Chapter 15/16: The Reproductive System

Male Reproductive System

• All humans start from a zygote

• Gender is determined by sperm from the father

• The sex-determining region of the Y (SRY) gene on the Y chromosome codes for a protein so that androgen receptors are produced in a male fetus

• Testosterone and androgen receptors are needed in the fetus for male anatomy to develop

• Major organs are testes

Descent of the Testes

• Testes belong to the endocrine and reproductive systems because they produce testosterone and sperm.

• Testes descend from the abdomen to the scrotum because of the gubernaculum (cord of some muscle/tisssue that anchors the testes)

  • Pulls testes to help them descend through the inguinal canal (allows testes to get from the abdominal cavity to the scrotum)

The Testes

• Each testis is divided into lobules

• Sperm are produced in the seminiferous tubules

• Interstitial cells, located between seminiferous tubules, produce testosterone 

• Ductus deferens (vas deferens)

The Scrotum

• The testes are housed in the scrotum

• The spermatic cord suspends each testis and is composed of the cremaster muscle (when contracted, it pulls testes if it's too cold), the ductus deferens, the testicular artery, and the pampiniform plexus

• Dartos muscle - loosens/tightens skin

Temperature Regulation

• For the testes to produce viable sperm, the temperature of each testis must be approximately 2°C cooler than the core body temperature

• The pampiniform plexus is a network of veins surrounding the testicular artery

• The temperature of the testes is maintained by the dartos muscle, the cremaster muscles, and the pampiniform plexus

Accessory Glands

• The five accessory glands in the male are:

  • Two seminal vesicles - mixture of sugar and protein that makes up 60% semen

  • One prostate gland - alkaline mixture containing prostaglandins that makes up 30% semen

  • Two bulbourethral glands - small amount of slightly alkaline lubricant

Spermatic Ducts

• The spermatic ducts are the: 

  • Efferent ductules – connect the testes to the epididymis

  • Epididymis – location of sperm maturation and storage

  • Ductus deferens – connects the epididymis to the pelvic cavity

  • Ejaculatory ducts – ductus deferens and a duct from the seminal vesicle combine

• Seminiferous tubules, rete testis, efferent ductule, epididymis, ductus deferens, ejaculatory ducts, out the penis

The Penis

• The penis has an internal root and an external shaft and glans

  • Glans covered by prepuce

• The penis is composed of three columns of erectile tissue

  • Paired corpora cavernosa

    • Trabecular muscle

    • Crus

  • Single corpus spongiosum

    • Bulbospongiosus muscle

Spermatozoon

• A spermatozoon is a single cell with two principal parts—a head and a tail

• The head (DNA is found) contains 23 chromosomes and an enzyme-filled acrosome (covers part of the head) used to penetrate an egg

• The tail contains a midpiece with large mitochondria to produce the energy to move the tail’s flagellum (does the swimming)

Sperm Production

• Mitosis is a one-division process that forms all body cells

• Meiosis is a two-division process that forms gametes

  • Splits chromosomes in half

• Crossing-over and independent assortment in meiosis create new combinations of DNA that provide genetic variety in sperm

• Sperm production involves two processes—spermatogenesis and spermiogenesis

• Spermatogenesis involves meiosis to form four spermatids from one spermatogonia.

• Spermiogenesis is the development of four sperm from four spermatids

Spermatogenesis

• A spermatogonium near the basement membrane of the seminiferous tubule divides by mitosis, producing two identical spermatogonia

  • One remains (A) near the basement membrane to serve as a spermatogonium later

  • The other spermatogonium (B) migrates slightly away from the wall toward the lumen of the seminiferous tubule. It will continue on in the production process

    • Crossing blood-testis barrier, after crossing become primary spermatocyte

• Spermatogonium B enlarges to become a primary spermatocyte

• Once protected by the BTB, the primary spermatocyte goes through meiosis I.

  • This produces two equal-size, genetically unique secondary spermatocytes, each having 23 chromosomes (n)

• Each secondary spermatocyte undergoes meiosis II, which produces in total four spermatids from the one original spermatogonium type B

Spermiogenesis

• Sperm production transforms spermatids to functional sperm (has to have head, middle piece, and tail) 

• Each spermatid forms a tail and sheds its cytoplasm to become a sperm

• Goes to epididymis to mature

Testosterone

• Testosterone has a positive effect on many tissues, but it also has a negative-feedback effect on the hypothalamus and the anterior pituitary.

• Sustentacular cells produce the hormone inhibin, when they are busy with sperm production, so that FSH from the anterior pituitary is inhibited 

• 1. Hypothalamus releases GnRH to stimulate the anterior pituitary to release LH and FSH

• 2. LH targets interstitial cells of testes to stimulate testosterone production

• 3. FSH targets sustentacular cells of seminiferous tubules to increase spermatogenesis and inhibin production

• 4. Testosterone stimulates spermatogenesis, development of sex organs, and secondary sex characteristics

• 5. Testosterone has negative feedback effect on the hypothalamus and anterior pituitary to reduce LH and FSH production 

• 6. Inhibin has a negative feedback effect on the anterior pituitary's production of FSH

Pathway of Sperm

• Sperm travel from the seminiferous tubules, to the rete testes, to the efferent ductules, to the epididymis, to the ductus deferens, to the ejaculatory ducts, to the prostatic urethra, to the penile urethra, and then to outside the body 

  • The four stages of the male sexual response during intercourse are arousal, emission, ejaculation, and resolution

    • Arousal results in an erection

    • During emission, sperm move to the urethra and accessory glands secrete fluids for semen.

