Anatomy & Physiology for the Health Sciences II Endocrine System I PDF

© 2022 Anatomy & Physiology for the Health Sciences II Block 2 | Lecture 6 Endocrine System I Dr. Simone Pierre [email protected]...

© 2022 Anatomy & Physiology for the Health Sciences II Block 2 | Lecture 6 Endocrine System I Dr. Simone Pierre [email protected] Department of Anatomical Sciences School of Medicine, St. George’s University Session ID: © 2022 Your Objectives will show here! Objectives 1. Distinguish between an endocrine gland and an exocrine gland. 2. Describe how hormones interact with receptor cells. 3. Discuss how hormone receptors can be blocked (clinical). 4. Distinguish between circulating and local hormones. 5. Describe lipid and water-soluble hormones, their transport in blood, the cell receptors they targets and their mechanism of action. 6. Describe the permissive, synergistic and antagonistic effects of hormones. 7. Describe three types of signals that can control hormone secretion. 8. Describe the anatomical and functional relationship between the hypothalamus and pituitary gland. BIOL202 | Block 2 | Lecture 6 | Endocrine System I a) Describe the hypophyseal portal system. 9. Describe the location and histology of the pituitary gland. 10.List the seven major hormones secreted by the anterior pituitary gland and the cells that secrete them. a) Describe the regulation and principal action of the anterior pituitary hormones. b) Discuss anterior pituitary gland disorder pituitary dwarfism, gigantism and acromegaly. 11.List two hormones released by the posterior pituitary gland. a) Describe the regulation and principal action of the posterior pituitary hormones. b) Discuss posterior pituitary gland disorder diabetes insipidus. Session ID: © 2022 Review of Glands 1. Exocrine glands: § Secrete product through ducts into body cavities, lumen of organs, or body surface. Sweat (sudoriferous), sebaceous (oil), mucous, salivary & digestive glands. § Not part of the endocrine system. BIOL202 | Block 2 | Lecture 6 | Endocrine System I Session ID: © 2022 Review of Glands 2. Endocrine glands: § Ductless glands that secrete products (hormones) into interstitial fluid that diffuse into blood. Pituitary, thyroid, parathyroid, adrenal, pineal glands. BIOL202 | Block 2 | Lecture 6 | Endocrine System I § There are many other organs that are not considered endocrine organs that secrete hormones: Hypothalamus, thymus, heart, GI tract, pancreas, liver, kidney, skin, adipose tissue, gonads and placenta. Session ID: © 2022 The Endocrine System o The endocrine system works along with the nervous system to control all body systems and maintain homeostasis. o Both the endocrine and nervous system secrete hormones and neurotransmitters that exert their effects by binding to receptors on or in their “target cells.” o There are some key differences: Characteristic Nervous System Endocrine System Mediator Molecules Hormones delivered to BIOL202 | Block 2 | Lecture 6 | Endocrine System I tissues throughout the body by blood. Site of mediator action Far from the site of release (usually); binds to receptors on or in target cells. Types of target cells Cells throughout the body Time to onset of action Seconds to hours or days Duration of action Generally, longer (seconds to days. Session ID: © 2022 Hormone Receptors o Although hormones travel in blood throughout the body, they only affect target cells with specific protein or glycoprotein receptors to which the hormones bind. o Receptors are constantly being synthesized and broken down. o Down-regulation BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Excess hormone leads to a decrease in number of receptors; receptors undergo endocytosis and are degraded. § Decreases sensitivity of target cell to hormone. o Up-regulation § Deficiency of hormone leads to an increase in the number of receptors. § Target tissue becomes more sensitive to the hormone. Session ID: © 2022 Pharmaceutical Application o Synthetic hormones that block the receptors for some naturally occurring hormones are available as drug. o Example: § RU486 (mifepristone), which is used to induce abortion, binds to the receptors for progesterone and prevents progesterone from exerting its normal effect, in this case BIOL202 | Block 2 | Lecture 6 | Endocrine System I preparing