Chapter 27/28:The

Reproductive system

BSC 1086C

Fall 2007

Essence of Sex

• Reproduction – one property of a living thing– great variety of methods

• Sexual reproduction – each offspring has 2 parents and receives genetic

material from both– provides genetic diversity that increases “fitness”

of the population and helps drive evolution

Two Sexes

• Male and female ___________(sex cells) combine their genes to form a fertilized egg (____________)– one gamete has motility (sperm)

• parent producing sperm considered male• has Y chromosome

– other gamete (egg or ovum) contains nutrients for developing zygote

• parent producing eggs considered female

Overview of Reproductive System

• ____________________– produce gametes (testes or ovaries)

• ____________________– male - ducts, glands, penis deliver sperm cells– female - uterine tubes, uterus and vagina receive

sperm and nourish developing fetus

• Secondary sex characteristics– develop at puberty to attract a mate

• pubic, axillary and facial hair, scent glands, body morphology and low-pitched voice in males

• Our cells contain 23 pairs of chromosomes– 22 pairs of autosomes– 1 pair of sex chromosomes (XY males: XX females)

• males produce 50% Y carrying sperm and 50% X carrying• all eggs carry the X chromosome

• Sex of child determined by type of sperm that fertilizes mother’s egg

Role of Sex Chromosomes

Hormones and Sex Differentiation• Gonads begin to develop at 6 weeks• 2 sets of ducts

– __________________ducts develop into male reproductive system or

– __________________ducts (müllerian ducts) develop into female reproductive tract

• SRY gene (Sex-determining Region of Y gene)– in males, codes for a protein that causes development of

testes • secrete testosterone • secrete müllerian-inhibiting factor degenerates paramesonephric

ducts

• Female development occurs in absence of hormones

27.3

Androgen-Insensitivity Syndrome

• Genetically male (XY)

• Testosterone secreted– target cells lack

receptors for hormone

• No masculizing effects occur

Embryonic Development

• External genitals of both sexes begin as a– _________________

• becomes glans of penis or • clitoris

– pair of__________________• enclose urethra of male or• form labia minora

– a pair of_________________• scrotum or• labia majora

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Homologous structures!

Male Reproductive System

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Scrotum• Pouch holding testes

– divided into 2 compartments by median septum

• Spermatic cord travels up from scrotum to pass through inguinal canal– contains testicular artery, vein, nerves,

lymphatics, and ductus deferens

27.7

Testicular Thermoregulation• Sperm not produced at core body

temperature– _________________= pulls testes close to body– _________________________

• wrinkles skin reducing surface area of scrotum • lifts it upwards

– ____________________= veins ascending near testicular artery

• countercurrent heat exchanger cools arterial blood entering testis

Testes• Oval organ, 4 cm long x 2.5 cm in diameter

• Tunica albuginea – white fibrous capsule on testes

• Septa divide testes into compartments containing____________________– each tubule lined with a thick germinal epithelium for

sperm– interstitial cells between tubules - testosterone

• Sustentacular cells – promote sperm cell development

27.9

Spermatic Ducts• Sperm flow from the seminferous tubules into

___________________then into a series of ducts:• Efferent ductules

– collect sperm from rete testes and transport it to epididymis

• ___________________ (head, body and tail)– site of sperm maturation and storage (fertile for 60 days)

• Ductus deferens • Ejaculatory duct

– 2 cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra

Male Accessory Glands

• _________________– posterior to bladder– empty into ejaculatory duct

• _________________– below bladder, surrounds

urethra and ejaculatory duct– 2 x 4 x 3 cm

• __________________– near bulb of penis– empty into penile urethra– lubricating fluid– neutralizes acidity

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Penis• Internal root, shaft, and glans• 3 cylindrical bodies of erectile tissue

– corpus spongiosum along ventral side of penis• encloses penile urethra• ends as a dilated bulb ensheathed by bulbospongiosus muscle

– corpora cavernosa • diverge like arms of a Y

• Vasodilation of deep artery fills lacunae in cavernosa with blood = erection

27.12

Hormones and Brain-Testicular Axis

27.13

Mitosis and Meiosis• _______________produces two genetically

identical daughter cells (for tissue repair, embryonic growth)

• _______________produces gametes – for sexual reproduction

• keeps chromosome number constant from generation to generation after fertilization

– 2 cell divisions (only one replication of DNA)

