College Histology Comprehensive Review: Nervous, Muscle, Blood, Integument, Endocrine, and Special Senses

A collection of 100 comprehensive vocabulary flashcards covering human histology based on Junqueira's Basic Histology (15th ed.), including Nervous Tissue, Muscle Tissue, Blood, Integumentary System, Endocrine Glands, and Special Senses (Eye and Ear).

Neural tube

Epithelial tubular structure derived from folded embryonic surface ectoderm that gives rise to the entire central nervous system (CNS).

Neural crest cells

Ectodermal cells that detach during neural tube formation and migrate to give rise to most peripheral nervous system (PNS) structures, including sensory and autonomic ganglia and Schwann cells.

Soma (Perikaryon)

The cell body and synthetic center of a neuron, characterized by a large euchromatic nucleus, prominent nucleolus, and abundant Nissl substance.

Nissl substance

Aggregations of rough endoplasmic reticulum and polyribosomes in neuronal soma and dendrites; highly basophilic due to RNA and absent from the axon and axon hillock.

Axon hillock

The pale, cone-shaped junctional region of the neuronal cell body that lacks Nissl substance and marks the transition to the initial segment where action potentials originate.

Multipolar neuron

The most common structural type of neuron, possessing a single axon and two or more branching dendrites, typical of motor neurons and CNS interneurons.

Bipolar neuron

A neuron with a single dendrite and a single axon extending from opposite ends of the soma, found in the retina, olfactory epithelium, and inner ear.

Pseudounipolar neuron

A sensory neuron with a single process that leaves the soma and divides into a peripheral branch and a central branch, typical of primary sensory ganglia.

Node of Ranvier

A microscopic gap between adjacent myelin sheath segments along an axon where the axolemma is exposed and depolarization is regenerated during saltatory conduction.

Oligodendrocyte

The myelin-forming glial cell of the central nervous system; a single cell can wrap and insulate axonal segments belonging to multiple neighboring neurons.

Schwann cell (Neurolemmocyte)

The supporting glial cell of the peripheral nervous system that wraps around an individual segment of a single axon to form myelin and an outer neurilemma.

Astrocyte

A star-shaped CNS neuroglial cell that provides structural and metabolic support, regulates ion and neurotransmitter concentrations, contributes to the blood–brain barrier, and forms glial scars.

Ependymal cell

Ciliated or microvillous epithelial-like cell lining the cerebral ventricles and the central canal of the spinal cord, assisting in the movement and production of cerebrospinal fluid (CSF).

Microglia

Resident mononuclear phagocytic immune cells of the CNS that become active to clear cellular debris and mediate responses to damage or infection.

Satellite cells (PNS ganglia)

Small glial cells forming a complete cellular ring around the cell bodies of pseudounipolar sensory neurons in peripheral sensory ganglia.

Purkinje cells

Large, conspicuous, flask-shaped neurons arranged in a single layer between the molecular and granular layers of the cerebellar cortex.

Blood–brain barrier (BBB)

A selective physiological barrier established by occluding tight junctions between CNS capillary endothelial cells, reinforced by a basal lamina and perivascular astrocyte end-feet.

Choroid plexus

Vascular folds of pia mater covered by modified simple cuboidal ependymal cells that project into ventricles to synthesize and secrete cerebrospinal fluid.

Endoneurium

A delicate layer of loose connective tissue directly surrounding a single myelinated or unmyelinated peripheral nerve fiber.

Perineurium

A sheath of concentric layers of flattened epithelioid fibroblastic cells surrounding each nerve fascicle, contributing to the blood–nerve barrier.

Epineurium

The thick, dense irregular connective tissue outer sheath enclosing an entire peripheral nerve trunk and binding its fascicles together.

Wallerian degeneration

The anterograde structural breakdown and fragmentation of an axon segment and its myelin distal to the site of peripheral nerve transection.

Epimysium

The dense connective tissue sheath that encloses an entire skeletal muscle organ.