    • During ejaculation, sperm are forcefully expelled from the urethra.

    • During resolution, excess blood is forced from the penis, thus causing it to become flaccid

Rectal Exams and Prostate Cancer

• Prostate cancer

  • Nine percent of men over the age of 50 will develop prostate cancer.

• Can be detected by:

  • A digital rectal exam is a procedure in which the doctor inserts fingers into the rectum to detect any abnormalities, such as an enlarged prostate

  • A prostate-specific antigen (PSA) test is a test that measures the presence of prostate-specific antigens in the blood; increased levels may indicate prostate cancer.

Female Reproductive System

• A female zygote has XX as the sex chromosomes

• Without the SRY gene on the Y chromosome, and therefore the lack of androgen receptors and testosterone, a zygote develops female reproductive anatomy

• Major organs are the ovaries

The Ovaries

• Ovaries produce ova (egg) and are therefore the primary sex organs of the female reproductive system.

• Ovaries are enclosed in a capsule called the tunica albuginea (outer membrane that encloses in a capsule).

  • An ovary has two layers: a cortex containing follicles (hold developing egg), and a medulla containing blood vessels.

  • Ligaments suspend the ovaries in the pelvic cavity and anchor them to the uterus

    • Broad ligament 

      • fan-shaped

    • Ovarian ligaments

      • Connects uterus to overies

    • Suspensory ligament

    • Round ligament

Major Structures of Female Reproductive System

• The ovaries, uterus (travels through uterine (fallopian) tube), and vagina are internal

• The vulva and the breasts are external. The uterus is held in place by the broad and round ligaments

• Thick wall has three layers:

  • Perimetrium – visceral peritoneum 

    • Outer most layer 

  • Myometrium – thick layer of smooth muscle

    • Contractions 

  • Endometrium – mucous membrane

The Uterus

• Uterus has three regions:

  • Fundus – broad superior curve 

  • Body – wide midportion

  • Cervix – inferior (neck) region

    • Narrows into the vagina

• The uterine tubes transport eggs to the uterus.

  • Also called fallopian tube or oviduct

  • End called infundibulum has fimbriae (hands for the fallopian tubes to catch the eggs)

  • Isthmus

  • Ampulla

  • Infundibulum

The Vagina

• The vagina allows for the flow of the menses (menstrual cycle), is a receptacle for sperm, and serves as the birth canal.

  • External opening covered by hymen in children

• Pubic symphysis - connection of the two sides of the pelvis 

  • Cartilage

The Vulva

• The vulva includes the following:

  • Mons pubis – pubic hair cover mound of adipose tissue superficial to the pubic symphysis

  • Labia – includes labia majora and labia minor

    • Frames the vestibule (opening or space in between)

  • Clitoris

    • Erectile tissue – external portion is glans

  • Vestibular bulbs – erectile tissue in labia majora

    • On the sides

  • Vestibular glands – lubricating glands in posterior vestibule

    • Inferior

Breasts

• The breasts contain mammary glands that do not fully develop until the first pregnancy

  • Process of producing milk called lactation

  • Breast tissue supported by suspensory ligaments

  • Dark skin around nipple called areola

    • Areolar glands - helps with lubricating 

• Starts as secretory cells, lactiferous ducts, lactiferous sinus

Puberty and Hormones

• Puberty begins when the GnRH from the hypothalamus stimulates the anterior pituitary to secrete FSH and LH

• FSH stimulates follicles in the ovaries to produce estrogen 

• Estrogen is responsible for the development of female sex characteristics

• Female Secondary Sex Characteristics

  • Breast development

  • Development of axillary (armpit) and pubic hair

  • Widening of the pelvis

  • Fat deposition 

  • Menstruation 

Oogenesis

• One haploid gamete is formed from each oogonium

• A follicle is responsible for caring for an oocyte and producing hormones 

• All oocytes have been produced from oogonia by birth

• Many oogonia and oocytes are lost by atresia

• Oogenesis is halted mid-meiosis I until puberty.

• Secondary oocytes are formed each month.

  • Meiosis I also produces a polar body

• Meiosis II is not completed unless an egg is fertilized

• Follicles develop along with an oocyte.

Folliculogenesis

• Some primordial follicles develop each month after puberty.

  • Mature follicles rupture to release an egg during ovulation.

