Midterm Review Chapter 1-7, 22

MIDTERM REVIEW CH1-7,22 (PHYSIO) Physiology is the study of the normal functioning of a living organism and its component parts, including all its chemical and physical processes. The term physiology literally means “knowledge of nature.” Human Genome Project scientists thought that by identifying and sequencing all the genes in human DNA, they would understand how the body worked. However, as research advanced, scientists had to revise their original idea that a given segment of DNA contained one gene that coded for one protein. It became clear that one gene may code for many proteins. LEVELS OF ORGANIZATION At the most basic level of organization shown in Figure 1.1, atoms of elements link together to form molecules. Collections of molecules in living organisms form cells, the smallest unit of structure capable of carrying out all life processes. A lipid and protein barrier called the cell membrane (also called the plasma membrane) separates cells from their external environment. Simple organisms are composed of only one cell, but complex organisms have many cells with different structural and functional specializations. Collections of cells that carry out related functions are called tissues {texere, to weave}. Tissues form structural and functional units known as organs {organon, tool}, and groups of organs integrate their functions to create organ systems. Chapter 3 reviews the anatomy of cells, tissues, and organs. LIST THE 10 ORGAN SYSTEMS The 10 physiological organ systems in the human body. Several of the systems have alternate names, given in parentheses, that are based on the organs of the system rather than the function of the system. The integumentary system {integumentum, covering}, composed of the skin, forms a protective boundary that separates the body’s internal environment from the external environment (the outside world). The musculoskeletal system provides support and body movement. 2 Four systems exchange materials between the internal and external environments. The respiratory (pulmonary) system exchanges gases; the digestive (gastrointestinal) system takes up nutrients and water and eliminates wastes; the urinary (renal) system removes excess water and waste material; and the reproductive system produces eggs or sperm. The remaining four systems extend throughout the body. The circulatory (cardiovascular) system distributes materials by pumping blood through vessels. The nervous and endocrine systems coordinate body functions. Note that the figure shows them as a continuum rather than as two distinct systems. Why? Because the lines between these two systems have blurred as we have learned more about the integrative nature of physiological function. The one system not illustrated in Figure 1.2 is the diffuse immune system, which includes but is not limited to the anatomical structures known as the lymphatic system. The specialized cells of the immune system are scattered throughout the body. They protect the internal environment from foreign substances by intercepting material that enters through the intestines and lungs or through a break in the skin. In addition, immune tissues are closely associated with the circulatory system. Traditionally, physiology courses and books are organized by organ system. Students study cardiovascular physiology and regulation of blood pressure in one chapter, and then study the kidneys and control of body fluid volume in a different chapter. In the functioning human, however, the cardiovascular and renal systems communicate with each other, so that a change in one is likely to cause a reaction in the other. For example, body fluid volume influences blood pressure, while changes in blood pressure alter kidney function because the kidneys regulate fluid volume. In this book, you will find several integrative physiology chapters that highlight the coordination of function across multiple organ systems. MAPING FUNTION AND MECHANISM The function of a physiological system or event is the “why” of the system or event: Why does a certain response help an animal survive in a particular situation? In other words, what is the adaptive significance of this event for this 3 animal?. Thinking about a physiological event in terms of its adaptive significance is the teleological approach to science. For example, the teleological answer to the question of why red blood cells transport oxygen is “because cells need oxygen and red blood cells bring it to them.” This answer explains why red blood cells transport oxygen— their function—but says nothing about how the cells transport oxygen. In contrast, most physiologists study physiological processes, or mechanisms—the “how” of a system. The mechanistic approach to physiology examines process. The mechanistic answer to the question “How do red blood cells transport oxygen?” is “Oxygen binds to hemoglobin molecules in the red blood cells.” This very concrete answer explains exactly how oxygen transport occurs but says nothing about the significance of oxygen transport to the animal. THEMES IN PHYSIOLOGY Four themes most related to physiology: structure-function relationships, biological energy use, information flow within an organism, and homeostasis and the control systems that maintain it. Theme 1: Structure and Function Are Closely Related