Endocrine System Module 10 PDF

Chapter 17. The Endocrine System Week 10 Module Objectives Identify How the endocrine system maintains homeostasis Describe the structure and function of major endocrine glands Describe the function, regulation and effects of hormones of major endocrine glands Describe negative feedba...

Chapter 17. The Endocrine System Week 10 Module Objectives Identify How the endocrine system maintains homeostasis Describe the structure and function of major endocrine glands Describe the function, regulation and effects of hormones of major endocrine glands Describe negative feedback mechanism in relation to hormone secretion Differentiate between endocrine and exocrine gland function Introduction Hormones are chemicals that originate in tissues and organs and affect the function of other tissue/organs Hormones can vary in composition from simple amino acids to complex combinations of lipids, proteins and carbohydrates Roles include: Metabolism, growth and development Muscle and fat distribution Fluid and electrolyte balance Sexual development and reproduction  Communication within the human body involves the transmission of signals to control and coordinate actions in an effort to maintain homeostasis. There are two major organ systems responsible for providing these communication pathways: the nervous system and the endocrine system. Neural communication includes both electrical and chemical signalling between neurons and target cells. Types of Hormones 1. Endocrine system – a collective group of tissues/organs capable of secreting hormones Pancreas – insulin – controls blood glucose How do your hormones work? - Emma Bryce – YouTube (5 minutes) 2. Neurons can synthesize and release neurotransmitters (hormones) – which can stimulate a neural response (fast response) Epinephrine – role in fight or flight responses Dopamine - dopamine pathways are involved in motor control and the release of various other hormones as well as learning, reward and motivation 3. An inflammatory and or immune response can trigger the release chemical mediators which function as hormones Cytokines, leukotrienes and prostaglandins – trigger defense mechanisms Neurologic, inflammatory and endocrine system are independent of each other The overall goal is to protect the body from injury and maintain homeostasis Hormones The hormones of the human body can be structurally divided into three major groups:  amino acid derivatives (amines)  peptides  Steroids Watch this video about the Endocrine System ( 2:14) https://www.youtube.com/watch?v=emvHa BiRY8Q Pathways for hormonal receptors 1-Pathways Involving Intracellular Hormone Receptors Intracellular hormone receptors are located inside the cell. Hormones that bind to this type of receptor must be able to cross the plasma membrane. Pathways for hormonal receptors 2-Pathways Involving Cell Membrane Hormone Receptors (Extra cellular): Hormones bind to cell membrane receptors that are located, at least in part, on the extracellular surface of the cell membrane.  Five major pathways of cell-to-cell communication that allow hormones to move from production to secretion to response 1.Paracrine pathway 2.Autocrine pathway 3.Endocrine pathway 4.Synaptic pathway 5.Neuroendocrine pathways Other Types of Chemical Signals Paracrine activity: when a chemical signal is released into the interstitial fluid and targets neighbouring cells. Autocrine activity: when chemicals released by a cell elicit a response in the same cell that secreted it.  Factors Affecting Target Cell Response The permissive effect, in which the presence of one hormone enables another hormone to act. For example, thyroid hormones have complex permissive relationships with certain reproductive hormones. A dietary deficiency of iodine, a component of thyroid hormones, can therefore affect reproductive system development and functioning. The synergistic effect, in which two hormones with similar effects produce an amplified response. In some cases, two hormones are required for an adequate response. For example, two different reproductive hormones—FSH from the pituitary gland and estrogens from the ovaries—are required for the maturation of female ova (egg cells). The antagonistic effect, in which two hormones have opposing effects. A familiar example is the effect of two pancreatic hormones, insulin and glucagon. Insulin increases the liver’s storage of glucose as glycogen, decreasing blood glucose, whereas glucagon stimulates the breakdown of glycogen stores, increasing blood glucose. Feedback Loops Role of Feedback Loops Positive Feedback loop – the presence of a hormone stimulates increased hormone production until the cycle is interrupted. Oxytocin stimulates more forceful contraction of the uterus which causes stretch in the cervix Increased stretch in the