Gametogenesis and Its Processes

Gametogenesis

• The process of producing gametes (sperm and eggs).
• Involves meiosis: cell division that halves the number of chromosomes in a cell

Spermatogenesis

• Process of producing sperm cells in the testes.
• Occurs in seminiferous tubules.
• Four sperm cells are produced from one spermatogonium.
• Proceeds from spermatogonium to primary spermatocyte to secondary spermatocyte to spermatid to spermatozoon.

Oogenesis

• Process of producing egg cells in the ovaries.
• Begins before birth and is completed after fertilization.
• One egg cell is produced from one oogonium.
• Proceeds from oogonium to primary oocyte to secondary oocyte to ovum.

Spermatogenesis vs Oogenesis

• Spermatogenesis produces a large number of sperm cells continuously from puberty, while oogenesis produces a limited number of egg cells, with one mature egg released each month.
• Spermatogenesis results in four functional gametes, whereas oogenesis results in just one functional gamete.
• Oogenesis pauses for years during development while spermatogenesis is continuous from puberty.

Number of Gametes

• Spermatogenesis produces millions of sperm cells every day.
• Oogenesis produces a limited number of egg cells, with one mature egg released each month.

Reproductive Tissue

• Testes: male reproductive organs that produce sperm and testosterone.
• Ovaries: female reproductive organs that produce eggs and hormones like estrogen and progesterone.

Reproductive Tissue - Seminiferous Tubule

• Found in the testes.
• Sites of spermatogenesis.
• Contain developing sperm cells.
• Have Sertoli cells that nourish and support sperm cells.
• Have Leydig cells that produce testosterone.

Reproductive Tissue - Ovary

• Contains follicles filled with developing egg cells (oocytes).
• Releases one egg each month during ovulation.
• Secretes hormones such as estrogen and progesterone.

Cross Section / Spermatogenesis

• Shows various stages of sperm development.
• Stages include spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa.

Cross Section / Oogenesis

• Shows different stages of egg development.
• Stages include oogonia, primary oocytes, secondary oocytes, and ova.

Cross Sections

• Show the progressive morphological changes in gametes during development.
• Help to understand the processes of spermatogenesis and oogenesis.

Semen Production

• Occurs in the seminiferous tubules and is a mixture of sperm and fluids.
• Seminal vesicles produce a viscous fluid rich in fructose and prostaglandins.
• Prostate gland produces a milky fluid containing citric acid and enzymes.
• Bulbourethral glands secrete a clear, alkaline mucus that lubricates the urethra.

Semen Production - Structures

• Seminiferous Tubules: Site of sperm production.
• Epididymis: Stores and matures sperm.
• Vas deferens: Carries sperm to the urethra.
• Seminal Vesicles: Produce a fluid rich in nutrients and prostaglandins.
• Prostate Gland: Produces an alkaline fluid that neutralizes vaginal acidity.
• Bulbourethral Glands: Secrete mucus to lubricate the urethra.

Male Sex Hormones

• Testosterone: Produced by Leydig cells in the testes.
• Promotes development of male secondary sexual characteristics.
• Stimulates spermatogenesis.
• Follicle stimulating hormone (FSH): Produced by the pituitary gland.
• Stimulates Sertoli cells to produce proteins needed for sperm development.
• Luteinizing hormone (LH): Produced by the pituitary gland.
• Stimulates Leydig cells to produce testosterone.

Egg & Sperm

• Sperm: Specialized, motile cells that have a head, midpiece, and tail.
• Head: Contains the nucleus with genetic material.
• Midpiece: Contains mitochondria, which provide energy for movement.
• Tail: Enables movement towards the egg.
• Egg: Large, non-motile cell with a nucleus containing genetic material.
• Contains cytoplasm rich in nutrients.
• Has a protective layer called the zona pellucida.

Human Fertilization

• Occurs in the fallopian tube when a sperm fertilizes an egg.
• Only one sperm can fertilize an egg.

Human Fertilization

• Acrosome reaction: Digestive enzymes from the sperm head break down the zona pellucida.
• Cortical reaction: Release of enzymes from the egg that prevents other sperm from entering.
• Zygote: The fusion of the egg and sperm nuclei forms a single cell, called the zygote.