Perimysium

The connective tissue septum that groups skeletal muscle fibers into bundles termed fascicles and transmits larger vessels and nerves.

Endomysium

The delicate connective tissue layer of reticular fibers and basal lamina surrounding each individual skeletal muscle fiber.

Sarcomere

The repeating contractile unit of striated myofibrils extending longitudinally from one Z disc to the consecutive Z disc.

A band

The dark, anisotropic band in a sarcomere representing the full length of thick myosin filaments; its width remains unaltered during muscle contraction.

I band

The light, isotropic band of a sarcomere composed of thin actin filaments not overlapping thick filaments; shortens during muscle contraction.

H zone

The pale central region within the A band containing only thick filaments without overlapping thin filaments; narrows or disappears during contraction.

M line

A transverse protein line at the center of the sarcomere H zone that anchors and cross-links adjacent thick filaments.

Titin

A massive elastic protein anchoring thick myosin filaments to the Z disc, centering filaments within the sarcomere and contributing to passive muscle tension.

Troponin C

The calcium-binding subunit of the troponin complex on thin filaments that triggers conformational movement of tropomyosin away from actin binding sites.

Triad

The functional coupling unit in skeletal muscle comprising one central transverse (T) tubule invagination flanked on both sides by terminal cisternae of the sarcoplasmic reticulum.

Motor unit

A single alpha somatic motor neuron together with all the individual skeletal muscle fibers it branches to innervate.

Type I muscle fibers

Slow oxidative skeletal muscle fibers rich in mitochondria, myoglobin, and capillaries, specialized for sustained, fatigue-resistant contractions such as posture.

Intercalated disc

A step-like junctional complex between adjacent cardiac myocytes containing fascia adherens, desmosomes, and gap junctions for electrical and mechanical coupling.

Dyad

The junctional arrangement characteristic of cardiac muscle consisting of one T-tubule associated with a single expanded terminal cisterna of the sarcoplasmic reticulum.

Dense bodies

Intracytoplasmic and membrane-associated protein structures containing $\alpha$-actinin in smooth muscle cells that anchor thin actin filaments.

Calmodulin

The intracellular calcium-binding regulatory protein in smooth muscle that complexes with $Ca^{2+}$ to activate myosin light-chain kinase (MLCK).

Caveolae

Small, pinocytotic-like invaginations of the smooth muscle sarcolemma involved in calcium ion sequestration and signaling, functional analogs to T-tubules.

Satellite cells (Skeletal muscle)

Mononucleated myogenic stem cells located between the sarcolemma and the external lamina of muscle fibers capable of limited division and repair after injury.

Muscle spindle

A stretch receptor proprioceptor encapsulated within skeletal muscle containing intrafusal fibers that monitors changes in muscle length.

Golgi tendon organ

An encapsulated proprioceptor situated at the myotendinous junction that senses tension generated across the tendon during contraction.

Albumin

The most abundant plasma protein, synthesized in the liver; acts as a major non-specific carrier and the chief determinant of plasma colloid osmotic pressure.

Serum

The pale straw-colored fluid that remains after whole blood has undergone coagulation, lacking fibrinogen and certain consumed clotting factors.

Spectrin

A flexible fibrous protein forming the submembranous cytoskeletal lattice of erythrocytes that maintains biconcave shape and cellular deformability.

Reticulocyte

An immature, non-nucleated circulating erythrocyte that retains residual ribosomal RNA, identifiable via vital or supravital staining techniques.

Neutrophil

The most numerous circulating leukocyte, featuring a 3- to 5-lobed nucleus and neutral specific granules; acts as a first responder in acute bacterial inflammation.

Eosinophil

A granulocyte characterized by a typically bilobed nucleus and large, refractive, orange-red granules that combat helminthic parasites and modulate allergic responses.

Basophil

The rarest granulocyte, recognized by coarse, metachromatic, dark blue-purple granules containing histamine and heparin that frequently obscure the nucleus.

