GENERAL HISTOLOGY Flashcards

Question

This is a type of neuron which contains three or more cytoplasmic processes, primarily one axon and multiple dendrites. A. Unipolar B. Bipolar C. Pseudounipolar or Pseudopolar D. Multipolar

Answer 1

D. Multipolar Explanation: Multipolar neurons have one axon and multiple dendrites, making them the most common type of neuron in the CNS (brain and spinal cord). They are involved in motor control, sensory processing, and cognitive functions. Why not the other options? ❌ A. Unipolar → Has only one process extending from the cell body (rare in vertebrates, found in invertebrates). ❌ B. Bipolar → Has one axon and one dendrite (found in the retina and olfactory epithelium). ❌ C. Pseudounipolar → Appears to have one process that splits into two branches (found in sensory neurons of the PNS, like dorsal root ganglia).

Answer 2

B. Bipolar Explanation: Bipolar neurons have two cytoplasmic processes: - One axon → Sends signals away from the cell body - One dendrite → Receives signals Where are bipolar neurons found? 🔹 Retina (for vision) 🔹 Olfactory epithelium (for smell) 🔹 Inner ear (for hearing and balance) Why not the other options? ❌ A. Unipolar → Has only one process (rare in vertebrates, found in invertebrates). ❌ C. Pseudounipolar → Has one process that splits into two (seen in sensory neurons of the PNS). ❌ D. Multipolar → Has one axon and multiple dendrites (most common in the CNS).

Answer 3

A. Mucosa-Submucosa-Muscularis-Serosa Explanation: The layers of the gastrointestinal (GI) tract from the lumen outward are: 1️⃣ Mucosa → Innermost layer, in direct contact with food Epithelium (varies by organ) Lamina propria cells) Muscularis mucosae (thin layer of smooth muscle) 2️⃣ Submucosa → Connective tissue layer Contains blood vessels, nerves (Meissner's plexus), lymphatics, and glands 3️⃣ Muscularis (Muscularis externa) → Responsible for peristalsis Inner circular layer (contracts to narrow the lumen) Outer longitudinal layer (contracts to shorten the GI tract) Auerbach's plexus (Myenteric plexus) between muscle layers 4️⃣ Serosa (or Adventitia) → Outermost layer Serosa (if the organ is within the peritoneal cavity, covered by visceral peritoneum) Adventitia (if outside the peritoneal cavity, like in the esophagus) Why Not the Other Options? ❌ B. Mucosa-Submucosa-Serosa-Muscularis → Incorrect order; Muscularis comes before Serosa ❌ C. Serosa-Submucosa-Muscularis-Mucosa → Incorrect; the sequence should start with Mucosa (innermost) ❌ D. Submucosa-Mucosa-Muscularis-Serosa → Incorrect; Mucosa should come first

Answer 4

C. Canaliculi Explanation: Osteocytes are located within small spaces called lacunae inside the bone matrix. They extend their cytoplasmic processes through small canals called canaliculi to connect with neighboring osteocytes via gap junctions. This allows the exchange of nutrients, waste, and signaling molecules. Why Not the Other Options? ❌ A. Lacunae → These are the small spaces housing the osteocytes, but the canals that connect them are called canaliculi. ❌ B. Howship's Lacunae → These are resorption bays where osteoclasts break down bone. ❌ D. Haversian Canal → These are central canals in osteons that contain blood vessels and nerves, but they are not the small canals connecting osteocytes.

Answer 5

B. Loose CT Explanation: The dental pulp is classified as loose connective tissue (CT) because it contains a high number of cells (fibroblasts, odontoblasts, immune cells) and an abundant extracellular matrix with collagen fibers, ground substance, and blood vessels. Why Not the Other Options? ❌ A. Dense CT → Dense CT has more collagen fibers and fewer cells, making it stronger but less flexible. The pulp is soft and rich in cells, so it doesn't fit this classification. ❌ C. Endothelial → Endothelial tissue lines blood vessels, but pulp is a connective tissue, not an epithelial or endothelial tissue. ❌ D. Nervous tissue → While the pulp contains nerve fibers, it is not primarily nervous tissue—it is connective tissue with nerves inside it.

Answer 6

C. Perichondrium Explanation: The perichondrium is a dense connective tissue sheath that surrounds most types of cartilage (except articular cartilage and fibrocartilage). It contains: - Vascular supply (blood vessels) that nourish cartilage - Nerve supply - Chondrogenic cells (which can differentiate into chondroblasts for cartilage growth and repair) Why Not the Other Options? ❌ A. Chondrocytes → These are the mature cartilage cells found within lacunae, not a connective tissue sheath. ❌ B. Chondronium → No such term exists in histology. ❌ D. Periosteum → This is a fibrous connective tissue sheath surrounding bone, not cartilage.

Answer 7

A. Reticular Explanation: The reticular connective tissue is characterized by a network of reticular fibers (a type of collagen) and is primarily found in organs that are involved in filtering blood or lymph, such as: - Kidney - Spleen - Lymph nodes - Bone marrow This tissue provides structural support for the cells within these organs and helps in the formation of the lymphatic and blood circulatory systems. Why Not the Other Options? ❌ B. Cartilage → Cartilage is a different type of connective tissue found in places like the joints, ears, and nose, but not in the organs listed here. ❌ C. Adipose → Adipose tissue is specialized for storing fat and is found beneath the skin and around internal organs, not in these particular organs. ❌ D. Collagen → While reticular fibers are made of collagen, collagen alone refers to the protein and is not a type of connective tissue.

Answer 8

C. Chylomicrons Explanation: Chylomicrons are large lipoprotein particles that transport dietary triglycerides (fats obtained from food) from the intestines to the adipocytes (fat cells), liver, and muscle cells. They are formed in the intestinal cells after the digestion of fats and are essential for fat metabolism. Why Not the Other Options? ❌ A. VLDL (Very Low-Density Lipoproteins): VLDLs are involved in transporting triglycerides synthesized in the liver, not dietary fats. ❌ B. LDL (Low-Density Lipoproteins): LDL is primarily involved in transporting cholesterol to cells, not triglycerides. ❌ D. HDL (High-Density Lipoproteins): HDL is involved in the reverse transport of cholesterol from tissues back to the liver, not the transport of triglycerides.

