Copyright © 2010 Pearson Education, Inc. Chapter 20 Is There Something in the Water? Reproductive...

Copyright © 2010 Pearson Education, Inc.

Chapter 20

Is There Something in the Water?Reproductive and Developmental Biology


Chapter 20 Section 1

Principles of Animal Reproduction


20.1 Principles of Animal Reproduction

Two main types of reproduction

1.Asexual reproduction

2.Sexual reproduction

Asexual Reproduction one parent produces offspring that are

genetically identical to the parent



Two main types of asexual reproduction

Binary fission – cells break away from parent to form offspring (e.g., sponges)

Budding – daughter cell remains attached to parent and breaks away when mature (e.g., hydra)


20.1 Principles of Animal Reproduction –

Sexual Reproduction Sexual reproduction combines genomes of

two individuals to create variable offspring Females = individuals that produce large

gametes (sex cells) Males = individuals that produce small

gametes

Gonads = Organs that produce gametes Male gonad = testes Female gonad = ovaries



Methods of fertilization

1.Internal fertilization – sperm deposited by copulation in or near female reproductive tract. Mammals, birds, reptiles, and sharks use

internal fertilization.

2.External fertilization – eggs laid, male deposits sperm over eggs (usually in water). Most fish and amphibians use external fertilization. Very susceptible to contaminants



Developing frogs are extremely sensitive to environmental chemicals Eggs develop in water Embryos absorb toxins

easily

Frogs are declining globally

Figure 20.2

Environmental Contaminants and Sexual Reproduction


20.1 Principles of Animal Reproduction -

Endocrine Disruptors Man-made chemicals alter endocrine

regulation interferes with normal gonad development.

Male amphibians have been feminized. These chemicals affect animals living in

water.

Are humans affected by drinking contaminated water?


End Chapter 20 Section 1

Principles of Animal Reproduction


Chapter 20 Section 2 Part A

Human Reproduction: Males


20.2 Human Reproduction

Male Reproductive Anatomy

Penis Contains spongy erectile

tissue Fills with blood to cause

erection

Testes Inside scrotum Produce sperm and

testosterone

Figure 20.4



Male Reproductive Anatomy Accessory Glands

Prostate & seminal vesicles Secrete fructose, mucous

Figure 20.4

Testes Inside scrotum produce sperm

and testosterone Epididymis

Stores sperm Vas deferens &

urethra



Endocrine Disruptors & Humans

Men Most common cause of male infertility is the

inability to produce healthy sperm. Sperm counts are declining globally



Gametogenesis

= production of gametes (germ cells) Involves meiosis

Reduces number of chromosomes by ½ Human body cells contain 46

chromosomes, gamete contain 23 (see chapter 5 for review)

Male and female gametes undergo further development to become functional



Spermatogenesis

Figure 20.6

• Seminiferous tubules = functional unit of testis• Contain developing sperm cells• Sertoli cells – nurse cells for sperm

• Leydig cells outside seminiferous tubules• Make and release testosterone



Cell types in Spermatogenesis

Figure 20.6

• Spermatogonia• Stem cells• Divide by mitosis

• Primary spermatocytes• Enter Meiosis I

• Secondary spermatocytes• Enter meiosis II

• Spermatids• Undergo spermiation

• Cytodifferentiation

• Spermatozoa



Spermatozoa Structure

Figure 20.6

• Head• Condensed nucleus• Acrosome

• Contains enzymes for fertiliztion

• Midpiece • Lots of mitochondria

• Tail• Flagellum for swimming


20.2 Human Reproduction - Male Infertility

Human infertility and endocrine disruptors 90% of male infertility is related to problems

with sperm formation or production Low sperm counts Improperly shaped sperm Low motility

Chemical exposure (e.g., pesticides) can decrease sperm viability Male infertility also increases with alcohol and

drug use, including cigarettes

Sperm counts declining globally since WWII



Animation—The Male Reproductive SystemPLAY


End Chapter 20 Section 2 Part A

Human Reproduction: Males


Chapter 20 Section 2 Part B

Human Reproduction: Females



Female Reproductive Anatomy

Figure 20.5

External genitalia Labia majora & labia minora clitoris

Reproductive tract Vagina Uterus Paired oviducts

Fertilization Separate urethral

opening



Female Reproductive Anatomy

Figure 20.5

Ovaries Endocrine

Estrogen Progesterone

Produces gametes Follicle contains:

Egg Endocrine cells



Endocrine Disruptors & Humans

Women DES is a drug that acts as an endocrine disruptor.

Given to women to prevent premature delivery Daughters of women who took DES have a

higher rate of infertility.



