Chapter 17 Anatomy and Physiology
FIGURE 17.3 Effect of Binding Proteins
(a) Free hormones (those that circulate freely in the blood) immediately activate target cells once they are delivered from the blood. Thus, the blood levels of these hormones tend to fluctuate to a greater degree than the levels of hormones that attach to binding proteins; water-soluble hormones bind their receptors, which are membrane bound. (b) Hormones that are transported in the blood attached to binding proteins circulate in the blood as bound or free hormones. As the concentration of free hormones decreases, bound hormones are released form the binding proteins. This provides a chronic, stable supply of hormone and, thus, more consistent control of target cells. This is especially important for hormones that regulate basal metabolism. Lipid-soluble hormones bind their receptors in either cytoplasm or the nucleus.
What are the four types of chemical messengers?
1. Autocrine 2. Paracrine 3. Neurotransmitters 4. Endocrine
What are some similarities between the endocrine system and nervous system?
1. Both systems use structures in the brain. In chapter 13, the hypothalamus is discussed as a critical area of the brain responsible for many functions, including nervous system functions and hormone production. An example of nervous function is when the hypothalamus detects changes in body temperature; it sends action potentials to either the sweat glands or skeletal muscle, depending on whether the body is too hot or too cold. On the other hand, an example of endocrine function is when the hypothalamus sends hormones to the pituitary gland that regulate the secretion of hormones from the pituitary. In addition, hypothalamic neurons synthesize two hormones, anitdiuretic hormone and oxytocin, which are secreted directly into the blood stream. Thus, the hypothalamus plays a role in both the nervous and endocrine system. 2. In many cases, the nervous system may use certain molecules as neurotransmitters, whereas the endocrine system may use these molecules as hormones. For example, when a neuron secretes epinephrine into a synaptic cleft, it is a neurotransmitter. In contrast, when cells of the adrenal gland secrete epinephrine into the bloodstream, it is a hormone. 3. The two systems work together to regulate critical body processes. For example, epinephrine, the hormone, is important in stressful situations. However, the initial, immediate release of epinephrine, the neurotransmitter, in times of crisis is from the nervous system. Thus, the two system work almost simultaneously. 4. Some neurons secrete hormones. In this case, the neuron's chemical messenger enters the bloodstream, where it functions as a hormone. As a strict part of their definition, recall that hormones circulate in the bloodstream. To help distinguish these chemical messengers from neurotransmitters and other hormones, they are often called neuropeptides, or neurohormones. An example of a neuropeptide is the labor-inducing hormone oxytocin. 5. Both neurotransmitters and hormones can affect their targets through receptors linked to G proteins.
What is Chronic hormone secretion?
1. Chronic hormone secretion results in relatively constant blood levels of hormone over long periods of time. For example, thyroid hormones circulate in the blood within a small range of concentrations. Recall that thyroid hormones are lipid soluble and thus bind to binding proteins, which also helps maintain them at chronic levels.
Describe chronic, acute, and episodic patterns of hormone secretion.
1. Chronic hormone secretion results in relatively constant blood levels of hormone over long periods of time. For example, thyroid hormones circulate in the blood within a small range of concentrations. Recall that thyroid hormones are lipid-soluble and thus bind to binding proteins, which also helps maintain them at chronic levels. 2. Acute hormone secretion occurs when the hormone's concentration changes suddenly and irregularly, and its circulating levels differentiations with each stimulus. For example, the amino acid derivative epinephrine is released in large amounts in response to stress or physical exercise. In addition, because epinephrine is small and usually circulates as a free hormone, it has a short half-life, which contributes to the fact that blood levels of epinephrine drop significantly within a few minutes of its secretion. 3. Episodic hormone secretion occurs when hormones are secreted at fairly predictable intervals and concentrations. An example of hormones secreted with this pattern are steroid reproductive hormones. Some reproductive steroid hormones fluctuate over a month in cyclic fashion during the human reproductive years. Additionally, because steroid hormones also often have binding proteins, they have longer half-lives than other hormones, which contributes to their relative stability.
