Human Histology and Organ Systems

Comprehensive practice flashcards formatted as question-and-answer pairs covering the four basic tissues, blood and hemopoiesis, the circulatory system, the integumentary system, the lymphoid system, the endocrine system, and the respiratory system.

What are the four basic tissue types found in the human body?

Epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

What are the two principal layers comprising the basement membrane, and what are their primary collagen types?

The basal lamina, containing type IV collagen (along with laminin, nidogen, and perlecan), and the reticular lamina, containing reticular fibers composed primarily of type III collagen.

Which major intercellular junction functions as a selective barrier by sealing adjacent epithelial cells and limiting paracellular movement?

Tight junction (zonula occludens).

How do adherens junctions, desmosomes, and hemidesmosomes differ in their anchoring roles?

Adherens junctions and desmosomes provide mechanical attachment between adjacent cells, whereas hemidesmosomes anchor the basal surface of epithelial cells to the underlying basal lamina.

What specialized terms describe the simple squamous epithelium lining blood and lymphatic vessels versus the simple squamous epithelium lining serous body cavities?

Endothelium lines blood and lymphatic vessels, whereas mesothelium lines serous body cavities and covers the organs within them.

What is the structural organization of the axoneme in typical motile cilia, and which motor protein drives its bending?

A $9 + 2$ axonemal arrangement (nine peripheral microtubule doublets and two central microtubules), driven by the ATP-hydrolyzing motor protein dynein.

How do stereocilia differ structurally from true motile cilia?

Stereocilia contain a cytoskeletal core of actin filaments and lack the microtubule-based axoneme found in true motile cilia; thus, they are nonmotile and structurally related to microvilli.

Why is pseudostratified columnar epithelium classified as a simple epithelium despite appearing multilayered?

All cells are in direct contact with the basement membrane, even though their nuclei lie at different levels and not all cells extend to the apical surface.

How do keratinized and non-keratinized stratified squamous epithelia differ histologically at their superficial surface?

Keratinized stratified squamous epithelium has anucleate, nonviable superficial cells filled with keratin, whereas non-keratinized stratified squamous epithelium retains viable, nucleated superficial cells and lacks a thick keratin layer.

What are umbrella cells and what is their functional significance in transitional epithelium (urothelium)?

Large, dome-shaped superficial cells that flatten upon distension and form a specialized permeability barrier protecting underlying tissues from urine.

How do merocrine, apocrine, and holocrine exocrine secretion mechanisms differ regarding cellular material loss?

Merocrine releases products via exocytosis without cell loss; apocrine releases the product along with a portion of the apical cytoplasm and membrane; holocrine involves the complete disintegration of the secretory cell.

How do serous cells and mucous cells differ in their cytoplasmic staining and nuclear morphology on routine H&E sections?

Serous cells have basophilic basal cytoplasm (rich in rough endoplasmic reticulum), protein-rich apical granules, and round central/basal nuclei; mucous cells display pale, foamy cytoplasm and flattened, basally displaced nuclei.

What type of cell is shown in this brown immunostained preparation embracing an acinus, and what is its role?

A myoepithelial cell; it contains actin and myosin and contracts to compress the acinus, expelling secretory products into the duct system.

What are the four most prominent collagen types and their primary distributions in connective tissues?

Type I: tendons, ligaments, dermis, bone, and fibrocartilage; Type II: hyaline and elastic cartilage; Type III: reticular fibers in lymphoid organs, bone marrow, and liver; Type IV: basal lamina of basement membranes.

What biologically active substances are stored in the prominent cytoplasmic granules of mast cells?

Histamine, heparin, and other inflammatory mediators that regulate vascular permeability and vasodilation.

What characteristic histological appearance identifies a plasma cell on routine microscopic examination?

An eccentric nucleus with coarse, clumped chromatin in a peripheral pattern, abundant basophilic cytoplasm, and a pale perinuclear area corresponding to the Golgi apparatus.

How do white adipose tissue and brown adipose tissue differ in adipocyte morphology and primary function?

White adipocytes are unilocular (single large lipid droplet, peripheral compressed nucleus) specialized for energy storage, insulation, and endocrine signaling; brown adipocytes are multilocular (multiple small droplets, central nucleus, abundant mitochondria with UCP1) specialized for thermogenesis.