Answer 9

A. Both statements are true. Explanation: The basement membrane is a specialized, felt-like sheet of extracellular material found beneath epithelial cells. It provides structural support, regulates molecular exchange, and plays a role in cell signaling. Additionally, all epithelial cells that are in contact with connective tissue rest on a basement membrane, which separates and connects the two tissue types. This membrane is essential for anchoring epithelial cells and supporting their function.

Answer 10

D. White adipocytes are specialized for long-term energy storage. Explanation: Adipocytes, also known as fat cells, are specialized cells primarily responsible for storing energy in the form of lipids (triglycerides). - (A) Incorrect: Adipocytes store lipids, not glucose in the form of sucrose. Glucose is converted into triglycerides for storage. - (B) Incorrect: Adipocytes appear as large, round cells with a central lipid droplet, not string-like structures. - (C) Incorrect: Brown adipocytes appear brown due to a high number of mitochondria, not melanin. - (D) Correct: White adipocytes store energy in the form of large lipid droplets for long-term energy storage.

Answer 11

D. Chromatin Explanation: Chromatin is the uncoiled form of DNA associated with proteins (mainly histones) found in the nucleus. It exists in this relaxed state during interphase, allowing gene expression and DNA replication. (A) Genes: Segments of DNA that code for proteins. (B) DNA: The molecule that carries genetic information. (C) Chromosome: A highly condensed form of chromatin seen during cell division (mitosis or meiosis).

Answer 12

D. Interneuron Explanation: Interneurons are the most abundant type of neurons in the cerebral cortex and function primarily in processing and integrating information between sensory and motor pathways. Motor neurons (C) are involved in sending signals from the brain to muscles, but they are not the most numerous in the cerebral cortex. The cerebral cortex contains a large number of interneurons, which help in complex processes like thought, memory, and decision-making.

Answer 13

E. Mucoid CT Explanation: Mucoid (Mucous) Connective Tissue is a type of embryonic connective tissue found primarily in the umbilical cord (Wharton's jelly) and fetal organs. It is rich in hyaluronic acid, which gives it a gelatinous consistency and helps in protecting blood vessels in the umbilical cord. It contains fibroblast-like cells and collagen fibers, providing structural support.

Answer 14

C. Langerhans cells Explanation: - Langerhans cells are dendritic cells found in the epidermis that function as antigen-presenting cells (APCs). - They phagocytize pathogens, process them, and present the antigens to T-cells, initiating an immune response. - These cells play a crucial role in the skin's immune defense. Why Not the Others? A. Keratinocytes → Primary cells of the epidermis that produce keratin but do not have a phagocytic function. B. Tonofilaments → These are structural proteins that provide mechanical strength but are not cells. D. Melanocytes → Produce melanin for pigmentation but do not participate in immune defense.

Answer 15

C. Type III Explanation: - During the proliferative phase of wound healing, Type III collagen is the primary collagen produced. - Type III collagen is found in granulation tissue, which helps provide a temporary matrix for wound repair. - Later, during the remodeling (maturation) phase, Type III collagen is gradually replaced by Type I collagen, which is stronger and more durable. Why Not the Others? A. Type I → Found in mature scars, skin, tendons, and bones; it replaces Type III collagen in the final stages of healing. B. Type II → Found in cartilage, not in wound healing. D. Type IV → Found in basement membranes, not in wound healing.

Answer 16

B. IgA Explanation: IgA (Immunoglobulin A) is the primary antibody found in mucosal secretions (such as saliva, tears, mucus, and breast milk). It plays a crucial role in mucosal immunity by neutralizing pathogens before they invade the body. Secretory IgA (sIgA) is produced by plasma cells in the mucosa-associated lymphoid tissue (MALT) and transported across epithelial cells into secretions. Why Not the Others? A. IgG → The most abundant antibody in the blood and extracellular fluid, mainly involved in systemic immunity. C. IgM → The first antibody produced in an immune response, mostly found in the blood. D. IgE → Involved in allergic reactions and protection against parasitic infections.

Answer 17

A. Both statements are true. Explanation: 1. Hydrostatic Pressure (First Statement ✅) - Caused by the pumping action of the heart - Pushes fluid out of the capillaries into the interstitial space - Higher at the arterial end of capillaries - Drives filtration at the capillary level 2. Colloid Osmotic (Oncotic) Pressure (Second Statement ✅) - Created by plasma proteins (mainly albumin) - Pulls fluid back into the capillaries from the interstitial space - More dominant at the venous end of capillaries - Helps with reabsorption to maintain blood volume

Answer 18

A. Haversian system Explanation: - The Haversian system (osteon) is the structural and functional unit of compact bone. - It consists of concentric lamellae (layers of bone matrix) arranged around a central Haversian canal, which contains blood vessels and nerves. - Osteocytes are located in small spaces called lacunae, which are connected by canaliculi for nutrient exchange. Other Options Explained: ❌ B. Haversian canal – This is the central canal within each osteon, but it is not the entire functional unit. ❌ C. Osteocytes – These are mature bone cells found in lacunae within the osteon but are not the structural unit itself. ❌ D. Osteoblasts – These are bone-forming cells responsible for bone matrix deposition, but they do not form the functional unit of compact bone.

Answer 19

D. Cortisol Explanation: - Cortisol is a glucocorticoid hormone produced by the adrenal cortex that acts as a potent anti-inflammatory agent by suppressing the immune response and reducing inflammation. - It inhibits the production of pro-inflammatory cytokines and reduces the activity of immune cells. Other Options Explained (Pro-Inflammatory Agents): ✅ A. Prostaglandins – These are lipid compounds that mediate inflammation, pain, and fever. ✅ B. Leukotrienes – These are involved in inflammatory and allergic responses, increasing vascular permeability and attracting white blood cells. ✅ C. Interleukin-6 (IL-6) – A cytokine that promotes inflammation and plays a role in immune response regulation.

