UNIT 7: REPRODUCTION.-
Introduction.-
Reproduction is essential to ensure the survival of human beings (similar to other species) because new individuals will replace those who die.
Human reproduction is sexual. This means that:
Human beings make special cells for reproduction: gametes or sex cells.
Two individuals with different sex participate: a man and a woman.
Each individual produces a different type of gamete: sperm in men and ovas in women.
Gametes are produced in special organs called gonads. They produce gametes and sex hormones.
The male gonads are testicles and the female gonads are ovaries.
Male and female gametes join together in the fertilization to make the egg cell or zygote.
The new individuals are similar to parents but not identical because they have characteristics of both.
Each individual is defined by two types of sexual characteristic (they are characteristic to distinguish individuals of different sex):
1) The primary sexual characteristics: they are the reproductive organs, the genital organs. We have these characteristics before birth. They are decided by the sexual chromosomes.
2) The secondary sexual characteristics: they are the characteristics that allow us to distinguish men and women without taking into account the reproductive organs. These characteristics appear in puberty when gonads start to release sex hormones.
The male reproductive system.-
Function:
To produce sperm
To transport sperm inside the female reproductive system
To produce male sex hormones: androgens (testosterone)

Anatomy of the male reproductive system:
1) Testicles, the male gonad. They produce sperm and testosterone.
These organs are made up of numerous coiled seminiferous tubules. They contain cells that form sperm and produce male sex hormones.
Testicles are outside the abdominal cavity and they are covered by a fold of skin called the scrotum.
2) Reproductive ducts. They are:
Epididymus: this is where sperm complete their maturation process.
Vas deferens: sperm are stored here.
Urethra: this also belongs to the urinary system. Urine and sperm exit through this but not at the same time.
3) Glands: They secrete substances that mix with sperm to produce semen. They are:
Seminal vesicles: They secrete seminal fluid with glucose, a nutrient in sperm.
Prostate: this secretes prostatii fluid , which contains substances that protect sperm.
Cowper’s glands: they secrete a lubricant, which facilitates penetration.
4) Penis: It is the male copulatory organ. It is made up of erectile tissue called the corpora cavernosa. At the end penis widens to form the glands, which is covered by a fold of skin called the foreskin.
The female reproductive system.-
Functions:
To produce ovas (the female gametes)
To supply an adequate place for fertilization and to feed the new being during gestation.
To produce female sex hormones (oestrogen and progesterone)
Anatomy:
1) The ovaries: they are the female gonads and they are found in the abdominal cavity.
Ovaries produce ovas and female sex hormones.

The external part of each ovary is called the cortex. This contains the ovarium follicles which produce the ovas. The follicles get bigger the closer they are to the surface of the ovary. The biggest, most external ones, the Graafian follicle, contain the ova.
2) Reproductive ducts: These ducts play a role in fertilization and gestation. They are:
Oviducts or Fallopian tubes: They collect the ova released by the ovaries.
Fertilization normally takes place here. They secrete a lubricating fluid which feeds the zygote.
Uterus or womb: Its wall has a thick muscular layer, the myometrium, lined with a mucous membrane called the endometrium. The uterus narrows at the bottom and is connected to the vagina via the uterine neck or cervix. Gestation takes place in the uterus.
Vagina: this elastic tract has glands that secrete lubricants to make it easier for the penis to be inserted. There is a partial membrane (hymen) over the opening to the vagina and it breaks during the first sex relation. Sperm are deposited in the vagina during intercouse.
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Vulva: The woman’s external genital organ. There are folds of skin on either side of the vaginal opening called the labia majora and the labia minora.
Between them is the clitoris, a sensitive organ with erectile tissue similar to the penis. The Bartolin’s glands are found on the labia. These glands produce fluids to libricate the externa genitals.
Gametogenesis.-
It is the process where the gametes are formed. This happens in the gonads. The gametes are formed by germ cells, and the process is different in each gonad.
1) Spermatogenesis:
It is the process of production of sperm.
It takes place in the walls or the semineferous tubules of the testicles.
This process starts in puberty and continues during a man’s entire lifetime, but decreases in intensity with the age.
Sperm are formed from cells called spermatogonic which, like all other human cells have 46 chromosomes.
The process has three stages: a) Growth: the initial cells grow in size and number.

