Chapter 6

Which two body systems maintain homeostasis by monitoring and responding to changes in the environment?

nervous and endocrine systems

What are the two routes for long-distance signal delivery in the body?

neurons and blood

Receptors for signal pathways may be found in the , , or of the cell.

nucleus, cytosol, cell membrane

In a negative feedback loop, the response moves the system in the (same/opposite) direction as the stimulus moves it.

opposite

An enzyme known as protein kinase adds the functional group to its substrate, by transferring it from a(n) molecule.

phosphate, ATP

What are the four steps of signal transduction?

(1) signal molecule binds to receptor that (2) activates a protein that (3) creates second messengers that (4) creates a response.

In each of the following situations, will a cell depolarize or hyperpolarize? (a) Cl- channel opens (b) K+ channel opens (c) Na+ channel opens

(a) Cl− channel opens: cell hyperpolarizes, (b) K+ channel opens: cell hyperpolarizes, (c) Na+ channel opens: cell depolarizes.

Explain the relationships of the terms in each of the following sets. Give a physiological example or location if applicable. A.gap junctions, connexins, connexon B.autocrine signal, paracrine signal C.cytokine, neurotransmitter, neurohormone, neuromodulator, hormone D.Receptor agonist, receptor antagonist, antagonistic control pathways E.transduction, amplification, cascade

(a) Gap junctions connect two cells using protein channels called connexons, made from connexin subunits. (b) Paracrine signals act on nearby cells; autocrine signals act on the cell that secretes them. (c) Cytokines are peptide autocrine and paracrine signals. Neurotransmitters, neuromodulators, and neurohormones are all chemicals secreted by neurons. Neurotransmitters act rapidly on nearby cells; neuromodulators act more slowly. Neurohormones and hormones are secreted into the blood for action on distant targets. (d) Receptor agonists activate receptors just like the normal ligand; receptor antagonists also bind to the receptor but block its activation. Antagonistic pathways create responses that oppose each other. (e) Transduction: A signal molecule transfers information from ECF to the cytoplasm. Cascade: a series of steps. Amplification: One signal molecule creates a larger signal.

In the simple neural reflex shown in Figure 6.18, which box or boxes represent the brain and spinal cord? (b) Which box or boxes represent the central and peripheral sense organs? (c) In the simple neural reflex, add a dashed line connecting boxes to show how a negative feedback loop would shut off the reflex [here].

(a) The "neural system integrating center" is the brain and spinal cord. (b) "Receptor" represents the sense organs. (c) The dashed line indicating negative feedback runs from "Response" back to "Internal or external change."

The three main amplifier enzymes are (a) , which forms cAMP; (b) , which forms cGMP; and (c) , which converts a phospholipid from the cell's membrane into two different second messenger molecules.

(a) adenylyl cyclase, (b) guanylyl cyclase, (c) phospholipase C

Place the following terms in the correct order for a signal transduction pathway: (a) cell response, receptor, second messenger, ligand (b) amplifier enzyme, cell response, phosphorylated protein, protein kinase, second messenger

(a) ligand, receptor, second messenger, cell response; (b) amplifier enzyme, second messenger, protein kinase, phosphorylated protein, cell response

Would the following reflexes have positive or negative feedback? glucagon secretion in response to declining blood glucose increasing milk release and secretion in response to baby's suckling urgency in emptying one's urinary bladder sweating in response to rising body temperature

(a) negative, (b) positive, (c) negative, (d) negative

Now identify the integrating center for examples (a), (c), and (d) in question 17.

(a) pancreatic endocrine cells that secrete glucagon, (c) and (d) nervous system

Identify the target tissue or organ for each example in question 17.

(a) tissues that respond to glucagon, such as liver; (b) breast; (c) bladder; (d) sweat glands

In a signal transduction pathway, the signal ligand, also called the first messenger, binds to a(n) , which activates and changes intracellular .

receptor, targets (effectors), or proteins

Match the communication method on the left with its property on the right. (a) autocrine signal (b) cytokine (c) gap junction (d) hormone (e) neurohormone (f) neurotransmitter (g) paracrine signal Communication is: 1.electrical 2.chemical 3.both electrical and chemical

1. no matches; 2. a, b, d, e, f, g; 3. c

One drug blocks leukotriene action in its target cells. A different drug blocks leukotriene synthesis. Use what you have learned about leukotrienes, signal molecules, and signal transduction to predict what these drugs are doing to have those effects.

A drug that blocks leukotriene action could act at the target cell receptor or at any step downstream. A drug that blocks leukotriene synthesis might inhibit lipoxygenase.

How can one chemical signal have opposite effects in two different tissues?

A signal can have opposite effects by using different receptors or different signal pathways.

What happens during amplification? In Figure 6.6b, amplification of one signal molecule binding to the receptor results in how many small dark blue intracellular signal molecules?

Amplification turns one signal molecule into multiple second messenger molecules. In Fig. 6.6b, 1 ligand amplifies into 18 intracellular molecules.

Distinguish between central and peripheral receptors.

Central: located within the central nervous system. Peripheral: found outside the CNS

To decrease a receptor's binding affinity, a cell might (select all that apply): (a) synthesize a new isoform of the receptor (b) withdraw receptors from the membrane (c) insert new receptors into the membrane (d) use a covalent modulator [Hint: here]

Choices (a) and (d) could decrease binding affinity. Changing receptor number would not affect binding affinity.

