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During phase three, or orgasm, rhythmic, involuntary contractions of muscles occur in both sexes. In the male, the reproductive accessory glands and tubules constrict placing semen in the urethra, then the urethra contracts expelling the semen through the penis. In women, the uterus and vaginal muscles contract in waves that may last slightly less than a second each. During phase four, or resolution, the processes described in the first three phases reverse themselves and return to their normal state. Men experience a refractory period in which they cannot maintain an erection or ejaculate for a period of time ranging from minutes to hours.

Gametogenesis (spermatogenesis and oogenesis)

Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. During meiosis, two cell divisions separate the paired chromosomes in the nucleus and then separate the chromatids that were made during an earlier stage of the cell’s life cycle. Meiosis produces haploid cells with half of each pair of chromosomes normally found in diploid cells. The production of sperm is called spermatogenesis    and the production of eggs is called oogenesis    .

Spermatogenesis

 Spermatogenesis begins when the 2n spermatogonium undergoes mitosis, producing more spermatagonia. The spermatogonia undergo meiosis I, producing haploid (1n) secondary spermatocytes, and meiosis II, producing spermatids. Differentiation of the spermatids results in mature sperm.
During spermatogenesis, four sperm result from each primary spermatocyte.

Spermatogenesis, illustrated in [link] , occurs in the wall of the seminiferous tubules ( [link] ), with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube. Immediately under the capsule of the tubule are diploid, undifferentiated cells. These stem cells, called spermatogonia (singular: spermatagonium), go through mitosis with one offspring going on to differentiate into a sperm cell and the other giving rise to the next generation of sperm.

Meiosis starts with a cell called a primary spermatocyte. At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte. This cell is haploid and must go through another meiotic cell division. The cell produced at the end of meiosis is called a spermatid and when it reaches the lumen of the tubule and grows a flagellum, it is called a sperm cell. Four sperm result from each primary spermatocyte that goes through meiosis.

Stem cells are deposited during gestation and are present at birth through the beginning of adolescence, but in an inactive state. During adolescence, gonadotropic hormones from the anterior pituitary cause the activation of these cells and the production of viable sperm. This continues into old age.

Visit this site to see the process of spermatogenesis.

Oogenesis

Oogenesis, illustrated in [link] , occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium (plural: oogonia), but this cell undergoes mitosis to increase in number, eventually resulting in up to about one to two million cells in the embryo.

Oogenesis begins when the 2n oogonium undergoes mitosis, producing a primary oocyte. The primary oocytes arrest in prophase I before birth. After puberty, meiosis of one oocyte per menstrual cycle continues, resulting in a 1n secondary oocyte that arrests in metaphase II and a polar body. Upon ovulation and sperm entry, meiosis is completed and fertilization occurs, resulting in a polar body and a fertilized egg.
The process of oogenesis occurs in the ovary’s outermost layer.

The cell starting meiosis is called a primary oocyte, as shown in [link] . This cell will start the first meiotic division and be arrested in its progress in the first prophase stage. At the time of birth, all future eggs are in the prophase stage. At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division. The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell. This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct. If the secondary oocyte is fertilized, the cell continues through the meiosis II, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm.

Egg production begins before birth, is arrested during meiosis until puberty, and then individual cells continue through at each menstrual cycle. One egg is produced from each meiotic process, with the extra chromosomes and chromatids going into polar bodies that degenerate and are reabsorbed by the body.

Section summary

As animals became more complex, specific organs and organ systems developed to support specific functions for the organism. The reproductive structures that evolved in land animals allow males and females to mate, fertilize internally, and support the growth and development of offspring. Processes developed to produce reproductive cells that had exactly half the number of chromosomes of each parent so that new combinations would have the appropriate amount of genetic material. Gametogenesis, the production of sperm (spermatogenesis) and eggs (oogenesis), takes place through the process of meiosis.

[link] Which of the following statements about the male reproductive system is false?

