Human Anatomy and Physiology BIO 217 Topic 7 – The Endocrine System PDF

Human Anatomy and Physiology BIO 217 Topic 7 – The Endocrine System Sections 4 (TuSu) and 5 (MoWe): Danielle Badro, PhD; Associate Professor of Molecular Oncology; College of Allied Health Sciences...

Human Anatomy and Physiology BIO 217 Topic 7 – The Endocrine System Sections 4 (TuSu) and 5 (MoWe): Danielle Badro, PhD; Associate Professor of Molecular Oncology; College of Allied Health Sciences [email protected]  Learning Objectives Identify the various glands of the endocrine system and discuss their functions. Recognize the characteristics of hormones. Explain mechanisms of hormonal control on homeostasis. Describe the activities of glands of the endocrine system including the hypothalamus, pituitary gland, adrenal gland, thyroid, parathyroid, and gonads.  Introduction The endocrine system and the nervous system coordinate their activities to maintain the body’s homeostasis. The endocrine system: – Consists of a group of endocrine glands. – Consists of glands that secrete hormones that diffuse into the bloodstream. – Acts much slower than the nervous system but has effects that last longer.  The endocrine system, like the nervous system, uses chemical signals that bind to receptor molecules. Cells of the endocrine system are called glandular cells; they release hormones into the bloodstream. Comparison of Neurotransmitters and Hormones.  Introduction Hormones, which are chemical messengers, act on target cells, regulating their metabolic functions. – Hormones are considered “long-distance” chemical signals. Many glands like, the hypothalamus and pancreas, have multiple functions. Exocrine glands are those that secrete nonhormonal substances outside the body, through ducts. Include sweat glands. Endocrine gland secretion.  Hormones There are three chemical classes of hormones: – Steroids – Amines – Peptides and proteins The chemical composition matters because it directly affects how the hormone relates to its receptor.  Steroid Hormones Steroid hormones include estradiol, testosterone, progesterone, mineralocorticoids, cortisol (stress hormone, and glucocorticoids. Steroid hormones are derived from cholesterol → lipid hormones. Cholesterol is a steroid that can be acquired through the diet and can be produced by the liver. It is found in liver, egg yolks, whole milk, butter, cheese, and meats - not found in plants. Can pass through cell membranes to reach receptors anywhere in the body.  Amine Hormones These hormones are derived from amino acids. Include thyroid hormones (T3 and T4), dopamine, epinephrine (adrenaline), norepinephrine, and melatonin. May or may not be able to cross cell membranes. E.g.: Thyroid hormone can easily pass across a cell membrane to reach a receptor inside the cell, while epinephrine cannot.  Protein Hormones Protein hormones are made of chains of amino acids. Include: – Insulin – Thyroid-stimulating hormone (TSH) – Follicle-stimulating hormone (FSH) – Luteinizing hormone (LH) – Growth hormone (GH, or human growth hormone HGH, or somatotropin) – Parathyroid hormone (PTH) – Antidiuretic hormone (ADH) – Adrenocorticotropic hormone (ACTH) – Glucagon – Calcitonin – Oxytocin – Hormones from the hypothalamus Proteins are too large to pass through cell membranes. Peptide and protein hormones are synthesized in stages, stored in secretory sacs, and only released when the hormone-secreting cell receives a proper stimulation to do so. After a hormone is secreted into the blood, three outcomes may take place.  Hormones and Homeostasis Homeostasis = dynamic mechanisms that detect and respond to deviations in physiological variables. The body continuously monitors the variable and has a place where the ideal level is stored. E.g.: the hypothalamus stores the ideal set-point for temperature. Both endocrine (hormones) and nervous systems work to keep levels at or near the set point. When a very abnormal metabolic value is detected, the control systems will activate a feedback loop, either negative feedback or positive feedback. Physiological Feedback Loop If the feedback opposes the stimulus, it is a negative feedback loop. Positive feedback increases the magnitude of a change versus resisting change. It increases a change away from a set point.  