

• Fusion of male and female gametes take place in the external environment, like water bodies.
• Numerous gametes are released.
• Both male and female release gametes into the external surroundings.
• Development (syngamy) happens outside the body.
• Examples include amphibians, algae, and fish.
• Results in a higher number of offspring.
• There is less competition between offspring and parents.
• There's a lower chance of offspring survival because of no parental care and increased predation.
• Survival rate is low, and can survive only in moist or wet environments.

Human Male Reproductive System

• A complex system that develops and functions under hormonal influence.
• Becomes functional after attaining sexual maturity around ages 13-14.
• Includes a pair of testes, ducts, accessory glands, and a penis.

Testis

• Oval bodies in a sac called the scrotum, hanging from the lower abdominal wall.
• Sperm development requires a temperature 2-3°C lower than normal body temperature, hence testes are outside the body.
• They produce sperm and testosterone, a male sex hormone.
• Testosterone promotes the development of accessory glands and secondary sexual characteristics.

Epididymis

• Mass of coiled tubules alongside the testes that stores sperm and makes them motile.
• Its lining produces chemicals essential for sperm maturation.

Vas Deferens

• Muscular tube that carries sperm from the epididymis.
• Joins with secretions from the seminal vesicle and urethra to form the ejaculatory duct.
• Seminal vesicles secrete a viscous fluid that is expelled along with the sperm, and semen is a mixture of this fluid and sperm.

Prostate Gland

• Lies below the bladder and discharges alkaline secretions directly into the urethra.
• These secretions make up 15-30% of the semen volume.
• Also secretes mucus during ejaculation to neutralize vaginal acidity, enhancing sperm motility.

Cowper's Gland

• Paired glands attached to the urethra below the prostate gland.
• Secretions make sperm motile, nourish them, and neutralize the acidic vaginal environment.

Penis

• The external male genital organ.

Seminal Vesicles

• Located at the base of the urinary bladder and secrete mucus and a watery alkaline fluid.
• The fluid contains nutrients like fructose, the energy source for sperm.
• Each seminal vesicle empties its contents into the ejaculatory duct, adding to the semen volume.

Female Reproductive System

• Includes a pair of Ovaries, Oviduct (Fallopian tube), a Uterus and the Vagina.

Ovaries

• Almond-shaped bodies on each side of the abdominal cavity.
• Produce ova and the female hormones estrogen and progesterone,.
• An ovary releases one ovum every 28 days (one menstrual cycle).

Oviduct (Fallopian Tube)

• Expanded, funnel-shaped near each ovary.
• Narrow tubes opening into the uterus with walls lined with cilia, that sweep the ovum towards the uterus.
• An ovum is released from one of the ovaries every four weeks and takes three days to travel down the oviduct to the uterus.
• Fertilization happens in the upper end of the fallopian tubes if sperm are present.
• An unfertilized ovum is discharged during the next menstrual flow.

Uterus

• A large, thick-walled, pear-shaped muscular organ connected to the fallopian tubes.
• The lower constricted part is called the cervix.
• The body of the uterus has three layers including the endometrium.
• The endometrium is glandular, containing blood vessels and uterine glands.
• The cervix is a sphincter muscle, that closes the uterine cavity and prevents foreign particles from entering.

Vagina

• A large muscular tube from the uterus to the outside.
• It receives sperm from the penis and serves as a birth canal.

Menstrual Cycle

• A cycle of events in female reproductive organs (ovary and uterus) controlled by sex hormones, occurring every approximately 28 days.
• Marked by bleeding or menstrual flow, also called menstrual cycle.
• Menstruation occurs in humans and primates which is shedding of the inner lining of the uterus along with disintegrated ova, bleeds through the vagina of adult females.
• Beginning of menstruation, or "menarche," typically occurs between ages 11-13.
• Menstrual flow stops at around age 50, know as menopause.
• The cycle of events from one menstruation to the next is called the Menstrual Cycle.
• Menstruation repeats about every 28/29 days in human females.
• One ovum is released (ovulation) mid-cycle.
• Ovulation is caused by LH.
• It is regulated by hormones (LH, FSH) secreted by the pituitary gland.
• Pituitary gland hormones influence the ovaries.
• Ovarian hormones (oestrogen, progesterone) repair or shed the uterus walls.

