Chapter 26: Reproductive System

when does the reproductive system activate?

puberty

4 tasks of reproductive system

1. produce gametes

2. bring gametes together (sex)

3. combine genetic info through fertilization (zygote)

4. support development of fetus (gestation) and birth

gonads

primary sex organs

male gonads

testes

female gonads

ovaries

2 products of gonads

1. gametes

   1. sex hormones (steriods)

male sex hormone

testosterone

female sex hormones

estrogens and progesterone

accessory reproductive organs

1. ducts

2. glands

3. external genitalia

hypothalamic-pituitary-gonadal (HPG) axis hormones

GnRH (hypo), FSH (AP), LH (AP), testosterone (gonads), and inhibin (gonads)

HPG axis

regulation of the production of gametes and sex hormones through hormonal events involving hypo, AP, and gonads

meiosis

nuclear division that occurs only in gametes

synapsis

homologous chromosomes pair up forming tetrads consisting of 4 chromatids

crossover (chiasmata)

exchange of genetic material between chromatids

testes function

produce sperm that lie in scrotum

ducts that deliver sperm to body

1. epididymis

2. ductus deferens

3. ejaculatory duct

4. urethra

male accessory sex glands

1. seminal glands

2. prostate

3. bulbo-urethral glands

seminiferous tubules (in testes)

site of sperm production

where does sperm travel to

from seminiferous tubules to the epididymis; where sperm is stored until ejaculation

accessory ducts function

carry sperm from testes to body exterior

epididymis

1. where sperm mature

2. expels sperm into ductus deferens during ejaculation

vasectomy

cutting and ligating ductus deferens

seminal glands

produce alkaline fluid (70% of semen)

prostrate function

1. secretes milk, slightly acidic fluid

2. sperm activation

3. enters urethra during ejaculation

bulbo-urethral glands

1. produce thick mucus during sexual arousal

   1. lubricate penis

   2. neutralizes acidic urine in urethra

spermatogenesis

process of forming male gametes

where does spermatogenesis occur

seminiferous tubules

when does spermatogenesis begin

at puberty

sustenocytes

1. support sperm

2. produce ABP + inhibin

inhibin

shuts down FSH release

spermatogenic cells

precursor to sperm

myoid cells

1. smooth-muscle like cells, surround seminiferous tubule

2. contract to squeeze sperm and testicular fluid through tubules

interstitial endocrine cells

produce androgens and some estrogen

spermatogenesis events

1. mitosis of spermatogonia (stem cell)

   1. forms 2 spermatocytes

2. meiosis

   1. forms secondary spermatocytes that form spermatids

3. Spermiogenesis

   1. spermatids become sperm

Mitosis of spermatogonia result

forms type A and type B daughter cells

type A daughter cell

remains at basal lamina to maintain pool of dividing germ cells

type B daughter cell

move toward lumen and becomes primary spermatocytes

Meiosis I of spermatocyte

produces 2 secondary spermatocytes (n)

meiosis II of secondary spermatocyte

forms 2 spermatids

spermiogenesis

spermatid elongates, loses excess cytoplasm, and forms a tail

head of sperm

1. nucleus

2. acrosome

acrosome

contains hydrolytic enzymes that enable sperm to penetrate egg

midpiece of sperm

mitochondria that produce ATP to move tail

tail

locomotor region that includes flagellum

time it takes for a spermatid to become a functional sperm

64-72 days

hormonal regulation of testicular function

by HPG axis: GnRH, FSH, LH, testosterone, and inhibin

testosterone function

prompts spermatogenesis and targets all accessory organs; anabolic effects

regulation of male reproductive system

amount of testosterone and sperm produced by testes reflects balance among interacting hormones of HPG axis—takes 3 years to achieve (puberty)

loss of GnRH and gonadotropins

testes atropy, and sperm and test production ceases

ovaries—female gonads

1. produce gametes (ova)

2. secrete sex hormones

female duct system

1. uterine tubes

2. uterus

3. vagina

ovaries

paired structures that flank the uterus; held in place by ligaments

ovary features

1. cortex

2. medulla

cortex

houses gametes (follicles)

medulla

contains blood vessels and nerves

follicles

immature egg (oocyte)

what surrounds a oocyte

1 or more layers of different cells

ovulation

when a ripened follicle ejects an oocyte

does the female duct system have direct contact with the ovaries?

no

uterine tubes function

1. site of fertilization

2. captures ovulated occyte

fimbriae

cilitated projections that drape over ovary and help carry oocyte towards the uterus

uterus function

receive, retain, and nourish fertilized ovum

layers of uterus

1. perimetrium (outermost)

2. myometrium

3. endometrium

myometrium

smooth muscle that contracts during childbirth

endometrium

1. proliferates with each hormonal cycle

2. fertilization: helps develop placenta

3. no fert: sloughs off as menstrual flow

stratums of endometrium

1. stratum functionalis

2. stratum basalis

stratum functionalis

1. changes in response to ovarian hormone cycles

2. shed during menstruation

stratum basalis

1. forms new functional layer

2. unresponsive to ovarian hormones

when does oogenesis begin

begins in fetal period

oogonia

diploid stem cells that divide mitotically to produce primary oocytes

primary oocytes undergo…

meiosis I to produce secondary oocytes

secondary oocytes undergo…

meiosis II to produce ova

primary oocytes meiosis I is…

arrested in prophase I, only a small fraction are recruited to continue

secondary oocytes meiosis II is…

arrested in metaphase II and is only completed if fertilized

2 fates of follicles

1. apoptosis

2. ovulation

dominant follicle

selected primary oocyte that resumes meiosis I and arrests in metaphase II (becomes secondary oocyte)

high levels of what hormone activate a few primary oocytes to mature

FSH

corpus luteum

composed of follicular cells, produces progesterone in ovulation

what happens to the secondary oocyte if fertilization does not occur

it deteriorates

what happens to the secondary oocyte if fertilization occurs

completes meiosis II to form one large ovum

how long does it take for an ovum to reach the uterus

6-7 days

cells surrounding oocytes

many granulosa cells sustain one oocyte

cells surrounding spermatocytes

one sustenocyte sustains many spermatocytes

ovarian cycle

monthly series of events associated with maturation of egg p

phases of ovarian cycle

1. follicular phase (days 1-14)

2. luteal phase (days 14-28)

follicular phase

dominant follicle becomes sensitive to FSH and outcompetes other follicles to resume meiosis I

luteal phase of ovarian cycle

ruptured follicle forms corpus luteum after ovulation

outcomes of luteal phase

1. no pregnancy = corpus luteum degenerates

2. pregnancy = corpus luteum produces hormones that sustain pregnancy until placenta takes over at 3 months

uterine (menstrual) cycle

1. menstrual phase (1-5)

2. proliferative (preovulatory) (6-14)

3. secretory (postovulatory) (15-28)

menstrual phase

1. ovarian hormones drop, gonadotropin levels rise

2. stratum functionalis detaches from uterine wall, expelled

3. day 5: ovarian follicles produce estrogen

proliferative phase

1. estrogen levels prompt generation of new functional layer

2. ovulation occurs on day 14

secretory phase

1. most consistent in duration

2. increase in progesterone from corpus luteum prepare functional layer for fertilized egg

secretory phase

if fertilization does not occur, it all breaks down