What kinds of activities are regulated by hormones with a short half-life? With a long half-life?
1. Chronic hormone secretion results in relatively constant blood levels of hormone over long periods of time. For example, thyroid hormones circulate in the blood within a small range of concentrations. Recall that thyroid hormones are lipid-soluble and thus bind to binding proteins, which also helps maintain them at chronic levels. 2. Acute hormone secretion occurs when the hormone's concentration changes suddenly and irregularly, and its circulating levels differentiations with each stimulus. For example, the amino acid derivative epinephrine is released in large amounts in response to stress or physical exercise. In addition, because epinephrine is small and usually circulates as a free hormone, it has a short half-life, which contributes to the fact that blood levels of epinephrine drop significantly within a few minutes of its secretion. 3. Episodic hormone secretion occurs when hormones are secreted at fairly predictable intervals and concentrations. An example of hormones secreted with this pattern are steroid reproductive hormones. Some reproductive steroid hormones fluctuate over a month in cyclic fashion during the human reproductive years. Additionally, because steroid hormones also often have binding proteins, they have longer half-lives than other hormones, which contributes to their relative stability.
What are three modifications to hormones that protect them from being destroyed?
1. Having a carbohydrate attached to them. These hormones are then called glycoproteins. 2. Having a modified terminal end. These modifications protect them from protease activity to a greater extent than water-soluble hormones lacking such modifications. 3. Having binding proteins. Bound hormones circulate in the plasma longer than free water-soluble hormones do.
What are the differences between the nervous system and the endocrine system?
1. Mode of transport. The endocrine system secretes hormones, which are transported in the bloodstream, whereas the nervous system secretes neurotransmitters, which are released directly onto their target cells. 2. Speed of response. In general, the nervous system responds faster than the endocrine system. However, it is not accurate to say the endocrine system responds slowly, rather, it responds more slowly than the nervous system. Neurotransmitters, such as acetylcholine, are delivered to their target cells in milliseconds, whereas some hormones are delivered to their target cells in seconds. 3. Duration of response. The nervous system typically activates its targets quickly and only for as long as action potentials are sent to the target. The target cells' response is terminated shortly after action potentials cease. In contrast, the endocrine system tends to have longer-lasting effects. Hormones remain in the bloodstream for minutes, days, or even weeks and activate their target tissues as long as they are present in the circulation. The target tissue products may remain active for a substantial length of time.
What are three characteristics of hormones?
1. Stability 2. Communication 3. Distribution
Explain stability.
1. Stability. Hormone concentrations are stable in the bloodstream; however, some hormones are more stable than others. The life span of a given hormone varies with its chemical nature. Larger, more complex hormones are more stable, whereas smaller, simpler hormones are less stable. A hormone's life span can be expressed as its half-life, which is the amount of time it takes for 50% of the circulating hormone to be removed from the circulation and excreted. Some hormones have a short half-life, whereas others have a much longer half-life. For example, thyrotropin-releasing hormone (TRH) is a three-amino-acid hormone with a short half-life. Because of TRH's simple composition, it is quickly degraded in the circulation and can activate only the target cells it can reach within 2 minutes of being secreted. On the other hand, cortisol is a steroid hormone with a longer half-life, 90 minutes. Due to its lipid-soluble nature, it is not easily degraded and can activate target cells for more than an hour.
Explain communication of hormones.
2. Communication. Hormones must be able to interact with their target tissue in a specific manner in order to activate a coordinated set of events. For example, the formation of reproductive organs in the fetus is activated by reproductive steroid hormones. This interaction occurs at a receptor on the target cells. Without proper functioning of the male reproductive steroid testosterone, a newborn will have the outward appearance of a female despite being genetically male. Hormones must be able to regulate specific cellular pathways once they arrive at their targets and bind to their receptors.