Monocyte

The largest leukocyte in a peripheral blood smear, featuring an indented, kidney-shaped nucleus and agranular gray-blue cytoplasm; differentiates into tissue macrophages.

Megakaryocyte

A gigantic, polyploid bone marrow hemopoietic cell with a lobulated nucleus that produces blood platelets via cytoplasmic fragmentation.

Hyalomere

The pale-blue, transparent, peripheral zone of a blood platelet containing cytoskeletal elements.

Granulomere

The central, darker-staining, granule-containing portion of a thrombocyte visible on a stained blood film.

Hematocrit

The volume percentage of packed red blood cells within an entire centrifuged sample of whole blood.

Stratum basale

The single deepest germinative layer of cuboidal to low columnar keratinocytes resting on the basement membrane, characterized by intense mitotic activity.

Stratum spinosum

Epidermal layer consisting of polygonal keratinocytes displaying abundant desmosomal junctions and tonofilament bundles that appear as spines during histological preparation.

Stratum granulosum

A 3- to 5-cell thick epidermal layer characterized by flattened cells filled with basophilic keratohyalin granules and lamellar bodies releasing barrier lipids.

Stratum lucidum

A clear, thin, eosinophilic, translucent layer of flattened, anucleate, dying keratinocytes found exclusively in thick skin of the palms and soles.

Stratum corneum

The outermost stratum of the epidermis consisting of multiple layers of flattened, dead, cornified, anucleate squames packed with mature keratin filaments.

Melanocyte

A pale-staining dendritic cell of the stratum basale derived from the neural crest that synthesizes melanin and transfers melanosomes to adjacent keratinocytes.

Langerhans cell

A dendritic, bone marrow-derived antigen-presenting cell situated primarily within the stratum spinosum of the epidermis.

Merkel cell

A modified epidermal tactile epithelial cell located in the stratum basale, complexed with an unmyelinated sensory nerve terminal for high-acuity light touch.

Papillary dermis

The thin, superficial subepidermal layer of dermis consisting of loose areolar connective tissue, capillary loops, and dermal papillae that interlock with rete ridges.

Reticular dermis

The thick, deep dermal layer composed of dense irregular connective tissue with prominent coarse collagen bundles and elastic networks.

Meissner corpuscle

An encapsulated, elongated mechanoreceptor situated within the dermal papillae of hairless (glabrous) skin that transduces light touch and low-frequency vibrations.

Pacinian corpuscle

A large, encapsulated sensory ending found deep in the dermis and hypodermis, featuring concentric cellular lamellae resembling a sliced onion that detects pressure and rapid vibration.

Arrector pili

A bundle of visceral smooth muscle attaching the connective tissue sheath of a hair follicle to the papillary dermis; contracts to elevate hair shafts.

Sebaceous gland

A branched holocrine acinar gland usually associated with hair follicles that discharges an oily lipid mixture (sebum) formed by the breakdown of whole secretory cells.

Eccrine sweat gland

A widely distributed, simple coiled tubular merocrine gland that discharges a watery hypotonic fluid directly onto the skin surface for evaporative cooling.

Apocrine sweat gland

A sweat gland characterized by a large, wide lumen that opens into hair follicles in the axillae and perineum, yielding a viscous secretion that develops odor upon bacterial decomposition.

Adenohypophysis

The anterior lobe of the pituitary gland originating from oral ectoderm (Rathke pouch), comprising glandular epithelial cells regulated by hypothalamic factors.

Neurohypophysis

The posterior lobe of the pituitary gland originating as a neural down-growth from the hypothalamus, consisting of unmyelinated axons, Herring bodies, and pituicytes.

Herring bodies

Focal, neurosecretory axonal swellings in the pars nervosa that store and release vasopressin (ADH) and oxytocin into neighboring fenestrated capillaries.

Pituicyte

A specialized supporting glial cell distributed through the pars nervosa of the posterior pituitary gland.

Somatotroph

An acidophilic parenchymal cell of the anterior pituitary pars distalis that synthesizes and secretes growth hormone (somatotropin).