Oogenesis

Figure 20.7

• Two parts

1. Oocyte development

2. Follicular development



Oocyte Development

Figure 20.7

• All oogonia (stem cells) become primary oocytes during her (the mother’s) embryonic development

• Each month during menstrual cycle• Primary oocytes enter meiosis I -> secondary oocytes• Secondary oocytes complete meiosis II at fertilization• Polar bodies will deteriorate



Follicular Development

Figure 20.7

• Follicles include oocytes and surrounding endocrine cells • Primary follicle stores primary oocytes until use• FSH causes development to secondary follicle and then

Graffian follicle (both with secondary oocyte)• Secrete estrogen

• LH causes ovulation• Follicle become corpus

luteum• Secretes estrogen &

progesterone



The Menstrual Cycle

Changes in the uterine endometrium

Prepares endometrium for pregnancy

Regulated by: Pituitary FSH & LH Ovarian estrogen &

progesterone

Figure 20.8



The Menstrual Cycle Days 1-4

Menstruation Only FSH elevated

causes new follicle to grow

Days 5-14 FSH causes follicle to

grow & release estrogen

Estrogen causes endometrium to grow

Figure 20.8



The Menstrual Cycle Day 14

Surge of LH causes ovulation & corpus luteum formation

Figure 20.8



The Menstrual Cycle Day 14-28

FSH & LH cause ovary to secrete estrogen & progesterone

Prepares for pregnancy Corpus luteum dies at

end of cycle Results in collapse of

endometrium and start of menstruation

Figure 20.8



Regulating The Menstrual Cycle

Regulation involves both positive & negative feedback loops

Figure 20.9

High estrogen causes positive feedback on LH Leads to LH surge

High progesterone causes negative feedback on LH & FSH



Pregnancy If the egg is fertilized, embryo secretes

human chorionic gonadotropin (hCG) hCG mimics LH and keeps corpus luteum alive Progesterone maintains endometrium during

pregnancy

Birth Control Pills Mimic pregnancy by providing estrogen and

progesterone prevent ovulation by blocking LH surge

Figure 20.9



Female Infertility

One cause of female infertility is endometriosis a condition where the endometrial cells can

attach to the ovaries & oviducts also grow and shed during menstrual cycle

Can cause damage and scarring to ovarian tissue

Can disrupt ovulation Painful May be related to exposure to environmental

chemicals like DEHP



Animation—The Female Reproductive SystemPLAY


End Chapter 20 Section 2 Part B

Human Reproduction: Females



Human Development


Is the Water Safe to Drink?


20.3 Human Development

Fertilization1. Sperm penetrate

follicle cells

2. Sperm head binds to zona pellucida

3. Acrosome enzymes released

4. Egg & sperm membranes fuse

5. Sperm nucleus enters egg cell

Figure 20.11



Endocrine Disruptors and Fertilization

Industrial solvents can mimic hormones and interfere with sperm development and fertilization. Misshapen sperm cannot swim effectively and

are unable to fertilize egg. Males exposed to solvents, working as

mechanics or dry cleaners, have a larger number of abnormal sperm.

While effect on adults lowers fertility, effects on developing fetus is more severe



Human Embryonic Development

Human zygote undergoes a series of cleavages to produce an embryo Embryo is stage from zygote until body

structures appear Blastocyst = hollow ball of cells Gastrula = tissue layers start to appear

Figure 20.12


20.3 Human Development - Human Embryonic Development

Gastrula has 3 tissue layers Endoderm – forms digestive & respiratory Mesoderm – forms muscles, skeleton,

excretory, circulatory, & gonads Ectoderm – forms skin, nervous &

sensory

Growth of a particular tissue or organ relies on chemical stimulus Very sensitive to chemical disruption



Development of Human Reproductive Organs

Table 20.3

• Male & female organs develop from same embryonic precursors

• Hormonal signals cause development of male and female reproductive organs



Endocrine Disruptors & Reproductive Organs

Table 20.3

• Chemicals can pass from mother’s blood to fetus

• Common herbicides & fungicides can cause cryptorchidism • Undescended testes• 2 to 4 % of human

males are now born with undescended testes



Pregnancy or Gestation A placenta must develop to

sustain pregnancy Embryo blastocyst implants in the

wall of the uterus Maternal and fetal blood supplies

are closely intertwined, allowing exchange of nutrients and wastes

9 week old fetus has all its limbs and organs in place

Environmental chemicals can seriously effect embryo & fetus



Childbirth Decreasing estrogen in late pregnancy induces

oxytocin receptors to form in uterine muscle Hormone oxytocin uses a positive feedback

loop to induce labor.

Figure 20.15


20.4 Is the Water Safe to Drink?

Human correlations with endocrine disruptors abnormal sperm lower sperm counts decreased fertility cryptorchidism endometriosis uterine abnormalities

EPA requires monitoring of municipal water supplies. But it’s unclear what chemicals to monitor and what

is a safe level of chemicals



Human Development


Is the Water Safe to Drink?


End Chapter 20 Section 2

Human Reproduction

Copyright © 2010 Pearson Education, Inc. Chapter 20 Is There Something in the Water? Reproductive...

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