Reproduction

MALE REPRODUCTIVE SYSTEMFEMALE REPRODUCTIVE SYSTEMIMPLANTATION AND PREGNANCY

Reproduction

11.1 Male Reproductive System

Inside the Scrotum

Male external genitalia consist of two structures; the scrotum containing the testes, and the penis

These are the beginning and the end of the route that sperm cells take through the male system

Sperm are produced in the seminiferous tubules of the testes by a process called spermatogenesis

Within the lining of these tubes is a specialized layer of cells called the ‘germ layer’

Sperm cells are derived from these unspecialized cells, which continuously divide by mitosis

One daughter cell remains as the new germ cell; the other daughter cell moves towards the inner wall of the tubule and divides by meiosis to form cells, which eventually become sperm

Spermatogenesis begins in the seminiferous tubules but the developing sperm move through the lumen of the tubules to the epididymis

Video

Each testis has an epididymis on one side of its surface that contains a coiled tube formed by seminiferous tubules after they join together

The tubes of the epididymis lead into the ductus (vas) deferens

The epididymis and the ascending portion of the vas deferens are the final maturation sites for sperm

Sperm

It is in these regions of the tubules that sperm gain their swimming ability, the whole process takes a few days

After puberty, spermatogenesis is ongoing, millions of sperm cells develop every day throughout a male’s reproductive life

Mature sperm have three identifiable regions:

The head

The mid-piece

The tail

The head contains the DNA (23 chromosomes)

It is encapsulated by the acrosome, a gel-like covering, which not only provides sperm with a chemical guidance system while swimming but also with enzyme capabilities required for penetrating an ovum (egg)

The mid-piece of a sperm contains mitochondria, which produce ATP required for the swimming activity

The tail (a flagellum) provides the locomotion

Testosterone Functions

Each testis also contains endocrine tissue located between the seminiferous tubules called interstitial cells that secrete androgens (male sex hormones), including testosterone

Testosterone is essential for the maturation of the primary sex organs and development of the secondary sex characteristics associated with puberty

The secondary sex characteristics in males include ancillary hair growth, enlargement of the larynx, muscle and skeletal growth, release of oils and sweat (potentially causing acne and BO), and baldness (given appropriate genetics)

A portion of the adrenal cortex also produces androgens; in this way, the adrenal cortex contributes to muscle mass and strength in both males and females

Penis

The penis is the organ of copulation; it contains erectile tissue and the urethra (this portion of the urethra serves a dual purpose)

It not only conducts urine to the outside for excretion, but also carries sperm during ejaculation

During sexual arousal, the arteries of the penis dilate (due to parasympathetic stimulation), and the veins constrict engorging the erectile tissue with blood making the penis erect

The changed angle of the penis allows sperm, bathed in seminal fluid, to enter the urethra

Seminal Fluid

The seminal fluid is a milky white solution contributed to by three glands: seminal vesicles, Cowper’s gland, and the prostate gland

It has a pH of 7.5, contains fructose to nourish the sperm, HCO3

- as a buffer, and a lipid-based chemical messenger called prostaglandins (promotes uterine contractions)

When semen (sperm plus seminal fluid) enters the urethra it promotes the rhythmic contractions leading to ejaculation

A sphincter at the base of the bladder is closed during this time, so that urine cannot enter the urethra

After ejaculation, the penis returns to its normal flaccid state for the duration of a refractory period

Hormones

With puberty the hypothalmus begins to promote the sexual functions of the testes through the release of gonadotropic releasing hormones (GnRHs) to the anterior pituitary

The anterior pituitary responds by releasing two hormones: luteinizing hormone (LH) and follicle stimulating hormone (FSH)

LH promotes the production of testosterone from the interstitial cells, where FSH promotes the maturation of sperm

Testosterone is maintained at a fairlyconstant level by negative feedbackwhile high levels of testosterone inhibitthe hypothalamus and the pituitary from releasing their hormones

11.2 Female Reproductive System

The ovaries are the structures where ova (ovum) are produced

The female reproductive tract consists of the oviducts, uterus, and vagina

This tract does not meet up with the urethra as it does in males

Oogenesis

Oogenesis is the development of ova; at birth, a female has several hundred thousand immature ova in structures called follicles in the cortical regions of her ovaries

After puberty these mature (roughly one a month) over her reproductive life

Only a few hundred ever mature

As a follicle matures, it undergoes changes to house the ovum in a fluid filled space

