Endocrine System PDF

Endocrine System Kristy Cheung [email protected] Learning Outcomes 1. Explain the difference between endocrine and exocrine glands 2. Describe similari8es & differences between endocrine and neural signalling 3. Explain how nega/ve & posi/ve feedback regulate hormone secre/on 4. Explain...

Endocrine System Kristy Cheung [email protected] Learning Outcomes 1. Explain the difference between endocrine and exocrine glands 2. Describe similari8es & differences between endocrine and neural signalling 3. Explain how nega/ve & posi/ve feedback regulate hormone secre/on 4. Explain the rela8onships between the hypothalamus and the pituitary gland 5. Describe the anatomy and histology of the pituitary gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas 6. Describe the func/on of the hormones of the endocrine glands & pancreas Exocrine VS Endocrine Glands Exocrine Glands Endocrine Glands Prefix Exo- : External Duct connects gland to external environment Secretory cells release chemical products onto epithelial surface via the duct Example: Prefix Endo- : Internal No connection to the epithelial layer = “ductless glands” Secrete chemical products (hormones) into surrounding tissue -> blood stream Example: A Endocrine System B A) Hypothalamus B) Pituitary Gland C, D C) Thyroid Gland D) Parathyroid Glands E) Adrenal / Suprarenal Glands F) Pancreas* Other organs with endocrine function that are not discussed in detail in this course: Pineal Gland Thymus Heart Digestive Tract Gonads (Testes / Ovaries) Adipose Tissue Martini, FH, Timmons, MJ, & Tallitsch, RB. (2014) Human Anatomy (8th ed.). Pearson. (Fig. 19.1) E F Clusters or cords of secretory cells Surrounded by support 2ssue Highly vascularized o Fenestrated or sinusoidal capillaries Common goal of maintaining homeostasis à “dynamic stability / equilibrium” Controlled via endocrine reflexes Modulate biochemistry of target cells Regulated by feedback loops Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (”The Endocrine System”; p.10) ✅ Secrete chemical signals, called hormones, that act on cells with compaBble receptors ✅ In ⚠ cr T ea o o s ra e m Col te e d ta bo l ic ⚠ Low Blood Sugar ✅ Breakdown of glycogen In ⚠ D cr e ea h y se dr re ate so d rp tio n Endocrine System Endocrine VS Neural Signaling Endocrine Signalling Neural Signalling Chemical signals (hormones) distributed through cardiovascular system à “wireless” Electrical signalling & chemical synaptic transmission (neurotransmitters) through nervous system à “wired” Speed of Onset Relatively slow (min à hrs) Relatively fast (msec à sec) Effect Duration Typically long-term Typically short-term Slow Fast Widespread / diffuse effects Localized / specific effects Function Mechanism of Action Recovery Location of Effects Hormones - Chemical Structures Amino Acid Derivatives Peptide Hormones Steroid Hormones Structurally similar to amino acids Composed of short chains of amino acids Lipids derived from cholesterol e.g., triiodothyronine/ thyroxine, (nor)epinephrine, melatonin e.g., oxytocin, growth hormone, follicle stimulating hormone e.g., progesterone, cortisol, testosterone, aldosterone Adapted from “Hypothalamic-Pituitary-Adrenal Axis”, by BioRender.com (2021). Retrieved from https://app.biorender.com/biorender-templates Stimulus Endocrine Reflexes Integrating Centre 1 (e.g. gland) Control endocrine activity Hormone 1 Can be triggered by 3 types of stimuli: a) Humoral stimuli o changes in the extracellular fluid composition Integra5ng Centre 2 (e.g. gland) b) Hormonal stimuli o changes in hormonal level(s) Hormone 2 c) Neural stimuli o presence of neurotransmitter at neuroglandular jxn. Target Tissue Response Hypothalamus Stimulus (Humoral/ Hormonal/ Neural) Coordination center Regulate activity of the nervous & endocrine systems via 3 mechanisms: 1. Secret Regulatory Hormones Hypothalamus 2. Function as an endocrine organ 3. Direct neural control over endocrine cells of the adrenal gland Anterior Pituitary (AP) Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.2) Posterior Pituitary (PP) Hypothalamic Control Stimulus (Humoral/ Hormonal/ Neural) 1. Regulatory Hormones Control activity of endocrine cells in the anterior pituitary gland 2 classes of hormones: a) Releasing Hormones – stimulate synthesis & secretion of hormones b) Inhibiting Hormones – prevent synthesis & secretion of hormones Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.2) 1. Hypothalamic Control Stimulus (Humoral/ Hormonal/ Neural) 2. Endocrine Organ Neurons act as secretory cells Release Antidiuretic hormones (ADH) & Oxytocin into circulation at the posterior pituitary gland 2. 1. Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.2) Hypothalamic Control STmulus (Humoral/ Hormonal/ Neural) 3. Direct Neural Control Hypothalamus contain ANS centers = control autonomic output SympatheGc acGvaGon -> suprarenal medulla release hormones into circulaGon 2. 