Chap 4 Review Sheet

Gametogenesis

produces gametes (sex cells)

Gametogenesis involves…

• meiosis (reduction division); cell division reducing chromosome number by half

Diploid stem cells

• 46 chromosomes

• form haploid sex cells

Haploid

• 23 chromosomes

• sex cells

Zygote

• sperm and egg meet

• first diploid

Egg (ooctye) releasd into

uterine (fallopian tube)

Sperm

• longer journey

• ejaculation emits 200 million

• 20-200 get close to egg

Sperm structure:

• Acrosome: digestive enzymes, penetrates and fertilize egg

• Head: nucleus, DNA

• Midpiece: Mitochondria, ATP

• Tail: flagellum

Capacitation

• destabilizes the sperm membrane in readiness to encounter egg and release nucleus

• increases lashing of the tail

Cumulus oophorus

• cells surround egg

• release attractants for the sperm

Where does the sperm burrow?

cumulus,

what gel layer does sperm reach

zona pellucida

Acrosomal reaction occurs…

exocytosis of acrosomal enzymes penetrate zona pellucida

Fusion of sperm and egg:

• sperm adheres to egg

• membranes fuse

• sperm components sink into egg

• sperm nucleus is released into egg cytoplasm

polyspermy

penetration by multiple sperm

Cortical reaction

• secretory vesicles called cortical granules release enzymes via exocytosis:

  • enzymes: prevents additional sperm attachment and creates fertilization membrane that acts as a barrier from more sperm

What does human gestation (pregnancy) begin with?

starts with conception (fertilization) and ends with parturition (childbirth)

How long does human gestation (pregnancy) last?

average 266 days (38 weeks)

Conceptus

• collective term for all the products of conception

  • developmental stages of embryo/fetus, umbilical cord, placenta, and amniotic sac

Three trimesters

• 1st: fertilization through first month of fetal life

• 2nd: organs complete most of their development

• 3rd: fetus grows rapidly, organs developed enough to support life outside womb

Preembryonic Stage includes:

• begins with zygote; 16 days

• 3 major events: cleavage (mitotic division of zygote into smaller blastomeres), implantation, and gastrulation (primary germ layers)

• after individual is called embryo

• morula: stage w 16 or more blastomeres

• Blastocyst: hollow sphere w 100 cells

Gastrulaton

• 3rd major event of preembryonic stage

• cell migration and proliferation that creates the three primary germ layers (ectoderm, mesoderm, endoderm)

Gastrulation includes:

Primitive streak , primitive groove

Primitive streak

• midline thickening that forms in epiblast

• establishes right and left (bilateral symmetry), dorsal and ventral, cephalic and caudal

Primitive groove

• forms along center of primitive streak

• pathway for migrating epiblast cells

Migrating cells replace hypoblast to form

endoderm

migrating cells create the middle _____ layer

mesoderm

epiblast soon become…..

ectoderm

ectoderm and endoderm are what?

epithelia

Mesoderm

• loosely organized

• becomes mesenchyme (embryonic connective tissue which gves rise to such tissues as cardiac &smooth muscle, cartilage, bone and blood)

Ectoderm derivatives

• epidermis

• hair follicles & piloerector muscles (makes hair stand up); cutaneous glands; nervous system

Mesoderm derivatives

• dermis

• skeleton

• skeletal, cardiac, most smooth muscle

• cartilage

• blood

Endoderm

• most of mucosal epitherlium of digestive and respiratory tracts

• thyroid

• thymus

Neurulation

• formation of the neural tube; developes into nervous system

Order:

• Neural plate: ectoderm forms along embryos midline, source of NS

• Neural grove

• Neural folds

• Neural tube: folds fuse together

Embryonic stage- what are the accessory organs external to the embryo?

placenta, umbilical cord and four extraembryonic membranes (amnion, umbilical vesical (yolk sac), allantois, chorion)

Amnion

• thin transparent membrane

• forms sac around embryo

• penetrated only by umbilical cord

• filled w amniotic fluid

  • protects embryo and enables proper development

Umbilical vesicle (yolk sac)

• connected to embryo via vitelline duct

• produces first blood cells and stem cells of gametogenesis

Allantois

• outgrowth of caual end of gut

• foundation for growth of umbilical cord

Chorion

• outermost membrane

• chorionic villi forms part of placenta

Amniotic fluid

• fills amniotic cavity

• enables embryo to develop symmetrically

• keeps surface tissues from adhering to each other

• protects from trauma, infection, and temperature fluctuations

• allows freedom of movement important to muscle development

• helps w lung development as fetus “breaths fluid”

Placenta

• organ attached to uterine wall

• connected to fetus by umbilical cord

• source of nutrients

Placenta Nutritional roles:

• transports nutrients such as glucose, amino acids, fatty acids, minerals and vitamins from maternal blood to fetal blood

Placenta Excretory roles

• transports nitrogenous wastes like ammonia, urea, uric acid, and creatinine from fetal blood to maternal blood

Placenta Endocrine roles

• secretes hormones

• allows other hormones synthesized by conceptus to pass into mothers blood and maternal hormones to pass into fetal blood

Placenta Immune role

• transports maternal antibodies into fetal blood to confer immunity on fetus

Developmental Events- End of week 4

• vertebral column and central nervous system forms

• heart begins beating around day 22

Developmental Events - End of week 8

• Eyes form

• bone calcification begins

Developmental Events- end of week 16

digestive glands forming meconium (fetal feces) accumulating in intestine

Congenital anomaly

• birth defect

• abnormal structure or positiion of an organ at birth

• Ex: cleft lip and palate lip

Teratology

study of birth defects

Mutations

• occur from mutagens (chemicals, viruses, radiation)

• change in genetic material

• 
  

Aneuploidy

• genetic disorders; abnormal chromosome number

• results from nondisjunction (failure of chromosome pair to seperate properly during meiosis)

• Ex: Down syndrome- extra copy of chromosome 21

Teratogens

• environmental agents that cause anatomical deformities in fetus

• ex: alcohol; fetal alcohol syndrome, FAS

Teratogens

• environmental agents that cause anatomical deformities (main types: drugs, radiation, infectious diseases)

• exert destructive effects at any stage of development

• greatest vulnerability is week 3-8

thalidomide

• teratogenic drug

• deformed or missing arms and legs

• defects: ears, heart, intestines

Less obvious effects of teratogens

• physical or mental retardation

• hyperirritability

• inattention

• strokes,

• seizures

• respiratory arrest

• crib death

• cancer

Most harmful teratogen: Alcohol

• effects may not be noticed until child begns school

• fetal alcohol syndrome

• small head, malformed facial features, cardiac and central nervous systems defects, stuned growth, behavioral symptoms (hyperactivity, nervousness, poor attention)