CR1 KCP2 Early Embryonic Development

Define Gametogenesis and name the two types.

The process of mature sex cell (gamete) formation. Types: Spermatogenesis (sperm formation in seminiferous tubules) and Oogenesis (ovum formation in ovarian cortex).

Outline the step-by-step cellular flow of Spermatogenesis with chromosome counts.

Primordial Germ Cell (46) → Spermatogonium (46, Mitosis) → Primary Spermatocyte (46, Mitosis) → Secondary Spermatocyte (23, Meiosis I) → Spermatids (23, Meiosis II) → Spermatozoa (23, Spermiogenesis).

What is Spermiogenesis and what 4 structural changes occur during it?

Cyto-differentiation converting round spermatids into motile spermatozoa. Changes: 1. Acrosomal cap formation from Golgi material; 2. Nucleus condensation forming the head; 3. Neck, body, and tail/flagellum formation from mitochondria and microtubules; 4. Shedding of excess cytoplasm.

Describe the hormonal axis regulating Spermatogenesis (GnRH, LH, FSH, Leydig, Sertoli).

GnRH (Hypothalamus) stimulates LH & FSH from Anterior Pituitary. LH acts on Leydig cells to produce Testosterone. FSH acts on Sertoli cells to promote spermatogenesis and secrete Androgen-Binding Protein (ABP) and Inhibin.

What are the specific functions of Androgen-Binding Protein (ABP) and Inhibin?

ABP: Concentrates testosterone locally inside seminiferous tubules for germ cell development. Inhibin: Provides negative feedback to pituitary to inhibit FSH, regulating sperm production rates.

Outline the cellular flow of Oogenesis with chromosome counts and timeline.

Primordial Germ Cell (46) → Oogonium (46) → Primary Oocyte (46, before birth) → Secondary Oocyte (23) + 1st Polar Body (at puberty) → Mature Ovum (23) + 2nd Polar Body (at fertilization).

Name the 2 specific meiotic arrest points in Oogenesis and when they resolve.

1st Arrest: Prophase I at the Diplotene stage (before birth until puberty). 2nd Arrest: Metaphase II (at ovulation, resolves ONLY if fertilized).

What is a Polar Body, why does it form, and what is its ultimate fate?

A small cell containing discarded chromosomes with minimal cytoplasm. It forms via unequal cytoplasmic division so the egg retains maximum nutrients. It serves no reproductive function and degenerates.

State 4 major differences between Spermatogenesis and Oogenesis.

1. Onset: Spermatogenesis starts at puberty; Oogenesis starts before birth. 2. Yield: 4 functional sperm vs. 1 functional ovum + 3 polar bodies. 3. Arrests: None in males; 2 in females (Prophase I & Metaphase II). 4. Completion: Continuous throughout life vs. completed only at fertilization.

How do the Ovarian Cycle and Menstrual (Endometrial) Cycle synchronize across 28 days?

Ovarian Cycle (Ovary): Follicular Phase (Days 1–14, FSH/Estrogen) → Ovulation (Day 14, LH Surge) → Luteal Phase (Days 14–28, Progesterone from Corpus Luteum). Menstrual Cycle (Uterus): Menstrual Phase (Days 1–4) → Proliferative Phase (Days 4–14, built by Estrogen) → Secretory Phase (Days 14–28, prepared by Progesterone).

What follicle stage persists from before birth until puberty, and what cells surround it?

Primordial Follicle; contains a Primary Oocyte surrounded by flat follicular cells and undifferentiated stromal cells.

List the key structural components of a mature Graafian Follicle.

Secondary oocyte (in Metaphase II), Zona pellucida, Corona radiata, Cumulus oophorus, fluid-filled Antrum, Granulosa cells, Theca interna, and Theca externa.

Fertilization and state its primary anatomical site.

The fusion of male and female gametes to form a diploid zygote. Occurs in the Ampulla of the uterine (fallopian) tube.

Capacitation?

A ~7-hour conditioning period in the female tract that removes the glycoprotein coat and seminal plasma from the sperm acrosome, allowing it to penetrate the corona radiata and undergo the acrosome reaction.

3 Phases of Fertilization and key enzymes/reactions in each.

Phase 1: Penetration of Corona Radiata (by capacitated sperm). Phase 2: Penetration of Zona Pellucida (Acrosome Reaction releasing Acrosin). Phase 3: Fusion of oocyte/sperm membranes, Cortical & Zonal Reactions (prevent polyspermy), and completion of Meiosis II.

3 main results/significance of Fertilization.

1. Restoration of diploid chromosome count (2n=46); 2. Determination of chromosomal sex (X vs. Y sperm); 3. Initiation of cleavage divisions.

Describe the structure of a Blastocyst and the fate of its 2 cell populations.

Structure: Fluid-filled sphere with a central cavity (blastocele). Embryoblast (Inner Cell Mass) → forms the Embryo proper. Trophoblast (Outer Cell Mass) → forms the Placenta.

State the normal site of Implantation and define Ectopic Pregnancy.

Normal: Endometrium of anterior or posterior wall of uterine body close to fundus. Ectopic: Implantation outside the uterine cavity (most common: ampulla of fallopian tube).