Zona glomerulosa

The outermost, narrow zone of the adrenal cortex directly deep to the capsule, organized in arched clusters that secrete mineralocorticoids (primarily aldosterone).

Zona fasciculata

The middle, thickest layer of the adrenal cortex containing straight parallel cords of lipid-rich, foamy spongiocytes that secrete glucocorticoids such as cortisol.

Zona reticularis

The innermost layer of the adrenal cortex composed of small, dark, anastomosing cell cords producing weak androgens such as dehydroepiandrosterone (DHEA).

Chromaffin cells

Modified sympathetic postganglionic neuroendocrine cells in the adrenal medulla that store catecholamines (epinephrine and norepinephrine) in electron-dense granules.

Islets of Langerhans

Pale-staining, rounded clusters of microvascularized endocrine cells interspersed throughout the exocrine acinar tissue of the pancreas.

Beta (β) cells

The predominant cell type situated centrally within pancreatic islets that synthesizes and secretes insulin to lower blood glucose.

Alpha (α) cells

Pancreatic islet cells located typically at the periphery that secrete glucagon to promote hepatic glycogenolysis and gluconeogenesis.

Thyroid follicles

Spherical structural and functional units of the thyroid gland lined by simple cuboidal follicular cells enclosing an internal lumen filled with colloid.

Thyroglobulin

The large iodinated glycoprotein stored within the follicular lumen of the thyroid gland, serving as the inactive precursor pool for $T_3$ and $T_4$.

Parafollicular (C) cells

Pale-staining endocrine cells located in or between thyroid follicular walls that secrete calcitonin to suppress osteoclastic bone resorption.

Chief cells (Parathyroid)

Small, polygonal principal secretory cells of the parathyroid gland with pale cytoplasm that produce parathyroid hormone (PTH) to elevate serum $Ca^{2+}$.

Oxyphil cells

Large, strongly eosinophilic, polyhedral cells of the parathyroid gland packed with abnormal mitochondria that appear at puberty and accumulate with age.

Corpora arenacea (Brain sand)

Concentric, basophilic, calcified mineral concretions of calcium and magnesium salts in the pineal gland that serve as recognizable histologic landmarks.

Diffuse neuroendocrine system (DNES)

Individual, scattered endocrine and paracrine cells located throughout the mucosal linings of the digestive and respiratory systems that secrete peptide hormones or biogenic amines.

Cornea

The transparent, avascular, anterior fifth of the ocular fibrous tunic consisting of a nonkeratinized stratified squamous epithelium, regular dense stroma, and posterior endothelium.

Ciliary processes

Radial vascular ridges extending from the ciliary body covered by a double layer of columnar epithelium that produce aqueous humor.

Lens accommodation

The ocular focusing mechanism whereby ciliary muscle contraction slackens zonular fibers, allowing the elastic lens to thicken and round for near vision.

Retinal pigment epithelium (RPE)

The melanin-rich outer monolayer of the retina that absorbs stray light, participates in the visual cycle, and phagocytoses shed photoreceptor outer segments.

Rods

Slender, highly photosensitive retinal photoreceptors specialized for monochromatic, low-light (scotopic) vision, distributed widely outside the fovea.

Cones

Retinal photoreceptors operating in bright light (photopic vision) that mediate high-resolution visual acuity and color discrimination, concentrated in the fovea centralis.

Fovea centralis

A tiny depression in the center of the macula lutea composed entirely of slender, densely packed cone photoreceptors with displaced inner retinal layers for maximum visual acuity.

Optic disc

The unmyelinated point of convergence of retinal ganglion cell axons exiting the eye as the optic nerve; lacks photoreceptors and constitutes the physiologic blind spot.

Müller cells

Large, radial, glial supporting cells that extend across nearly the entire thickness of the neural retina, organizing its architectural scaffolding.

Organ of Corti

The auditory sensory epithelium situated upon the basilar membrane within the cochlear duct, comprising sensory hair cells, supporting cells, and an overlying tectorial membrane.