Reproduction HL

Puberty

life stage when an individual becomes sexually mature → under the control of hormones

• Hypothalamus → Gonadotropin-releasing hormone (GnRH)

• Steroid sex hormones (e.g, oestrogen & testosterone)

  • the increases in sex hormones production leads to the changes associated w. puberty

• The pituitary gland secretes 2 further hormones → LH & FSH

Male Secondary Sexual Characteristics

• larynx increases in size → deepens voice

• increases skeletal muscle development

• Hair: armpit, growth of pubic hair, facial, chest

• development (/enlargement) of testes, scrotum, penis & glands of reproductive tract

• continuous production of sperm → outside of sexual intercourse, erections & discharge of seminal fluid

• general changesin behaviour associated w/ increased sex drive

Female Secondary Sexual Characteristics

• development of breasts

• widening of pelvis

• growth of pubic hair/armpit hair

• enlargement of vagina & uterus

• maturation of ovaries

• monthly ovulation & menstruation

• deposition of fat under skin of buttocks & thighs

• general changes in behaviour associated w/ an increased sex drive

Gametogenesis

process of gamete formation → involves both mitosis & meiosis

• cells dividing by mitosis to produce many new cells → have potential to develop into gametes

• cells growing & differentiating

• cells dividing by meiosis to produce hapoloid gametes

Spermatogenesis #1: Background & Structure

• testes → loocaed outside of body →to maintain optimum temp range

• contains seminiferous tubules

  • gaps/interstices filled with Leydig cells

  • intersittial cells produce testosterone

Spermatogensis #2: Begginning

1. cells in germinal epithelium divide by mitosis → produces diploid cells (spermatogonia)

2. Spermatogonia begin to migrate from germinal epithelium toards lumen → move through gaps between Sertoli cells (inner lining)

3. spermatogonia differentiate into immature sperm cells → primary spermatocytes

Spermatogenesis #2: Development of Spermatozoa

Mitosis & growth

• mitosis can undergo mitosis to increase the supply of stem cells

• a spermatogonium first enters meiosis → must grow

• spermatogonium (2n) → must undergo meiosis to mature

1. Primary spermatocytes mature & divide by meiosis

2. Meiosis I forms secondary spermatocytes

3. Meiosis 2 forms spermatids

4. Spermatids differentiate.

5. developed spermatozoa

LH (lutenizing hormone)

stimulates Leydig cells to make testosterone

FSH (follicle-stimulating hormone)

helps testosterone to stimulate the process of spermatogenesis

Sertoli Cells

provides nutrients for sperm development

Spermiogenesis (Differentiation)

4 spermatids (n) → 4 Spermatozoa (n)

• flagellum for motility & acrosome (destructive enzymes)

Oogenesis: Pre-Puberty

ovaries → surrounded by germinal epithelium → cells divide by mitosis to form oogonia (7months)

• oogonia migrate throughout tissue

• during first months, oogonia grows in size & enters meioisis I → follicle cells develop around them

• once oogonia develop into primary follicles → oogenesis pauses until puberty

Oogenesis: Puberty

• FSH stimulates the continued development of primary follicles → only one reaches maturity

• Meiosis I continues → 2 new cells → division of cytoplasm is unequal

  • secondary oocyte & polar body (doesn’t mature, little cytoplasm)

• secondary oocyte enters meiosis II → leaves w/ Graafian follicles for ovulation.

• remaining follicular cells develop into corpus luteum.

Oogenesis: After Ovulation

secondary oocyte remains in meiosis II unless sperm fertilizes it

1. Spermatozoa (n) reaches the egg (n) & fertilize it

2. Fertilization triggers the egg to complete Meiosis II

3. On set of DNA becomes the pronucleus & the other, a polar body → incomplete cytokinesis

4. the two pronuclei (from sperm & egg) will fuse to form a diploid nucleus (zygote)

Oogenesis: Context

• What: the process of forming mature egg (ova)

• When: before birth = meiosis I (P1), puberty (P1 to MII), after fertilization

• Where: first part in the ovary, second part in the fallopian tube

• Quantitiy: one egg per month

Oogenesis: Summary

Meiosis & Differentiation

• one oogonium (2n) → one primary follicle (primary oocyte (2n) + follicular cells)

  • they stop at prophase I

  • occurs during fetal stage

• one primary follicle → graafian follicle (secondary oocyte (n) + follicular cells)

  • they finish meiosis I & stop at metaphase II

  • occurs during puberty

  • first polar body is formed

• ovulation releases secondary oocyte into fallopian tube

• when secondary oocyte is fertilized by sperm, meiosis II is completed

  • zygote is formed

  • another polar body is formed

Preventing Polyspermy

the rare event of more than one spermatozoon fertilizng the ovum → results in ovum not developing

1. Spermatozoa traverse the follicular cells (corona radiata)

2. Acrosome reaction → releases hydrolytic enzymes from acrosome to penetrate the zona pellucida

3. cortical reaction → cortical granules in cytoplasm fuse w/ plasma membrane → enzymes are released that result in a chemical change in the zona pellucida

