The Endocrine System Flashcards
Hormones
• A hormone is a chemical that is made by specialist cells, usually within an endocrine gland, and it is released into the bloodstream to send a message to another part of the body.
Hormones are used for two types of communication
• Communication between two endocrine glands, where one gland releases a hormone which stimulates another target gland to change the levels of hormones that it is releasing.
• Communication between an endocrine gland and a target organ/tissue which responds to the secretion of a hormone.
Specificity of hormones
• In response to specific stimuli, the hormone is secreted from the gland into the bloodstream.
• The hormones then are carried via the blood everywhere in the body
• The target cells for each hormone have specific receptors located within the cell or on the cell surface.
• The interaction between the hormone and its receptor triggers a cascade of biochemical reactions in the target cell that eventually modify the cell’s function or activity.
Types of hormone
• Hormones can be categorised into three distinct groups according to their chemical composition
• The three types of hormones are steroid hormones, peptide hormones and amino acid derivatives
• The different types of hormones will have different mechanisms of action due to their distinct chemical properties. Some can cross cell membranes but others trigger reactions when the bind to the cell surface as they cannot enter
Negative feedback loops
• Almost all hormones work on a negative feedback cycle. Understanding this is crucial to understanding the endocrine system and homeostasis.
• This is an example of the negative feedback loop of puberty in men
• The negative part means that we have a mechanism to turn off the production of hormones once the desired level is reached
The Hypothalamus
About the size of a cherry and secretes hormones that are called ‘releasing factors’ that simulate
other endocrine glands to secrete hormones and inhibit the secretion of others.
Use the hormones, glands and primary function sheet to see what hormones are secreted by the hypothalamus and what they target.
Pituitary Gland
Situated under the hypothalamus, secretes several hormones when simulated by the hypothalamus The anterior (front facing) and posterior (rear facing) parts secretes hormones which in turn inhibit secretion by the pituitary gland
Thyroid and Parathyroid
• The hypothalamus secretes Thyroid releasing Hormone (TRH) which causes the anterior pituitary gland to release Thyroid Simulating Hormone (TSH) which targets the thyroid gland which is a H shaped gland that straddles the trachea in the neck.
• This is causes the secretion of three hormones by the thyroid gland although only thyroxine is listed in the T level. The parathyroid gland secretes a hormone called Parathyroid hormone (PTH) which controls calcium levels in the body
Thyroxine
• Thyroxine is a hormone the thyroid gland secretes into the bloodstream. Once in the bloodstream, thyroxine travels to the organs, like the liver and kidneys, where it is converted to its active form.
• Thyroxine plays a crucial role in heart and digestive function, metabolism, brain development, bone health, and muscle control. It affects almost all of the body’s systems, which means proper thyroxine levels are vital for health.
• Having too little thyroxine or too much thyroxine can cause health problems.
• If your body releases too much thyroxine, you will suffer a condition commonly caused by hyperthyroidism. The body can also produce too little thyroxine, a condition known as hypothyroidism
Adrenal glands
• Each gland contains a central medulla surrounded by a cortex. Each part secretes different hormones
• The medulla secretes aldosterone which causes water and sodium to be reabsorbed from the kidneys which raises blood pressure. It also secretes cortisol
• The cortex secretes noradrenaline which promotes vasoconstriction and adrenaline which strengthens the response and length of action of the sympathetic nervous system
Cortisol
• Cortisol is the body’s long term stress hormone that maintains the heightened state caused by adrenaline over the longer period of time.
• It has a very wide range of other functions as shown.
• When given in medication is a called hydrocortisone – an anti- inflammatory for skin conditions
Growth Hormone and Growth
• Growth hormone-releasing hormone is a hormone produced in the hypothalamus. The main role of growth hormone-releasing hormone (GHRH) is to stimulate the pituitary gland to produce and release
growth hormone (GH) into the bloodstream.
• Growth hormone acts on many parts of the body to promote growth in children. Once the growth plates in the bones have fused growth hormone does not increase height. In adults, it does not cause growth
but it helps to maintain normal body structure and metabolism, including helping to keep blood glucose levels within set levels
Action of growth hormone
• Secretion of growth hormone:
• It stimulates the linear growth of the bones
• promotes the growth of internal organs, fat (adipose) tissue, connective tissue, endocrine glands, and muscle
• controls the development of the reproductive organs.
• These interaction then may lead to the increased DNA production and cell division that underlie the growth process. Lack of GH can lead to shortness in adults and overproduction leads to gigantism
Digestion and Gastrin
• Gastrin is a hormone that is produced by ‘G’ cells in the lining of the stomach and upper small intestine. During a meal, gastrin stimulates the stomach to release gastric acid. This allows the stomach to break down proteins swallowed as food and absorb certain vitamins. It also acts as a disinfectant and kills most of the bacteria that enter the stomach with food, minimising the risk of infection within the gut.
• Gastrin stimulates the gallbladder to empty its store of bile and the pancreas to secrete enzymes. Gastrin also stimulates growth of the stomach lining and increases the muscle contractions of the gut to aid digestion
Adrenaline action in the body
• Adrenaline is produced in the medulla of the adrenal glands
• Adrenaline has many different actions depending on the type of cells it is acting upon. However, the overall effect of adrenaline is to prepare the body for the ‘fight or flight’ response in times of stress, i.e. for vigorous and/or sudden action.
• Key actions of adrenaline include increasing the heart rate, increasing blood pressure, expanding the air passages of the lungs, enlarging the pupil in the eye, redistributing blood to the muscles and altering the body’s metabolism, so as to maximise blood glucose levels (primarily for the brain)
