Sexual Reproduction

Topic 11.4

Understanding:Spermatogenesis & oogenesis both involve mitosis, cell growth, 2 divisions of meiosis & differentiation.

SIMILARITIES

• Both processes result in the formation of haploid gametes• Both processes involve mitosis, growth and meiosis

Differences

OOGENESIS

SPERMATOGENESIS

SPERMATOGENESIS

TESTESInside testes:1. Seminiferous tubules make sperm2. Leydig cells (interstitial cells) make

testosterone• Basement membrane made of germline epithelial

divide by meiosis to make spermatogonia• Sertoli cells (nurse cells) nourish germ cells

Seminiferous tubules

ovary

Skill:Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis.

OOGENESIS

Skill:Annotation of diagrams of mature sperm and egg to indicate functions.

Label it!

Draw!

Understanding:Processes in spermatogenesis & oogenesis result in different numbers of gametes with different amounts of cytoplasm.

Space……….. the final frontier……

Understanding:Processes in spermatogenesis & oogenesis result in different numbers of gametes with different amounts of cytoplasm

• Why is the egg bigger than sperm?• All the requirements for beginning growth of early

embryo must be present in the egg!

Understanding:Fertilization involves mechanisms that prevent polyspermy.

• Fertilization = union of egg & sperm to form zygote• Chemical attraction of sperm to egg

• Steps to prevent polyspermy:1. Acrosome Rxn2. Penetration of egg membrane3. Cortical Rxn

1. Acrosome Rxn

2. Penetration of egg membrane

3. Cortical Rxn

Understanding:Fertilization in animals can be internal or external.• Aquatic animals: externally

• E.g. fish, coral, starfish• Spawning = release of egg & sperm into

water

• Terrestrial animals: internally• E.g. salamanders, scorpions, octopus

Understanding:Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy.

Understanding:hCG stimulates the ovary to secrete progesterone during early pregnancy

• Pregnancy depends on maintaining uterus lining (Endometrium)

• Endometrium supplies embryo with everything it needs

• Endometrium remains if enough estrogen & progesterone

• Embryo produces hCG = human chorionic gonadotropin

• hCG stimulates corpus luteum to produce estrogen & progesterone

Role of hCG in early pregnancy

Understanding:The placenta facilitates the exchange of materials between mom & embryo

Placenta3 types of mammals:1. Placental – live birth (humans)2. Monotremes – lay eggs (duck-billed platypus; anteater)3. Marsupials – offspring finish developing inside pouch (kangaroo, opossum)

Placenta needed as fetus grows and surface area/volume ratio gets smaller. Placenta = fetal + maternal tissue Amniotic sac = fetal tissue; contains amniotic fluid = supports & protects fetus Placental villi = functional unit of placenta; exchange of materials with mom;

increase in # Maternal blood flows into inter-villous spaces around villi Fetal blood circulates in capillaries in villi Placental barrier = cells that separate maternal & fetal blood (~5μm);

selectively permeable

Exchange of materials in placenta

Understanding:Estrogen & progesterone are secreted by the placenta once it has formed.

• 0 – 8th week corpus luteum secretes enough estrogen & progesterone to maintain pregnancy

• 9th week – birth placenta starts to secrete enough estrogen & progesterone to maintain pregnancy; corpus luteum no longer needed so it degenerates

•Danger of miscarriage at this stage if switch-over fails!

Understanding:Birth is mediated by positive feedback involving estrogen & oxytocin.2 different feedback mechanisms in homeostasis:• Positive feedback enhances a change• Negative feedback reverses a change

Role of hormones in parturitionParturition = labor & delivery; childbirth

Endometrium = uterus liningMyometrium = muscular uterus wallProgesterone = hormone secreted by placenta to maintain endometriumOxytocin = hormone secreted by pituitary to cause myometrium to contract

2 different feedback mechanisms in homeostasis:• Positive feedback enhances a change• Negative feedback reverses a change

During pregnancy, high progesterone inhibits oxytocin & uterine contractions.At end of pregnancy, fetus produces hormones which signal placenta to stop secreting progesterone. Then oxytocin secreted.

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

Stages of labor & deliveryhttps://www.youtube.com/watch?v=ZDP_ewMDxCo

How long is a full-term pregnancy?(in weeks)

38

Nature of Science: assessing risks & benefits of scientific research:The risks to human male fertility were not adequately assessed before steroids related to progesterone & estrogen were released into the environment as a result of the use of the female contraceptive pill.

• Birth control pills = mimics pregnancy; contains high amount of estrogen• Estrogen inhibits FSH, so no follicles develop, no ovulation• Synthetic estrogen levels in water have increased through sewage• 1980’s – large birth control pill hormones reported in water = “estrogen pollution”

• 1992 – human male sperm count declined by 50% over 50 years, according to 61 studies• 2004 – UK, 86% male fish in 51 sites were “intersex” (feminized)• Limited scientific consensus on causation

• One solution: 2012 – European Commission proposed policy to limit conc. in H2O

• Another solution: upgrade technology for wastewater treatment & preventing livestock from urinating close to rivers

• Who should pay costs? Water companies? Drug companies? Public?

Application:The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size & the development of the young at birth for other mammals.

• Altricial = helpless at birth• Precocial = mobile at birth

Good advice….

Prostate Cancer

Prostate exam recommended starting age: 40

D.R.E.

Cervical Cancer

Pap smearrecommended for ages 21 – 65

Good for ~ 3 years!

HPV DNA test