• Spermatogonia produce 2 kinds of daughter cells– type A remain outside

blood-testis barrier and

produce more daughter

cells until death– type B differentiate into

primary spermatocytes• meiosis I 2 secondary

spermatocytes• meiosis II 4 spermatids

• Spermiogenesis = – Transformation of

spermatids into mature sperm

Spermatogenesis

27.15

Spermatozoon• Head is pear-shaped front end

– 4 to 5 microns long structure containing the nucleus, acrosome and basal body of the tail flagella

• nucleus contains haploid set of chromosomes

• acrosome contains enzymes that penetrate the egg

• Tail is divided into 3 regions– midpiece contains mitochondria around

axoneme of the flagella (produce ATP for flagellar movement)

– principal piece is axoneme surrounded by fibers

– endpiece is very narrow tip of flagella

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Female reproductive system

• Primary sex organ: _________________(2)• Secondary sex organs: _______________(2),

___________________ (1) and _____________

28.3

The Ovaries• Small, almond

shaped ~ 3 cm long, 1.5 cm wide, 1 cm thick

• Covered in a white capsule of connective tissue (tunica albuginea)

• Held in place in the dorsal pelvic wall by several connective tissue ligaments– Ovarian ligament – attaches medial pole of ovary to the uterus– Suspensory ligament – attaches lateral pole of ovary to pelvic wall– Mesovarium – anchors anterior margin

• This is an extension of a sheet of peritoneum called the broad ligament

Ligaments suspend ovaries

28.3

Note: ovarian artery/veinentering via the suspensoryligament (functional equivalentof testicular artery)

The uterine tubes (fallopian tubes)

• Uterine tubes = fallopian tubes = oviduct• Carries ovulated gametes from the ovary to the uterus• NOT directly connected to ovary!• Gametes are washed into fimbriae by ciliated epithelial

cells and then travel along tube via cilia movement and muscular contraction of the tube

The uterus• Thick muscular

chamber• Function – shelter

and feed developing fetus and expel fetus to complete pregnancy (muscle!)

• 3 parts: fundus, body, and cervix• In nonpregnant women, the uterus is a potential

space (walls are pressed together)

The uterine wall

• External serosa (________________________)• Middle muscular layer (_______________________)

– Function: produce labor contractions to expel fetus• Inner mucosa (_________________________)

– Superficial half to two-thirds (___________________) is shed each menstrual cycle

– Deep layer (_____________________) regenerates new functionalis

28.6

The Vagina• Tube 8-10 cm long• Allows for discharge of

menstrual fluid, receipt of penis/semen, and birth of baby

• NO glands! Lubrication via transudation

• Epithelial cells rich in glycogen – this is converted to lactic acid by bacteria (fermentation) to produce a low vaginal pH (3.5-4.0)

The breasts and mammary glands

• Usually little glandular tissue – however, during pregnancy 15-20 glandular lobes develop radially around the nipple

• Each lobe drained by lactiferous ducts that drain into lactiferous sinus opening onto the nipple.

• Mound of tissue overlying pectoralis major

• Two regions: body and axillary tail

• Composed mostly of adipose tissue (fat) and collagenous tissue

• Suspensory ligaments attach breast to skin and to fascia of pectoralis major

28.9

• The follicular cells divide, become stratified and start to release estrogens and the primary oocyte completes meiosis I to form the secondary oocyte

Oogenesis

28.12

Why only 1 oocyte/follicle per month?

• Primary follicles compete to become the “dominant” follicle: each follicle secretes estradiol which inhibits FSH release from the anterior pituitary (and increases LH output).

• At the same time estradiol increases the receptors for FSH on the local follicle that released the estradiol

• Thus the follicle that secretes the most estradiol will be the most sensitive to FSH and therefore continue to grow at the lower FSH levels while the other follicles will degenerate

ovulation

• The growing dominant follicle secretes increasing levels of estrogen to trigger the acute release of LH from the Ant. Pituitary

• This surge in LH triggers completion of meiosis I and rupturing of follicle (ovulation)

28.14

The Menstrual Cycle

• Following ovulation, follicle becomes_______ ____________

• the corpus luteum secretes progesterone

• Progesterone causes a thickening of the endometrium (ready for implantation if fertilization has occured)

• Eventually, corpus luteum degenerates, progesterone levels decrease and the endometrium breaks down.

28.15