Module 9 - The Endocrine System Flashcards
What are the components of the endocrine system?
The endocrine glands - groups of cells that secrete chemical substances directly into the blood or lymph. The chemical’s substances are hormones.
Hormones - chemical secretions that get produced by the endocrine glands. They can be proteins, steroids, or neurotransmitters.
Target organs - specific areas of the body that the hormones have an affect on. For a hormone to affect a target, the target cell has to have a receptor that recognizes the hormone - that helps to give specificity. Not all cells will recognize all hormones.
What are the major endocrine glands?
In the brain there’s the pineal gland - secretes melatonin which helps to regulate the body’s circadian rhythm.
Also the pituitary gland - the way the central nervous system connects anatomically and functionally to the endocrine system.
And the hypothalamus - releases hormones that guide the pituitary’s release of multiple tropic hormones that guide the rest of the endocrine glands.
Thyroid gland - thyroid hormone; major regulator of all of our cell’s metabolism
Thymus - releases thymosin which assists in maturation of T cells in the thymus.
Adrenals - sit atop the kidneys; release various hormones including the catecholamines which we call adrenaline. They release corticosteroids, mineralosteroids, and gonadocorticoids.
Pancreas - releases hormones that regulate our blood glucose levels - insulin and glycogen.
Testis/Ovaries - release sex hormones that help to maintain the repro organs, give secondary sex characteristics and help to maintain pregnancy.
What are the 4 classes of hormone based on structure
Amines/amino acid - two iodinated tyrosine aminos make thyroid hormone (dopamine, epinephrine, norepinephrine, thyroid hormone).
Peptide/protein - must bind to a plasma membrane receptor to have an affect on a target cell; insulin; cannot pass through the cellular membrane. Each receptor will have an affinity for a certain hormone and once the hormone binds to the receptor, it will cause a cascade of events - second messenger pathway. It causes intracellular signaling molecules to carry out some sort of cellular response (thyroid stimulating hormone, ADH, oxytocin, insulin, glucagon, corticotropin-releasing hormone, follicle simulating hormone, growth hormone-releasing hormone).
Steroids - derived from cholesterol; bind to nuclear receptors inside the target cell. The hormone can enter the plasma membrane on its own, but inside the cell it can bind to the receptor and it is then ushered into the nucleus of the cell where it interacts with the DNA and can change the transcription of the DNA to make new proteins (aldosterone, estrogen, progesterone, glucocorticoids).
Fatty acids - prostaglandins
What are the functions of hormones
Open or close ion channels affecting membrane potential.
Stimulate gene expression to influence protein synthesis.
Activate or inhibit enzyme systems.
Induce secretory activity in other endocrine organs.
Stimulate mitosis for growth or healing.
What role does the hypothalamus play in the endocrine system?
The hypothalamus integrates the nervous and endocrine systems by directing control over their regulation. It regulates homeostasis, body temperature, hunger, behavior, emotion, and pain. The hypothalamus produces releasing hormones, which stimulate the pituitary to release stimulating hormones.
3 major functions:
Endocrine organ that releases ADH (blood volume/pressure) and oxytocin hormones.
Secretes regulatory hormones that control the anterior lobe of the pituitary gland - 1. releasing hormones - causes the pituitary gland to send stimulatory signals and 2. inhibitory signals - stops the pituitary gland from releasing hormones.
Directs neural control of the sympathetic stimulation of the adrenal medulla to release adrenaline (epinephrine) which helps the body deal with longer stress responses
Describe the process of how hormones are released by the endocrine glands
The CNS takes in information internally and externally to understand the environment and integrate what the body needs and how the endocrine system can help. The higher cerebral areas send signals to the hypothalamus on how to regulate the body.
The hypothalamus will then regulate the endocrine system by communicating with the pituitary gland.
The anterior pituitary gland will send out stimulating hormones to trigger the release of additional hormones from other endocrine glands: growth hormone to simulate muscle and bone cell mitosis so those organ systems can grow; FSH and LH to the repro glands; thyroid stimulating hormone; adrenocorticotropic hormone to stimulate adrenals.
Describe the positive and negative feedback loops
Negative feedback is how the body maintains homeostasis, or equilibrium. The brain is constantly monitoring hormone levels to keep levels within its certain range or set-point. Negative feedback prevents over-secretion of any hormone. The action of ADH, which dilutes the blood, is one example. Once the blood is dilute, the hypothalamus detects the dilute levels and stops releasing ADH.
Positive feedback enhances or increases the amount of the hormone that is released. One example is oxytocin, a hormone that causes the uterus to contract. The action of the uterus contracting causes more oxytocin to be released.
Define endocrine, paracrine, and autocrine.
Endocrine: Hormones are released to circulation to act on a target organ (i.e. TSH, ADH) Paracrine: Hormones act locally on cells close to where they are released (i.e. estrogen and testosterone)
Autocrine: Hormones produce a biologic action on the cell that released them (i.e. insulin)
What is the role of the pituitary gland?
