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Introduction to the Endocrine System
The endocrine system, along with the nervous system, functions in the regulation of body activities. The nervous system acts through electrical impulses and neurotransmitters to cause muscle contraction and glandular secretion. The effect is of short duration, measured in seconds, and localized. The endocrine system acts through chemical messengers called hormones that influence growth, development, and metabolic activities. The action of the endocrine system is measured in minutes, hours, or weeks and is more generalized than the action of the nervous system.
There are two major categories of glands in the body - exocrine and endocrine.
Exocrine Glands
Exocrine glands have ducts that carry their secretory product to a surface. These glands include the sweat, sebaceous, and mammary glands and, the glands that secrete digestive enzymes.
Endocrine Glands
The endocrine glands do not have ducts to carry their product to a surface. They are called ductless glands. The word endocrine is derived from the Greek terms "endo," meaning within, and "krine," meaning to separate or secrete. The secretory products of endocrine glands are called hormones and are secreted directly into the blood and then carried throughout the body where they influence only those cells that have receptor sites for that hormone.
内分泌系统简介
内分泌系统与神经系统一起调节身体活动。神经系统通过电脉冲和神经递质作用，引起肌肉收缩和腺体分泌。这种影响持续时间短，以秒为单位，并且是局部的。内分泌系统通过被称为荷尔蒙的化学信使发挥作用，荷尔蒙影响生长、发育和代谢活动。内分泌系统的活动以分钟、小时或周为单位，比神经系统的活动更广泛。
身体中有两大类腺体——外分泌腺体和内分泌腺体。
外分泌腺
外分泌腺有导管，将分泌产物输送到表面。这些腺体包括汗腺、皮脂腺和乳腺，以及分泌消化酶的腺体。
内分泌腺
内分泌腺没有导管将其产品输送到表面。它们被称为无导管腺体。“内分泌”一词来源于希腊语术语“endo”，意为“内”，“krine”意为分离或分泌。内分泌腺的分泌产物称为激素，直接分泌到血液中，然后携带到全身，在那里它们只影响那些有激素受体的细胞。
Characteristics of Hormones
Chemical Nature of Hormones
Chemically, hormones may be classified as either proteins or steroids. All of the hormones in the human body, except the sex hormones and those from the adrenal cortex, are proteins or protein derivatives.
Mechanism of Hormone
Action Hormones are carried by the blood throughout the entire body, yet they affect only certain cells. The specific cells that respond to a given hormone have receptor sites for that hormone. This is sort of a lock-and-key mechanism. If the key fits the lock, then the door will open. If a hormone fits the receptor site, then there will be an effect. If a hormone and a receptor site do not match, then there is no reaction. All the cells that have receptor sites for a given hormone make up the target tissue for that hormone. In some cases, the target tissue is localized in a single gland or organ. In other cases, the target tissue is diffuse and scattered throughout the body so that many areas are affected. Hormones bring about their characteristic effects on target cells by modifying cellular activity.
Protein hormones react with receptors on the surface of the cell, and the sequence of events that results in hormone action is relatively rapid. Steroid hormones typically react with receptor sites inside a cell. Because this method of action actually involves synthesis of proteins, it is relatively slow.
激素的特征
激素的化学性质
在化学上，激素可分为蛋白质或类固醇。人体内的所有激素，除了性激素和肾上腺皮质激素外，都是蛋白质或蛋白质衍生物。
激素机制
作用荷尔蒙由整个身体的血液携带，但它们只影响某些细胞。对特定激素有反应的特定细胞具有该激素的受体位点。这是一种锁匙机制。如果钥匙适合锁，那么门就会打开。如果一种激素适合受体部位，那么就会产生效果。如果激素和受体位点不匹配，则没有反应。所有具有给定激素受体位点的细胞构成了该激素的靶组织。在某些情况下，目标组织位于单个腺体或器官中。在其他情况下，目标组织是扩散并分散在整个身体中，因此许多区域受到影响。激素通过改变细胞活性对靶细胞产生特有的影响。
蛋白质激素与细胞表面的受体发生反应，导致激素作用的事件顺序相对较快。类固醇激素通常与细胞内的受体位点发生反应。因为这种作用方法实际上涉及蛋白质的合成，所以相对较慢。
Control of Hormone Action
Hormones are very potent substances, which means that very small amounts of a hormone may have profound effects on metabolic processes. Because of their potency, hormone secretion must be regulated within very narrow limits in order to maintain homeostasis in the body.