4. Zona pellucidea is now hardened → impermeable to penetration → prevents polyspermy

Oogenesis & Spermatogenesis #1

Similarities

• both involved production of haploid (n) cells

• both require mitosis for growth

• both have cell growth in prep for meioiss

• both are differentiation processes

Oogenesis & Spermatogenesis #2

Differences

• sperma.. occurs in testes, oogen….occurs in ovaries

• 4 gametes vs. 1 gamete (+2 or 3 polar bodies)

• unequal vs. equal cytokinesis

• produces small motile gametes w/ minimal cytoplasm & organelles vs. produces large, non-motile gametes w/ abundant cytoplasm, organelles & nutrients

• begins at puberty vs. begins at fetus stage

• millions of sperm vs. 1 per menstural cycle

• no breaks in meiosis vs. breaks in meiosis (PI & MII)

Blastocyst Development & Implantation

Blastocyst: a hollow ball of cells found in the oviduct (w/ an internal group of blastomeres)

• eventually develops into the foetus

• implants itself into the endometrium (uterus lining) to obtain an external supply of nutrients

• around embryo stage → there is an exchange of nutrients & oxygen w/ mother’s blood → embryo continues to grow & develop rapidly after

Trophoblast

outer layer of cells

Composed of:

• foetal portion of the placenta

• embryonic membranes

• umbilical cord

Zona Pellucida

a protective extracellular coat that surrounds the blastocyst → coat breaks down around 7 days of age

Pregnancy Tests

confirmation of a pregnancy → presence of hCG

• Where: detected in mother’s blood & urine

• When: hCG is produced at the blastocyst stage

• Who: first—trophoblastic layer, later—placenta cells

• Why: continuation of corpus luteum (makes progesterone) → permits the vascular tissue of the uterine endometrium to continue

Pregnancy Tests Process

monoclonal antibody (mAb) reacts to a specific antigen in hCG

1. mother urinates on test strip → urine contains higher levels of hCG if pregnant

2. urine containing hCG will travel along the test strip of the pregnancy test → test strip contains the monoclonal antibodies, which bind to hCG (if present) & lead to a color change w/in the pregnancy test

3. if no color change → hCG is not present (in high enough conc.) to bind to the monoclonal antibodies & give the colour change

Mechanism of hCG detection

• culture B-lymphocytes that produce only one type of antibody (monoclonal antibodies)

• antibodies are chemically bonded to an enzyme that changes color when exposed to a selected substrate

Mammals & Foetal Nourishment

Types of mammals

• placental mammals (e.g humans)

• monotremes (egg-laying mammals → platypus)

• Marsupials, kangaroos → whose offspring develops in a pouch

Placental Mammals

• placental mammals → rely on the complex system of blood vessels

  • designed to maximize exchange of substances between mother & foetus w/out direct connection

  • also responsible for production of hormones (e.g, oestrogen & progesterone)

  • connected to placenta via umbilical cord → w/in amniotic sac

Placenta Structure

• made up of arrangement of blood vessels arranged into villi → # of villi increase to meet demand of foetus

• maternal blood & foetal blood → never mix directly

Chorionic Vili

smalll divsion from main vessles (provides large surface area) small division

Placenta: Blood Vessels

Uterine Artery / Umbilical Vein

• carries nutrients & other substances towards → from mother to foetus

  • O2

  • antibodies → crosses the placenta through endocytosis

  • water

  • glycose

  • unwanted or harmful substances (e.g, alcohol, drugs or small pathogens)

Uterine Vein / Umbilical Artery

• carries waste & other substances away → from foetus to mother

  • CO₂

  • H2O

  • Urea

Labour & Birth

a time when uterine contractions begin till delivery

“progesterone maintains the placenta”

1. when fetus matures, placenta secretes less progesterone

2. Decreasing progesterone stimulates oxytocin production in the anterior pituitary.

3. receptors in the muscle of the uterus respond w/ contraction

4. pressure from contraction results in positive feedback w/ the pituitary.

5. cycle repeats until the uterine contraction are very intense & very frequent

6. loop only terminates w/ birth → since pressure is gone once baby is out

Role of Oestrogen

hormone oestrogen is produced by the fetus & placenta.

• oestrogen makes the uterine wall more sensitive to oxytocin

• progesterone is also inhibited by oestrogen

Positive Feedback

feedback system that reinforces or amplifies a response

Role of Progesterone

• hormone progesterone is secreted by placenta throughout pregnancy

• Progesterone inhibits the production of oxytocin (by pituitary gland)

  • inhibits contractions of muscles of myometrium → induces birth if not inhibited

• at end of pregnancy → foetus produces oestrogen → signals to stop production of progesterone → initiates production of oxytocin

Menopause

the period in a female’s life when her menstrual cycle ends → commonly ages 45-55, but the age at which it happens can vary significantly.

• Why: occurs b/c ovaries stop producing estradiol & progesterone.

• Effects of menopause: include trouble sleeping, hot flushes, some loss of musculature & other symptoms.

HRT & Coronary Heart Disease

hormone replacement therapy in the form of estradiol to alleviate symptoms of menopause

Health Risks

• Early reports showed reduced incidence of coronary heart disease (CHD) w/ HRT

• later studies indicated that HRT led to a small increase in the risk of CHD

• now believed → no connection