Answer 20

D. Actin Explanation: - Actin is one of the most abundant proteins in muscle cells and plays a crucial role in muscle contraction. - It is a key component of thin filaments in the sarcomere, the basic unit of muscle fibers. - Actin interacts with myosin (a motor protein) to generate force for muscle contraction. Other Options Explained: ❌ A. Keratin – Found in skin, hair, and nails, but not a major muscle protein. ❌ B. Collagen – A structural protein found in connective tissues like tendons and ligaments, but not in muscle fibers. ❌ C. Albumin – A blood plasma protein that helps with fluid balance, not a structural component of muscle.

Answer 21

A. Both statements are true. Explanation: 1. Brunner's glands - Found only in the submucosa of the duodenum (first part of the small intestine). - They secrete alkaline mucus to neutralize acidic chyme from the stomach and protect the intestinal lining. 2. Peyer's patches - Found only in the submucosa of the ileum (last part of the small intestine). - They are lymphoid tissue aggregates that play a role in immune defense by detecting pathogens in the intestines.

Answer 22

B. Cytokinesis Explanation: - Cytokinesis is the final step of cellular division where the cytoplasm divides, resulting in two physically separate daughter cells. - It usually begins during telophase and is completed after mitosis ends. Other Options: A. Telophase → Nuclear membranes reform, chromosomes de-condense, but the cell is not yet fully split. C. Karyokinesis → Division of the nucleus, not the entire cell. D. Anaphase → Sister chromatids separate and move to opposite poles, but the cell is still one entity.

Answer 23

A. Autophagy Explanation: Autophagy is the process by which a cell uses lysosomes to degrade and recycle excess or non-functioning organelles or cellular components. It helps maintain cell homeostasis and provides energy during starvation. Other Options: B. Apoptosis → Programmed cell death, but not specifically for organelle disposal. C. Pyroptosis → A type of inflammatory cell death triggered by infections. D. Autolysis → Self-digestion of the entire cell after death, not a controlled degradation process like autophagy.

Answer 24

B. Apoptosis Explanation: - Apoptosis is a highly regulated, controlled process of programmed cell death that allows the body to eliminate defective, damaged, or unneeded cells without causing inflammation. It plays a crucial role in development, immune function, and tissue homeostasis by preventing uncontrolled cell growth. Other Options: A. Autophagy → Cellular self-cleaning process that degrades unnecessary organelles, not whole cells. C. Pyroptosis → Inflammatory cell death, often triggered by pathogen infections. D. Autolysis → Uncontrolled self-destruction of a cell after death, unlike apoptosis.

Answer 25

D. Autolysis Explanation: - Autolysis occurs when digestive enzymes leak out of lysosomes, leading to self-destruction of the cell. This process is usually uncontrolled and happens after cell death or in pathological conditions. Other Options: A. Autophagy → Controlled self-digestion of damaged organelles to maintain cellular health. B. Apoptosis → Programmed cell death, highly regulated, does not involve lysosomal enzyme leakage. C. Pyroptosis → Inflammatory cell death, triggered by infections, involves the formation of pores in the cell membrane.

Answer 26

C. Pyroptosis Explanation: - Pyroptosis is a type of inflammatory cell death that occurs due to microbial infections. - It is triggered by the activation of inflammasomes, leading to caspase-1 activation, which causes cell membrane rupture, release of inflammatory cytokines (IL-1β, IL-18), and immune system activation. Other Options: A. Autophagy → A normal cellular process for degrading and recycling cellular components. B. Apoptosis → Programmed cell death, which is non-inflammatory and part of normal cellular regulation. D. Autolysis → Self-digestion due to lysosomal enzyme leakage, usually post-mortem or due to tissue damage.

Answer 27

C. Necrosis Explanation: - Necrosis refers to uncontrolled cell death caused by disease, injury, or lack of blood supply (ischemia). - It is different from apoptosis because it is not programmed and often leads to inflammation and damage to surrounding tissues. Examples: Myocardial infarction (heart attack), gangrene, stroke, severe burns. Other Options: A. Apoptosis → Programmed cell death (regulated, does not cause inflammation). B. Autophagy → A cell survival mechanism where the cell degrades its own components for recycling. D. Autolysis → Self-digestion by lysosomal enzymes, usually after death.

Answer 28

A. AUG Explanation: - AUG (Adenine-Uracil-Guanine) is the start codon in mRNA that signals the beginning of protein synthesis (translation). - It codes for the amino acid Methionine (Met), which is the first amino acid in a newly formed protein chain. - The ribosome recognizes AUG and starts translating the mRNA into a polypeptide. Other Options: B. UAG, C. UAA, and D. AUU are NOT start codons. UAG, UAA, and UGA → Stop codons (end translation). AUU → Codes for the amino acid Isoleucine, not a start codon.

Answer 29

D. Circumvallate Explanation: - Circumvallate papillae are the largest but least numerous papillae on the tongue. - They are arranged in a V-shape at the back of the tongue, just in front of the sulcus terminalis. - They contain taste buds and are associated with Von Ebner's glands, which help in taste perception by secreting a watery fluid that washes away food particles. Other Options: A. Foliate → Found on the lateral sides of the tongue, have taste buds. B. Filiform → Most numerous, but do not contain taste buds. They help with texture and sensation. C. Fungiform → Scattered across the tongue, mushroom-shaped, contain taste buds.

Answer 30

B. Both statements are false. Explanation: - Somatic cells (body cells) are diploid (2n), meaning they contain two sets of chromosomes (46 total, or 23 pairs)—one from each parent. - Germ cells (sperm and egg cells) are haploid (n), meaning they contain only one set of chromosomes (23 total). Why both statements are false? ❌ First statement: Incorrect because somatic cells are diploid (2n), not haploid (n). ❌ Second statement: Incorrect because germ cells are haploid (n), not diploid (2n).

Answer 31

B. IgY Explanation: - IgY is the functional equivalent of IgG in mammals but is found in birds, amphibians, and reptiles. - It is the main class of serum antibodies in these species and plays a crucial role in immune defense. - In birds, IgY is also found in egg yolk, where it provides passive immunity to the developing embryo. Other options: ❌ IgG – Main serum antibody in mammals. ❌ IgA – Found in mucosal secretions (e.g., saliva, tears, milk). ❌ IgM – First antibody produced in response to infection.

