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NSG 100
Anatomy and Physiology in
Nursing
Learning Outcome:
Cell structure and its function. Diffusion and concentration gradient. Osmosis and pressure Carrier-mediated transport Endocytosis and exocytosis Nucleus, Endoplasmic Reticulum, Golgi apparatus, secretory vesicles, lysosomes, peroxisomes, mitochondria, cytoskeleton and centrioles. Cilia, flagella and microvilli Process of gene expression, mitosis and cell development.
Cell Structure
Cell- A basic structural, functional, and
reproductive unit of all multicellular
organism.
Organelles: specialized structures in cells that perform specific functions Example: nucleus, mitochondria, ribosomes Cytoplasm: jelly-like substance that holds organelles Cell membrane: also termed the plasma membrane a structure that encloses the cytoplasm
Generalized Cell
Functions of the Cell
Cell metabolism and energy use Synthesis of molecules Communication Reproduction and inheritance
Cell Membrane
The cell membrane , or plasma membrane, is the outermost component of a cell. It forms a boundary between material in inside the cell and the outside. Materials inside the cell are intracellular and those outsides are extracellular. It acts as a selective barrier.
Cell Membrane Structure
The fluid-mosaic model is the model used to describe the cell membrane structure. The membrane contains phospholipids, cholesterol, proteins, and carbohydrates. Phospholipids form a bilayer. Phospholipids contain 2 regions: polar and nonpolar.
Phospholipid Structure
A phospholipid molecule has a polar head region that is hydrophilic and a nonpolar tail region that is hydrophobic.
The polar region is exposed to water around the membrane. The nonpolar region is facing the interior of the membrane. Movement through the Cell Membrane The cell membrane has selective permeability, which allows only certain substances to pass in and out of the cell. Substances such as enzymes, glycogen, and potassium are found in higher concentrations inside the cell. Substances such as sodium, calcium, and chloride are found in higher concentrations outside the cell. Cell Membrane Passage Some substances, like O 2 and CO 2 , can pass directly through the cell membrane’s phospholipid bilayer. Some substances must pass through transmembrane protein channels, such as Na+ through its channels. The route of transport through the membrane depends on the size, shape, and charge of the substance. Some substances require carrier molecules to transport them across the cell membrane, such as glucose. Some substances require a vesicular transport across the membrane. The vesicle must fuse with the cell membrane for transport. Active Transport and Passive Transport Passive membrane transport does not require the cell to expend energy. Active membrane transport does require the cell to expend energy, usually in the form of ATP. Passive membrane transport mechanisms include diffusion , osmosis , and facilitated diffusion. Active membrane transport mechanisms include active transport , secondary active transport , endocytosis , and exocytosis. Passive Transport
A. Diffusion
movement of substances in a solution down a concentration gradient. solution= solutes ( substances dissolved) + ( liquid/gas) solvent. Solutes (e.g., ions or molecules) tend to move from an area of higher concentration of a solute to an area of lower concentration of that same solute in solution. concentration gradient- the difference in the concentration of a solute in a solvent between two points divided by the distance between the two points. Factors that Influence the diffusion rate of substances across plasma membrane:
- Steepness of contration gradient.
- Temperature
- Mass of the diffusing substances
- Surface area
- Diffusion distance
Types of Diffusion
A. Simple diffusion
substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins Nonpolar, hydrophobic molecules Molecules that can pass: oxygen, carbon dioxide, and nitrogen gases; fatty acids; steroids; and fat- soluble vitamins (A, D, E, and K). Small, uncharged polar molecules such as water, urea, and small alcohols e.g., movement of oxygen and carbon dioxide between blood and body cells, and between blood and air within the lungs during breathing, absorption of some nutrients and excretion of some wastes by body cells.
area of lower solute concentration to an area of higher solute concentration. lower solute---> higher solute It occurs only when a membrane is permeable to water but is not permeable to certain solutes. 3.1. Osmosis
Osmotic Pressure and the Cell
A force required to prevent movement of water across cell membrane A solution’s tonicity(tension) is a measure of solution’s ability to change the volume of cells by altering their water content. A cell may be placed in solutions that are either hypotonic , isotonic , or hypertonic compared to the cell cytoplasm.