The integration of structure and function extends across all levels of organization, from the molecular level to the intact body. This theme subdivides into two major ideas: molecular interactions and compartmentation Molecular Interactions The ability of individual molecules to bind to or react with other molecules is essential for biological function. A molecule’s function depends on its structure and shape, and even a small change to the structure or shape may have significant effects on the function. The classic example of this phenomenon is the change in one amino acid of the hemoglobin protein. (Hemoglobin is the oxygen-carrying pigment of the blood.) This one small change in the protein converts normal hemoglobin to the form associated with sickle cell disease. Many physiologically significant molecular interactions that you will learn about in this book involve the class of biological molecules called proteins. Functional groups of proteins include enzymes that speed up chemical reactions, signal molecules and the receptor proteins that bind signal molecules, and specialized proteins that function as biological pumps, filters, motors, or transporters. Interactions between proteins, water, and other molecules influence cell structure and the mechanical properties of cells and tissues. Mechanical properties you will encounter in your study of physiology include compliance (ability to stretch), elastance (stiffness or the ability to return to the unstretched state), strength, flexibility, and fluidity (viscosity). Compartmentation Compartmentation is the division of space into separate compartments. Compartments allow a cell, a tissue, or an organ to specialize and isolate functions. Each level of organization is associated with different types of compartments. At the macroscopic level, the tissues and organs of the body form discrete functional compartments, such as body cavities or the insides of hollow organs. At the microscopic level, cell membranes separate cells from the fluid surrounding them and also create tiny compartments within the cell called organelles. 4 Theme 2: Living Organisms Need Energy Growth, reproduction, movement, homeostasis—these and all other processes that take place in an organism require the continuous input of energy. Theme 3: Information Flow Coordinates Body Functions Information flow in living systems ranges from the transfer of information stored in DNA from generation to generation (genetics) to the flow of information within the body of a single organism. At the organismal level, information flow includes translation of DNA’s genetic code into proteins responsible for cell structure and function.In the human body, information flow between cells coordinates function. CellHOMEOSTASIS If the body fails to maintain homeostasis of the critical variables listed by Walter Cannon, then normal function is disrupted and a disease state, or pathological condition {pathos, suffering}, may result. Diseases fall into two general groups according to their origin: those in which the problem arises from internal failure of some normal physiological process, and those that originate from some outside source. Internal causes of disease include the abnormal growth of cells, which may cause cancer or benign tumors; the production of antibodies by the body against its own tissues (autoimmune diseases); and the premature death of cells or the failure of cell processes. Inherited disorders are also considered to have internal causes. External causes of disease include toxic chemicals, physical trauma, and foreign invaders such as viruses and bacteria. In both internally and externally caused diseases, when homeostasis is disturbed, the body attempts to compensate (Fig. 1.4). If the compensation is successful, homeostasis is restored. If compensation fails, illness or disease may result. The study of body functions in a disease state is known as pathophysiology. You will encounter many examples of pathophysiology as we study the various systems of the body. INTERNAL ENVIROMENT--->INTRACELLULAR FLUID VS EXTRACELLULAR FLUID it is the watery internal environment that surrounds the cells, a “sea within” the body called the extracellular fluid (ECF) {extra-, outside of}. For multicellular animals, Extracellular fluid serves as the transition between an organism’s external environment and the intracellular fluid (ICF) inside cells {intra-, within}. Because extracellular fluid is a buffer zone between cells and the outside world, elaborate physiological processes have evolved to keep its composition relatively stable. When the extracellular fluid composition varies outside its normal range of values, compensatory mechanisms activate and try to return the fluid to the normal state. 5 HOMEOSTASIS DEPENDS ON MASS BALANCE To maintain homeostasis, the body must maintain mass balance. The law of mass balance says that if the amount of a substance in the body is to remain constant, any gain must be offset by an equal loss. The amount of a substance in the body is also called the body’s load, as in “sodium load.” For example, water loss to the external environment (output) in sweat and urine must be balanced by water intake from the external environment plus metabolic water production (input). • • • TOTAL AMOUNT OF SUBSTANCE X IN THE BODY= INTAKE +PRODUCTION –EXCRETION AND METABOLISM To maintain mass balance, the body has two options for output. The simplest option is simply through: 1. EXCRETION: excrete the material. through the urine, feces, lungs, or skin 2. A second output option for maintaining mass balance is to convert the substance to a different substance through metabolism. Nutrients that enter the body become the starting point for metabolic pathways that convert the original nutrient to a different molecule. 