ESC - Hormones Lesson
Hormones
Hormones are chemicals secreted in small amounts into the bloodstream that are used to communicate between organs and tissues. Various organs throughout the body are sources of hormones. Although hormones travel through the bloodstream, they only have an effect on certain cells. Cells with receptors for a particular hormone are called target cells. Hormones are essential to maintaining homeostasis, controlling actions such as metabolism, sleep, growth and development, reproduction, and many other functions.
Types of Hormones
Different types of hormones are secreted depending upon their biological role and function. Hormones in the human body can be divided into two major groups based upon their chemical structure: amino acid-based hormones and lipid-based hormones. Amino acid-based hormones include amines, peptides, and proteins. Lipid-based hormones include steroids. The chemical make-up of the hormone affects its distribution, the type of receptor it binds to, and other aspects of its function.
How Hormones Work
Download the note sheet here Links to an external site. and complete the interactive here Links to an external site. to learn how hormones work.
Binding of Lipid-Based Hormones
Steroid hormones are able to directly initiate the production of proteins within a target cell. Since they are lipid-based, steroid hormones can easily diffuse through the cell membrane and bind to its receptor in the cytoplasm. This forms the receptor-hormone complex, which enters into the nucleus, binds to the target gene of DNA, and causes the production of the desired protein within the cytoplasm.
Binding of Amino Acid-Based Hormones
The chemical makeup of amino acid-based hormones makes the hydrophilic, or water-soluble. This means that they are unable to diffuse directly through the lipid bilayer, and they must pass their message by means of a cell receptor at the surface of the cell membrane. This receptor initiates a second-messenger system by means of a cell signaling pathway that activates proteins in the cell to carry out changes specified by the hormone.
Factors Affecting Target Cell Response
Several factors can influence a target cell's response to a hormone. For example, target cells can alter their sensitivity towards a hormone depending upon the hormone's concentration within the bloodstream. Downregulation can occur if a significant amount of a hormone is found in the bloodstream. This causes target cells to reduce their number of receptors for that hormone allowing the cell to become less reactive to the excessive levels. Conversely, during upregulation, target cells increase their amount of receptors due to a low concentration of their hormone in the bloodstream, allowing cells to become more sensitive to the hormone that is present.
Hormones can also interact with one another affecting the response of target cells. Learn about these interactions in the table below.
Permissive Effect | Synergistic Effect | Antagonistic Effect |
The presence of one hormone enables another hormone to act. | Two hormones with a similar effect cause an amplified response. | Two hormones have opposing effects. |
Example: Thyroid hormones and certain reproductive hormones have a permissive relationship. This means if there is an issue with thyroid hormones, it can cause problems with the development and functionality of the reproductive system. | Example: FSH and estrogen are both required for the maturation of egg cells in females. | Example: Insulin increases the liver's storage of glucose as glycogen (lowering blood sugar) while glycogen causes glycogen to break down (raising blood sugar). |
Regulation of Hormone Secretion
In order to maintain homeostasis, hormone levels must be strictly regulated. To maintain this control, the body must balance hormone production and degradation. Feedback loops in the body are used to maintain this balance for most hormonal secretions. Learn about feedback loops in the interactive below.
Review
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