• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off

Card Range To Study



Play button


Play button




Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

46 Cards in this Set

  • Front
  • Back
Chemical Messengers
Produced by the Nervous and Endocrine Systems

Allow cells to communicate with each other to regulate body activities
Controlled release of chemicals from a cell
Autocrine Chemical Messengers
Stimulates the cell that originally secreted it

ex. White blood cells can stimulate their own replication
Paracrine Chemical Messengers
Secreted by one cell type into the extracellular fluid and affect surrounding cells

ex. During allergic reactions, histamine is released by white blood cells to stimulate vasodialation in nearby blood vessels
Chemical messengers secreted by neurons that activate adjacent cells.

Secreted into the synaptic cleft rather than the bloodstream.

ex. Epinephrine and acetylcholine
Endocrine Chemical Messengers
Secreted into the bloodstream by certain glands and cells, which together constitute the endocrine system.

Affect cells distant from their source.

ex. Thyroid hormones, growth hormone, testosterone
Endocrine System
Composed of endocrine glands and specialized endocrine cells located throughout the body.

Endocrine glands secrete hormones (chemical messengers) into the bloodstream which travel to target tissues or effectors.
Exocrine Glands
Carry secretions to the outside of the body or into a hollow organ like the stomach or mouth.
Similarities between the Nervous System and the Endocrine System
Both have structures associated with the brain.
ex. The hypothalamus detects temperature and sends hormones to the pituitary gland that regulate the secretion of hormones from the pituitary.

Both use the same molecules
ex. A neuron can secrete epinephrine into a synaptic cleft as a neurotransmitter, and the adrenal gland can secrete epinephrine into the bloodstream as a hormone.

Both systems work together to regulate critical body processes.
ex. In a stressful situation, the initial release of epinephrine is through the nervous system, but is also released as a hormone.

Some Neurons secrete hormones rather than communicating directly with another cell.
ex. Oxytocin - the labor inducing hormone.

Both neurotransmitters and hormones can affect their targets through receptors linked to G proteins.
A chemical messenger released by a neuron into the bloodstream that functions as a hormone

ex. Oxytocin - the labor inducing hormone.
Differences between the Nervous System and the Endocrine System
Mode of Transport
The endocrine systems secretes hormones into the bloodstream.
The Nervous systems releases neurotransmitters directly to target cells.

Speed of Response
The endocrine system responds more slowly than the nervous system.

Duration of Response
The endocrine system's hormones can remain in the bloodstream for days and weeks and activate target tissues as long as they are present.
The nervous system activates targets quickly for as long as the action potential lasts.
Amplitude-modulated signals
Consist of fluctuations in the concentration of hormones in the bloodstream. The greater the concentration of hormone, the stronger the signal.
Frequency-modulated signals
All-or-none action potentials carried along axons. Can vary in frequency, but not amplitude. the higher the frequency, the stronger the stimulus.
General Characteristics of Hormones
Stability - Hormones remain stable in the blood stream

Communication - Hormones must be able to interact with their target tissue in specific ways to activate a coordinated set of events.
ex. A male having the outward appearance of a female without properly functioning male reproductive steroid.

Distribution - Hormones are transported by the bloodstream and have the potential to activate any cell in the body.
The life-span of a hormone, which varies with its chemical nature.

The amount of time it takes for 50% of the hormone to be removed from circulation and excreted.
Two reasons why hormones require assistance to arrive at target tissues
Small, water-soluble hormones are quickly digested by enzymes in the blood and become inactive with little change in their structure. They are also easily filtered from the blood and kidneys.

The chemical nature of some hormones do not allow them to dissolve in the blood. Lipid-soluble hormones must be bound to a protein to to become water-soluble.
Binding Proteins
Hormones requiring transport assistance bind to blood proteins called binding agents and are called bound hormones.

Hormones bind only to selective binding proteins.
ex. thyroid hormones bind to transthyretin but testosterone binds to a different protein.
Free Hormones
The binding of hormones to binding proteins is reversible. Hormones dissociate from their binding proteins at their target tissues and become free hormones. Some hormones always exist as free hormones, and do not bind to any proteins.

Only free hormones are able to diffuse through capillary walls to reach target tissues.

If blood levels of a hormone begin to decline, some of the bound hormone is released from the binding proteins.

Bound hormones are more stable in the blood than free hormones.
Lipid-Soluble Hormones
Non-polar, and include steroid hormones, thyroid hormones, and fatty acid derivative hormones.

Are small in size and have low solubility in aqueous fluids, so they travel in the bloodstream bound to proteins. Without binding, these hormones would quickly diffuse out of capillaries and would be degraded and removed from the body.

Long half lives.
Lipid soluble hormones can be removed from circulation when enzymes in the liver attach water-soluble molecules to the hormone.

These molecules are usually sulfate or glucuronic acid.
Water-Soluble Hormones
Polar molecules that include protein hormones, peptide hormones, and most amino acid derivatives except thyroxin.

Many circulate as free hormones and can dissolve in blood. They are large and do not diffuse through the walls of the capillaries, so they tend to diffuse from the blood into tissue spaces more slowly.

