Unit 1 Exam

Organizational Levels of Living Systems

Overview of Organizational Levels

Living systems are organized into several levels, starting from the chemical level to the organism level.
The levels include:
Chemical: atoms and molecules
Cellular: cells and their organelles
Tissue: group of similar cells with a common function
Organ: contains 2 or more types of tissues
Organ system: organs that work closely together
Organism: all organ systems comprise organism
Each level builds upon the previous one, with increasing complexity and functionality.
Example: Atoms combine to form molecules, which form cells, the basic unit of life.
Understanding these levels is crucial for studying anatomy and physiology.

Importance in Biology

Each organizational level plays a critical role in maintaining life processes.
Disruption at any level can lead to disease or dysfunction.
For instance, cellular dysfunction can lead to tissue damage, affecting organ function.
The study of these levels helps in understanding how systems interact within the body.

Homeostatic Mechanisms

Components of Homeostasis

Homeostasis refers to the maintenance of a stable internal environment despite external changes.
Key components include:
Receptor (sensor and afferent pathway): monitors environment, responds to stimuli (changes in controlled variables)
Control center: determines the set point at which the variable is maintained, receives input from receptor and determines appropriate response
Effector (efferent pathway): receives output from control center and responds by feedback to reduce or increase the variable
Example: In temperature regulation, thermoreceptors detect temperature changes, the hypothalamus acts as the control center, and sweat glands serve as effectors.

Feedback Mechanisms

Positive Feedback: Less common mechanism, enhances or accelerates a process, amplifying effect (labor contractions release oxytocin enhancing each contraction)
Negative Feedback: Most common mechanism, reduces the output or activity of a system and decreases it within a narrow range (set point) (regulation of blood glucose levels)
Both mechanisms are essential for maintaining homeostasis and responding to changes in the environment.

Atomic Structure and Bonding

Components of the Atom

Atoms consist of protons, neutrons, and electrons.
Protons and neutrons are found in the nucleus, while electrons orbit around the nucleus.
Atomic number is determined by the number of protons, while atomic mass is the sum of protons and neutrons.
An isotope is a different form of an element distinguished by different numbers of neutrons (C^12, C^13, C^14)
A valence shell is the outermost electron shell of an atom, atoms are stable if valance shell is full (usually contains 8 electrons) meaning electrons are unlikely to be pulled away. If valence shell is not full, the atom is reactive (Ex: Hydrogen)

Types of Chemical Bonds

Ionic Bonds: Formed when electrons are transferred from one atom to another creating an electrical charge (loss or gain of electrons) and ongoing close association between ions of opposite charges creating cations; have positive charge due to loss of electron (+) and anions; have negative charge due to gain of electrons (-).
Covalent Bonds: Formed when atoms share electrons in a mutually stabilizing relationship and stronger than ionic bonds (like next-door neighbors whose kids hang out first at one home than at the other).
Nonpolar Covalent bonds: electrons in two atoms' overlapping atomic orbitals are shared to fill the valance shell of both atoms, stabilizing both atoms involved (electrically neutral as in CO2). Single covalent bonds, a single electron is shared between 2 atoms. In double covalent bonds, 2 pairs of electrons are shared between 2 atoms. In triple covalent bonds, 3 electron pairs are shared between 2 atoms.
Polar covalent bonds: Electrons are not shared equally between atoms of molecules. Molecule has a positive and negative side or a pole (Ex: water)
Peptide bond: covalent bond between 2 amino acids that forms by dehydration synthesis.
Disulfide bond: a covalent bond between sulfur atoms and polypeptides.
In biological molecules, anytime you see a O2, or N atom bound to a C or a H atom it will always be a polar bond
Understanding these bonds is crucial for grasping molecular interactions in biological systems.
Hydrogen bonds: forms when a weakly positive hydrogen atom already bonded to one electronegative atom (oxygen in water molecule) is attracted to another electronegative atom from another molecule. Provides attraction between molecules and is responsible for the surface tension of water. Also, important for forming intramolecular bonds, as in protein structure.

