PSIO 241 CH 18

functions of mature gonads

– Producing gametes

• Spermatozoa (sperm) in male

• Ova (eggs) in female

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– Secreting sex hormones 

• Testosterone in males

• Estrogen and progesterone in females

reproductive tract

System of specialized ducts that transport or house gametes after they are produced

accessory sex glands

empty supportive secretions into reproductive tract

external genitalia

externally visible portions of reproductive system

male gonads and glands

• Functions: production of sperm (spermatogenesis) and delivery of sperm to female

• **Testes:**

– Sperm-producing organs

– Suspended outside abdominal tract in skin-covered sac (scrotum)

• **Accessory sex glands**:

– Seminal vesicles, prostate gland, bulbourethral glands

seminal vesicles

– supply more than half the semen

• Supply fructose for energy

• Supply prostaglandins to promote smooth muscle motility in both male and female reproductive tracts (enhances sperm transport)

prostate gland

• Contributes alkaline fluid; neutralizes acidic vaginal secretions

• Provides clotting enzymes

bulbourethral glands

release lubricating mucus prior to ejaculation

penis

– Organ used to deposit semen in female 

– Contains erectile tissue

male reproductive tract

– Epididymis, ductus (vas) deferens, ejaculatory duct-

– Delivers sperm and semen into urethra of penis that empties into exterior

penile structure

• Erectile tissue corpus cavernosum on **top side of penis.**

• Corpus spongiosum **on bottom of penis, houses the urethra.** 

• Veins on **top side of penis.** 

testes

•**Sperm production occurs within seminiferous tubules**

•**Testosterone produced by Leydig** (interstitial) cells that lie in connective tissue between seminiferous tubules

• Testosterone diffuses **into Sertoli cells** (high concentration) and into the blood. (**do not turn into sperm, help sperm develop**)

• Circulating testosterone provides negative feedback to regulate LH secretion

male reproductive system

• Spermatozoa formed in the testis **stored in the epididymis**, where they are stored for 2-3 months. 

• These sperm lack motility. 

• During  this time, they **undergo maturation processes**. Final maturation is completed in the female reproductive tract.

• **During ejaculation**, sperm are transported via the peristaltic action of muscle layers within the **vas deferens.**

spermatogenesis

• ceases at abdominal cavity temperatures.

• Scrotum provides **environment 4°C cooler** than abdominal cavity. 

• **Countercurrent heat exchanger** in spermatic cord. 

• Temperature of scrotum/testes regulated by contraction and relaxation of **cremasteric muscles and scrotal skin rugae**

spermatozoan

• **Head**-consists primarily of the nucleus (contains DNA)

• **Acrosome**- enzyme-filled vesicle that caps tip of the head; used to penetrate ovum

• **Midpiece**- area where mitochondria are concentrated 

•**Tail**-Provides mobility for spermatozoan

emission

• Movement of semen from epididymis, vas deferens, seminal vesicles, and prostate to ejaculatory ducts

• Mediated **by sympathetic adrenergic transmitters**

• Simultaneously with emission, there is also a sympathetic stimulated contraction of internal sphincter of bladder

• Emission precedes ejaculation but also continues during ejaculation

ejaculation

• Caused by rhythmic contraction of bulbospongiosus and ischiocavernous muscles

• Contraction of these **striated muscles are innervated by somatic motor nerves** causes semen to exit rapidly through the urethra

vulva

collective term for female external genitalia

vaginal opening

Located between urethral opening and anal opening

labia minora and labia majora

skin folds that surround vaginal and urethral openings

clitoris

small erotic structure located at end of folds of labia minora

oviducts

(uterine or Fallopian tubes)

– Pick up ova on ovulation

–**Serve as site for fertilization**

uterus

– Maintenance of fetus

Expelling fetus at end of pregnancy

vagina

–Muscular, expandable tube that connects uterus to external environment

–**Cervix:** the single, small opening that serves as pathway for sperm and passageway for delivery of baby from uterus

ovaries

• Produce ova/eggs (oogenesis).

• Site of follicle maturation and ovulation.

• Secrete female sex hormones estrogen and progesterone.

estrogen

• Essential for ova maturation and ovulation

• Stimulates repair of uterine endometrium each cycle

• Establishment of female secondary sexual characteristics

• Essential for transport of sperm from vagina to fertilization site in oviduct

• Contributes to breast development in anticipation of lactation

progesterone

• Important in **preparing suitable environment** for nourishing a developing embryo/fetus 

• **Inhibits uterine contractions**

• Contributes to breasts’ ability to produce milk

ovarian cycle

• Average ovarian cycle lasts 28 days

• Normally interrupted only by pregnancy

• Finally terminated by menopause

• Consists of two alternating phases:

follicular phase

dominated by presence of **maturing follicles**, estrogen

luteal phase

characterized by presence of **corpus luteum**, progesterone

primary follicle

• an oocyte surrounded by single layer of granulosa cells

• after development starts there are two possible fates:

– reach maturity and ovulate

– degenerate to form scar tissue

Ovarian Cycle- Follicular Phase 

•**Two** cell types important for hormonal production.