Many hormones are controlled by some form of a negative feedback mechanism. In this type of system, a gland is sensitive to the concentration of a substance that it regulates. A negative feedback system causes a reversal of increases and decreases in body conditions in order to maintain a state of stability or homeostasis. Some endocrine glands secrete hormones in response to other hormones. The hormones that cause secretion of other hormones are called tropic hormones. A hormone from gland A causes gland B to secrete its hormone. A third method of regulating hormone secretion is by direct nervous stimulation. A nerve stimulus causes gland A to secrete its hormone.
激素作用的控制
激素是非常有效的物质，这意味着极少量的激素可能对代谢过程产生深远的影响。 由于它们的效力，激素分泌必须在非常窄的范围内进行调节，以维持体内的体内平衡。
许多激素受某种形式的负反馈机制控制。 在这种类型的系统中，腺体对其调节的物质的浓度很敏感。 负反馈系统会导致身体状况的增加和减少发生逆转，以保持稳定或体内平衡状态。 一些内分泌腺响应其他激素而分泌激素。 引起其他激素分泌的激素称为热带激素。 来自腺体 A 的激素会导致腺体 B 分泌其激素。 第三种调节激素分泌的方法是直接刺激神经。 神经刺激导致腺体 A 分泌其激素。
Endocrine Glands & Their Hormones
Illustration showing the different types and locations of endocrines glands in both males and females
The endocrine system is made up of the endocrine glands that secrete hormones. Although there are eight major endocrine glands scattered throughout the body, they are still considered to be one system because they have similar functions, similar mechanisms of influence, and many important interrelationships.
Some glands also have non-endocrine regions that have functions other than hormone secretion. For example, the pancreas has a major exocrine portion that secretes digestive enzymes and an endocrine portion that secretes hormones. The ovaries and testes secrete hormones and also produce the ova and sperm. Some organs, such as the stomach, intestines, and heart, produce hormones, but their primary function is not hormone secretion.
内分泌腺及其激素
显示雄性和雌性内分泌腺的不同类型和位置的插图
内分泌系统由分泌激素的内分泌腺组成。尽管有八个主要内分泌腺散布在全身，但它们仍然被认为是一个系统，因为它们具有相似的功能、相似的影响机制和许多重要的相互关系。
一些腺体也有非内分泌区域，除了激素分泌外还有其他功能。例如，胰腺有分泌消化酶的主要外分泌部分和分泌激素的内分泌部分。卵巢和睾丸分泌激素，也产生卵子和精子。一些器官，如胃、肠和心脏，产生激素，但它们的主要功能不是激素分泌。
Pituitary & Pineal Glands
Pituitary Gland
The pituitary gland or hypophysis is a small gland about 1 centimeter in diameter or the size of a pea. It is nearly surrounded by bone as it rests in the sella turcica, a depression in the sphenoid bone. The gland is connected to the hypothalamus of the brain by a slender stalk called the infundibulum.
垂体和松果体
垂体
垂体或垂体是直径约 1 厘米或豌豆大小的小腺体。 它几乎被骨头包围，因为它位于蝶鞍，蝶骨的凹陷处。 腺体通过称为漏斗部的细长柄与大脑的下丘脑相连。
There are two distinct regions in the gland: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis). The activity of the adenohypophysis is controlled by releasing hormones from the hypothalamus. The neurohypophysis is controlled by nerve stimulation.
