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Endocrine glands and hormones

Endocrine system maintains balance in the internal environment of our body, adapts it to changing conditions, regulates metabolism, controls growth and development. It is composed of endocrine glandsendocrine glandendocrine glands, also known as hormonal glands or internal secretion glands. It is there where production and secretion of hormones takes place.

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Ilustracja przedstawia schemat blokowy hormone functions. W kolorowych prostokątach opisano funkcje hormonów. Informuje o tym biały prostokąt na samej górze. Po lewej strzałka w dół prowadzi do niebieskiego prostokąta, regulacji funkcjonowania organizmu człowieka, regulation of the functioning of the human body. Hormony za to odpowiedzialne działają na: rozmnażanie, reproduction, utrzymanie stałego poziomu wody i soli mineralnych, maintaining a constant level of water and mineral salts, trawienie i wchłanianie, digestion and absorption, wzrost i rozwój, growth and development. Po prawej strzałka w dół prowadzi do: procesów adaptacyjnych do zmiennych warunków środowiska poprzez regulację metabolizmu, adaptation to changing environmental conditions through regulation of metabolism, for example seasonal changes, odpowiedzi na stres : walka lub ucieczka, response to stress: fight or flight.

Endocrine glands are highly vascularized and don’t have their own excretory ducts, which means that hormoneshormoneshormones are secreted directly to the blood stream. They work in very low concentration and only on target cells which they reach with blood. These cells have special receptors – protein particles (rarely fat particles), which hormones connect with in order to make the cell start or finish a certain process. As a result of a hormone connecting with a receptor, the target cell begins or finishes a specific process that depends on a given hormone.

Types of endocrine glands and their functions

Endocrine glands are situated in different parts of the body and are not connected with each other. Thanks to blood and hormones in it they create an integrated system that works together. Endocrine glands: hypothalamus, pituitary gland and pineal gland are the structures of the nervous system, pancreas – of the digestive system, and testicles and ovaries – of the reproductive system.

Endocrine glands are divided into 2 groups: those that produce and secrete hormones and mixed glands, which produce hormones and other substances (e.g. pancreas – digestive enzymes, and reproductive glands – gametes).

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Galeria przedstawia ilustracje przedstawiające działania gruczołów. Ilustracja przedstawia porównanie gruczołu trawiennego i wewnątrzwydzielniczego, endocrine gland. Po lewej stronie, przedstawiono różowy kulisty gruczoł trawienny, gland with a lead-out line, e.g a salivary gland. Wydziela on enzymy, enzymes: ciemnoróżowe strzałki biegnące przewodem, conduit w dół. Przewód łączy się z poziomą, różową rurą układu trawiennego, digestive system. Taki działający gruczoł to na przykład ślinianka, salivary gland. Po prawej schemat działania gruczołu wewnątrzwydzielniczego, endocrine gland. Niebieska kulka to gruczoł. Trzy niebieskie strzałki to hormony, hormones. Prowadzą one do wygiętej, niebieskiej rurki naczynia krwionośnego, blood vessels. Taki gruczoł to na przykład tarczyca, thyroid gland.

Hormones are produced not only by highly specialized endocrine glands, but also by other organs and tissues, e.g. kidneys, heart, intestinal mucosa cells and nervous tissue.

Hormonal regulation

The most important task of the system is to maintain the balance in the organism (homeostasis)homeostasis(homeostasis) with changing conditions of the environment. It is mainly the task of hormones. They are produced by endocrine glands nearly all the time. This is why in blood at the same time there are numerous different hormones. They can simultaneously react on one or many organs and regulate one or many physiological processes. The hormonal level is controlled 24‑hour a day by 2 superior endocrine glands: hypothalamus and pituitary gland.

The nervous system controls the endocrine system using hypothalamus, which is part of the brain. Changes in the level of hormones in blood or information from different parts of the brain cause the hypothalamus to produce 2 types of hormones: stimulating ones, which stimulate pituitary gland to produce hormones or supressive ones, which stop the pituitary gland from producing hormones.

Hypothalamus, together with pituitary gland, regulate e.g. how thyroid works. Elevated level of thyroid hormones (e.g. thyroxine) in blood is for the hypothalamus and for the pituitary gland a signal to stop producing the hormones that stimulate secreting functions of the thyroid. And the other way round – when thyroid hormone levels are too low, hypothalamus and pituitary gland release hormones that stimulate thyroid to secrete its hormones.

This regulatory mechanism is called negative feedback. The rule of negative feedback is very simple – any divergence from the given norm starts the mechanism that is responsible for maintaining the norm. This rule regulates most of the processes in your body, which allows you to maintain homeostasis.

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Ilustracja w formie schematu blokowego przedstawia proces samoregulacji na przykładzie wydzielania tyroksyny, thyroxine. Na szczycie schematu znajduje się hypothalamus, od niego strzałka w dół do a hormone regulating pituitary work. Następnie strzałka w dół do the pituitary gland, następnie strzałka w dół do hormone regulating thyroid function, następnie strzałka w dół do thyroid, następnie strzałka w dół do thyroxine. Od tyroksyny biegną dwie strzałki, jedna do high levels of the hormone in the blood, druga do low hormone levels in the blood. Od high level of the hormone in the blood biegnie strzałka z podpisem repression do the pituitary gland oraz hypothalamus. Natomiast od low hormone levels in blood biegnie strzałka z podpisem stimulation do do the pituitary gland oraz hypothalamus.

On the same basis your body regulates glucose levels. If it is too high, it begins secreting insulin. This hormone causes glucose to be converted in glycogen which is stored in the liver, which leads to lowering the amount of glucose in blood. Insulin is produced as long as the optimum level of sugar in blood is achieved. When the amount of glucose drops dramatically, other mechanism starts. Then your body produces other hormone, glucagon, which releases glucose by breaking down glycogen. Other example of homeostasis are the thermoregulatory processes. Feeling hot initiates the mechanism that is aimed at lowering the body temperature, e.g. sweating. When your body temperature drops, sweating ceases.

Incorrect functioning of endocrine glands can cause imbalance in your body. When endocrine gland produces too little hormones, we are talking about decrease in gland functioningdecrease in gland functioningdecrease in gland functioning and when it produces too many hormones, we talk about increase in gland functioningincrease in gland functioningincrease in gland functioning.

Summary

• Endocrine system is composed of endocrine glands and specialized cells that produce hormones.

• Endocrine glands as glands of internal secretion do not have ducts, they secrete hormones directly to the blood.

• Hormones are spread throughout the entire body, but they influence only the target cells – this is the specific aspect of how they work.

• Hormones allow you to maintain all your physiological processes in balance.

• Lack of hormone in blood is caused by decrease in gland functioning, and when there is too much of that hormone, we talk about increase in gland functioning.

Keywords

hormones, endocrine glands, endocrine system

Glossary