Histology Quiz on Epithelial Tissue and Apoptosis

Cell Biology

• Necrosis is a pathological process that occurs in response to acute injury. Cells rupture, release digestive enzymes that damage nearby cells, and swell. It causes a burst and release of enzymes and inflammatory signals.
• Apoptosis is a genetically-programmed cell suicide. It is a normal or developmental process, like removing fetal cells, and is deliberate, not accidental. A doomed cell receives a chemical signal that turns on genes, initiates and completes apoptosis (Caspase Enzyme Cascade). Characteristics are cell shrinkage (pyknosis), loss of cell-cell contact, cytoplasmic budding, and formation of apoptotic bodies (cell fragments with nuclear material). Apoptosis does not trigger an inflammatory response. Phagocytes clean up the apoptotic debris.

Epithelium & Glands

• Simple squamous epithelium is characterized by its width being greater than its height, a flat nucleus, and a covering function. It lines body cavities and organs (mesothelium), lines blood and lymph vessels (endothelium), the thin loop of Henle (kidney), the vestibular membrane in the cochlea, alveoli in the lungs, and Bowman's capsule in the renal corpuscle (kidney).
• Simple cuboidal epithelium is characterized by a width equal to its height, a spherical and central nucleus, and a similar depth, height, and width. It is typically found lining the ducts of small exocrine glands, the thyroid (lining the thyroid follicle), the germinal epithelium (ovary), and the choroid plexus of ventricles (brain).

Specialized Epithelia

• Keratinized stratified squamous epithelium has dead squamous cells (keratinocytes) at the surface that form a protective layer against dryness, bacteria, and friction, with the cells continuously shedding. Location: epidermis of skin (thicker on palms and feet). Non-keratinized stratified squamous epithelium has squamous surface cells with nuclei that are still alive, typically found on moist surfaces like the oral cavity, esophagus, anus, and vagina.
• Stratified cuboidal epithelium is characterized by circular nuclei and a few layers of cuboidal cells.
• Pseudostratified epithelium appears stratified due to nuclei at various levels, but all cells rest on the basement membrane. It consists of columnar cells (with goblet cells) and basal cells. Location: trachea and bronchi of the respiratory tract.
• Transitional epithelium is characterized by stratified cuboidal-like cells that transition to squamous cells (distended) and cuboidal (contracted) shapes in response to stretching, typically found in the urinary system (ureters, urinary bladder, and portions of urethra).

Connective Tissue

• Connective tissue proper is classified based on fiber type, density, arrangement, and location.

Nervous Tissue

• Neuron cell bodies (soma/perikaryon) contain nissl substance (free ribosomes in RER). Microtubules and neurofilaments are networks in cytoplasm for intracellular transport and structural integrity. Lipofuscin granules are residues of lysosomal activity. Cytoplasm includes mitochondria, lysosomes, and the Golgi complex. Dendrites transmit impulses towards the cell body. Axons transmit impulses away from the body, with a single axon per neuron, but can have collaterals(branches). No nissl substance or Golgi complex in the axon. Telodendria are the terminal branches of axons. Neurons have characteristics of irritability (reception) and conductivity (transmission). Three types of neurons are described (bipolar, pseudounipolar, multipolar).

• Synapses allow neuron communication with effector cells for transmission of chemical messages due to action potentials. Synaptic vessels contain neurotransmitters.

Adipose Tissue and Cartilage

• Hyaline cartilage ECM is a smooth appearance (glassy), with type 2 collagen and ground substance (mostly water with proteoglycans, such as GAGs). Chondrocytes are oval/round and are located in lacunae. Perichondrium is a dense irregular CT that forms the outer fibrous layer and the inner cell layer (chondrogenic cells) surrounding hyaline cartilage excluding articular cartilage.
• Elastic cartilage ECM is similar to hyaline cartilage but with elastic fibers. Chondrocytes lie in lacunae closer together. Perichondrium is similar to hyaline cartilage.
• Fibrocartilage ECM is type 1 collagen. Chondrocytes lie in lacunae in the abundance of collagen fibers (looking like cells in the dense irregular CT). Perichondrium is absent.