Sperm: b) Meiosis: This is the most important stage, as this is when the number of chromosomes on the cells is halved, so it obtain cells with only 23 chromosomes. c) Maturation: The cells obtained in meiosis transform into sperm. The main changes that happen are: a flagellum is formed that permits the sperm to move, reducing all structures to the minimum.
Sperm are male gametes. They are highly specialised, small, mobile cells made up of three parts:
The head that contain the nucleus with the genetic information of the father and the acrosome, an organelle with enzymes necessary to break the cover of the ovum during the fertilization.
The midpiece: it has a lots of mitochondria that provide the energy required to propel the sperm torward the ovum. It also contains a centriole, which controls the sperm’s movement.
Tail: The flagellum is made of proteins. When it moves it propels the sperm forward.
Sperm determine the sex of the future child. This is because sperm can be one of two types: some have the X chromosome, so after the ovum is fertilized a female embryo develops; other has the Y chromosome, which results in a male embryo. Ova always have the X chromosome.
Ova:
The ovum is a large round cell visible to the naked eye (0’1 mm).
It is immobile, because it doesn’t have any structure form movement.
It contains a reserve food supply (deutoplasm) to feed the embryo for the first few days after fertilization.
In the ovum we can distinguish the following parts:
Nucleus with the genetic information of the woman, with 23 chromosomes like sperm.
Deutoplasm: reserves food
Vitelline membrane: it is similar to the cell membrane.
The ovum is covered by complex protective layers, the zone pellucida and the corona radiate, which contain cells and mucus.

2) Oogenesis:
It is the process to produce the ova. This process happens in the ovaries in two stages:
First stage: it happens before birth.
Second stage: it starts in puberty and continues to menopause. This stage includes the ovarian cycle or female reproductive cycle.
The female reproductive cycle.-
It is a cyclic process that happens in the ovaries and is accompanied by cyclic changes in the mucous membrane of the uterus. For that there are two cycles: the ovarian cycle and the uterine cycle.
This starts in puberty with the first period (menarche) and it ends at menopause, the climacteric phase. It happens approximately every 28 days, an ovum develops, matures and is released each time.
It is a complicated process because:
Changes happen in the ovaries and in the uterus at the same time.
Different hormones take part: FSH(follicle-stimulating hormone), LH
(luteinizing hormone), folliculine and progesterone.
The cycle has three phases:
1) Follicular phase: Lasts around 14 days and is caused by FSH, which is produced by the pituitary gland. FSH stimulates the development of one or several follicles in the ovary at a time, but usually only one of them reaches full maturity.
The wall of the uterus grows and increases the number of capillaries. This happens to prepare the uterus for implantation of an embryo if the ovum is fertilized.
2) Ovulation: The release of an ovum by the ovary as a result of the production of
LH by the pituitary gland.
3) Luteal phase: once the ovum has been released, the corresponding area in the follicle transforms into a mass of cells, the corpus luteum, which produces and secretes progesterone. The progesterone go by the blood to the uterus a d continue its preparation.
When the ovum travel to the Fallopian tube two things can happen: a) The ovum is not fertilized. In this case the corpus luteum decays and stops secreting hormones, and the mucous membrane of the uterus is shed and