This development increases until the structure bulges out from the ovary surface

At this point the follicle is mature and is known as a Graafian follicle

Ovulation, the bursting of the follicle and the release of the ovum, is under hormonal control

The ovum is directed into the oviduct by the undulations of the fimbriae at the opening of the oviduct

The oviduct is a muscular tube that is lined with cilia that sweeps the fluid towards the uterus

In this manner the ovum (which has no means of locomotion itself) is moved over a period of four or five days, along the female tract

The remaining follicular structure in the ovary develops into a glandular tissue known as the corpus luteum

Womb

The uterus is sometimes called the womb (a thick-walled muscular pear-shaped organ)

The inner lining (endometrium) has two layers: a basal layer, which is adjacent to the muscle and elastic fibers, and a functional inner lining

The thickness of the inner lining varies according to a hormonally controlled reproductive cycle

Video

Review

Which of these is a male primary sex characteristic?

a) Deepening of the voice

b) Facial and pubic hair growth

c) External reproductive organs

d) Muscle and skeletal development

Which of these is a male primary sex characteristic?

a) Deepening of the voice

b) Facial and pubic hair growth

c) External reproductive organs

d) Muscle and skeletal development

After sperm cells are produced, they are stored mainly in the

a) Urethra

b) Prostate

c) Epididymis

d) seminal vesicles

After sperm cells are produced, they are stored mainly in the

a) Urethra

b) Prostate

c) Epididymis

d) seminal vesicles

Reducing of the release of GnRH from the hypothalamus will

a) stimulate LH and FSH secretion.

b) decrease the release of gonatotropic hormones

c) stimulate an increase in progesterone and estrogen levels

d) initiate ovulation in females and reduce spermatogenesis in males.

Reducing of the release of GnRF from the hypothalamus will

a) stimulate LH and FSH secretion.

b) decrease the release of gonatotropic hormones

c) stimulate an increase in progesterone and estrogen levels

d) initiate ovulation in females and reduce spermatogenesis in males.

Which of the following produces testosterone?

a) Sperm cells

b) Hypothalamus

c) Interstitial cells

d) Anterior pituitary

Which of the following produces testosterone?

a) Sperm cells

b) Hypothalamus

c) Interstitial cells

d) Anterior pituitary

Which of the following BEST describes how an ovum enters an oviduct once ovulation occurs?

a) It swims

b) Peristalsis

c) It is drawn in the action of fimbriae and cilia

d) It is propelled by the force of the bursting follicle

Which of the following BEST describes how an ovum enters an oviduct once ovulation occurs?

a) It swims

b) Peristalsis

c) It is drawn in the action of fimbriae and cilia

d) It is propelled by the force of the bursting follicle

Vagina

The vagina is the tube that extends from the cervix (neck of the uterus) to the outside

Its inner lining consists of mucosal cells and serves as the birth canal as well as the female organ of copulation

The clitoris is the female structure that is homologous to the penis in males (located at the anterior end of the labia, folds of skin, that surround the vaginal opening)

Where the male penis becomes engorged with blood during sexual arousal, the clitoris, labia and vaginal walls of the female become engorged

Hormones

FSH stimulates the maturation of an ovum in the ovary

LH stimulates the secretion of progesterone and estrogen from other cells of the follicle

Progesterone stimulates the maturation of the endometrium lining of the uterus

Estrogen

It is necessary for egg maturation and also for the development of secondary sex characteristics: uterine cycle, fat and hair distribution, growth of the uterus and vagina, pelvic growth, and it contributes to breast development, along with progesterone

As secretion of estrogen increases, the levels of LH and FSH begin to decrease until the follicle is mature in which there is a sharp increase in LH and (to a lesser extent) FSH

Ovulation

It is believed that this significantly high level of estrogen exerts positive feedback on the hypothalmus, thus causing a surge of LH (and FSH) resulting in ovulation

After ovulation, the corpus luteum temporarily retains an endocrine function secreting estrogen which stimulates the continues thickening of the endometrium

Progesterone stimulates the endometrium to become secretory

The changes to the endometrium are to prepare for the possibility of fertilization and pregnancy

If fertilization does not occur, the corpus luteum degenerates after about ten days

Menstruation

When it degenerates, the levels of estrogen and progesterone drop suddenly and the endometrium that was built up and maintained is shed

The shedding of the endometrium (mostly blood tissue) is known as menstruation (menses)

The period of menses typically lasts about five days

During menses, the anterior pituitary begins to release LH and FSH and the cycles of change that occur in the ovaries and uterus begin again