Hormones of the Anterior Lobe (Adenohypophysis)
Growth hormone is a protein that stimulates the growth of bones, muscles, and other organs by promoting protein synthesis. This hormone drastically affects the appearance of an individual because it influences height. If there is too little growth hormone in a child, that person may become a pituitary dwarf of normal proportions but small stature. An excess of the hormone in a child results in an exaggerated bone growth, and the individual becomes exceptionally tall or a giant.
腺体中有两个不同的区域：前叶（腺垂体）和后叶（神经垂体）。腺垂体的活动是通过从下丘脑释放激素来控制的。神经垂体受神经刺激控制。
前叶激素（腺垂体）
生长激素是一种刺激骨骼、肌肉和其他器官生长以促进蛋白质合成的蛋白质。这种激素会极大地影响一个人的外表，因为它会影响身高。如果孩子体内的生长激素太少，这个人可能会变成一个比例正常但身材矮小的垂体侏儒。儿童体内过多的激素会导致骨骼过度生长，个体变得异常高大或巨人。
Thyroid-stimulating hormone, or thyrotropin, causes the glandular cells of the thyroid to secrete thyroid hormone. When there is a hypersecretion of thyroid-stimulating hormone, the thyroid gland enlarges and secretes too much thyroid hormone.
Adrenocorticotropic hormone reacts with receptor sites in the cortex of the adrenal gland to stimulate the secretion of cortical hormones, particularly cortisol.
Gonadotropic hormones react with receptor sites in the gonads, or ovaries and testes, to regulate the development, growth, and function of these organs.
Prolactin hormone promotes the development of glandular tissue in the female breast during pregnancy and stimulates milk production after the birth of the infant.
促甲状腺激素或促甲状腺激素使甲状腺的腺细胞分泌甲状腺激素。当促甲状腺激素分泌过多时，甲状腺会增大并分泌过多的甲状腺激素。
促肾上腺皮质激素与肾上腺皮质中的受体部位发生反应，以刺激皮质激素，特别是皮质醇的分泌。
促性腺激素与性腺或卵巢和睾丸中的受体部位发生反应，以调节这些器官的发育、生长和功能。
催乳激素在怀孕期间促进女性乳房腺体组织的发育，并在婴儿出生后刺激产奶量。
Hormones of the Posterior Lobe (Neurohypophysis)
Antidiuretic hormone promotes the reabsorption of water by the kidney tubules, with the result that less water is lost as urine. This mechanism conserves water for the body. Insufficient amounts of antidiuretic hormone cause excessive water loss in the urine.
Oxytocin causes contraction of the smooth muscle in the wall of the uterus. It also stimulates the ejection of milk from the lactating breast.
Pineal Gland
The pineal gland, also called pineal body or epiphysis cerebri, is a small cone-shaped structure that extends posteriorly from the third ventricle of the brain. The pineal gland consists of portions of neurons, neuroglial cells, and specialized secretory cells called pinealocytes. The pinealocytes synthesize the hormone melatonin and secrete it directly into the cerebrospinal fluid, which takes it into the blood. Melatonin affects reproductive development and daily physiologic cycles.
后叶激素（神经垂体）
抗利尿激素促进肾小管对水的重吸收，从而减少作为尿液流失的水。 这种机制可以为身体节约水分。 抗利尿激素量不足会导致尿液中过多的水分流失。
催产素引起子宫壁平滑肌的收缩。 它还刺激乳汁从哺乳期的乳房排出。
松果体
松果体，也称为松果体或大脑骨骺，是一个小的锥形结构，从大脑的第三脑室向后延伸。 松果体由部分神经元、神经胶质细胞和称为松果体细胞的特殊分泌细胞组成。 松果体细胞合成激素褪黑激素并将其直接分泌到脑脊液中，脑脊液将其带入血液。 褪黑激素影响生殖发育和日常生理周期。
Thyroid & Parathyroid Glands
Thyroid Gland
Illustration of the thyroid and parathyroid glands
The thyroid gland is a very vascular organ that is located in the neck. It consists of two lobes, one on each side of the trachea, just below the larynx or voice box. The two lobes are connected by a narrow band of tissue called the isthmus. Internally, the gland consists of follicles, which produce thyroxine and triiodothyronine hormones. These hormones contain iodine.
