Reproduction & Development Chp 21. GAMETE FORMATION Meiotic division produces Haploid Gametes Egg Sperm.

Reproduction & Development

Chp 21

GAMETE FORMATION

Meiotic division produces Haploid Gametes

• Egg

• Sperm

Anatomy Of A Sperm Cell

• Arcosome

• head

• Midpiece

• tail

Anatomy Of Egg Cell

• Jelly coat

• Membrane

• Organelles

• Sperm and egg unite: 6-24 hours after intercourse, sperm survives days

• One sperm fertilizes one egg

• Acrosome: rich in digestive enzymes

• Sperm penetrates corona radiata and zona pellucida

• Sperm proteins lock with egg membrane receptors

• Zona pellucida made impermeable to other sperm

Fertilization

Arcosomal Reaction

• Arcosome opens & releases digestive enzyme

• Fertilization tube forms

• DNA moves into egg & joins w/Egg DNA

Prevention of Polyspermy

• Wave of depolarization - Fast block to polyspermy

• Cortical reaction - fertilization membrane

1. Fraternal: more than one oocyte fertilized by different sperm, may be different sex

2. Identical: one oocyte fertilized, split before 16 cell stage, same sex

3. Conjoined twins: separation not complete

Twins

Developmental Processes

1. Cell division or mitosis - cell division without cell growth

2. Differentiation - individual cells take on specialized forms and functions

3. Morphogenesis - physical development of organism, ongoing

4. Growth - at implantation, growth in size

1. Cleavage -

2. Blastulation -

3. Gastrulation -

4. Organogenesis/Nerulation -

Summary Early Developmental Events

Process

• Travels through oviduct

• Implantation into uterine lining

• Growth, differentiation, and morphogenesis begins

• Morula to blastocyst to embryonic disk

• Ectopic pregnancy possible

Pre-embryonic Development:The First Two Weeks

Tissues and organs: derived from three germ layers

• Ectoderm: body covering & neural structures -brain, spinal cord, & nerves.

• Mesoderm: skeleton, muscles, blood vessels, heart, kidneys, gonads, & dermis.

• Endoderm: primitive gut, lungs, liver & pancreas [+ most organs]

Embryonic Development: Weeks Three to Eight, Embryo

Placenta and Umbilical Cord

Figure 21.8

• Development

• Chorion digests into endometrium, creating pool of blood

• Placenta seals off the pool and projects chorionic villi into blood

• Villi contain blood capillaries connected through the umbilical vessels to the fetus

Placenta

• Functions

• Filters nutrients, waste, and antibodies for fetus without mixing mother or fetal circulations

• Some toxins or viruses may pass through

• Hormonal: produce estrogen and progesterone

Placenta (cont.)

Embryo Development: Third and Early Fourth Week

Figure 21.9

• Day 15

• Primitive streak: appears in embryonic disk, elongates along one axis

• Day 19-24

• Neural groove: brain and spinal cord

• Somites: bone, muscle, skin

• Pharyngeal arches: part of face, neck, and mouth

• Limb buds: arms and legs

Rapid Embryo Development

• Months three and four: organ development, beginnings of organ function

• Months five and six: fetal movement begins, responds to external sounds, survival possible outside mother

• Months seven through nine (third trimester): growth and maturation

Fetal Development: Eight Weeks to Birth

Stages of Birth

Figure 21.13A

Stages of Birth (cont.)

Figure 21.13B, C

Labor & delivery

• Stages of labor:

• Stage 1: dilation

• Stage 2: expulsion

• Stage 3: afterbirth

• Cesarean delivery: surgical delivery of baby

Birth

• Transition from fetus to newborn• Taking the first breath: pulmonary surfactants

necessary

• Changes in cardiovascular system• Umbilical circulation cut off

• Ductus venosus regresses to connective tissue

• Foramen ovale and ductus arteriosus close in days/weeks

• All blood from the digestive tract goes to liver

• Lactation: colostrum to milk

Early Postnatal Period

• Neonatal period: helpless period, movement by reflex

• Infancy; rapid development and maturation of organ systems

• Childhood: continued development and growth

• Adolescence: transition to adulthood

Birth to Adulthood

• Causes of aging: theories

• Internal cellular program that counts finite number of cell divisions, thus determining cell death

• Cell DNA damaged beyond repair

• Aging a whole body process; all systems interdependent

Aging: Change Over Time

• Body systems: age at different rates; musculoskeletal, skin, cardiovascular, respiratory, immune, nervous, sensory, reproductive, endocrine, digestion and nutrition, urinary

• Aging well: life style, exercise, diet

Aging: Change Over Time (cont.)

• Legal and medical criteria• Irreversible cessation of circulatory and

respiratory functions• Irreversible cessation of all functions of the entire

brain, including the brain stem

Death: Final Transition