Ovarian and Uterine CyclesOvarian Cycle Uterine Cycle

Phase (Time) Events Phase (Time) Events

Follicular Phase(Day 1 to 13)

LH and FSH secretion by the anterior pituitary gland

Maturation of a follicle and secretion of estrogen (and progesterone) to build the endometrium

Menstrual Phase(Day 1 to 5)

Proliferation Phase(Day 6 to 14)

Endometrium lining breaks down and is discharged = menses

Rebuilding and thickening of the endometrium

Ovulation(Day 14)

Ovum is released by the ovary.Corpus luteum is formed

Luteal Phase(Day 15 to 28)

Estrogen secretion by the corpus luteum causing the endometreum to continue to thicken and mature.

Progesterone secretion is making the endometrium secretory

Secretory Phase(Day 15 to 28)

Endometrium continues to thicken

Maturation of the secretory glands of the endometrium

11.3 Implementation and Pregnancy

Fertilization

During copulation semen (containing as many as 400 million sperm) is ejaculated into the vagina and begin to swim towards the ovaries

An ovum is only viable for fertilization for six to twenty-four hours after ovulation, hence fertilization usually occurs in the oviduct

Implantation

The zygote (after fertilization) begins to divide and the structure continues to the uterus where it embeds itself in the endometrium wall; this process is called implantation

Placental tissue results from the combination of embryonic and maternal tissues following implantation

Pregnancy

This new tissue secretes the hormone, HCG ( human chorionic gonadotropin), which maintains the corpus luteum; this marks the beginning of pregnancy

Pregnancy tests test for the presence of HCG in urine

Because the corpus luteum is maintained, its production of progesterone and estrogen continues until the placenta fully develops and begins to secrete estrogen and progesterone

The progesterone maintains the endometrium and prevents menstruation from occurring

The estrogen inhibits LH and FSH to release from the anterior pituitary

By the tenth week of a pregnancy, the placenta is developed enough to produce the quantities of estrogen and progesterone required maintaining the pregnancy

The secretions of HCG diminish and the corpus luteum finally degenerates; by this time, the pregnancy is well established and the embryo will continue to grow and develop

Labor

The muscular uterus continues to contract slightly throughout a pregnancy

Near the end of the pregnancy these contractions become more severe (false labor); true labor begins when the contractions become sustained

The birth process is considered to have three stages: dilation of the cervix, birth, and expulsion of the afterbirth

Oxytocin is a hormone that is released by the posterior pituitary

Its release is stimulated by the contractions of the uterus and it causes further contractions of the uterus leading to birth (positive feedback)

Review

Implantation normally occurs

a) several days after fertilization

b) immediately after fertilization

c) about ten weeks after fertilization

d) about ten minutes after fertilization

Implantation normally occurs

a) several days after fertilization

b) immediately after fertilization

c) about ten weeks after fertilization

d) about ten minutes after fertilization

What is the source of the discharge that is released during menstruation?

a) Cervix

b) Vagina

c) Oviduct

d) Endometrium

What is the source of the discharge that is released during menstruation?

a) Cervix

b) Vagina

c) Oviduct

d) Endometrium

What occurs if progesterone is not secreted in the female?

a) The corpus luteum develops in the ovary

b) Secondary sex characteristics do not develop

c) The endometrium will not mature completely

d) Uterine contractions begin stimulating childbirth

What occurs if progesterone is not secreted in the female?

a) The corpus luteum develops in the ovary

b) Secondary sex characteristics do not develop

c) The endometrium will not mature completely

d) Uterine contractions begin stimulating childbirth

What are the sources of the four hormones that regulate the ovarian and uterine cycles?

a) Uterus and the ovaries

b) Anterior pituitary gland and the ovaries

c) Anterior and posterior pituitary gland and the ovaries

d) Adrenal gland, anterior pituitary gland and the ovaries.

What are the sources of the four hormones that regulate the ovarian and uterine cycles?

a) Uterus and the ovaries

b) Anterior pituitary gland and the ovaries

c) Anterior and posterior pituitary gland and the ovaries

d) Adrenal gland, anterior pituitary gland and the ovaries.

The presence of HCG in a woman’s urine indicates that

a) she has just ovulated

b) menstruation is about to begin

c) her levels of estrogen are decreasing

d) implantation of an embryo has occurred

The presence of HCG in a woman’s urine indicates that

a) she has just ovulated

b) menstruation is about to begin

c) her levels of estrogen are decreasing

d) implantation of an embryo has occurred