Cytology and Histology (ISK 101) Lecture Notes

Comprehensive review flashcards covering cytology and histology concepts, including cell organelles, membrane transport, nuclear ultrastructure, cytoskeleton, and cytoplasmic inclusions.

How is the science of histology defined?

Histology is the science that studies the microscopical structure of normal body components (cells, tissues, and organs) of humans, animals, and plants, and correlates these structures with their physiological functions.

How do light microscopy (LM) and electron microscopy (EM) compare in magnification and image appearance?

Light microscopy (LM) magnifies up to $1500\times$ and yields colored images, whereas electron microscopy (EM) achieves magnifications between $1000\times$ and $100,000\times$ and produces black-and-white images.

What are the staining properties of Hematoxylin and Eosin (H&E)?

Hematoxylin is a basic, blue dye that stains acidic structures (basophilic, such as nuclei). Eosin is an acidic, red dye that stains basic cellular structures (acidophilic, such as cytoplasm in certain cells).

What is the biological definition and typical size range of a cell?

A cell is the structural and functional unit of living tissues, typically measuring between $4\,\mu m$ and $150\,\mu m$ in diameter.

Which human blood components normally lack a nucleus?

Mature red blood cells (RBCs) and platelets.

How do active and inactive nuclei appear under light microscopy (LM)?

An active nucleus is pale-staining with a prominent nucleolus (vesicular nucleus, as seen in nerve and liver cells). An inactive nucleus is dark-staining and condensed (condensed nucleus, as seen in small lymphocytes).

What four nuclear components are identified by labels 1, 2, 3, and 4 in this diagram?

1: Nuclear membrane (nuclear envelope) 2: Nucleolus 3: Chromatin 4: Nuclear sap (nucleoplasm)

What are the structural features of the outer and inner nuclear membranes under electron microscopy?

The outer nuclear membrane is granular due to attached ribosomes and is continuous with the cisternae of the rough endoplasmic reticulum (rER). The inner nuclear membrane is fibrillar due to chromatin contact and is stabilized by the nuclear lamina, composed mainly of lamins.

What is the primary function of nuclear pores in the nuclear envelope?

Nuclear pores permit and regulate the transport of proteins and ribosomal subunits between the nucleus and the cytoplasm.

How do euchromatin and heterochromatin differ regarding conformation, transcriptional activity, and EM appearance?

Euchromatin represents uncoiled (extended) chromatin containing active genes in active cells; it appears electron-lucent on EM and pale basophilic on LM. Heterochromatin represents coiled, condensed chromatin containing inactive genes in inactive cells; it appears electron-dense on EM and deeply basophilic on LM.

Which three topographical sites of heterochromatin are indicated by labels 1, 2, and 3 in this nuclear diagram?

1: Peripheral chromatin (attached to the inner nuclear membrane) 2: Chromatin islands (masses within the nuclear sap) 3: Nucleolus-associated chromatin (surrounding the nucleolus)

What is the function of the nucleolus, and what is its clinical significance in malignancy?

The nucleolus is a non-membrane-bound spongy mass responsible for the formation of ribosomal RNA ($rRNA$) and ribosomal subunits. Rapidly growing malignant cells characteristically feature abnormally large nucleoli.

What are the three constitutional components of the cytoplasm?

1. Cytosol: a fluid solution containing carbohydrates, lipids, proteins, and enzymes.
2. Organelles: essential, living, permanent structures performing vital functions.
3. Inclusions: non-living, temporary, non-essential storage materials (except hemoglobin and myoglobin) such as stored food and pigments.

How are cytoplasmic organelles classified based on the presence of a membrane?

Membranous organelles (covered by a membrane) include the plasma membrane, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. Non-membranous organelles (not covered by a membrane) include ribosomes and the cytoskeleton.

What ultrastructural model of the plasma membrane is illustrated here, and what is its trilamellar composition under EM?

It shows the trilamellar (unit membrane) structure, which consists of two electron-dense (dark) outer lines separated by an electron-lucent (light) middle layer, plus a fuzzy outer cell coat (glycocalyx).

What is the molecular composition, location, and functional significance of the cell coat (glycocalyx)?

The glycocalyx is composed of glycoproteins and glycolipids located exclusively on the outer surface of the plasma membrane. Its functions include serving as surface receptors (for drugs, hormones, and bacteria), mediating cell recognition, cell immunity, cell protection, and cell adhesion.

Which special stains can demonstrate the cell membrane under light microscopy?

Periodic acid–Schiff (PAS) and Silver (Ag) stains.

What are the three types of endocytosis and their specific mechanisms?