Answer: The pituitary gland is known as the “master gland,” since it stimulates target organs to secrete their hormones.
The anterior secretes: GH, ACTH, TSH, FSH, LH, prolactin
The posterior secretes: ADH, oxytocin
Explain the ways in which hormones can be over-secreted:
Increased hormone secretion can occur from any of the following reasons: (1) the target gland over-secretes due to pathology; (2) the pituitary or hypothalamus over-stimulates the target gland; (3) hormones are being produced from a different site (i.e. hormone producing tumor); (4) hyperactive genetic mutation of the target hormone receptors.
Explain the ways in which hormones can be Under-secreted:
Decreased hormone secretion can result from any of the following reasons: (1) a congenital or acquired disorder of the target gland; (2) the pituitary does not secrete enough stimulating hormone; (3) the hypothalamus does not secrete enough releasing hormone; (4) the hormone is defective; (5) the receptors of the target organ do not respond.
Explain thyroid hormone regulation and functions
The hypothalamus releases thyroid releasing hormone (TRH) which will cause the anterior pituitary gland to release thyroid stimulating hormone (tropic) (TSH). TSH will travel to the thyroid and cause it to release T3 and T4. As the hormone circulates in the bloodstream, it will circle back bia negative feedback.
Thyroid hormone (TH) functions to change its target cell’s gene expression to favor metabolism and protein synthesis. It increases the metabolic rate (increases cellular use of glucose, fat, and protein); cardiovascular and respiratory systems as metabolism increases and oxygen consumption increases, and metabolic wastes increase, the physiological response is vasodilation, increased cardiac output/blood volume/ventilation to get rid of excess CO2, and increased cardiac contracility and pulse increase; neuromuscular effects such as - muscular tone and contractility, brain development, and sympathetic nervous system responses.
What do the different sections of the adrenal glands secrete
The inner medulla is an extension of the sympathetic nervous system and released epinephrine and norepinephrine into the bloodstream under stressful situations.
The outer cortex secretes 3 adrenocortical hormones:
Glucocorticoids - regulate glucose and protein metabolism. Cortisol is thought of as a stress hormone. Because the adrenals are an outcropping of the sympathetic nervous system, it makes sense that they would also secrete hormones in response to longterm stress for the body. As such, cortisol keeps blood glucose levels relatively constant so that energy will be available for the tissues to repair themselves and helps to maintain our blood pressure by increasing the action of vasoconstrictors. It acts as an antiinflammatory.
Mineralocorticoids - regulate kidney’s excretion/absorption of sodium and potassium. Aldosterone is the main mineralocorticoid - it increases the absorption of sodium and excretes potassium in response to angiotensin II to increase blood volume.
Gonadocorticoids - affect sexual characteristics, libido, reproduction
How does cortisol act on the body
Cortisol is released because of the hypothalamus pituitary axis. The hypothalamus will receive info from our higher brain areas about stress. This will cause the hypothalamus to release CRH (corticotropin releasing hormone) that will travel to the anterior pituitary gland, which will release ACTH (adrenocorticotropic hormone). That will stimulate the adrenal cortex to release cortisol, which is part of its own negative feedback loop.
Metabolic effects: Cortisol causes gluconeogenesis - creating of glucose from amino and fatty acids. That will cause a rise in our blood glucose levels. Glucose in the periphery might not be as utilized, so cortisol can cause insulin resistance. That’s why people who are under long term stress can gain weight and insulin resistance.
Psychological effects: cortisol receptors in the brain, and patients treated with pharmaceutical preparations of the hormone do report emotional instability as a side effect.
Immunologic and Inflammatory effects: the pharmaceutical dosages can decrease prostaglandin formation, stop capillary permeability, and the release of inflammatory mediators which decreases the inflammatory response. They also reduce humoral and cellular mediated immunity. This can be of use to people with autoimmune and inflammatory disorders, however long term use can have adverse effects like metabolic syndromes and immunosuppression issues.
Describe Addison’s Disease, including clinical presentation, diagnosis, treatment
Adrenal gland
Insufficient cortisol and aldosterone secretion accompanied by elevated ACTH levels. With low aldosterone, there will be low sodium and increased potassium. Low sodium will cause hypotension.
Etiology - mostly autoimmune
Primary - destruction of the gland
Secondary - an issue at the level of the pituitary gland not releasing ACTH or the hypothalamus not releasing CRH.
Clinical manifestations - not until most of gland is destroyed.
Hyperpigmentation from high ACTH levels - similar amino acid sequence to the melanocytes.
Mineralocorticoid deficiency - affects electrolyte and water balance. Increase in sodium, chloride, and water excretion and a lowering of the blood volume, which decreases blood pressure and cardiac output. Hyperkalemia occurs without aldosterone secretion. Dehyrdation.
Glucocorticoid deficiency - hypoglycemia, weight loss, lethargy, GI symptoms like anorexia, nausea, vomiting, and diarrhea.
Treatment - hormone replacement therapy
