Reproduction & Development- unit 11

bio 1203

Function of male reproductive system

• produce sperm

• transfer sperm into female reproductive tract → fertilization

Scrotum

• muscular sac around penis (testes outside of body)

• 2-4c lower temp (for survival)

Testes

• gonads

• Leydig cells produce testosterone → formation of sex organs, develops secondary sex characteristics, sperm production

Sperm Production

in seminiferous tubules of testes

2 cells:

1. Sertoli cells

   • supportive cells, produce signals to promote/inhibit sperm production

2. Germ cells

   • become sperm through spermatogenesis (puberty)

Sperm Transport Pathway

seminiferous tubules → epididymis → van deferens → ejaculatory duct → urethra

Epididymis

• comma shaped, posterior to testes

• sperm maturation (mobility/ability to fertilize egg)

• sperm stored up to 4 weeks

• before ejaculation: moves from tail of ep → vas deferens

Vas Deferens

transport sperm to ejaculatory duct

Ejaculatory Duct

• short duct, contents from VD/seminal vesicles merge

• semen (sperm/fluids) ejected into prostatic urethra

Urethra- Male

• last duct: through prostate glands → out to penis

• also carries urine out

Accessory Reproductive Glands- Seminal Vesicles

• paired, under urinary bladder

• secrets alkaline viscous fluid (helps neutralize acidic female environment)

• high fructose, supplies sperm w ATP

Accessory Reproductive Glands- Prostate Gland

• anterior to rectum, base of bladder

• muscular/glandular tissue

• produces milky/alkaline substance → contains enzymes/citric acid (sperm mobility)

Accessory Reproductive Glands- Bulbourethral glands

• inferior to prostate

• secretes alkaline mucous before ejaculation (lubrication of end of urethra/vagina, removes urine/old sperm from urethra)

Male External Genitalia

Peen

• shaft surrounds urethra

• high concentration of nerve endings at ends (promotes ejaculation)

Hormonal control of Spermatogenesis

• Hypothalamus releases GnRH

• A.P. releases FSH/LH

• FSH→ release of ABP, keeps local high testosterone maintained

• LH→ testosterone production

• T: stimulates final stages of spermatogenesis

Mechanism of Sperm Release

• erect → penis produces sperm into vagina

  1. Erection “aim”

     • parasympathetic

     • dilation of sinuses, fill w venous blood

  2. Ejaculation “fire”

     • sympathetic

     • emission = sperm/fluids moved to urethra

     • expulsion= contraction of urethral/penile muscle forces semen out

Functions of Female Reproductive System

• develop ova/egg

• prepare for fertilization

• produces: estrogen/progesterone

• carries fertilized egg

Ovaries

• paired female gonads→ produce ova/oocytes

• produces hormones→ develops primary/secondary sex characteristics

• prepares endometrium for implantation

Fallopian Tubes

• undulation of fimbriae draws oocytes from ovary into fallopian tubes

• site of fertilization/transports ovum/zygote to uterus

• cant implant zygote in tubes

Uterus

• site of menstruation

• implantation of fertilized ovum

• fetal development

• labour

• 3 layers

• cervix = lower uterine opening to vagina

3 Layers of Uterus

1. Perimetrium: outer serous, part of visceral peritoneum

2. Myometrium: middle, interlacing layers of SM (birth)

3. Endometrium: mucosal lining, 2 layers

2 Layers of Endometrium

1. Stratum Functionalis

   • shed during menstruation

   • changes due to ovarian hormones

2. Stratum Basalis

   • never goes away

Vagina

• birth canal

• menstrual flow

• produces organic acids (maintains acidic environment)

• thin walls

• cervix to exterior

Female Reproductive Accessory Gland: Bartholins Glands

secretes muscos lubricant

1. Ovarian Cycle

• events associated w maturation of ovum

• follicular/luteal phases

2. Menstrual (uterine) cycle

• development/shedding of uterine lining (menstruation)

• non pregnant people

• prepares uterus to receive fertilized ovum

Ovarian Cycle

• includes oogenesis/folliculogenesis

• 1 egg released per month

• cycle = 28 days

Regulated by:

• Hypothalamus (GnRH)

• A.P. (FSH/LH)

• Ovaries (estrogen/progesterone)

Day 1 - 5: Folliculogenesis/Follicular Phase

hypothalamus releases GnRH → A.P. releases FSH/LH

• 4/5 primary follicles (ovum layer of supporting cells) begin development

• end of stage = all primary follicles degenerate

• except 1 → develops into secondary follicle

Day 6 - 13: Follicular Phase

• follicle grows, fluid inside increases

• ovum pushed to side

• moderate estrogen levels (negative feedback on hypothalamus, stops FSH/lH secretion)

Day 14: Ovulation

• estrogen levels peak (positive feedback on hypothalamus, more LH)

• levels of LH peak → ovulation

• follicle bursts → ovum released into fallopian tubes

• LH transforms ruptured follicle into corpus lute (produces pro/estrogen)

Day 15 - 28- Luteal Phase

• high progesterone, decreasing estrogen (inhibits GnRH)

