Nursing 3 Quiz 2

What properties of a cell membrane contribute to its permeability? Give examples of substances that typically are permeable and impermeable to human cell membranes.

- Cell membranes are selectively permeable, which means that some molecules can cross them but others cannot. -The lipid and protein composition of a given cell membrane determines which molecules will enter the cell and which will leave -If a membrane allows a substance to pass through it, the membrane is said to be permeable to that substance. -If a membrane does not allow a substance to pass, the membrane is said to be impermeable to that substance. -Some molecules, such as oxygen, carbon dioxide, and lipids, move easily across most cell membranes. -On the other hand, ions, most polar molecules, and very large molecules (such as proteins), enter cells with more difficulty or may not enter at all.

What are cytokines?

-Cytokines are peptides, synthesized and secreted by all nucleated cells in response to stimuli -Cytokines may act as both local and long-distance signals -In development and differentiation, cytokines usually function as autocrine or paracrine signals -In stress and inflammation, some cytokines may act on relatively distant targets

Why do some cells respond to a chemical signal while other cells ignore it?

-A cell responds to a particular chemical signal only if the target has a receptor, a binding protein.

Distinguish between primary (direct) active transport and secondary (indirect) active transport.

-Active transport can be divided into two types. In primary (direct) active transport, the energy to push molecules against their concentration gradient comes directly from the high energy phosphate bond of ATP. -Secondary (indirect) active trans- port uses potential energy stored in the concentration gradient of one molecule to push other molecules against their concentration gradient. -All secondary active transport ultimately depends on primary active transport because the concentration gradients that drive secondary transport are created using energy from ATP.

What is active transport? Why does it require the input of energy?

-Active transport is a process that moves molecules against their concentration gradient—that is, from areas of lower concentration to areas of higher concentration. -Rather than creating an equilibrium state, where the concentration of the molecule is equal throughout the system, active transport creates a state of disequilibrium by making concentration differences more pronounced. -Moving molecules against their concentration gradient requires the input of outside energy. -The energy for active transport comes either directly or indirectly from the high-energy phosphate bond of ATP.

Describe caveolae and list their functions.

-Caveolae are membrane regions with lipid rafts, membrane receptor proteins, and specialized membrane proteins named caveolins and cavins. -The receptors in caveolae are lipid- anchored proteins. -In many cells, caveolae appear as small indented pockets on the cell membrane, which is how they acquired their name. -Caveolae have several functions: to concentrate and in- ternalize small molecules, to help in the transfer of macromolecules across the capillary endothelium, and to participate in cell signaling. -Caveolae appear to be involved in some disease pro- cesses, including viral and parasitic infections.

Describe a typical channel protein.

-Channel proteins are made of membrane-spanning protein subunits that create a cluster of cylinders with a tunnel or pore through the center. -Nuclear pore complexes and gap junctions can be considered very large forms of channels.

Compare channel proteins and carrier proteins.

-Channel proteins create water-filled passageways that directly link the intracellular and extracellular compartments. -Carrier proteins, also just called transporters, bind to the substrates that they carry but never form a direct connection between the intracellular fluid and extracellular fluid. - Channel proteins allow more rapid transport across the membrane but generally are limited to moving small ions and water. -Carriers, while slower, can move larger molecules than channels can.

List three types of gated channels.

-Chemically gated channels -Voltage-gated channels - Mechanically gated channels

How does endocytosis differ from phagocytosis?

-Endocytosis, the second process by which large molecules or par- ticles move into cells, differs from phagocytosis in two important ways. -First, in endocytosis the membrane surface indents rather than pushes out. -Second, the vesicles formed from endocytosis are much smaller. In addition, some endocytosis is constitutive; that is, it is an essential function that is always taking place. In contrast, phagocytosis must be triggered by the presence of a substance to be ingested.

How is exocytosis related to endocytosis? Is exocytosis active or passive? Is exocytosis constitutive or intermittent?

-Exocytosis is the opposite of endocytosis. -In exocytosis, intracellular vesicles move to the cell membrane, fuse with it, and then release their contents to the extracellular fluid. -Cells use exocytosis to export large lipophobic molecules, such as proteins synthesized in the cell, and to get rid of wastes left in lysosomes from intracellular digestion. -Exocytosis, like endocytosis, requires energy in the form of ATP. -Exocytosis takes place continuously in some cells, making it a constitutive process.

Compare and contrast facilitated diffusion and simple diffusion.

