17.1: Maelezo ya jumla ya Mfumo wa Endocrine
- Page ID
- 178415
Malengo ya kujifunza
- Tofautisha aina ya mawasiliano ya intercellular, umuhimu wao, taratibu, na madhara
- Kutambua viungo kuu na tishu za mfumo wa endocrine na eneo lao katika mwili
Mawasiliano ni mchakato ambapo mtumaji hupeleka ishara kwa mpokeaji mmoja au zaidi ili kudhibiti na kuratibu vitendo. Katika mwili wa mwanadamu, mifumo miwili ya chombo kuu hushiriki katika mawasiliano ya “umbali mrefu”: mfumo wa neva na mfumo wa endocrine. Pamoja, mifumo hii miwili ni hasa inayohusika na kudumisha homeostasis katika mwili.
Neural na Endocrine Ishara
Mfumo wa neva hutumia aina mbili za mawasiliano baina ya seli—umeme na kemikali-ama kwa hatua ya moja kwa moja ya uwezo wa umeme, au katika kesi ya mwisho, kupitia hatua ya nyurotransmita kemikali kama vile serotonini au norepinephrine. Neurotransmitters hufanya kazi ndani ya nchi na kwa haraka. Wakati ishara ya umeme katika mfumo wa uwezo wa hatua hufika kwenye terminal ya sinepsi, huenea katika ufafanuzi wa sinepsi (pengo kati ya neuroni ya kutuma na neuroni ya kupokea au seli ya misuli). Mara baada ya nyurotransmita kuingiliana (kumfunga) na vipokezi kwenye kiini cha kupokea (baada ya sinepsi), kichocheo cha receptor kinabadilishwa kuwa majibu kama vile kuashiria umeme ulioendelea au urekebishaji wa majibu ya seli. Kiini cha lengo hujibu ndani ya nukta za kupokea “ujumbe” wa kemikali; jibu hili halafu hukoma haraka sana mara moja ishara ya neural inaisha. Kwa njia hii, mawasiliano ya neural huwezesha kazi za mwili zinazohusisha vitendo vya haraka, vifupi, kama vile harakati, hisia, na utambuzi.Kwa upande mwingine, mfumo wa endocrine hutumia njia moja tu ya mawasiliano: ishara ya kemikali. Ishara hizi zinatumwa na viungo vya endocrine, ambavyo hutoa kemikali-homoni —ndani ya maji ya ziada. Homoni ni kusafirishwa hasa kupitia damu katika mwili, ambapo wao kumfunga kwa receptors juu ya seli lengo, inducing majibu tabia. Matokeo yake, ishara ya endocrine inahitaji muda zaidi kuliko ishara ya neural ili kuchochea majibu katika seli za lengo, ingawa kiasi sahihi cha muda hutofautiana na homoni tofauti. Kwa mfano, homoni zilizotolewa wakati unakabiliwa na hali ya hatari au ya kutisha, inayoitwa majibu ya kupigana-au-kukimbia, hutokea kwa kutolewa kwa homoni za adrenal-epinephrine na noradrenaline-ndani ya sekunde. Kwa upande mwingine, inaweza kuchukua hadi saa 48 kwa seli za lengo kujibu homoni fulani za uzazi.
Kwa kuongeza, ishara ya endocrine ni kawaida kidogo kuliko ishara ya neural. Homoni hiyo inaweza kuwa na jukumu katika aina mbalimbali za michakato mbalimbali ya kisaikolojia kulingana na seli lengo kushiriki. Kwa mfano, homoni oxytocin inakuza contractions uterine katika wanawake katika kazi. Pia ni muhimu katika kunyonyesha, na inaweza kushiriki katika majibu ya ngono na katika hisia za attachment kihisia katika wanaume na wanawake.
Kwa ujumla, mfumo wa neva unahusisha majibu ya haraka kwa mabadiliko ya haraka katika mazingira ya nje, na mfumo wa endokrini ni kawaida polepole kazi-kutunza mazingira ya ndani ya mwili, kudumisha homeostasis, na kudhibiti uzazi (Jedwali\(\PageIndex{1}\)). So how does the fight-or-flight response that was mentioned earlier happen so quickly if hormones are usually slower acting? It is because the two systems are connected. It is the fast action of the nervous system in response to the danger in the environment that stimulates the adrenal glands to secrete their hormones. As a result, the nervous system can cause rapid endocrine responses to keep up with sudden changes in both the external and internal environments when necessary.
| Endocrine system | Nervous system | |
|---|---|---|
| Signaling mechanism(s) | Chemical | Chemical/electrical |
| Primary chemical signal | Hormones | Neurotransmitters |
| Distance traveled | Long or short | Always short |
| Response time | Fast or slow | Always fast |
| Environment targeted | Internal | Internal and external |
Structures of the Endocrine System
The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function. The endocrine gland is the major player in this system. The primary function of these ductless glands is to secrete their hormones directly into the surrounding fluid. The interstitial fluid and the blood vessels then transport the hormones throughout the body. The endocrine system includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands (Figure \(\PageIndex{1}\)). Some of these glands have both endocrine and non-endocrine functions. For example, the pancreas contains cells that function in digestion as well as cells that secrete the hormones insulin and glucagon, which regulate blood glucose levels. The hypothalamus, thymus, heart, kidneys, stomach, small intestine, liver, skin, female ovaries, and male testes are other organs that contain cells with endocrine function. Moreover, adipose tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.