3. Scientists use mass flow to follow material throughout the body. Mass flow describes the rate of transport of a substance x as it moves through body fluids or into and out of the body. The equation for mass flow is where volume flow describes the flow of blood, air, urine, and the like. CLEARENCE Clearance is usually expressed as a volume of blood cleared of substance x per unit of time. The kidney and the liver are the two primary organs that clear solutes from the body. Clearance also takes place in tissues other than the liver and kidneys. Saliva, sweat, breast milk, and hair all contain substances that have been cleared from the body. Salivary secretion of the hormone cortisol provides a simple noninvasive source of hormone for monitoring chronic stress. 6 STEADY VS EQUILIBRIUM HOMEOSTASIS DOES NOT MEAN EQUILLIBRIUM Steady state is not the same as equilibrium The modifier dynamic indicates that materials are constantly moving back and forth between the two compartments. Equilibrium implies that the composition of the body compartments is identical. For living organisms, the goal of homeostasis is to maintain the dynamic steady states of the body’s compartments, not to make the compartments the same. CONTROL SYTEMS AND HOMEOSTASIS 1)input signal; (2) a controller, or integrating center {integrate, to restore}, that integrates incoming information and initiates an appropriate response; and (3) an output signal that creates a response. Long-distance reflex control systems are more complex than this simple model, however, as they may include input from multiple sources and have output that acts on multiple targets. • Local control is restricted to a tissue In local control, a relatively isolated change occurs in a tissue. A nearby cell or group of cells senses the change in their immediate vicinity and responds, usually by releasing a chemical. One example of local control can be observed when oxygen concentration in a tissue decreases. Cells lining the small blood vessels that bring blood to the area sense the lower oxygen concentration and respond by secreting a chemical signal. The signal molecule diffuses to nearby muscles in the blood vessel wall, bringing them a message to relax. Relaxation of the muscles widens (dilates) the blood vessel, which increases blood flow into the tissue and brings more oxygen to the area. (ENDOCRINE VS NEURO-) 7 REFLEX CONTROL USES LONG DISTANCE-SIGNALING Changes that are widespread throughout the body, or systemic in nature, require more complex control systems to maintain homeostasis. A physiological reflex can be broken down into two parts: a response loop and a feedback loop. As with the simple control system just described, a response loop has three primary components: an input signal, an integrating center to integrate the signal, and an output signal. These three components can be expanded into the following sequence of seven steps to form a pattern that is found with slight variations in all reflex pathways: The input side of the response loop starts with a stimulus—the change that occurs when the regulated variable moves out of its desirable range. A specialized sensor monitors the variable. If the sensor is activated by the stimulus, it sends an input signal to the integrating center. The integrating center evaluates the information coming from the sensor and initiates an output signal. The output signal directs a target to carry out a response. If successful, the response brings the regulated variable back into the desired range. • RESPONSE LOO BEGINS WITH A STIMULUS The heater and air conditioner have antagonistic control over house temperature because they work in opposition to each other. Similar situations occur in the human body when two branches of the nervous system or two different hormones have opposing effects on a single target. FEEDBACK LOOP The response loop is only the first part of a reflex. Information about a homeostatic response that is sent back to the integrating center. The response feeds back. NEGATIVE FEEDBACK LOOP 8 For most reflexes, feedback loops are homeostatic—that is, designed to keep the system at or near a setpoint so that the regulated variable is relatively stable. Negative feedback loops stabilize the regulated variable and thus aid the system in maintaining homeostasis. Negative feedback loops can restore the normal state but cannot prevent the initial disturbance. POSITIVE FEEDBACK LOOP • • • Are not homeostatic. The response reinforces the stimulus rather than decreasing or removing it. In positive feedback, the response sends the regulated variable even farther from its normal value. This initiates a vicious cycle of everincreasing response and sends the system temporarily out of control Because positive feedback escalates the response, this type of feedback requires some intervention or event outside the loop