-Facilitated diffusion has the same properties as simple diffusion. -The transported molecules move down their concentration gradient, the process requires no input of outside energy, and net movement stops at equilibrium, when the concentration inside the cell equals the concentration outside the cell. -Facilitated diffusion carriers always transport molecules down their concentration gradient. -If the gradient reverses, so does the direction of transport.

What are hormones? How do they reach their targets?

-Hormones are secreted by endocrine glands or cells into the blood. -Only target cells with receptors for the hormone respond to the signal.

Distinguish between the terms isosmotic, hyposmotic, and hyperosmotic.

-If two solutions contain the same number of solute particles per unit volume, we say that the solutions are isosmotic. -If solution A has a higher osmolarity (contains more particles per unit volume, is more concentrated) than solution B, we say that solution A is hyperosmotic to solution B. -In the same example, solution B, with fewer osmoles per unit volume, is hyposmotic to solution A.

Describe the process of transcytosis. When is it used? What role does the cytoskeleton play in transcytosis?

-It is a combination of endocytosis, vesicular transport across the cell, and exocytosis. -In this process, the molecule is brought into the epithelial cell via receptor-mediated endocytosis. -The resulting vesicle attaches to microtubules in the cell's cytoskeleton and is moved across the cell by a process known as vesicular transport. -Transcytosis makes it possible for large proteins to move across an epithelium and remain intact. I

What are membrane enzymes? How are they different in function from intracellular enzymes?

-Membrane enzymes catalyze chemical reactions that take place either on the cell's external surface or just inside the cell. -For example, enzymes on the external surface of cells lining the small intestine are responsible for digesting peptides and carbohydrates. -Enzymes attached to the intracellular surface of many cell membranes play an important role in transferring signals from the extracellular environment to the cytoplasm

What is the role of membrane receptor proteins?

-Membrane receptor proteins are part of the body's chemical signaling system. -The binding of a receptor with its ligand usually triggers another event at the membrane. -Sometimes the ligand remains on the cell surface, and the receptor-ligand complex triggers an intracellular response. -In other instances, the receptor-ligand complex is brought into the cell in a vesicle. -Membrane receptors also play an important role in some forms of vesicular transport, as you will learn later in this chapter.

Describe the structure and function of integrins.

-Membrane-spanning proteins -Outside the cell, integrins bind to extracellular matrix proteins or to ligands -Inside the cell, integrins attach to the cytoskeleton via anchor proteins

Contrast paracellular transport and transcellular transport.

-Movement across an epithelium, or epithelial transport, may take place either as paracellular transport through the junctions between adjacent cells or as transcellular transport through the epithelial cells themselves.

Define diffusion.

-Movement from high concentration to low concentration -No energy needed -Goes with concentration gradient

What is pinocytosis?

-Nonselective process of allowing extracellular fluid to enter the cell

Give examples of contact-dependent signaling. What are some of the proteins involved?

-Occur in the immune system and during growth and development, such as when nerve cells send out long extensions that must grow from the central axis of the body to the distal (distant) ends of the developing limbs.

How can cells increase their transport capacity and avoid saturation?

-One way is to increase the number of carriers in the membrane.

Distinguish between an open channel and a gated channel.

-Open channels spend most of their time with their gate open, allowing ions to move back and forth across the membrane without regulation. -These gates may occasionally flicker closed, but for the most part these channels behave as if they have no gates. -Open channels are sometimes called either leak channels or pores, as in water pores. -Gated channels spend most of their time in a closed state, which allows these channels to regulate the movement of ions through them. -When a gated channel opens, ions move through the channel just as they move through open channels. -When a gated channel is closed, which it may be much of the time, it allows no ion movement between the intracellular and extracellular fluid.

Contrast osmolarity and osmolality.

-Osmolality is concentration expressed as osmoles of solute per kilogram of water. -Because biological solutions are dilute and little of their weight comes from solute, physiologists often use the terms osmolarity and osmolality interchangeably. -Osmolality is usually used in clinical situations because it is easy to estimate people's body water content by weighing them.

Define and describe osmosis.

-Osmosis is the movement of water across a membrane in response to a solute concentration gradient. -Water moves to dilute the more concentrated solution. -Once concentrations are equal, net movement of water stops.

What is the difference between active transport and passive transport?

-Passive transport does not require the input of energy other than the potential energy stored in a concentration gradient. -Active transport requires the input of energy from some outside source, such as the high-energy phosphate bond of ATP.

Describe the process of phagocytosis. What is a phagosome?

