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studies the structure of the body parts and their relations to one another.
concerns the function of the body and it often focuses on events at the molecular and cellular levels.
all cells have common functions, but there is cell differentiation
Necessary life functions
is the ability of the organism to maintain relatively stable internal conditions even though the outside environment changes continuously. It indicates a dynamic state of equilibrium, in which internal conditions vary but always within relatively narrow limits.
Communication within the body is essential for homeostasis. It is accomplished by the nervous system and the endocrine system through electrical and chemical messages. These are the control systems of the organisms.
are those in which the result or response enhances the original stimulus. The change that occurs proceeds in the same direction as the initial disturbance. There are few examples in Nature, such as the clotting of blood vessels (Fig. 1.6 p.11) and the rising phase of the axonal action potential.
underlie all physiological processes.
the capacity to do work or to put matter into motion. Its forms are kinetic (energy in motion) or potential (stored energy). In living organisms:
Chemical: energy stored in the bonds of chemical substances
Electrical: results from the movement of charge particles
Mechanical: energy directly involved in moving matter.
never achieve 100% efficiency, always some of the initial energy supply is “lost” to the environment as heat. The part given off as heat is at least partly unusable. All processes in Nature tend to increase the disorder of matter. “Life is a continuous fight against this general principle, the Second Law of Thermodynamics.”
are those that we detect with our senses (such as color and texture) or measure (such as boiling point and freezing point). Chemical properties pertain to the way atoms interact with other atoms (bonding features). the nucleus is positively charged, but the atom is electroneutral since the number of protons equals that of electrons in all atoms.Protons are charged positively, electron are charged negatively and they surrounding the neutron (charge neutral)
are the combination of two or more atoms held together by chemical bonds.
occur when two or more different kinds of atoms bind, forming a molecule of a compound (example: water). A molecule is the smallest particle of a compound that still displays the specific characteristics of the compound.
homogeneous mixtures of compounds that may be gases, liquids or solids (air, seawater). In biological systems water is the solvent (substance present in the greatest amount), and the rest are the solutes.
heterogeneous mixtures of compounds, which can undergo sol-gel transformations (occur in the cytosol of cells).
heterogeneous mixtures with large solutes and particles that tend to settle out (example: blood).
A chemical bond is not a physical structure, it is an energy relationship between the electrons of the reacting atoms. Electrons are at different energy levels, depending on their distance from the nucleus. Each energy level can hold a specific number of electrons The number of electrons that can participate in bonding is limited to 8. The maximal number of electrons in the first shell is 2, and from there on, the outer most shell will have a maximal of 8 electrons.
is a chemical bond between atoms formed by the transfer of one or more electrons from one atom to the other. The atom that looses the electron(s) becomes charged positively and is called a cation (+), while the one that gains the electron(s) is charged negatively and is called an anion (-). Complete transfer electron, separate ions charged particles form
produce molecules in which the shared electrons occupy a single orbital common to both atoms. covalent bonds are formed when atoms share electrons pairs. If the electron pair are shared equally, the molecule is nonpolar charge balanced amoung atoms. If the they shared unequally, it is polar (a dipole), slight negative charge (& -) at one end of the molecule,slight positive charge (& +) at other end .
Water is the most abundant and important inorganic compound in all living organisms. It makes up from 60 to 80% of the volume of most living cells. What makes water so vital to life is several of its properties:
a group of molecules that includes sugars and starches, represent 1-2% of cell mass. They can be classified according to size and solubility.
Carbohydrates building blocks are monosaccharides, the most important of which are hexones(glucose, fructose, galactose) and pentoses (ribose, deoxyribose).
Carbohydrates, particulary glucose, are the major energy fuel for forming ATP, excess of the carboxydrates are stored as glycogen or converted to fat storage.
are molecules made of four interlocking hydrocarbon rings. Examples: cholesterol, sex hormones.
The steroid cholesterol is found in cell membranes and is the basis of steroids hormones, bile, salts, and vitamin D.
they are amphipathic molecules, since they have a polar region, called “head” and an hydrophobic region, called “tail” .
They are modified phoushorous-containing triglycerides taht have polar and nonpolar portions. They are founds in all plasma membranes.
Protein composes 10-30% of cell mass and is the basic structural material of the body, and many play vital roles in cell function. They have the most varied functions of any molecules in the body. All proteins contain C, O, H, N and many also contain S (sulfur) and P. The building blocks of proteins are the amino acids, which are amphipatic molecules. Amino acids posses 2 functional groups: acidic and amine (Fig. 2.17a p 48). Differences in the R group make each amino acid chemically unique
The sequence of amino acids forms the polypeptide chain.