to stop the response. FEEDFOWARD CONTROL • • • Allow the body to anticipate change. A few reflexes have evolved that enable the body to predict that a change is about to occur and start the response loop in anticipation of the change EX: control is the salivation reflex. The sight, smell, or even the thought of food is enough to start our mouths watering in expectation of eating the food THE SCIENCE OF PHYSIOLOGY But physiology is an experimental science, one in which researchers generate hypotheses {hypotithenai, to assume; singular hypothesis}, or logical guesses, about how events take place. They test their hypotheses by designing experiments to collect evidence that supports or disproves their hypotheses, and they publish the results of their experiments in the scientific literature. manipulated element, is the independent variable. Observation and experimentation are the key elements of scientific inquiry In scientific experimentation, the factor manipulated by the investigator is the independent variable, and the observed factor is the dependent variable. All well-designed experiments have controls to ensure that observed changes are due to the experimental manipulation and not to some outside factor. •Good scientific experiments must be carefully designed –Independent vs. dependent variables –Experimental controls –Data 9 –Replication –Model vs. scientific theory . MOLECULES AND BONDS CH2 10 Electron-” NEGATIVE PEOPLE STAY OUTSIDE THE CLUB” Neutron-DETERMINE THE ISOTOPE .NEUTRAL “NEUTRON GET INSIDE THE CLUB AT NO CHARGE” Proton-DETERMINE THE ELEMENT (ATOMIC NUMBER) ” POSITIVE PEOPLE LIVE IN THE CLUB.” =oxygen, carbon, and hydrogen—make up more than 90% of the body’s mass. • • • • • • • • • • • • • • • • • • 11 Molecules that contain carbon are known as organic molecules, Biomolecules are associated with living organisms= There are four major groups of biomolecules: carbohydrates, lipids, proteins, and nucleotides. The body uses carbohydrates, lipids, and proteins for energy and as the building blocks of cellular components. The fourth group, the nucleotides, includes DNA, RNA, ATP, and cyclic AMP. DNA and RNA are the structural components of genetic material. ATP (adenosine triphosphate) and related molecules carry energy, while cyclic AMP (adenosine monophosphate; cAMP) and related compounds regulate metabolism. Lipids are mostly carbon and hydrogen (have a backbone of glycerol and are nonpolar divided into FATS AND OIL. Carbohydrates are primarily carbon, hydrogen, and oxygen, in the ratio (divided into monosaccharides, disaccharides, polysaccharides. )-formula: CH2O Proteins and nucleotides contain nitrogen in addition to carbon, hydrogen, and oxygen, two amino acids, the building blocks of proteins, also contain sulfur. Conjugated proteins-molecules of protein combined with either lipid or carbohydrate. Lipoproteins are found in cell membranes and in the blood, where they act as carriers for less soluble molecules, such as cholesterol. Proteins combined with carbohydrates form glycoproteins Lipids bound to carbohydrates become glycolipids The phosphate group plays a role in many important cell processes, such as energy transfer and protein regulation. Addition of a phosphate group is called phosphorylation; removal of a phosphate group is dephosphorylation. Covalent and ionic bonds are strong bonds because they require significant amounts of energy to make or break. POLAR – molecules that develop regions of partial +- charge when 1 or more atoms in the molecule have strong attraction for electrons. Ex: H2O NONPOLAR-A molecule whose electrons are distributed so evenly that there are no regions of partial positive or negative charge Ionic bonds, hydrogen bonds, and van der Waals forces are noncovalent bonds. IONIC BOND-result from the attraction between ions with opposite charges. HYDRIGEN BONDS -No electrons are gained, lost, or shared in a hydrogen bond. Instead, the oppositely charged regions in polar molecules are attracted to each other. VAN DER WAALS FORCES-are weaker bonds that require much less energy to break. Two atoms that are weakly attracted to each other by van der Waals forces move closer together until they are so close that their electrons begin to repel one another. allow atoms to pack closely together and occupy a minimum amount of space. NONCOVALENT INTERACTIONS •Solutions –Solutes dissolved in solvent –Biological solutions are water-based = aqueous ▪Example: Ions (solute) dissolved in water (solvent) •Solubility –Ability of solute to dissolve in a solvent –Hydrophilic – soluble in water ▪Polar molecules ▪Ionic molecules –Hydrophobic – not soluble in water Nonpolar molecules PROTEIN INETERACTIONS In protein binding, when the ligand and protein come close to each other, noncovalent interactions between the ligand and the protein’s binding site allow the two molecules to bind. 12 CLASSES: • • • • • • • Enzymes. Some proteins act as enzymes biological catalysts that speed up chemical reactions. Enzymes play an important role in metabolism. Membrane transporters. Proteins in cell membranes help move substances back and forth between the intracellular and extracellular compartments. These proteins may form channels in the cell membrane, or they may bind to molecules and carry them through the membrane. Signal molecules. Some proteins and