Short half-life, and rapidly degraded by enzymes called proteases.
The capillaries of organs that are regulated by protein hormones are usually very porous, or fenestrated,
Water-soluble Hormones (the exceptions)
Some water-soluble hormones are more stable in circulation than others. Peptide and protein hormones have a carbohydrate attached to them, or their terminal ends are modified. This protects them from protease activity. Some also attach to binding proteins.
Chronic Hormone Secretion
A stable concentration of hormone is maintained in the circulating blood over a relatively long period.

ex. Thyroid hormone and growth hormone.
Acute Hormone Secretion
A hormone rapidly increases in the blood for a short time in response to a specific stimulus.

ex. insulin following a meal and epinephrine in response to stress
Episodic Hormone Secretion
A hormone is stimulated so that it increases and decreases the blood at a relatively consistent time and amount.

ex. reproductive hormones regulating menstruation
Control of Hormone Release by Humoral Stimuli
Blood-borne molecules can directly stimulate the release of some hormones.

These hormones are sensitive to the blood levels of a particular substance like glucose or calcium. When the blood level of this molecule changes, the hormone is released.

ex. elevated blood glucose stimulate insulin secretion by the pancreas.
Control of Hormone Release by Neural Stimuli
Following action potentials, neurons release a neurotransmitter into the synapse with the cells that produce the hormone.

ex. In response to exercise, the sympathetic division of the ANS stimulates the adrenal gland to secrete norepinephrine.
Neuropeptides/Releasing hormones
Some neurons secrete chemical messengers directly into the blood when they are stimulated, making these messengers stimulate hormones.
Control of Hormone Release by Hormonal Stimuli
A hormone is secreted, and in turn stimulates the secretion of other hormones.

ex. Tropic hormones - The hypothalamus stimulates the release of a tropic hormone from the pituitary gland. The pituitary tropic hormone then travels to a third endocrine gland, and stimulated the release of a third hormone.
Inhibition of Hormone Release by Humoral Stimuli
There are often companion hormones.

ex. To raise blood pressure, the adrenal cortex secretes aldosterone. If the blood pressure goes up, the atria of the heart secrete the hormone atrial natriuretic peptide (ANP) to lower blood pressure.
Inhibition of Hormone Release by Neural Stimuli
If the neurotransmitter is inhibitory, the target endocrine gland does not secrete its hormone.

Hormones from the hypothalamus that prevent the secretion of tropic hormones from the pituitary gland are called inhibiting hormones.
Inhibition of Hormone Release by Hormonal Stimuli
Some hormones prevent the secretion of other hormones.

ex. Thyroid hormones can control their own blood levels by inhibiting their pituitary tropic hormone.
Negative Feedback
The hormone's secretion is inhibited by the hormone itself once blood levels have reached a certain point and there is adequate hormone to activate the target cell.

The hormone may inhibit the action of other, stimulatory hormones to prevent the secretion of the hormone in question.

ex. Thyroid hormones inhibit the secretion of TRH from the hypothalamus and TSH from the anterior pituitary.
Positive Feedback
Some hormones, when stimulated by a tropic hormone, promote the synthesis and secretion of the tropic hormone in addition to stimulating their target cell. In turn, this stimulated further secretion of the original hormone.

ex. Prolonged estrogen stimulation promotes the release of LH.
Hormones exert their actions by binding to proteins called receptors.

Hormones can stimulate only the cells that have the receptor for that hormone.

The tendency for a hormone to attach to one type of receptor and not to others is called specificity.
Decrease in Receptor Number/Down Regulation
The response of some target tissues decreases through time as a result of desensitization. Cell's nutrients and energy supplies become depleted, causing the cell to lose the ability to respond to the hormone. This causes a decrease in receptor molecules.
Increase in Receptor Number/Up Regulation
Target tissue can periodically increase sensitivity by increasing the number of receptor molecules.

ex. Increased number of receptor molecules for LH in ovary cells during each menstrual cycle.
Lipid-soluble Hormones Bind to Nuclear Receptors
LSH are relatively small and diffuse through the plasma membrane to bind to nuclear receptors that are found in the cell nucleus. The hormone receptor complex interacts with the DNA in the nucleus or with cellular enzymes to regulate the transcription of certain genes in the target tissue.

ex. Thyroid and steroid hormones
Water-Soluble Hormones Bind to Membrane Bound Receptors
Large molecules that cannot pass through the plasma membrane interact with membrane-bound-receptors. These are proteins that extend across the plasma membrane with their hormone binding sites exposed on the plasma membrane's outer surface. When a hormone binds to these receptors, the hormone-receptor complex initiates a response inside the cell.

ex. Peptides, amino acids derivatives such as epinepherine and norepinepherine
Hormone Response Elements
After lipid-soluble hormones diffuse across the membrane and bin to their receptors, the hormone-receptor complex binds to the DNA to produce a response. The receptors that bind to DNA have finger like projections that recognize and bind to specific nucleotide sequences in the DNA Called hormone response elements.
Transcription Factor
The combination of a hormone and its receptor forms a transcription factor. When the hormone-receptor complex binds to the hormone-response element, it activates the transcription of specific messenger RNA molecules. The mRNA molecules move to the cytoplasm to be translated into specific proteins at the ribosomes. The newly synthesized proteins produce the cell's response to the hormone.
Membrane-Bound Receptors and Amplification
MBR activate responses in two ways
1. Some receptors alter the activity of G proteins at the inner surface of the plasma membrane

2. Some receptors directly alter the activity of intracellular enzymes
Intracellular Mediators
Some MBR directly alter the activity of intracellular enzymes. These intracellular pathways elicit specific responses in cells, including the production of intracellular mediators or second messengers. This is a chemical produced inside a cell once a hormone or another chemical messenger binds to a certain MBR. The ICM then activates specific cellular processes inside the cell in response to the hormone. This is sometimes referred to as the second messenger system.
Receptors that Activate G Proteins
G Proteins
Consist of three subunits - Alpha, beta, and gamma

One of the subunits binds to guanine nucleotides