6.6 Part II and 11.4- Reproduction - PowerPoint Presentation

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6.6 Part II and 11.4-

ReproductionSlide2

Embryonic development into male/female

A. Embryos identical until about 8 weeks - The same embryonic structures give rise to ovaries and testes, clitoris and penis

B. Females – genes on 2 X chromosomes interact to produce high estrogen and progesterone levels -> female reproductive structures

C. Males – genes on Y chromosome responsible for testosterone production and testes developmentSlide3

II. Male Reproductive SystemSlide4
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Spermatogenesis – starts at puberty and continues for life

Seminiferous tubules of testesSlide6

Arise from

spermatogonia

(germinal epithelial cells) near outer edge of seminiferous tubules

a. Undergo mitosis to replenish supply of

spermatogonia

b. Undergo meiosis to produce spermatozoa (millions/day) – stimulated by follicle stimulating hormone (produced by pituitary)Slide7

Daughter cells must mature into fully motile spermatozoa

a.

Sertoli

cells – provide nutrients for developing sperm

b. Leydig cells – leutinizing hormone from pituitary stimulates production of testosterone c

. Move closer to

the center of the

seminiferous tubule as they develop d. Move to epididymis to finish maturationSlide8

Mature sperm

a. Acrosome – contains hydrolytic enzymes to help get into egg

b. Mitochondria – produce ATP for swimming

c. Flagellum – tail for swimming

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Production of semen

a. Mature sperm moves from epididymis to vas deferens

b. As it moves through vas deferens, fluid is added

i. Seminal vesicle adds 70% of fluid - high in fructose (sugar) to provide energy ii. Prostate adds alkaline fluid – to help neutralize low pH in vaginaSlide10

Hormones involved

Leutinizing

hormone (LH) - stimulates

Leydig

cells in testes to produce testosterone

Follicle Stimulating Hormone (FSH) - along with testosterone, stimulates meiosis of

spermatogoniaSlide11

III. Female Reproductive SystemSlide12
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Oogenesis

1. Events before birth - in ovaries of female fetus

a.

O

ogonia in the ovaries undergo mitosis to increase in number b. Oogonia grow into larger cells called primary oocytes c. Primary oocytes start meiosis, but pause in prophase I

d. Follicle cells undergo mitosis forming a layer around the primary oocyte (together this is called a primary follicle)

e. At birth, ovaries contain about ½ million primary follicles – remain unchanged until pubertySlide15

Events during the menstrual cycle

a. Each month, a few primary follicles finish meiosis I

b. Results in 1 polar body and 1 secondary oocyte (both haploid)

c. Ring of follicle cells divides and forms fluid, resulting in a double ring of cells with fluid in between called Graafian follicle Slide16

Increase of fluid causes

Graafian

follicle to push on wall of ovary until the secondary oocyte is released from the ovary

Left over follicle cells become corpus luteum – secretes progesteroneSlide17

The Mature Egg

A. Secondary Oocyte – largest cell in most species – contains all nutrients for early developmentSlide18

IV.

Comparison of spermatogenesis and oogenesis

Spermatogenesis

Oogenesis

Millions of sperm/day from puberty throughout life

1

secondary oocyte/month between puberty and menopause

4 gametes from each germinal

cell

1 gamete from each germinal cell (+ 3 polar bodies)

Gametes are small with little cytoplasm and organellesGamete is large with substantial cytoplasm, organelles, and nutrients

Mitosis replaces germinal cells daily

Mitosis only replaces germinal cells in early development

Some cell

growth before meiosis I

Substantial

cell growth before meiosis I

Spermatids remain in seminiferous

tubules until differentiation into spermatozoa occurs

Differentiation begins in the ovary but finishes

after fertilization

Occurs in testes

Occurs in ovariesSlide19

The Menstrual Cycle

A. Purpose – release ovum for potential fertilization and implantation into uterus

B. Implantation must occur when endometrium is highly vascularized (increased number of blood vessels)

C. If implantation does not occur, excess blood vessels are broken down and discarded by menstruationSlide20

Hormones involved

1.

GnRH

– gonadotropin-releasing hormone – from hypothalamus, stimulates pituitary to release LH and FSH

2. Follicle Stimulating Hormone and

Leutinizing

Hormone a. Stimulate production of estrogen by the ovary b. Stimulate production of

Graafian

follicles

c. Lead to ovulation and creation of corpus luteum 3. Estrogen – increases vascularization of endometrium 4. Progesterone – maintains thickened endometrium - Slide21
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VI. Fertilization

In animals, can be internal or external

1. External usually results in large numbers of offspringSlide24

Events of fertilization in humans

Sperm make their way along endometrium to Fallopian tubes

Many sperm start breaking down the

zona

pellucida

(glycoprotein layer surrounding the secondary oocyte) by releasing hydrolytic enzymes from acrosome (acrosome reaction) a. Also triggers oocyte to finish meiosis II3. One

spermatozoan

reaches plasma membrane, releases more hydrolytic enzymes to penetrate egg

4. Plasma membranes fuse

http://www.youtube.com/watch?v=BFrVmDgh4v4Slide25

5.

Cortical reaction – prevents more than one sperm from fertilizing egg – cortical granules fuse with plasma membrane and release enzymes

outside, chemically changing the

zona

pellucida

so that no other sperm can penetrate6. Nuclei of egg and sperm fuse to restore diploid chromosome numberSlide26

VII. Early development

A. Zygote starts undergoing mitosis within 24 hours of fertilization

B. Moves down Fallopian tube to uterus

C. Consists of about 100 cells when it reaches uterus = blastocyst Slide27

Implantation – embryo sinks down into endometrial lining

Around a week after fertilization

Has not increased in size, just number of cells (nutrients used for metabolism, not growth)

Embryo can start getting nutrients from endometrium rather than yolk

http://www.youtube.com/watch?v=UgT5rUQ9EmQSlide28

The Placenta

1. Forms from both mother and embryo

2. Umbilical cord forms on fetal side, consists of 3 blood vessels Slide29

http://www.youtube.com/watch?v=kZeZ62UXyzMSlide30

Hormones involved

1.

HCG (human chorionic gonadotropin) – secreted by embryo, enters mother’s bloodstream, goes to her ovaries to maintain the corpus luteum

2. Progesterone – first secreted by corpus luteum, later by placenta, maintains vascularization of the endometrium and suppresses contractions of the uterus

3. Estrogen – secreted by placenta, stimulates muscle growth of uterus, antagonizes progesterone’s suppression of contractions, stimulates mammary glands development, and induces production of oxytocin receptors in uterine muscles

*Both progesterone and estrogen inhibit production of further oocytes during pregnancySlide31
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VIII. Childbirth

A. Oxytocin – secreted by pituitary to stimulate uterine contractions

1. Positive Feedback Slide33

In Vitro

Fertilization (IVF)

A. Reasons for infertility

1. low sperm count/motility in males

2. males with impotence 3. females who can’t ovulate normally 4. females with blocked Fallopian tubes

B. Harvest eggs from female

1. Injections of FSH to stimulate production of many

Graafian follicles (superovulation) 2. Eggs surgically removedSlide34

Eggs mixed with sperm in culture dishes

Use microscope to see which eggs are fertilized and healthy

1-3 eggs introduced into uterus

Extra embryos can be frozen