Histology Practice Questions with Answers: 50 Questions for Exam Preparation

During cleavage, mitotic divisions occur without cell growth phases; therefore, the resulting blastomeres become smaller with each division while the overall volume of the embryo remains constant.

The albumen layer (tertiary egg envelope) contains a large reserve of water necessary for embryo development, as well as the enzyme lysozyme, which exhibits strong antibacterial activity.

The second meiotic division is completed only after a sperm penetrates the oocyte, resulting in the formation of a mature ovum whose nucleus becomes the haploid female pronucleus. The second polar body is also extruded in the process.

Due to the evolution of intrauterine development and placental nutrition, mammalian eggs have secondarily lost yolk reserves, becoming secondary oligolecithal and isolecithal.

During ovulation, the follicle ruptures and a secondary oocyte, arrested at metaphase of the second meiotic division, is released into the peritoneal cavity.

Yolk granules are intracellular inclusions bounded by a single lipoprotein membrane and containing nutrient reserves.

During embryogenesis, the intraembryonic coelom is divided by partitions into three types of serous cavities: the pericardial, two pleural, and the peritoneal cavity.

During the cleavage period, the embryo is located inside the zona pellucida and does not increase in size, while its nutrition is provided primarily by yolk inclusions accumulated in the cytoplasm of the ovum.

Specific DNA methylation of genomic imprinting genes occurs de novo during gametogenesis separately in the male and female germlines.

The pronephros in the human embryo is a vestigial organ that forms in the third week of embryogenesis and completely regresses by the end of the fourth week.

Indifferent dyes (e.g., Sudan III) do not form ionic bonds with tissue structures, but physically dissolve in lipids due to their hydrophobic and lipophilic nature.

To visualize structures in electron microscopy, heavy metal salts (osmium, lead, uranium) are used; they scatter the electron beam and create electron-dense areas, a process known as contrasting.

For rapid and uniform fixation of the material (e.g., with glutaraldehyde and osmium tetroxide), tissue pieces must be very small, usually not exceeding 1 mm³ in size.

To saturate the tissue with water after paraffin removal, alcohols with progressively decreasing concentrations are used, which prevents drastic structural deformation.

For the gentle removal of water without severe deformation and shrinkage of structures, tissue pieces are sequentially passed through ethanol solutions with gradually increasing concentrations.

Hyaline cartilage forms the articular surfaces of most bones, the cartilages of the respiratory tract, rib cartilages, and constitutes the basis of the embryonic skeleton, making it the most widespread type of cartilage tissue in the body.

The metaphyseal (epiphyseal) cartilage plate consists of hyaline cartilage and ensures longitudinal growth of tubular bones due to continuous chondrocyte proliferation.

During bone tissue remodeling, old osteons are partially degraded by osteoclasts, and their surviving fragments lie between new osteons as interstitial lamellae.

Negatively charged glycosaminoglycans within proteoglycans attract sodium ions and water, generating high hydrostatic pressure (turgor) that resists cartilage compression.

In direct osteogenesis, primary bone trabeculae consist of immature woven-bone tissue, which is remodeled into lamellar bone only at subsequent stages.

In non-synaptic transmission (volume neurotransmission), the neurotransmitter is released from axonal varicosities directly into the wide intercellular space, diffusing to receptors on multiple target cells.

Silver salts are reduced on nervous tissue structures, staining nerve fibers and terminals within the encapsulated corpuscle a deep black color (argyrophilia).

In the neuromuscular junction area, muscle fiber nuclei accumulate (forming the synaptic sole), and the axon terminal is externally covered by lemmocytes (Schwann cells).

Acetylcholinesterase is localized in the synaptic cleft on the postsynaptic membrane and hydrolyzes the neurotransmitter acetylcholine into choline and an acetic acid residue.

Non-synaptic (volume) interneuronal transmission is based on the diffuse action of neuromodulators in the extracellular environment and provides tonic regulation of nerve cell excitability.

Properly speaking, the vascular tunic of the eye is formed by loose fibrous connective tissue, which contains a large number of blood vessels and pigment cells (melanocytes).