About 95 percent of the active thyroid hormone is thyroxine, and most of the remaining 5 percent is triiodothyronine. Both of these require iodine for their synthesis. Thyroid hormone secretion is regulated by a negative feedback mechanism that involves the amount of circulating hormone, hypothalamus, and adenohypophysis.
If there is an iodine deficiency, the thyroid cannot make sufficient hormone. This stimulates the anterior pituitary to secrete thyroid-stimulating hormone, which causes the thyroid gland to increase in size in a vain attempt to produce more hormones. But it cannot produce more hormones because it does not have the necessary raw material, iodine. This type of thyroid enlargement is called simple goiter or iodine deficiency goiter.
Calcitonin is secreted by the parafollicular cells of the thyroid gland. This hormone opposes the action of the parathyroid glands by reducing the calcium level in the blood. If blood calcium becomes too high, calcitonin is secreted until calcium ion levels decrease to normal.
甲状腺和甲状旁腺
甲状腺
甲状腺和甲状旁腺的插图
甲状腺是位于颈部的血管丰富的器官。它由两个肺叶组成，一个在气管的每一侧，就在喉部或语音盒的下方。两个裂片由称为峡部的窄带组织连接。在内部，腺体由产生甲状腺素和三碘甲状腺原氨酸激素的卵泡组成。这些激素含有碘。
大约 95% 的活性甲状腺激素是甲状腺素，其余 5% 的大部分是三碘甲状腺原氨酸。这两种物质的合成都需要碘。甲状腺激素分泌受负反馈机制调节，涉及循环激素、下丘脑和腺垂体的量。
如果碘缺乏，甲状腺就不能产生足够的激素。这会刺激垂体前叶分泌促甲状腺激素，从而导致甲状腺体积增大，徒劳地试图产生更多的激素。但它不能产生更多的激素，因为它没有必要的原料碘。这种类型的甲状腺肿大称为单纯性甲状腺肿或碘缺乏性甲状腺肿。
降钙素由甲状腺的滤泡旁细胞分泌。这种激素通过降低血液中的钙水平来对抗甲状旁腺的作用。如果血钙过高，就会分泌降钙素，直到钙离子水平降至正常水平。
Parathyroid Gland
Four small masses of epithelial tissue are embedded in the connective tissue capsule on the posterior surface of the thyroid glands. These are parathyroid glands, and they secrete parathyroid hormone or parathormone. Parathyroid hormone is the most important regulator of blood calcium levels. The hormone is secreted in response to low blood calcium levels, and its effect is to increase those levels.
Hypoparathyroidism, or insufficient secretion of parathyroid hormone, leads to increased nerve excitability. The low blood calcium levels trigger spontaneous and continuous nerve impulses, which then stimulate muscle contraction
甲状旁腺
四个小块上皮组织嵌入甲状腺后表面的结缔组织囊中。 这些是甲状旁腺，它们分泌甲状旁腺激素或甲状旁腺素。 甲状旁腺激素是血钙水平最重要的调节剂。 这种激素是响应低血钙水平而分泌的，其作用是提高这些水平。
甲状旁腺功能低下或甲状旁腺激素分泌不足会导致神经兴奋性增加。 低血钙水平触发自发和持续的神经冲动，然后刺激肌肉收缩
Adrenal Gland
Illustration of the adrenal gland and its position near the kidneys
The adrenal, or suprarenal, gland is paired with one gland located near the upper portion of each kidney. Each gland is divided into an outer cortex and an inner medulla. The cortex and medulla of the adrenal gland, like the anterior and posterior lobes of the pituitary, develop from different embryonic tissues and secrete different hormones. The adrenal cortex is essential to life, but the medulla may be removed with no life-threatening effects.