Phases of Menstrual Cycle

Menstrual Phase

• Occurs on cycle days 3-5 in a 28-day cycle.
• LH production from the anterior pituitary lobe is reduced.
• Degeneration of the corpus luteum due to the withdrawal of hormones, therefore progesterone production is reduced.
• Oestrogen production is also reduced.
• The endometrium of the uterus breaks down initiating menstruation.
• Cells of the endometrium secretions, blood, and unfertilized ovum make up menstrual flow.

Follicular Phase

• Usually includes cycle days 6-13 or 14 in a 28-day cycle.
• The anterior pituitary gland secretes Follicle stimulating hormone (FSH).
• Oestrogen stimulates the proliferation of the endometrium of the uterine wall.
• The endometrium thickens by rapid cell multiplication, accompanied by an increase in uterine glands and blood vessels.

Ovulatory Phase

• Both LH & FSH attain a peak level in the middle of cycle (about the 14th day).
• Oestrogen concentration in blood increases.
• Rapid secretion of LH induces rupturing of graffian follicle and thereby the release of ovum, also known as ovulation.

Luteal Phase

• Includes cycle days 15 to 28
• Post-ovulation phase determine the fate of the corpus luteum
• Corpus luteum secretes progesterone.
• If fertilization occurs, pregnancy starts, if not, it marks the onset of another cycle.

Sperm

• A typical human sperm can be divided into the head, mid-piece and tail
• The head contains three structures which includes a haploid nucleus, an acrosome cap and paired centrioles
• The haploid nucleus contains the DNA
• The acrosome cap contains hydrolytic enzymes, that help penetrate the jelly coat of the egg
• The centrioles are needed by a zygote in order to divide.
• The mid-piece contains high numbers of mitochrondria, providing the energy (ATP) to move.
• The tail (flagellum) is composed of a microtubule structure called the axoneme that bends to facilitate movement.

Egg

• An egg cell is surrounded by two layers; the jelly coat and corona radiata.
• The jelly coat acts as a barrier to entry from sperm.
• The corona radiata is an external layer of follicular cells, that support and nourish the egg cell.

Birth Control and Contraception

• Contraception can limit family size by preventing the fertilization of ova.
• Preventing fertilization results in birth control and is the basis of familiy planning.
• It requires the use of certain methods to prevent fertilization,.

Natural Methods

• Avoiding copulation during ovulation helps to prevent fertilization, also called Rhythm Method.

Mechanical Methods

• Mechanical methods are used to prevent the passage of semen to the fallopian tubes.
• Condoms are worn on on the male penis before intercourse that collects the sperm from entering the vagina.
• Is simple with no side effects.
• Prevent sexually transmitted infections, also known as STDs.
• Diaphragm prevents the entrance of sperms into the cervical canal.
• Inta Uterine Device is made of copper or stainless steel.
• Insertion causes secretion preventing implanatation of an embryo.
• Can be placed for up to 5 years.

Chemical Methods

• Spermicides are spermicidal creams to prevent fertilization.
• Contraceptive pills preven ovulation by containing synthetic hormones resembling oestrogen and progesterone.
• It prevents ovulation also controlling the monthly shedding of the uterine lining.

Surgical Methods

• A portion of the sperm duct cut ends are then tied preventing them from passing.
• This is a surgical procedure known as a vasectomy.
• In women, fallopian tubes are cut (tubectomy) preventing ova down the fallopian tube.

STI's

• Sexually transmitted infections are spread through sexual contact.
• Some sexually transmitted infections are;
  • AIDS
  • Syphilis
  • Gonorrhea

AIDS

• Is caused by the HIV virus.

Transmission

• Passed one person to another during sexual intercourse.
• Transmitted from blood, sharing needles and through an cut or scratch.
• Weakens the immune system making it uncurable.

Gonorrhea

• Is caused by the bacteria, Nisseria gonorrhea.
• Can be treated with antibiotics.
• Inflammation of the mucous membrane of the urogenital tract.

Syphilis

• Is caused by the bacteria, Treponema pallidum.
• Is a chronic illness.
• Cured with antibiotics.
• Effects the mucous membrane of the genital.