9: Reproductive System

Question 1

how do we become male or female?

Answer 1

first 5-6 weeks in womb all embryos sexually indifferent
testes 7-8 weeks that secrete testosterone, other hormones produced that cause uterus and fallopian tubes to disappear
ovaries 8-9 weeks produce oestrogen, lack of testosterone causes male organs to disappear

Question 2

main structures of reproductive system

Answer 2

gametes = functional male and female reproductive cell
gonads = reproductive organs that produce gametes and hormones
ducts = receive and transport the gametes
accessory glands and organs = secrete fluids into the ducts
external genitalia = perineal structures collected together

Question 3

males

Answer 3

testes produce sperm which is expelled from the body in semen during ejaculation
semen is mixture of sperm and other secretions from accessory glands
testes first develop in posterior abdomen wall, then migrate to external position because temperature too warm

Question 4

scrotum

Answer 4

serous membrane lines scrotal cavity, reducing friction between the inner surface of the scrotum and outer surface of the testis
scrotum consists of thin layer of skin - its dermis contain dartos muscle (layer of smooth muscle)
a layer of skeletal muscle called cremaster muscle lies beneath the dermis - can control pull of testes closer to body
normal sperm development requires 1.1 degrees C lower than the body, cremaster and dartos relax or contract to move testes
each testis wrapped in tough fibrous capsule, the tunica albuginea - subdivides testes into 250 lobules
in lobules are approximately 800 slender, tightly coiled seminiferous tubules (produce sperm which can leave through passageways called the rete testis)
interstitial endocrine cells produce male sex hormones (androgens) the most important one being testosterone
nurse cells nourish the developing sperm cells

Question 5

spermatogenesis

Answer 5

the origin and develop of sperm, begins at puberty and ends relatively late in life
3 stages:
- mitosis of sperm cells called spermatogonia leads to primary spermatocytes
- 2 stages of meiosis turn primary spermatocytes into secondary and then spermatids
- last stage called spermiogenesis where spermatids turn into mature spermatozoa which enter the fluid within the lumen of the seminiferous tubules
whole process takes approx. 64 days

Question 6

sperm anatomy

Answer 6

head = contains nucleus filled with densely packed chromosomes, tip of head called the acrosome containing enzymes essential for fertilisation
neck = short, attaches head to middle piece
middle piece = contain mitochondria, provide the ATP for the tail
tail = corkscrew motion moves the sperm

Question 7

male reproductive tract

Answer 7

the epididymis = where sperm are transported to via fluid currents created by cilia lining the efferent ducts, stores and protects maturing sperm, sperm immotile until undergo capacitation
the ductus deferens = ascends into abdominal cavity, contractions in the muscular wall propel the sperm and fluid along, joins with the seminal gland to form ejaculatory duct
accessory glands = secrete fluid for semen which activate sperm, provide nutrients for mobility, and produce buffers to counteract acidity of urethral and vaginal environments
(seminal glands, prostate and bulbo-urethral glands)

Question 8

semen

Answer 8

fluid that contains sperm and the secretions of the accessory glands, contains 3 components
- sperm: 20-100 million sperm per ml of semen
- seminal fluid: mixture of glandular secretions
- enzymes: protease helps dissolve mucus in vagina, seminal plasmin kills variety of bacteria, prostatic enzyme causes semen to clot after ejaculation

Question 9

male hormone regulation

Answer 9

anterior lobe of pituitary gland releases follicle stimulating hormone FSH and luteinising hormone LH
their release occurs in response to gonadotropin-releasing hormone which is secreted by hypothalamus and carried to anterior lobe by hypophyseal portal system
FSH targets primary nurse cells of the seminiferous tubules, which then promote spermatogenesis
LH causes the secretion of testosterone and other androgens by the interstitial endocrine cells of the testes
testosterone production begins around the seventh week of foetal development and reaches a peak after 6 months
testosterone production low at birth, accelerates at puberty, negative feedback in adult males

Question 10

females

Answer 10

ovaries produce immature ovum called oocytes, travel along the uterine tube toward to uterus
fertilisation matures the oocytes into an ovum
vagina connects the uterus with the exterior of the body
main organs are ovaries, uterine tubes, uterus and vagina

Question 11

the overaires

Answer 11

three main function: produce female gametes (oocytes), secrete female sex hormones, and secrete inhibin (involved in the feedback control of FSH)
stabilised by the broad ligament
the suspensory ligament contains the major blood vessels
follicles = functional unit

Question 12

oogenesis

Answer 12

oogenesis = ovum production, begins before birth
process accelerates at puberty and ends at menopause
takes place in the ovaries each month as part of menstrual cycle
oogonia (female reproductive stem cells) go through mitosis before birth and their daughter cells (primary oocytes) begin meiosis between third and seventh month of foetal development
2 million oocytes at birth, only 400,000 when reach puberty
then go through meiosis at puberty