Capacitation

• The process by which the sperm becomes capable of fertilizing an egg.
• Occurs as the sperm travels through the female reproductive tract.
• Changes in the sperm include changes in its membrane, increased mobility, and a modification of the acrosome.

Acrosome Reaction

• Occurs when the sperm contacts the egg's zona pellucida.
• The acrosome releases enzymes that digest a pathway for the sperm.
• Enables the sperm to penetrate the zona pellucida and reach the egg plasma membrane.

Cortical Reaction

• Occurs after the sperm enters the egg.
• Release of enzymes from the egg that alter the zona pellucida.
• Prevents other sperm from entering the egg.
• Prevents polyspermy (fertilization by more than one sperm).

Embryo Development

• Cleavage: Series of rapid cell divisions without significant growth.
• Morula: Solid ball of cells.
• Blastocyst: Hollow ball of cells with an inner cell mass and a trophoblast.

Embryo Development

• Inner cell mass: Gives rise to the embryo.
• Trophoblast: Contributes to the formation of the placenta.
• Implantation: Attachment of the blastocyst to the lining of the uterus.

Implantation of Blastocyst

• Occurs in the endometrium (lining of the uterus).
• The trophoblast secretes enzymes that digest the endometrium and help anchor the blastocyst.
• The trophoblast gives rise to the placenta.

Implantation

• Trophoblast: Outer layer of the blastocyst that interacts with the maternal endometrium.
• Endometrium: Lining of the uterus that provides nourishment to the developing embryo.

hCG

• Human Chorionic Gonadotropin.
• Hormone secreted by the trophoblast after implantation.
• Maintains the corpus luteum and its production of progesterone.
• Detected in pregnancy tests.

hCG

• Corpus luteum: Endocrine structure that produces progesterone until the placenta takes over.
• Progesterone: Hormone that maintains the pregnancy by supporting the endometrium and preventing menstruation.

Role of hCG and progesterone in early pregnancy

• After implantation, hCG is secreted by the trophoblast and maintains the corpus luteum's progesterone production.
• Progesterone is crucial for maintaining the endometrium and prevents menstruation.
• As the placenta develops, it takes over the role of producing progesterone.

Placenta

• Organ that develops from the trophoblast and the endometrium.

Structure of the Placenta

• Chorionic villi: Finger-like projections that extend from the chorion (derived from the trophoblast).
• Maternal blood spaces: Areas within the placenta where maternal blood circulates.
• Fetal blood vessels: Located within the chorionic villi, carry fetal blood.

Placenta

• Enables exchange of nutrients, oxygen, and waste products between the mother and fetus.
• Produces hormones like progesterone, estrogen, and human placental lactogen (hPL).

Placenta - Material Exchange

• Oxygen and nutrients: Diffuse from maternal blood to fetal blood.
• Carbon dioxide and waste products: Diffuse from fetal blood to maternal blood.

Placenta - Hormonal Role

• Progesterone: Maintains pregnancy.
• Estrogen: Promotes uterine growth and development of mammary glands.
• Human placental lactogen (hPL): Prepares the mammary glands for lactation.

Birth Process

• Labor: Series of contractions that expel the fetus from the uterus.
• Starts with the release of oxytocin from the posterior pituitary gland.
• Oxytocin stimulates more contractions and dilation of the cervix.
• The placenta is expelled after the baby.

Birth Process

• Cervical dilation: Widening of the cervix.
• Effacement: Thinning of the cervix.
• Expulsion: Delivery of the baby.
• Placental delivery: Expulsion of the placenta.

Birth Process - Hormonal Control

• Oxytocin: Stimulates uterine contractions.
• Prostaglandins: Promote cervical dilation and contractions.
• Relaxin: Relaxes pelvic ligaments and soften the cervix.

Birth Process - Hormonal Control

• Estrogen: Increases oxytocin receptors in the uterus, increasing the sensitivity to oxytocin.
• Progesterone: Levels decrease, allowing uterine contractions to begin.
• Relaxin: Relaxes pelvic ligaments and the cervix, facilitating the passage of the baby.

Explore the fascinating processes of gametogenesis, including spermatogenesis and oogenesis. This quiz covers the stages of gamete formation in both males and females, highlighting differences and similarities. Test your knowledge about the production of sperm and egg cells.