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• Cell biology is for first-year students in the Biotechnology & Genetic Engineering Program at Helwan National University for the academic year 2024-2025.
• A cell is a functional and structural unit of living organisms.
• Cells are surrounded by a plasma membrane (plasma lemma).
• The plasma membrane contains cytoplasm and organisms like mitochondria, lysosomes, endoplasmic reticulum, and ribosomes.
• Cell theory, developed by Schleiden and Theodore Schwann, makes several key points.
• All organisms are composed of cells.
• Cells are the structural and functional unit of life.
• Cells arise from pre-existing cells.
• Cells vary in shape and size.

Different Human Cells

• Epithelial cells cover and protect the outer (skin) and inner layers of the body, such as internal organs and the small intestine.
• Epithelial cells can be modified to perform specific functions like secretion.
• There are several types of epithelial cells, including squamous, cuboidal, and columnar cells.
• Muscular cells are responsible for movement.
• There are several types of muscular cells, including cardiac (in the heart), skeletal, and smooth muscles.
• Nervous cells are responsible for sensation and transportation of nerve impulses.
• Neurons (nerve cells) are the functional building unit of the nervous system.
• Examples of the cuboidal epithelial cells have a round and central nucleus.
• Smooth muscles cover internal organs and are involved in involuntary movements.
• Neurons or nerve cells are formed from a soma (cell body) and a long axon.

Cell Modifications

• Cell modification refers to any structural or functional change in a cell that helps a cell perform a specific function.
• Types of cell modification include epithelial cells, muscle cells, and nervous cells as modified cells.
• Epithelial cells that are modified include epithelial cells with brush borders, microvilli, secretory cells, and basket cells.
• Muscle cells as modified cells refer to smooth muscle cells in internal human organs.
• Nervous cells as modified cells refer to sensory cells (neurons).
• Brush borders are dense layers of microvilli on the surface of some epithelial cells.
• Microvilli are tiny finger-like projections on the surface of some epithelial cells.
• The main function of brush borders and microvilli is to increase the surface area for absorption at their sites.
• The location of brush borders and microvilli is in the small intestine and kidney tubules.
• A cuboidal epithelial cell with a brush border has a group of microvilli to increase the surface area for absorption and are found in kidney tubules.
• Secretory epithelial cells contain secretory vacuoles which secrete from the rough endoplasmic reticulum (RER).
• The main function of secretory epithelium is the secretion of enzymes.
• Secretory epithelium is found in the stomach, faces the gastric cavity, and releases digestive enzymes.
• Smooth muscles are non-striated and considered involuntary muscles.
• Smooth muscle cells have an elongated nucleus and are found in internal organs such as the stomach and small intestine.
• The main function of smooth muscles is to be responsible for involuntary internal organ movement.
• Neurons are the functional and structural unit of the nervous system.
• Neurons contain groups of Nissl's bodies (groups of RER and ribosomes), which produce proteins of neurons.
• Basket cells are modified epithelial cells that turn into myofibroblasts and become contractile cells.
• Basket cells are found around glands.
• The main function of basket cells is the squeezing of glands for excretion.
• Sensory cells are specialized cells that detect stimuli like light, sound, touch, or chemicals.
• Sensory cells convert stimuli into nerve impulses for the brain to process.
• Examples of sensory cells are photoreceptors (in eyes), mechanoreceptors (in skin), and taste cells (on tongue).