Hypotonic
A solution that has a lower
concentration of solutes than the cytosol inside the cell.
The solution has less tone, or osmotic
pressure, than the cell.
Water molecules enter faster than
they leave.
Swell and eventually burst called
lysis.
Given to dehydrated
Isotonic
Any solution in which cells maintain its normal shape and volume. The concentration of solutes that cannot cross the plasma membrane are the same on both sides of the membrane. The cell will neither shrink nor swell. e.g., 0.9% NaCl (Normal Saline sol), D5Water
Hypertonic
It has a higher concentration of solutes than does of the cytosol inside the cell. Water molecules moves out of the cells faster than they enter. Shrink called Crenation e.g., 2%NaCl, Mannitol (sugar alcohol) Useful for cerebral edema Red Blood Cell Changes in Differing Solutions Active Transport It is a carrier-mediated process, requiring ATP, that moves substances across the cell membrane from regions of lower concentration to those of higher concentration against a concentration gradient. Na+, K+, H+, Ca2+, I− (iodide ions), and Cl−; amino acids; and monosaccharides. Two (2) sources of cellular energy: Primary Active Transport - Energy obtained from hydrolysis of adenosine triphosphate (ATP) carrier proteins that mediate primary active transport are often called pumps. Secondary Active transport - energy stored in an ionic concentration gradient.
A. Primary Active Transport
Sodium-Potassium Pump action of the sodium- potassium pump present in cell membranes. The sodium-potassium pump moves Na+^ out of cells and K+^ into cells. The result is a higher concentration of Na+^ outside cells and a higher concentration of K+^ inside cells.
B. Secondary Active Transport
Secondary active transport uses the energy provided by a concentration gradient established by the active transport of one substance, such as Na+^ to transport other substances. No additional energy is required above the energy provided by the initial active transport pump. In cotransport, the diffusing substance moves in the same direction as the initial active transported substance. In counter transport, the diffusing substance moves in a direction opposite to that of the initial active transported substance.
C. Endocystosis
The interior of a cell is composed of the cytoplasm , which a jelly-like fluid that surrounds the organelles. Organelles are specialized structures that perform certain functions. Organelles include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, cytoskeleton, centrioles, cilia, flagella, and microvilli. Cell Nucleus Large organelle usually located near the center of the cell. Bounded by a nuclear envelope, which consists of outer and inner membranes with a narrow space between them. The nuclear membrane contains nuclear pores, through which materials can pass into or out of the nucleus. contain 23 pairs of chromosomes which consist of DNA and proteins. Within the nucleus are Nucleoli, which are diffuse bodies with no surrounding membrane. There are usually one to several nucleoli within the nucleus. The subunits of ribosomes, a type of cytoplasmic organelle, are formed within a nucleolus. These ribosomal components exit the nucleus through nuclear pores.
Chromosome Structure
Ribosomes Components are produced in the nucleolus Produced proteins are May be attached to other organelles, such as the endoplasmic reticulum. free ribosomes if not attached to other organelles.
Endoplasmic Reticulum (ER) is a series of membranes forming sacs and tubules that extends from the outer nuclear membrane into the cytoplasm. The rough ER is involved in protein synthesis and is rough due to attached ribosomes. The smooth ER has no attached ribosomes and is a site for lipid synthesis, cellular detoxification , and it stores calcium ions in skeletal muscle cells. Golgi Apparatus Also called the Golgi complex, consists of closely packed stacks of curved, membrane- bound sacs. It collects, modifies, packages, and distributes proteins and lipids manufactured by the ER. It forms vesicles, some of which are secretory vesicles, lysosomes, and other vesicles. Lysosomes are membrane-bound vesicles formed from the Golgi apparatus. They contain a variety of enzymes that function as intracellular digestive systems. Vesicles formed by endocytosis may fuse with lysosomes in order to breakdown materials in the endocytotic vesicles. One example is white blood cells phagocytizing bacteria. Peroxisomes are small, membrane-bound vesicles containing enzymes that break down fatty acids , amino acids , and hydrogen peroxide (H 2 O 2 ). Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell. The enzymes in peroxisomes break down hydrogen.