Secondary: the chain of amino acids twist or bend upon themselves to form more complex structures, such as a beta-sheet or and alpha-helix. The alpha-helix is stabilized by hydrogen bonds formed between NH and CO groups in amino acids of the primary chain.
The primary chain forms spirals (a-helices) and sheets (b-sheets).
Structural levels of proteins (Tertiary)
Tertiary: is achieved when the secondary level structures fold upon one another to produce a compact ball-like, globular molecule. This unique structure is maintained by both covalent and hydrogen bonds between amino acids that are often far apart in the primary sequence.
Tertiary structure of prealbumit (transthyretin), a protein thattransports the thyroid hormone
thyroxine in serum and cerebro-spinal fluid.
Structural levels of proteins (Quaternary)
Quaternary structure of a functional prealbumin molecule. Two identical prealbumin subunits
join head to tail to form the dimer
Enzymes are globular proteins that function as biological catalysts. Enzymes increase the speed of reactions that will occur anyhow, i.e. that will give products that have more disorder than the reactants. Each enzyme is chemically specific and in most cases it is stereospecific, i.e. it requires a certain spatial configuration of the molecule(s) that will join to the enzyme. For example, enzymes will recognize the L-isomers from the D-isomers of monosaccharides and amino acids.
Examples: hydrolases (participate in hydrolytic reactions).
In many cases enzymes are part of cellular membranes, thus the product of one reaction is the substrate of the next. Some enzymes are produced by the cells in an inactive form.
Every chemical reaction requires an activation energy, which is the amount of energy required to break the bonds of the reactants so they can become the products. Enzymes decrease the activation energy required by specified reactants Enzymes decrease the randomness of reactions by binding the reacting molecules temporarily to the enzyme surface and presenting them to each other in the proper position for chemical interaction to occur.
Three basic steps appear to be involved in the mechanism of enzyme action:
Nucleic acids (DNA and RNA)
Nucleic acids (DNA and RNA) Cont
Five major types of nitrogen-containing bases can contribute to nucleotide structure:
Deoxyribonucleic acid (DNA) is typically found in the nucleus of the cell, where it constitutes the genetic material (genes, genome). It replicates itself before the cell divides and provides the basic instructions for synthesizing every protein in the body
DNA is a long, double-stranded polymer, a double chain of nucleotides (Fig. 2.22b p 54). The bases in DNA are A, C, G and T, and its pentose is deoxyribose. Its 2 nucleotide chain are held together by hydrogen bonds between the bases, so that a ladder-like molecule is formed. Alternating sugar and phosphate molecules of each chain form the backbones of the ladder. The whole molecule forms what is called a double helix.
Nucleic acids (RNA)
Ribonucleic acid (RNA) molecules are single strands of nucleotides. RNA bases are A, C, G, and U (replaces the T in DNA), and its sugar is ribose. There are 3 major varieties:
- messenger RNA (mRNA)
- ribosomal RNA (rRNA)
- transfer RNA (tRNA)
Each of these varieties participates in protein synthesis.
Adenosine triphosphate (ATP)
Adenosine triphosphate (ATP)None of the chemical energy contained in the bonds of glucose molecules is used directly to power cellular work. Energy released during glucose catabolism is coupled to ATP synthesis. ATP acts as small packets of energy
Adenosine triphosphate (ATP) (Structure)
Structure: ATP is an adenine-containing RNA nucleotide to which 2 additional phosphate groups have been added (Fig. 2.23 p 55). ATP is a very unstable energy-storing molecule because its 3 negatively charged phosphate groups are closely packed and repel each other.
Adenosine triphosphate (ATP) (Structure) Cont
For liberating that energy, a hydrolysis reaction, catalyzed by an enzyme named ATPase, has to occur. The synthesis of ATP requires an energy source, and an enzyme called ATP synthase. The same amount of energy that is liberated when ATP’s terminal phosphate is cleaved off must be captured and used to reverse the direction of the reaction.
ATP supplies are replenished as glucose and other fuel molecules are oxidized and their bond energy is released.
Tendency of molecules or ions to scatter evenly throughout the entire volume of a solution (system) (Fig. 3.6 p 68) due to their continuously random motion provoked by their kinetic (thermal) energy. The overall effect is that particles move away from areas of higher concentration to those of lower concentration, so they diffuse along (down) their concentration gradient (gradient means difference). Fat-soluble solutes can difuse directely thorugh the membrane by dissolving in the lipids.
The greater their concentration gradient, the faster the diffusion. Other factors affecting the velocity of diffusion are: the size of the particles (the smaller, the faster) and the temperature (the higher, the faster).