1. Phagocytosis (cell eating): pseudopodia extend to engulf solid particles (e.g., bacteria ingested by WBCs) to form a phagosome.
2. Pinocytosis (cell drinking): the plasma membrane invaginates to take up extracellular fluid into pinocytic vesicles (e.g., during thyroid hormone synthesis).
3. Receptor-mediated endocytosis: selective uptake where ligands bind specific surface receptors coated on the cytoplasmic side with clathrin, pinching off into coated vesicles (e.g., uptake of growth hormones).

Which special stains are utilized to identify mitochondria under light microscopy, and what color do they produce?

Iron Hematoxylin stains mitochondria dark blue, while Janus green stains them green.

What are the structural features of the inner mitochondrial membrane and its elementary particles?

The inner membrane is selective and folded into shelf-like projections called cristae to expand its surface area. The cristae carry elementary particles containing enzymes for ATP production and oxidative phosphorylation.

What substances are contained in the mitochondrial matrix, and how do mitochondria replicate?

The matrix contains oxidative enzymes of the Krebs cycle, $Ca^{2+}$ and $Mg^{2+}$ (enzymatic catalysts), as well as mitochondrial circular DNA and RNA, which enable mitochondria to divide by self-replication.

What is the clinical consequence of an inherited or acquired defect in mitochondrial enzymes?

It leads to muscular weakness due to a failure in ATP synthesis, which is required for essential cellular functions including muscle contraction.

How are ribosomes attached to the rough endoplasmic reticulum (rER) under electron microscopy?

The large ribosomal subunit binds to specific receptor proteins called ribophorins on the outer surface of rER cisternae, aligned over translocational pores that permit nascent polypeptide chains to pass into the cisternal lumen.

What are the five primary functions of the rough endoplasmic reticulum (rER)?

1. Protein synthesis (via membrane-bound ribosomes)
2. Protein isolation from the cytosol
3. Initial glycosylation (the initial addition of sugar moieties to nascent proteins)
4. Packaging of proteins into transfer vesicles destined for the Golgi apparatus
5. Protection of the cytoplasm from hydrolytic lysosomal enzymes

What are the structural characteristics and primary functions of the smooth endoplasmic reticulum (sER)?

sER is composed of irregular, anastomosing tubular cisternae lacking ribosomes. Its functions include: lipid synthesis (phospholipids of membranes), steroid hormone synthesis (e.g., cortisone), glycogen synthesis and breakdown in liver cells, detoxification of drugs, alcohol, and hormones, and acting as a $Ca^{2+}$ pump/reservoir for muscle contraction and relaxation.

How does the Golgi apparatus appear under light microscopy in H&E and silver stains?

In H&E-stained protein-secreting cells with intensely basophilic cytoplasm, it appears as an unstained perinuclear area called the 'negative Golgi image.' With silver (Ag) stain, it appears as a brown network that is perinuclear in nerve cells and apical/supranuclear in secretory cells.

How do the cis and trans faces of the Golgi apparatus differ structurally and functionally?

The cis face is convex, immature, and acts as the entry face that receives transfer vesicles from the rER. The trans face is concave, mature, and acts as the exit face that releases secretory vesicles and primary lysosomes.

What are the five functions of the Golgi apparatus?

1. Protein and lipid chemical modifications (such as carbohydrate addition)
2. Protein concentration and packaging
3. Secretory vesicle formation
4. Cell membrane renewal and maintenance
5. Lysosome formation

What is the enzymatic content of lysosomes, and which two organelles cooperate in their biogenesis?

Lysosomes contain hydrolytic enzymes (such as acid phosphatase). Their origin requires the rough endoplasmic reticulum (which synthesizes the hydrolytic enzymes) and the Golgi apparatus (which packages and releases them as primary lysosomes).

What are the four types of secondary lysosomes?

1. Heterolysosomes: formed by the fusion of a primary lysosome with a phagosome.
2. Multivesicular bodies: formed by the fusion of a primary lysosome with a pinocytic vesicle.
3. Autolysosomes: formed by the fusion of a primary lysosome with old or damaged organelles.
4. Residual bodies: lysosomes containing undigested materials.

What is the biological fate of residual bodies in long-lived post-mitotic cells?

If not eliminated by exocytosis, undigested materials remain within the cytoplasm as lipofuscin (an age-related wear-and-tear pigment), accumulating prominently in cardiac muscle cells and neurons.

What are the five digestive and defensive functions of lysosomes?

1. Digestion of cellular nutrients
2. Defense by degrading engulfed bacteria and viruses
3. Autophagy of worn-out organelles to maintain cell health
4. Autolysis of dead cells following cell death
5. Facilitating fertilization by enabling the sperm head to penetrate the ovum

Where are ribosomal components synthesized and assembled into functional subunits?

$rRNA$ is transcribed in the nucleolus, while ribosomal proteins are synthesized in the cytoplasm and enter the nucleus via nuclear pores; both join in the nucleolus into small and large subunits, which exit to the cytoplasm and only combine during protein translation.

