Endocrine System 2024 PDF

Unit 8 The Endocrine System Function: communication and control 1 ORGAN SYSTEMS OF THE BODY: endocrine system Endocrine system Glands that secrete hormones into blood Sustained response to stimuli Main regulators of metabolism, reproduction,...

Unit 8 The Endocrine System Function: communication and control 1 ORGAN SYSTEMS OF THE BODY: endocrine system Endocrine system Glands that secrete hormones into blood Sustained response to stimuli Main regulators of metabolism, reproduction, hemostasis (wound healing) Endocrine glands – secrete hormones into blood Hormones – small compounds or proteins that bind to a target cell to elicit a response Q: What are glands? Answer: Organs in the body that synthesize a particular substance and then release it 2 EXOCRINE VS. ENDOCRINE GLANDS Exocrine glands: secrete molecules and/or hormones via ducts; local effects on neighboring cells and tissues; not part of the endocrine system (i.e. salivary glands, sweat glands). Ducts are channels or passageways lined with epithelial cells – do not connect to the blood stream. Endocrine glands: secrete hormones in extracellular spaces (no ducts) which are then picked up by the blood stream to affect a cell, tissue, or organ elsewhere in the body (target tissue) 3 HOW THE ENDOCRINE SYSTEM WORKS: GENERAL OVERVIEW Endocrine system can elicit a negative feedback or a positive feedback stimulus Binds to receptor on endocrine cell to have an effect gland *Note that depending on the stimulus, some glands can signal to other glands in the body to produce the appropriate hormone 4 ENDOCRINE SYSTEM AND NEGATIVE FEEDBACK MECHANISMS What is the hormone? What is the endocrine gland? What is the target tissue? 5 ENDOCRINE SYSTEM: Mechanisms of hormone action Receptors on the plasma membrane of the target cells detect the hormone 6 ENDOCRINE SYSTEM AND FEEDBACK MECHANISMS Oxytocin is a strong stimulant of uterine contraction Extension of cervix increases Oxytocin secretion Positive or negative feedback? + feedback uterine contractions cervical distension Birth stops the cervical distension7 ENDOCRINE ORGANS Hypothalamus Pituitary Pineal Thyroid and parathyroids Thymus Adrenals Pancreas Testes (male) Ovaries (female) However, please note that these are not all the organs responsible for releasing hormones in the body… many influential hormones are produced and released from the kidneys, skin, intestines, stomach, placenta, etc… Endocrine organs produce and release hormones to induce a biological function 8 TYPES OF HORMONES The classification of hormone generally depicts its: Origin Mechanisms of function Targets Effect on cells, tissues, and organs 9 NEUROTRANSMITTERS vs HORMONES Both NEUROTRANSMITTERS and HORMONES affect human behavior by binding to receptors on cells… TYPES OF HORMONES: ENDOCRINE, PARACRINE, AUTOCRINE Endocrine hormone action: hormones secreted in extracellular spaces which are then picked up by the blood stream to affect a cell, tissue, or organ elsewhere in the body; “typical” hormone Paracrine hormone actions: a hormone is secreted by a cell, which influences a neighboring cell…total distance traveled is very short… Autocrine hormone actions: a hormone secreted by a cell that affects the same cell from which it came Note: some tissues secrete hormones that can have autocrine, paracrine, and endocrine functions 11 ENDOCRINE HORMONE Endocrine or Exocrine? Example: insulin released by pancreas, travels through the blood, binds to receptors on skeletal muscle, liver, etc 12 AUTOCRINE and PARACRINE HORMONES (Bahadoran et al Acta Phys 2020) (Segers et al JAHA 2021) Autocrine example: Fibroblasts (cells that make up connective tissue) release cytokines that stimulate growth of the fibroblasts. More cytokines = more fibrosis (tissue injury) Paracrine example: Blood vessels contain smooth muscle and endothelial cells. Release of nitric oxide (NO) from the endothelial cells acts on the smooth muscle cells to increase muscle contraction. More NO = higher blood pressure TYPES OF HORMONES: STEROID AND NON-STEROID Steroid hormones are cholesterol based Non-steroid hormones are protein based 14 STEROID HORMONES 1. Are released from a hormone-secreting organ and travel through bloodstream 2. Are lipid soluble, therefore can pass through the cell membrane. 3. Bind to a receptor inside the cell’s cytoplasm. The receptor/hormone complex then enters the nucleus. 