Facilitated diffusion: passive transport of hydrophilic molecules (glucose, other sugars, amino acids) and ions with the participation of specialized transmembrane proteins, that may be classified as carriers or channels (for ions). .
Núcleo: esta limitado por una envoltura a través de la cual intercambian moléculas con el citoplasma. Contienen el material genético o ADN asociado a proteínas que en conjunto se denomina cromatina
Centríolos: son dos cuerpos cilíndricos que participan en la división celular. Esta organela se encuentra solo en las células animales
Mitocondrias: estructuras limitadas por una doble membrana externa e interna. Esta ultima forma o pliegue o crestas donde se realiza la respiración celular
Membrana plasmática: esta constituida por lípidos y proteínas y regula el pasaje de sustancias de un lado a otro
Lisosomas: vesículas especiales con membrana que participan en la degradación de las moléculas que ingresan en la célula
The chemical composition of the plasma membrane is:
· Phospholipids (the most abundant component)
· Cholesterol (in small quantities)
· Proteins (most with globular tertiary structure, some with quaternary)
· Polysaccharides (different from glycogen and starch)
There are 2 types of proteins associated with the lipid bilayer:
· Integral, which cross the lipid bilayer from one side to the other;
· Peripheral, which interact with only one face of the membrane, either the outer or the inner.
According to the chemical composition and structure of the plasma membrane, the substances that may cross it would be:
· Lipid-soluble molecules (=hydrophobic) and certain small molecules as gases (O2 and CO2) that may move through the lipid bilayer;
· Water-soluble substances (=hydrophilic) that cannot go through the lipid bilayer and that have to interact with certain integral transport proteins to move through the membrane, such as glucose and ions.
between them. This process is called diffusion and it may occur in an aqueous solution or in a mixture of gases, as the air we breathe.
· Temperature: the higher the temperature, the faster the diffusion of the particles, since there is an increase of their thermal kinetic energy;
· Size of particles: the smaller the particles, the faster the diffusion, since they can move farther at the same temperature;
· Concentration gradient: the bigger the concentration difference between the 2 regions, the faster the diffusion because the region at higher concentration looses particles faster and the one at lower concentration gains them also faster. When there is no concentration gradient, then the net flux equals zero because diffusion in both directions has the same magnitude.
Passive processes that ONLY require thermal kinetic energy (in the movement of ions also electric energy influences), without the need of ATP produced by the cell’s metabolism (=chemical reactions);; the substances move down their concentration (for non-electrolytes) or electrochemical gradient (for ions). Simple diffusion, osmosis and facilitated diffusion
Active processes that require thermal kinetic energy (in ions also electric energy) AND the energy contained in ATP.
Active processes: the cell provides the metabolic energy (ATP) needed to move the substances through the membrane. Primary and secondary active transport, and vesicular transport.
The increase of disorder provoked by the solute moving down its electrochemical gradient is greater than the decrease produced by the solute moving against its electrochemical gradient. These proteins move more than one substance at a time, and according to their relative directions they are classified as:
Symport: when the 2 solutes move in the same direction. Example: Na+ influx down its electrochemical gradient together with glucose influx against its concentration gradient in the absorptive cells of the intestine .
Antiport: when the 2 solutes move in opposite directions. Example: Na+ influx down its electrochemical gradient together with Ca++ efflux against its electrochemical gradient in skeletal muscular cells.
Endocytosis: movement of substances into the cell from the extracellular fluid.
Pinocytosis: a part of infolding plasma membrane surrounds a small volume of extracellular fluid, and the vesicle enters the cell (Fig. 3.13b p.77). This is a routine process of most cells, and is specially important in absorptive intestinal cells
non-electrolytes: each molecule constitutes a single particle, as sugars
electrolytes: are the salts that dissociate into ions, and the number of particles depends on the number of ions into which they dissociate. Examples: NaCl dissociates in 2 particles (Na+ and Cl-); CaCl2 dissociates in 3 particles (1Ca++ and 2 Cl-).
Cellular consequences of osmosis: when osmosis occurs there are dramatic changes in cell volume, and even the cell may be killed. If there is a water influx, the cell volume increases, and if it surpasses a critical value, the cell bursts. If on the contrary there is a water efflux, the volume decreases and the cell shrinks due to its dehydration; this process can also kill a cell.
Osmolarity is determined by multiplying molarity of the solute by the number of particles resulting from dissolving the substance in water. Thus, the osmolarity of a non-electrolyte is the same as its molarity since each molecule is a particle in the solution, for example 1 mol of glucose is a 1 osmolar solution.