Answer 32

B. IgY Explanation: - IgY is the primary antibody found in egg yolk of birds, amphibians, and reptiles. - It serves as a maternal antibody, providing passive immunity to the developing embryo. - Functionally, IgY is equivalent to IgG in mammals but has structural differences. Other options: ❌ IgG – Main serum antibody in mammals, but not in egg yolk. ❌ IgA – Found in mucosal secretions (e.g., milk, saliva, tears). ❌ IgM – First antibody produced in immune response, but not in egg yolk.

Answer 33

C. Stratified squamous Explanation: - The oral cavity is lined by stratified squamous epithelium to withstand friction, abrasion, and mechanical stress from chewing and speaking. - This epithelium can be keratinized (in areas like the gingiva, hard palate, and dorsal tongue) or non-keratinized (in softer areas like the cheeks, lips, and ventral tongue). Other options: ❌ Stratified columnar – Found in rare locations (e.g., conjunctiva, male urethra). ❌ Stratified cuboidal – Found in sweat gland ducts, mammary glands, and salivary glands. ❌ Pseudostratified columnar – Found in the respiratory tract, not the oral cavity.

Answer 34

C. Monocytes Explanation: - Macrophages originate from monocytes, which are a type of white blood cell (WBC). - Monocytes circulate in the blood and, upon entering tissues, differentiate into macrophages or dendritic cells, depending on the tissue environment. - Macrophages play a key role in phagocytosis, immune defense, and tissue repair. Other options: ❌ Mast cells – Release histamine and are involved in allergic reactions. ❌ Basophils – Circulate in the blood and also release histamine, playing a role in allergies. ❌ Neutrophils – First responders in acute inflammation, but do not differentiate into macrophages.

Answer 35

C. Dental follicle Explanation: - Cementoblasts are the cells responsible for forming cementum, which covers the roots of teeth. - These cells originate from the dental follicle (dental sac), a mesenchymal structure that surrounds the developing tooth germ. - The dental follicle also gives rise to periodontal ligament (PDL) fibroblasts and osteoblasts (which form alveolar bone). Other Options: ❌ Enamel organ – Gives rise to ameloblasts, which produce enamel. ❌ Dental papilla – Gives rise to odontoblasts, which produce dentin, and also contributes to the dental pulp.

Answer 36

D. Protein fibers and ground substance Explanation: The extracellular matrix (ECM) of connective tissue consists of two main components: 1. Protein fibers – Provide structural support and strength, including: - Collagen fibers – Strong and resistant to stretching - Elastin fibers – Allow flexibility and elasticity - Reticular fibers – Form a supportive network in organs like lymph nodes and bone marrow 2. Ground substance – A gel-like material that fills spaces between cells and fibers. It consists of: - Water - Proteoglycans (e.g., hyaluronic acid) - Glycoproteins (e.g., fibronectin, laminin) Other Options: ❌ A. Resident cells and water – Resident cells (e.g., fibroblasts, macrophages) are part of connective tissue but do not make up the ECM. ❌ B. Plasma and resident cells – Plasma is mainly found in blood, not in general connective tissue. ❌ C. Water and plasma – ECM contains water, but not plasma; it contains ground substance and fibers instead.

Answer 37

B. Cuboidal epithelium Explanation: The salivary gland ducts are lined by different types of epithelial cells depending on the section of the duct: 1. Intercalated ducts → Simple cuboidal epithelium - Smallest ducts, receive saliva from acini. - Lined by cuboidal cells for ion exchange and modification of saliva. 2. Striated ducts → Simple columnar epithelium - Larger ducts with columnar cells that modify saliva by actively reabsorbing Na⁺ and secreting 3. Excretory ducts → Stratified columnar epithelium - Largest ducts leading to the oral cavity.

Answer 38

B. Coding strand Explanation: During RNA transcription, DNA has two strands: 1. Template strand (non-coding strand) → This is the strand that is read by RNA polymerase to synthesize mRNA. 2. Non-template strand (coding strand) → This strand has the same sequence as the mRNA (except that thymine (T) is replaced by uracil (U) in RNA). Since the non-template strand has the same sequence as the mRNA, it is called the coding strand because it "codes" for the protein.

Answer 39

A. Fibroblasts Explanation: Fibroblasts are the most common cells found in connective tissue. Their primary functions include: - Synthesizing and secreting collagen, elastin, and other extracellular matrix (ECM) components (such as glycosaminoglycans and proteoglycans). - Providing structural support to tissues. - Aiding in wound healing by producing new connective tissue. Other options: ❌ B. Adipocytes → Store fat and provide insulation. ❌ C. Macrophages → Function in immune defense, engulfing pathogens and debris. ❌ D. Red blood cells → Transport oxygen and do not synthesize ECM components.

Answer 40

C. They speed up chemical reactions in the human body and regulate metabolism. Explanation: Enzymes are biological catalysts that speed up chemical reactions in the body without being consumed in the process. Their primary functions include: - Facilitating digestion (e.g., amylase breaks down carbohydrates, protease breaks down proteins, lipase breaks down fats). - Regulating metabolism by controlling biochemical pathways (e.g., ATP synthase helps in energy production). - DNA replication and repair (e.g., DNA polymerase). Why not the other options? ❌ A. "They are instructions needed for an organism to develop, survive, and reproduce." → This describes DNA, not enzymes. ❌ B. "Contain information for making specific molecules and proteins..." → This also refers to DNA and genes, not enzymes. ❌ D. "All of the above." → Since A and B are incorrect, D is incorrect as well.

Answer 41

B. Both statements are false. Explanation: - Antidiuretic hormone (ADH) and oxytocin ARE produced in the neurosecretory cells of the hypothalamus (specifically in the supraoptic and paraventricular nuclei). - These hormones ARE stored and released from the posterior pituitary gland (but NOT produced there). Why are both statements false? ❌ First statement ("not produced in the hypothalamus") is false → They are produced in the hypothalamus. ❌ Second statement ("not stored in the posterior pituitary") is false → They are stored in and released from the posterior pituitary.