Molecular Properties

Size: refers to the overall dimensions of a molecule, described as the molecules bond lengths, bond angles, and overall shape. Factors influencing size are the number and types of atoms it contains, as well as the arrangement of these atoms.
Polarity: measurement of how evenly electric charged is distributed across a molecule. Rises from differences in electronegativity between atoms in a molecule.
Charge: Refers to the excess of deficiency of electrons in a molecule, resulting in a positive or negative charge.

pH

Acid: substances that release hydrogen ions (H+) when dissolved in water, acids have a pH below 7
Base: substances that accept hydrogen ions (H+) and release hydroxyl ions (OH-) when dissolved in water, pH is greater than 7.
pH: measures relative concentration of hydrogen ions, based on the number or protons in solution, expressed in terms of mole per liter. Each successive change on pH scale represents a tenfold changed in H+ concentration
pH 7 = neutral.
pH below 7 = acidic.
pH above 7 = basic.
Buffers: chemicals that regulate pH change.

Chemical Reactions

Polymer: chainlike molecules made of many similar or repeating units (monomers), many biological molecules are monomers such as a carbohydrates and proteins.
Dehydration synthesis: monomers are joined to form polymers through the removal of water molecules. A hydrogen ion is removed from on monomer while a hydroxyl group is removed from the monomer it is to be joined with. Monomers united and water is released.
Hydrolysis: polymers are broken into monomers through the addition of water molecules. As water molecule is added to each bond, the bond is broken, and the monomers are released.
Reactant: general terms for one or more substances that enter into the reaction (Na + Cl ions are reactants of table salt), the one or more substances produced by chemical reactions are called the product.
Synthesis reactions: chemical reaction that results in 2 components bonding to make larger molecule (Note + book = Notebook)
Decomposition reaction: Bonds between larger molecules are broken down (Bookworm = Book + Worm)
Exchange reaction: Bonds are both formed and broken such that the components of the reactants are rearranged (Notebook + Worm = Note + Bookworm).

Fundamental Macromolecules

Carbohydrates: contain carbon, hydrogen, and oxygen. Include sugars and starches. Classified according to size.
Monosaccharides: simple sugars. Single chain or single-ring structures. Contains 3 to 7 carbon atoms. Ex: glucose (blood sugar), fructose, galactose, ribose, and deoxyribose.
Disaccharides: 2 simple sugars joined by dehydration synthesis. Ex: sucrose, lactose, and maltose.
Polysaccharides: long, branching chains of linked simple sugars. Large, insoluble molecules, function as storage products. Ex: starch and glycogen.
Lipids: most abundant are the triglycerides, phospholipids, and steroids. Contain carbon, hydrogen, and oxygen (carbon and hydrogen outnumber oxygen). Insoluble in water but soluble in other lipids.
Neutral fats (triglycerides): Found in fat deposits. Source of stored energy and composed of 3 fatty acids and on glycerol molecule.
Saturated fats: contain only single covalent bonds. Chains are straight and exist as solids at room temperature since molecules packed closely together.
Unsaturated fats: contains 1 or more double covalent bonds causing chains to kink. Exist as liquid oils at room temperature and heart healthy.
Phospholipids: contain 2 fatty acids rather than 3. Phosphorus-containing "head" carries an electrical charge and is polar. Charged region interacts with water and ions while the fatty acid chains "tails" do not. Form cell membranes.
Steroids: Formed of 4 interlocking rings, include cholesterol, bile salts, vitamin D, and some hormones. Some cholesterol is ingested from animal products, but the liver also makes cholesterol. Cholesterol is the basis for all steroids in the body.
Prostaglandins: one of a group of signaling molecules, derived from unsaturated fatty acids. Omega-3 fatty acids in fish stimulate the production of certain prostaglandins that help regulate aspects of blood pressure and inflammation, reducing risk of heart disease. Also, sensitive nerves to pain.
Proteins: account for over half of the body's organic matter. Provide for construction materials for body tissues, play a vital role in cell function, and acts as enzymes, hormones, and antibodies. Contain C, O2, H, N, and sometimes sulfur. Built from amino acids.
Amino acid structure: contains an amine group (NH2) and acid/ carboxyl group (COOH), vary only by R groups. All consist of a central C bonded to a H atom, alkaline base (NH2), acidic carboxyl group (COOH) and an R group. All amino acids contain an acid and a base making them great buffers, helping the body regulate acid-base balance.
R groups: 20 unique R groups. Polar and nonpolar side chains charged and uncharged side chains, and sulfur containing side chains.