  1. The vas deferens carries sperm from the testes to the penis.
  2. Sperm mature in seminiferous tubules in the testes.
  3. Both the prostate and the bulbourethral glands produce components of the semen.
  4. The prostate gland is located in the testes.

[link] D

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Questions & Answers

what is ecology
volex Reply
ecology is the study of living organisms in interaction to the environment
Mwansa
show the diagram of sponge
Favour Reply
explain the processes found in a carbon cycle
Elvas Reply
photosynthesis;this is the process by which grean plants make there own food by using carbon,oxygen, sunlight in the precess of chlorophyll combusion ;this is the process by which fossil fuels are converted in form of a gas of carbon dioxide by an enzyme called a foillitrrion respiration;a proces
Mwansa
Respiration;this is a process by which living organism release energy from food there eat
Mwansa
decoposition;this process is carried by dead matters or decomposes such as bacteria and fungi where dead matters decay buried for thousand of years excretions the remove of toxic metabolism waste product from the body through excretory or gain such as anus and skin etc
Mwansa
also tarnspiratiom where by a plant losses water inform of water vapour into the at mosphere by rhisombium ezyme
Mwansa
so not enzyme but bacteria
Mwansa
sorry not enzyme but bacteria
Mwansa
what is a base?
Alice Reply
base can be define as the anatomy of structure
Ogundipe
what are somatic cells
KAKU Reply
Somatic cells responsible for making the body
Ahsan
vegetative cells, they divide by mitosis.
Ishitha
what is angiosperms
Papillon Reply
what is the function of bile
Papillon
what is neurologist
Benjamin Reply
A neurologist is a brain doctor,a physician who diagnose and treat all categories of conditions and disease involving the central and peripheral nervous system eg.covering, blood vessels and all effector tissue such as muscle
Favour
what is a cell
God Reply
is a basic unit of living organism
Mwansa
or a basic building blocks of all living things
Mwansa
explain cell biology
Grace Reply
cell biology is a biology branch which study about function,size,definition ,....of cells.
fitsum
what are endotherms
angelina Reply
pls can someone elaborate more on biomagnification
angelina
Hey,what?
Peter
Biomagnification, also known as bioamplification or biological magnification, is any concentration of a toxin, such as pesticides, in the tissues of tolerant organisms at successively higher levels in a food chain.
chance
An endotherm (from Greek ἔνδον endon "within" and θέρμη thermē "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat.
chance
these are substances that absorbs heat energy
Alice
What diffusion
Oseres Reply
it is the movement of water molecules from the region of higher concentretion to a region of lower concentration
Lukas
is the movement of anything from region of higher concentration to a region of lower concentration.
chance
is a movemnt of H2O molecule from a region of higher concentration to the legion of lower Concentration.
Benjamin
diffusion is the movement of particles from a region of higher concentration to a region of lower concentration resulting into an even distribution
Alice
is the movement of water molecules,ions from the region of higher concentration to the region of lower concentration in a semi permeable membrane.
Favour
pls I don't know how to read very well so how can I understand all this
Mercy Reply
But you wrote all this ur self so please continue till you become perfect thanks
Favour
What's succession
Talabi Reply
an acid is a substance that produces hydrogen ions in an aqueous solution
angelina Reply
how? give a reason to support ur answer
SSEJJO
Types of acids and there definitions
SSEJJO
what is acid
asaa Reply
An acid is a substance which gives Hydrogen ions in aqueous solutions.
Ahsan
food poison
asaa
an acid is a chemical substance that produces or gives out hydrogen ions as the only positively charged ion when dissolved in water
Alice
what is salt?
Basit
a sait is a substance formed when hydrogen ions in an acid are partially or fully replaced by a metal or ammonium ions
Alice
When an acid and base react chemically, a salt is form.
Ahsan
what is nervous system
kumkum
nervous system is rensposible of homeostasis
Mwansa
a sait is a compound which tests beta
Mwansa

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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