male reproductive cycle p. 488489 - lushman's...

Unit 2 Review.notebook

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January 18, 2014

Male Reproductive Cycle p. 488489

Testis (plural Testes) Organs which produce the sperm.

Scrotum Sack that contains the testes. It is outside the body to keep the testes 1oC cooler than core body temperature.

Seminiferous tubules Tubes in the testes that produce the sperm.

Epididymis Where sperm mature after being produced and become motile.

Sperm ducts (vas deferens) Where sperm travel when they leave the body during ejaculation.

Cowpers (bulbourethal) gland Gland that produces part of the seminal fluid. It is alkaline (basic) to neutralize the acidic environment of the female reproductive tract.

Seminal vesicle Produce a mucus like secretion that is mixed with the sperm. It contains fructose, which the sperm use as energy as they leave the body.

Prostate Gland that produces part of the seminal fluid. It is alkaline (basic) to neutralize the acidic environment of the female reproductive tract.

Urethra Tube used by urine and semen to leave the body.


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• The male reproductive cycle begins at puberty and continues for the rest of a person’s life.• It is regulated by two negative feedback loops.

• 1. Luteinizing hormone (LH) and testosterone. Puberty is triggered by the hypothalamus, which produces releasing factors that causes the anterior pituitary to release LH.• LH stimulates the cells surrounding the seminiferous tubules to produce the steroid hormone testosterone.


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• Testosterone is responsible for enlarging the primary sexual characteristics (penis and testes) and secondary sex characteristics (facial hair, enlargement of the larynx).

Testosterone also regulates male sexual behaviour, increases muscle development, increases aggression, and increases the rate at which glucose reaches the muscles.


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Male Reproductive Cycle Levels of testosterone are monitored by the

hypothalamus. When it is too low the hypothalamus release more

releasing factors. These releasing factors cause the anterior pituitary

to release more LH, so more testosterone is released. When testosterone is too high, less releasing

factors are released, and testosterone is reduced.


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Male Reproductive Cycle2. Follicle stimulating hormone (FSH) and inhibin.

FSH is produced by the anterior pituitary. FSH stimulates the seminiferous tubules to

produce sperm and inhibin. Inhibin acts on the hypothalamus to reduce

the amount of releasing factors it produces. Fewer releasing factors reduces the amount of

FSH the anterior pituitary produces. Together these two hormones control the rate

of sperm formation.


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Ovary Organ that produces the eggs.

Follicles Groups of cells located in the ovary that contain the cell that will become the egg (oocyte). Normally only one develops each month.

Oviduct (fallopian tube) Tubes that eggs are released into during ovulation. Fertilization occurs here.

Fimbriae Fingerlike projections of the oviduct that rub against the ovary and help with the release of an egg.

Uterus Muscular organ where implantation and development of the embryo and fetus occurs.

Endometrium Lining of the uterus. This thickens and is eventually removed during each menstrual cycle. It becomes part of the placenta during pregnancy.

Cervix Opening of the uterus.

Vagina Where the penis enters the body. Along with the cervix it is considered the birth canal, because fully developed babies leave through here.


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January 18, 2014

Female Reproductive Cycle p.490492

• The female reproductive cycle begins at puberty and continues until menopause.

• During puberty, releasing factors are secreted which trigger the production of reproductive hormones.

• These hormones stimulate the production of secondary sex characteristics (development of breasts, widening of hips, increase in body fat).


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January 18, 2014

Female Reproductive Cycle p.490492 The female reproductive cycle generally follows a 28 day cycle and is called the menstrual cycle.

• The menstrual cycle can be divided into two parts, and also involves negative feedback loops.

• 1. Follicular stage – FSH, released by the anterior pituitary, increases causing follicles (groups of cells that will contain a ovum) to release more estrogen.


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January 18, 2014

Female Reproductive Cycle Estrogen stimulates the endometrium to

thicken in preparation for a possible pregnancy.

Estrogen also inhibits FSH production (negative feedback) and stimulates the hypothalamus to produce releasing factors, causing the anterior pituitary to produce more LH.

Increased LH causes the follicle to release an ovum (around day 14).


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Female Reproductive Cycle2. Luteal Stage

Ovulation marks the start of this stage.

• Once the ovum is released, what remains of the follicle becomes the corpus luteum.

• The corpus luteum secrete progesterone.

• Progesterone inhibits the development of other follicles and LH production.


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Female Reproductive Cycle

• As LH decreases, the corpus luteum degenerates and progesterone levels also drop.

• This ends the luteal stage and menstruation begins.

Menstruation The degeneration of the endometrium, which is shed through the vagina.

http://www.youtube.com/watch?v=sfEwiNqD4zw

http://www.youtube.com/watch?v=sfEwiNqD4zw


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The Causes of Infertility p.500501

• Infertility can be caused by disorders of the female or male reproductive systems.

Female Reproductive Issues:1. Blocked oviducts – If the oviduct is blocked,

sperm can not reach the egg for fertilization.This can be caused by STIs which result in pelvic

inflammatory disease (PID).

2. Failure to ovulate – If an egg is not produced fertilization can not occur.This is generally caused by a hormonal

imbalance, which could be caused by being overweight or underweight.

3. Endometriosis – The endometrium grows outside the uterus. A fertilized egg therefore can not implant.

This is characterized by pain in the abdomen during menstruation.

4. Damaged eggs – The egg may not develop correctly or be damaged, preventing fertilization. This is caused by exposure to chemicals.


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Male Reproductive Issues:

1. Blocked vas deferens or epididymus – If the sperm can not exit the body, fertilization can not

occur.

This could be the result of an STI or varicose

veins in the testicles.