Structural Levels of Proteins

Primary structure: linear sequence of amino acids
Secondary structure: Alpha helixes and beta-pleated sheets. Formed by polar interactions of nearby amino acids.
Tertiary structure: 3D shape of protein formed by side-chain interactions of different amino acids. Most significant in determination of protein function. Impacted heavily by changed in pH or temperature.
Quaternary structure: formed when multiple peptide molecules interact (hemoglobin).
Denaturation: is a change in structure of a molecule through physical or chemical means. Denatured proteins lose their functional shape and are no longer able to carry out their jobs.

Proteins Function as Enzymes

Enzymes: specific type of protein that functions as a catalyst; a molecule that speeds up the rate of a chemical reactions (means more Rxns/sec). Essential in allowing organisms to complete the amount of chemistry they need to stay alive (metabolism). Enzymes do this by lowering the amount of energy required for a reaction to take place (activation energy). Like all proteins, enzymes are very specific and must have a proper 3D structure in order to function, commonly end in -ase prefix indicates what is being broken down (lipase breaks down lipids)
Substrate: reactant in an enzymatic reaction. This occurs on regions of the enzyme known as active sites. Any given enzyme catalyzes just one type of chemical reaction. This characteristic, called specificity, is due to the fact that a substrate with a particular shape and electrical charge can bind only to an active site corresponding to that substrate.
Other functions of proteins: Protein is important for building, repairing, and maintaining muscle tissues but also contributes to all body tissues, from skin to brain cells. Also, certain proteins act as hormones. basic and acidic components enable proteins to function as buffers in maintaining acid–base balance, but they also help regulate fluid–electrolyte balance. Proteins attract fluid, and a healthy concentration of proteins in the blood, the cells, and the spaces between cells helps ensure a balance of fluids in these various “compartments.” Moreover, proteins in the cell membrane help to transport electrolytes in and out of the cell, keeping these ions in a healthy balance. Like lipids, proteins can bind with carbohydrates. They can thereby produce glycoproteins or proteoglycans, both of which have many functions in the body. Proteins can also be used for energy when carbohydrates and fat intake is inadequate.

Nucleic Acids

Nucleotides: one of a class of organic compounds composed of 3 subunits:
1) one or more phosphate groups
2) a pentose sugar (5-carbon), either deoxyribose or ribose.
3) a nitrogen-containing base: adenine, cytosine, guanine, thymine or uracil.
Deoxyribonucleic acid (DNA): nucleotide that stores genetic information. DNA contains deoxyribose (one less atom of oxygen than ribose) plus one phosphate group and on nitrogen-containing base. "Choices" of a base are adenine, thymine, guanine, and cytosine. Provides instructions for every protein in the body. Organized by complementary bases to form a double-stranded helix. Replicates before cell division.
Ribonucleic acid (RNA): a ribose-containing nucleotide that carries out DNA's instructions for protein synthesis. RNA contains a ribose, 1 phosphate group, and one nitrogen-containing base, the "choices" are adenine, cytosine, guanine, and uracil. Created from a template of DNA. Organized by complementary bases to form a single-stranded helix. The 3 varieties are messenger (mRNA), transfer (tRNA) and ribosomal RNA.
Pyramidine: is a nitrogen-containing base with a single ring structure (cytosine, thymine, and uracil)
Purine: a nitrogen-containing molecule with a double ring structure (adenine and guanine).