Answer 42

✅ D. Delta cells Explanation: - The pancreatic islets (Islets of Langerhans) contain different types of endocrine cells, each secreting specific hormones: - Alpha (α) cells → Secrete glucagon (raises blood sugar). - Beta (β) cells → Secrete insulin (lowers blood sugar). - Delta (δ) cells → Secrete somatostatin (inhibits insulin and glucagon secretion, regulates digestion). - PP (Pancreatic Polypeptide) cells → Secrete pancreatic polypeptide (regulates pancreatic secretions).

Answer 43

D. Adrenal medulla Explanation: - Chromaffin cells are specialized neuroendocrine cells found in the adrenal medulla of the adrenal glands. They secrete catecholamines: - Epinephrine (adrenaline) - Norepinephrine (noradrenaline) - Dopamine These hormones are crucial for the fight-or-flight response, increasing heart rate, blood pressure, and glucose metabolism. 🔹 Why not the other options? Zona Glomerulosa → Produces mineralocorticoids (e.g., aldosterone). Zona Fasciculata → Produces glucocorticoids (e.g., cortisol). Zona Reticularis → Produces androgens (e.g., DHEA).

Answer 44

A. Bands of Hunter-Schreger Explanation: - Hunter-Schreger bands (HSB) are optical phenomena seen in dental enamel as alternating light and dark bands. - These occur due to the alternating orientation of enamel rods as they extend from the dentinoenamel junction (DEJ) to the enamel surface during enamel formation. - Their function is believed to enhance enamel strength and resist fractures. 🔹 Why not the other options? Enamel spindle → Extensions of odontoblast processes into the enamel. Enamel lamellae → Thin, leaf-like defects extending from the enamel surface toward the DEJ. Enamel tufts → Small, brush-like defects filled with enamel proteins, extending from the DEJ.

Answer 45

B. Medium-sized myelinated fibers Explanation: These fibers correspond to Aδ fibers, which are responsible for transmitting acute, fast, sharp pain. They are thinly myelinated, allowing for relatively fast conduction of pain signals to the central nervous system. This type of pain is well-localized and helps in immediate withdrawal from harmful stimuli. In contrast: - Large myelinated fibers (Aα, Aβ fibers): Mainly involved in proprioception and touch, not pain transmission. - Large unmyelinated fibers: These are not a typical category in nerve fiber classification. - Small unmyelinated fibers (C fibers): Transmit slow, dull, burning, and aching pain, which is poorly localized.

Answer 46

B. Autocrine Explanation: Autocrine signaling occurs when a cell secretes a hormone or chemical messenger that binds to receptors on the same cell, affecting its own function. This type of signaling is common in immune responses and certain growth factor regulations. Other options: A. Paracrine – The hormone acts on nearby cells. C. Endocrine – The hormone is released into the bloodstream and acts on distant target cells. D. Juxtacrine – The hormone requires direct cell-to-cell contact for signaling.

Answer 47

A. Aldosterone Explanation: Aldosterone is a mineralocorticoid, primarily involved in sodium and water retention by acting on the kidneys. It has little to no anti-inflammatory effects compared to glucocorticoids. Other options (Glucocorticoids with anti-inflammatory effects): B. Prednisone – A synthetic glucocorticoid with strong anti-inflammatory properties. C. Hydrocortisone – Also known as cortisol, it has moderate anti-inflammatory effects. D. Corticosterone – A less potent glucocorticoid compared to cortisol but still has anti-inflammatory properties.

Answer 48

B. Buccopharyngeal membrane Explanation: The buccopharyngeal membrane (also called the oropharyngeal membrane) is a thin bilaminar structure that separates the primitive oral cavity (stomodeum) from the primitive foregut during early embryonic development. It eventually ruptures around the 4th week to establish continuity between the oral cavity and the developing digestive tract. Other options: A. Stomodeum – The primitive oral cavity, located in front of the buccopharyngeal membrane. C. Rathke’s pouch – A structure that gives rise to the anterior pituitary gland. D. Forebrain – The anterior part of the developing brain, not related to the separation of the oral cavity and foregut.

Answer 49

C. Eosin Explanation: Eosin is the most commonly used acidic dye in histology. It stains basic (acidophilic) structures in cells, such as the cytoplasm, collagen, and muscle fibers, in pink to red hues. It is often used in combination with hematoxylin in the H&E (Hematoxylin and Eosin) stain, one of the most widely used staining techniques in pathology. Other options: A. Acid fuchsin – Another acidic dye used in special stains (e.g., Masson’s trichrome) for collagen and cytoplasm. B. Hematoxylin – A basic dye that stains acidic structures (e.g., nuclei) blue to purple. D. Methylene blue – A basic dye used in bacterial staining and some histological applications.

Answer 50

B. Peroxisomes Explanation: Peroxisomes are small, spherical, membrane-bound organelles that contain oxidative enzymes, such as catalase and oxidases. They play a key role in detoxification by breaking down harmful substances like hydrogen peroxide (H₂O₂) and metabolizing fatty acids through β-oxidation. They originate from the endoplasmic reticulum and are essential for lipid metabolism and cellular detoxification. Other options: A. Lysosomes – Contain hydrolytic enzymes for breaking down waste materials and cellular debris. C. Ribosomes – Non-membranous organelles responsible for protein synthesis. D. Vesicles – General term for membrane-bound sacs that transport materials within the cell.

Answer 51

A. Lysosomes Explanation: Lysosomes are spherical, membrane-bound organelles that originate from the Golgi apparatus and contain digestive (hydrolytic) enzymes such as proteases, lipases, and nucleases. They function in breaking down microbes, ingested materials, worn-out organelles, and even the entire cell (autophagy/apoptosis). They play a crucial role in cellular digestion and waste removal. Other options: B. Peroxisomes – Contain oxidative enzymes for detoxification but are formed from the endoplasmic reticulum, not the Golgi. C. Ribosomes – Non-membranous organelles responsible for protein synthesis. D. Vesicles – General term for membrane-bound sacs that transport materials in the cell.

