Concept 32.2

Positive feedback differs from negative feedback in that

• positive feedback benefits the organism, whereas negative feedback is detrimental.
• the positive feedback's effector responses are in the same direction as the initiating stimulus rather than opposite to it.
• the effector's response increases some parameter (such as body temperature), whereas in negative feedback it can only decrease the parameter.
• positive feedback systems have only effectors, whereas negative feedback systems have only receptors.
• positive feedback systems have control centers that are lacking in negative feedback systems.

In a typical nerve cell, the nucleus is found in the

• cell body.
• synaptic terminals.
• axonal region.
• dendritic region.
• synapse.

Most types of communication between cells utilize

• the exchange of cytosol between the cells.
• a direct electrical connection between the cells.
• the release of chemical signals by the cell sending the message.
• the exchange of DNA between the cells.
• the movement of the cells.

Coordinating body functions via chemical signals is accomplished by

• the respiratory system.
• the endocrine system.
• the immune and lymphatic systems.
• the integumentary system.
• the excretory system.

All hormones

• are produced by endocrine glands.
• are lipid-soluble molecules.
• are carried to target cells in the blood.
• are protein molecules.
• elicit the same biological response from all of their target cells.

A cell with membrane-bound proteins that selectively bind a specific hormone is called that hormone's

• secretory cell.
• plasma cell.
• endocrine cell.
• target cell.
• regulatory cell.

The reason that the steroid hormone aldosterone affects only a small number of cells in the body is that

• only its target cells get exposed to aldosterone.
• only its target cells contain aldosterone receptors.
• it is unable to enter nontarget cells.
• nontarget cells destroy aldosterone before it can produce any effect.
• nontarget cells convert aldosterone to a hormone to which they do respond.

Different body cells can respond differently to the same peptide hormones because

• different target cells have different sets of genes.
• each cell converts that hormone to a different metabolite.
• a target cell's response is determined by the components of its signal transduction pathways.
• the circulatory system regulates responses to hormones by routing the hormones to specific targets.
• the hormone is chemically altered in different ways as it travels through the circulatory system.

When a steroid hormone and a peptide hormone exert similar effects on a population of target cells, then

• the steroid and peptide hormones must use the same biochemical mechanisms.
• the steroid and peptide hormones must bind to the same receptor protein.
• the steroid hormones affect the synthesis of effector proteins, whereas peptide hormones activate effector proteins already present in the cell.
• the steroid hormones affect the activity of certain proteins within the cell, whereas peptide hormones directly affect the processing of mRNA.
• the steroid hormones affect only the release of proteins from the target cell, whereas peptide hormones affect only the synthesis of proteins that remain in the target cell.

For hormones that homeostatically regulate cellular functions,

• negative feedback typically regulates hormone secretion.
• the circulating level of a hormone is held constant through a series of positive feedback loops.
• both lipid-soluble hormones and water-soluble hormones bind to intracellular protein receptors.
• endocrine organs release their contents into the bloodstream via specialized ducts.
• it is impossible to also have neural regulation of that system.