What are the functional destinations of proteins synthesized by free ribosomes versus attached ribosomes?

Free ribosomes synthesize proteins utilized within the cell for its own metabolic functions (such as glycolytic enzymes). Attached ribosomes synthesize proteins destined for cellular export/secretion (hormones and enzymes), lysosomal enzymes, or incorporation into the plasma membrane.

What three patterns of cytoplasmic basophilia can be produced by ribosomes under light microscopy?

1. Diffuse basophilia (in rapidly proliferating embryonic cells)
2. Localized basophilia (in basal regions of pancreatic acinar cells)
3. Focal or spotty basophilia (Nissl's granules in nerve cell bodies)

What is the structural diameter and molecular composition of microtubules?

Microtubules are hollow cylindrical tubules with a constant diameter of $24\,nm$ and variable length, composed of polymerized heterodimers of $\alpha$-tubulin and $\beta$-tubulin, organized by the microtubule-organizing center (MTOC) containing $\gamma$-tubulin.

How does cancer chemotherapy exploit microtubule biology to halt tumor growth?

Chemotherapeutic drugs arrest tumor proliferation by preventing microtubule polymerization and disrupting mitotic spindle formation, thereby blocking mitosis.

What organelle is shown in this electron micrograph, and what is the specific arrangement of its labeled sub-elements?

It shows a centriole in transverse section, composed of $27$ microtubules organized into $9$ peripheral triplets (labeled a, b, and c from the inner to outer margin).

What cellular structure is shown in this cross-section, and what is its microtubule formula?

It depicts the shaft (axoneme) of a cilium, formed of $9$ peripheral microtubule doublets surrounding $2$ central single microtubules ($9\times 2 + 2 = 20$ microtubules), enclosed by the plasma membrane.

What clinical pathologies result from defective, immotile cilia and immotile flagella?

Immotile cilia cause recurrent, chronic respiratory tract infections due to impaired mucus and particle clearance. Immotile flagella prevent sperm motility, leading to male infertility.

What is the diameter, subunit composition, and molecular architecture of microfilaments?

Microfilaments have a diameter of $5 - 7\,nm$ and are composed of globular G-actin monomers polymerized into two helical strands coiled around each other to form filamentous F-actin.

How do microvilli and stereocilia compare in structure, core composition, and biological function?

Both structures possess a core of parallel actin microfilaments (no microtubules) covered by plasma membrane. Microvilli are short projections forming an apical brush border that increases surface area for absorption in the small intestine. Stereocilia are extremely long, non-motile, branching microvilli that facilitate fluid absorption in the male reproductive tract (epididymis).

What is the diameter range of intermediate filaments, and why are they diagnostic markers in oncology?

Intermediate filaments measure $8 - 10\,nm$ in diameter. Because specific classes of intermediate filaments are expressed exclusively in distinct cell lineages, identifying them immunohistochemically helps determine the cellular origin of poorly differentiated tumors.

What are the six site-specific types of intermediate filaments and their corresponding tissue locations?

1. Cytokeratin: epithelial cells, hair, and nails
2. Vimentin: connective tissue cells and muscle
3. Desmin: muscle tissue
4. Neurofilaments: neurons
5. Glial fibrillary acidic protein (GFAP): glial cells
6. Lamins: inner nuclear membrane (nuclear lamina)

How does glycogen appear under light microscopy when prepared with H&E, Best's carmine, and PAS stains?

In standard H&E preparation, glycogen dissolves, leaving empty vacuoles. Best's carmine stains glycogen granules red, and Periodic acid–Schiff (PAS) stains them magenta red.

What characteristic cell morphology is depicted here, and how does intracellular lipid appear in H&E versus Sudan III stains?

It shows a signet-ring adipocyte. In standard H&E, stored fat dissolves, leaving a single large clear vacuole that flattens and displaces the nucleus to the cell periphery. In frozen sections, Sudan III stains the stored lipid droplets bright orange.

What are the two categories of cytoplasmic pigments and common examples of each?

Endogenous pigments (synthesized by cells) include hemoglobin (RBCs), myoglobin (muscles), melanin (skin and eye), and lipofuscin (cardiac and nerve cells). Exogenous pigments (introduced from outside) include carbon and dust particles (in lung dust cells), dietary carotene (from carrots), and tattoo marks (dyes engulfed by dermal phagocytes).

What are the light and electron microscopic hallmarks of protein-synthesizing cells?

Under light microscopy (LM): a vesicular, pale-staining nucleus with a prominent nucleolus (PBP) and deeply basophilic cytoplasm. Under electron microscopy (EM): a predominantly euchromatic nucleus, extensive rough endoplasmic reticulum (rER), numerous mitochondria, and a well-developed Golgi apparatus.