Reproduction and Development Flashcards
Asexual reproduction
Asexual reproduction is a mode of reproduction where offspring are produced from a single parent without the involvement of gametes (sex cells) or fertilization. Key characteristics of asexual reproduction include:
Single Parent: Offspring are genetically identical to the parent organism, as they are produced from mitotic division of the parent’s cells.
No Genetic Variation: Since offspring inherit all of their genetic material from a single parent, there is no genetic variation among offspring.
Various Mechanisms: Asexual reproduction can occur through various mechanisms, including binary fission, budding, fragmentation, and parthenogenesis.
Sexual reproduction
Sexual reproduction is a mode of reproduction where offspring are produced by the fusion of gametes (sex cells) from two parent organisms. Key components of sexual reproduction include:
Gametes: Specialized reproductive cells produced by each parent. In males, the gametes are called sperm, while in females, they are called eggs (or ova). Gametes are haploid, containing half the number of chromosomes as somatic cells.
Fertilization: The process by which a sperm cell fuses with an egg cell to form a zygote. Fertilization typically occurs in the female reproductive tract, such as the fallopian tubes in humans.
Sperm: Male gametes produced in the testes. Sperm are motile cells with a tail that allows them to swim toward the egg for fertilization. They contain genetic material (DNA) that combines with the DNA of the egg to form a zygote.
Egg (Ovum): Female gametes produced in the ovaries. Eggs are larger than sperm and contain stored nutrients to support early embryonic development. Once fertilized by a sperm, the egg initiates the process of embryogenesis.
Zygote: The single-celled organism formed by the fusion of sperm and egg during fertilization. The zygote contains a complete set of chromosomes, half from the sperm and half from the egg. It undergoes rapid cell division (cleavage) to form an embryo.
Sexual reproduction allows for genetic variation among offspring, which promotes evolutionary adaptability and diversity within populations. It is the primary mode of reproduction in most animals and many plants.
Male reproductive anatomy
Penis: transfers sperm to egg during coitus. It contains erectile tissues that consist of modified veins and capillaries that can fill with blood and cause erections.
The penis consists of a shaft that that supports a highly sensitive glans (head).
Prepuce: also known as foreskin covers the glans.
Testes: the male gonads, located outside the abdominal cavity in a sac called the scrotum. A testis and a scrotum togheter are called a testicle.
Vas deferens: the sperm leave the epididymis and travel through the duct (vas deferens)
Prostate gland: nourishes and protects sperm.
Urethra: each vas deferens empties into the urethra. (pee hole and ejaculation hole).
Female reproductive anatomy
Vulva: outer features of the female reproductive system collectively known as vulva.
Vagina: birth canal, opens to the outside behind the opening of the urethra. The labia majora protects the entire genital region and the labia minora borders the openings.
Hymen: partly covers the vaginal openinguntil coitus.
Clitoris: engorges with bloodand becomes erect when horny.
short shaft supporting rounded glans or head covered by small hood of skin called prepuce.
Ovaries: female gonads, the site of gamete production. consisting of a bumpy surface.
Follicles: bumps on the surface of the ovaries. consists of a single developing egg surrounded by cells that protect and nourish it.
Ovalation: one follicle mature and eject an immature egg cell.
Corpus luteum: after ovulation, what remains of the follicles grows and forms a solid mass an thats corpus luteum.
Oviduct: The released egg enters an oviduct (fallopian tube), where cillia sweep it toward the uterus.
If the egg is not fertilized it will shed during menstruation. If it is then fertillization takes place on the upper part of the oviduct.
Uterus: site of pregnancy.
Endometrium: the uterus has a thick muscular wall lined with a blood rich layer of tissue.
Embryo: stage in development from the first divisionof the zygote until body structures begin to appear, about the ninth week.
Fetus: developing human (from ninth week).
Cervix: the narrow neck at the bottom of the uterus.
Gametogenesis
The production of gametes is called gametogenisis. Human gametes (sperm and eggs) are haploid cells with 23 chromosomes that develop by meiosis from diploid cells with 46 chromosomes.
Spermatogenesis
The formation of sperm cells is called spermatogenesis. Sperm develops inside the testes in coiled tubes called the seminferous tubules.
Spermatogonia: Diploid stem cells divide by mitosis to form primary spermatocytes.
Primary Spermatocytes: Undergo the first meiotic division to produce secondary spermatocytes.
Secondary Spermatocytes: Undergo the second meiotic division to form spermatids.
Spermatids: Differentiate and mature into spermatozoa (sperm cells).
Hormonal Regulation: Controlled by hormones such as testosterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH).