Answer 52

D. Vesicles Explanation: Vesicles are spherical-shaped, membrane-bound sacs that transport various materials within the cell, out of the cell (exocytosis), and into the cell (endocytosis). They play a crucial role in intracellular transport, secretion, and storage of substances such as proteins, lipids, and waste products. Other options: A. Lysosomes – Contain digestive enzymes and break down cellular debris. B. Peroxisomes – Contain oxidative enzymes for detoxification. C. Ribosomes – Non-membranous organelles responsible for protein synthesis.

Answer 53

C. Karyotype Explanation: A karyotype refers to an individual's complete set of chromosomes, including their number, size, and shape, as seen under a microscope. It is often used in genetics to detect chromosomal abnormalities. Humans typically have 46 chromosomes (23 pairs) in their karyotype. Other options: A. Genes – Segments of DNA that encode proteins. B. DNA – The molecule that carries genetic information. D. Diploid – Refers to cells that contain two sets of chromosomes (2n = 46 in humans), but it does not specifically describe the complete chromosomal set like a karyotype does.

Answer 54

A. Human sex cells contain haploid chromosomes Explanation of the options: A. Human sex cells contain haploid chromosomes – ✅ Correct! - Sex cells (gametes: sperm and egg cells) contain haploid (n = 23) chromosomes, meaning they have half the number of chromosomes compared to somatic cells. B. Human somatic cells are either haploid or diploid chromosomes – ❌ Incorrect - Somatic cells (all body cells except sex cells) are always diploid (2n = 46), never haploid. C. Human germ cells are epithelial cells, cardiac cells, etc. – ❌ Incorrect - Germ cells refer to sex cells (sperm and egg cells) or their precursors, NOT epithelial, cardiac, or other somatic cells. D. Human somatic cells are sperm cells and egg cells. – ❌ Incorrect - Somatic cells make up the body’s tissues and organs, while sperm and egg cells are gametes (sex cells), NOT somatic cells.

Answer 55

D. Plasmin Explanation: Plasmin is NOT involved in the formation of blood clots; instead, it is responsible for breaking down blood clots in a process called fibrinolysis. Plasmin helps dissolve fibrin, preventing excessive clotting. Other options (involved in blood clot formation): A. Calcium (Ca²⁺) – Essential for activating clotting factors in the coagulation cascade. B. Fibrinogen – A plasma protein that is converted into fibrin, forming the clot’s structural framework. C. Thrombin – A key enzyme that converts fibrinogen to fibrin, essential for clot formation.

Answer 56

E. Gap junctions Explanation: Gap junctions are specialized intercellular connections that allow the direct transfer of small molecules, ions, and electrical signals between adjacent cells. They are formed by connexin proteins, which create channels called connexons. Gap junctions are especially important in cardiac and smooth muscle cells, where they enable coordinated contractions. Other options: A. Desmosomes – Provide strong adhesion between cells but do not allow molecular transfer. B. Hemidesmosomes – Anchor cells to the extracellular matrix, rather than linking two cells together. C. Adherent junctions (Adherens junctions) – Help cells stick together but do not facilitate molecular exchange. D. Tight junctions – Create a seal between cells to prevent leakage, rather than allowing molecular transfer.

Answer 57

A. Small intestine Explanation: The brush border (or striated border) consists of microvilli, which are finger-like projections of the plasma membrane that increase the surface area for absorption. These are found in cells specialized for absorption, such as the enterocytes lining the small intestine. Microvilli help in the efficient uptake of nutrients. Other options: B. Liver – Does not have a brush border; hepatocytes are involved in metabolism, detoxification, and bile production. C. Pancreas – Produces digestive enzymes and hormones but does not have a brush border. D. Lungs – Contain cilia, not microvilli, which help in clearing mucus and debris from the airways.

Answer 58

C. Urinary tract Explanation: Umbrella cells are specialized epithelial cells found in the urothelium, which lines the urinary tract, including the renal pelvis, ureters, bladder, and proximal urethra. These cells are located at the surface of the transitional epithelium and play a crucial role in protecting underlying tissues from urine and allowing the bladder to stretch and contract. Other options: A. Respiratory tract – Lined by pseudostratified ciliated columnar epithelium with goblet cells. B. Epidermis – Composed of keratinized stratified squamous epithelium, not umbrella cells. D. Esophagus – Lined by non-keratinized stratified squamous epithelium, suited for resisting friction from food passage.

Answer 59

A. Spontaneous, repeated muscular contractions Explanation: Acetylcholinesterase (AChE) is an enzyme responsible for breaking down acetylcholine (ACh) in the synaptic cleft after neurotransmission. If AChE is absent or inhibited, ACh will continue to stimulate postsynaptic receptors, leading to persistent depolarization and continuous muscle contraction (spontaneous, repeated contractions). This is similar to the effect of organophosphate poisoning (e.g., nerve gas, pesticides), which inhibits AChE and causes excessive neuromuscular activity, leading to muscle spasms and even respiratory failure. Why the other options are incorrect: B. Motor neurons will produce more acetylcholine in the axon terminals ❌ ACh production is not directly affected by AChE absence; rather, existing ACh is not broken down. C. Muscular paralysis ❌ The opposite occurs—muscles remain overstimulated, not paralyzed. Paralysis would result from ACh depletion or receptor blockade (e.g., curare poisoning). D. Inhibition of depolarization ❌ Instead of inhibition, continuous depolarization occurs due to persistent ACh activity.

Answer 60

A. Foramen cecum Explanation: The foramen cecum is a small depression located at the junction between the anterior two-thirds (body) and posterior one-third (root) of the tongue. It represents the remnant of the thyroglossal duct, which is the embryonic structure from which the thyroid gland develops. During normal development, the thyroglossal duct disappears, but if remnants persist, they can form a thyroglossal duct cyst. Other options: B. Tuberculum impar – A midline structure in early tongue development that contributes to the anterior part of the tongue but is not a remnant of the thyroglossal duct. C. Copula – Forms part of the posterior third of the tongue, arising from the second pharyngeal arch. D. Midline swelling – A general term that does not specifically refer to the thyroglossal duct remnant.