The hypothalamus of the brain influences both portions of the adrenal gland but by different mechanisms. The adrenal cortex is regulated by negative feedback involving the hypothalamus and adrenocorticotropic hormone; the medulla is regulated by nerve impulses from the hypothalamus.
肾上腺
肾上腺及其在肾脏附近的位置的图示
肾上腺或肾上腺上的腺体与位于每个肾脏上部附近的一个腺体配对。 每个腺体分为外皮层和内髓质。 肾上腺的皮质和髓质与垂体的前叶和后叶一样，由不同的胚胎组织发育而来，分泌不同的激素。 肾上腺皮质对生命至关重要，但髓质可以被切除而不会危及生命。
大脑的下丘脑影响肾上腺的两个部分，但通过不同的机制。 肾上腺皮质受下丘脑和促肾上腺皮质激素的负反馈调节； 髓质受下丘脑的神经冲动调节。
Hormones of the Adrenal Cortex
The adrenal cortex consists of three different regions, with each region producing a different group or type of hormones. Chemically, all the cortical hormones are steroid.
Mineralocorticoids are secreted by the outermost region of the adrenal cortex. The principal mineralocorticoid is aldosterone, which acts to conserve sodium ions and water in the body. Glucocorticoids are secreted by the middle region of the adrenal cortex. The principal glucocorticoid is cortisol, which increases blood glucose levels.
The third group of steroids secreted by the adrenal cortex is the gonadocorticoids, or sex hormones. These are secreted by the innermost region. Male hormones, androgens, and female hormones, estrogens, are secreted in minimal amounts in both sexes by the adrenal cortex, but their effect is usually masked by the hormones from the testes and ovaries. In females, the masculinization effect of androgen secretion may become evident after menopause, when estrogen levels from the ovaries decrease.
肾上腺皮质激素
肾上腺皮质由三个不同的区域组成，每个区域产生不同的激素组或类型。化学上，所有的皮质激素都是类固醇。
盐皮质激素由肾上腺皮质的最外层分泌。主要的盐皮质激素是醛固酮，它起到保存体内钠离子和水的作用。糖皮质激素由肾上腺皮质的中间区域分泌。主要的糖皮质激素是皮质醇，它会增加血糖水平。
肾上腺皮质分泌的第三组类固醇是促性腺激素或性激素。这些是由最里面的区域分泌的。雄性激素（雄激素）和雌性激素（雌激素）在两性中由肾上腺皮质分泌微量，但它们的作用通常被来自睾丸和卵巢的激素所掩盖。在女性中，当卵巢中的雌激素水平下降时，雄激素分泌的男性化作用可能会在绝经后变得明显。
Hormones of the Adrenal Medulla
The adrenal medulla develops from neural tissue and secretes two hormones, epinephrine and norepinephrine. These two hormones are secreted in response to stimulation by sympathetic nerve, particularly during stressful situations. A lack of hormones from the adrenal medulla produces no significant effects. Hypersecretion, usually from a tumor, causes prolonged or continual sympathetic responses.
肾上腺髓质激素
肾上腺髓质由神经组织发育而来，分泌两种激素，肾上腺素和去甲肾上腺素。 这两种激素是响应交感神经的刺激而分泌的，尤其是在压力大的情况下。 肾上腺髓质缺乏激素不会产生显着影响。 通常来自肿瘤的分泌过多会导致长期或持续的交感神经反应。
Pancreas—Islets of Langerhans
Illustration of the pancreas
The pancreas is a long, soft organ that lies transversely along the posterior abdominal wall, posterior to the stomach, and extends from the region of the duodenum to the spleen. This gland has an exocrine portion that secretes digestive enzymes that are carried through a duct to the duodenum. The endocrine portion consists of the pancreatic islets, which secrete glucagons and insulin.
