D) Liver

Explanation: The liver becomes the major site of definitive hematopoiesis from 6 to 30 weeks of gestation, producing red blood cells, white blood cells, and platelets with adult-type hemoglobin.

B) The neural tube

Explanation: The neural plate forms from the ectoderm and folds into the neural tube, which is crucial for the development of the central nervous system (CNS).

C) Forming parts of the peripheral nervous system and other tissues

Explanation: Neural crest cells break away from the edge of the neural tube and contribute to the formation of the peripheral nervous system, as well as other tissues like melanocytes and facial cartilage.

B) Growth from within

Explanation: Interstitial growth refers to the process of bone or cartilage growth from within, distinguishing it from appositional growth, which adds new layers to the surface.

B) A neural tube defect where the brain fails to form

Explanation: Anencephaly is specifically described as a neural tube defect resulting from the failure of the rostral portion of the neural tube to close, leading to the absence of major parts of the brain and skull, and it is typically fatal.

B) FACIT collagens, proteoglycans, and small leucine-rich proteins

Explanation: These components work together to control the diameter and assembly of collagen fibers, ensuring proper tissue function and structure.

C) Water and salts

Explanation: Eccrine glands primarily secrete water and salts (sweat), which play a crucial role in thermoregulation.

B) Vision, hearing, and motor control

Explanation: The mesencephalon, or midbrain, is responsible for basic functions such as vision, hearing, and motor control, making it a crucial part of the brain's functionality.

C) Yolk sac stage (3-8 weeks)

Explanation: Primitive hematopoiesis occurs in the yolk sac from around 3 to 8 weeks of embryonic development, marking the earliest site of blood cell formation.

C) 28 weeks

Explanation: By 28 weeks of gestation, the bone marrow becomes the primary site of hematopoiesis, continuing to produce all blood cell types throughout life.

C) The upper portion of the neural tube fails to close

Explanation: Anencephaly occurs when the rostral (upper) portion of the neural tube fails to close, leading to the absence of most of the brain and skull.

A) Prosencephalon, Mesencephalon, Rhombencephalon

Explanation: During development, the brain initially forms three primary vesicles: the Prosencephalon (forebrain), Mesencephalon (midbrain), and Rhombencephalon (hindbrain), which later subdivide into more complex structures.

B) The birth of neurons

Explanation: Neurogenesis refers to the process of neuron formation, which begins as vesicles form and is essential for the rapid development of the brain's structure and function.

B) Synaptic plasticity without NMDA receptors

Explanation: Long-term depression (LTD) in the cerebellum is a type of synaptic plasticity that does not involve NMDA receptors but relies on Ca2+, diacylglycerol (DAG), and IP3 signaling, playing a significant role in motor learning and coordination.

B) A process of bone degradation

Explanation: Osteocytic osteolysis refers to the small-scale breakdown of the bone matrix initiated by osteocytes to maintain calcium homeostasis.

B) They differentiate into osteoblasts

Explanation: Osteoprogenitor cells are precursor cells that differentiate into osteoblasts, which are responsible for forming new bone and eventually become osteocytes that maintain the bone matrix.

C) Calmodulin

Explanation: In smooth muscle, calcium ions bind to calmodulin, which activates myosin light-chain kinase (MLCK) to enable muscle contraction.

B) T cell development and immune tolerance regulation

Explanation: Hassall’s corpuscles are structures in the thymic medulla that are believed to play a role in T cell development and the regulation of immune tolerance, which is crucial for the immune system's function.

B) Regions that develop into adult brain structures

Explanation: Primary brain vesicles are regions formed during early brain development that eventually develop into the adult brain structures, including the prosencephalon and mesencephalon.

B) Formation of bone directly from mesenchymal cells

Explanation: Intramembranous ossification is the process where mesenchymal cells differentiate into osteoblasts, forming bone directly without a cartilage precursor, primarily responsible for forming flat bones like those in the skull.

B) Collagen IV, laminin, and entactin

Explanation: These molecules provide structural support and stability to the basement membrane, facilitating proper cell anchorage.

B) An Rh-negative mother with an Rh-positive fetus

Explanation: This condition occurs when an Rh-negative mother produces antibodies against the Rh-positive fetal red blood cells, leading to hemolysis.

B) It is key to grasping the formation of the brain and origins of congenital defects

Explanation: Understanding how vesicles develop is essential for comprehending not only brain formation but also the origins of various congenital defects, highlighting its significance in developmental biology.

B) They give rise to various structures, including parts of the peripheral nervous system

Explanation: Neural crest cells emerge from the edges of the neural tube and are crucial for developing various structures, including components of the peripheral nervous system.

C) Increase the levels of acetylcholine at the synapse

Explanation: AChE inhibitors work by inhibiting the enzyme acetylcholinesterase (AChE), which increases acetylcholine levels at the synapse, compensating for the reduced function of acetylcholine receptors in myasthenia gravis.

C) VEGF

Explanation: During hypertrophy, cells release vascular endothelial growth factor (VEGF) to promote the formation of new blood vessels, which is essential for tissue growth and repair.

