PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 9/e by Shier, Butler, and Lewis

Chapter 3 Cells

An adult human body consists of about 75 million cells, the basic units of an organism. All cells have much in common, but are distinctive in several ways. They vary in size, shape, and function.

Cell Structures Nucleus Cytoplasm Cytoplasmic organelles Cell membrane

Cell Membrane Outermost limit of the cell Thin, flexible, elastic Maintains integrity of the cell Controls entrance and exit of substances, selectively semipermeable Receives and responds to messages, signal transduction

Figure 3.3

Membrane Structure Lipids, proteins, with some carbohydrates Phospholipid bilayer Water-soluble heads containing phosphate groups (hydrophilic) form the surface Water-insoluble tails composed of fatty acids (hydrophobic) form the interior

Membrane Transport Molecules that are soluble in lipids can easily pass through the membrane. Molecules that are water-soluble do not move through the membrane. Cholesterol molecules embedded in the inside of lipid bilayer make it impermeable and stabilize the membrane.

Membrane Proteins Fibrous proteins that span the membrane function as receptors Globular, integral proteins that span the membrane allow passage of certain molecules Globular, peripheral proteins that do not span the membrane function as enzymes or signal transducers. These often aid in cell recognition and cell binding

Figure 3.7

Intercellular Junctions Cells are often connected to each other by intercellular junctions. Tight junctions occur when cell membranes of adjacent cells are tightly fused.

Intercellular Junctions Desmosomes form small reinforced regions of cell membranes of cells. Gap junctions connect the cell membranes of adjacent cells, but have channels to allow ions to move.

Figure 3.8

Cell Adhesion Molecules Cellular adhesion molecules, CAMs, guide cells on the move. Selectin coats white blood cells and provides traction to aid white blood cells in reaching injury site. Integrin directs the white blood cells between the capillary cell wall.

Cytoplasm Network of membranes and organelles are suspended in a clear gel called cytosol. Protein rods and tubules form the cytoskeleton, a supportive framework. Organelles perform specific cellular functions.

Endoplasmic Reticulum Membrane-bound flat sacs, canals, and vesicles are widely distributed Tubular transport system Synthesis of proteins and lipids Rough endoplasmic reticulum is studded with ribosomes Smooth endoplasmic reticulum lacks ribosomes

Figure 3.10b

Figure 3.10c

Ribosomes Ribosomes are found on the endoplasmic reticulum and free in the cytoplasm Composed of protein and RNA Provide a structural support and enzymes necessary for protein synthesis

Golgi Apparatus Stack of flat membranous sacs called cisternae Refines, packages, and delivers proteins synthesized by the ribosomes of the ER Movement of substances within cells by way of vesicles is vesicle trafficking Substances can be packaged for immediate release or stored until the cell is stimulated

Figure 3.12

Mitochondria Fluid-filled sacs that contain their own DNA and can divide on their own. There are two layers, an outer membrane and an inner membrane. The inner membrane is folded into cristae. Enzymes of the mitochondrion control reactions of energy release from nutrients.

Figure 3.13b

Lysosomes Tiny, membranous sacs containing enzymes that break down proteins, carbohydrates, and nucleic acids White blood cells digest bacteria with lysosomal enzymes Lysosomes dismantle worn cells and cell parts

Peroxisomes Membranous sacs found in all cells, but abundant in liver and kidneys Enzymes, peroxidases, catalyse metabolic reactions that release hydrogen peroxide as a byproduct Catalase decomposes hydrogen peroxide

Biochemical reactions of Peroxisomes Synthesis of bile acids Breakdown of very long chain fatty acids Degradation of rare biochemicals Detoxification of alcohol

Centrosome Located in the cytoplasm near the nucleus Consists of two hollow cylinders called centrioles built of microtubules Centrioles function in cell division Centrioles form spindle fibers that distribute chromosomes to dividing cells

Cilia and Flagella Motile processes that extend from the surface of certain cells Cilia are tiny hair like processes which attach just beneath the cell membrane to a basal body. Cilia create a wave action A flagellum is much longer than a cilium and has a wavelike motion that allows a cell to swim

Figure 3.16

Vesicles Membranous sacs that vary in size and contents They may form as a pinched off portion of the cell membrane Golgi and ER also form vesicles Vesicles transport substances into and out of the cell

Microfilaments and Microtubules Threadlike structures in the cytoplasm Microfilaments are tiny rods of the protein actin. They function in cellular movements Microtubules are long, slender tubes composed of the protein tubulin. They form the cytoskeleton and help move organelles within the cells

Figure 3.19

Inclusions Chemicals stored temporarily in the cell. Nutrients such as glycogen and lipids can be stored. Pigments such as melanin can be stored.

Cell Nucleus Large, spherical structure Enclosed in a double-layered nuclear envelope, composed of an inner and outer lipid bilayer Layers are joined at openings, the nuclear pores, channels made of more than 100 different proteins that allow movement in and out of the nucleus

Nucleoli and Chromatin Nucleoli are small, dense bodies composed of RNA and protein. It is the site of ribosome production. Chromatin fibers are composed of continuous DNA molecules wrapped around eight proteins called histones.

Movements into and out of the Cell The cell membrane controls the movement of substances into and out of the cell. Movements involve physical or passive processes such as diffusion, facilitated diffusion, osmosis, and filtration. Movements can be physiological or active processes such as active transport, endocytosis, and exocytosis.

