A&P Exam 4 (Ch 29 pt 1)

2 Periods of Human Life Span

prenatal

postnatal

Prenatal

major period of human life span before birth, from fertilization to birth

Postnatal

major period of human life span after birth

3 Stages of Prenatal Period

germinal

embryonic

fetal

Germinal Period

first stage of prenatal period, begins at fertilization and ends at 14 days (weeks 1-2), primitive germ layer forms

Embryonic Period

second stage of prenatal period, days 14-56 after fertilization (weeks 3-8), major organ systems form

Fetal Period

third stage of prenatal period, 56 days to birth (the last 30 weeks of development), organ systems grow and become more mature

Clinical Age of Unborn Child

determined by the mother’s last menstrual period (lmp), starts 14 days prior to ovulation/fertilization

5 Stages of Postnatal Period

neonatal

infancy

childhood

adolescence

adult

Neonatal Period

first stage of postnatal period, from birth to 1 month after birth

Infancy

second stage of postnatal period, from 1 month to 1-2 years of age, end is sometimes set when the child begins walking

Childhood

third stage of postnatal period, age 1-2 years to puberty, individual develops considerably, form many emotion characteristics that last throughout life

Adolescence

fourth stage of postnatal period, puberty (age 11-14) to 20 years, puberty typically occurs earlier in females (age 11-13) than males (age 12-14), period of rapid growth usually accompanies onset of puberty

Adult

fifth sate of postnatal period, from around age 20 to death, full adult status occurs by age 17-18 in females and 19-20 in males

3 Periods of Adulthood and Ages

young adult: 20-40

middle age: 40-65

older adult: 65-death

Fertilization

begins prenatal development, occurs when a sperm cell attaches to the secondary oocyte, contents of the sperm head enter the oocyte cytoplasm and join the oocyte pronucleus

Sperm in Fertilization

several hundred million sperm cells are deposited in the vagina during sexual intercourse, only a few dozen reach the vicinity of the secondary oocyte in the ampulla of the uterine tube

Corona Radiate

around the oocyte that act as a barrier that slows down sperm cells

Glycoproteins (P3) Role in Fertilization

in the zona pellucida act as a species-specific sperm cell receptor to molecules on the acrosomal cap, binding initiates acrosomal reaction that activates digestive enzymes in the acrosome

First Sperm in Fertilization

first sperm cell through the zone pellucida attaches to the receptor molecule on the surface of the oocyte plasma membrane causing depolarization (fast block to polyspermy) for 2-3 seconds

What are the purposes of the sperm causing depolarization of an oocyte?

prevents additional sperm cells from attaching

stimulates secretory vesicles (cortical granules)

creation of perivitelline space

slow block to polyspermy

Secretory Vesicles (Cortical Granules)

depolarization of the oocyte by sperm stimulates release of intracellular ca+2 causing the oocyte to release water and other molecules from this structure

Perivitelline Space

fluid filled space between the oocyte and plasma membrane of the zona pellucida, formed when sperm causes depolarization of the oocyte and released fluid causes oocyte to shrink and zona pellucida to denature

Slow Block to Polyspermy

zp3 is inactivated and no more sperm can attach

Formation of Second Polar Body in Fertilization

formed when sperm cell entering oocyte stimulates female nucleus to undergo second meiotic division

Female Pronucleus

haploid, nucleus remaining after second meiotic division, moves to the center of the oocyte and meets male pronucleus (haploid)

What completes fertilization?

fertilization is complete when pronuclei fuse, restores diploid number of chromosomes, produces zygote

Zygote

divides to form two cells about 18-36 hours after fertilization, cells continue to divide/double, accounts for early cell division

2 Cells Formed From Zygote

totipotent

pluripotent

Totipotent Cells

cell formed from division of zygote, present from days 1-4 and have the potential to give rise to any tissue type necessary for development

Differentiation (Specialization)

occurs in the cells of the developing embryo

Pluripotent Cells

cell formed by division of zygote, cells that have gone through differentiation and have the ability to develop into a wide range of tissue but not all tissues necessary for development

What happens after the zygote has divided and those cells have differentiated?

the number of embryonic cells can decrease, increase, or reorganize without affecting normal development of the embryo

Morula

solid ball of 12 or more cells that forms from zygotic division

Blastocyst

hollow sphere of cells containing fluid-filled blastocele

Trophoblast

single layer of cells around blastocele, becomes placenta and extraembryonic membranes

Inner Cell Mass

thickened area of blastocyst, becomes embryo proper

2 Types of Twins

monozygotic

dizygotic

Monozygotic Twins

identical, totipotent cell separates from embryo and develops to form another individual, genetically identical, can arise from other mechanisms later in development

Dizygotic Twins

fraternal, female ovulates two or more secondary oocytes at the same time, secondary oocytes are fertilized by two sperm cells, not genetically identical