C) Cilia have microtubules, microvilli have actin

Explanation: Cilia are motile structures composed of microtubules, while microvilli are non-motile and contain actin filaments, enhancing surface area for absorption.

B) Keratin, lamellar granules, and keratohyaline granules

Explanation: Keratinocytes produce keratin for structural strength and secrete lamellar granules for waterproofing, along with keratohyaline granules to aid in skin toughness.

C) Telencephalon

Explanation: The prosencephalon divides into the telencephalon and diencephalon, with the telencephalon forming structures such as the cerebral hemispheres and basal ganglia.

B) It loses its totipotency and embryonic stem cell status

Explanation: After implantation into the uterine wall, a cell loses its totipotency and embryonic stem cell status, committing to specific developmental pathways as part of the growing embryo.

B) Sensory and motor pathways

Explanation: The SAME DAVE mnemonic stands for Sensory Afferent, Motor Efferent, Dorsal Afferent, and Ventral Efferent, which helps in remembering the pathways of sensory and motor neurons in relation to the central nervous system.

B) G-proteins and second messengers

Explanation: Metabotropic receptors are coupled to G-protein-coupled receptors (GPCRs) and utilize second messengers like cAMP or IP3 to amplify signals inside the cell, resulting in a large intracellular response from a small external signal.

C) Calcitonin

Explanation: Calcitonin is a hormone that inhibits osteoclast activity, thereby reducing bone resorption and helping to maintain bone density.

B) Randomly arranged

Explanation: In dense irregular connective tissue, the type I and III collagen fibers are arranged irregularly, which provides strength in multiple directions.

B) IL-1 and TNFα

Explanation: IL-1 and TNFα are pro-inflammatory cytokines that play major roles in promoting the inflammatory response and recruiting immune cells.

B) A defect in the lower neural tube

Explanation: Spina Bifida is a defect where the caudal (lower) portion of the neural tube does not close properly, leading to malformations of the spinal cord and vertebrae.

C) The most severe form of spina bifida

Explanation: Myelomeningocele is the most severe form of spina bifida, where both the spinal cord and meninges protrude through an opening in the spine, potentially causing paralysis and other complications.

B) Through the dorsal root

Explanation: Sensory (afferent) signals enter the spinal cord through the dorsal root, while motor (efferent) signals exit through the ventral root, which is crucial for the organization of the spinal cord's function.

B) They are involved in motor coordination

Explanation: Purkinje cells are large neurons in the cerebellum that play a crucial role in coordinating motor movements.

B) Type I and III

Explanation: Loose connective tissue contains a mix of type I and III collagen fibers along with elastic fibers, providing flexibility and support.

B) Yolk sac, liver, spleen, and bone marrow

Explanation: These sites sequentially take over the role of blood cell production during development, with the yolk sac being the earliest and the bone marrow becoming primary by 28 weeks.

C) Metencephalon and Myelencephalon

Explanation: The rhombencephalon develops into the metencephalon, which forms the pons and cerebellum, and the myelencephalon, which forms the medulla oblongata.

C) Regulation of heart rate and respiration

Explanation: The medulla oblongata, formed from the myelencephalon, regulates essential autonomic functions such as heart rate, blood pressure, and respiration.

B) They are involved in vesicle fusion

Explanation: SNARE proteins are critical for the fusion of vesicles with the presynaptic membrane, facilitating the release of neurotransmitters like acetylcholine at the neuromuscular junction.

C) Fibroblast cells

Explanation: Mucous connective tissue, such as Wharton's jelly, is rich in fibroblasts, which are responsible for producing the extracellular matrix, unlike undifferentiated mesenchymal cells.

C) Acetylcholine receptors

Explanation: In myasthenia gravis, antibodies target acetylcholine receptors at the neuromuscular junction, leading to reduced muscle contraction and weakness.

C) Thalamus

Explanation: The diencephalon gives rise to the thalamus, hypothalamus, and epithalamus, with the thalamus serving as a sensory relay center.

C) Cytocrine secretion

Explanation: Melanocytes utilize cytocrine secretion to transfer melanin pigment to neighboring keratinocytes, which helps protect the skin against UV radiation.

C) Simple cuboidal

Explanation: Both the mammary gland and apocrine sweat gland are composed of simple cuboidal epithelium, which is important for their secretory functions.

A) They lack a nucleus

Explanation: Red blood cells do not present MHC I molecules because they lack a nucleus, which means they do not interact with T cells for immune surveillance.

D) Osteoporosis increases the risk of fractures

Explanation: Osteoporosis is a more severe condition than osteopenia, characterized by significant decreases in bone density and quality, leading to an increased risk of fractures.

C) Pseudostratified columnar with stereocilia

Explanation: The epididymis is lined with this type of epithelium, which aids in sperm maturation and transport due to the presence of stereocilia.

B) Destruction of erythrocytes

Explanation: An acute hemolytic reaction occurs when incompatible blood is transfused, leading to the immune system attacking and destroying the transfused red blood cells.

B) Production of antibodies by plasma cells

Explanation: Medullary cords in lymph nodes contain plasma cells that secrete antibodies, playing a crucial role in the immune response.