smaller peptides act as hormones and other signal molecules. Receptors. Proteins that bind signal molecules and initiate cellular responses are called receptors. Binding proteins. These proteins, found mostly in the extracellular fluid, bind and transport molecules throughout the body. Examples you have already encountered include the oxygen-transporting protein hemoglobin and the cholesterol-binding proteins, such as LDL, low-density lipoprotein. Immunoglobulins. These extracellular immune proteins, also called antibodies, help protect the body from foreign invaders and substances. Regulatory proteins. Regulatory proteins turn cell processes on and off or up and down. For example, the regulatory proteins known as transcription factors bind to DNA and alter gene expression STRUCTURE OF PROTEINS: 13 1. PRIMARY STRUCTUREORDER OF AMINO ACIDS FORMS A POLYPEPTIDE CHAIN. The 20 protein-forming amino acids assemble into polymers called peptides. The sequence of amino acids in a peptide chain is called the primary structure. Helix b-sheets 2. SECONDARY STRUCTURE Repeated coil or folded portions of the polypeptide chain as a result of hydrogen bonding at regular intervals along the backbone. ▪Globular proteins 14 ▪Disulfide bonds (S-S) ▪Fibrous proteins 2. TERTIARY STRUCTURE Tertiary structures can be a mix of secondary structures. Beta-sheets are shown as flat ribbon arrows and alpha helices are shown as ribbon coils.3D SHAPE (FIBROUS AND GLOBULAR PROTEINS) 3. QUARTERY STRUCTURE Are made out at least of 2 polypeptides chains refer to as subunits. Multiple subunits combine with noncovalent bonds. Hemoglobin molecules are made from four globular protein subunits. ----->>>>Functional Compartments of the Body – Review all the cavities in the body and be able to understand the breakdown of the fluid compartments in the body. The human body is a complex compartment separated from the outside world by layers of cells. Anatomically, the body is divided into three major body cavities: the cranial cavity (commonly referred to as the skull), the thoracic cavity (also called the thorax), and the abdominopelvic cavity . The cavities are separated from one another by bones and tissues, and they are lined with tissue membranes. 15 •Three major cavities –Cranial –Thoracic –Abdominopelvic •Fluid-filled compartments –Circulatory system –Eyes –Cerebrospinal fluid (CSF) –Pleural and pericardial sacs 16 There are two major fluid compartments in the human body: 1. Intracellular fluid (ICF): This is the water within the cells and accounts for approximately 65% of total body water This is the matrix in which intracellular organelles are suspended, and chemical reactions take place. 2. Extracellular fluid (ECF): This is the water outside of the cells Intracellular vs extracellular fluid The composition of ions between the fluid compartments varies, but within any one compartment, electrical neutrality is maintained with the total number of positive charges always being equal to the total number of negative charges. The most important difference between the ICF and the ECF is the relative concentration of cations (positively charged ions): The potassium ion (K+) concentration is much higher in the ICF than in the ECF Conversely, the sodium ion (Na+) concentration is much higher in the ECF than in the ICF Calcium ion (Ca2+) and chloride ion (Cl–) concentrations are also higher in the ECF. These compartments are separated by the plasma membrane of the cells and differ markedly in terms of the concentrations of the ions dissolved in them. • The extracellular fluid is further divided into three other compartments: •Extracellular fluid (ECF) –Plasma –Interstitial fluid •Intracellular fluid (ICF) 1. Interstitial fluid (ISF): This is the tissue fluid found in the spaces between the cells and accounts for approximately 65% of the ECF (10 L of fluid). 2. Intravascular fluid: This is the plasma, which is the liquid component of the blood and accounts for approximately 25% of the ECF (3.5 L of fluid). 3. Transcellular fluid: This is the final 1.5 L of fluid and comprises intraocular fluid, cerebrospinal fluid, urine in the bladder, and fluid within the lumen of the bowel. 17 ----->>>>Biological Membranes- Review the cell membrane, all the components that make up the phospholipid bilayer. CELL MEMBRANE ( There are two synonyms for the term cell membrane: plasma membrane and plasmalemma.) –SERVES AS BOTH GATEWAY AND BARRIER FOR SUBSTANCE MOVING IN AND OUT OF THE CELL. thin layer of lipids that separated the aqueous fluids of the interior and outside environment. general functions: • • • • Physical isolation. The cell membrane is a physical barrier that separates intracellular fluid inside the cell from the surrounding extracellular fluid. Regulation of exchange with the environment. The cell membrane controls the entry of ions and nutrients into the cell, the elimination of cellular wastes, and the release of products from the cell. Communication between the cell and its environment. The cell membrane contains proteins that enable the cell to recognize and respond to molecules or to changes in its external environment. Any alteration in the cell membrane may affect the cell’s activities. Structural support. Proteins in the cell membrane hold the cytoskeleton, the cell’s interior structural scaffolding, in place to maintain cell shape. The lipids of biological membranes are mostly phospholipids arranged in a bilayer so that the phosphate heads are on the membrane surfaces and the lipid tails are hidden in the center of the membrane. Three main types: 1. Phospholipids -make up all the cell membranes and play a large role in determining what gets in and out of the cell. 18 2. Sphingolipids- Sphingolipids also have fatty acid tails, but their heads may be either phospholipids or glycolipids. Sphingolipids are slightly longer than phospholipids. 