Explain distribution of hormones.
3. Distribution. Hormones are transported by the blood to many locations and therefore have the potential to activate any cell in the body, including those far away from where they were produced. However, the blood contains many hydrolytic enzymes, which break down substances. In addition, blood is an aqueous solution. These factors can present a challenge when transporting hormones to their targets. Small, water-soluble hormones are quickly digested by hydrolytic enzymes in the blood. With their small size, they become inactive with very little alteration in their structure. In addition, water-soluble hormones are easily filtered from the blood in the kidneys because they are so small. Still other hormones, such as lipid-soluble hormones, have low solubility in the blood plasma. The chemical nature of lipid-soluble hormones does not allow these hormones to easily dissolve in the plasma. Thus, some hormones require a chaperone, which binds to and protects hormones so that they arrive safely at their target. Hormones requiring a transport chaperone bind to blood proteins called binding proteins. Once hormones attach to a binding protein, they are then called bound hormones. For small hormones, the binding protein protects them from degradation by hydrolytic enzymes and from being filtered from the blood in the kidney. For lipid-soluble hormones that are insoluble in plasma, being bound to a binding protein causes them to become more water-soluble. Hormones bind only to selective binding proteins. For example, thyroid hormones bind to a specific binding protein, transthyretin; testosterone binds to a different type of binding protein, called testosterone-binding globulin; and progesterone binds to yet another type of binding protein, called progesterone-binding globulin.
Episodic hormone secretion.
A hormone is stimulated so that it increases and decreases in the blood at a relatively consistent time and thoroughly the same amount. Examples are the reproductive hormones regulating menstruation.
Acute hormone secretion.
A hormone rapidly increases in the blood for a short time inresponse to a specific stimulus-for example, insulin (the blood sugar-regulating hormone) secretion following a meal. Note that the size of the stimulus arrow represents the stimulus strength. A smaller stimulus does not activate as much hormone secretion as a larger stimulus.
Chronic hormone secretion.
A relatively stable concentration of hormone is maintained in the circulating blood over a fairly long period, up to several weeks. This pattern is exemplified by the thyroid hormones.
What is acute hormone secretion?
Acute hormone secretion occurs when the hormone's concentration changes suddenly and irregularly, and its circulating levels differ with each stimulus. For example, the amino acid derivative epinephrine is released in large amounts in response to stress or physical exercise. In addition, because epinephrine is small and usually circulates as a free hormone, it has a short half-life, which contributes to the fact that blood levels of epinephrine drop significantly within a few minutes of its secretion.
Liu Dan was one of the top wrestlers on his high school team, but he knew that his small size would make it difficult to compete at the college level. He had tried lifting weights, but that did not seem to be working. So Liu decided to try something he had never thought he would do--he began taking anabolic steroids. At first he was excited, because his muscles were larger and he felt stronger. After a few more weeks, though, he started noticing some troublesome changes: His pectoral muscles were getting larger, but they looked more feminine than masculine; his testes had shrunk; and he'd had some frightening episodes that could only be described as temper tantrums. After reading this chapter, explain any anabolic steroids were able to alter muscle tissue growth and cause unintended changes in other tissues of the body.
After using anabolic steroids, Liu Dan's muscles increased in size, but he also experienced some unintended changes, including slight breast development, reduced testes size, and mood swings. We learned in this chapter that steroid hormones are all derived form cholesterol, a type of lipid, and are thus lipid-soluble. We also know that hormones, chemical messengers produced by the endocrine system, travel through the body via the bloodstream until they arrive at their target tissues. The cells of target tissues posses specific receptors that the hormones bind to an initiate changes in cellular metabolism or cell growth. Steroid hormones, because they are lipid-soluble, bind to intracellular receptors in the cell's cytoplasm or nucleus. Once the steroid hormone has bound to its receptor, the hormone-receptor complex stimulates increased gene expression and therefore increased protein production. In muscle cells, this leads to the increased muscle mass that Liu Dan experienced. However, other tissues of the body contain receptors that can also bind the anabolic steroids, so using anabolic steroids can cause some unintended effects. The anabolic steroids Liu Dan used also led to the abnormal breast tissue growth, decreased testes size, and behavioral changes. Thus, although it may be tempting to take anabolic steroids to increase muscle mass, the risk for side effects is simply too great.