Cellular Processes and Metabolism

Organelle Functions

Ribosomes: Protein builders/protein synthesis. Made of protein and ribosomal RNA.
Cytoplasm: Maintains cell shape and consistency throughout the cytoskeleton. Contains cytosol (fluid that suspends other elements), organelles (metabolic machinery of the cell, "little organs") and inclusions (chemical substances, such as stored nutrients or cell products).
Cell membrane: acts as a barrier, separating cell organelles from external surroundings. Also, it is semi-permeable, composed of back-to-back phospholipids. Contains cholesterol which contributes to the fluidity of the membrane. Acts in transport of substances in and out of the cell.
Intermediate filament: Regulates cell shape, anchors the nucleus and organelles in place, integrates the cytoskeleton, regulates signaling pathways, and moves proteins to specific locations.
Rough Endoplasmic reticulum: Where material is made, produces membranes that are going to be used within the cell. Also, synthesis and modification or proteins destined for the cell membrane or for export from the cell. Stubbed with ribosomes.
Nucleus: Control center, genetic material of the cell is found inside. Determines what type of cell is going to become and controls it. Contains holes allowing material to move in and out.
Nucleolus: Ribosome production area within the nucleus. Chromosomes produce ribosomal RNA.
Chromatin: Packages DNA into smaller volumes to fit in cells, strengthens DNA to allow mitosis and meiosis and prevents DNA damages, organize genetic information and carry the genetic material of an organism in the form of DNA plus structural proteins called histones.
Nuclear envelope: Separates the nucleoplasm from the cytoplasm and regulates passage of substances to and from the nucleus.
Golgi Apparatus: responsible for sorting, modifying, and shipping off the products that come from the rough ER (post office/shipping).
Golgi vesicle: transport, modify, and package proteins and lipids, deliver molecules to certain destinations.
Vacuole: stores water and keeps the balance and pressure to keep cell inflated. In animal cell, it is mainly used for endo and exocytosis.
Peroxisome: metabolizes lipids, chemical detoxifications, serves to transfer hydrogen from various molecules to oxygen, producing hydrogen peroxide (H2O2) can neutralize poisons like alcohol.
Secretory vesicle: stores and transports material (hormones, etc.)
Smooth Endoplasmic Reticulum: produces lipids, cholesterol, steroid hormones, regulates the concentration of Ca++, metabolizes carbohydrates and important role for detoxification (breaking down toxins)
Lysosome: has digesting enzymes that break down and digest unneeded cellular material (Autophagy = self-eating) important for breaking down foreign material as well.
Microfilament: involved in endo and exocytosis, cytokinesis, amoeboid movements, cell motility, and changes in cell shape.
Centrosome: organizing centers, provides structure for the cell and organizes cells cytoskeleton, as well in cellular function such as cell mobility, adhesion, polarity, and intracellular trafficking.
Microtubule: have a role in cell movement, cell division, and transporting materials within cells.
Mitochondria: in the inner membrane proteins, enzymes and other molecules perform a biochemical reaction (cell respiration) these reactions covert energy stored in nutrient molecules in ATP (ATP generator/powerhouse of the cell).
Cytoskeleton: network of protein structures that extend throughout the cytoplasm. Provides the cell with an internal framework. 3 different types of elements: microfilaments (actin), intermediate filaments (fibrous), and microtubules (tubulin).

Metabolism Overview

Catabolism: metabolic process that breaks down complex molecules into simpler ones, releasing energy in the process. This energy is then used by the body for various functions such as maintaining body temperature, muscle contraction, and cellular activities. Ex: during digestion, large food molecules like carbohydrates, proteins, and fats are broken down into smaller molecules like glucose, amino acids, and fatty acids. This breakdown releases energy that the body can use immediately or store for later use.
Anabolism: involves the synthesis of complex molecules from simpler ones, requiring energy input. This process is essential for growth, repair, and maintenance of tissues in the body (building up). Ex: during protein synthesis, amino acids are assembled into proteins, which are then used to build and repair muscles and other tissues. Similarly, in the process of glycogenesis, glucose molecules are combined to form glycogen, which is stored in the liver and muscles for future energy use.
Together they create metabolism
Metabolism: is the sum of all chemical reactions that occur within a living organism to maintain life. It consists of two main processes: catabolism and anabolism.
ATP (adenosine triphosphate): composed of a ribose sugar, an adenine base, and 3 phosphate groups. ATP is classified as a high energy compound between 2 covalent bonds linking its 3 phosphates store a significant amount of potential energy. This energy helps fuel the body's activities, from muscle contraction to the transport of substances in and out of cells to anabolic chemical reactions. Energy is released by breaking high-energy phosphate bond (3rd). ATP is replenished by oxidation of food fuels. Fuels reactions requiring an input of energy (ATP - ADP + P1 + Energy)
Phosphorylation: the addition of a phosphate group to an organic compound, in this case, resulting in ATP.