Question 13

ovarian follicle development

Answer 13

ovarian follicles are the sites of both oocyte growth and phase I of meiosis during oogenesis
primordial ovarian follicles = primary oocytes surrounded by single layer of follicle cells
follicle development begins with activation of primordial ovarian follicles into primary ovarian follicles
wall of follicle thickens to become secondary ovarian follicle, then doubles in size for tertiary ovarian follicle

Question 14

the ovarian cycle

Answer 14

tertiary ovarian follicles ready to complete their maturation as part of the 28-day ovarian cycle
bleeding = first day of circle
follicular phase - 14 days average, egg develops in follicle, fuelled by FSH and produces oestrogen, destruction and shedding of cells in functional zone due to no fertilisation, in proliferative phase there is repair and regeneration of functional zone, ovulation happens at end of follicular phase when egg is released by follicle
luteal phase - 14 days average, progesterone and oestrogen, corpus lithium will generate into corpus albicans if no pregnancy

Question 15

the uterine tubes

Answer 15

end closest to ovaries form an expanded funnel called infundibulum
has numerous finger like projections that extend into the pelvic cavity and drape over the ovary called fimbriae - cilia that beat towards the uterus
secondary oocytes transported through ciliary movement and peristaltic contractions in the walls of the tubes

Question 16

the uterus

Answer 16

protects, nourishes and removes waste from the developing embryo and foetus
contractions of the muscular uterus important when giving birth
body = largest region, body ends laterally at constriction called isthmus
cervix = inferior portion of uterus, projects a short distance into the vagina, surface surrounds the external os of the uterus, cervical canal opens into the uterine cavity at the internal os (os = opening or mouth)
uterine walls made up of an inner endometrium and a muscular myometrium, covered by the perimetrium
endometrium consists of superficial functional layer and deeper basal layer - functional layer undergoes changes in response to sex hormone levels which produce the characteristics of the menstrual cycle

Question 17

the uterine (menstrual) cycle

Answer 17

the uterine cycle = a repeating series of changes in the structure of the endometrium
begins at puberty, first cycle called menarche (ages 11-12 usually)
continues till ages 45-55, when menopause (the last cycle) occurs
3 phases…

Question 18

the menstrual phase

Answer 18

marked by shedding of the endometrial functional layer, leading to menstruation
process triggered by decline in progesterone and oestrogen levels as the corpus lithium disintegrates
endometrial arteries constrict, reduced blood flow, functional layer begins to die, weakened arterial walls rupture and blood pours into connective tissues of the functional layer
blood cells and degenerating tissue break off and are lost through the vagina
shedding of tissue until whole functional layer lost, usually lasts 1-7 days
pain from uterine inflammation or myometrial contractions (cramps)

Question 19

the proliferative phase

Answer 19

begins in the days after menstruation
repair process, stimulated by rising oestrogen levels that accompany the growth of another set of ovarian follicles
by ovulation, functional layer back to several mm thick

Question 20

the secretory phase

Answer 20

uterine glands enlarge and increase their rates of secretion
stimulated by progesterone and oestrogens from the corpus luteum
begins at ovulation and lasts as long as corpus luteum stays intact

Question 21

vestibular glands

Answer 21

lesser vestibular glands - discharge secretions onto the exposed surface of the vestibule, keeping it moist
greater vestibular glands - discharge secretions during sex into the vestibular

Question 22

the mammary glands

Answer 22

lactation (milk production) occurs at maternal mammary glands
each breast has a mammary gland within the subcutaneous tissue of the pectoral fat pad
nipple = where ducts open onto body’s surface
areola = reddish-brown skin surrounding nipple, large sebaceous glands beneath the areolar give it grainy texture
ducts leaving lobules merge into single lactiferous duct, forms an expanded chamber near the nipple called a lactiferous sinus

Question 23

hormones during the follicular phase

Answer 23

begins each month when FSH from the anterior lobe of the pituitary gland stimulates the rapid growth of a dominant tertiary ovarian follicle
as follicle cells enlarge and multiply, steroid hormones released called oestrogens - most important one is oestradiol
early in follicular phase, oestrogen and inhibin are low which inhibit LH and FSH
at day 14 - high oestrogen levels trigger surge of LH which triggers rupture of follicular wall and ovulation

Question 24

hormones during the luteal phase

Answer 24

begins at high LH levels
progesterone is principle hormone of this phase, from corpus luteum
after 12 days, corpus luteum becomes non functional and progesterone and oestrogen levels fall
GnRH no longer inhibited, increased FSH production, restarting cycle