Control of Hormones and Negative Feedback Hormones in the bloodstream fluctuate resultantly but remain relatively stable. Secretion → Release → Elimination → Secretion... – Glands secrete hormones → Released into the blood → Hormones are continually excreted in the urine and broken down mostly by liver enzymes. Negative feedback is the mechanism that controls hormone secretion: – Negative feedback counteracts a change. Thus, as blood pressure rises, negative feedback works to bring it down to the set point. If blood pressure falls, negative feedback raises it back up to normal. – As hormone levels rise, negative feedback inhibits the system and secretion decreases. As hormone levels decrease, system starts up again.  Control of Hormones and Negative Feedback Negative feedback is triggered by internal or external stimuli. Three types of stimuli trigger endocrine gland actions: 1. Humoral stimuli: changing blood levels of certain vital ions and nutrients. They are the simplest type of endocrine controls. E.g.: when parathyroid gland cells monitor blood calcium and secrete parathyroid hormone (PTH) when they detect lower levels. 2. Neural stimuli: nerve fibers directly stimulates certain glands. E.g.: the sympathetic nervous system responds to stress by stimulating the adrenal medulla to release norepinephrine and epinephrine (slide 56). 3. Hormonal stimuli: hormone release due to the production of other hormones. A tropic hormone is a hormone that controls the secretion of another hormone. E.g.: when the hypothalamus regulates secretion of pituitary hormones. Control by plasma concentrations of mineral ions and organic nutrients. Control of hormonal secretion by neurotransmitters. Control of Hormones and Negative Feedback Inputs that control hormonal changes.  The Endocrine Organs The endocrine system is composed of glands that secrete chemical hormones into the blood stream. Their functions: – Regulate metabolism – Control chemical reactions – Transport substances – Regulate water and electrolyte balances – Aid in reproduction, growth, and development The hypothalamus is a neuroendocrine organ. Several organs may secrete hormones, including the stomach, small intestine, kidneys, and heart. The endocrine glands and their hormones. Endocrine Organ Functions. Endocrine Organ Functions (continued).  The Endocrine Organs A gland may be: – A separate structure all on its own – or it may be made up of groups of cells within an organ that function together to produce hormones. Hormones are secreted outside the cells that produce them. – No special ducts carry hormones to their target cells. – Instead, the bloodstream is the transportation system - hormones are picked up by the blood and travel everywhere the blood travels A hormone travels everywhere, but it has an effect only on its target tissue. The Hypothalamus and Pituitary Gland The pituitary is divided into anterior and posterior pituitary. It is commonly known as the “master gland” because of its role in controlling other endocrine glands. It acts only under orders from the hypothalamus to which it is directly connected. Hormones produced by the hypothalamus are called hypophysiotropic and the ones produced by the posterior pituitary are tropic hormones. – The anterior pituitary is connected to the hypothalamus through blood vessels. – The posterior pituitary is connected to the hypothalamus through hypothalamic neurons that secrete the antidiuretic hormone (ADH) and oxytocin hormone.  The hypothalamus-pituitary relationship. Memorize annotations underlined in green (Hypophysis) (Capillaries at the base of the hypothalamus) (Adenohypophysis) (Neurohypophysis) Control Systems Involving the Hypothalamus and Pituitary Sequential pattern by which a hormone of the hypothalamus controls the secretion of an anterior pituitary hormone, which in turn controls the secretion of a hormone by a 3rd endocrine gland. 27  Antidiuretic Hormone (ADH) Antidiuretic hormone (Vasopressin) is involved in regulation of water balance and osmolarity. – It is secreted by the hypothalamus when the hypothalamus senses decreased blood volume or increased blood osmolarity. It targets the kidneys, causing them to reabsorb more water. It is very important in long-term control of blood pressure, especially during dehydration.  