The adrenal glands are small structures attached to the top of each kidney. The human body has two adrenal glands that release chemicals called hormones into the bloodstream. These hormones affect many parts of the human body. About Contact Events News. Search Search. You and Your Hormones. Students Teachers Patients Browse. In contrast, the endocrine system uses just one method of communication: chemical signaling.
These signals are sent by the endocrine organs, which secrete chemicals—the hormone —into the extracellular fluid. Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones.
For example, the hormones released when you are confronted with a dangerous or frightening situation, called the fight-or-flight response, occur by the release of adrenal hormones—epinephrine and norepinephrine—within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones. In addition, endocrine signaling is typically less specific than neural signaling.
The same hormone may play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone oxytocin promotes uterine contractions in women in labor. It is also important in breastfeeding, and may be involved in the sexual response and in feelings of emotional attachment in both males and females.
In general, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting—taking care of the internal environment of the body, maintaining homeostasis, and controlling reproduction Table 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.
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 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. Figure 1. Endocrine glands and cells are located throughout the body and play an important role in homeostasis. 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.
The epithelium of the tissue invaginates to form a simple or complex tube. The tube comprises a blind end to secrete things out, and the other end blows up to form round shaped bags called alveolar or acinus.
The structure of a multicellular exocrine gland with acini is shown in figure 2. Figure 2: Multicellular exocrine gland. Three types of exocrine glands can be identified based on the mode of secretion : merocrine glands, apocrine glands, and holocrine glands. The merocrine glands secrete their own cellular products.
All cells of the gland are involved in the secretion in holocrine glands. Three types of exocrine glands can be identified based on the type of secretion. They are serous glands, mucous glands, and mixed glands. The serous glands secrete proteins, which may serve as enzymes.
The mucous glands secrete mucus. The mixed glands secrete both proteins and mucus. Endocrine Glands: Endocrine glands are a type of glands that secrete substances hormones into the blood stream. Exocrine Glands: Exocrine glands are a type of glands which release its secretion external to or at the surface of an organ with the help of a canal or duct. Endocrine Glands: Endocrine glands are a type of ductless glands.
Exocrine Glands: Exocrine glands may or may not have ducts. Endocrine Glands: Exocrine glands secrete into the blood. Exocrine Glands: Endocrine glands pour their secretions directly at the site of action.
Endocrine Glands: Endocrine glands secrete hormones. Exocrine Glands: Exocrine glands secrete enzymes. Endocrine Glands: The target of the endocrine glands is located away from the gland.
Exocrine Glands: The target of the exocrine glands is found very close to the gland.
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