• end of cycle, egg not fertilized = corpus luteum degrades, no more progestogen

• FSH/LH no longer blocked, cycle continues

Uterine/Menstrual Cycle

changes undergone by uterine endometrium each month in response to ovarian hormones in blood

Uterine Cycle: Days 1 - 5

Menses Phase

• uterus sheds all but deepest layer of endometrium

• low estrogen/progesterone → triggers shedding of stratum functionalis

Uterine Cycle: Days 6 - 14

Proliferative Phase

• endometrium rebuilds

• high estrogen

• tertiary follicles prompt LH surge

• fallopian tube contracts

Uterine Cycle: Days 15 - 28

Secretory Phase

• Endometrium prepares for implantation of embryo (thick/vascular)

• high progesterone from corpus luteum

If Fertilization doesn’t occur

• progesterone falls (deprives endometrium of hormonal support)

• endometrial cells die

• functional layer digests itself, sloughed off

Corpus Luteum

• maintained by hCG (human chorionic gonadotropin) produced by developing placenta

• secretes pro/estrogen (maintains endometrium)

Placenta

• 4 months: well developed

• corpus lutem begins to degenerate

• placenta produces pro/estrogen

Pregnancy Tests

• production of hCG after fertilization (basis of test)

• hCG detachable from day 8

Fertilization

• union of nucleic of sperm + ovum

• in outer third of fallopian tubes within 12-24h of ovulation

• forms zygote from 2 gametes

• head of one sperm enters ovum

Path of Sperm Cell

corona radiata → zona pellucida → plasma membrane of secondary oocyte → cytoplasm of secondary oocyte

Implantation

• blastocyst attaches to endometrium

• trophoblast produces enzyme (aids penetration of endometrium)

• enzyme removes zona pellucida

Monozygotic Twins

• genetically identical (same sex)

• division of single fertilized ovum

• division after 8 days = conjoined twins

Dizygotic Twins

• 2 ova released during ovulation

• fraternal twins

Fetal Development

• formation of blastocyst → cells continue dividing/differentiate

• inner cell mass becomes primary germs layers (fetus)

• trophoblast → extra embryonic membranes

Primary Germ Layers

Ectoderm: skin, NS

Mesoderm: muscle/bone, CT

Endoderm: epithelium of GI tract, gall bladder, trachea, lungs

Chorion

• outermost membrane

• from trophoblast

• becomes part of placenta

• absorbs nutrients from endometrium

• secretes hCG

Amnion

• produces insulating fluid (temp maintenance/shock absorber)

• fluid for embryo

Yolk Sac

• from blastocyst cavity

• forms part of umbilical cord

• not important in humans

Allantois

• becomes stalk of embryo

• helps form: blood cells, umbilical blood vessels

• later forms umbilical cord

Placenta

• formed from: embryonic chorion/maternal endometrium

• chorionic villi erode endometrium → forms sinuses (fill w maternal blood)

• allantois in cord grows into placenta (bring umbilical blood vessels)

Placental Functions

maternal fetal exchange:

• nutrients from mom → fetus

• wastes from fetus → mom

endocrine secretion of:

• hCG

• estrogen/progesterone

Umbilical Cord

formed by: allantois, yolk sac

contains:

• 1 vein (carries blood from placenta → fetus)

• 2 arteries (carry blood from fetus → placenta)

Zygote

Embryo

Fetus

Z: fertilized egg

E: after fertilization - 8 weeks

F: week 9 - birth

Fetal Circulation

• nutrients/oxygen passed from placenta → fetus

• fetal lungs not useable, diff blood circulation than adults

• purpose: bypass lungs

Inefficiency of Fetal Circulation

• mixing of oxygenated + deoxygenated blood in fetal inferior v.c.

• problem: needs to transfer oxygen from maternal → fetal blood

• compensation: fetal hemoglobin binds to O w higher affinity compared to adult hemo

Pregnancy

progesterone/estrogen levels steadily increase

Labour

• progesterone inhibits uterine contraction

• estrogen stimulates uterine contraction (increases # of oxytocin receptors in uterine miscue layer)

• end of gestation: progesterone decreases, estrogen increases (begins contractions)

Stages of Labour: stage of dilation

• cervix progressively dials to 10 cm

• amnion stretched + bursts

• amniotic fluid released

Stages of Labour: Stage of Expulsion

• full cervical dilation → fetal expulsion

Stages of Labour: Placental Stage

• uterine contractions resume

• placenta expelled

• contractions reduce post part hemorrhage

Fetal Lungs

• filled w fluid before delivery

• during labour: fetal thoracic cavity compressed (expels 33% of fluid)

• Initial breaths pushes fluid into cardiovascular/lymphatic

Surfactant

• phospholipid

• produced by fetal lungs (weeks 26-28)

• reduces surfaces tension in alveoli (prevents collapse on exhalation)

Lactation

• pregnancy: progesterone helps develop mammary glands

• milk = prolactin

• effects of prolactin inhibited by pro/estrogen in pregnancy

Colostrum

• 1st milk produced

• high in proteins

• low in carbs/fats