4. Receptor/hormone complex directly targets binding sites on the DNA 5. Influences gene expression directly 15 NONSTEROID HORMONES 1. Cannot pass the lipid membrane (lipid-insoluble)… 2. …and therefore needs help from a membrane-bound receptor. Binds to this membrane-bound receptor. 3. This triggers a series of events called a second-messenger cascade. 4. Ultimately, one of the “downstream” proteins from the cytoplasm will enter the nucleus, bind, and direct gene expression. Back to our insulin example… Is insulin a steroid hormone or a non-steroid hormone? Take home: the ultimate actions of steroid and non-steroid hormones are the same (influencing gene expression), but their mechanisms of action are different. RECALL: ENDOCRINE ORGANS Pituitary Hypothalamus Pineal Thyroid and parathyroids Thymus Adrenals Pancreas Testes (male) Ovaries (female) The synthesis and release of hormones from each of the endocrine organs is highly controlled by the hypothalamus and pituitary gland 18 HYPOTHALAMUS-PITUITARY-TARGET ORGAN AXIS The endocrine system in a nutshell: 1. The hypothalamus produces releasing (RHs) and inhibiting (IHs) hormones 2. RHs and IHs act on the pituitary gland to stimulate or inhibit the release of anterior pituitary hormones 3. The anterior pituitary releases tropic hormones that control other endocrine organs 4. Peripheral endocrine organs release hormones that control bodily functions 5. Release of hormones from endocrine organs serve as positive or negative feedback on the hypothalamus and anterior pituitary HYPOTHALAMUS-PITUITARY-TARGET ORGAN AXIS 20 HYPOTHALAMUS-PITUITARY-TARGET ORGAN AXIS Hypothalamus Releasing/ Inhibiting Positive/ Anterior Pituitary negative Tropic feedback Hormones Endocrine Gland Peripheral Hormone Tissues of the Body 21 HYPOTHALAMUS Composed of neurons that evade the blood-brain barrier of the CNS. It measures the levels of hormones in the blood and will stimulate or shut down feedback loops depending on changes. Influences hormones produced by the hypothalamus pituitary gland. Also influences hormone levels of other glands by producing releasing and inhibiting hormones. 22 Makes its own hormones that are stored in the pituitary gland. 22 HYPOTHALAMUS hypothalamus hormones: Oxytocin (stored in posterior pituitary) Antidiuretic hormone (ADH; stored in posterior pituitary) Gonadotropin-releasing hormone (Gn-RH) Thyrotropin-releasing hormone (TRH) Cortico-releasing hormone (CRH) Growth hormone-releasing hormone (GH-RH) Prolactin -releasing hormone (PRH) Somatostatin …inhibits growth hormone and Thyroid Stimulating Hormone Prolactin-inhibiting hormone (PIH) (dopamine) … Releasing Released to the anterior pituitary gland to stimulate the … Inhibiting release or inhibit the release of hormones  Hypothalamus Releasing/ Inhibiting Positive/ Anterior Pituitary negative Tropic feedback Hormones Endocrine Gland Peripheral Hormone Tissues of the Body Problems with the hypothalamus Because the hypothalamus only influences the release or inhibition of hormones from the pituitary, problems with the hypothalamus will ultimately effect the release of pituitary hormones Hypo (low) secretion: low hormone secretion by the pituitary Hyper (high) secretion: high hormone secretion by pituitary 24 PITUITARY GLAND Size of a single pea Located deep in the cranial cavity Attached to the hypothalamus (neurons and blood circulation) Anterior pituitary gland releases tropic hormones Posterior pituitary gland stores and releases hormones made by the hypothalamus 25 ANTERIOR PITUITARY GLAND HORMONES Anterior pituitary gland: Tropic control over the thyroid, adrenals, reproductive organs, and bone Also release some additional hormones that are not considered “tropic” (ie GH and prolactin) Many of the hormones secreted by the pituitary gland act on tissues to stimulate the release of additional hormones (Tropic Hormones) ANTERIOR PITUITARY GLAND HORMONES Thyroid-stimulation hormone (TSH) - acts on the thyroid to stimulate release of thyroid hormone Adrenocorticotropic hormone (ACTH) - acts on adrenal cortex tropic to grow in size and stimulate hormone secretion (i.e. hormones = hydrocortisone) hormones Follicle stimulating hormone (FSH)- stimulates ovarian follicles that target to continue follicle development; stimulates follicle cells to release estrogen other Luteinizing hormone (LH)- stimulates estrogen release by endocrine ovarian follicles; promotes ovulation; promotes formation of corpus glands luteum (ruptured follicle) Growth hormone (GH)- stimulates cells to grow by taking up digested proteins (amino acids) from the blood Prolactin- stimulates