REPRODUCTIVE SYSTEM

 

 

OUTLINE

A- MALE REPRODUCTIVE SYSTEM

      I- ANATOMY

 

      II- PHYSIOLOGY

            a- puberty

            b- spermatogenesis

 

B- FEMALE REPRODUCTIVE SYSTEM

            I- ANATOMY

            II- PHYSIOLOGY

                        Menstrual cycle

                                    a1- Oogenesis

                                    a2- Hormonal and ovarian cycles

                                    a3- Uterine cycle

                       

C- Human sexual response, intercourse and fertilization

 

D- Birth control methods         

 

E- Infertility

 

Reproduction is the process by which new individuals of a species are produced and genetic material passed to the next generation.

 

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookREPROD.html

 

A- MALE REPRODUCTIVE SYSTEM

 

I- ANATOMY

      1- Scrotum: Formed by two pouches divided by a septum (connective tissue) and containing the testes. They are attached to the abdominal wall by a smooth muscle.  If the temperature is too cold the muscle contracts bringing the testes near the warmer abdominal wall.  Vice versa, if the temperature is too hot, both muscles relax and the testes move away from the abdominal wall.  This response to temperature is important for sperm development.  Sperms mature at temperatures 2o F lower than body temperature.. 

 

 

 

      2- Testes: About 5 cm long oval organs located within the scrotum.  They contain  many seminiferous tubules, where sperm is being made (200 millions/day).  Between the seminiferous tubules, other cells are responsible for testosterone secretion.

     3- Epididymis: Comma-shaped organs formed by a coiled duct (6 m long).  Site of sperm maturation.  They become fertile there and can be stored up to a month.  They are either expelled into the vas deferens or resorbed by the lining. 

     4- Vas deferens:  45 cm long, bringing sperm from the epididymis to the urethra.    On its way into the abdomen, it passes through the inguinal canal.  It is flanked by blood, lymphatic vessels, nerves and a smooth muscle to form the spermatic cord.

     5- Urethra:  The duct originates at the base of the bladder, passes through the prostate gland, continues into the abdomen, and runs through the penis to open at the external urethral orifice.

     6- Seminal vesicles:  Glands lying under the bladder, communicating with the urethra by the ejaculatory ducts.  They secrete a liquid rich in nutrients to nourish the active sperm.

     7- Prostate gland:  secretes a milky, alkaline product which neutralizes the acids formed by sperm metabolism.

     8- Bulbourethral glands (Cowper's glands):  secrete mucous to facilitate semen passage into the long urethra.

     9- Penis:  formed by 3 columns of spongy, erectile tissue.  Its swollen tip forms the penis glans which is rich is sensory receptors for pleasure.  The skin covering the shaft of the penis folds at the tip to form the prepuce or foreskin (removed in some culture by circumcision).

 

II- PHYSIOLOGY

             Before puberty little androgen hormones are secreted, the testes remain small. Androgens are the general term for the male hormones, testosterone being the most common.  The male characters, thus, are not yet developed.  At puberty, the hypothalamus secretes high amount of gonadotropin releasing hormone (GnRH), which stimulates the secretion and release by the anterior pituitary of  follicle-stimulating hormone (FSH) and luteinizing hormone (LH).  FSH promotes spermatogenesis while LH stimulates testosterone synthesis. 

 

 

Testosterone has several  functions:

            1- to help spermatogenesis

            2- promote the development of secondary sexual characters and behavior:

                        - stimulate the development of the reproductive organs

                        - stimulate the male pattern growth of hair (chest, legs...)

                        - the skin become thicker, coarser and darker

                        - cause hypertrophy of the larynx with a deepening of the voice

                        - stimulate increase of bone and muscle mass

                        - stimulate the activity of the sebaceous glands

                        - increase the metabolic rate

                        - promote also epiphyseal disc closure so growth in length will stop

                        - promote male sexual behavior

            3- has a negative feed-back effect on the hypothalamus.

 

            b- Spermatogenesis:

Sperms develop in the seminiferous tubules, in the testes.  The germ cells are located at the base of the Sertoli's cells which support and nourish them with stimulation from FSH and testosterone.  The most primitive germ cells are the spermatogonia.  They are still diploid and divide by mitosis to form primary spermatocytes.   Meiosis begins with these cells.  They become haploid secondary spermatocytes which undergo the second meiotic division to become the spermatids.  By that time, they arrive in the lumen of the seminiferous tubule and start to form a head and a flagellum and are called spermatozoa.

They mature and become fertile into the epididymis.  It takes about 2 months for  spermatozoa to form and mature.  Secretions from the seminal vesicle, prostate, Cowper's glands will be added to the sperm to form the semen.

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

B- FEMALE REPRODUCTIVE SYSTEM

    I- ANATOMY

 

 

 

      1- Ovaries: Located in the lower pelvis, on each side.  They contain all the eggs that a female will need for a lifetime.

 

 

      2- Uterine tubes or fallopian tubes or oviducts:  Located on each side of the uterus and associated with each ovary.    

     3- Uterus: Attached to the pelvic cavity.  Receives the fertilized egg which implants into the lining or endometrium.  The egg will develop into an embryo, then fetus and being expelled as a baby.

    4- Vagina: organ of copulation and birth canal, it has a tube like shape.  The vaginal orifice is partially covered by a thin membrane, the hymen, usually ruptured during the first intercourse.