Compare Nondisjunction vs. Anaphase Lag during cell division.

Nondisjunction: Failure of chromosomes to separate in Anaphase → yields 1 Trisomic (2n+1) and 1 Monosomic (2n-1) cell. Anaphase Lag: Loss of a lagging chromosome in Anaphase → yields 1 Normal (2n) and 1 Monosomic (2n-1) cell.

What is the specific meiotic error that causes Down Syndrome (Trisomy 21)?

Chromosomal Nondisjunction during Meiosis I of gametogenesis.

Define Asthenozoospermia and state which step of spermatogenesis is defective.

Poor sperm motility; caused by a failure during Spermiogenesis (defect in tail/flagellum or mitochondrial assembly).

What is a Hydatidiform Mole (Molar Pregnancy) and which blastocyst component is absent?

An abnormal pregnancy with extensive trophoblastic proliferation without embryonic tissue. The Embryoblast (Inner Cell Mass) is absent/disappears.

Why is the second week of development called the "Week of Twos"?

1. Trophoblast forms 2 layers (Cytotrophoblast & Syncytiotrophoblast); 2. Embryoblast forms 2 layers (Epiblast & Hypoblast); 3. Two cavities form (Amniotic cavity & Yolk sac). 

Define Gastrulation, state when it occurs, and name its cell source.

The process during the 3rd week that converts the bilaminar disc into a trilaminar germ disc (Ectoderm, Mesoderm, Endoderm). Derived entirely from the Epiblast. 

What structure induces Gastrulation and marks the site of epiblast invagination?

The Primitive Streak (with the primitive node and primitive pit at its cephalic end). 

Outline the order in which the 3 germ layers are formed during Gastrulation.

1. Endoderm (1st epiblast wave displaces hypoblast); 2. Mesoderm (2nd epiblast wave fills space between epiblast and endoderm); 3. Ectoderm (remaining surface epiblast cells). 

What is the origin, inducer function, and adult remnant of the Notochord?

Origin: Prenotochordal epiblast cells migrating from the primitive pit. Function: Induces overlying ectoderm to form the neural tube. Remnant: Nucleus Pulposus of intervertebral discs. 

Define Neurulation and state its origin and primary inducer.

Formation of the closed Neural Tube (future CNS). Origin: Ectoderm. Inducer: Notochord. 

Name the closing days for the Anterior (Cranial) and Posterior (Caudal) Neuropores.

Cranial/Anterior Neuropore closes at Day 25. Caudal/Posterior Neuropore closes at Day 27. 

Differentiate between Anencephaly and Spina Bifida based on neuropore defects.

Anencephaly: Failure of cranial neuropore closure (absence of major brain structures). Spina Bifida: Failure of caudal neuropore closure. 

Differentiate between Meningocele and Myelomeningocele.

Meningocele: Herniation of meninges and spinal fluid only. Myelomeningocele: Herniation of meninges, spinal fluid, AND spinal cord/nerves. 

What process do Neural Crest Cells undergo during migration, and where do they originate?

Originate from the lateral borders/crest of the neural folds. They undergo an Epithelial-to-Mesenchymal Transition (EMT) and migrate into underlying mesoderm. 

5 high-yield Nervous System and Endocrine derivatives of Neural Crest Cells.

1. Dorsal Root (Spinal) Ganglia; 2. Sympathetic & Parasympathetic (enteric) Ganglia; 3. Adrenal Medulla; 4. Schwann cells & Glial cells; 5. C cells of thyroid gland. 

List 4 non-neurological structures derived from Neural Crest Cells.

1. Melanocytes of skin; 2. Bones & connective tissue of face/skull; 3. Conotruncal septum of heart; 4. Odontoblasts (dentin). 

What congenital defects result from abnormal neural crest cell migration in the heart and gut?

Heart: Tetralogy of Fallot (conotruncal septum defect). Gut: Hirschsprung's Disease (congenital aganglionic megacolon). 

5 major anatomical structures derived from Ectoderm.

1. Central & Peripheral Nervous System; 2. Epidermis of skin, hair, nails; 3. Mammary & sweat glands; 4. Tooth enamel; 5. Inner ear (otic) & lens placodes. 

What structures arise from the Paraxial Mesoderm?

Somitomeres (head mesenchyme) and Somites (subdivided into: Sclerotome = axial skeleton/vertebrae, Myotome = muscle tissue, Dermatome = dermis of skin). 

What system develops from the Intermediate Mesoderm?

The Urogenital System (kidneys, gonads, urinary and genital ducts). 

Differentiate between Somatopleuric (Parietal) and Splanchnopleuric (Visceral) Lateral Plate Mesoderm.

Somatopleuric: Limb bones/joints & parietal layer of pleura/pericardium/peritoneum. Splanchnopleuric: Heart, gut smooth muscle/connective tissue, & visceral serous layers. 

5 major structures derived from Endoderm.

Epithelial linings of GI tract, respiratory tract, and bladder, plus parenchyma of Liver, Pancreas, Thyroid, and Parathyroid glands.