Solute Membrane Transport

Intracellular fluid: nucleoplasm and cytosol. Solution containing gases, nutrients, and salts dissolved in water.
Interstitial fluid: fluid on the exterior of the cell. Contains thousands of ingredients, such as nutrients, hormones, neurotransmitters, salts, and waste products.
Simple diffusion: moving molecules across an area of higher concentration to an area of lower concentration until equilibrium is reached. (higher concentration to lower concentration). No energy is required, it is a passive process relies on the concentration gradient. Ex: small polar molecules (water).
Channel-Mediated facilitated diffusion: move down specific channel proteins and specialized transport mechanisms in the membrane. (higher concentration to lower concentration). no energy required, molecules move down their specific channel proteins, relies on the concentration gradient. channel proteins are involved from pores in the membrane. allows ions such as Na+, K+. Ca++, and Cl-, water, and small polar molecules (glucose and amino acids).
Carrier-Mediated facilitated diffusion: move down their gradient with the help of carrier proteins, these proteins bind to specific molecules which transport, undergo a conformational change, then release molecules on the other side of the membrane. (higher concentration to lower concentration). no energy required, relies on the concentration gradient. carrier proteins involved (glucose transporter, nucleosides transporters, etc.). small polar molecules (glucose and amino acids), ions, and nucleosides
Active transport: moves against concentration gradient, molecules move from a lower concentration to a high concentration. requires energy which is ATP because it works in the opposite direction of the gradient. sodium-potassium pump (Na+ and K+), sodium-hydrogen antiporter, (Na+ and H+), and calcium pump (Ca+).
Secondary Active transport: moves against their gradient (lower to higher concentration) and uses the electrochemical energy created by the primary active transport rather than from ATP. proteins are called cotransporters or exchangers (Ex: sodium-glucose cotransporters). sodium ions (Na+), glucose, calcium ions (Ca+), amino acids, and protons (H+).
Pinocytosis: referred to as “cell drinking” brings fluid containing dissolved substances into a cell through membrane vesicles, brings in small particles in fluid. Process starts with initiation; cell membrane forms a small pocket around extracellular fluid. Next is engulfment; cell membrane pocket deepens, enclosing the fluid and solutes within a vesicle. Next is internalization; vesicle moves into cytoplasm where it fuses with lysosomes for digestion or transport the contents to other cells. Not particularly picky, brings in ions, nutrients, hormones, and small proteins.
Phagocytosis: referred to as “cell eating” is the endocytosis of large particles. Process starts with recognition and attachment; cell recognizes and attaches itself to the particle it will engulf. Next is engulfment; cell membrane extends around particle. Next, the membrane forms a vesicle containing the particle. Next, the vesicle fuses with a lysosome. Next, the lysosome uses enzymes and digests and breaks down material. Lastly, the digested material is expelled from the cell or used for other cellular functions. Particles brought into cells are bacteria, dead or dying cells, large particles, foreign particles, and pathogens.
Receptor-mediated endocytosis: endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance. Process starts with ligands binding to receptor proteins on the cell surface. Next, the binding triggers the formation of receptor-ligand complexes. Next, these complexes cluster in regions of the membrane forming a coated pit. Next, these pits pinch off to form vesicles. Next, the coat is removed and the vesicle fuses with endosomes. Lastly, the contents are sorted, ligands may be transported to lysosomes for digestion while receptors can be recycled back to the cell surface. Particles brought into the cell are hormones, nutrients, vitamins, and antibodies.
Exocytosis: referred to as “taking out of the cell” is the process of a cell exporting material using vesicular transport. Process starts with materials packaged into vesicles within the cell. Next, vesicles are transported to the cell membrane along the cytoskeleton. Next, vesicle membrane fuses with the cell membrane. Next, the contents are released from the vesicles into extracellular space. Lastly, the vesicle membrane becomes part of the cell membrane. Particles brought into the cell are neurotransmitters, hormones, enzymes, waste products, proteins and lipids.
Endocytosis: cellular process in which a cell engulfs external substances, bringing them into the cell. This process involves the cell membrane folding around the substance to form a vesicle, which then pinches off into the cell's interior. 2 main types; phagocytosis and pinocytosis.

