Human Anatomy

Lecture 2

Study of Cells

Cell shapes and sizes
Shapes – organs and tissues are often described according to the shapes of their cells
______– thin, flat, scaly
Cuboidal- roughly equal in length, width, and height
______- distinctly taller than they are wide
Polygonal- having irregularly angular shapes with four or more sides
______- having multiple pointed processes, which give the cells a somewhat starlike shape
Spheroid to ovoid- round to oval in shape
Discoid- disc-shaped
______- spindle-shaped; elongated with a thick middle and tapered ends
Fibrous- long, slender, and threadlike
Sizes
A micrometer is one-millionth of a meter
Most human cells are about 10 to 15 micrometers wide
Cell size is limited:
If a cell were too large, molecules could not ______from place to place fast enough to support metabolism
Time required for diffusion is proportional to the ______of distance, so if cell size is doubled, the travel time for molecules within the cell is quadrupled
Cells size is limited by the relationship between its volume and surface area
The surface area is proportional to the square of its diameter, while the volume is proportional to the ______of its diameter, so volume increases much faster than surface area as diameter increases.
At some point a cell becomes so large that there isn’t enough surface area to absorb nutrients and to get rid of wastes

The major components of a cell
Plasma membrane – forms the surface boundary of the cell
Cytoplasm – material between the cell membrane and the nucleus
Cytoskeleton – supportive framework of protein filaments and tubules
Organelles – diverse structures that perform various ______
Inclusions- include stored cell products such as lipids and pigments and foreign bodies such as dust and bacteria
Cytosol- a clear gel or fluid inside the cell
Nucleoplasm – material within the ______

Cell Surface

Plasma membrane – essentially a two-layered lipid film with proteins embedded in it
Membrane Lipids
Phospholipids make up 75% of the membrane lipid molecules
Two fatty acid tails are ______, while the phosphate-containing head is hydrophilic.
The tails orient away from the water, while the heads orient towards the intracellular fluid and extracellular fluid
The molecules drift from place to place, keeping the membrane ______
Fat soluble substances pass in and out of the cell through this phospholipid bilayer
Membrane Proteins
Proteins may pass all the way through the plasma membrane (integral proteins), or they may simply adhere to the face of the membrane (peripheral proteins)
Roles:
______– some hormones and neurotransmitters bind to cells at these proteins to trigger physiological changes inside the cell
Enzymes – after chemical messages are received, some membrane proteins break down those messengers
Channel proteins – water and solutes may pass through tunnels made of proteins to enter or leave the cell membrane
Cell ______markers – some proteins function as genetic identification tags to allow the body to determine if cells belong to the body or are foreign
Cell adhesion molecules – some proteins allow cells to stick to each other
______– some proteins actively bind to a substance on one side of the membrane and then release it on the other side
Membrane Transport – One of the most important functions of the plasma membrane is to control the passage of materials into and out of the cell
______– a process in which a physical pressure forces material through a membrane
Example: blood pressure forces fluid to seep through the walls of the blood capillaries into the tissue fluid
This allows water, salts, and nutrients to be passed from the blood to the cells surrounding a blood vessel
Simple diffusion- the net movement of particles from a ______concentration to a lesser concentration
Molecules diffuse through a membrane if the membrane has large enough pores
Selectively permeable membranes allow some molecules to pass through, but not all of them
Osmosis – the diffusion of water through a selectively permeable membrane, from the side where water is more concentrated to where water is less concentrated
Facilitated ______– movement of a solute through a membrane, down its concentration gradient, with the aid of a carrier
The carrier binds to the particle on one side, where the solute is more concentrated, and releases it on the other side, where it is less concentrated
Active ______– carrier mediated transport of a solute through a membrane up its concentration gradient, with the expenditure of adenosine triphosphate
ATP is essential to the process because moving particles up a concentration gradient requires an input of energy
Vesicular transport – movement of larger particles or droplets of fluid through the membrane in bubble-like vesicles
Movement of material into the cell is ______
Movement of material out of the cell is exocytosis
Glycocalyx – A layer of carbohydrates on the glycoproteins and glycolipids of the plasma membrane forms a fuzzy, sugary coating
The coating cushions the plasma membrane and protects it from ______
The coating functions in cell identity (distinguishing cells from diseased cells or invading organisms)
The coating contains cell-adhesion molecules that help bind tissues together
Microvilli, Cilia, and Flagella
Microvilli- extensions of the plasma membrane that increase surface area
Cilia- ______processes that extend from cells
Motile cilia beat in waves that move materials (such as mucus or egg cells) along the outside surface of the cell
Non-motile cilia are not well-understood, but some are sensory
Flagella- long whiplike tails for movement of sperm cells
Intercellular Junctions – arrangements of proteins that link cells together and attach them to extracellular material
Tight Junctions- A zipperlike junction between epithelial cells that limits the passage of substances between them
______-A patchlike intercellular junction that mechanically links two cells together
Gap ______- A junction between two cells consisting of a pore surrounded by a ring of proteins in the plasma membrane in each cell
The pore allows solutes to diffuse from the cytoplasm of one cell to the next, which makes communication between cells possible

