Biology 30 AP - Reproduction & Development

Male reproductive system flow chart

primary reproductive organs (gonads) → testes → produce sperm

Male gonads function

secret sex hormones → testosterone

puberty (point where reproduction is possible) → males must be able to produce and ejaculate semen

controlled by specific hormones

Hypothalamus secretions

GnrH (gonadotropin releasing hormone)

Anterior pituitary secretions (male)

FSH (follicle stimulating hormone) → simulates sperm production in seminiferous tubules

LH (luteinizing hormone) → stimulates testosterone production in interstitial cells

Male secondary sex characteristics

caused by testosterone

development of pubic and facial hair

maturation of internal and external genitalia

increase in shoulder width and muscle mass

voice → larynx enlarges, vocal cords thicken and lengthen

skin → sebaceous gland secretion thickens and increases (acne)

mental → increased aggression, sex drive

Prepuce (foreskin)

serves a protective function

sometimes removed in circumcision)

Glans

expanded tip of the penis

Corpus cavernosa

erectile tissue

fills with blood thus producing an erection

Corpus spongiosa

soft erectile tissue

Urethra

carries sperm and urine (NEVER AT THE SAME TIME)

sphincter controls urine excretion

Erection

produced by trapping of blood in corpus cavernosa in response to stimulation of parasympathetic nervous system

arteries dilate (increased blood flow in)

veins constrict (decreased blood flow out)

Prostate gland

produces mucous for lubrication and buffer to protect sperm from acidic vagina

Vas deferens

ductus deferens

tube that carries sperm from testes to urethra

Seminal vesicle

sacs under bladder

secret fructose (food for sperm) & prostaglandins (stimulates uterine contractions → helps sperm move up uterus)

60% of total semen volume

Ejaculatory duct

connects vas deferens to urethra

Cowper’s gland (bulbourethral) gland

secretes clear, salty mucous for lubrication and neutralizes acidic male urethra and vagina

Epididymus

coiled tube attached to outer edge of testis

where sperm completes development/matures

Seminiferous tubules

250m of twisting tubes in testis

site of sperm production

part of testicles

Scrotum

sac that contains testis

made of elastic skin

temperature regulation (sperm develop best at 3 degrees lower than regular body temperature)

part of testicles

Spermatogenesis

production of sperm begins at puberty and continues until death

1 - spermatogonium (46 chr,) → mitosis → 2 - primary spermatocytes (46 chr.) → meiosis I → 2 - secondary spermatocytes (23 chr.) → meiosis II → 4 spermatids (23 chr.) → 4 mature sperm (23 chr.)

seminiferous tubules: spermatogonium → secondary spermatocytes

epididymus: spermatids → sperm (maturation)

stimulated by FSH and testosterone

Sertoli (nurse) cells

in seminiferous tubules

nourish the sperm as they mature

Sperm structure

over 300 000 000 produced daily

designed for travel

nucleus contains DNA

semen includes sperm and secretions from supportive fluids for nourishment and protection against acidic vagina

Acrosome

head of the sperm

contains enzymes to penetrate the egg

Sperm tail

contains centriole for structure of flagellum

Sperm mid-piece

contains mitochondria to provide the energy for whipping motion

Vasectomy

snipping of vas deferens thus preventing sperm from entering ejaculate

What happens if testicles don’t descend?

viable sperm will not develop

Hernia

rupture occurs in thin membrane separating testes and small intestine → small intestine slips through → impairs blood supply for either testis or small intestine

Testicular cancer

found primarily in young males

Prostate problems

found in older males

enlargement leads to urinary problems

prostate cancer → treated with excision

Path of sperm development to the outside world

seminiferous tubules (site of spermatogenesis)

collecting duct

epididymus (“mature”)

vas deferens

• seminal vesicles: add sugar solution to the semen and prostaglandin to increase sperm movement (triggers contractions)

• prostate gland: secretes an alkaline buffer to combat the acidic vagina

• Cowper’s gland: produce a mucous-rich alkaline secretion

urethra

semen

Female reproductive system flow chart

primary reproductive organs (gonads) → ovaries → produce ova (eggs)

Female gonads function

secretion of sex hormone from gonads → estrogen & progesterone

puberty (point where reproduction is possible) → females must be able to ovulate (release eggs)

controlled by specific hormones

Anterior pituitary secretions (female)

FSH (follicle stimulating hormone) → stimulates follicle in ovary

LH (luteinizing hormone) → stimulates follicle release and formation of corpus lutetium

Female secondary sex characteristics

development of pubic hair

maturation of internal and external genitalia

increase in hip width

voice changes

skin → sebaceous gland secretion thickens and increases (acne)

distribution of fat in breasts and buttocks

Labia

protective flaps of skin on either side of vaginal opening

majora: homologous to male scrotum

minora: homologous to male urethra and penile tissue

vulva

Clitoris

packed with sensory nerves

homologous to male penis

Vagina

connects the uterus with outside world

site of sperm deposition, birth canal, protection from bacterial invasion (highly acidic)

