Human Physiology, 5e (Silverthorn) Chapter 6 Communication, Integration, and Homeostasis

Cells that respond to signals are usually called

targets.

Which is NOT a basic method of cell-to-cell communication?

mechanical signals

The most significant difference between a paracrine and an autocrine is

the cell that responds to it.

Neurotransmitters and neurohormones both

are released by neurons.

affect only cells with a specific receptor.

Why do some normal cells fail to respond to a chemical signal?

Some cells lack the necessary receptors.

Receptor molecules on the surface of a cell

may allow a particular ligand to bind.

determine that cell's response.

Receptor molecules are located

in the outer cell membrane.

in the cytosol.

in the nucleus.

Down-regulation may allow a target cell to

decrease its number of receptors for a ligand.

Inositol triphosphate

binds to the calcium channel of the endoplasmic recticulum.

is involved in the release of calcium into the cytosol.

Lipophilic hormones

bind to receptors inside the cytoplasm or nucleus.

When adenylyl cyclase is activated,

cAMP is formed.

Second messenger molecules directly

change the regulation of ion channels.

increase intracellular calcium concentration.

change enzyme activity.

Cyclic AMP activates

protein kinase A.

Diacylglycerol is produced from

phosphatidylinositol bisphosphate

Usually, cytokine binding activates

JAK kinase.

What by-product results during the production of nitric oxide?

citrulline

An integrating center

evaluates incoming signals and compares it with the setpoint.

Negative feedback

stabilizes the variable being regulated.

The increasingly forceful uterine contractions that lead to childbirth are an example of

positive feedback.

Match each term with its description:

the desired target value for a parameter

setpoint

Match each term with its description:

the allowable distance away from the setpoint before a response starts

sensitivity

Match each term with its description:

the minimum stimulus to trigger a response

threshold

Match each term with its description:

the organ or gland that performs the change

effector

Match each term with its description:

to move back and forth, or higher and lower

oscillate

Peripheral cells sensitive to the presence of hormones are called __________.

targets

A few gases are known to act as signal molecules, including __________, __________, and __________.

nitric oxide, carbon monoxide, hydrogen sulfide

Before nitric oxide was identified, its action was observed in __________ and it was given the name __________.

endothelial cells (blood vessel lining), endothelial-derived relaxing factor (EDRF)

__________ can be caused by alterations in receptors or by problems with G protein or second messenger pathways.

Answer: Diseases

Lipid signal molecules include __________ and __________.

eicosanoids, sphingolipids

__________ is a process by which an extracellular signal molecule, called the __________, activates a membrane receptor that in turn alters intracellular molecules, called the __________, to create a response.

Signal transduction, first messenger, second messenger

A gap junction forms when opposing membrane-spanning proteins called __________ on two adjacent cells unite, creating a protein channel that is capable of opening and closing.

connexins

A chemical that is secreted by a cell to act on cells in its immediate vicinity is called a(n) __________.

paracrine

If the signal molecule acts on the cell that secreted it, the chemical is called a(n) __________.

autocrine

All molecules secreted by nerve cells (neuromodulators, neurotransmitters, and neurohormones) are known as __________.

neurocrines

__________ are molecules that bind to the receptor in such a way that they block the normal ligand from binding and turning the receptor on. As a result, the signal pathway remains inactive.

Antagonists (or Competitive inhibitors)

If the concentration of an endocrine ligand decreases, the target cell may insert more receptors into the cell membrane in an attempt to keep its response at a normal level, in a process known as __________.

up-regulation

The adaptation of physiological processes to a given set of environmental conditions is known as __________ if it occurs naturally and as __________ if the process is induced artificially.

acclimatization, acclimation

The __________ link membrane receptors to either ion channels or to membrane enzymes located on the cytoplasmic face of the membrane.

G proteins

Many second messenger systems activate __________, enzymes that transfer a phosphate group from ATP to a protein. The phosphorylation of proteins sets off a series of intracellular events that lead to the ultimate cellular response.

protein kinases

Explain how epinephrine can cause intestinal blood vessels to constrict and cause skeletal muscle blood vessels to dilate.

Epinephrine can bind to different isoforms of the adrenergic receptor. Epinephrine binds to the alpha receptor on the intestinal blood vessels and beta receptors on the skeletal muscle blood vessels

The process of maintaining a relatively stable internal environment is called __________.

homeostasis

The control of homeostasis resides primarily in the __________ and __________ systems with their combination of chemical and electrical signals.

nervous, endocrine

In __________ feedback, the initial stimulus produces a response that escalates the stimulus.

positive

The secretion of the hormone insulin in response to changes in blood glucose level is an example of a(n) __________ reflex.

simple endocrine

Homeostatic regulation usually involves a(n) __________ that is sensitive to a particular stimulus and a(n) __________ whose activity has an effect on the same stimulus.

receptor; effector

When epinephrine combines with beta-2 adrenergic receptors on blood vessels, the __________ is relaxation of the smooth muscle while the __________ is increased blood flow through the vessel as a result of the relaxation.

cellular response, systemic response

The intracellular effector in chemical signaling is often

protein kinase.

Compare and contrast the four basic methods of cell-to-cell communication.

The cells can:

1. transfer signal molecules to adjacent cells through gap junctions

2. use contact-dependent signals, which rely on interactions between cell surface molecules on different cells

3. use locally acting chemicals, called paracrines, autocrines, or neuromodulators

4. use long-distance means, which rely on combinations of electrical and chemical signals

Explain the two forms of down-regulation

Either the number of receptors decreases or the binding affinity of the receptors for the ligand decreases. In both cases the result is a lessened response of the target cell even though the concentration of the signal molecule remains high.

What is the half-life of a signal?

the time required for a signal to lose half its activity

The most important factor determining which type of receptor a signal molecule will bind to is

the lipid solubility of the ligand.

An ion widely important in intracellular signaling is

calcium

When calcium becomes available inside a cell, it comes from

extracellular fluid.

intracellular storage

One intracellular calcium-binding protein is

Acalmodulin.

Signal molecule receptors exhibit

specificity.

competition.

saturation.

The binding of lipophilic messengers, such as steroid hormones, to their receptors triggers

gene transcription.

Both insulin and glucagon are peptide hormones that target liver cells. The response of the target cells to each of these two hormones is opposite. This information implies that

the two hormones bind to different cell surface receptors.

each of the two hormones uses a different second messenger.

Each of the following is an example of homeostasis except one. Identify the exception.

A rise in estrogen during the menstrual cycle increases the number of progesterone receptors in the uterus.

Which type of feedback promotes homeostasis?

negative