Describe the destruction of hormones.
All hormones are destroyed either in the circulation or at their target cells. The destruction and elimination of hormones limit the length of time they are active, and body processes change quickly when hormones are secreted and remain functional for only short periods. The water-soluble hormones have relatively short half-lives because they are rapidly broken down by hydrolytic enzymes, called proteases, within the bloodstream. The kidneys then remove the hormone breakdown products from the blood. Target cells also destroy water-soluble hormones when the hormones are internalized via endocytosis. Once the hormones are inside the target cell, lysosomal enzymes degraded them. Often, the target cell recycles the amino acids of peptide and protein hormones and uses them to synthesize new proteins. Thus, hormones with short half-lives normally have concentrations that change rapidly within the blood and tend to regulate activities that have a rapid onset and short duration.
What are autocrine chemical messengers?
An autocrine (auto-, self) chemical messenger stimulates the cell that originally secreted it. Good examples of autocrine chemical messengers are those secreted by white blood cells during an infection. Several types of white blood cells can stimulate their own replication, so that the total number of white blood cells increases rapidly.
What determines the blood levels of hormones?
As a result of the variation in transport and removal of lipid-soluble hormones and water-soluble hormones, the blood levels of hormones differ. In addition, blood levels of hormones are further determined by the overall pattern of secretion.
What do hormones stimulate?
At their target tissues, hormones stimulate a specific response.
Name and describe the four classes of chemical messengers.
Autocrine- From a cell to act on that cell, Eicosanoids Paracrine- From a cell, travels a short distance to act on local cells. histamine, somatostatin, eicosanoids. Neurotransmitters- into the synaptic cleft. Acetylcholine, Epinephrine. Endocrine- into the blood, hormones
Describe how the chemical nature of a hormone affects its transport in the blood, its removal from circulation, and its half-life.
Based on chemical structure and size of the hormone determines where it can travel how quickly and if it needs help or not.
Where do lipid-soluble hormones travel?
Because of their small size and low solubility in aqueous fluids, lipid-soluble hormones travel in the bloodstream bound to binding proteins, proteins that chaperone the hormone. As a result, the rate at which lipid-soluble hormones are degraded or eliminated from the circulation is greatly reduced and their life spans range from a few days to as long as weeks.
Describe how water-soluble hormones circulate?
Because water-soluble hormones can dissolve in the plasma of the blood, many circulate as free hormones, meaning that most of them dissolve directly into the plasma and are delivered to their target tissue without binding to a binding protein. Because may water-soluble hormones are quite large, they do not readily diffuse through the walls of all capillaries. Instead, they tend to diffuse from the blood into tissue spaces more slowly. Thus, capillaries of organs that are regulated by protein hormones tend to be very porous, or fenestrated.
Describe the similarities between the nervous system and the endocrine system.
Both send chemical messengers throughout the body to maintain the physiological process of cells, organs and organ systems.
What is the main similarity and difference between the nervous system and endocrine system?
Both the nervous system and the endocrine system work to maintain homeostasis using chemical messengers, but they differ from each other in the way their chemical messengers work to activate their target cells.