Alpha cells in the pancreatic islets secrete the hormone glucagons in response to a low concentration of glucose in the blood. Beta cells in the pancreatic islets secrete the hormone insulin in response to a high concentration of glucose in the blood.
胰腺——朗格汉斯岛
胰腺的插图
胰腺是一个长而柔软的器官，横向位于后腹壁，在胃的后面，从十二指肠区域延伸到脾脏。 这个腺体有一个外分泌部分，可以分泌消化酶，这些消化酶通过导管输送到十二指肠。 内分泌部分由分泌胰高血糖素和胰岛素的胰岛组成。
胰岛中的 α 细胞会分泌激素胰高血糖素，以响应血液中低浓度的葡萄糖。 胰岛中的 β 细胞响应血液中的高浓度葡萄糖而分泌激素胰岛素。
Gonads
The gonads, the primary reproductive organs, are the testes in the male and the ovaries in the female. These organs are responsible for producing the sperm and ova, but they also secrete hormones and are considered to be endocrine glands.
Testes
Illustration of a testis within the male reproductive system
Male sex hormones, as a group, are called androgens. The principal androgen is testosterone, which is secreted by the testes. A small amount is also produced by the adrenal cortex. Production of testosterone begins during fetal development, continues for a short time after birth, nearly ceases during childhood, and then resumes at puberty. This steroid hormone is responsible for:
The growth and development of the male reproductive structures
Increased skeletal and muscular growth
Enlargement of the larynx accompanied by voice changes
Growth and distribution of body hair
Increased male sexual drive
Testosterone secretion is regulated by a negative feedback system that involves releasing hormones from the hypothalamus and gonadotropins from the anterior pituitary.
性腺
性腺是主要的生殖器官，是男性的睾丸和女性的卵巢。这些器官负责产生精子和卵子，但它们也分泌激素，被认为是内分泌腺。
睾丸
男性生殖系统内睾丸的插图
男性性激素，作为一个群体，被称为雄激素。主要的雄激素是睾丸激素，由睾丸分泌。肾上腺皮质也产生少量。睾酮的产生在胎儿发育期间开始，在出生后持续很短的时间，在儿童时期几乎停止，然后在青春期恢复。这种类固醇激素负责：
男性生殖结构的生长发育
增加骨骼和肌肉生长
喉部扩大并伴有声音变化
体毛的生长和分布
男性性欲增加
睾酮分泌受负反馈系统调节，该系统涉及从下丘脑释放激素和从垂体前叶释放促性腺激素。
Ovaries
Illustration of ovaries in the female reproductive system
Two groups of female sex hormones are produced in the ovaries, the estrogens and progesterone. These steroid hormones contribute to the development and function of the female reproductive organs and sex characteristics. At the onset of puberty, estrogens promotes:
The development of the breasts
Distribution of fat evidenced in the hips, legs, and breast
Maturation of reproductive organs such as the uterus and vagina
Progesterone causes the uterine lining to thicken in preparation for pregnancy. Together, progesterone and estrogens are responsible for the changes that occur in the uterus during the female menstrual cycle.
卵巢
女性生殖系统中卵巢的插图
卵巢中会产生两组女性性激素，即雌激素和黄体酮。 这些类固醇激素有助于女性生殖器官和性特征的发育和功能。 在青春期开始时，雌激素促进：
乳房的发育
臀部、腿部和胸部的脂肪分布明显
子宫和阴道等生殖器官的成熟
黄体酮会导致子宫内膜增厚，为怀孕做准备。 孕酮和雌激素共同负责女性月经周期中子宫发生的变化。
Other Endocrine Glands
In addition to the major endocrine glands, other organs have some hormonal activity as part of their function. These include the thymus, stomach, small intestines, heart, and placenta.
Thymosin, produced by the thymus gland, plays an important role in the development of the body's immune system.
The lining of the stomach, the gastric mucosa, produces a hormone, called gastrin, in response to the presence of food in the stomach. This hormone stimulates the production of hydrochloric acid and the enzyme pepsin, which are used in the digestion of food.
