Reproductive Physiology

Dr. AndersonRowan University

Chromosomal Gender Determination• Gender differentiation is largely determined by week 20 in fetal

development

Y-Chromosome Effects

• Y-Chromosome has the SRY gene which causes the undifferentiated gonads to turn into testes when expressed.

• If this gene is not expressed, then the fetus will develop as a female

Ovaries/Testes• In the embryo, ovaries start as

mesonephric ducts or paramesonephric ducts

• If SRY gene is expressed, mesonephric ducts develop and hormones cause paramesonephric ducts to regress (male child)

• If SRY gene is absent (or not expressed) the opposite will happen (female child)

Female Differentiation• Lack of testosterone,

DHT, and anti-mullerian hormone allow the paramesonephric ducts to develop

• Uterus• Fallopian tubes• Vagina

Further Differentiation

• Once testes are formed, testosterone will continue to shape the male to form

• Epididymis• Seminal vesicle• Vas Deferens

External Genitalia• Very similar between males and females! (in derivation)

• Hormonal influences (or lack of) determine the final external genital arrangement

https://www.youtube.com/watch?v=jFh4iStyW3c

Final Phenotypes

• Given that the genitalia derive from the same tissue…

• How could the development of the genitalia vary?

• Male, female, intersexed

Puberty ( Males)

• Begins at roughly 11-12 years old

• Gonadotropin stimulating hormone causes a marked increase in testosterone production

• Testosterone causes:• Increase in facial, axillary and pubic hair length• Apocrine glands increase activity (axillary and perineal regions)• Deeper voice• Increase in testicular and penis size• Muscle and bone growth (size and thickness)

Puberty (Females)• Begins at roughly 10-11 years old (as early as 8)

• Why so early?

• Gonadotropin stimulating hormone causes a marked increase in estrogen production

• Estrodiol (estrogen) production causes:• Axillary and pubic hair appears• Apocrine glands increase activity (axillary and perineal regions)• Deeper voice (larynx increases)• Increase in labia minora and clitoris size• Menarche• Breast tissue develops

Gamete Production• Sperm and eggs cells are produced

via meiosis, not mitosis

• When sperm and eggs are produced, genes are randomly mixed during meiosis I (prophase I)

• This means that every sperm and egg produced will be unique

Crossing Over

• During meiosis I, chromosomes lined up in metaphase can exchange chromatids (sections of DNA containing whole genes)

• This leads to every sperm being slightly different, genetically

Sperm Production

• Sperm are produced in the seminiferous tubules via meiosis

• Sperm have half of the genetic material of the father

• So are all sperm the same?

Sperm Production

• Temperature is important! (controlled by cremaster muscle scrotum)• Optimal temperature is roughly 92° F.

• Activated by the secretion of Follicle-Stimulating Hormone (FSH) and testosterone

• Androgen-binding protein in the testes increases the amount of testosterone in the seminiferous tubules

• Up to 200 million sperm produced daily

Primary spermatocytes (diploid)

Meiosis ISecondary spermatocytes (Diploid)

Meiosis II

Haploid spermatids

Sperm Life Cycle

Sperm Release

• Sperm are stored in the epididymis until ejaculation

• Sperm cannot swim until they mix with the “activating” fluids produced by the prostate and seminal vesicles

• Roughly 0.1 – 10 ml of ejaculate produced, with up to 300 million sperm/ml

Oogenesis• Of about 15 follicles that begin to develop, only one dominant follicle

continues after 9 days of the cycle – the others are resorbed into the ovary

• This dominant follicle starts to produce large amounts of estrogen

Mechanics of Sex - Male

• Erection – caused by the release of nitric oxide which causes blood vessels to dilate• Corpora cavernosa of the penis

• Hydrostatic pressure increases penis size and rigidity enabling insertion

• Upon arousal, pre-ejaculate is produced by Cowper’s glands (bulbo-urethral gland)

• This fluid is slightly alkaline – why?

Mechanics of Sex - Male

Mechanics of Sex - Female

• Arousal leads to production of vaginal secretions that lubricate it for penis insertion

• Vaginal secretions are thought to derive from the blood plasma• Released upon engorgement of vaginal

blood vessels

• Clitoris will also enlarge and emerge from the clitoral hood

Birth Control

• Condoms (male and female)• The “pill”• Birth control pills• The Morning After Pill• The Abortion Pill

• Implants (vaginal, subdermal)- release hormones that prevent ovulation• Intrauterine Devices (IUD’s)• Diaphragm

Conception and Pregnancy

Dr. Robert AndersonRowan University

Conception

• Sperm cells are released into the female reproductive tract

• After ovulation, egg cells (oocytes) are most receptive to fertilization

Conception - Location• Most often, conception

happens in the ampulla of the fallopian tube

• What is the point of such an arduous trip for sperm cells?

