Seeley's Anatomy And Physiology 9Th Edition Chapter 17

Front 1

Chemical Messengers

Back 1

Produced by the Nervous and Endocrine Systems

Allow cells to communicate with each other to regulate body activities

Front 2

Secretion

Back 2

Controlled release of chemicals from a cell

Front 3

Autocrine Chemical Messengers

Back 3

Stimulates the cell that originally secreted it

ex. White blood cells can stimulate their own replication

Front 4

Paracrine Chemical Messengers

Back 4

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

Front 5

Neurotransmitters

Back 5

Chemical messengers secreted by neurons that activate adjacent cells.

Secreted into the synaptic cleft rather than the bloodstream.

ex. Epinephrine and acetylcholine

Front 6

Endocrine Chemical Messengers

Back 6

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

Front 7

Endocrine System

Back 7

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.

Front 8

Exocrine Glands

Back 8

Carry secretions to the outside of the body or into a hollow organ like the stomach or mouth.

Front 9

Similarities between the Nervous System and the Endocrine System

Back 9

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.
ex.

Front 10

Neuropeptide/Neurohormone

Back 10

A chemical messenger released by a neuron into the bloodstream that functions as a hormone

ex. Oxytocin - the labor inducing hormone.

Front 11

Differences between the Nervous System and the Endocrine System

Back 11

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.

Front 12

Amplitude-modulated signals

Back 12

Consist of fluctuations in the concentration of hormones in the bloodstream. The greater the concentration of hormone, the stronger the signal.

Front 13

Frequency-modulated signals

Back 13

All-or-none action potentials carried along axons. Can vary in frequency, but not amplitude. the higher the frequency, the stronger the stimulus.

Front 14

General Characteristics of Hormones

Back 14

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.

Front 15

Half-life

Back 15

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.

Front 16

Two reasons why hormones require assistance to arrive at target tissues

Back 16

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.

Front 17

Binding Proteins

Back 17

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.

Front 18

Free Hormones

Back 18

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.

Front 19

Lipid-Soluble Hormones

Back 19

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.

Front 20

Conjugation

Back 20

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.

Front 21

Water-Soluble Hormones

Back 21

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.

Front 22

Fenestrated

Back 22

The capillaries of organs that are regulated by protein hormones are usually very porous, or fenestrated,

Front 23

Water-soluble Hormones (the exceptions)

Back 23

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.

Front 24

Chronic Hormone Secretion

Back 24

A stable concentration of hormone is maintained in the circulating blood over a relatively long period.

ex. Thyroid hormone and growth hormone.

Front 25

Acute Hormone Secretion

Back 25

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

Front 26

Episodic Hormone Secretion

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A hormone is stimulated so that it increases and decreases the blood at a relatively consistent time and amount.

ex. reproductive hormones regulating menstruation

Front 27

Control of Hormone Release by Humoral Stimuli

Back 27

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.

Front 28

Control of Hormone Release by Neural Stimuli

Back 28

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.

Front 29

Neuropeptides/Releasing hormones

Back 29

Some neurons secrete chemical messengers directly into the blood when they are stimulated, making these messengers stimulate hormones.

Front 30

Control of Hormone Release by Hormonal Stimuli

Back 30

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.

Front 31

Inhibition of Hormone Release by Humoral Stimuli

Back 31

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.

Front 32

Inhibition of Hormone Release by Neural Stimuli

Back 32

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.

Front 33

Inhibition of Hormone Release by Hormonal Stimuli

Back 33

Some hormones prevent the secretion of other hormones.

ex. Thyroid hormones can control their own blood levels by inhibiting their pituitary tropic hormone.

Front 34

Negative Feedback

Back 34

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.

Front 35

Positive Feedback

Back 35

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.

Front 36

Receptors

Back 36

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.

Front 37

Decrease in Receptor Number/Down Regulation

Back 37

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.

Front 38

Increase in Receptor Number/Up Regulation

Back 38

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.

Front 39

Lipid-soluble Hormones Bind to Nuclear Receptors

Back 39

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

Front 40

Water-Soluble Hormones Bind to Membrane Bound Receptors

Back 40

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

Front 41

Hormone Response Elements

Back 41

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.

Front 42

Transcription Factor

Back 42

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.

Front 43

Membrane-Bound Receptors and Amplification

Back 43

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

Front 44

Intracellular Mediators

Back 44

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.

Front 45

Receptors that Activate G Proteins

Back 45

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Front 46

G Proteins

Back 46

Consist of three subunits - Alpha, beta, and gamma

One of the subunits binds to guanine nucleotides