the lining of the uterus for implantation. § Can you give another example? Session ID: © 2022 Action of Hormones o Hormones may have a stimulatory or inhibitory effect on target cell § Local: The hormone can act on nearby cells; paracrine. It can also act on the cell that released it; autocrine. E.g.; Interleukin-2 (IL-2), is released by helper T cells ( a type of white blood cell) during immune responses. IL-2 helps activate other nearby immune cells, a paracrine effect. It also acts as an autocrine by stimulating the same cell that released it to proliferate and secrete even more IL-2 and thus strengthen the immune response. BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Circulating: travel in blood stream to reach distant targets (endocrine glands have well developed blood supply). Session ID: © 2022 Chemical Classes of Hormones o Lipid-soluble Hormones 1. Steroid hormones § Derived from cholesterol: different chemical groups attached at various sites on the four rings at the core of its structure. § Aldosterone, cortisol, androgens, calcitriol, testosterone, estrogens, progesterone 2. Thyroid hormones (T3 and T4) BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Derived from attaching iodine to the amino acid tyrosine. § The two benzene rings make these very lipid-soluble. 3. Nitric Oxide § A gas, is both a hormone and a neurotransmitter. Session ID: © 2022 Chemical Classes of Hormones o Water-soluble Hormones 1. Amine hormones § Synthesized by decarboxylating and otherwise modifying certain amino acids. § Catecholamine (epinephrine, norepinephrine), dopamine, melatonin, serotonin, histamine. 2. Peptide and protein hormones § Modified amino acid or amino acids put together. BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Eg: ADH (Antidiuretic Hormone), FSH (Follicle Stimulating Hormone), LH (Luteinizing Hormone), hGH (Human Growth Hormone), TSH (Thyroid Stimulating Hormone), ACTH (Adrenocorticotropic Hormone), PTH (Parathyroid Hormone), MSH (Melanocyte Stimulating Hormone), insulin, glucagon, prolactin, oxytocin. 3. Eicosanoids § Derived from arachidonic acid (20-carbon fatty acid) § Two major types § Prostaglandins and leukotrienes. Session ID: © 2022 Hormone Transport in Blood o Most water-soluble hormones molecules circulate in free form in blood. o Most lipid-soluble hormones molecules are bound to transport proteins [in blood]. § The transport proteins are synthesized by the liver: They make lipid-soluble hormones temporarily water-soluble thus increasing their solubility in blood. BIOL202 | Block 2 | Lecture 6 | Endocrine System I Ø They slow down the passage of small hormone molecules through the filtering mechanism in the kidneys, thus slowing the rate of hormone loss in the urine. Ø They provide a ready reserve of the hormone. o In general, 0.1 – 10% of the molecules of a lipid-soluble hormone are not bound to a transport protein. Session ID: © 2022 Mechanism of Hormone Action o Hormone binds to receptors on cell surface (water soluble hormones) or inside target cell (lipid-soluble hormones). o Cell may then: § Synthesize new molecules (intracellular receptors). § Change permeability of membrane (ACh). BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Stimulating transport of substances into or out of the target cells. § Alter rates of reactions. o Each target cell responds to hormone differently: § At liver cells (hepatocytes) à insulin stimulates glycogen synthesis § At fat cells (adipocytes) à insulin stimulates triglyceride synthesis Session ID: © 2022 Action of Lipid-soluble Hormones e.g., steroid & thyroid hormones, nitric oxide o Hormone diffuses through phospholipid bilayer & into cell. o Binds to receptor turning on/off specific genes or alter gene expression. o New mRNA is formed & directs synthesis of new proteins on ribosomes. BIOL202 | Block 2 | Lecture 6 | Endocrine System I o New protein alters cell’s activity. Session ID: © 2022 Action of Water-soluble Hormones e.g., amines, peptides and protein hormones, eicosanoids o They bind the receptors (first messenger) that protrude from the target-call surface. o The first messenger then causes production of a second messenger inside the cell. o The second messenger activates protein kinases. BIOL202 | Block 2 | Lecture 6 | Endocrine System I o Protein