  • After ovulation, the follicle becomes a corpus luteum, which secretes hormones

• If the egg does not become fertilized, the corpus luteum becomes a corpus albicans

Ovarian Cycle

• A sexual cycle is composed of two parts: an ovarian cycle and a menstrual cycle

• A sexual cycle is typically 28 days and begins on the first day of a woman’s period

  • Menstrual phase (days 1 to 5)

• The ovarian cycle has a follicular phase (days 1 to 14) and a luteal phase (days 14 to 28)

  • Around 14 day, ovulation happens

Menstrual Cycle

• The menstrual cycle has the following phases:

  • Menstrual (days 1 to 5)

  • Proliferative (days 5 to 14)

    • Thickening of uterine wall

    • Estradiol increases 

  • Secretory (days 14 to 26)

    • Estradiol decreases slightly

    • Progesterone increases

  • Premenstrual (days 26 to 28)

    • Reset and sheds

    • Hormone levels drop

• Ovulation typically occurs on day 14

• Estradiol and progesterone

Sexual Response

• The female sexual response includes four stages: arousal, plateau, orgasm, and resolution

• Unlike the male, a woman does not have a refractory period in her sexual response

Menopause

• A woman’s body goes through a climacteric in midlife due to the decreased production of estrogen and progesterone.

  • Menstruation ceases during menopause

  • Hot flashes are common

  • The tissues of the vagina, labia minora, clitoris, uterus, uterine tubes, and breast atrophy.

  • Bone mass declines.

  • Skin becomes thinner.

  • Cholesterol levels rise.

Mammography and Breast Cancer

• Breast cancer is the abnormal growth of breast tissue, usually occurring in the lactiferous ducts and lobules of the breast.

• Age, family history, genetic mutations, personal history, and lifestyle choices affect breast cancer risk.

• Detection of breast cancer usually begins with a monthly self-exam and mammography

Ovarian and Cervical Cancer

• Ovarian Cancer

  • Often lacks symptoms and is difficult to diagnose

  • Treatment options include surgery, chemotherapy, and radiation

• Cervical cancer

  • often caused by human papillomavirus (HPV) infection 

  • Usually detected with a Papsmear

  • Treatment options include the removal of the uterus - Hysterectomy

Fertilization

• An egg must be fertilized in the uterine tube within 24 hours of ovulation if it is to survive.

• Sperm must go through capacitation (head taken off but it is the important part, like a rocket ship) to fertilize an egg

  • Cell membrane of sperm is weakened by vaginal acids so acrosome can release enzymes

• Many sperm may be needed to break through the cells surrounding the egg 

• Only one sperm will be allowed to penetrate the egg—the rest will be rejected

Zygote Development

• The nuclei of the sperm and egg rupture, the chromosomes mix, and a new nucleus forms.

• The zygote undergoes mitotic divisions on its way to the uterus.

• The blastocyst implants in the lining of the uterus six days after fertilization

• Takes 6 days from fallopian tubes to uterus

Gestation

• The developing fertilized egg will be called: 

  • A blastocyst from implantation to week 3

  • An embryo from weeks 3 to 9

  • A fetus from week 9 until birth

• Gestation (the time from fertilization to birth) is 266 days, or 280 days from the start of last menstrual period.

• Hormones are made by the fertilized egg, the corpus luteum, and the placenta, along with other endocrine glands during a pregnancy

• The hormones that control a pregnancy include HCG, estrogen, progesterone, HCS, thyroid hormone, PTH (parathyroid hormone), ACTH (adrenocorticotropic hormone), glucocorticoids, and aldosterone

Hormones (Female Reproductive System)

• Human chorionic gonadotropin (HCG)

  • From the developing blastocyst causes the corpus luteum to continue to secrete estrogen and progesterone

• Estrogen levels

  • Rise to 30 times normal during a pregnancy

    • Breasts to double in size, encourages external genitalia and uterus to grow, causes uterus to be more irritable (prone to contract), and causes pubic symphysis to become more elastic.

Parturition

• The fetus has a role in the timing of parturition

• The hormones involved in initiating parturition lead to a positive-feedback mechanism that ends with the birth of the baby.

Child Birth: Stage 1

• Stage begins with regular uterine contractions

• Cervical canal widens (dilation) and the cervix thins (effacement)

• Stage 1 ends when the cervical canal reaches 10 cm (the diameter of a fetal head).

• The amniotic sac, in which the fetus floats, often ruptures during this stage.

• This event is called the breaking of the waters

Child Birth: Stage 2

• Stage the baby is expelled

• The crowning of the baby’s head is usually seen first

• Doctor may make an incision (episiotomy) in perineum to widen the vaginal opening

  • Angled away from her anus to prevent the perineum tearing into her anus as the baby is born

Child Birth: Stage 3

• The placenta detaches from uterus and is expelled during this stage

• Further contractions of the uterus ensure that all of the placenta and its associated membranes (afterbirth) are expelled

• These contractions also help close blood vessels that had led to the placenta.

• About 350 mL of blood is normally lost when the placenta detaches.

Breast Feeding

• Throughout the pregnancy, estrogen and progesterone suppress the effects of prolactin

  • Once the placenta is delivered and the source of estrogen and progesterone is gone, prolactin stimulates milk production

• Milk production is preceded in the first few days after birth by colostrum

• Suckling on the breast causes oxytocin release and the milk ejection reflex

• Prolactin levels surge with each feeding to ensure ample milk production to meet the baby’s needs