Answer 61

C. Both statements are true. Explanation: Enamel has a low water content (~4%) because it is highly mineralized (96% hydroxyapatite, 4% organic material and water). This makes it the hardest tissue in the body. Dentin has a higher water content (~20%) because it contains 70% hydroxyapatite, 20% organic material (mostly collagen), and 10% water. The higher water and organic content contribute to its flexibility compared to enamel.

Answer 62

A. Okazaki (Okazaki fragments) Explanation: During DNA replication, the lagging strand is synthesized in short, discontinuous fragments called Okazaki fragments. These fragments are later joined together by DNA ligase to form a continuous strand. Other options: B. Nucleic base – Refers to the building blocks of DNA (Adenine, Thymine, Cytosine, Guanine). C. Nucleotide – The basic unit of DNA and RNA, consisting of a sugar, phosphate, and nitrogenous base. D. Topoisomers – Related to topoisomerases, enzymes that relieve DNA supercoiling during replication, but not involved in fragment synthesis.

Answer 63

C. Junctional epithelium Explanation: During tooth eruption, the reduced enamel epithelium (REE) fuses with the oral epithelium to form the junctional epithelium. This specialized epithelium forms a seal around the tooth at the gingival margin, helping to protect the underlying structures from bacterial invasion. Other options: A. Lamina propria – The connective tissue layer beneath the epithelium, not directly related to REE fusion. B. Sulcular epithelium – Lines the gingival sulcus but does not originate from the fusion of REE and oral epithelium. D. Dental lamina – A structure in early tooth development, responsible for forming the enamel organ, but unrelated to the formation of junctional epithelium.

Answer 64

A. The fluoroapatite crystals in the enamel is less soluble than the hydroxyapatite crystals. Explanation: Fluoroapatite (formed when fluoride replaces hydroxyl groups in hydroxyapatite) is less soluble and more resistant to acid demineralization than hydroxyapatite. This is why fluoride strengthens enamel and helps prevent cavities. Why the other options are incorrect: B. It is not permeable to any kind of substance. ❌ Enamel is slightly permeable to ions and small molecules, allowing for remineralization and fluoride uptake. C. It has higher organic content than inorganic content. ❌ Enamel is 96% inorganic (hydroxyapatite), 4% water and organic material—it has very low organic content. D. The enamel tissue is capable of regenerating as long as the environment is not acidic. ❌ Enamel cannot regenerate because it has no living cells (ameloblasts disappear after tooth eruption). However, remineralization can occur with fluoride and calcium/phosphate ions.

Answer 65

B. Patients with Amelogenesis imperfecta are expected to have denser enamel tissue. ❌ (This is NOT a common feature of the disease.) Explanation: Amelogenesis imperfecta (AI) is a genetic disorder that affects enamel formation, leading to thin, weak, or defective enamel. Enamel in AI patients is actually less dense, making teeth more prone to wear, breakage, and sensitivity. Why the other options are correct: A. Patients with Amelogenesis imperfecta have yellowish teeth. ✅ Since enamel is defective or missing, the dentin (naturally yellow) becomes more visible. C. Patients with Amelogenesis imperfecta have more sensitive teeth. ✅ Thin or absent enamel exposes dentin, making teeth highly sensitive to hot, cold, and pressure. D. Patients with Amelogenesis imperfecta may produce pitted enamel. ✅ Some forms of AI cause pitted, grooved, or rough enamel surfaces, affecting aesthetics and function.

Answer 66

C. IV, V, X Explanation: The conversion of prothrombin (Factor II) to thrombin (Factor IIa) occurs in the common pathway of the coagulation cascade and requires the following factors: - Factor X (Stuart-Prower factor) → Directly converts prothrombin to thrombin when activated. - Factor V (Labile factor) → Acts as a cofactor that enhances Factor X activity. - Factor IV (Calcium, Ca²⁺) → Essential for stabilizing and activating the coagulation enzymes. Why the other options are incorrect: A. IV, V, VII ❌ → Factor VII is part of the extrinsic pathway, not the direct conversion of prothrombin to thrombin. B. V, VII, X ❌ → Factor VII is not directly involved in this step; it is part of the extrinsic pathway. D. V, VII, IX ❌ → Factor IX is part of the intrinsic pathway, not the direct conversion process.

Answer 67

A. The first statement is true and the second statement is false. Explanation: First statement: "The average pH of blood plasma is around 7.4." ✅ True - The normal pH of arterial blood is 7.35–7.45, with an average of 7.4, which is slightly alkaline. Second statement: "Generally, the venous blood is more alkaline than the arterial blood." ❌ False - Venous blood is actually more acidic than arterial blood because it contains higher levels of CO₂, which forms carbonic acid (H₂CO₃) when dissolved in water. - Venous blood typically has a pH of around 7.35, which is slightly lower (more acidic) than arterial blood. Conclusion: Arterial blood = More alkaline (pH ~7.4) Venous blood = Slightly more acidic (pH ~7.35) due to CO₂ accumulation.

Answer 68

C. Junctional epithelium Explanation: The junctional epithelium (JE) is derived from the reduced enamel epithelium (REE) after tooth eruption. It is located at the collar of the tooth, forming a seal between the gingiva and the enamel/cementum. This specialized epithelium is crucial for: - Protecting the periodontal tissues from bacterial invasion. - Allowing passage of immune cells to maintain periodontal health. Why the other options are incorrect: A. Oral epithelium ❌ – The outermost layer of the gingiva, but not directly formed from REE. B. Sulcular epithelium ❌ – Lines the gingival sulcus but does not originate from REE. D. Dental lamina ❌ – A structure involved in tooth development, not related to the junctional epithelium.

Answer 69

A. The first statement is true and the second statement is false. Explanation: - First statement: "Nervous tissue, epidermis, enamel, mammary glands, cutaneous glands, and epithelium of skull cavities and sinuses are derived from ectoderm." ✅ True The ectoderm gives rise to: - Nervous system (brain, spinal cord, peripheral nerves) - Epidermis (outer skin layer) - Enamel of teeth - Mammary and cutaneous glands - Epithelium of nasal, oral, and skull cavities - Second statement: "Muscles, connective tissues and GI tract epithelium are derived from mesoderm." ❌ False - While muscles and connective tissues are indeed derived from the mesoderm, - The GI tract epithelium actually originates from the endoderm, not the mesoderm. - The endoderm also gives rise to the epithelium of the respiratory, digestive, and urinary tracts. Conclusion: Ectoderm → Nervous tissue, epidermis, enamel, mammary glands, etc. Mesoderm → Muscles, connective tissue, bones, blood vessels, etc. Endoderm → GI tract epithelium, respiratory epithelium, liver, pancreas, etc.

