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MCB 135E Exam I Review

Prepare for your exam on reproductive systems, fertilization, and embryonic development with detailed information on gametogenesis in males and females, and the stages of fertilization and implantation.

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MCB 135E Exam I Review

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  1. MCB 135E Exam I Review Jason Lowry Fall 2005

  2. General Information • Exam I – Wednesday 10/5/04 • In-class exam (50 minutes, 100 points) • You will need a pencil and a pen • If you write short answers in pencil, they are not eligible for regrade • We will provide a scantron • You will need to place everything except pen/pencil at the front of room or in the aisle (NOT UNDER THE CHAIR) • The exam will not begin until everyone has complied

  3. General Information • Exam I • Material for exam will cover everything through the lecture on Monday (10/3/05) • Exam breakdown • Exam questions are based on lecture material (not website nor discussion)

  4. Review Material • Reproductive Systems • Fertilization and Implantation • Embryonic Development • The placenta and hormones of pregnancy • Nervous System Development • Sexual Differentiation • Metabolism and Growth

  5. Gametogenesis • Spermatogenesis • What is it • Where does it occur • What are the hormones involved • What is the progression of sperm maturation • What are the major characteristics of sperm

  6. Spermatogenesis • Formation of Spermatozoa (Sperm) • Occurs in seminiferous tubules • Involves two distinct maturational processes • Spermatocytogenesis • 1st Stage of sperm formation • Spermatogonium  Spermatids • Involves mitosis(46 Chromosomes) initially and then meiosis (23 Chromosomes) • Spermiogenesis • Spermatids  Spermatozoa

  7. Male Reproductive Endocrinology

  8. Gametogenesis • Oogenesis • What is the function of the ovaries • What is the process of oogenesis • What are the hormones involved • How are these hormones regulated

  9. The Ovaries • Gamete producers • 3 cm long solid mass of cells • Suspended in the abdomen by ligaments and mesenteries • Oocytes found on outside surface of ovaries

  10. Oogenesis • Primary Oocytes form at 3 months during fetal development • 2 million primary oocytes by birth in prophase of first meiotic division • Maturation • Increased size and Meiosis • First meiotic division resumes a few hrs before ovulation due to LH Surge • Second meiosis after fertilization • Division produces unequal mass of cells most food goes to ovum and none to polar body. • All polar bodies die eventually. • Oocyte+specialized cells=follicle: Nourish ovum and secrete estrogens • Mature follicle bursts releasing ovum. • Many follicles enlarge but only one bursts.

  11. Male Sperm Small Size Elongated Shape Millions in # Vigorous Motility No protecting envelope Minimal Cytoplasm Lacks yolk Centrosome Retained Mitochondria in body Golgi Apparatus in acrosome Nucleus condensed in head XY Female Ovum Large size Spheroidal shape Few in # Lack motility Egg envelopes for protection Bulky Cytoplasm Little Yolk Centrosome Disappears Diffuse mitochondria Diffuse golgi apparatus Open structured nucleus XX Gamete Comparison

  12. Fertilization and Implantation • Fertilization • Sperm Morphology • Organization of ovum after ovulation • Role of ovum in fertilization • Role of sperm in fertilization • Stages of fertilization • What is capacitation, acrosomal reaction, zona pelucida • Implantation • Pre-implantation events • Act of implantation

  13. Morphology

  14. Fertilization • Role of Ovum • Contribute the maternal complement of genes • Reject all sperms but one • Provide food reserve until the embryo begins to feed upon exogenous material • Role of Sperm • Reach and penetrate the egg • Activate the egg to nuclear and cytoplasmic division necessary to embryonic development • Contribute the paternal complement of genes

  15. Stages of Fertilization • Penetration • Random contact between sperm and egg • Sperm propel past corona cells and attach to zona pelucida • One sperm-One Egg • Activation • Completion of Meiosis of ovum – forms female pronucleus • Sperm Changes – Sperm travels toward center of egg, head swells, becomes male pronucleus • Rearrangement in egg – biochemical changes necessary prior to nuclear fusion • Nuclear Fusion • Union of two pronuclei • Loss of nuclear envelope, contribution of chromosomes to first mitotic cleavage

  16. Uterine Preparation • Estrogen • Involved in proliferation of uterus (hypertrophy) • 3-5 Days post-ovulation E dominates and is thought to play a role in transport of ovum • Progesterone • Increased Vascularization (hypervascularization) • 5-7 days post-ovulation, P increases and counters the effect of E thus relaxing uterine contractions

  17. Implantation • Days 1-8 • Fertilized egg begins to divide by cleavage into smaller blastomeres • Blastomere increase follows a double synchronous sequence initially, but later becomes asynchronous • Later stage cleavage forms a ball of cells or morula • Fluid begins accumulating in morula and a conversion occurs to the blastula (blastocyst) • Blastocyst attaches to uterine stroma • Outer layer of cells begin to proliferate and invade stroma of uterus

  18. Implantation • Days 8-16 • Blastocyst lodged in uterine stroma • Trophoblast (outer cells) invades uterine stroma and begins to form placenta • Blastocele becomes chorionic cavity • Inner cell mass begins to proliferate and form germ disc and primitive entoderm • Complex sequence of chemical and physical interactions occur between ovum and mother • Only about 50% of fertilized eggs successfully implant

