• how cells reproduce
• asexual reproduction, exact duplicates of parents, accommodates growth and replaces mature cells

Mitosis

5 Phases

interphase

prophase

metaphase

anaphase

telophase

Gametogenesis

aka meiosis

sexual reproduction, union of two germ cells (gametes)

egg+sperm=zygote

46 chromosomes  (23 pair)

meiosis

• end up with 4→ survival mechanism, more variety allows for genetic diversity, diminishes likelihood of things like fragile X & down syndrome
• reduction of # of chromosomes
• diploid>haploid
• female 22 + x
• male 22 + x or males 22 + y
• gamete has 23 pair

Period of the Zygote: fertilization to implantation (2 weeks)

• nucleus of the sperm and egg unite to form a zygote (46 chromosomes)
• usually occurs in the upper 1/3 of fallopian tubes
• mitosis begins
• cleavage begins at 36 hours after fertilization
• progressively smaller cells produced blastomeres which become a solid mass known as a morula

• morula moves into uterine cavity
• ball becomes hollow and referred to as a blastocyst 
• blastocyst differentiates into 2 layers:
• trophectoderm→placenta & umbilical cord (nurtures)
• inner cells→embryo (embrionic stem cells- undifferentiated at this point-pluripotent), fluid-filled blastocoel

potential uses

• identify drug targets and test medications
• toxicity testing
• generate tissue for transplantation
• understanding prevention and treatment of birth defects

period of the zygote: fertilization to implantation

continued

• implantation occurs 7-8 days post fertilization
• implantation of blastocyst to the endometrium of the uterus
• ezymes liquefy endometrial cells allowing blastocyst to penetrate lining and development of placenta (hormones have to be at right level)
• progesterone→ hormone that sustains pregnancy
  

• beginning of organ systems
• development of membranes to protect and nourish embryo/fetus
• yolk sac→ initially primary nutrient to embryo, becomes non-functional part of umbilical cord, derived from inner cells (connections with the mom have not yet been formed) 

• amnion→thin protective membrane, formed by the 8th day
• amnion derived from inner cell mass, eventually becomes fluid filled and act as a schock absorber (amniotic fluid)
• chorion→becomes principle part of placenta, becomes fused with amnion, derived from trophectoderm
• allantosis→ small, vascularized membrane, becomes part of the umbilical cord
  

differentiates into 3 germ layers

1. ectoderm-
2. endoderm
3. mesoderm

forms embryonic disc that becomes embyro

• chorionic villi- extend from trophoblast, later forms placenta, allows for exchange of O2 and waste, no blood exchange
• body stalk- extension of mesoderm, eventually forms umbilical cord
• placenta- exchange of nutrients/waste and secrets hormones; established by 3 mos

Period of the Fetus

(8 weeks to birth)

• organs completely formed
• human appearance
• ossification and hair growht
• heart beat detected end of three months
• capable of survival at 26 weeks
• subscutaneous fat at end of 8th month
• double wt in 8th and 9th months
• major nerve tracts of the brain, new brain cells
• movement by 12 weeks
• 26 weeks- respiratory system

• primitive streak forms at caudal end of embryonic disc (continues to grow in all 3 planes)
• growth in three planes to form notocord (primitive axial skeleton- bones)
• neural tube thicken over the notocord
• eventually forming the CNS
• somites- rise to all muscular, connective and dermal tissue (external bumps- beginning of the PNS)

anterior end of the neural tube: 3 enlargements

• forebrain- prosencephalon
• midbrain- mesencephalon
• hindbrain-rhombencephalon

remainder of neural tube becomes spinal cord

neural crest becomes PNS(formed by somites)

lining of the neural tube beomes neurons

Growth and Differentiation of the Brain

• proliferation- neuronal & glial cells are produced
• migration- immunoglobulins and chemokines (follow tract of chemicals, not random; too few= cognitive delays/mr, too many=schizophrenia)
• differentiation- axons grow first→migrate→then dendrites form
• myelination- 1st in spinal cord→hindbrain→midbrain→forebrain
• synaptogenesis- start communicating, continues throughout life; more = better