-Phagocytosis is the actin-mediated process by which a cell engulfs a bacterium or other particle into a large membrane- bound vesicle called a phagosome. -The phagosome pinches off from the cell membrane and moves to the interior of the cell, where it fuses with a lysosome whose digestive enzymes destroy the bacterium. -Phagocytosis requires energy from ATP for the movement of the cytoskeleton and for the intracellular transport of the vesicles. -In humans, phagocytosis occurs in certain types of white blood cells called phagocytes, which specialize in "eating" bacteria and other foreign particles.

Diagram the process of receptor-mediated endocytosis. What role does clathrin play? What is an endosome?

-Receptor-mediated endocytosis takes place in regions of the cell membrane known as coated pits, indentations where the cytoplasmic side of the membrane has high concentrations of protein. -The most common protein found in coated pits is clathrin. -An endosome moves to a lysosome if the ligand is to be destroyed

Define the following terms: uniport carriers, cotransporter, symport carriers, and antiport carriers.

-Some carrier proteins move only one kind of molecule and are known as uniport carriers. -A carrier that moves more than one kind of molecule at one time is called a cotransporter. -If the molecules being transported are moving in the same direction, whether into or out of the cell, the carrier proteins are symport carriers. -If the molecules are being carried in opposite directions, the carrier proteins are antiport carriers.

How does chemical disequilibrium in the body give rise to electrical disequilibrium? What is the result of electrical disequilibrium?

-The body as a whole is electrically neutral, but a few extra negative ions are found in the intracellular fluid, while their matching positive ions are located in the extracellular fluid. -As a result, the inside of cells is slightly negative relative to the extracellular fluid. -This ionic imbalance results in a state of electrical disequilibrium.

Describe the action of the Na+-glucose secondary active transporter (SGLT) as a representative example of secondary active transport. How does an SGLT transporter compare with a GLUT transporter?

-The mechanism of the Na+-glucose secondary active transporter (SGLT) -Both Na+ and glucose bind to the SGLT protein on the extracellular fluid side. Sodium binds first and causes a conformational change in the protein that creates a high-affinity binding site for glucose. -In contrast, GLUT transporters are reversible and can move glucose into or out of cells depending on the concentration gradient. -Both SGLT and GLUT are needed to move glucose from one side of an epithelium to the other.

What is bulk flow? Give some examples of bulk flow in the body.

-The most general form of biological transport is the bulk flow of fluids within a compartment. -In bulk flow, a pressure gradient causes fluid to flow from re-gions of higher pressure to regions of lower pressure. -As the fluid flows, it carries with it all of its component parts, including substances dissolved or suspended in it. -Blood moving through the circulatory system is an excellent example of bulk flow. -The heart acts as a pump that creates a region of high pressure, pushing plasma with its dissolved solutes and the suspended blood cells through the blood vessels. -Air flow in the lungs is another example of bulk flow that you will encounter as you study physiology.

How does competition relate to specificity

-The property of competition is closely related to specificity. -A transporter may move several members of a related group of substrates, but those substrates compete with one another for binding sites on the transporter.

Describe how the principle of saturation applies to carrier-mediated transport. Include a description of transport maximum.

-The rate of substrate transport depends on the substrate concentration and the number of carrier molecules, a property that is shared by enzymes and other binding proteins.

How is the relatively high extracellular [Na+] used to drive transport of other molecules against their concentration gradient across a membrane? Give some specific examples.

-The sodium concentration gradient, with Na+ concentration high in the extracellular fluid and low inside the cell, is a source of potential energy that the cell can harness for other functions. -For example, nerve cells use the sodium gradient to transmit electrical signals, and epithelial cells use it to drive the uptake of nutrients, ions, and water. 0Membrane transporters that use potential energy stored in concentration gradients to move molecules are called secondary active transporters.

Compare and contrast the apical membrane and the basolateral membrane of a transporting epithelial cell. What is the physiological significance of transporting epithelial cell polarization?

-The tight junctions of epithelia separate the cell membrane into two regions, or poles. -The surface of the epithelial cell that faces the lumen of an organ is called the apical membrane. -It is often folded into microvilli that increase its surface area. -Below the tight junctions, the three surfaces of the cell that face the extracellular fluid are collectively called the basolateral membrane. -The apical membrane is also called the mucosal membrane. -The corresponding term for the basolateral membrane is serosal membrane.

What is membrane recycling?

-The vesicle with the receptors moves to the cell membrane and fuses with it. -The vesicle membrane then is incorporated back into the cell membrane by exocytosis.

What are the different ways a molecule can move across a membrane?

-Vesicular transport (ATP) -Primary Active Transport -Secondary Active Transport -Facilitated Diffusion -Ion Channel -Aquaporin Channel -Simple Diffusion

What kinds of signals pass through gap junctions?