  19. Embryonal Development • Germ Layer Theory • Gastrulation • Tissues generated

  20. Germ Layer Theory • Embryo’s Method of sorting out its parts • Ectoderm – Outer covering of embryo • Entoderm (Endoderm) – Lies under the ectoderm and forms lining of the primitive gut cavity • Mesoderm – Develops between ectoderm and entoderm • Gastrulation – The process by which germ layers come to occupy their characteristic positions

  21. Germ Layers and Their Systems • Ectoderm • Epidermis and lining cells of glands • Appendages of skin • Nervous system • Posterior Pituitary • Chromafin organs - adrenal medulla • Anterior Pituitary • Some Epithelium • Entoderm • Epithelial lining of alimentary canal • Lining cells of glands that open to alimentary canal • Epithelium of most of the urinary bladder and urethra • Epithelium of prostate • Mesoderm • Remaining organs and tissues not made by Ectoderm or Entoderm • Connective tissue • Teeth • Musculature • Blood • Adrenal Cortex

  22. Placenta and Hormones of Pregnancy • Structure of placenta • Include • Fetal membranes • Maternal membranes • Functions of placenta • Hormones • Role of hormones • Hormone Biosynthesis • Respiration • Protection • Excretion • Fetal circulation • Trace blood flow • Know obstacles • Know modifications

  23. Fetal Yolk Sac Center of blood formation in early embryonal life Facilitates transfer of nutrients from developing trophoblast to embryo Allantois Blood vessels develop around allantoic tube Tube eventually fuses with chorion By 6th week – 1 umbilical vein and 2 umbilical arteries Amnion Membranous sac that surrounds embryo Fluid fills amnion that has protective role throughout pregnancy Maternal Deciduas Highly modified uterine endometrium Basalis Portion between ovum and uterine wall Capsularis Region of decidua where ovum is embedded Parietalis Lines remainder of uterus Placenta

  24. Placenta Functions • Gas Exchange • Nutrient Delivery • Antibody Delivery • Removal of Waste • Secretion of hormones • Protection

  25. Hormones of Pregnancy • Estrogen • Progesterone • hCG • Placental Lactogen (hCS) • Placental Growth Hormone

  26. Steroid Hormone Synthesis

  27. Challenges and Adaptations • Challenge • Oxygen and Nutrients are less in umbilical vein than in adult arteries • Adaptations • Establish priorities • Establish specific structures to supply priorities • Embryonal Hemoglobin

  28. Specific Structures • Ductus Venosus • Shunts Umbilical Vein to Inferior Vena Cava • Foramen Ovale • Shunts between atria • Ductus Arteriosus • Shunts pulmonary artery to aorta

  29. Nervous System • Major Functions • Communication with external/internal environment • Regulation of… • Major Components • Neurons • Neuroglia • Mylenated nerve fibers • Microglia • Ground Substance • Blood Vessels and CSF

  30. Development of the Nervous System • Morphological Development • Biochemical Development • Functional Development • Sexual Differentiation

  31. Neurulation • N.S. – Arises from ectoderm on dorsal portion of embryo • 3-4 Weeks – Cells proliferate along middle plate • 5-6 Weeks – Plate folds to form neural groove • 6-7 Weeks – Groove closes into neural tube • Brain develops from anterior portion • Spinal cord develops from the posterior portion

  32. Neural Epithelium • Neuroblast • Neuron • Spongioblast • Migratory Spongioblast • Oligodendria • Astrocytes • Astrocytes • Ependyma

  33. Carbohydrates Primarily maternal glucose Stored as glycogen Under influence of glucocorticoids In fetus Insulin levels high Insulin sensitivity high Hypoglycemic Anaerobic Glycolysis Glyceraldehyde-P-Dehydrogenase Glycolitic enzyme High in postnatal brain During same period the oxidative enzyme Succinic Dehydrogenase Much lower Energy Sources

  34. Thyroid Hormone • Functions • Promotion of body growth • Development of CNS through: • Promotion of neorogenesis • Promotion of myelination • Promotion of brain metabolism • Stimulates oxygen consumption in all cells • Abnormalities • Hypothyroidism • Cretinism • Short stature, low metabolic rate, skin changes • Treatable if given Thyroxine at an early age

  35. Functional Development • Differential Development of N.S. • Neurotransmitter activity in different brain regions • Perinatal Behavior • Reflexes – Refer to table in reader • Motor • Respiratory (17-24 weeks) • Gastrointestinal (24th week) • Suckling • Startle (Presence of excessive activity after birth is an indicator of delayed development of certain brain centers) • Education • Better educated appear to live longer with less disability • Several pieces of evidence discussed for this in class

  36. Sexual Differentiation

  37. Sexual Differentiation • Steroid hormone action on brain development • Androgen action on sexually dimorphic nucleus of the preoptic area (SDN-POA) • Male Rats – After puberty responsible for male behavior, large SDN-POA present • Female Rats (low androgen levels) – After puberty -Small SDN-POA (reversible with androgen treatment) • Lordosis (arching of back when sexually receptive)

  38. Metabolism and Growth • Metabolism and Growth information: • Reader / Handout • Class Today • Discussion Today

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