Implantation

blastocyst burrows into the uterine wall, occurs about 7 days after fertilization, typically occurs in the area of the uterine fundus

Blastocyst Invasion of Uterine Wall During Implantation

two populations of trophoblast cells develop and form the embryonic portion of the placenta

Placenta

organ of nutrient and waste exchange between embryo and mother, site of implantation and integrity of the placental attachment are important for a successful pregnancy

Cytotrophoblast

first proliferating population of individual trophoblast cells in the uterus during implantation, remains nearer the other embryonic tissues

Syncytiotrophoblast

other trophoblast population formed during implantation into uterus, nondividing syncytium (multinucleated cell), invades the endometrium of the uterus, nonantigenic so it does not trigger maternal immune reaction

When Syncytiotrophoblast Encounters Maternal Blood Vessels

surrounds and digests the vessel wall forming cavities (lacunae) containing maternal, lacunae are connected to intact maternal vessels allowing circulating maternal blood to enter the lacunae

Cords That Surround Syncytiotrophoblast and Lacunae

made of cytotrophoblast, embryonic mesoderm and blood vessels grow into these cords

Chorionic Villi

branches of placenta that sprout from cords of cytotrophoblasts and protrude into the lacunae

Chorion

entire embryonic structure facing the maternal tissue of placenta

Mature Placenta

cytotrophoblast disappears leaving only embryonic capillary wall, basement membrane, and thin layer of syncytiotrophoblast separating the maternal and embryonic blood supply

2 Alternate Conditions of Placenta

placenta previa

abruptio placentae

both conditions can result in miscarriage and threaten the mother’s life

Placenta Previa

condition that occurs if the blastocyst implants near the cervix, growing placenta can partially or completely cover the internal cervical opening, region covering the cervical opening may tear causing hemorrhaging as the fetus and placenta grow and uterus stretches

Abruptio Placentae

occurs when the placenta attachment is not strong, placenta tears away from the uterine wall causing hemorrhaging

Amniotic Cavity

forms around the inner cell mass after implantation, formation of amniotic cavity causes part of the inner cell mass nearest the blastocele to separate as a flat disk of tissue (embryonic disk)

Amniotic Sac (Amnion)

layer of cells surrounding the amniotic cavity, enlarges to surround the developing embryo

2 Layers of Embryonic Disk

epiblast

hypoblast

Epiblast

layer of embryonic disk adjacent to the amniotic cavity, gives rise to the three germ layers

Hypoblast

layer of embryonic disk on the side opposite the amnion, gives rise to extraembryonic membranes

Yolk Sac

forms inside the blastocele from the hypoblast

Gastrulation

phase of development that occurs 13-14 days after fertilization, embryonic disk becomes a slightly elongated oval structure, epiblast cells move, formation of three distinct germ layers that give rise to body structures

Steps 1-3 of Gastrulation

proliferating cells of the epiblast migrate toward the center and caudal end of the disk forming the primitive streak (thickened line)

some epiblast cells migrate through the primitive streak

cells that do not migrate form the ectoderm

Steps 4-7 of Gastrulation

some cells that moved through the primitive streak migrate towards and displace the hypoblast to form the endoderm

some cells emerge between the ectoderm and endoderm as the mesoderm

three germ layers are the beginning of the embryo proper

all tissues of the adult develop from the three germ layers

Notochord

rodlike structure that extends form the cephalic end of the primitive streak

Ectoderm Specialization

specialization of the ectoderm develops into portions of the nervous system

Ectoderm 18 Days After Fertilization

ectoderm near cephalic end of primitive streak is stimulated to form neural plate

Neural Folds

lateral edges of the neural plate that begin to rise, underlying notochord stimulates folding of the neural plate at the neural groove

Neural Groove

groove between the neural folds

Neural Tube and Neural Crest Formation

early neural plate forms

neural folds form with neural crest in between

neural crest cells form

crests of neural fold meet at the midline and fuse into the neural tube

Neuroectoderm

cells of the neural tube

Neural Crest Cells

cells that break away from neuroectoderm all along the crests of the folds

contribute to the skull, dentin of teeth, few small skeletal muscles, and general connective tissue

Neuroectoderm Becomes

brain, spinal cord, and part of the peripheral nervous system

Neural Tube

closes by day 26 of development

3 Routes of Neural Crest Cells

migrate down along the side of the developing neural tube to become autonomic ganglia neurons, adrenal medullary cells, or enteric nervous system neurons

migrate into the somites to become sensory ganglia neurons

migrate laterally between the somites and ectoderm become melanocytes

Mesenchyme

general term for neural crest cells of the head and mesoderm

Somites

distinct segments that form from the mesoderm immediately adjacent to the neural tube

First Few Somites in the Head

do not become clearly divided but form indistinct segmented structures called somitomeres

Somites and Somitomeres of Head

give rise to part of the skull, vertebral column, and skeletal muscles

most head muscles are derived from somitomeres