cervix, stimulates more oxytocin production The cycle continues until the baby is born – no more cervical stretch Negative feedback loop – is like an internal thermometer Anti Diuretic hormone (ADH) is released by the posterior pituitary gland in response to low fluid levels in the body Once the fluid volume is restored – pituitary slow or stops the production of ADH  Negative feedback is characterized by the inhibition of further secretion of a hormone in response to adequate levels of that hormone. This allows blood levels of the hormone to be regulated within a narrow range. An example of a negative feedback loop is the release of glucocorticoid hormones from the adrenal glands, as directed by the hypothalamus and pituitary gland. As glucocorticoid concentrations in the blood rise, the hypothalamus and pituitary gland reduce their signaling to the adrenal glands to prevent additional glucocorticoid secretion  Role of Endocrine Gland Stimuli Three major types of hormonal stimuli Humoral stimuli are changes in ion or nutrient levels in the blood. Hormonal stimuli are changes in hormone levels that initiate or inhibit the secretion of another hormone. a neural stimulus occurs when a nerve impulse prompts the secretion or inhibition of a hormone.  Hypothalamus–pituitary complex “command center” of the endocrine system. This complex secretes several hormones that directly produce responses in target tissues, as well as hormones that regulate the synthesis and secretion of hormones of other glands. Watch this video about the 2-Minute Neuroscience: Hypothalamus & Pituitary Gland (2 min) https://www.youtube.com/watch?v=TVhm2rBGhB0  Hypothalamic - pituitary Axis Hypothalamus – located in the brain, contains neurons that produce hormones which act on the anterior and posterior pituitary gland Releasing (stimulating) hormones Growth hormone releasing hormone (GhRH) Thyrotropin releasing hormone (TRH) Inhibitory hormones Dopamine (inhibits prolactin) Somatostatin(inhibits growth & thyroid stimulating hormones) 2-Minute Neuroscience: Hypothalamus & Pituitary Gland - YouT ube Thyroid Gland Thyroid Gland: The thyroid gland is located in the neck where it wraps around the trachea. (a) Annterior view of the thyroid gland. (b) (b) Posterior view of the thyroid gland. (c) (c) The glandular tissue is composed primarily of thyroid follicles. The larger parafollicular cells often appear within the matrix of follicle cells. Watch this video Thyroid gland - What's the function of the thyroid?(1:54) https://www.youtube.com/watch?v=xKQa-MbZUPY Thyroid Gland The thyroid hormones, T3 and T4, are often referred to as metabolic hormones because their levels influence the body’s basal metabolic rate, the amount of energy used by the body at rest. When T3 and T4 bind to intracellular receptors located on the mitochondria, they cause an increase in nutrient breakdown and the use of oxygen to produce ATP. In addition, T3 and T4 initiate the transcription of genes involved in glucose oxidation. These mechanisms prompt cells to produce more ATP which causes an increase in heat production. This so-called calorigenic effect (calor- = “heat”) raises body temperature. Regulation of TH Synthesis The release of T3 and T4 from the thyroid gland is regulated by thyroid-stimulating hormone (TSH). low blood levels of T3 and T4 (TRH) from the hypothalamus, TSH from the anterior pituitary thyroid gland to secrete T3 and T4. Note: The levels of TRH, TSH, T3, and T4 are regulated by a negative feedback system Goiter Insufficient amounts of iodine in the diet can lead to goiter, cretinism, and many other disorders. Parathyroid Glands: The small parathyroid glands are embedded in the posterior surface of the thyroid gland. Most people have four parathyroid glands It secrete the parathyroid hormone (PTH), the major hormone involved in regulating blood calcium levels. Watch this video Parathyroid Glands - Parathyroid hormone (PTH or Parathormone) - Calcium - Endocrine System ( 9 Min) https://www.youtube.com/watch?v=jkc lT3U5vKY Parathyroid Glands: The parathyroid glands are tiny, round structures usually found embedded in the posterior surface of the thyroid gland. A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands, but occasionally there are more in tissues of the neck or chest. The primary functional cells of the parathyroid glands are the chief cells. These epithelial cells produce and secrete the parathyroid hormone (PTH), the major hormone involved in the regulation of blood calcium levels. The gland also contains oxyphil cells but their function is not clear. Parathyroid Parathyroid and Calcium Low serum calcium – parathyroid gland is stimulated Releases parathyroid hormone (PTH) Send the hormones thru bloodstream Hormones bind with receptor cells: On bones to release calcium Intestines to absorb more