Cytology

Cell Structure and Function

• Cell morphology relates to function and tissue type
• Cell shapes: squamous, cuboidal, columnar, spindle/fusiform, cylindrical, round, polygonal, pyramidal
• Cells, tissues, organs, and systems work together to form an organism

Nucleus

• Most conspicuous organelle in a cell
• Usually one nucleus per cell, but some cells have more
• Nucleus is involved in heredity and cell division
• Nuclear pores allow passage of RNA and proteins into the cytoplasm

Organelles

• Rough Endoplasmic Reticulum (RER): site of protein synthesis
• Golgi apparatus: modifies and packages proteins for secretion
• Lysosomes: contain hydrolytic enzymes for intracellular digestion
• Mitochondria: site of ATP production, self-replicating with circular DNA
• Peroxisomes: contain catalase to break down toxic molecules
• Centrioles: involved in formation of cilia, flagella, and spindle fibers
• Cytoskeleton: microfilaments, intermediate filaments, and microtubules provide structural support and shape

Microfilaments

• Composed of actin and myosin
• Involved in cell shape, intracellular movement, and muscle contraction

Intermediate Filaments

• Characterize 4 basic tissue types: epithelium, connective tissue, muscle, and nerve
• Cytokeratins in epithelium, vimentin in mesenchymal cells, desmin in muscle, and neurofilaments in neurons

Microtubules

• Hollow tubes composed of tubulin dimers
• Involved in intracellular transport, chromosome separation, and cilia/flagella movement

Surface Specializations

• Microvilli: small, absorptive projections
• Stereocilia: larger, non-motile projections (considered large microvilli)
• Cilia: motile projections with microtubules

Cytoplasmic Inclusions

• Haemosiderin: brown granular pigment for iron storage in macrophages
• Melanin: brown granular pigment for UV protection in epidermis
• Lipofuscin: brown granular pigment for 'wear and tear' in post-mitotic cells
• Lipid: large single clear space in adipocytes

Cell Types and Morphology

• Skeletal muscle cells: multinucleated, round, oval, or lobed
• Osteoclasts: multinucleated
• Megakaryocytes: multinucleated
• Hepatocytes: polygonal with prominent nucleolus
• Pancreatic acinar cells: pyramidal with basophilic nucleus
• Adipocytes: large, single clear space (white fat)### Cell Structure
• Multinucleated cells: skeletal muscle cells, osteoclasts, megakaryocytes
• Hepatocytes (liver cells) have 40X, HE, round, oval, elongated, lobed shape

Nuclear Pores and Envelope

• Nuclear pores allow passage of RNA and proteins into the cytoplasm
• Nuclear envelope connects to Rough Endoplasmic Reticulum (RER)
• Nucleolus produces rRNA
• DNA → RNA → PROTEIN

Chromatin

• Chromatin is a complex of DNA and protein
• Euchromatin: active genes, less compact, and more accessible
• Heterochromatin: inactive genes, more compact, and less accessible

Cellular Inclusions

• Adipocytes: store energy, insulation (white fat), and heat production (brown fat)
• Glycogen: stores glucose, patchy clear spaces in hepatocytes, skeletal muscle, and neurons
• Pigment melanin
• Lipid droplet
• Hemosiderin: iron-containing pigment, differentiates from other intracytoplasmic pigments using Perls Prussian Blue stain
• Lipofuscin granules: present in cardiac muscle

Plasma Membrane and Receptors

• Plasma membrane expresses receptors
• Receptors are constantly expressed and recycled on both inner and outer surfaces of plasma membrane and organelle membranes
• Receptors are coded for within the genome and produced/processed within cells by specialized structures