Tonicity depends on 2 factors:
Leakage: they are always open;
Gated: are open or closed according to changes in membrane voltage, the presence of certain chemical signals (as neurotransmitters), and/or mechanical stimuli.
Like carriers, channels tend to be specific (for a certain ion, as Na+, K+, Ca++), show saturation, and their activity can be modulated (increased or decreased) by certain molecules.
Extracellular materials (p 107): these are substances contributing to body mass that are found outside the cells. They can be divided as:
Body fluids: such as interstitial fluid (between cells), blood plasma, and cerebrospinal fluid. These fluids are important transport and dissolving media. All are aqueous solutions.
Cellular secretions: include substances that aid in digestion (gastric and intestinal fluids), and those that act as lubricants (saliva, mucus, serous fluids).
Extracellular matrix: it is the most abundant extracellular material. It is a jellylike substance compose of proteins and polysaccharides with which most body cells are in contact. These molecules are secreted by the cells and self-assemble into an organized mesh in the extracellular space. It is the universal “cell glue” that helps to hold body cells together. It is particularly abundant in connective tissues, where its texture ranges from soft to hard rock.
Tissue: a group of cells that are similar in structure and perform a common or related function.
Primary types: There are 4 basic tissues, each with numerous subclasses:
muscle: movement (to be described in Chapter 9)nervous: control ,
Nervous tissue: Internal communication
• Brain, spinal cord, and nerves
Muscle tissue: Contracts to cause movement
• Muscles attached to bones (skeletal)
• Muscles of heart (cardiac)
• Muscles of walls of hollow organs (smooth)
Epithelial tissue: Forms boundaries between different
environments, protects, secretes, absorbs, filters
• Skin surface (epidermis)
• Lining of GI tract organs and other hollow organs
Connective tissue: Supports, protects, binds
other tissues together
• Fat and other soft padding tissue
Epithelial tissue: a sheet of cells that covers a body surface or lines a body cavity. There are 2 main types:
1. covering and lining: outer layer of the skin, lines body cavities, covers the walls and organs of the ventral cavity.
2. glandular: glands
Epithelia form boundaries between different environments. Nearly all substances received or given off by the body must pass through an epithelium. In its role as an interface tissue, epithelium accomplishes functions as:
- sensory reception
Differential characteristics of epithelia (cont.) (Supported by connective tissue)
Differential characteristics of epithelia (cont.) (Innervated and avacular)
Innervated and avascular: Epithelium is supplied by nerve fibers (innervated) and contains no blood vessels (avascular). Epithelial cells receive nutrients (including oxygen) by diffusion from blood vessels in the underlying connective tissue.
Differential characteristics of epithelia (cont.) (Regeneration)
Criteria for classifying epithelia
Each epithelium is given 2 names: the first indicates the number of cell layers present, and the second describes the shape of its cells.Based on the number of cell layer:
Simple epithelia: composed by a single cell layer;it is a very thin barrier;functions in absorption, secretion and filtration
Stratified epithelia: consisting of 2 or more cell layers stacked one on top of the other; common in high-abrasion areas where protection is important as the skin surface and the lining of the mouth
Criteria for classifying epithelia
- Squamous cells: flattened and scale-like;
- Cuboidal cells: boxlike, approximately as tall as they are wide;- Columnar cells: are tall and column shaped
A gland consists of one or more cells that synthesize and secrete a particular product named secretion, which is an aqueous fluid that usually contains proteins or lipids (including steroids). Secretion is an active cellular process. Glands can be classified according to:
Glandular epithelia (cont.)
- Endocrine glands: secrete their products to the interior of the body; they are structurally diverse; they secrete hormones (regulatory substances secreted by exocytosis directly into the extracellular fluid). We will describe them when we study the endocrine system.- Exocrine glands: secrete their products into body surfaces (skin) or into body cavities. Examples: mucous, sweat, oil and salivary glands, liver, pancreas
Glandular epithelia (cont.)Where they release their secretion: (Exocrine glands cont and Unicellular exocrine glands)
Exocrine glands can be classified according to the number of cells that form the gland in unicellular and multicellular.- Unicellular exocrine glands: goblet cells are sprinkled in the epithelial linings of the intestinal and respiratory tracts together with columnar cells with other functions. Goblet cells produce mucin, a complex glycoprotein that dissolves in water when secreted. Once dissolved, mucin forms mucus, a slimy coating that protects and lubricates surfaces
Glandular epithelia (cont.) Multicellular exocrine glands
Criteria for classifying multicellular exocrine glands.