calcium Kidney's to reabsorb Ca+ and activation of vitamin D Causing an increase in serum calcium levels Adrenal Gland Adrenal glands : Both adrenal glands sit atop the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all producing different types of hormones. The adrenal glands are glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule. https://www.youtube.com/watch?v=Z DS3vJ_qTQ8 Adrenal Gland hormones: Flight or Flight response One of the major functions of the adrenal gland is to respond to stress. Stress can be either physical, psychological, or both. Physical stresses may include injury, exposure to severe temperatures, or malnutrition. Psychological stresses include the perception of a physical threat, a fight with a loved one, or just a bad day at school. Adrenal glands : The adrenal cortex, as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for the regulation of the long- term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation. The HPA axis involves the hypothalamus stimulating the release of adrenocorticotropic hormone (ACTH) from the pituitary. ACTH then stimulates the adrenal cortex to produce the hormone from the cortex (corticosteroids). This pathway will be discussed in more detail below. The adrenal medulla is neuroendocrine tissue composed of postganglionic sympathetic neurons. It is really an extension of the autonomic nervous system. This neuroendocrine pathway, controlled by the hypothalamus, involves stimulation of the medulla by impulses from preganglionic sympathetic neurons originating in the thoracic spinal cord. Stimulation causes the medulla to secrete the amine hormones epinephrine and norepinephrine. Reproductive Hormones The male and female reproductive system is regulated by follicle- stimulating hormone (FSH) and luteinizing hormone (LH) produced by the anterior lobe of the pituitary gland in response to gonadotropin- releasing hormone (GnRH) from the hypothalamus. In males, FSH stimulates sperm maturation, which is inhibited by the hormone inhibin. The steroid hormone testosterone, a type of androgen, is released in response to LH and is responsible for the maturation and maintenance of the male reproductive system, as well as the development of male secondary sex characteristics. Reproductive Hormones In females, FSH promotes egg maturation and LH signals the secretion of the female sex hormones, the estrogens and progesterone. Both of these hormones are important in the development and maintenance of the female reproductive system, as well as maintaining pregnancy. The placenta develops during early pregnancy, and secretes several hormones important for maintaining the pregnancy. Reproductive Hormones Pancreas endocrine function involves the secretion of insulin (produced by beta cells) and glucagon (produced by alpha cells) it regulates the rate of glucose metabolism in the body. The pancreas has  exocrine  endocrine functions.  Alpha cells -> glucagon,  beta cells -> insulin.  delta cell ->peptide hormone somatostatin Note: Insulin and glucagon are involved in the regulation of glucose metabolism. Watch this video: The Endocrine Pancreas (Insulin, Glucagon, and Somatostatin) | Endocrine Biology (11 Min) https://www.youtube.com/watch?v=6ozTqeOWjGg Homeostatic Regulation of Blood Glucose Levels: Blood glucose concentration is tightly maintained between 70 mg/dL and 110 mg/dL. The Effect of Insulin: When blood sugar levels rise after eating, the pancreas releases insulin. Insulin helps glucose enter cells, and the excess glucose is stored in the liver as glycogen. The Effect of glucagon: Glycogenolysis: Glucagon stimulates the liver to convert its glycogen stores back into glucose. Gluconeogenesis= stimulates the liver to take up amino acids from the blood and convert them into glucose Glucagon stimulates lipolysis, breaking stored triglycerides into free fatty acids and glycerol. Organs with Secondary Endocrine Functions Development and Aging of the Endocrine System The endocrine system originates from three layers of the embryo: Endoderm, Ectoderm, Mesoderm. Aging affects the endocrine glands, The hormone decreased with aging are human growth hormone, Cortisol, Aldosterone, Sex hormones, Thyroid hormones Knowledge Check!! Which hormone is known as the “fight-or-flight” hormone? 1. Cortisol 2. Insulin What is the main hormone 3. Epinephrine produced by the parathyroid 4. Growth hormone gland? A- Insulin ADH hormone released by the posterior pituitary gland is mainly B-Calcitonin responsible for: C-T3 & T4 A- Fluid reabsorption by the kidneys D-Cortisone B-Metabolism Regulation C- Calcium Reabsorption D- Reproductive regulation Which of the following is NOT a function of the pancreas? 1.Secretion of insulin 2.Secretion of glucagon 3.Regulation of body temperature 4.Regulation of the rate of glucose metabolism