-When gap junctions are open, ions and small molecules such as amino acids, ATP, and cyclic AMP diffuse directly from the cytoplasm of one cell to the cytoplasm of the next. -Larger molecules cannot pass through gap junctions. -In addition, gap junctions are the only means by which electrical signals can pass directly from cell to cell. -Movement of molecules and electrical signals through gap junctions can be modulated or shut off completely.

Define Fick's law.

-a relationship that involves the factors just mentioned for diffusion across membranes plus the factor of concentration gradient. -In an abbreviated form, Fick's law says that the diffusion rate increases when surface area, the concentration gradient, or the membrane permeability increase:

What is the physiological significance of the "70-kg man"? What is his total body water volume?

. The 70-kg Reference Man has 60% of his total body weight, or 42 kg (92.4 lb), in the form of water.

Distinguish between paracrine and autocrine signals.

Autocrine signals act on the same cell that secreted them. Paracrine signals are secreted by one cell and diffuse to adjacent cells.

What are the rules for predicting tonicity

1. Assume that all intracellular solutes are nonpenetrating. 2. Compare osmolarities before the cell is exposed to the solution. (At equilibrium, the cell and solution are always isosmotic.) 3. Tonicity of a solution describes the volume change of a cell at equilibrium. Rules for Osmolarity and Tonicity 4. Determine tonicity by comparing nonpenetrating solute con- centrations in the cell and the solution. Net water movement is into the compartment with the higher concentration of nonpenetrating solutes. 5. Hyposmotic solutions are always hypotonic.

List four electrical principles important to the understanding of physiological electricity.

1. The law of conservation of electrical charge states that the net amount of electrical charge produced in any process is zero. This means that for every positive charge on an ion, there is an electron on another ion. Overall, the human body is electrically neutral. 2. Opposite charges (+ and −) are attracted to each other. The protons and electrons in an atom exhibit this attraction. Like charges (two charges of the same type, such as +/+, or −/−) repel each other. 3. Separating positive charges from negative charges requires energy. For example, energy is required to separate the pro- tons and electrons of an atom. 4. When separated positive and negative charges can move freely toward each other, the material through which they move is called a conductor. Water is a good conductor of electrical charge. When separated charges cannot move through the material that separates them, the material is known as an insulator. The phospholipid bilayer of the cell membrane is a good insulator, as is the plastic coating on electrical wires.

What features do all signal pathways share in common?

1. The signal molecule is a ligand that binds to a protein recep- tor. The ligand is also known as a f irst messenger because it brings information to the target cell. 2. Ligand-receptor binding activates the receptor. 3.The receptor in turn activates one or more intracellular signal molecules. 4. The last signal molecule in the pathway creates a response by modifying existing proteins or initiating the synthesis of new proteins.

What are the three major roles of structural proteins?

1. They help create cell junctions that hold tissues together, such as tight junctions and gap junctions. 2. They connect the membrane to the cytoskeleton to maintain the shape of the cell. The microvilli of transporting epithelia are one example of membrane shaping by the cytoskeleton. 3. They attach cells to the extracellular matrix by linking cytoskeleton fibers to extracellular collagen and other protein fibers.

List seven properties of diffusion

1.Diffusion uses the kinetic energy of molecular movement and does not require an outside energy source. 2. Molecules diffuse from an area of higher concentration to an area of lower concentration. 3. Diffusion continues until concentrations come to equilibrium. Molecular movement continues, however, after equilibrium has been reached. 4. Diffusion is faster — along higher concentration gradients. — over shorter distances. — at higher temperatures. — for smaller molecules. 5. Diffusion can take place in an open system or across a partition that separates two systems. 6. The rate of diffusion through a membrane is faster if — the membrane's surface area is larger. — the membrane is thinner. — the concentration gradient is larger. — the membrane is more permeable to the molecule. 7. Membrane permeability to a molecule depends on — the molecule's lipid solubility. — the molecule's size. — the lipid composition of the membrane

How does a woman's total body water content compare to a man's?

Adult women have less water per kilogram of body mass than men because women have more adipose tissue.

What is chemical disequilibrium? Give some examples of specific solutes that exist in a state of chemical disequilibrium in our body.

Although the over- all concentrations of the ECF and intracellular fluid (ICF) are equal, some solutes are more concentrated in one of the two body compartments than in the other. -For example, sodium, chloride, and bicarbonate (HCO3- ) ions are more concentrated in extracellular fluid than in intracellular fluid. -Potassium ions are 5 more concentrated inside the cell. Calcium (not shown in the figure) is more concentrated in the extracellular fluid than in the cytosol, although many cells store Ca2+ inside organelles such as the endoplasmic reticulum and mitochondria.