Oogenesis
Occurs in the ovarian follicles within the ovaries. Oocyte=female gametocyte or germ cell involved in reproduction.
Oogonia: Diploid stem cells divide by mitosis to form primary oocytes before birth.
Primary Oocytes: Begin meiosis I but are arrested in prophase I until puberty.
Secondary Oocytes: At puberty, during each menstrual cycle, a primary oocyte completes meiosis I to form a secondary oocyte and a polar body; the secondary oocyte is arrested in metaphase II until fertilization.
Ovum: If fertilization occurs, the secondary oocyte completes meiosis II, forming an ovum and another polar body.
Hormonal Regulation: Controlled by hormones such as estrogen, follicle-stimulating hormone (FSH), and luteinizing hormone (LH).
Gamete formation in males vs females
Location: testes in the male and ovaries in the female.
Frequency:
Males = new sperm everyday from pubery til old age.
Females: create primary oocytes only during their fetal development.
Amount:
During spermatogenisis four gametes result from each diploid parent.
During oogenesis only one gamete from each parent cell.
Appearance:
Sperm are small, move by whiplike flagellum and contain few nutritions.
Eggs are large, not self-propelled, contain lots of nutrients.
Female Reproductive Cycle
The regular, cyclic changes in the female reproductive system that prepare the body for potential pregnancy.
Phases:
Menstrual Phase: Shedding of the uterine lining (endometrium); lasts about 3-7 days.
Follicular Phase: The pituitary gland secretes FSH, stimulating the growth of ovarian follicles; one follicle matures and secretes estrogen, causing the endometrium to thicken.
Ovulation: A surge in LH triggers the release of a mature egg from the ovary; occurs around day 14 of a 28-day cycle.
Luteal Phase: The ruptured follicle forms the corpus luteum, which secretes progesterone and estrogen to further thicken the endometrium; if fertilization does not occur, the corpus luteum degenerates, leading to a drop in hormone levels and the start of menstruation.
Hormonal Regulation:
-FSH (Follicle-Stimulating Hormone): Stimulates follicle growth.
-LH (Luteinizing Hormone): Triggers ovulation.
-Estrogen: Promotes the growth and maintenance of the endometrium.
-Progesterone: Stabilizes and prepares the endometrium for possible implantation.
Fertilization by sperm
1) A sperm touches the egg´s jelly coat.
2) The sperm´s acrosomal enzymes digest the jelly coat around the egg.
3) The plasma membranes of the sperm and the egg fuse.
4) The sperm enters the egg cytoplasm.
5) The sperm and the egg chromosomes intermingle.
Embryonic development
The process by which a fertilized egg (zygote) develops into a fully formed embryo, involving multiple stages of cell division, differentiation, and morphogenesis.
Stages:
Fertilization: The union of sperm and egg to form a zygote.
Cleavage: Rapid mitotic cell divisions of the zygote without growth, forming a multicellular structure called a blastula.
Blastulation: Formation of the blastocyst (in mammals), a hollow ball of cells with an inner cell mass that will become the embryo.
Gastrulation: The process by which the blastula reorganizes into a three-layered structure (gastrula) with the primary germ layers: ectoderm, mesoderm, and endoderm.
Organogenesis: The formation and differentiation of organs and tissues from the germ layers.
Germ Layers:
- Ectoderm: Develops into the nervous system, skin, and hair.
- Mesoderm: Forms muscles, bones, blood vessels, and the heart.
- Endoderm: Gives rise to the digestive tract, liver, pancreas, and lungs.
- Implantation: The blastocyst attaches to the uterine wall and embeds into the endometrium, initiating pregnancy.
Pregnancy
1) Ovulation releases secondary oocyte, which enters oviduct.
2) Mature egg (ovum) is fertilized by a sperm, forming a zygote.
3) Cleavage (cell division) of embryo starts.
4) The embryo develops into a blastocyst.
5) The blastocyst implants in the endometrium.
Stem cells
Undifferentiated cells with the remarkable ability to develop into various specialized cell types and self-renew through cell division.
Embryonic Stem Cells (ESCs): Derived from early-stage embryos; pluripotent, capable of developing into any cell type in the body.
Placenta
An organ that develops in the uterus during pregnancy, serving as a connection between the mother and the developing fetus, facilitating nutrient and waste exchange, and producing hormones to support pregnancy.
Umbilical cord
A flexible cord-like structure containing blood vessels that connects the developing fetus to the placenta in the uterus during pregnancy. Serves as a lifeline between the fetus and the placenta, ensuring the exchange of essential substances for fetal growth and development during pregnancy.