Osmosis

Osmosis: the diffusion of water through a semipermeable membrane down its concentration gradient. Water molecules move through the membrane to balance solute concentrations. Water will equalize its own concentration by diffusing to the side of lower water concentration until its equal on both sides of the membrane. Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water, based on the solute concentration relative to the inside of the cell.
Hypotonic: When a cell is placed in a hypotonic solution there is a massive water influx, water enters the cell from an area of lower concentration to a higher concentration. The cell begins to swell as it takes in more water. This excessive water intake can cause the cell to burst.
Hypertonic: When a cell is placed in a hypertonic solution there is a water efflux, water leaves the cell from an area of lower concentration to a higher concentration. Cell begins to shrink as it loses water. The cell shrinks and becomes wrinkled.
Isotonic: When a cell is placed in an isotonic solution, water moves in and out of the cell at equal rates. Cell maintains its shape and size because there is no gain or loss of water. The cell remains in equilibrium.

Fundamental Cellular Processes

Mitosis: cells have the same number of chromosomes as the parent cell and is used in the body to produce new somatic cells (growth and repair).
Meiosis: cells have half the number of chromosomes as the parents' cell and is used to produce gametes (egg and sperm) for sexual reproduction.
Transcription: the process by which the genetic information in DNA is copied into messenger RNA (mRNA). This is the first step in gene expression, leading to the production of proteins. Here's a brief overview of the transcription process

Initiation: The enzyme RNA polymerase binds to a specific region of the DNA called the promoter. This signals the start of a gene.
Elongation: RNA polymerase moves along the DNA, unwinding the double helix and synthesizing a complementary RNA strand from the DNA template. The RNA strand grows in the 5' to 3' direction.
Termination: When RNA polymerase reaches a terminator sequence on the DNA, it releases the newly formed mRNA strand and detaches from the DNA.

Translation: refers to the process by which the genetic code carried by messenger RNA (mRNA) is decoded to produce a specific sequence of amino acids, which then fold into a functional protein. This process occurs in the ribosome, a cellular structure that facilitates the linking of amino acids in the correct order.

Initiation: The ribosome assembles around the target mRNA. The first tRNA (transfer RNA) binds to the start codon on the mRNA.
Elongation: The ribosome travels along the mRNA, and tRNAs bring the appropriate amino acids to the ribosome. Each tRNA matches its anticodon with the codon on the mRNA, ensuring the correct amino acid sequence.
Termination: When the ribosome reaches a stop codon, the translation process ends. The newly formed polypeptide chain is released and will fold into a functional protein.

Tissue Types and Functions

Four General Tissue Types

Epithelial Tissue (epithelium): sheet of cells that covers body surfaces or cavities. 2 main forms: covering and lining epithelia (on external and internal surfaces, ex: skin) and glandular epithelia (secretory tissue in glands, ex: salivary glands). Main functions are protection, absorption, filtration, excretion, secretion, and sensory reception.
Cells have polarity (top and bottom)
– Apical surface, upper free side, is exposed to surface or cavity
▪ Most apical surfaces are smooth, but some have specialized fingerlike
projections called microvilli
– Basal surface, lower attached side, faces inwards toward body
▪ Attaches to basal lamina, an adhesive sheet that holds basal surface of
epithelial cells to underlying connective tissues
– Both surfaces differ in structure and function
• Epithelial tissues need to fit closely together
▪ Specialized structures bind adjacent epithelial cells together forming sheets
– Tight junctions
– Desmosomes
• No blood vessels are found in epithelial tissue
▪ Must be nourished by diffusion from underlying connective tissues
• Epithelia are supplied by nerve fibers, however

