1. Cross-Sectional Anatomy Lesson I

2. Human Development
Fertilization of the ovum occurs in the fallopian tubes
After fertilization, the united sperm and ovum (zygote) travel into the uterus
Major cellular events occur in the uterus, one of the events being the formation of a blastocyst which is implanted in the uterine wall (Endometrial Layer)
Implantation occurs approximately seven (7) days after ovulation or around the twenty-first (day 21) of the menstrual cycle.
Implantation occurs as the endometrial tissue grows and surrounds the blastocyst (takes about 7 days)

3. Human Development
HCG secreted by the blastocyst keeps it from being aborted
HCG- Human Chorionic Gonadotropin secretion is only produced in pregnant women
Pregnancy tests are based on the presence of this hormone in blood or urine

4. Formation of Primary Germ Layers
During implantation, changes occur in the inner cell mass of the blastocyst, resulting in the formation of the primary germ layers
Amnionic cavity develops in the inner cell mass
Two layered flattened embryonic disk develops
Ectoderm, endoderm, and mesoderm develop
ALL TISSUES AND ORGANS DEVELOP FROM THESE THREE PRIMARY GERM LAYERS
Embryonic stage of development begins, lasting 6 weeks (from beginning of week three thru week eight)

5. Development of the Human Brain
CNS (brain and spinal cord) develops from a thickened area of the embryonic ectoderm called the neural plate
18 – 20 days after conception
Neural plate is altered to form a neural tube and neural crest
Neural tube forms the brain and spinal cord
Neural crest forms most structures within the peripheral nervous system

6. Neural Tube
Temporarily open at both caudal and cranial ends (portions)
Cranial portion closes approximately 24 days after conception
Caudal portion closed about 2 days later
Differentiation and growth of the neural tube is greatest at the cranial end

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9. Neural Tube Development
Four weeks after conception – cranial end differentiates into three primary vesicles;
Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)

10. Further Differentiation of the Neural Tube Divisions
During the next week:
Prosencephalon (forebrain) = telencephalon and diencephalon
Rhomencephalon (hindbrain) = metencephalon and myelencephalon
3 now equal 5

13. Ectoderm Epidermis of the skin Hair, nails, skin glands
Lens of the eye
Enamel of the teeth
All nervous tissue
Adrenal medulla
Sense organ receptor cells
Linings of the oral and nasal cavities, vagina, and anal canal

14. Endoderm Epithelial lining of digestive tract
Epithelium of the liver and pancreas
Epithelium of urinary bladder & urethra
Epithelium of the respiratory tract
Thyroid, parathyroid, and thymus glands

15. Mesoderm Dermis of the skin Skeletal, smooth, cardiac muscle
Connective tissue including cartilage and bone
Epithelium of serous membranes
Epithelium of joint cavities
Epithelium of blood vessels
Kidneys and ureters
Adrenal cortex
Epithelium of gonads and reproductive ducts

16. Fetal Images

17. Fetal Images

18. The Brain Weighs about 3 lbs.(2% of body weight)
Larger in the male than in the female
Composed of organized regions of gray and white matter
Gray matter = nerve cell bodies and unmyelinated fibers (regions of synapse –electrical communication between neurons)
Gray matter grouping = Basal Ganglia
White matter = nerve fibers covered in myelin (fatty substance)

19. Basal Ganglia

20. Regions of the Brain
Cerebrum
Diencephalon
Brainstem
Cerebellum

21. Brain Regions