    5- External genitalia or vulva:  Externally bordered by thick fleshy folds, the labia majora.  They are lined inside by smaller, thin folds, the labia minora.   The clitoris, a small erectile tissue, anterior to the vestibule plays a role in sexual stimulation and pleasure.  It is the equivalent of the male penis.

    6- Mammary gland: Consist of about 20 lobes, themselves divided into lobules, filled by grape-shaped modified sweat glands.  They secrete milk which flows into the mammary ducts lined with smooth muscles.  They end at the nipple.  Around it is a pigmented area, the areola.  The amount of milk secreted is a function of the lobules and not of the size of the breast which is directly related to the amount of adipose tissue filling the space between the lobules.

 

 III- PHYSIOLOGY

   A- Menstrual cycle    

a1- Oogenesis:  It is the production of mature oocytes within the ovarian cortex.  About 2 million of primary oocytes  are formed in the ovaries and present at birth.  Most of them degenerate during childhood and about 300 000 remain at puberty.  These cells are surrounded by a single cell layer, the granulosa cells.

 

   At puberty, under the influence of FSH, a few of these primary oocytes will be activated during each menstrual cycle:  The cells around the oocyte multiply and the oocyte mature during the next menstrual cycle.  The cells surrounding the eggs secrete estrogen.    

    During ovulation, a surge of LH triggers the expulsion (=ovulation) of the eggs into the fallopian tubes.  The cells remaining behind secrete progesterone.

 

  a2- Hormonal and ovarian cycle: Composed of 3 consecutive phases lasting typically 28 days.

 

   1- The follicular phase:  Stimulated by FSH, lasts the first 10 days of the menstrual cycle. Characterized by the maturation of the egg and the rise in estrogen level.

   2- Ovulation: At day 14 of the menstrual cycle, due to a sudden release of LH 

   3- Luteal phase: LH stimulates progesterone secretion from the cells surrounding the eggs.

 

   a3- Uterine cycle:  also composed of 3 phases.

   1- Menstrual phase (menses):  Shedding of the uterine lining.  Last up to 7 days. 

   2- Proliferative phase: Under the influence of rising level of estrogen, the uterine lining thickens, the cervical mucus becomes thinner.

   3- Secretory phase: Rising level of progesterone stimulates further development of the uterine lining.  Nutrients accumulate in the cells for possible egg implantation.  Later during the cycle, falling level of progesterone can no longer sustain the uterine lining which sloughs off --> menstruation begins.  

 

  

  

C- Inter course and fertilization

There are 4 phases to the human response to sexual intercourse:

1- excitation: increase sexual awareness and arousal

2- Plateau: Intense and continuing arousal.  For phases 1 and 2, veins in the secondary sex organs dilate bringing larger amount of blood to these organs and stimulating gland secretion.  In men, the penis becomes erects, in women, mucus glands around the labia increase secretion for lubrication.  This stage is under the control of the parasympathetic nervous system.

3- Orgasm:  Peak of sexual sensations.  Brief and intensely pleasurable expulsion of semen in men (ejaculation) and vaginal contractions in women.  This phase is under the control of the sympathetic nervous system.

4- Resolution: period of intense relaxation.

 

The sperms released by ejaculation travel up the vagina, uterus and fallopian tubes were they may encounter an ovum.  The egg can be fertilized by only 1 sperm.  The fertilized egg will travel up to 6 days along the fallopian tube before implanting in the uterus and develop into a baby.

 

 

D- Birth control methods

a- Abstinence: no intercourse. Full proof against pregnancy and sexually transmitted diseases. 

b- Surgical sterilization:  vasectomy and tubal ligation. Almost full proof, however, it is difficult to reverse

c- Hormonal methods: pills, patches, implants.  Most contains estrogen and progesterone which block the secretion of FSH and thus of follicle development.

d- Intra-uterine devices UID.  They create a mild chronic inflammation that prevents egg implantation and development.

e- Mechanical barriers: diaphragm and condom: used with or without spermicide.  Low tech, efficient.  Condoms made of latex also protect against STDs.  10% failure rate.

f- Rhythm method and withdrawal: the rhythm method is based on the fact that a woman ovulates once a month, around the 14 th day.  A more exact time can be estimated based on daily temperature or changes in vaginal secretion.  Not very effective.  The Withdrawal method (penis withdrawal before ejaculation) is not effective because some sperm can leak out before ejaculation.

g- Elective abortion: termination of the embryo or fetus for various reasons.  Controversial at this moment.

 

E- Infertility

About 10-15% of couples are infertile.

- Due to man: often due to a low sperm count (testes temperature too high, hormonal imbalances..)

- Due to woman: hormonal imbalances, pelvic inflammatory disease (PID), endometriosis

 

Treatments to infertility

- artificial insemination:Sperm is placed in the vagina with a syringe

- In vitro fertilization (IVF): eggs are fertilized with donor sperms.  The embryos are either frozen or inserted in the woman uterus

- Gamete intrafallopian transfer (GIFT) or zygote (ZIFT).  Sperms, eggs or zygotes can be placed into the fallopian tubes.

- Fertility-enhancing drugs: they promote ovulation

- Surrogate mothers: a parent can contribute sperm only or the embryos.  The surrogate will carry the baby to term.