A specific type of intermediate filament is keratin , a protein associated with skin cells. Centrioles The centrosome is a specialized area of cytoplasm close to the nucleus where microtubule formation occurs. It contains two centrioles, which are normally oriented perpendicular to each other. Each centriole is a small, cylindrical organelle composed of microtubules. The centriole is involved in the process of mitosis. Cilia Cilia project from the surface of certain cells. cylindrical structures that extend from the cell and are composed of microtubules. Responsible for the movement of materials over the top of cells, such as mucus. Flagella a structure similar to that of cilia but are much longer, and they usually occur only one per cell. Sperm cells each have one flagellum, which propels the sperm cell. Microvilli Microvilli are specialized extensions of the cell membrane that are supported by microfilaments. They do not actively move as cilia and flagella do. Microvilli are numerous on cells that have them and they increase the surface area of those cells. They are abundant on the surface of cells that line the intestine, kidney, and other areas in which absorption is an important function. Whole Cell Activity A cell’s characteristics are determined by the type of proteins produced. The proteins produced are in turn determined by the genetic information in the nucleus. Information in DNA provides the cell with a code for its cellular processes. DNA DNA contains the information that directs protein synthesis; a process called gene expression. consists of nucleotides joined together to form two nucleotide strands. The two strands are connected and resemble a ladder that is twisted around its long axis. Gene Expression Gene expression, which is protein synthesis, involves transcription and translation. Transcription involves copying DNA into messenger RNA. Translation involves messenger RNA being used to produce a protein.
Overview of Gene Expression
The Cell Cycle During growth and development, cell division occurs to increase the number of cells or replace damaged or dying ones. This cell division involves a cell cycle. The cell cycle includes two major phases: a nondividing phase, called interphase , and a cell dividing phase, termed mitosis. A cell spends most of its life cycle in interphase performing its normal functions. During interphase, the DNA (located in chromosomes in the cell’s nucleus) is replicated. The two strands of DNA separate from each other, and each strand serves as a template for the production of a new strand of DNA. Cell Genetic Content Each human cell (except sperm and egg) contains 23 pairs of chromosomes, a total of 46. The sperm and egg contain 23 chromosomes total. One pair of chromosomes are the sex chromosomes, which consist of two X chromosomes if the person is a female or an X and Y chromosome if the person is a male. Mitosis Mitosis involves formation of 2 daughter cells from a single parent cell. Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase.
Stages of Mitosis
1. Prophase
During prophase the chromatin condenses to form visible chromosomes. Microtubules, termed spindle fibers, form to assist in breaking the centromere between the chromatids and move the chromosomes to opposite sides of the cell. The nuclear membrane dissolves.
2. Metaphase
During metaphase, the chromosomes align near the center of the cell. The movement of the chromosomes is regulated by the attached spindle fibers.
3. Anaphase
At the beginning of anaphase, the chromatids separate and each chromatid is called a chromosome. Each of the two sets of 46 chromosomes is moved by the spindle fibers toward the centriole at one of the poles of the cell. At the end of anaphase, each set of chromosomes has reachedan opposite pole of the cell, and the cytoplasm begins to divide.
4. Telophase
During telophase, the chromosomes in each of the daughter cells become organized to form two separate nuclei, one in each newly formed daughter cell. The chromosomes begin to unravel and resemble the genetic material during interphase.