• specificity of axon connections
• chemical gradients (help find destination)
• competition among axons- neural darwinism→trial synapse/attachments- if good neurogrowth factors, synapses will contine to grow→if not (bad connection, no neurogrowth factors)will die off...if they do start to grow, then dendrites start to form→richer connections

myelomeningocele

meningocele

spina bifida

depending on the severity and location of the defect, people who have spina bifida can experience a wide frange of medical complications:

• allergic reactions caused by prolonged exposure to latex (especially kids with multiple disabilities and or hospitalizations)
• bladder, bowel and kidney problems
• eye problems
• fractures
• hydrocephalus
• learning disorders
• seizures
• skin problems
• tethered spinal cord
• weight gain

prevention- orange juice→folic acid

development of respiratory system

(not fully functional until birth!!!)

part 1

• embryonic phase (3-7wks)→initial budding and branching of the lung buds from the primitive foregut. ends with teh development of the presumptive broncho-pulmonary segments
• Pseudoglandular phase (7-16 wks)→further branching of the duct system (up to 21 further orders) up to the level of the terminal bronchioles
• Canallcular phase (16-24*wks)→forms a dense capillary network. the diameter of the airway increases. the terminal bronchioles branch to form several orders of respiratory bronchioles (24 weeks=key)

development of the respiratory system

(babies can survive at 26-28weeks)

part 2

*at 26 weeks, very basic respiratory system is there

• terminal sac phase (24-36wks)→branching and growth of the terminal sacs or primitive alveolar ducts. by 26 weeks, a rudimentary though functional blood/gas barrier has formed. maturation of the alveoli continues by futher enlargement of the terminal sacs
• alveolar phase (36 weeks-term/adult)→maturation of the lung indicated by teh appearance of fully mature alveoli begins at 36 weeks, though new alveoli will continue to form for approximately 3 years. significant growth for 1-2 years after birth, thereafter all components grow proportionately until adulthood

• affected an estimated 24,000 infants born alive in the US in 2003
• incidence f RDS declines with degree of maturity at birth. it occurs in 60% of babies born at less than 28 weeks gestation, 30% of those born at 28-34 weeks and less than 5% of those born after 34 weeks.
• annual RDS deaths decreased from 25,000 in the 1960s to 831 in 2003 (4% of infant fatalities); in 2003, this was the 7th ranking cause of infant deaths
• in 2003, the RD mortality rate (per 100,000 live births) among African Americans was 43.7 vs. 16.8 among whites

• characterized by rapid breathing, nasal flaring, grunting noise with each breath and blue around lips and anil beds, whih indicates a lack of oxygen. symptoms usually appear shortly after birth and become more sever over time
• RDS is treated by general supportive therapy, such as the adminstration of intravenous fluids, by the use of mechanical resprators designed to prevent the alveoli from collapsing, by the administration of surfactant and for htose with sever RDS, the use of partial liquid ventilation

development of the auditory system

outer ear

•  pinna-auricle→initially on neck, moves cranially during mandible development
• external auditory meatus→ week 5, extends inwards to pharynx, until week 18 has ectodermal plug

development of the auditory system

middle ear

tympanic membrane

ossicles

eustachian tube

development of the auditory system

inner ear

begins middle of 3rd week, formation of cochlear duct by 5th week, semicircular canals by 6th week

7th week first turn of the cochlea continues until 3rd month

atresia external auditory meatus (EAM remains occluded)

congenital deafness

microtia (pinna doesnt form properly)

development of face and mouth

weeks 3-5

• weeks 3 & 4→primitive mouth, oral groove; frontonasal process, maxillary process and nasal placodes become nasal plate
• week 5→frontal nasal process continues to develop; maxillary process fuses, mandibular arch and hyoid begin to form

development of face and mouth

weeks 6 & 7

• week 6→maxillary continues to fuse with nasal process, begin anterior growth , formation of primary palate, nasal septum begins to form
• week 7→further development of primary palate, upper lip, anterior portion of alveolar process and premaxillary portion of palate

development of face and mouth

week 8 on

• week 8→ increase in vertical growth of face with incrase in oral cavity, secondary palate formed with fusion of palatine process adn maxillae, soft palate and medial portion of hard palate
• complete by week 12

• 1/1000 births
• males 2:1
• incomplete, uni, or bilateral
• interruption of fusion between primitive plate and palatine process
• requires multiple surgeries
• thought to have genetic link
• certain drugs may increase risk of cleft lip and palate