•**Theca cells** in response to LH produce androgens.

•**Granulosa cells** in response to FSH convert the androgens to estrogen. This occurs by the activity of **aromatase.**

**•Estrogen** targets the uterus endometrium to repair itself and proliferate and produces negative feedback to the anterior pituitary

ovulation

•Follicle ruptures to release oocyte from ovary.

•Event is called ovulation.

•Released oocyte enters oviduct where it may or may not be fertilized.

•Signal for ovulation to occur is hormonally controlled **by LH.**

luteal phase

• Last 14 days of ovarian cycle.

• Old follicular cells undergo structural transformation to form corpus luteum.

• Corpus luteum **produces progesterone and estrogen, with progesterone dominating the period.**

• If successful pregnancy does not occur corpus luteum degenerates within about 14 days.

• If pregnancy occurs, fetal tissue produces human chorionic gonadotropin, **HcG** which prevents the corpus luteum from degenerating

estrogen

**Peripheral effects** of estrogen produced by the granulosa cells during the follicular phase include:

• Circulating estrogens **stimulate the female sex accessory organs and secondary sex characteristics.**

• Rising levels of estrogens cause the endometrial cells of the uterine mucosal layers to **increase their rate of mitotic division (proliferate).**

• Circulating estrogens cause the cervical mucus to be thin and watery, **making the cervix easy for sperm to traverse**.

progesterone

Increased plasma levels of progesterone:

• Causes **uterine endometrium to become secretory**, providing nutrients for blastocyst

• Causes **cervical mucus to become thick**, sealing off uterus from further sperm entry or bacteria

• Has thermogenic properties, causing basal body temperature to increase by 0.5–1.0° F

Uterine Cycle- Menstrual Phase 

• Discharge of blood/endometrial debris from vagina.

• First day of menstruation is start of new cycle.

• Vasoconstriction of endometrial vessels; disrupts blood supply, death of endometrium

• Mild rhythmic contractions (cramps) of uterine myometrium; expel blood and endometrial debris from uterine cavity through vagina.

Uterine Cycle- Proliferative Phase

• Coincides with end of ovarian follicular phase.

• Endometrium starts to repair itself and proliferate __**under influence of estrogen**__ from newly growing follicles.

• This phase ends when ovulation occurs.

• Peak estrogen levels during this phase trigger LH surge responsible for ovulation.

Uterine Cycle- Secretory Phase

• Uterus enters this phase after ovulation when new corpus luteum is formed.

• Corpus luteum secretes large amounts of progesterone and estrogen.

• __**Progesterone**__ converts endometrium to highly vascularized, glycogen-filled tissue.

• Endometrial glands actively secrete glycogen.

monitoring menstrual cycle

• Low progesterone metabolites and low but slowly rising estrogen metabolites =**follicular phase.**

• Low progesterone metabolites and rapidly rising estrogen metabolites =**follicular phase just before ovulation.**

• Elevated levels of progesterone metabolites = **luteal phase and pregnancy**. 

placenta

• Acts as  to provide nutrients (fuel and oxygen) and remove wastes

• Acts as endocrine organ, produces:

• *Human chorionic gonadotropin (hCG)* to maintain corpus luteum which in turn produces E2 and P

• Peak hCG @ 60 days then decline after 10 weeks

• Around the 12th week placenta takes over and produces:

• **Estrogen** which stimulates myometrial growth and milk duct development

• **Progesterone** inhibits myometrial contractions, enhances mucus plug, stimulates milk glands

parturition reflex

1. **Prostaglandins** cause contraction of the uterus and are thought to initiate the labor process. 
2. Contraction of the myometrium pushes the fetus towards the cervix.
3. Dilation of the cervix stimulates afferent neurons that cause the release of oxytocin from the posterior pituitary gland. 
4. Oxytocin contracts the myometrium and stimulates local production of prostaglandins. 
5. __**Positive feedback**__

role of oxytocin

– causes stronger contractions

– positive-feedback cycle progressively increases until cervical dilation and delivery are complete

lactation

• During gestation elevated placental estrogen and progesterone promote development of ducts and alveoli in mammary glands via increased prolactin production.

• Milk production is **inhibited by high levels of estrogen.**

• Process sustained by suckling:

– Triggers release of oxytocin and prolactin

– **Oxytocin** causes milk ejection by stimulating cells surrounding alveoli to squeeze out milk

– **Prolactin** stimulates production of more milk to replace milk ejected as baby nurses 

sucking reflex

Prolactin

– **suppresses GnRH**