Reproductive System and Development

Douglas Todey

FunctionsThe reproductive system has four functions

To produce sperm and egg cellsTransportation and sustenance of cellsDevelopment and nurturing of offspringProduction of hormones

ReproductionSexual Reproduction

Male and female sex cells, produced by meiosis so each cell is genetically different providing for genetic variation in the offspring, combine to create an offspring

Asexual ReproductionThis is when one organism breaks in half and each

half regrows as an exact replica of the originalExamples

Tapeworms Jellyfish Echinoderms

SpermatogenesisThe diploid germinal cells of the seminiferous

tubules produce the spermatidsMultiplication Phase

Germ cells increase their number by undergoing repeated mitotic divisions. As a result of this a large number of cells called sperm

mother cells are formed

Growth PhaseThe formed cells absorb nutrition from the

surrounding cells of germinal epithelium and grow in size These enlarged cells are called spermatocytes

Spermatogenesis, Cont.Maturation Phase

The process of reduction division or meiosis will be completed

The two haploid cells that are formed after meiosis I are called secondary spermatocytes

The two secondary spermatocytes undergo meiosis II to produce four cells which are called spermatids The spermatids do not undergo any further division but

simply undergo metamorphosis to pro duce the sperms At the end of maturation phase, each germinal cell

would have produced four spermatids.

Spermatogenesis, Cont.

OogenesisMultiplication Phase

The primordial germ cells divide repeatedly by means of mitosis to produce a large number of daughter cells, oogonia

They divide several mitotically to produce a large number of primary oocytes

Growth PhaseThe primary oocyte increases in size considerablyThe cytoplasm of the oocyte is very rich in RNA,

DNA, and enzymes and other cytoplasmic organelles like mitochondria, golgi complex and ribosomes are also found in large numbers

Oogenesis, Cont.Maturation Phase

Oocyte undergoes meiosis to produce an egg or ovum

One large haploid egg is formed along with three small polar bodies

The cytoplasm divides unevenly to provide the maximum amount of nutrients for the developing embryo

The polar bodies will eventually ooze out and degenerate while the egg is ready for fertilization

Oogenesis, Cont.

Menstrual and Estrous CyclesMenstrual Cycle

This is a 28-day cycle in women when the egg leaves the ovary and is available to be fertilized

On day 14, ovulation occurs, which is when the egg leaves the ovary

Estrous CycleThe estrous cycle is the period when animals

such as dogs, cattle, or horses are considered “in heat” and should be bred

Females will only allow males to mate during this period to increase the chance of being bred

Menstrual CycleThe menstrual cycle is a 28-32 day cycle found

in both humans and primatesThe ovarian cycle involves the ovulation of the

egg from the ovaries in which a woman then becomes fertile

Hormonal ControlWomen also make estrogen and progesterone hormonesThe synthesis and secretion of estrogens is stimulated by

follicle-stimulating hormone (FSH), which is controlled by the hypothalamic gonadotropin releasing hormone(GnRH)

Secretion of GnRH depends on neurons in the hypothalamus which express a gene encoding a protein of 145 amino acids. From this, several short peptides are cut collectively called kisspeptin. These are secreted and bind to G-protein-coupled receptors on the surface of the GnRH neurons stimulating them to release GnRH. However, high levels of estrogen inhibit the secretion of kisspeptin and suppress further production of those hormones

Development of the EmbryoThe fertilized egg starts dividing in which the cleavage of the

egg determines whether it is a protostome or a deuterostome. This is called the morula

Then the coelom forms in the gastrulation stage. The cells push inward and form a double layered cell wall and the hole created is called the blastopore. This group of cells is called the blastulaFrom the blastopore

Deuterostomes The mouth develops from the blastopore

Protostomes The anus develops from the blastopore

These blastopores are called the gastrula

Germ LayersGerm layers are the concentric layers that form

various tissues and organsEctoderm

Creates the outer covering of the animal Can also make the central nervous system

Endoderm Creates the digestive tract Also makes the liver and lungs

Mesoderm This creates the muscles It also makes most other organs between the outer covering and the digestive tract

InfertilityThis means that a person cannot have a childThe main symptom is the inability to become

pregnantApproximately 9% of women are infertileTreatment includes education and counseling,

fertility treatments, medicines to treat infections and clotting disorders, and medicines that help the woman grow and release eggs from the ovaries

Ovarian CancerThis is cancer that is found in a woman’s

ovariesSymptoms include bloating or swollen belly

area, difficulty eating or feeling full quickly, and pelvic or lower abdominal pain

There will be approximately 22,280 new cases of ovarian cancer in 2012 and 15,500 will die of it

Treatment includes surgery to remove the uterus, both ovaries, or the fallopian tubes

Sources http://www.livestrong.com/article/37137-reproductive-system-functions / http://www.biotopics.co.uk/genes1/asexual_and_sexual_reproduction.html http://

users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AsexualReproduction.html

http://www.preservearticles.com/2012042131003/short-notes-on-the-process-of-spermatogenesis.html

http://www.preservearticles.com/2012042131004/short-notes-on-the-process-of-oogenesis.html

http://www.uwyo.edu/wjm/repro/estrous.htm http://

www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.cfm

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/SexHormones.html

AP Biology Campbell and Reece textbook http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002173 / http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001891 /