- Compound: branched duct
- Tubular: secretory cells form tubes
- Alveolar: secretory cells form small, flasklike sacs (aveolus)
- Tubuloalveolar: with both of these types
- Merocrine: secrete their products by exocytosis as they are produced; secretory cells are not altered. Example: most sweat glands, salivary glands- Holocrine: secretory cells accumulate their products within them until they rupture. These cells are replaced by the division of underlying cells. These secretions include the synthesized product and cell fragments. Only example: sebaceous (oil) glands of the
It is found everywhere in the body; it is the more abundant and most widely distributed of the tissues. It can be classified in 4 main classes and several subclasses:
- connective tissue proper
- cartilage tissue (to be described in Chapter 6: Bones and skeletal tissues)
- bone tissue (to be described in Chapter 6: Bones and skeletal tissues)- blood
The major functions of the connective tissue are:
- binding and support
- thermal insulation
- transportation of substances within the body
The properties of the cells and the composition and arrangement of extracellular matrix elements vary tremendously among the classes. There is an amazing diversity, with each class (subclass) adapted to perform its specific function.
Areolar connective tissue
-Ground substance: unstructured material that fills the space between the cells and contains the fibers. Its composition in this subclass is:
- Interstitial fluid- Cell adhesion proteins: as fibronectin, laminin, etc, which serve as a connective tissue “glue” that allows connective tissue cells to attach themselves to matrix elements
- Proteoglycans: protein core to which glycosaminoglycans are attached, for example chondroitin, keratan sulfates, hyaluronic acid. Proteoglycans tend to form huge aggregates. They form a substance that varies from a fluid to a viscous gel.The ground substance holds large amounts of fluid and functions as a molecular sieve, through which nutrients and other dissolved substances can diffuse between the blood capillaries and the cells
Fibers: they provide support to this class of connective tissue. There are 3 types:
Elastic: long, thin fibers forming branching networks in the extracellular matrix. These fibers contain a rubberlike protein named elastin, that allows them to stretch and recoil. Elastic fibers are found where greater elasticity is needed, as in the skin, lungs, and blood vessel walls
- fat cells: function as nutrient storing
- white blood cells: such as neutrophils, eosinophils, lymphocytes, all playing a role in the defense of the organism
- mast cells, macrophages and plasma cells: all playing a role in the tissue response to injury. The textbook describes mast cells and macrophages.
Connective tissue proper: classified as loose (areolar, adipose, and reticular) and dense (regular and irregular).
Areolar connective tissue: It is the most widely distributed connective tissue in the body. It is present in all mucous membranes forming the lamina propria.
Its main functions are:
- supporting and binding other tissues (role of its fibers);
- holding body fluids (role of the ground substance);
- defending against infection (role of white blood cells and macrophages);
- storing nutrients as fat (role of the fat cells).
It usually accumulates in subcutaneous tissue, where it acts as shock absorber, as thermal insulation, and as energy storage site. It is present also around the kidneys, behind the eyeballs and as fat depots in the abdomen and hips.
Reticular tissue :It is similar to areolar tissue, but the only fibers present in its extracellular matrix are the reticular fibers. It is present in lymph nodes, spleen, and bone marrow.
This tissue forms the tendons (cords that attach muscles to bones), fascia (fibrous membranes that wrap around muscles, groups of muscles, blood vessels, and nerves), and ligaments (structures that bind bones together at joints).
Dense irregular tissue : In this tissue the bundles of collagen fibers are much thicker and are arranged irregularly (they run in more than one plane). It forms sheets in body areas where tension is exerted from many different directions, as in the dermis of the skin, and in fibrous joint capsules.
Dense elastic tissue: Contains a high proportion of elastic fibers and allows recoil of tissue following stretching, as in walls of large arteries.
Connective Tissue (Covering and lining membranes)
The body’s membranes incorporate more than one type of tissue, thus they can be considered as simple organs. There are 3 types of covering and lining membranes:
- serousAll have a common feature: they are continuous multicellular sheets composed of at least 2 primary tissue types: an epithelium bound to an underlying layer of connective tissue proper
Body cavities.Mucous membranes: they line body cavities that open to the exterior of the organism, such as those of hollow organs of the digestive, respiratory, and urogenital tracts. They are moist membranes bathed by secretions or urine. The term mucosa refers to the location of the membrane, not to its cell composition, which varies. Most of these membranes contain either stratified squamous or simple columnar epithelia.
- pleura: serosa lining the thoracic wall and covering the lungs
- pericardium: serosa enclosing the heart
- peritoneum: serous membranes of the abdominopelvic cavity and viscera.
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