Glandular epithelia

Gland
– One or more cells that makes and secretes an aqueous fluid called a secretion
• Classified by:
– Site of product release:
▪ Endocrine: internally secreting (example: hormones)
▪ Exocrine: externally secreting (example: sweat)
– Relative number of cells forming the gland
▪ Unicellular (example: goblet cells) or multicellular (example: salivary)

Endocrine glands

– Ductless glands
▪ Secretions are not released into a duct; are released into surrounding
interstitial fluid, which is picked up by circulatory system
– Secrete (by exocytosis) hormones, messenger chemicals that travel through
lymph or blood to their specific target organs
– Target organs respond in some characteristic way

• Unicellular exocrine glands
– The only important unicellular glands are mucous cells and goblet cells
– Found in epithelial linings of intestinal and respiratory tracts
– All produce mucin, a sugar-protein that can dissolve in water to form mucus, a
slimy protective, lubricating coating
• Multicellular exocrine glands
– Multicellular exocrine glands are composed of a duct and a secretory unit
– Mode of secretion
▪ Merocrine: most secrete products by exocytosis as secretions are produced
(sweat, pancreas)
▪ Holocrine: accumulate products within, then rupture (sebaceous oil glands)
▪ Apocrine: accumulate products within, but only apex ruptures; whether this
type exists in humans is controversial (maybe mammary cells?)

Connective tissue

Connective tissue is the most abundant and widely distributed of primary tissues
• Major functions: binding and support, protecting, insulating, storing reserve fuel, and
transporting substances (blood)
• Four main classes
– Connective tissue proper
– Cartilage
– Bone
– Blood

Ground Substance and ECM

Cells are suspended/embedded in extracellular matrix (ECM) (protein-sugar mesh)
– Matrix supports cells so they can bear weight, withstand tension, endure abuse
– Unstructured gel-like material that fills space between cells
▪ Cell adhesion proteins and Proteoglycans (sugar proteins): the “glue”
▪ Interstitial Fluid (water amount affects viscosity of ground substance)
▪ Protein Fibers
– Collagen: Strongest and most abundant type
– Elastic fibers: Networks of fibers that allow for stretch and recoil
– Reticular: branched collagenous fibers (unique composition) that offer more “give”
“Blast” cells
▪ Immature form of cell that actively secretes ground substance and ECM fibers
▪ Fibroblasts found in connective tissue proper, Chondroblasts found in
cartilage, Osteoblasts found in bone
– “Cyte” cells
▪ Mature, less active form of “blast” cell that maintains health of matrix
▪ Chondrocytes found in cartilage, Osteocytes found in bone
– Fat cells
▪ Store nutrients
– Immune Cells
▪ Neutrophils, eosinophils, lymphocytes
– Tissue response to injury
▪ Mast cells
– Initiate local inflammatory response
▪ Macrophages
– Phagocytic cells that “eat” dead cells, microorganisms
Connective tissue proper
– Consists of all connective tissues except bone, cartilage, and blood.
Two subclasses
▪ CT proper: loose connective tissues
– Areolar
– Adipose
– Reticular
▪ CT proper: dense connective tissues
– Dense regular
– Dense irregular
– Elastic

Muscle Tissue

Highly vascularized
• Responsible for most types of movement
– Muscle cells possess myofilaments made up of actin and myosin proteins that
bring about contraction

Nervous Tissue

Neurons are branching cells; cell processes that may be quite long extended from the nucleus-containing cell body; also contributing to nervous tissue are nonexcitable cells.
Function: Neurons transmit electrical signals from sensory receptors and to effectors (muscles and glands); supporting cells support and protect neurons.
Location: Brain, spinal cord, and nerve.