Cervix

cervical canal

muscular band that prevents fetus from delivering prematurely

dilates during birth

Uterus

womb

pear shaped

fertilized ovum embeds in endometrium (uterine lining)

Ovary

store and produce ova

generally one mature ovum produced monthly (alternating ovaries)

Oviduct

fallopian

tube carrying mature ova to uterus

site of fertilization

ova swept in by fimbria at open ends

Oogenesis

girls are born with all of their primary ooctyes in Prophase I of meiosis

every month after puberty until menopause, a primary oocyte continues with meiosis I and meiosis II to develop into a secondary ooctye

ovulation occurs at Metaphase II

meiosis II proceeds through Anaphase II and Telophase II if the egg is fertilized

Oogenesis flow chart

1 - oogonium (46 chr.) → 1 - primary oocyte (46 chr.) → 1 - secondary oocyte (23 chr. + 1 polar body) → 1 - mature ovum (23 chr. + 3 polar bodies)

before birth in ovary: oogonium → primary oocyte

monthly in oviduct: secondary oocyte → mature ovum

Male hormonal regulation

Sertoli cell inhibin (hormone) negatively feeds back to hypothalamus and anterior pituitary in males to inhibit sperm production

Menstruation

periodic discharge of blood and fluid from uterus

caused by low levels of estrogen and progesterone at end of monthly cycle (hormone withdrawal)

Menstrual cycle

repetitive sequence of shedding the uterine lining (menstruation), development and release of egg (ovulation), and replacement of the endometrium

continues from puberty to menopause

What are uterine contractions triggered by?

by prostaglandins

cause much of the pain felt during menstrual cramps

contractions inhibit blood flow to the lining of the uterus (endometrium)

Flow phase

day 1-5

marked by the shedding of endometrial lining

triggered by a decrease in ovarian hormones (esp. progesterone) → stimulates FSH & LH from pituitary

corpus luteum degenerates forming corpus albicans

low hormone levels → headaches, cramps, nausea, mood changes

Follicular phase

day 6-13

until ovulation

governed by estrogen released by developing follicle (which is stimulated by FSH)

endometrial lining thickens (estrogen)

FSH decreases (negative feedback from estrogen)

LH production increases (positive feedback by estrogen)

follicle matures

Ovulation

day 14

estrogen peaks just before

LH & FSH peaks at ovulation

follicle erupts

ovum is released into the fallopian tube

female’s temperature peaks (contraceptive method or to help in impregnation)

Luteal phase

day 15-28

corpus luteum develops

until menstruation

governed by progesterone released by the corpus luteum (stimulated by LH)

further ovulation and uterine contractions are inhibited (progesterone)

endometrial lining continues to thicken (preparing for pregnancy) → progesterone and estrogen from corpus luteum

progesterone and estrogen inhibit LH release (negative feedback) → corpus luteum starts to degenerate = breakdown of endometrium = flow phase

3 things to remember about female hormones

drop in progesterone = menstruation OR miscarriage

peak/spike/increase in LH = positive ovulation test (for trying to get pregnant)

peak/spike/increase in HCG = positive pregnancy test as it is ONLY made by cells in the placenta

• detected via urine/blood test

Tubal ligation

tying or cutting of the tubes

method of “permanent” birth control

How is cervical cancer tested for?

PAP smear

sampling cells

looking for signs of irregular cells

Endometriosis

sometimes debilitating disease caused by endometrial lining forming inside the abdominal cavity (and is still shed monthly)

How do birth control pills work?

prevent ovulation through increased progesterone levels

What determines the degree of secondary sex characteristics?

the relative quantities of androgens and estrogens present in BOTH males and females

Ectopic pregnancies

result from implantation in the fallopian tube instead of the uterus

pregnancy will rupture the fallopian tube if allowed to continue

Male perspective of fertilization

several hundred million sperm released into vagina per ejaculation

many sperm destroyed by vaginal acidity

sperm then travel up vagina (cervix → uterus → oviduct (fallopian tube))

Fertilization

only a few dozen to a few hundred sperm survive to reach egg

usually occurs in a single oviduct (fallopian tube)

head of one sperm cell penetrates egg plasma membrane → triggers completion of meiosis II in egg → sperm nucleus (n=23) & egg nucleus (n=23) → formation of zygote (2n=46)

Cleavage process

zygote (~0.1 mm) undergoes first mitotic division within 30 hours of fertilization as it travels down oviduct

2 cells → 4 cells → 8 cells (stays the same size)

Blastocyst formation

morula (16 cells) reaches uterus 3-5 days after fertilization

• fills with uterine fluid and two different groups of cells form a sphere called a blastocyst (blastula)

inner blastocyst → becomes embryo

outer cells (trophoblast) → become chorion → eventually forms placenta