Aim to answer every question before checking. Missed questions point you to the sections you need most.
1. (3.1) Following fertilization, the zygote undergoes:
C. The zygote undergoes rapid mitotic cleavage divisions (no growth between them) to form a morula (~16 cells), then cavitates into a fluid-filled blastocyst with an inner cell mass and trophoblast.
2. (3.1) The inner cell mass of the blastocyst gives rise to:
B. The inner cell mass (embryoblast) becomes the embryo. The outer trophoblast becomes the fetal portion of the placenta and extraembryonic membranes.
3. (3.2) Gastrulation is the process by which:
D. Gastrulation rearranges the blastula into a gastrula with ectoderm, mesoderm, and endoderm - the foundation for all later tissues.
4. (3.2) Invagination at the primitive streak establishes:
A. Cells migrate through the primitive streak to form mesoderm (middle) and endoderm (inner); cells remaining at the surface become ectoderm (outer).
5. (3.3) Neurulation refers to:
C. The neural plate (ectoderm above the notochord) folds upward and fuses into the neural tube - the future brain and spinal cord. Failure to close causes spina bifida or anencephaly.
6. (3.3) The notochord, which signals neural induction, is derived from:
D. The notochord is a mesodermal rod. It releases Sonic hedgehog and other signals that induce the overlying ectoderm to become neural plate.
7. (3.4) Organogenesis refers to:
B. After gastrulation, the germ layers interact and differentiate into organs over weeks 3-8, the embryonic period.
8. (3.4) Most teratogen-induced malformations result from exposure during:
A. Organ primordia are most sensitive when they are actively forming. Teratogens during weeks 3-8 (when most mothers don't yet know they are pregnant) produce structural defects.
9. (3.5) Which of the following is an ectodermal derivative?
D. "Attractive and smart" - Ectoderm = epidermis + nervous system (plus hair, nails, enamel, lens of eye). Mesoderm = muscle, bone, blood, kidney, heart. Endoderm = gut epithelium, lungs, liver, pancreas.
10. (3.5) The liver and pancreas are derivatives of:
C. Both bud off the primitive gut tube (endoderm). Endoderm supplies the epithelial lining of the GI tract plus the liver, pancreas, thyroid, and lung epithelium.
11. (3.6) Induction in development refers to:
A. Classic example: the notochord induces the overlying ectoderm to become neural plate. Without the right inducer, the responding tissue follows a different developmental path.
12. (3.6) Cells within a single developmental field typically share:
B. A morphogenetic field is a group of cells whose fates are specified together (e.g., the early limb field). Cells in the field respond coordinately to local cues.
13. (3.7) A totipotent cell:
C. Totipotent = "total potential" (zygote through ~8-cell morula). Pluripotent cells (ICM, ES cells) can make all three germ layers but not placenta. Multipotent cells make a limited range (e.g., hematopoietic).
14. (3.7) Adult stem cells (e.g., hematopoietic stem cells) are typically:
D. Adult/somatic stem cells are tissue-restricted. A hematopoietic stem cell makes all blood cell types but no muscle, nerve, or liver cells.
15. (3.8) A morphogen gradient specifies cell fate by:
B. Morphogens diffuse from a source and set up a concentration gradient; cells at high, medium, and low levels turn on different transcription factors, producing distinct fates along the axis.
16. (3.8) Sonic hedgehog (Shh) in limb and neural development acts as:
A. Shh is secreted from the notochord and the zone of polarizing activity in the limb bud and establishes gradients that pattern the neural tube (ventral fates) and digit identity.
17. (3.9) The foramen ovale in the fetus allows:
C. The foramen ovale is a hole in the interatrial septum. Because fetal lungs are collapsed and pulmonary resistance is high, blood crosses right-to-left through the foramen to reach the systemic circulation.
18. (3.9) The ductus arteriosus shunts blood from:
B. The ductus arteriosus is the second right-to-left shunt, redirecting blood that does enter the pulmonary artery into the aorta. It closes shortly after birth to become the ligamentum arteriosum.
19. (3.10) When the newborn takes its first breath:
A. Inflation drops pulmonary resistance, more blood flows through the lungs to the left atrium, and higher left-atrial pressure shuts the flap over the foramen ovale. Rising arterial oxygen also constricts the ductus arteriosus.
20. (3.10) Pulmonary surfactant in the fetal lung:
D. Surfactant (dipalmitoylphosphatidylcholine) is produced by type II pneumocytes starting around week 24 and is essential by birth. Insufficient surfactant in preterm infants causes neonatal respiratory distress syndrome.
21. (3.2) The three primary germ layers, from outside to inside, are:
B. Ectoderm (outer) → mesoderm (middle) → endoderm (inner). Useful mnemonic: "Ecto-outside, Endo-inside, Meso-middle."
22. (3.5) Skeletal muscle, kidneys, and the cardiovascular system develop from:
C. Mesoderm is the "muscle/blood/bone" layer: skeletal and smooth muscle, heart, vessels, blood cells, kidneys, gonads, dermis, and connective tissue.
23. (3.7) Which stem cell source is pluripotent and can give rise to all three germ layers (but not placenta)?
D. Embryonic stem cells derived from the ICM of the blastocyst are pluripotent - they cannot make placenta (a trophoblast derivative) but can produce every tissue of the embryo.
24. (3.1) Implantation of the human blastocyst into the uterine wall typically occurs:
A. The blastocyst reaches the uterus ~4 days after fertilization and implants into the endometrium around days 6-9. The trophoblast then starts secreting hCG.