How can a solution be isosmotic and also hypotonic?

As you can see in, an isosmotic solution may be isotonic or hypotonic. It can never be hypertonic because it can never have a higher concentration of nonpenetrating solutes than the cell. If all solutes in the isosmotic solution are non- penetrating, then the solution is also isotonic. If there are any penetrating solutes in the isosmotic solution, the solution will be hypotonic.

Contrast penetrating solutes and nonpenetrating solutes. What does it mean when a solute is considered "functionally nonpenetrating"?

By nature of the solutes, we mean whether the solute particles can cross the cell membrane. -If the solute particles (ions or molecules) can enter the cell, we call them penetrating solutes. -We call particles that cannot cross the cell membrane nonpenetrating solutes. -Tonicity depends on the concentration of nonpenetrating solutes only.

What are target cells (targets)?

Cells that respond to electrical or chemical signals

How does osmolarity differ from molarity? What equation converts molarity to osmolarity?

Consequently, for biological solutions we express the concentration as osmolarity, the number of osmotically active particles (ions or intact molecules) per liter of solution. molarity (mol/L) X particles/molecule (osmol/mol) = osmolarity (osmol/L)

Contrast electrical signals with chemical signals.

Electrical signals-Changes in the membrane potential of a cell Chemical signals-Secreted by cells into extracellular fluid (ECF) and are esponsible for most communication within the body.

Give examples of molecules exported by exocytosis.

For example, goblet cells in the intestine continuously release mucus by exocytosis, and fibroblasts in connective tissue release collagen -In other cell types, exocytosis is an intermittent process that is initiated by a signal. -In many endocrine cells, hormones are stored in secretory vesicles in the cytoplasm and released in response to a signal from outside the cell.

Distinguish between a neurotransmitter, neuromodulator, and neurohormone.

If a neurocrine molecule diffuses from the neuron across a narrow extracellular space to a target cell and has a rapid-onset effect, it is called a neurotransmitter. If a neurocrine acts more slowly as an autocrine or paracrine signal, it is called a neuromodulator. If a neurocrine molecule diffuses into the blood for body-wide distribution, it is called a neurohormone (Fig. 6.1f ).

What are the major categories of membrane receptors?

Ligand-gated G protein-coupled Receptor-enzymes Integrin receptors

What are the differences in behavior of lipophobic vs. lipophilic signal molecules

Lipophilic signal molecules diffuse through the cell membrane and bind to receptors in the cytosol or nucleus Lipophobic signal molecules bind to receptors on the cell membrane

List and describe the basic methods of cell-to-cell communication.

Our bodies use four basic methods of cell-to-cell communication. Local communication includes (1) gap junctions, which allow direct cytoplasmic transfer of electrical and chemical signals between adjacent cells; (2) contact-dependent signals, which occur when surface molecules on one cell mem- brane bind to surface molecules on another cell's membrane; (3) chemicals that diffuse through the extracellular fluid to act on cells close by. Long-distance communication (4) uses a combination of chemical and electrical signals carried by nerve cells and chemical signals transported in the blood.

Where can receptor proteins be found in target cells?

Receptors Are Located Inside the Cell or on the Cell Membrane

What two properties of a molecule determine whether it can diffuse across a membrane?

The size of the molecule and its lipid solubility.

Give examples of how specificity applies to carrier-mediated transport.

Specificity refers to the ability of a transporter to move only one molecule or only a group of closely related molecules.

Give examples of molecules that might cross a membrane by facilitated diffusion.

Sugars and amino acids are examples of molecules that enter or leave cells using facili- tated diffusion.

Describe the distribution of water among the body compartments.

The distribution of water among body compartments is less variable. When we look at the relative volumes of the body com-partments, the intracellular compartment contains about two- thirds (67%) of the body's water. The remaining third (33%) is split between the interstitial fluid (which contains about 75% of the extracellular water) and the plasma (which con- tains about 25% of the extracellular water).

In the nervous system, what kinds of signals are used to transmit information?

The nervous system uses a combination of chemical and electrical signals for long-distance cell-to-cell communication

What is osmotic pressure?

The pressure on the piston that exactly opposes the osmotic movement of water into a compartment is known as the osmotic pressure of a solution.

What types of molecules pass through channel proteins?

Water molecules and ions

What is osmotic equilibrium?

When the extracellular and intracellular compartments reach a state of osmotic equilibrium in which the fluid concentrations are equal on the two sides of the cell membrane.