The Causes of Infertility

2. Low sperm count – Sperm count is considered low if there are less than 20 million per ml of ejaculate.The fewer sperm released, the less likely

fertilization is.Causes include: overheated testicles, smoking,

consuming alcohol.

3. Abnormal sperm – If there is an abnormality in the shape of sperm, they are less likely to reach the egg and successfully fertilize.Causes include: overheated testicles, exposure to

toxins, or STIs.


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2. In vitro fertilization (IVF) – When fertilization is done outside the body. Eggs and sperm are collected and fertilization

occurs in a lab and the fertilized egg is implanted into the uterus. This can be used if there is an issue with

either the male or female reproductive system.

3. In vitro maturation (IVM) – Immature oocytes are removed and maturation occurs in the lab. This is followed by IVF. Particularly useful when there are issues with

the female reproductive system.

• Some solutions exist that can increase the chances of successful fertilization.

• These include:

• 1. Artificial insemination (AI) – When sperm is placed in the uterus or cervix using artificial means rather than natural copulation. This is particularly good if the infertility

problem is caused by an issue with the male reproductive system.

Treatment of Infertility p.501

4. Surrogate motherhood – After IVF or IVM, the fertilized egg is placed into a woman who was not the egg donor. Particularly useful when there are issues with

the female reproductive system.

5. Superovulation Using fertility drugs. Drugs are given to a woman who has an issue producing eggs and each ovary makes more eggs.

This can often result in multiple fertilizations and implantations (i.e. twins, triplets, etc.).

6. Embryo storage – Technology exists to store embryos in early stages of development at low temperatures for long periods of time.

An IVF or IVM procedure usually involves the creation of several fertilized eggs. These can be stored so that a person can have

more children in the future. Useful when there are issues with either the

male or female reproductive systems.


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The Journey: Fertilization and Implantation

I. The First Trimester (Weeks 1 to 12, 3 months)

Ovulation & Fertilization (0 7 days)

• During the menstrual cycle, a follicle releases a haploid (n) ovum, it travels down the oviduct.

• If sperm (n) are present, one will fertilize the ovum in the oviduct.

• The fertilized egg is called a zygote (diploid 2n) continues its journey until it reaches the uterus

• The zygotes starts to divide (but not fully) the first divisions of the cell are called cleavage

• Once two cells are formed, it is considered an embryo.

• when the embryo consists of a few cells that form a solid ball, it is called a morula.

Follicle > Ovum > Oviduct > fertilization > Zygote > Cleavage > Division > Embryo > Morula


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Fraternal and Identical Offspring

Fraternal twins: If two eggs were released (one or more from each ovary) then genetically distinct fraternal twins will be produced.

Identical Twins: Sometimes the zygote or morula will split into two groups of cells. This creates genetic clones called identical twins.


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Embryonic Development

Implantation ( ~ 7 days)

the embryo reaches the uterus, cell division has occurred and a hollow ball of cells, called a blastocyst, has formed.

The blastocyst implants itself in the endometrium of the uterus by the end of the first week.

human chronic gonadotrophin (HCG) which prevents the corpus luteum from breaking down.

For three more weeks the corpus luteum produces progesterone which maintains the endometrium and prevents menstruation.


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Gastrulation (week 2)


the cells of the inner cell mass begin to become different (specialize).

the embryo is now called a gastrula.

In the early embryo, cells specialize into three types of tissue called germ layers:

1. Endoderm which will become the digestive tract and internal organs like the lungs.

2. Mesoderm which will become muscles, kidneys, and reproductive organs.

3. Ectoderm which will become the skin and nervous system.


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Neural Development (week 3)

By weeks 8 to 9 the first bone has formed and the embryo is now called a fetus.

By the end of this trimester all the major organs have begun to form and the fetus is about 10cm long.

A hollow tube of ectoderm will become the spinal cord and brain forms.

By week four the limbs, eyes and spine are beginning to form.



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Primary MembranesPrimary membranes are not part of the embryo

help the embryo develop by aiding with: protection, nourishment, and waste removal

1. Chorion Outer covering membrane involved in gas exchange. In humans it becomes part of the placenta.

2. Amnion Contains fluid which the embryo floats in. This provides protection and shock absorption.

3. Allantois Collects waste produced by the embryo. In humans it becomes blood vessels of the umbilical cord.

4. Yolk sac Contains food for the developing embryo. In humans food is provided by the umbilical cord so little yolk is provided.

*Placental mammals, like humans, basically keep their egg inside the body.*

Primary Membranes:


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Process of Childbirth

The Placenta

• The placenta is a blood vessel rich organ that is present only during pregnancy.

• The developing fetus has its own blood cells and that only materials carried by the blood cross the placenta, not the mother’s blood cells.

• The placenta produces the hormones progesterone and estrogen.These maintain the uterine lining and prevent other follicles from maturing. • Therefore ovulation and menstruation do not occur during pregnancy.

The Umbilical Cord

• The umbilical cord connects the developing embryo and fetus to the placenta.

• This cord delivers nutrients and oxygen as well as removes waste and carbon dioxide.


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Birth

• We do not understand exactly what triggers the onset of birth.

I. Dilation Stage

• Contractions start and oxytocin cause the cervix to open (dilate).

• The amnion breaks and the fluid is expelled through the vagina (water breaks).

II. Expulsion Stage

• Contractions push the baby through the cervix and birth canal (vagina).

• The head rotates as it passes making it easier to pass through the birth canal.

III. Placenta Stage• The placenta and umbilical cord (together called the afterbirth) are expelled after the baby is born.

• We know estrogen and progesterone levels drop.

http://www.youtube.com/watch?v=R8M0NUJVwoI

http://www.youtube.com/watch?v=R8M0NUJVwoI

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