Muscle Tissue

• Skeletal muscle is striated and voluntary. Skeletal muscle cells, also called muscle fibers, are characterized by endomysium - delicate CT around individual fibers.

Bone Tissue

• Osteoblasts originate from osteogenic cells, are cuboidal with basophilic cytoplasm, and have abundant rough endoplasmic reticulum. They secrete osteoid (procollagen, proteoglycans/GAGs, non-collagen proteins) including osteocalcin (which binds to hydroxyapatite crystals)., osteonectin, and bone sialoprotein (ECM via integrins), and osteopontin (ECM via integrins). They initiate and control mineralization.
• Osteoclasts are large, multinucleated, and acidophilic. They are responsible for bone resorption.
• Osteocytes are osteoblasts enclosed in ECM. They have reduced organelles and cytoplasmic processes that extend into canaliculi (communication via gap junctions). Their function is to maintain bone matrix.

Integument

• The layers of the epidermis, in thick skin, include a stratum basale (deepest layer) that is single cuboidal, anchored by hemidesmosomes and mitotic layer of keratinocytes, melanocytes (protect nuclei from UV), and Merkel cells (mechanical receptors). Stratum spinosum are several layers of cells connected by desmosomes for tensile strength.

Hyology of Lymphoid Tissue

• Thymus: Primary lymphoid organ in superior mediastinum with a capsule and consists of cortex and medulla. The cortex is characterized by lymphocytes, epithelioreticular cells (forming network around lymphocytes for lymphocyte maturation). The medulla contains fewer lymphocytes, macrophage for phagocytosis of non-functional cells, and Hassal corpuscles. Cells in the thymus are predominantly immune cells.

Histology of Blood Vessels

• Elastic arteries: Thick tunica media with multiple layers of elastic tissue.
• Muscular arteries: Thick tunica media with smooth muscle and some elastic.
• Arterioles: Thin tunica media with one or two layers of smooth muscle and little elastic.
• Medium veins: Thin tunica media with a thin layer of smooth muscle.

Histology of Respiratoy System

• Trachea: Pseudostratified ciliated epithelium, lamina propria of loose CT, mucosa, serous/mucous, elastic lamina, submucosa (dense irregular CT with fewer glands and MALT), and C-shaped hyaline cartilage rings.
• Bronchi: similar to the trachea but have transitional epithelium, fewer glands, and plates of hyaline cartilage.
• Bronchioles: have simple ciliated cuboidal epithelium, clara cells (replace goblet cells), no glands, and complete muscularis mucosa.
• Alveolar ducts & Alveoli: Simple squamous epithelium, thin lamina propria, lacking muscularis mucosa, but containing bundles of smooth muscle.

Histology of Digestive System

• Parietal cells secrete gastric acid and intrinsic factor.
• Chief cells secrete pepsinogen.
• Enteroendocrine cells secrete various hormones.
• Paneth cells secrete antimicrobial proteins.
• Enterocytes are absorbent cells.

Histology of Liver/Gall Bladder/exocrine pancrease

• The liver is arranged in hepatic lobules where bile is produced and stored in the gallbladder. The gallbladder's mucosa is composed of simple tall columnar epithelium and has smooth muscle in its muscularis externa.
• The exocrine pancreas has serous alveoli that produce pancreatic enzymes. It has ducts that deliver the enzymes into the duodenum.

Histology of Urinary System

• The uriniferous tubule in the kidney is part of the nephron and the collecting duct. The nephron begins with the renal corpuscle, followed by the proximal convoluted tubule (PCT), the loop of Henle, and the distal convoluted tubule.
• The collecting duct is a component of the uriniferous tubule.

Histology of Reproductive Systems

• Sertoli cells have a columnar shape and remove excess cytoplasm. They form a blood-testis barrier, are phagocytic, and supply plasma factors for growth and differentiation. Leydig cells secrete testosterone.
• Follicle development includes the formation of fluid-filled spaces (liquor folliculi) and antrum. The cumulus oophorus surrounds the primary oocyte.

Test your knowledge on essential concepts of histology, including the characteristics of necrosis versus apoptosis and the types of epithelial tissues. This quiz covers key functions and locations of various epithelial types found in the body, as well as the processes of cell death. Perfect for students in biology or health sciences.