Chemical Messenger: Paracrine
Description: Produced by a wide variety of tissues and secreted into extracellular fluid; has a localized effect on nearby tissues Example: Somatostatin, histamine, eicosanoids
Chemical Messenger: Neurotransmitter
Description: Produced by neurons; secreted into a synaptic cleft by presynaptic nerve terminals; travels short distances; influences postsynaptic cells Example: Acetylcholine, epinephrine
Chemical Messenger: Autocrine
Description: Secreted by cells in a local area; influences the activity of the same cell from which it was secreted Example: Eicosanoids (prostaglandins, thromboxjnes, prostacyclin, leukotrienes)
Chemical Messenger: Endocrine
Description: Secreted into the blood by specialized cells; travels some distance to target tissues; results in coordinated regulation of cell function Example: Thyroid hormones, growth hormone, insulin, epinephrine, estrogen, progesterone, testosterone.
What are endocrine chemical messengers?
Endocrine chemical messengers. Endocrine chemical messengers are secreted into the bloodstream by certain glands and cells, which together make up the endocrine system. These chemical messengers travel through the general circulation to their target cells.
What are exocrine glands?
Endocrine glands are not to be confused with exocrine glands. Exocrine glands have ducts that carry their secretions to the outside of the body, or into a hollow organ, such as the stomach or intestines. The pancreas is endocrine and an exocrine gland.
What do endocrine glands secrete?
Endocrine glands secrete very small amounts of chemical messengers called hormones into the interstitial fluid.
How does an endocrine gland differ from an exocrine gland?
Endocrine glands secrete very small amounts of chemical messengers called hormones into the interstitial fluid. Exocrine glands are not to be confused with exocrine glands. Exocrine glands have ducts that carry their secretions to the outside of the body, or into a hollow organ, such as the stomach or intestines.
What are episodic hormone secretion?
Episodic hormone secretion occurs when hormones are secreted at fairly predictable intervals and concentrations. An example of hormones secreted with this pattern are steroid reproductive hormones. Some reproductive steroid hormones fluctuate over a month in cyclic fashion during the human reproductive years. Additionally, because steroid hormones also often have binding proteins, they have longer half-lives than other hormones, which contributes to their relative stability in the circulation.
What are some examples of exocrine secretions?
Examples of exocrine secretions are saliva, sweat, breast milk, and digestive enzymes.
Chemical Nature: Water-Soluble Hormones
Examples: Amino Acid Derivatives Epinephrine
Chemical Nature: Lipid-Soluble Hormones
Examples: Amino acid derivative (only one example of lipid-soluble) Thyroid hormone (thyroxine)
Chemical Nature: Lipid-Soluble Hormones
Examples: Fatty acid derivatives Prostaglandins
Chemical Nature: Water-Soluble Hormones
Examples: Peptides Insulin, thyrotropin-releasing hormone
Chemical Nature: Lipid-Soluble Hormones
Examples: Steroids (all cholesterol-based) Testosterone, aldosterone
Chemical Nature: Water-Soluble Hormones
Examples: Thyroid-stimulating hormone, growth hormone
FIGURE 17.1 Major Endocrine Glands and Tissues
Glands that secrete chemical messengers that are transported to their targets by the blood are endocrine glands.
Where do hormones circulate through?
Hormones circulate through the bloodstream to specific sites called target tissues, or effectors.
What are free hormones?
Hormones dissociate (detach) from their proteins at their target tissues. Once the hormones detach from the binding protein, they are then called free hormones.
What are the two chemical categories of hormones?
Hormones fit into two chemical categories: (1) lipid-soluble hormones and (2) water-soluble hormones, a distinction based on their chemical behavior.
What role do hormones take?
Hormones have a role in most physiological processes in the body. However, the endocrine system does not work completely alone for every process it regulates.
What effects does a bound hormone have on the concentration of a free hormone in the blood?
Hormones requiring a transport chaperone bind to blood proteins called binding proteins. Once hormones attach to a binding protein, they are then called bound hormones. For small hormones, the binding protein protects them from degradation by hydrolytic enzymes and from being filtered from the blood in the kidney. For lipid-soluble hormones that are insoluble in plasma, being bound to a binding protein causes them to become more water-soluble.
What is conjugation?
