Chapter 26c

Reproduction and Development

Pregnancy Prevention

• Contraceptives (birth control methods)• Abstinence• Total abstinence• Abstinence during periods of female fertility

• Interventional methods• Barriers• Surgery• Blocking implantation• Hormone treatments to reduce gamete production

Pregnancy Prevention

Table 26-5

Fertilization

• Sperm capacitation occurs in vagina• Sperm swim “upstream”

• Sperm reach oocyte in Fallopian tube• Acrosomal reaction digestive enzymes• Zona pellucida and cell junctions dissolve

• Membranes fuse and sperm nucleu enters• Cortical reaction blocks polyspermy• Nuclear fusion creates a diploid cell

• 1 sperm + 1 oocyte 1 zygote

Fertilization

Figure 26-16a

Acrosome Reaction Allows Sperm to Reach Egg

Figure 26-16b

Sperm and Egg Fuse to Form a Zygote

Figure 26-17 (1 of 4, 2 of 4)

Spermnucleus

Sperm andegg plasma

membranes fuse.

Sperm nucleusmoves intocytoplasm of egg.

Egg

First polarbody

Oocyte Completes Meiosis and Nuclei Fuse

Figure 26-17 (3 of 4, 4 of 4)

Oocyte nucleuscompletes meiotic

division.

Egg

Sperm and eggnuclei fuse toform zygote nucleus.

Secondpolar body

Spermnucleus

Early Development

• Rapid cell divisions follow fertilzation• Blastocyst • Hollow ball of ~ 100 cells• Arrives in uterus on day 4 or 5

• Implantation• Blastocyst invades the endometrium

Early Development: Ovulation to Implantation

Figure 26-18

Blastocyst

Inner cell mass

Days 5-9:Blastocyst implants.

Ovulation

Day 1:Fertilization

Days 2-4: Celldivision takes place.

Day 4-5: Blastocystreaches uterus.

Zygote Fallopiantube

Egg

UterusOvary1

23 4

5

Early Development: Ovulation

Figure 26-18, step 1

Ovulation

Fallopiantube

Egg

UterusOvary1

Early Development: Fertilization

Figure 26-18, steps 1–2

Ovulation

Day 1:Fertilization

Zygote Fallopiantube

Egg

UterusOvary1

2

Early Development: Rapid Cell Divisions

Figure 26-18, steps 1–3

Ovulation

Day 1:Fertilization

Days 2-4: Celldivision takes place.

Zygote Fallopiantube

Egg

UterusOvary1

23

Early Development: Blastocyst Reaches Uterus

Figure 26-18, steps 1–4

Blastocyst

Inner cell mass

Ovulation

Day 1:Fertilization

Days 2-4: Celldivision takes place.

Day 4-5: Blastocystreaches uterus.

Zygote Fallopiantube

Egg

UterusOvary1

23 4

Early Development: Implantation of Blastocyst

Figure 26-18, steps 1–5

Blastocyst

Inner cell mass

Days 5-9:Blastocyst implants.

Ovulation

Day 1:Fertilization

Days 2-4: Celldivision takes place.

Day 4-5: Blastocystreaches uterus.

Zygote Fallopiantube

Egg

UterusOvary1

23 4

5

Placenta and Continuing Development

• The chorion is a tissue layer that encloses the developing embryo

• The amnion is a tissue layer that secretes amniotic fluid, suspending the embryo

• Chorionic villi form a close connection with blood vessels of the endometrium

• The placenta continues to grow during pregnancy

The Placenta

Figure 26-19a

The Placenta: Microscopic Anatomy

Figure 26-19b

The Placenta Makes Numerous Hormones

• Human chorionic gonadotropin (hCG)• “Rescue” of corpus luteum• Basis of pregnancy tests

• Human placental lactogen (hPL)• Breast development, metabolic effects

• Estrogen and progesterone• Critical for maintaining pregnancy, and for

normal development• Several additional hormones are produced

Parturition: Birth Process

• Prior to labor: softening of the cervix• Labor• Rhythmic uterine contractions• Positive feedback cycle of oxytocin release• Cervical dilation

• Delivery of the baby• Placental release and expulsion

Parturition: Birth Process

Figure 26-20a

Parturition: Birth Process

Figure 26-20b

Parturition: Birth Process

Figure 26-20c

Parturition: Birth Process

Figure 26-20d

Regulators of Parturition

• Labor onset• Possible role of CRH• Stretch of cervix as a stimulus

• Role of oxytocin in labor• Stretch stimulates release• Oxytocin stimulates prostaglandin release• Positive feedback (contractions stimulate more

oxytocin release)

Parturition Is Controlled by a Positive Feedback Loop

Figure 26-21

Hormones and Mammary Gland Development

• Puberty• Estrogen stimulates grow of ducts and fat

deposition• Pregnancy• Estrogen, growth hormone, and cortisol

stimulate further gland development • Late pregnancy• Progesterone stimulates conversion of some

ducts to secretory epithelium

Mammary Gland Anatomy

Figure 26-22a

Mammary Glands - Microscopic View

Figure 26-22b

Lactation: Control of Milk Secretion

• Before birth• Prolactin-inhibiting hormone (PIH) blocks

prolactin secretion• High sex steroid levels suppress milk

production• After birth• High prolactin & low estrogen lactation• Breast milk = nutrients + immunity

• Suckling • Inhibits PIH, allowing milk production• Oxytocin stimulates “let-down reflex”

Hormonal Control of Milk Secretion and Release

Figure 26-23

Oxytocin neuron

Portal system

PIH cell

Sound ofchild’s cry

Anteriorpituitary

Posteriorpituitary

Hypothalamus

Higherbrain

centers

PIH

OxytocinProlactin

Inhibition ofprolactin cells

is removed

Milksecretion

Mechanoreceptorsin nipple

Babysuckling

Smooth musclecontraction

Milkejected

Ascending sensory inform

ation

Reproductive Maturation: Puberty

• Maturation of reproductive organs, increased hormone levels, and onset of gamete production

• Notable characteristics of puberty• Females: menarche, pubic hair, and breasts• Males: pubic hair, beard, and deep voice

• Hormone changes at puberty• Increased secretion of GnRH• Increased LH/FSH levels stimulate gonads• Possible role of leptin

Aging and Menopause

• Causes• Ovaries cease responding to LH/FSH• Low levels of estrogen and progesterone• Cessation of egg development

• Symptoms and therapies• Hot flashes and increased osteoporosis risk• Hormone replacement debate

Aging and “Andropause”

• Controversial (only affects 50% of men over 50 years)• Lower levels of testosterone impact some

men’s lives• Many men remain reproductively active, despite

low testosterone levels

Summary

• Sex and genetics• Hormonal regulation of reproduction• Tissues and hormones involved in

spermatogenesis and oogenesis• Procreation and contraception• Fertilization and zygote development• Labor and delivery• Puberty, menopause, and andropause