The mucosa of the small intestine secretes the hormones secretin and cholecystokinin. Secreting stimulates the pancreas to produce a bicarbonate-rich fluid that neutralizes the stomach acid. Cholecystokinin stimulates contraction of the gallbladder, which releases bile. It also stimulates the pancreas to secrete digestive enzyme.
The heart also acts as an endocrine organ in addition to its major role of pumping blood. Special cells in the wall of the upper chambers of the heart, called atria, produce a hormone called atrial natriiuretic hormone, or atriopeptin.
The placenta develops in the pregnant female as a source of nourishment and gas exchange for the developing fetus. It also serves as a temporary endocrine gland. One of the hormones it secretes is human chorionic gonadotropin, which signals the mother's ovaries to secrete hormones to maintain the uterine lining so that it does not degenerate and slough off in menstruation.
其他内分泌腺
除了主要的内分泌腺外，其他器官也有一些激素活性作为其功能的一部分。这些包括胸腺、胃、小肠、心脏和胎盘。
胸腺素由胸腺产生，在人体免疫系统的发育中起着重要作用。
胃的内层，即胃黏膜，会产生一种称为胃泌素的激素，以响应胃中食物的存在。这种激素刺激盐酸和胃蛋白酶的产生，用于消化食物。
小肠黏膜分泌激素分泌素和胆囊收缩素。分泌刺激胰腺产生富含碳酸氢盐的液体，中和胃酸。胆囊收缩素刺激胆囊收缩，从而释放胆汁。它还刺激胰腺分泌消化酶。
心脏除了泵血的主要作用外，还充当内分泌器官。心脏上腔壁中的特殊细胞（称为心房）会产生一种称为心房利钠素或 atriopeptin 的激素。
胎盘在孕妇体内发育，作为发育中胎儿的营养和气体交换来源。它也用作临时内分泌腺。它分泌的一种激素是人绒毛膜促性腺激素，它会向母亲的卵巢发出信号，分泌激素来维持子宫内膜，使其不会在月经期间退化和脱落。
Review: Introduction to the Endocrine System
Here is what we have learned from Introduction to the Endocrine System:
Chemical messengers from the endocrine system help regulate body activities. Their effect is of longer duration and is more generalized than that of the nervous system.
Neurons are the nerve cells that transmit impulses. Supporting cells are neuroglia.
Endocrine glands secrete hormones directly into the blood, which transports the hormones through the body.
Cells in a target tissue have receptor sites for specific hormones.
Many hormones are regulated by a negative feedback mechanism; some are controlled by other hormones; and others are affected by direct nerve stimulation.
Even though the endocrine glands are scattered throughout the body, they are still considered to be one system because they have similar functions, similar mechanisms of influence, and many important interrelationships.
Major glands include: pituitary gland, thyroid gland, parathyroid gland, adrenal (suprarenal) gland, pancreas, gonads (testes and ovaries), pineal gland, and other endocrine glands.
回顾：内分泌系统简介
以下是我们从《内分泌系统导论》中学到的：
来自内分泌系统的化学信使有助于调节身体活动。它们的作用持续时间更长，并且比神经系统的作用更普遍。
神经元是传递冲动的神经细胞。支持细胞是神经胶质细胞。
内分泌腺将激素直接分泌到血液中，从而将激素输送到全身。
靶组织中的细胞具有特定激素的受体位点。
许多激素受负反馈机制的调节；有些受其他激素控制；其他人则受到直接神经刺激的影响。
尽管内分泌腺分布在全身各处，但它们仍然被认为是一个系统，因为它们具有相似的功能、相似的影响机制以及许多重要的相互关系。
主要腺体包括：垂体、甲状腺、甲状旁腺、肾上腺（肾上腺）、胰腺、性腺（睾丸和卵巢）、松果体和其他内分泌腺。 |
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发表于 2022-9-23 11:29:57