Diffusion Diffusion is the tendency of atoms, molecules, and ions in solution to move from areas of higher concentration to areas of lower concentration. The difference in concentration is the concentration gradient. Diffusion occurs because these particles are in constant motion.

Diffusion Diffusion progresses until there is no net movement, diffusional equilibrium.

Diffusion in Living Systems Diffusional equilibrium does not normally occur in living systems Physiological steady state occurs Diffusion of substances occurs if the membrane is permeable to that substance and if a concentration gradient exists Examples: oxygen, carbon dioxide, cholesterol

Facilitated Diffusion Substances that are insoluble in lipids and too large to move through pores move by facilitated diffusion. Facilitated diffusion includes protein channels and protein carriers.

Facilitated Diffusion Molecules fit into the carrier and are transported across the membrane. The number of carriers limits the rate of movement.

Figure 3.23

Osmosis Osmosis is the diffusion of water molecules from a region of higher water concentration to a region of lower water concentration across a selectively permeable membrane.

Osmosis The greater the concentration of nonpermeable particles in a solution, the lower the water concentration and the greater the osmotic pressure.

Osmotic Pressure Solutions with the same osmotic pressure as body fluids are called isotonic. Solutions with a higher osmotic pressure than body fluids are called hypertonic. Solutions with a lower osmotic pressure than body fluids are called hypotonic.

Figure 3.25a

Figure 3.25b

Figure 3.25c

Filtration Molecules can be forced though membranes by the process of filtration.

Filtration Tissue fluid forms when water and dissolved substances are forced out through the walls of capillaries, but cells and large molecules, such as proteins, are left inside.

Filtration This is a passive process since gravity can be the applied force.

Active Transport Active transport occurs when the net movement of particles passing through membranes is in the opposite direction, from a region of lower concentration to one of higher concentration.

Active Transport Active transport utilizes protein carriers. This process requires energy from cell metabolism.

Endocytosis Endocytosis moves particles too large to move by diffusion or active transport. Pinocytosis is the intake of liquid droplets.

Endocytosis Phagocytosis is the intake of solids, often with the fusion of lysosomes which digest the material. Pinocytosis and phagocytosis bring material indiscriminately into the cell.

Receptor-mediated Endocytosis Receptor mediated endocytosis moves specific kinds of particles into the cell.

Receptor-mediated Endocytosis Protein receptors present on the cell membrane bind to specific ligands. The ligand-receptor complex is drawn into the cell and fuses with lysosomes to allow lysosomal enzymes to break down the ligand.

Exocytosis Exocytosis is the reverse of endocytosis.

Exocytosis Exocytosis often expels the residue after lysosomal enzymes have digested solids brought in through phagocytosis. Exocytosis allows cells to secrete material produced by the cell, for example, neurotransmitters.

Transcytosis Transcytosis combines exocytosis and endocytosis.

Transcytosis It is the selective and rapid transport of a substance or particle from one end of the cell to the other. It enables substances to cross barriers formed by tightly connected cells.

The Cell Cycle The series of changes that a cell undergoes from the time it forms until it divides is called the cell cycle.

The Cell Cycle Interphase is the period of cell growth and function. Interphase is composed of G1, S Phase, and G2.

The Cell Cycle G 1 is the first Gap or Growth phase. During this period, cell growth occurs. S phase is the period of DNA synthesis as the cell prepares for cell division.

The Cell Cycle G 2 is the second Gap or Growth phase. During this period, the cell replicates organelles in preparation for cell division.

Mitosis Mitosis occurs in somatic cells, all body cells with the exception of sex cells. Cell division results in two genetically identical cells with 46 chromosomes each. Karyokinesis is nuclear division. Cytokinesis is division of the cytoplasm.

Figure 3.37

Mitosis Prophase: chromosomes condense from chromatin and centrioles move to the poles.

Mitosis Metaphase: spindle fibers attach to centromeres and chromosomes align in the center of the cell.

Mitosis Anaphase: Spindle fibers contract and the chromosomes move to the opposite poles.

Mitosis Telophase: Nuclear envelope reforms and chromosomes unwind into chromatin.

Cytoplasmic Division Cytokinesis begins in anaphase when the cell membrane starts to constrict in the middle. Cytoplasmic inclusions and organelles are divided between the two new cells.

Cellular Differentiation The process by which different cells develop different structures and specialized functions is called differentiation. Cellular differentiation begins in the first weeks after fertilization. It reflects genetic control. Special proteins activate some genes and repress others.

Figure 3.44

Control of Cell Division How often cells divide is strictly controlled. Cells appear to keep track of their divisions, the “mitotic clock”. DNA at tips of chromosomes, telomeres, wear down as the cell divides and may be a signal for the cell to stop dividing. Size, space, hormones, and growth factors influence cell division.

Abnormal Cell Growth Abnormal growth or neoplasm can produce a disorganized mass called a tumor. Benign tumors remain in place and grow, interfering with function of healthy tissue. Malignant (cancerous) tumors are invasive and extend into surrounding tissue. Cancer is a collection of disorders.

Genes and Cancer Oncogenes activate genes that increase cell division.

Genes and Cancer Tumor suppressor genes hold mitosis in check.

Genes and Cancer Environmental factors may induce cancer by altering oncogenes and tumor suppressor genes in cells.