In order to terminate a lipid-soluble hormone response, these hormones are removed from the circulation through a process called conjugation. Conjugation occurs when specific enzymes in the liver attach water-soluble molecules to the hormones. These water-soluble conjugation molecules are usually sulfate or glucuronic acid. Once the hormones are conjugated, the kidneys and liver can excrete them into the urine and bile at a greater rate.
Are hormones always free?
It is important to note that some hormones always exist as free hormones because they do not have specific binding proteins to which they attach. Thus, some hormones are "always free," whereas other hormones are "sometimes free."
What does the endocrine system work with?
It works in conjunction with the body's other major regulatory system, the nervous system.
What are the two chemical categories of hormones? Give examples of both types.
Lipid soluble= steroid hormones, thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids. Water soluble= protein hormones, peptide hormones, and most amino acid derivative hormones.
Describe lipid-soluble hormones.
Lipid-soluble hormones are non polar and include steroid hormones, thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids.
What in the blood stream can directly stimulate the release of some hormones?
Metabolites and other molecules in the bloodstream can directly stimulate the release of some hormones. These metabolites and molecules in the blood are referred to as humoral stimuli. The term humoral refers to body fluids, including blood.
In what ways does the nervous system differ from the endocrine system?
Nervous system differs in how long it takes for them to send a signal and how long that signal lasts. They differ in what secrete, nervous system secretes neurotransmitters, while the endocrine system secretes hormones. Some neurotransmitters are hormones, because they travel in the blood. Endocrine signals last longer than nervous signals depending on the the strength of the stimulus or the half life of the hormone.
What are neurotransmitters?
Neurotransmitters. Neurotransmitters are chemical messengers secreted by neurons that activate an adjacent cell, whether it is another neuron, a muscle cell, or a glandular cell. Neurotransmitters are secreted into a synaptic cleft, rather than into the bloodstream. Therefore, in the strictest sense neurotransmitters are paracrine agents, but for our purposes it is most appropriate to consider them as a separate category
What are paracrine chemical messengers?
Paracrine chemical messengers. Paracrine chemical messengers act locally on neighboring cells. These chemical messengers are secreted by one cell type into the extracellular fluid and affect surrounding cells. An example of a paracrine chemical messenger is histamine, released by certain white blood cells during allergic reactions. Histamine stimulates vasodilation in nearby blood vessels.
amplitude-modulated signal
Signal that varies in magnitude or intensity, such as the large versus small concentrations of hormones.
Why do some hormones require a binding protein during transport in the blood?
Some hormones can not survive in the blood because of their chemical nature or enzymatic proteins that break them down. In order to survive they travel with proteins that allow them to arrive at their target tissues.
What are the three general characteristics of hormones?
Stability. Hormones can survive for a long time based off of their chemical structure and modifications. And if they are bound to a protein. Communication. Hormones act as chemical messengers to produce a response at target tissues to maintain homeostasis. Distribution. Hormones are transported throughout the blood, it is important that they stay alive in order to carry out their response.
Hormone
Substance secreted by endocrine tissues into the blood that acts on a target tissue to produce a specific response.
What can all-or-none action potentials carried along axons be described as?
The all-or-none action potentials carried along axons can be described as frequency-modulated signals.
Amplitude-modulated system.
The concentration of the hormone determines the strength of the signal and the magnitude of the response. For most hormones, a small concentration of a hormone is a weak signal and produces a small response, whereas a larger concentration is a stronger signal and results in a greater response.
What is the endocrine system based on?
The endocrine system is based on changing the concentration of hormones.
What is the endocrine system composed of?
The endocrine system is composed of endocrine glands and specialized endocrine cells located throughout the body.
How does the endocrine system work?
The endocrine system works more like Twitter. Your tweets are broadcast, so anyone can see them, but only those following you actually get them. But, instead of tweets, the endocrine system broadcasts information to the whole body through chemical messengers called hormones circulating in the bloodstream.