kinases phosphorylate cellular proteins. o Phosphorylated proteins cause reactions that produce physiological responses. Session ID: © 2022 Control of Hormone Secretions o The release of hormones occurs in short bursts, with little or no secretion between bursts. o Regulated by signals from: § Signals from nervous system E.g., nerve impulses to the adrenal gland regulate epinephrine release. § Chemical changes in the blood E.g., blood Ca2+ level regulates parathyroid hormone secretion. BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Other hormones E.g., adrenocorticotropic hormone stimulates release of cortisol o Negative Feedback § Increase in the amount of the product has a negative feedback or goes back to the controlling organ (pituitary gland or hypothalamus), decreasing the production of the stimulating hormones. o Positive Feedback § The change produced by the hormone causes more hormone to be released Disorders involve either hypo-secretion or hyper-secretion of a hormone. Session ID: © 2022 Hormone Interactions o Permissive Effect § A second hormone, strengthens the weak effects of the first. § E.g.: thyroid hormone strengthens epinephrine’s effect on lipolysis. o Synergistic Effect § The effect of two hormones acting together is greater than the effect of each hormone acting alone. § E.g.: Normal development of oocytes in the ovaries requires both follicle-stimulating hormone from BIOL202 | Block 2 | Lecture 6 | Endocrine System I the anterior pituitary and estrogens from the ovaries. Neither hormone alone is sufficient. o Antagonistic Effect § Two hormones with opposite effects § Eg: insulin promotes glycogen formation in liver & glucagon stimulates glycogen breakdown in liver. Session ID: © 2022 Summary o Exocrine glands have ducts whereas endocrine glands are ductless. o Endocrine glands produce hormones. o Hormones produced only affect target cells with specific protein or glycoprotein receptors to which the hormones bind. o Hormones may have a stimulatory or inhibitory effect on target cell and are classified as BIOL202 | Block 2 | Lecture 6 | Endocrine System I autocrine and paracrine or circulating. o Hormones are water or lipid soluble. o Hormones can have a permissive, synergistic or antagonistic effect. o Hormone secretion is controlled by nervous system signals, chemical changes in the blood and other hormones. Session ID: © 2022 Hypothalamus o The hypothalamus is the major integrating link between the nervous and endocrine systems § Small region in the brain below the thalamus. § Controls pituitary gland with nine different releasing & inhibiting hormones. Hypothalamus BIOL202 | Block 2 | Lecture 6 | Endocrine System I The hypothalamus and the pituitary gland regulate virtually all aspects of growth, development, reproduction, metabolism and homeostasis. Pituitary gland in sphenoid bone Infundibulum Session ID: © 2022 Hypophysis or Pituitary Gland o Secretes hormones that regulate other endocrine organs. o Stimulated and inhibited by hypothalamus and feedback mechanisms from target organs. o Connected to hypothalamus by infundibulum. BIOL202 | Block 2 | Lecture 6 | Endocrine System I Hypothalamus o Composed of two distinct lobes: anterior and posterior. Session ID: Pituitary gland in sphenoid bone Infundibulum © 2022 Pituitary Gland Lobes o The anterior pituitary (adenohypophysis) has two parts: § Pars distalis (anterior lobe) § Pars tuberalis (forms a sheath around the infundibulum). o The posterior pituitary (neurohypophysis) consists of two parts: § Pars nervosa BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Infundibulum Session ID: © 2022 Anterior Pituitary (Adenohypophysis) o Secretes hormones that regulate a wide range of bodily activities, from growth to reproduction. o Anterior pituitary hormones act on other endocrine glands (tropic hormones). o Release of anterior pituitary hormones is stimulated by releasing hormones BIOL202 | Block 2 | Lecture 6 | Endocrine System I and suppressed by inhibiting hormones from the hypothalamus. § Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system. Session ID: © 2022 Hypophyseal Portal System o Superior hypophyseal arteries bring blood into the hypothalamus. o These arteries divide into a capillary network called the primary plexus of the hypophyseal portal system. o