Oxytocin Oxytocin is important in maintaining uterine contractions during labor and is involved in milk ejection from the breasts in nursing mothers. Oxytocin’s function in males is unknown. Anterior Pituitary Hormones Anterior Pituitary Hormones and the Hypothalamus 33 Long and Short-Term Feedback Loop Selected Hypothalamic and Pituitary Hormones.  (function in males is unknown) Selected Hypothalamic and Pituitary Hormones.  Thyroid Gland This gland resembles a bow tie - it is anterior and lateral to the trachea, just inferior to the larynx. Gland produces: – T3 (triiodothyronine) and T4 (thyroxine) ▪ Produced mainly from tyrosine and iodide. ▪ Collectively called thyroid hormone. ▪ T4 is secreted in much larger amounts than T3 but T3 is more active - T3 regulates metabolic rate, growth, brain development and function. ▪ Their function is to increase metabolism in most tissues. – Calcitonin: ▪ It stimulates the deposition of calcium in the bone, making it more relevant for children than adults. The Endocrine Organs – Thyroid Gland Thyroid gland.  Parathyroid Glands There are two pairs of parathyroid glands in the body. Embedded in the posterior surface of the thyroid gland, with two on each side of the trachea.  Parathyroid Glands Produces the parathyroid hormone (PTH) which regulates the level of calcium in the blood: – reabsorption of calcium from bones – absorption of calcium in the small intestine If calcium levels in the blood become too low, the parathyroid glands are stimulated to release PTH, which stimulates bone dissolving cells and releases calcium into the blood stream. Parathyroid Hormone and Plasma Calcium Concentration.  The Pancreas The pancreas is part of the endocrine and digestive systems. It is an elongated gland with a pebbly appearance. It is inferior and posterior to the stomach. Only ~2% of the gland produces hormones: – The endocrine cells are grouped to form 1 to 2 million pancreatic islets (islets of Langerhans). – They produce two hormones - insulin and glucagon - that regulate blood glucose levels.  The Endocrine Organs – Pancreas Pancreas. The pancreatic ducts are used for digestive secretions only.  The Endocrine Organs – Pancreas Glucose levels are important because: – All cells need glucose for cellular respiration. – Blood glucose levels affect the fluid balance of the cells. When blood sugar rises, the pancreas releases insulin: – Helps glucose get into cells. – Causes excess glucose to be stored as glycogen in the liver. When blood sugar falls, the pancreas releases glucagon: – Causes glucose to be released from the liver. The Endocrine Organs – Adrenal Glands These glands sit as a cap, superior and medial to kidneys. The two parts of the adrenal gland are: Adrenal cortex – It is the outer layer of the adrenal gland. – More than 30 steroid hormones (adrenocorticosteroids) are produced in the cortex; they can be divided into three functional categories: mineralocorticoids, glucocorticoids, and androgens. – Produced under the direct stimulation of the anterior pituitary. Adrenal medulla – It is the middle of the adrenal gland. – Stimulated by sympathetic system in situations of fear, pain, and stress. – It releases epinephrine (adrenaline) and norepinephrine (noradrenaline). – In times of stress, cells from the medulla stimulate cells of the cortex to secrete cortisol.  Synthesis of steroid hormones by the adrenal cortex Androstenedione: androgen that might be related to sex drive. Cortisol: glucocorticoid hormone that causes increased glucose availability. Aldosterone: mineralocorticoid hormone that enhances water and sodium retention in the kidneys. Adrenal cells secreting hormones.  Relevant Resources Endocrine gland hormone review | Endocrine system physiology | NCLEX-RN | Khan Academy https://www.youtube.com/watch?v=ER49EweKwW8 Types of hormones | Endocrine system physiology | NCLEX-RN | Khan Academy https://www.youtube.com/watch?v=KSclrkk_Ako The hypothalamus and pituitary gland | Endocrine system physiology | NCLEX-RN | Khan Academy https://www.youtube.com/watch?v=9dS7bc_2bUE Endocrine Glands & Functions | Parathyroidism Nursing | Made Easy NCLEX https://www.youtube.com/watch?v=foswyzQ_6bU 47