Where do hormones diffuse into?
The hormones diffuse into the blood to be transported to their target.
What can the hormones secreted by most endocrine glands be described as?
The hormones secreted by most endocrine glands can be describe as amplitude-modulated signals.
Explain how the half-life of a hormone relates to its stability.
The life span of a given hormone varies with its chemical nature. Larger, more complex hormones are more stable, whereas smaller, simpler hormones are less stable. A hormone's life span can be expressed as its half-life, which is the amount of time it takes for 50% of the circulating hormone to be removed from the circulation and excreted. Some hormones have a short half-life, whereas others have a much longer half-life.
What is the nervous system based on?
The nervous system is based on changing the frequency of the messages.
What is the nervous system like?
The nervous system operates similarly to how you send a text to one or more people.
FIGURE 17.4 Patterns of Hormone Secretion
The overall pattern of hormone secretion is a result of the secretion, transport, and removal of the hormones, which is further dependent on the chemical nature of the hormones. (a) Chronic hormone secretion occurs over a relatively long period. (b) Acute hormone secretion occurs over a relatively short period. (c) Episodic hormone secretion occurs in relatively predictable bursts.
Frequency-modulate system
The strength of the signal depends on the frequency, not the size, of the action potentials. All action potentials are the same size in a given tissue. A low frequency of action potentials is a weak stimulus, and a higher frequency is a stronger stimulus.
Describe amplitude.
The term amplitude refers to the total amount of a single that is produced. This type of signal consists of fluctuations in the concentration of hormones in the bloodstream, over a period of time. This time period can range from minutes to hours.
Describe the term frequency.
The term frequency refers to how often a signal is sent in a certain period of time. These types of signals vary in the number of signals sent but not in the amount of signal sent.
Where is the word hormone derived from?
The word hormone is derived from the Greek word hormone, which means "set into motion." Hormones are very powerful molecules, which all share general characteristics.
What happens to the half-life when a hormone binds to a binding protein? What kinds of hormones bind to binding proteins?
Their half-life lengthens. For example, thyroid hormones bind to a specific binding protein, transthyretin; testosterone binds to a different type of binding protein, called testosterone-binding globulin; and progesterone binds to yet another type of binding protein, called progesterone-binding globulin.
What are the three main patterns of hormone secretion?
There are three main patterns of hormone secretion, however, individual hormones can be secreted in more than one pattern. These three main patterns are (1) chronic, (2) acute, and (3) episodic.
What is the role of chemical messengers in the body?
They allow cells to communicate with each other to regulate body activities.
What are the three types of stimuli regulate hormone release?
Three types of stimuli regulate hormone release: (1) humoral, (2) neural, and (3) hormonal.
How are the homeostatic ranges of hormones regulated?
Through negative and positive feedback mechanisms.
What is the word endocrine derived from?
Thus, the term endocrine, derived from the Greek words endocrine, meaning "within," and krino, "to secrete," appropriately describes this system.
What do the nervous system and endocrine system regulate?
Together, the nervous system and the endocrine system regulate and coordinate the activities of essentially all body structures to achieve and maintain homeostasis.
What are water-soluble hormones?
Water-soluble hormones are polar molecules; they include protein hormones, peptide hormones, and most amino acid derivative hormones.
How do hormones act as reservoirs?
When bound to a binding protein, a hormone is too large to pass through a capillary wall. The bound hormone thus serves as a reservoir for the hormone. If blood levels of the hormone begin to decline, some of the bound hormone is released form the binding proteins. because of this reservoir function of the bound hormones, the circulating concentration of free hormones remains more stable than that of hormones that do not use binding proteins.
What would happen to lipid-soluble hormones without binding proteins?
Without the binding proteins, the lipid-soluble hormones would quickly diffuse out of capillaries and be degraded by enzymes of the liver and lungs or be filtered from the blood by the kidneys and would be unable to effectively regulate their targets.