Tissue Subtypes and Locations

Simple squamous epithelium: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia.
Function: Allows materials to pass by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae (linings of ventral body cavity).
Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; serosae.
Simple cuboidal epithelium: Single layer of cubelike cells
with large, spherical central nuclei
Function: Secretion and absorption.
Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface.
Simple columnar epithelium: Single layer of tall cells with
round to oval nuclei; many cells bear microvilli, some bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells).
Function: Absorption; secretion of mucus,
enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action.
Location: Nonciliated type lines most of the digestive tract (stomach to rectum), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus.
Pseudostratified columnar epithelium: Single layer of cells of differing
heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting cells and bear cilia.
Function: Secrete substances, particularly mucus; propulsion of mucus by ciliary action.
Location: Ciliated variety lines the trachea and
most of the upper respiratory tract; nonciliated type in males’ sperm-carrying ducts and ducts of large glands
Stratified squamous epithelium: Thick epithelium composed of
several cell layers: basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers.
Function: Protects underlying tissues in areas subjected to abrasion
Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the
epidermis of the skin, a dry epithelium.
Transitional epithelium: Resembles both stratified
squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous like, depending on degree of organ stretch
Function: Stretches readily, permits stored urine to distend urinary organ
Location: Lines the ureters, bladder, and part of the urethra
Connective tissue proper loose areolar: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some white blood cells
Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid
Location: Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; packages organs; surrounds capillaries
Connective tissue proper loose adipose: Matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet.
Function: Provides reserve food fuel; insulates against heat loss; supports and protects organs
Location: Under skin in subcutaneous tissue; around kidneys and eyeballs; within abdomen; in breasts.
Connective tissue proper loose reticular: Loose network of reticular fibers in a gel-like ground substance; reticular cells lie on the fibers
Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages
Location: Lymphoid organs (lymph nodes, bone marrow, and spleen)
Connective tissue proper dense regular: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the
fibroblast.
Function: Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction
Location: Tendons, most ligaments, aponeuroses
Connective tissue proper dense irregular: Primarily irregularly arranged collagen fibers; some elastic fibers; fibroblast
is the major cell type
Location: Fibrous capsules of organs and of joints; dermis of the skin; submucosa of digestive tract.
Function: Withstands tension exerted in many directions; provides structural strength
Connective tissue proper dense elastic: Dense regular connective tissue containing a high proportion of elastic fibers
Function: Allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration
Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes
Connective tissue cartilage hyaline: Amorphous but firm matrix;
collagen fibers form an imperceptible network; chondroblasts produce the matrix and when mature (as chondrocytes) lie in lacunae
Function: Supports and reinforces; serves as resilient cushion; resists compressive stress
Location: Forms most of the embryonic skeleton; covers the ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx.
Connective tissue proper cartilage elastic: Similar to hyaline cartilage, but more elastic fibers in matrix
Function: Maintains the shape of a structure while allowing great flexibility
Location: Supports the external ear (pinna), epiglottis
Connective tissue cartilage fibrocartilage: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate
Function: Tensile strength allows it to absorb compressive shock.
Location: Intervertebral discs; pubic symphysis; discs of knee joint
Connective tissue cartilage bone: Hard, calcified matrix containing
many collagen fibers: osteocytes lie in lacunae. Very well vascularized
Function: Supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis)
Location: Bones.
Connective tissue cartilage blood: Red and white blood cells in a fluid matrix (plasma).
Function: Transports respiratory gases, nutrients, wastes, and other substances
Location: Contained within blood vessels.
Skeletal muscle: Long, cylindrical, multinucleate cells; obvious striations
Function: Voluntary movement; locomotion; manipulation of the environment; facial expression; voluntary control
Location: In skeletal muscles attached to bones or occasionally to skin.
Cardiac muscle: Branching, striated, generally uninucleate cells that connect at specialized junctions (intercalated discs)
Function: As it contracts, it propels blood into the circulation; involuntary control
Location: The walls of the heart
Smooth muscle: Cells are spindle shaped
(tapered on both ends) with central nuclei; no striations; cells arranged closely to form sheets.
Function: Propels substances or objects (foodstuffs, urine, a baby) along internal passageways; involuntary control
Location: Mostly in the walls of hollow organs