Which signal molecules listed in the previous question are transported through the circulatory system? Which are released by neurons?

Cytokines, hormones, and neurohormones travel through the blood. Cytokines, neurohormones, and neurotransmitters are released by neurons.

What is the difference between a first messenger and a second messenger?

First messengers are extracellular; second messengers are intracellular.

What is the difference between local control and reflex control?

In local control, the stimulus, integration of the signal, and response all take place in or very close to the target cell. With reflex control, integration of the input signal and initiation of a response may take place far from the location where the change occurred.

Insulin increases the number of glucose transporters on a skeletal muscle cell but not on the membrane of a liver cell. List two possible mechanisms that could explain how this one hormone can have these two different effects.

It could be one receptor with different second messenger systems or two different receptor isoforms.

A cat sees a mouse and pounces on it. Do you think the internal signal to pounce could have been transmitted by a paracrine signal? Give two reasons to explain why or why not.

It could not have been a paracrine signal because the eyes are too far away from the legs. Also, the response was too rapid for it to have taken place by diffusion.

List two ways a cell may decrease its response to a signal.

It may down-regulate receptor number or decrease receptor affinity for the substrate.

List and compare the four classes of membrane receptors for signal pathways. Give an example of each.

Ligand-gated channels (ATP-gated K+ channel); integrin receptors (platelet receptors); receptor enzymes (tyrosine kinase receptor); G protein-coupled receptors (adenylyl cyclase/cAMP-linked receptors).

Compare and contrast the advantages and disadvantages of neural versus endocrine control mechanisms.

Neural control is faster than endocrine and better for short-acting responses. Endocrine control can affect widely separated tissues with a single signal and better for long-acting responses.

Name the four categories of membrane receptors.

Receptors are either ligand-gated ion channels, receptor-enzymes, G protein-coupled receptors, or integrins.

Name three cellular locations of receptors.

Receptors are on cell membrane or in cytosol or nucleus.

List four components of signal pathways.

Signal pathways have a signal molecule, receptor, intracellular signal molecule(s), and target proteins.

Why do steroid hormones not require signal transduction and second messengers to exert their action? (Hint: Are steroids lipophobic or lipophilic? [here])

Steroids are lipophilic, so they can enter cells and bind to intracellular receptors.

Arrange the following terms in the order of a reflex and give an anatomical example of each step when applicable: input signal, integrating center, output signal, response, sensor, stimulus, target.

Stimulus to sensor (sensory receptor) to input signal (sensory nerve) to integrating center. Integrating center (the brain or an endocrine cell) sends an output signal (through nerve or hormone) to target cell (muscles and glands), which reacts to the stimulus with a response.

Name the seven steps in a reflex control pathway in their correct order.

Stimulus, sensor or sensory receptor, input signal (afferent pathway), integrating center, output signal (efferent pathway), target or effector, response (tissue and systemic)

The extracellular fluid Ca2+ concentration averages 2.5 mmol/L. Free cytosolic Ca2+ concentration is about 0.001 mmol/L. If a cell is going to move calcium ions from its cytosol to the extracellular fluid, will it use passive or active transport? Explain.

The cell must use active transport to move Ca2+ against its concentration gradient.

Who was Walter Cannon? Restate his four postulates in your own words.

The father of American physiology. (1) The nervous system keeps body functions within normal limits. (2) Some functions have tonic control rather than on-off control. (3) Some signals act in opposition to each other. (4) Cell response depends on the cell's receptor for a signal.

What do receptors, enzymes, and transporters have in common that explains why they all exhibit saturation, specificity, and competition?

They are all proteins.

What is the difference between tonic control and antagonistic control?

Tonic control usually involves one control system, but antagonistic control uses two.

Match the following terms for parts of the knee jerk reflex to the parts of the simple neural reflex shown in Figure 6.19 : blow to knee, leg muscles, neuron to leg muscles, sensory neuron, brain and spinal cord, stretch receptor, muscle contraction.

blow to knee = internal or external change, leg muscles = targets, neuron to leg muscles = efferent neuron, sensory neuron = input signal, brain and spinal cord = CNS integrating center, stretch receptor = sensor or receptor, muscle contraction = response

What two types of physiological signals does the body use to send messages? Of these two types, which is available to all cells?

chemical (available to all cells) and electrical

Down-regulation results in a(n) (increased or decreased?) number of receptors in response to a prolonged signal.

decreased

Match the following terms with the appropriate parts of the simple neuroendocrine reflex in Fig. 6.19 (terms may be used more than once): food in stomach following a meal, brain and spinal cord, endocrine cells of pancreas, stretch receptors, efferent neuron to pancreas, insulin, adipose cell, blood, sensory neuron.

food in stomach = stimulus, brain and spinal cord = CNS integrating center, endocrine cells of pancreas = E (integrating center), stretch receptors = receptor, efferent neuron to pancreas = efferent neuron, insulin = classic hormone, adipose cell = target cell, sensory neuron = afferent neuron. Blood is the anatomical route that hormones use to reach their target but is not part of the reflex pathway.