Cytoplasm

The Cytoskeleton – system of filaments and tubules that provide physical support, allow cellular movement, and control routing of molecules and organelles to their destinations within the cell
Organelles
The nucleus – round or oval shaped structure near the center of the cell containing DNA
______Reticulum – An extensive system of interconnected tubules or channels enclosed in a membrane
Rough endoplasmic reticulum – contains ribosomes and synthesizes proteins for export from the cell
Smooth endoplasmic reticulum – involved in detoxification, steroid synthesis, and storage of calcium ions (in muscle cells)
Ribosomes – Granules composed of ribosomal RNA and enzymes that read sequences of messenger RNA to assemble sequences of amino acids to make proteins
______Complex – Organelle that modifies and packages newly synthesized proteins and synthesizes carbohydrates
Lysosomes – Organelles that contain enzymes that are used to digest foreign matter, pathogens, and expired organelles
Peroxisomes – Organelles containing enzymes that detoxify drugs and break down fatty acids, producing hydrogen peroxide in the process
______– Organelles specialized to synthesize ATP (for energy)
Centrioles- Organelles composed of a short cylinders of microtubules, that are the origin of the mitotic spindles (used in cell division)
Inclusions- Any visible object in the cytoplasm of a cell other than an organelle or cytoskeletal element, such as a dust particle, lipid droplet, or pigment

Life Cycle of Cells

Cell Cycle – the life cycle of a cell, extending from the time that a cell is produced by cell division until it produces daughter cells by cell ______.
Cell Division
Meiosis – the production of egg and sperm cells (haploid cells)
Mitosis – produces identical cells for growth or replacement of damaged cells
Several phases are involved in mitosis
Interphase actually precedes replication activities, and it’s the phase in which most cells remain for long periods of time. It’s important for mitosis because it’s a phase in which the ______is replicated
Prophase is a phase in which the DNA chromosomes coil into short, dense rods called chromatids.
The ______are two genetically identical bodies joined together at a pinched spot called the centromere
The nuclear envelope disintegrates
Centrioles sprout microtubules called spindle fibers, which push the centrioles towards opposite poles
Metaphase is a phase in which the chromosomes line-up on the equator of the cell
The spindle fibers from opposite poles attach to the chromatids

Anaphase is a phase in which the two sister chromatids separate and are pulled by the spindle fibers towards opposite poles
The identical chromatids are now called ______chromosomes
Telophase is a phase in which the chromosomes are surrounded by a new nuclear envelope and the DNA uncoils to return to its dispersed form
Cytokinesis overlaps with telophase and is a process in which a crease (called a cleavage ______) begins to form and eventually pinches one cell into two