expelled from the body via the vagina along with blood from the capillaries.
This is the menstrual phase or period. Now a new cycle stars. b) The ovum is fertilized. In this case the corpus luteum continues to secrete progesterone and the uterine lining is not shed. The fertilizated ovum travels from the Fallopian tube to the uterus where the implantation of the embryo happens. This is the start of the embryonic development.
The emotional and psychological circumstances of the woman influence the ovarian and menstrual cycle a lot. This is because ovulation and menstruation are produced by variations in the hormones secreted by the pituitary gland.
Fertilization.-
It is the process where the sperm and the ovum join together. It takes place inside the female reproductive system, in the Fallopian tube.
When the man, during the coitus, puts semen into the woman’s vagina, this process is called ejaculation.
From the vagina, the sperm go up through the uterus until they reach the Fallopian tubes. If they meet an ovum here, fertilization may take place.
Sperm only live for 5 days after ejaculation, and the ovum, only lives for 48 hours after ovulation. This means that the two gametes must come together during this time.
When the sperm surround the ovum, the acrosome secretes a substance that breaks down its outer membrane.
When the first sperm passes through the ovaris membrane, the nucleus of the two gametes join together, and the zygote or egg cell is formed.
Once fertilized, a barrier forms around the ovum to stop other sperm from getting in.
Gestation.-
Gestation is the period of time between fertilization and labour.
It lasts around 280 days or 9 months.
During gestation, the zygote transforms into an embryo and then a foetus with cells which develop into different tissues and organs.
After the fertilization the zygote moves down the Fallopian tube to the uterus. There, the zygote sticks to the mucous membrane of the uterine wall. This process is know as implantation. After this the embryo grows in the uterus (pregnancy).
During the first few weeks, the bundle of cells developing inside the uterus is called the embryo, and it looks nothing like a baby. When it begins to look like a human body, it is called a foetus.

The embryo, and later the foetus, develops inside a membrane called the amnion, submerged in amniotic fluid.
The embryo receives the nutrition it needs via the placenta, a membrane that develops in the second month of gestation. It is formed from the membranes that surround the embryo (the chorion and other) and cells from the mucous membrane of the uterus. The placenta is the place where the interchange of substances between mother and foetus happens. The foetus in connected to the placenta via the umbilical cord.
Labour and birth.-
The labour starts when the mucous plug is expelled from the uterine neck, and it takes place in three phases:
1) Dilation of the cervix or uterine neck: a series of contractions of the myometrius start which become more and more intense and frequent, pushing the foetus towards the vagina. At the end of this phase, the amnion breaks and the amniotic fluid flows out (the water breaks).
2) Foetal expulsion: The foetus comes out head first. Once it has come out, the umbilical cord is clamped and cut, leaving behind a wound which will heal to form a scar known as the navel or belly button.
3) Delivery of the placenta: after the baby is born, the uterus undergoes further contractions to expel the placenta and the umbilical cord.
In the first few days after the birth, the mother’s mammary glands produce a very nutritions liquid rich in antibodies called calostrum. On the third day, they start to produce milk.
Infertility.-
Infertility refers to the inability to have children using natural methods. It can occur in both men and women, and there are many different causes:
Male infertility: low sperm count, defective sperm, sperm incompatible with vaginal mucous.
Female infertility: no ovulation or problems with ovulation, Fallopian tube obstruction, uterine abnormalities which make it difficult for the zygote to implant.
Assisted reproductive techniques.-
They are techniques used to help people who have fertility problems to have children.
The main techniques are: stimulation of ovulation, artificial insemination, in vitro fertilization, etc.

Contraceptive methods.-
They are methods used by couples who want to have sex without pregnancy. There are lots of different methods, and each couple must choose the one best for them.
Some of them also prevent the transmission of sexual illness.
The main methods are:
Natural methods of contraception: basal body temperature, billings, symptothermal, coitus interrumptus.
Artificial methods of contraception:
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Barrier methods like male condoms, female condoms, diaphragms and IUDs
(intrauterine devices).
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Chemical methods such as spermicide, hormonal contraceptives, the morning-after pill and the five-day morning after pill.

Surgical methods, like a tubal ligation (women) and vasectomy (men).