The ductless endocrine glands are not to be confused with the body’s exocrine system, whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. As just noted, the pancreas also has an exocrine function: most of its cells secrete pancreatic juice through the pancreatic and accessory ducts to the lumen of the small intestine.
Other Types of Chemical Signaling
In endocrine signaling, hormones secreted into the extracellular fluid diffuse into the blood or lymph, and can then travel great distances throughout the body. In contrast, autocrine signaling takes place within the same cell. An autocrine (auto- = “self”) is a chemical that elicits a response in the same cell that secreted it. Interleukin-1, or IL-1, is a signaling molecule that plays an important role in inflammatory response. The cells that secrete IL-1 have receptors on their cell surface that bind these molecules, resulting in autocrine signaling.
Local intercellular communication is the province of the paracrine, also called a paracrine factor, which is a chemical that induces a response in neighboring cells. Although paracrines may enter the bloodstream, their concentration is generally too low to elicit a response from distant tissues. A familiar example to those with asthma is histamine, a paracrine that is released by immune cells in the bronchial tree. Histamine causes the smooth muscle cells of the bronchi to constrict, narrowing the airways. Another example is the neurotransmitters of the nervous system, which act only locally within the synaptic cleft.
CAREER CONNECTIONS: Endocrinologist
Endocrinology is a specialty in the field of medicine that focuses on the treatment of endocrine system disorders. Endocrinologists—medical doctors who specialize in this field—are experts in treating diseases associated with hormonal systems, ranging from thyroid disease to diabetes mellitus. Endocrine surgeons treat endocrine disease through the removal, or resection, of the affected endocrine gland.
Patients who are referred to endocrinologists may have signs and symptoms or blood test results that suggest excessive or impaired functioning of an endocrine gland or endocrine cells. The endocrinologist may order additional blood tests to determine whether the patient’s hormonal levels are abnormal, or they may stimulate or suppress the function of the suspect endocrine gland and then have blood taken for analysis. Treatment varies according to the diagnosis. Some endocrine disorders, such as type 2 diabetes, may respond to lifestyle changes such as modest weight loss, adoption of a healthy diet, and regular physical activity. Other disorders may require medication, such as hormone replacement, and routine monitoring by the endocrinologist. These include disorders of the pituitary gland that can affect growth and disorders of the thyroid gland that can result in a variety of metabolic problems.
Some patients experience health problems as a result of the normal decline in hormones that can accompany aging. These patients can consult with an endocrinologist to weigh the risks and benefits of hormone replacement therapy intended to boost their natural levels of reproductive hormones.
In addition to treating patients, endocrinologists may be involved in research to improve the understanding of endocrine system disorders and develop new treatments for these diseases.
Chapter Review
The endocrine system consists of cells, tissues, and organs that secrete hormones critical to homeostasis. The body coordinates its functions through two major types of communication: neural and endocrine. Neural communication includes both electrical and chemical signaling between neurons and target cells. Endocrine communication involves chemical signaling via the release of hormones into the extracellular fluid. From there, hormones diffuse into the bloodstream and may travel to distant body regions, where they elicit a response in target cells. Endocrine glands are ductless glands that secrete hormones. Many organs of the body with other primary functions—such as the heart, stomach, and kidneys—also have hormone-secreting cells.
Interactive Link Questions
Visit this link to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?
Answer: cAMP
Review Questions
Q. Endocrine glands ________.
A. secrete hormones that travel through a duct to the target organs
B. release neurotransmitters into the synaptic cleft
C. secrete chemical messengers that travel in the bloodstream
D. include sebaceous glands and sweat glands
Answer: C
Q. Chemical signaling that affects neighboring cells is called ________.
A. autocrine
B. paracrine
C. endocrine
D. neuron
Answer: B
Critical Thinking Questions
Q. Describe several main differences in the communication methods used by the endocrine system and the nervous system.
A. The endocrine system uses chemical signals called hormones to convey information from one part of the body to a distant part of the body. Hormones are released from the endocrine cell into the extracellular environment, but then travel in the bloodstream to target tissues. This communication and response can take seconds to days. In contrast, neurons transmit electrical signals along their axons. At the axon terminal, the electrical signal prompts the release of a chemical signal called a neurotransmitter that carries the message across the synaptic cleft to elicit a response in the neighboring cell. This method of communication is nearly instantaneous, of very brief duration, and is highly specific.
Q. Compare and contrast endocrine and exocrine glands.
A. Endocrine glands are ductless. They release their secretion into the surrounding fluid, from which it enters the bloodstream or lymph to travel to distant cells. Moreover, the secretions of endocrine glands are hormones. Exocrine glands release their secretions through a duct that delivers the secretion to the target location. Moreover, the secretions of exocrine glands are not hormones, but compounds that have an immediate physiologic function. For example, pancreatic juice contains enzymes that help digest food.
Q. True or false: Neurotransmitters are a special class of paracrines. Explain your answer.
A. True. Neurotransmitters can be classified as paracrines because, upon their release from a neuron’s axon terminals, they travel across a microscopically small cleft to exert their effect on a nearby neuron or muscle cell.
Glossary
- autocrine
- chemical signal that elicits a response in the same cell that secreted it
- endocrine gland
- tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion
- endocrine system
- cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes
- exocrine system
- cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts
- hormone
- secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body
- paracrine
- chemical signal that elicits a response in neighboring cells; also called paracrine factor