Point of Conception• Acrosome contains

enzymes that penetrate the jelly coat of the egg

• When one sperm penetrates the plasma membrane of the egg, other sperm are prevented from entering• Why?

• Cortical granules “seal” the egg from other sperm, preventing polyspermy

Week 1 (GH)

• Sperm has reached egg and the cells have fused to become a zygote

• Cells proliferate via mitosis (morula stage) on their way to the uterus where they will implant

Week 1 (Continued)

• Morula becomes a multi-cellular, ring-shaped blastocyst

• The blastocyst “hatches” – frees itself from the zona pellucida, allowing to implant into the endometrium of the uterus (day 8-9)

Week 2 - Implantation

• Surge of progesterone (from ovulation) makes the lining of the uterus “receptive” to implantation (days 20-24 of the menstrual cycle)

• Gastrulation starts (the formation of primitive “germ layers”)

Gastrulation

Week 3• Ectoderm folding creates the

neural tube

• Brain starts to develop and differentiate into sections

• Musculoskeletal system starts to develop

Week 4

• CNS further differentiates into spinal cord, ganglia and brain proper – neural tube closes

• Heart begins to beat (first fully functional organ) at day 23 with blood vessels

• Liver develops

• Skin starts to form (epithelia)

Week 5 • Heart develops septa (atria and

ventricles)

• Eye lenses form

• Cerebral hemispheres form

• Upper and lower limb buds grow

Week 5 – Umbilical Cord

• Composed of one umbilical arteries and two umbilical veins

• Derived from the zygote and develops as food stores in the embryo are used up

• Attaches to the placenta

Placenta

• Close association of blood vessels between maternal and fetal portions of the placenta allows for exchange

• Of what?

• What won’t go through?

Week 6

• Endocrine development (pituitary, thyroid, parathyroid, thymus, adrenal glands)

• Tongue forms

• Olfactory nerves enter the brain

Morning Sickness

• Generally starts around week 6• Sometimes the first sign of pregnancy!

• Due to increased estrogen levels in the blood

• Usually gone by week 12

• Why is morning sickness a thing?

Week 7• Limb bones form

(endochondrial ossification)

• Muscles of abdominal wall separate

• Mullerian ducts invaginate the body wall

• Eyelids meet

Week 8

• Gastrointestinal tract perforates body wall (anus)

• Most components of axial skeleton visible

• Fingers and toes separate

• Gonads start to differentiate in accordance with secreted hormones

Week 9• Hearing and olfactory anatomy

developed

• Femur length at this point is 6mm long

• Gender (external) not yet differentiated

Week 10

• Intestines in abdomen

• Fingernails appear

• Outer ears (pinnae) form

• De novo hormones produced from pancreas and pituitary (HGH)

Second Trimester (Weeks 12- 16)

• External genitalia differentiate

• Milk teeth are present in the mandible and maxilla

• Growth hormone levels peak (pituitary)

• Vellus body hair emerges from skin

Second Trimester (Weeks 17 – 21)

• Vernix caseosa covers skin • Functions?

• Antimicrobial • Protection• ??

• Spleen formed and contains lymphocytes

Vernix

Second Trimester (Weeks 22 – 26)

• Alveoli start to appear in lungs• Beginning to secrete surfactant

• Why need surfactant in the lungs?

• Why is it not necessarily important at this stage?

Second Trimester (Weeks 27 – 38)

• Lungs formed

• Testes descend into scrotum (male)

• Nails reach end of fingers

• All sulci present in brain

• Thyroid and adrenal hormones secreted

Birth!

• Much safer than it used to be!• Up to 50% mortality for mom

AND baby 150 years ago

• Very stressful for mom and baby (obviously)

Maternal Post-Birth Effects

• Organs move to accommodate baby

• Breathing difficulties

• Uncomfortable sleeping

Lactation

• Release of prolactin from the pituitary causes the production of milk

• Negative feedback regulates production (Milk loss increases production and vice-versa)

Stretch Marks

• Caused by separation of collagen fibers that lie over rapidly growing tissue

• Will disappear with time!