Answer 70

D. Ameloblast differentiation → Odontoblast differentiation → Dentin matrix secretion → Enamel matrix secretion Explanation of Sequential Events in Tooth Development: 1. Ameloblast differentiation - Cells of the inner enamel epithelium differentiate into ameloblasts, which will later produce enamel. 2. Odontoblast differentiation - Ameloblasts induce ectomesenchymal cells of the dental papilla to differentiate into odontoblasts, which will form dentin. 3. Dentin matrix secretion - Odontoblasts begin secreting predentin, which later mineralizes into dentin. - Dentinogenesis always occurs first before enamel formation. 4. Enamel matrix secretion - Once dentin is deposited, ameloblasts begin secreting enamel matrix, which will later mineralize into mature enamel. Why the other options are incorrect: A. Ameloblast differentiation → Enamel matrix secretion → Odontoblast differentiation → Dentin matrix secretion ❌ Enamel matrix secretion does not happen before dentin formation. B. Odontoblast differentiation → Enamel matrix secretion → Ameloblast differentiation → Dentin matrix secretion ❌ Ameloblasts differentiate before odontoblasts and dentin is secreted before enamel. C. Ameloblast differentiation → Dentin matrix secretion → Enamel matrix secretion → Odontoblast differentiation ❌ Odontoblast differentiation happens before dentin matrix secretion, not after.

Answer 71

C. RAS Explanation: RAS is a proto-oncogene that plays a crucial role in promoting cell cycle progression and mitosis. It encodes a GTP-binding protein that acts as a molecular switch in signal transduction pathways, stimulating cell proliferation, differentiation, and survival. Mutations in RAS can lead to uncontrolled cell division and cancer. Why the other options are incorrect: A. p21 ❌ p21 (CDKN1A) is a cell cycle inhibitor that halts mitosis by inhibiting cyclin-dependent kinases (CDKs), preventing progression from G1 to S phase. B. BAX ❌ BAX is a pro-apoptotic gene that promotes programmed cell death (apoptosis) rather than mitosis. D. p53 ❌ p53 is a tumor suppressor gene that prevents mitosis when DNA damage is detected, activating repair mechanisms or inducing apoptosis if the damage is severe.

Answer 72

C. Polyps Explanation: - Mesenchymal tissues originate from the mesoderm and include connective tissue, bone, cartilage, fat, muscle, and blood vessels. - Tumors of mesenchymal origin are called sarcomas, while epithelial-origin tumors are carcinomas. - Polyps are not mesenchymal; they are typically epithelial in origin, arising from the mucosal lining of organs such as the colon, stomach, or nasal cavity. Why the other options are mesenchymal in origin: A. Fibrosarcoma ✅ Malignant tumor of fibrous connective tissue (mesenchymal origin). B. Chondroma ✅ Benign tumor of cartilage (mesenchymal origin). D. Liposarcoma ✅ Malignant tumor of fat tissue (adipocytes) (mesenchymal origin).

Answer 73

C. Merocrine Explanation: Merocrine glands release their secretion through exocytosis without causing any damage to the cell. The glandular cell remains intact and continues producing secretions. Why the other options are incorrect: A. Apocrine ❌ Involves partial loss of the cell's cytoplasm along with the secretion. Example: mammary glands. B. Accine ❌ This is not a recognized category of exocrine glands. Likely a misspelling or confusion with acinar glands (a structural classification). D. Holocrine ❌ The entire cell disintegrates, releasing its contents. Example: sebaceous glands.

Answer 74

A. HERS (Hertwig's Epithelial Root Sheath) Explanation: Hertwig's Epithelial Root Sheath (HERS) is a structure derived from the cervical loop of the enamel organ. It plays a crucial role in root formation by: - Determining the number of roots a tooth will develop. - Inducing odontoblast differentiation to form root dentin. - Fragmenting to allow cementoblasts from the dental sac to deposit cementum on the root surface. Why the other options are incorrect: B. Nasmyth’s membrane ❌ Also called the reduced enamel epithelium, it covers the enamel surface after eruption but has no role in root development. C. Cervical loop ❌ The cervical loop is the point where the inner and outer enamel epithelium meet, and it gives rise to HERS but does not directly determine root number. D. Dental sac ❌ The dental sac (dental follicle) gives rise to cementoblasts, periodontal ligament, and alveolar bone, but it does not determine root number.

Answer 75

D. Pregnenolone Explanation: Pregnenolone is the precursor for all steroid hormones. It is synthesized from cholesterol in the mitochondria and serves as the starting molecule for the production of: - Glucocorticoids (e.g., cortisol) - Mineralocorticoids (e.g., aldosterone) - Androgens (e.g., testosterone) - Estrogens (e.g., estradiol) - Progestogens (e.g., progesterone) Why the other options are incorrect: A. Presterone ❌ (Not a real hormone) B. Prestrogen ❌ (Not a real hormone, likely confused with Estrogen) C. Prestosterone ❌ (Not a real hormone, likely confused with Testosterone)

Answer 76

D. Thermal test Explanation: A thermal test is used to assess pulp vitality, not to detect dental caries. It evaluates whether the pulp is still alive and responsive to temperature changes, which helps in diagnosing pulpitis or necrosis. Why the other options are correct for detecting dental caries: A. Radiograph ✅ X-rays (bitewing, periapical, panoramic) help detect interproximal and occlusal caries not visible clinically. B. Fluorescence ✅ Devices like DIAGNOdent use laser fluorescence to identify early enamel demineralization. C. Transillumination ✅ A bright light is used to detect enamel cracks, interproximal caries, and early decay by shining through the tooth.