Where is mucoid connective tissue (Wharton's jelly) typically found, and what characterizes its matrix?

In the fetal umbilical cord; it is characterized by abundant gelatinous ground substance rich in hyaluronan, sparse collagen fibers, and relatively few fibroblasts.

Why does cartilage have a very limited capacity for repair compared to other connective tissues?

Cartilage is avascular, lacking internal blood vessels, lymphatic vessels, and nerves; nutrients and repair factors must diffuse slowly through the dense extracellular matrix.

What is the defining structural difference among hyaline cartilage, elastic cartilage, and fibrocartilage?

Hyaline cartilage has a glassy, homogeneous matrix of fine type II collagen; elastic cartilage contains a dense branching network of elastic fibers; fibrocartilage contains prominent, thick parallel bundles of type I collagen with rows of chondrocytes and lacks a perichondrium.

What histological structures are shown in this compact bone micrograph?

Osteons (Haversian systems) featuring central canals, concentric lamellae, lacunae containing osteocytes, and radiating canaliculi.

What are the five functional zones of the epiphyseal growth plate listed from the epiphyseal toward the diaphyseal side?

1. Resting (reserve) zone; 2. Proliferation zone; 3. Hypertrophy zone; 4. Calcification zone; 5. Ossification zone.

What three structural components constitute a skeletal muscle triad?

One central transverse tubule (T-tubule) associated with two adjacent terminal cisternae of the sarcoplasmic reticulum.

In this longitudinal muscle section, what feature is indicated by arrow A, and what tissue type is present?

Arrow A indicates an intercalated disc; the tissue is cardiac muscle (characterized by branched fibers, cross-striations, and centrally located nuclei indicated by B).

Which major glial cells of the central nervous system form myelin sheaths around axons?

Oligodendrocytes.

What specialized central nervous system cell is depicted in this silver-stained specimen?

A microglial cell, showing its characteristic small soma, multiple branching processes, and role as the resident immune/phagocytic cell of the CNS.

What are the three connective tissue coverings of a peripheral nerve, from innermost to outermost?

Endoneurium (surrounds individual nerve fibers), perineurium (surrounds a nerve fascicle), and epineurium (surrounds the entire peripheral nerve).

What is the typical lifespan and average diameter of a mature human erythrocyte in circulation?

Lifespan of approximately $120\text{ days}$ and an average diameter of approximately $7\text{--}8\,\mu\text{m}$ (or $7.5\,\mu\text{m}$).

What are the five types of circulating leukocytes and their approximate normal percentages?

Neutrophils ($50\text{--}70\%$), lymphocytes ($20\text{--}40\%$), monocytes ($2\text{--}8\%$), eosinophils ($1\text{--}4\%$), and basophils ($0.5\text{--}1\%$).

What leukocyte is demonstrated in this high-magnification blood film, characterized by coarse dark granules obscuring the nucleus?

A basophil.

What are the three successive stages of intrauterine hematopoiesis?

1. Yolk sac period; 2. Hepatic period (with splenic contribution); 3. Bone-marrow period.

What two types of arteries are compared here in sections (a) and (b)?

An elastic artery (a), containing numerous concentric fenestrated elastic lamellae in a very thick tunica media, and a muscular artery (b), featuring a prominent scalloped internal elastic lamina and circularly arranged smooth muscle in the tunica media.

What are the vasa vasorum and which layers of large blood vessel walls do they supply?

Small blood vessels ('vessels of the vessels') located in the tunica adventitia and the outer portion of the tunica media to supply oxygen and nutrients to thick vessel walls.

What are the three principal types of capillaries and their distinguishing structural features?

Continuous capillaries (intact endothelial lining and continuous basement membrane), fenestrated capillaries (endothelial pores/fenestrations with continuous basement membrane), and sinusoidal/discontinuous capillaries (large endothelial gaps and a discontinuous or absent basement membrane).

What histological characteristics distinguish cardiac Purkinje fibers from neighboring contractile myocytes under light microscopy?

Purkinje fibers are significantly larger in diameter, stain more palely, contain abundant glycogen, and have sparse myofibrils restricted strictly to the cytoplasm periphery.