From the primary plexus, blood drains into the hypophyseal portal veins that pass down outside the infundibulum. BIOL202 | Block 2 | Lecture 6 | Endocrine System I o In the anterior pituitary, the hypophyseal portal veins divide again and form another capillary network called the secondary plexus of the hypophyseal portal system. o The blood and the products of the anterior pituitary will then drain into the anterior hypophyseal veins. Session ID: © 2022 Hypophyseal Portal System o Specialized neurons called neurosecretory cells synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies. o The hormones diffuse into the primary plexus of the hypophyseal portal system. BIOL202 | Block 2 | Lecture 6 | Endocrine System I Session ID: © 2022 Hypophyseal Portal System o The hypothalamic hormones flow with the blood through the portal veins and into the secondary plexus. o This direct route permits hypothalamic hormones to act immediately on anterior pituitary cells, before the hormones are diluted or destroyed in the general circulation. BIOL202 | Block 2 | Lecture 6 | Endocrine System I Session ID: © 2022 Hypophyseal Portal System o Hormones secreted by the anterior pituitary cells pass into the secondary plexus capillaries, which drain into the anterior hypophyseal veins and out into general circulation. o These hormones that act on other endocrine glands are called tropic hormones. BIOL202 | Block 2 | Lecture 6 | Endocrine System I Session ID: © 2022 Anterior Pituitary (Adenohypophysis) o Has five different cell types that produce seven hormones: 1. Somatotrophs - secrete human growth hormone (hGH) 2. Thyrotrophs - secrete thyroid-stimulating hormone (TSH) 3. Gonadotrophs - secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH) BIOL202 | Block 2 | Lecture 6 | Endocrine System I 4. Lactotrophs – secrete prolactin 5. Corticotrophs - secrete adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH) Session ID: © 2022 Human Growth Hormone (hGH) o Hypothalamic Hormone/s: § Growth hormone releasing hormone (GHRH) § Growth hormone inhibiting hormone (GHIH) AKA somatostatin o Anterior Pituitary Cell Type: § Somatotrophs o Target Cell/Organs: § Liver, skeletal muscle, adipose tissue, cartilage and bone. BIOL202 | Block 2 | Lecture 6 | Endocrine System I o Action: § Target cells synthesize Insulin-like growth factors (IGF). Stimulate lipolysis in adipose tissue so fatty acids can used for ATP production. Increases cell growth & cell division by increasing their uptake of amino acids & synthesis of proteins. Decrease glucose uptake in skeletal muscle and fat, so that it is available to neurons for ATP production in times of glucose scarcity. Session ID: © 2022 Gigantism vs. Acromegaly o Disease due to hyper secretion of growth hormone by the pituitary gland. o If it happens in childhood or adolescence, it is called Gigantism. o If it happens in adulthood, it is called Acromegaly. o Signs and symptoms § Excessive soft tissue growth BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Growth of hand and feet § Increased ring & shoe size § Large tongue § Thickened skin § Enlarged jaw & forehead In Gigantism there is an abnormal increase in length of long bones, the person grows to be very tall. This does not happen in Acromegaly because the epiphyseal growth plates have already closed. Session ID: © 2022 Dwarfism o Hyposecretion of growth hormone o Signs and symptoms § Slow bone growth, slow organ growth, slow growth rate, early closure of epiphyseal plates, proportions normal, intelligence normal, appears younger than age. o Causes BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Variable/Congenital § Tumor § Trauma o Treatment: § Give Human Growth Hormone Session ID: © 2022 Thyroid Stimulating Hormone (TSH) o Hypothalamic hormone/s: § Thyrotropin Releasing Hormone (TRH) o Anterior Pituitary Cell Types: § Thyrotrophs o Target cell/organ: BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Thyroid gland o Action: § Stimulates the synthesis and secretion of T3 and T4 hormones by the thyroid gland. There is no thyrotropin-inhibiting hormone. Session ID: © 2022 Follicle Stimulating Hormone o Hypothalamic hormone/s: § Gonadotropin Releasing Hormone (GnRH) o Anterior Pituitary Cell Types: § Gonadotrophs o Target cell/organ: § Ovaries BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Testes o Action: § Initiates the formation of follicles within the ovary. § Stimulates follicle cells to secrete estrogen. § Stimulates sperm production in testes. Release of GnRH and FSH is suppressed by estrogens in females and by testosterone in males through negative feedback system. There is no gonadotropin-inhibiting hormone. Session ID: © 2022 Luteinizing Hormone (LH) o Hypothalamic hormone/s: § Gonadotropin Releasing Hormone (GnRH) o Anterior Pituitary Cell Types: § Gonadotrophs o Target cell/organ: § Ovaries § Testes BIOL202 | Block 2 | Lecture 6 | Endocrine System I o Action: § Secretion of estrogen § Triggers ovulation § Formation of corpus luteum § Secretion of progesterone § Stimulates interstitial cells of the testes to secrete testosterone. Release of GnRH and LH is suppressed by estrogens in females and by testosterone in males through negative feedback system. There is no gonadotropin-inhibiting hormone. Session ID: © 2022 Prolactin (PRL) o Hypothalamic hormone/s: § Prolactin-releasing hormone (PRH) § Prolactin inhibiting hormone AKA Dopamine o Anterior Pituitary Cell Types: § Lactotrophs o Target cell/organ: § Mammary Gland BIOL202 | Block 2 | Lecture 6 | Endocrine System I o Action: § Initiates and maintains milk production by the mammary glands. § Suckling reduces the level of hypothalamic inhibition (dopamine) and prolactin level rise along with milk production. § By itself, prolactin has only a weak effect. Only after the mammary glands have been primed by estrogens, progesterone, glucocorticoids, human growth hormone, thyroxine and insulin, which exerts permissive effects. The function is not known in males, but its hypersecretion causes erectile dysfunction. In females, hypersecretion causes galactorrhea (inappropriate lactation) and amenorrhea (absence of menstrual cycles). Session ID: © 2022 Adrenocorticotropic Hormone (ACTH) o Hypothalamic hormone/s: § Corticotropin releasing hormone. o Anterior Pituitary Cell Types: § Corticotrophs o Target cell/organ: BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Adrenal cortex o Action: § Stimulates the production of glucocorticoids. Stress-related stimuli, such as low blood glucose or physical trauma, interleukin-1 also stimulate the release of ACTH. Melanocyte-Stimulating Hormone is also stimulated by CRH. The exact role in humans is unknown. Session ID: BIOL202 | Block 2 | Lecture 6 | Endocrine System I © 2022 Session ID: Summary © 2022 Posterior Pituitary (Neurohypophysis) o Does NOT synthesize hormones (stores and releases hormones produced by the hypothalamus. o The cell bodies of the neurosecretory cells are in the hypothalamus and their axons form the hypothalamic- hypophyseal tract. o This tract begins in the hypothalamus and ends near blood capillaries in the posterior pituitary. BIOL202 | Block 2 | Lecture 6 | Endocrine System I o Neurons release two neurotransmitters in the capillary plexus § Antidiuretic hormone (ADH) § Oxytocin o The posterior pituitary receives blood from the inferior hypophyseal artery (a branch of the internal carotid) which drains into the capillary plexus of the infundibular process when then drains into the posterior hypophyseal veins. Session ID: © 2022 Oxytocin o During delivery § Stretching of cervix stimulates release of oxytocin § Oxytocin enhances smooth muscle contraction of uterus o After delivery § Oxytocin stimulates contraction of the uterus and ejection (let- down) of milk from the breasts. BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Nursing a baby after delivery stimulates oxytocin release, promoting uterine contractions and the expulsion of the placenta (Clinical Application). § Suckling & hearing baby’s cry stimulates milk ejection. Session ID: © 2022 Antidiuretic Hormone (ADH) o Antidiuretic hormone (vasopressin) stimulates: § Water reabsorption by the kidneys § Decreased perspiration § Arteriolar constriction o The effect of ADH is to decrease urine volume and conserve body water BIOL202 | Block 2 | Lecture 6 | Endocrine System I § Alters blood volume and blood pressure o ADH is controlled primarily by osmotic pressure of the blood (serum osmolarity). Stimuli include: § Dehydration § Hypovolemia. Session ID: BIOL202 | Block 2 | Lecture 6 | Endocrine System I © 2022 Session ID: Summary