3. Cholesterol.- Cholesterol helps make membranes impermeable to small water-soluble molecules and keeps membranes flexible over a wide range of temperatures. ---->>Intracellular Compartments – Review the major organelles in the cell and their function. -------->>>> Tissues of the Body - Know the function of all 4 major types of the tissues in the body. Be able to distinguish key features in each type of tissues. Review tissue histology and the purposes for the different There are 4 different types of tissue: 19 (The cell junctions in epithelia are variable.) • • • • • • • • • • Epithelial- protect the internal environment of the body and regulate the exchange of materials between the internal and external environments, •Structure of epithelia –One or more layers of epithelial cells –Separated from underlying tissue by basal lamina (basement membrane) –Tight vs. leaky epithelia simple squamous epithelium Connective- provide structural support and sometimes a physical barrier that, along with specialized cells, helps defend the body from foreign invaders such as bacteria. The distinguishing characteristic of connective tissues is the presence of extensive extracellular matrix containing widely scattered cells that secrete and modify the matrix. Connective tissues include blood, the support tissues for the skin and internal organs, and cartilage and bone. Loose connective tissues (Fig. 3.13a) are the elastic tissues that underlie skin and provide support for small glands. Dense connective tissues (irregular and regular) provide strength or flexibility. Examples are tendons, ligaments, and the sheaths that surround muscles and nerves. Muscle- as the ability to contract and produce force and movement. The body contains three types of muscle tissue: cardiac muscle in the heart; smooth muscle, which makes up most internal organs; and skeletal muscle. neural, or nerve. - has two types of cells. Neurons, or nerve cells, carry information in the form of chemical and electrical signals from one part of the body to another. They are concentrated in the brain and spinal cord but also include a network of cells that extends to virtually every part of the body. • •Histology – study of tissue structure and function1. the shape and size of the cells, 2. the arrangement of the cells in the tissue (in layers, scattered, and so on), 3. the way cells are connected to one another 4. the amount of extracellular material present in the tissue ---->??Tissue Remodeling- Review how adipose tissue is utilized as an energy source in the body 20 ADIPOSE: The adipose tissue is a critical regulator of systemic energy homeostasis by acting as a caloric reservoir. In excess nutrient conditions, the adipose tissue stores surplus nutrients in the form of neutral lipids whereas in nutrient deficit conditions, it supplies nutrients to other tissues through lipolysis (1). TISSUE REMODELING: The tissues of the body are constantly remodeled as cells die and are replaced Cell death occurs two ways, one messy and one tidy. In necrosis, cells die from physical trauma, toxins, or lack of oxygen when their blood supply is cut off. Apoptosis, also called cell suicide, is a complex process regulated by multiple chemical signals. Some signals keep apoptosis from occurring, while other signals tell the cell to self-destruct. When the suicide signal wins out, chromatin in the nucleus condenses, and the cell pulls away from its neighbors. That cell and those that follow reproduce themselves by undergoing the cell division process known as mitosis. They can be replaced, however, by new cells created from stem cells, less specialized cells that retain the ability to divide. Organs- Know what organs are responsible for processing which macromolecules in the body. 21 ADDITIONAL STUDY MATERIAL: ❖ Animal cell junctions fall into three categories. Gap junctions allow chemical and electrical signals to pass directly from cell to cell. Tight junctions restrict the movement of material between cells. Anchoring junctions hold cells to each other or to the extracellular matrix. ❖ Membrane proteins called cell adhesion molecules (CAMs) are essential in cell adhesion and in anchoring junctions. ❖ Desmosomes and adherents junctions anchor cells to each other. Focal adhesions and hemidesmosomes anchor cells to matrix ❖ Exchange epithelia permit rapid exchange of materials, particularly gases. Transporting epithelia actively regulate the selective exchange of nongaseous materials between the internal and external environments. Ciliated epithelia move fluid and particles across the surface of the tissue. Protective epithelia help prevent exchange between the internal and external environments. The secretory epithelia release secretory products into the external environment or the blood 22 23