What are the five histological layers of the epidermis in thick skin, ordered from deep to superficial?

1. Stratum basale; 2. Stratum spinosum; 3. Stratum granulosum; 4. Stratum lucidum; 5. Stratum corneum.

What are Langerhans cells and where are they primarily located within the epidermis?

Dendritic antigen-presenting cells that capture and process foreign antigens; they are located predominantly in the stratum spinosum.

What encapsulated sensory receptor is shown here located within a dermal papilla?

A tactile (Meissner's) corpuscle, specialized for detecting light touch and low-frequency vibration.

What is the complete sequence of lymph flow through a lymph node?

Afferent lymphatic vessels $\rightarrow$ subcapsular sinus $\rightarrow$ cortical (trabecular) sinuses $\rightarrow$ medullary sinuses $\rightarrow$ efferent lymphatic vessel at the hilum.

What are Hassall corpuscles, and in which specific lymphoid organ and zone are they found?

Distinct concentric whorls of epithelial reticular cells (which may show central keratinization); they are located exclusively in the medulla of the thymus.

How do the white pulp and red pulp of the spleen differ functionally and histologically?

White pulp consists of lymphoid tissue (periarteriolar lymphoid sheaths rich in T cells surrounding central arterioles, and lymphoid nodules rich in B cells) for immune responses; red pulp consists of splenic cords (of Billroth) and sinusoids that filter blood and remove damaged erythrocytes.

What five major subdivisions of the pituitary gland are labeled in this overview section?

Adenohypophysis: pars distalis (PD), pars tuberalis (PT), and pars intermedia (PI); Neurohypophysis: pars nervosa (PN) and infundibular stalk (IS).

What are the three concentric zones of the adrenal cortex and what major class of hormones does each produce?

Zona glomerulosa produces mineralocorticoids (aldosterone); zona fasciculata produces glucocorticoids (cortisol); zona reticularis produces weak androgens (DHEA).

What are the four primary endocrine cell types of the pancreatic islets and their major hormones?

$\beta$ cells (insulin), $\alpha$ cells (glucagon), $\delta$ cells (somatostatin), and PP cells (pancreatic polypeptide).

What calcified concretions (labeled CA) are visible in this pineal gland specimen, and what is their clinical utility?

Corpora arenacea (brain sand); they increase in number and size with age and serve as useful radio-opaque anatomical landmarks in cranial radiological imaging.

Which two cell types constitute the parenchyma of the thyroid gland, and what are their respective secretory products?

Follicular cells (thyrocytes), which synthesize and secrete $T_3$ and $T_4$, and parafollicular (C) cells, which produce calcitonin.

What are the labeled histological layers of the tracheal wall shown in this micrograph?

Respiratory epithelium (RE), lamina propria (LP), seromucous glands (G) in the submucosa, and hyaline cartilage ring (C) surrounded by perichondrium (P).

What characteristic structural features identify this intrapulmonary airway as a bronchus?

Folded respiratory mucosa, a layer of smooth muscle (SM), supporting hyaline cartilage plates (C), and submucosal seromucous glands (G).

What defining histological criteria distinguish bronchioles from bronchi in lung sections?

Bronchioles completely lack supporting cartilage and submucosal glands, possess a prominent layer of smooth muscle in their walls, and are lined by simpler ciliated or cuboidal epithelium containing club cells.

What are the major physiological functions of club cells in bronchioles?

Secreting airway-protective surfactant-like components, detoxifying inhaled harmful substances, producing antimicrobial molecules, and acting as progenitor cells for bronchiolar epithelial renewal.

How do type I and type II alveolar cells (pneumocytes) differ in structure and primary function?

Type I pneumocytes are extremely thin squamous cells that cover most of the alveolar surface and facilitate gas diffusion; type II pneumocytes are cuboidal cells containing lamellar bodies that synthesize and secrete pulmonary surfactant and serve as stem cells for epithelial repair.

What are the three essential anatomical layers of the blood-air barrier (respiratory membrane)?

1. Thin cytoplasm of the type I alveolar cell; 2. Fused basal laminae of the alveolar epithelium and capillary endothelium; 3. Thin cytoplasm of the pulmonary capillary endothelial cell.