The cerebral cortex is the material substrate of consciousness; therefore, nerve impulses from receptors that lack cortical representation (e.g., many interoceptors) do not elicit conscious sensations.

Lens fibers are formed continuously throughout life: primary fibers form the embryonic nucleus, secondary fibers form the fetal nucleus, and fibers of the third (postnatal) generation, formed in the equator region, layer on the outside and constitute the lens cortex.

The ciliary body forms characteristic folds—ciliary processes covered by a bilayered epithelium—whereas the sclera is a dense irregular connective tissue without outgrowths.

The spaces of the iridocorneal angle and the scleral venous sinus participate in the outflow of aqueous humor from the anterior chamber of the eye into the venous system, which is why they are lined with endothelium.

The myoepicardial plate, which is a derivative of the visceral layer of the splanchnotome, differentiates during embryogenesis into cardiac muscle tissue (myocardium) and the outer serous membrane (epicardium).

The internal tunic (intima) of the veins of the extremities, which belong to veins with moderately developed muscular elements, forms folds—venous valves—that prevent the backflow of blood.

The lymphangion is the structural and functional unit of a lymphatic vessel, and its active contraction is ensured by smooth myocytes that are maximally concentrated in the area of the muscular cuff.

Venous valves are folds of the internal tunic (intima), the core of which is formed by connective tissue covered with endothelium.

To propel lymph against the force of gravity (e.g., in the vessels of the lower extremities), active contraction of the wall is required, which is provided by a powerful layer of smooth myocytes in the middle tunic.

The apical processes of odontoblasts (Tomes' fibers) penetrate into the dentinal tubules and extend radially through the entire thickness of the dentin up to the amelodentinal junction.

Tooth enamel consists of 96–97% mineral salts, so it is completely destroyed during standard decalcification; thin unstained ground sections are prepared for its study.

Upon completion of amelogenesis, the outer enamel epithelium and enamel pulp cells regress and fuse, forming a cuticle (Nasmyth's membrane) on the surface of the tooth crown that protects the enamel prior to eruption.

Ameloblasts secrete specific proteins (amelogenins and enamelins) that form the organic matrix of tooth enamel followed by its mineralization.

In the upper third of the esophagus, the muscular layer is formed exclusively by striated muscle tissue; in the lower third, exclusively by smooth muscle tissue; whereas in the middle third, a gradual transition occurs and both types of muscle tissue are present.

The lamina propria of the mucous membrane in all hollow organs, including the respiratory organs, is formed by loose fibrous connective tissue, which provides nutrition to the epithelium and immune defense.

The lung parenchyma is functionally and morphologically divided into the air-conducting region, represented by the intrapulmonary bronchial tree, and the respiratory region, whose structural and functional unit is the acinus.

The perichondrium consists of an outer fibrous layer and an inner cellular layer. The inner layer contains chondroblasts and prechondroblasts, which ensure appositional growth of cartilage.

The inner surface of medium-sized bronchi has a pronounced folded relief due to the well-developed muscularis mucosae, which contracts during histological preparation.

The core of the true vocal fold is formed by the vocalis muscle, consisting of striated skeletal muscle tissue, voluntary contractions of which regulate ligament tension.

Prostatic concretions (corpora amylacea) are formed from condensed glandular secretion and desquamated epithelial cells, and with age, they can undergo calcification due to the deposition of calcium phosphate.

Sustentocytes (Sertoli cells) secrete the hormone inhibin, which suppresses the secretion of follicle-stimulating hormone (FSH) by the anterior pituitary via a negative feedback mechanism.

The ejaculatory duct (ductus ejaculatorius) is formed by the fusion of the excretory duct of the seminal vesicle and the ampulla of the ductus deferens, after which it penetrates the prostate gland and opens into the urethra.

The acrosome is a modified secretory vesicle formed from the elements of the Golgi complex during spermiogenesis. It contains hydrolytic enzymes necessary for dissolving the egg membranes during fertilization.

In prophase II of meiosis, fragmentation and breakdown of the nuclear envelope (karyolemma), disappearance of the nucleolus, and formation of the mitotic spindle take place.