milk production/lactation Tropic hormones – hormones who’s targets are another endocrine gland 27 PITUITARY GLAND: CLINICAL ABNORMALITIES Growth hormone (GH): promotes normal growth by increaseing movement of digested proteins into the cells to accelerate anabolism; increase blood glucose levels by maintaining glucose in the cell Gigantism vs. pituitary dwarfism: Pre-adult hypersecretion of GH vs. pre-adult hyposecretion GH Acromegaly: Post-adult hypersecretion GH From: www.gigantism.com/ 28 POSTERIOR PITUITARY GLAND HORMONES Posterior pituitary – secretes hormones that affect the kidney and uterus ADH and oxytocin are stored and released from the pituitary gland, but they are produced in the hypothalamus Antidiuretic hormone (ADH) – stimulates reabsorption of water by the kidney Diabetes insipidus: hyposecretion of ADH oxytocin – stimulates contraction of uterine walls and stimulates the release of milk from the breast ducts 29 RECALL: ENDOCRINE ORGANS Pituitary Hypothalamus Pineal Thyroid and parathyroids Thymus (unit 9) Adrenals Pancreas Testes (male) (unit 13) Ovaries (female) (unit 13) 30 THYROID AND PARATHYROID Found within the neck, below the larynx Parathyroid – on the posterior side of the thyroid; “para” = by, near 31 THYROID AND PARATHYROID Thyroid Parathyroid T3 and T4 Parathyroid hormone (PTH) 32 Calcitonin THYROID AND T3, T4 Stimulate cellular metabolism (speed up the release of energy from nutrients) Require iodine for function; iodine assists in the activation and release of T3, T4 Stored in colloid of the thyroid follicles (different than most endocrine glands which don’t store hormones) 33 THYROID, PARATHYROID, and CALCIUM BALANCE Calcitonin Parathyroid Hormone (PTH) Decreases calcium in the blood Increases calcium in the blood Maintains blood calcium levels. Decreased calcium in blood trigger PTH Functions to use release excess calcium in the bloodstream by Increasing osteoclast producing more activity bone Increasing Why is nutrition most osteoblast activity important during pregnancy… why is dairy a must? PANCREAS The presence of this duct makes the pancreas an exocrine gland Endocrine and Exocrine gland Exocrine: secretes pancreatic juice containing enzymes to aid in small intestine digestion of food Endocrine: Glucagon (alpha (A) cells) Insulin (beta (B) cells) The secretion of hormones directly into the blood 35 makes the pancreas an endocrine gland PANCREAS Insulin and Glucagon are functional opposites Glucagon Insulin Glucagon is released when the blood Insulin is released when the blood glucose is low glucose is high Lowers blood glucose levels by: Its major target is the liver, where it promotes: Enhances transport of glucose into body cells (liver, skeletal muscle, neurons) Glycogenolysis – the breakdown of Counters metabolic activity that would glycogen to glucose enhance blood glucose levels (i.e. Gluconeogenesis – synthesis of glycogenolysis and gluconeogenesis). glucose from noncarbohydrates Release of glucose to the blood from liver cells 36 PANCREAS Putting it all together… 37 CLINICAL ABNORMALITIES: DIABETES MELLITUS (DM) Results from hyposecretion or hypoactivity of insulin which results in hyperglycemia The three signs of diabetes are: Polyuria – huge urine output including glucose (yes, urine will actually taste sweet!!!) Polydipsia – excessive thirst Polyphagia – excessive hunger and food consumption vs. Hyperinsulinism – excessive insulin secretion, resulting in hypoglycemia; causes anxiety, tremors, and weakness 38 OTHER ORGANS THAT SECRETE HORMONES Heart – produces atrial natriuretic Kidneys – secrete erythropoietin, peptide (ANP): reduces blood which signals the production of red pressure, blood volume, and blood blood cells…more on EPO in the sodium concentration section about respiration Gastrointestinal tract – Skin – produces cholecalciferol, the enteroendocrine cells release local- precursor of vitamin D…largely acting digestive hormones influenced by sunlight exposure Placenta – releases hormones that Adipose tissue – releases leptin, influence the course of pregnancy which is involved in the sensation of satiety, and stimulates increased energy expenditure 39 DISORDERS OF THE ENDOCRINE SYSTEM Hypothyroidism Group 2 (October 29): Gigantism and pituitary dwarfism Laron Syndrome Diabetes insipidus Diabetes mellitus Addison’s Disease Cushing’s Disease Hyper/hypothyroidism Prolactinoma Laron Syndrome Type 1 Diabetes 40 Unit 8 quiz now available on Canvas: Complete by October 28 @ 11:59 pm QUESTIONS? 41