1. 3. Suprarenal Gland Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.2) Pituitary gland (Hypophysis) Hypothalamus ic pt sm O ia Ch Overall Functions: Modulate other endocrine glands (i.e., tropic functions) Acts directly on non-endocrine systems (i.e., non-tropic functions) Infundibulum Anterior Pituitary (AP) (adenohypophysis) Posterior Pituitary (PP) (neurohypophysis/ pars nervosa) Sella Turcica Hypophyseal fossa of sphenoid (“Turkish saddle”) Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.3a) Pituitary gland – Anterior Pituitary (I) Can be subdivided into 3 regions: 1. 2. 3. AP PP Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.3a) Pars distalis Pars intermedia Pars tuberalis Controlled by regulatory hormones from hypothalamus via the hypophyseal portal system Hypophyseal Portal System - AP 2 1 Superior Hypophyseal Artery 2 Primary (1o) Capillary Plexus 3 Hypophyseal Portal Veins 1 3 4 4 5 5 Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.5) o Branch of internal carotid artery o Hypothalamic neurons release regulatory hormones into this plexus o Carries hypothalamic hormones to AP Secondary (2o ) Capillary Plexus o Regulatory hormones modulate AP activity o AP cells release hormones into this plexus Hypophyseal Veins o Drain blood into general circulation via cavernous sinus Pituitary gland – Anterior Pituitary (II) Contain specialized cells that produce & secrete hormone (control by hypothalamic regulatory hormones) 2 types of cells: a) Chromophils o Acidophils: AP PP 1. 2. Prolactin (PRL) Growth Hormones (GH) o Basophils: 1. 2. 3. 4. Adrenocorticotropic hormone (ACTH) Thyroid stimulating hormone (TSH) Follicle stimulating hormone (FSH) Luteinizing hormone (LH) b) Chromophobes Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.3a) Histology – Ant. Pituitary Acidophil Chromophils Basophil AP PP Chromophobe Ross, MH & Pawlina, W. (2011) Histology: A Text and Atlas (6th ed.). Lippincott Williams & Wilkins. (Fig. 21.3a); Anterior Pituitary © Peter Takizawa. Director of Medical Studies @ Yale School of Medicine (http://medcell.med.yale.edu/histology/endocrine_systems_lab.php) Pituitary gland – Anterior Pituitary (III) Hormones: Prolactin (PRL) - lactotropes Growth hormone (GH) - somatotropes Adrenocorticotropic hormone (ACTH) - corticotropes Thyroid stimulating hormone (TSH) - thyrotropes Follicle stimulating hormone (FSH) Luteinizing hormone (LH) Created with BioRender.com gonadotropes Pituitary gland – Posterior Pituitary (I) SON PVN Neurons from paraventricular & supraoptic nuclei of hypothalamus project into PP o Axons travel through infundibulum These neurosecretory cells produce hormones -> travel along the axon -> synaptic terminals of PP AP PP o Supraoptic nucleus (SON) – produce ADH o Paraventricular nucleus (PVN) – produce oxytocin (OXT) Hormones released into PP interstitium & taken up by the capillaries Blood supply - PP SON PVN 1 2 Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig.19.5) 1 Inferior Hypophyseal Artery 2 Hypophyseal Veins o Branch of meningohypophyseal trunk of internal carotid artery o Drain the ADH & Oxytocin from the capillary bed back into general circulation Pituitary gland – Posterior Pituitary (II) Hypothalamic Nuclei: Supraoptic nucleus (SON) Paraventricular nucleus (PVN) Hormones: Antidiuretic hormone (ADH) Oxytocin (OXT) Created with BioRender.com Histology – Posterior Pituitary Herring Body AP PP o Terminal end of axons where hormones are stored Blood Vessel Pituicyte (Glial Cell) Ross, MH & Pawlina, W. (2011) Histology: A Text and Atlas (6th ed.). Lippincott Williams & Wilkins. (Fig. 21.3a); Posterior Pituitary © Peter Takizawa. Director of Medical Studies @ Yale School of Medicine (http://medcell.med.yale.edu/histology/endocrine_systems_lab.php) Thyroid Gland Two-lobed butterfly-shaped gland situated across the ant. surface of the trachea o At the level of 2nd – 3rd cartilage rings o lobes connected by the isthmus o Surrounded by CT capsule Isthmus Highly vascularized – deep red appearance Easily palpable with fingers, especially when enlarged (i.e goitre) Martini, FR, Timmons, MJ, & Tallitsch, RB. (2009) Human Anatomy (6th ed.). Pearson. (Fig. 19.6) Trachea Thyroid Gland - Blood Supply Arterial Supply: 1. External carotid artery 2. Superior thyroid artery 3. Subclavian artery 4. Thyrocervical trunk 5. Inferior thyroid artery Venous Drainage: 6. Internal jugular veins 7. Superior thyroid vein 8. Middle thyroid vein 9. Brachiocephalic vein 10. Inferior thyroid vein Thyroid Gland Enclosed in a fibrous capsule o Send trabeculae deep into the gland -> form irregular lobules Functional unit = spherical thyroid follicle o Lined with simple cuboidal epithelium (*size & shape of cell can change to columnar depending on gland’s activity level) o Cavity filled with colloid (viscous fluid) Follicular cells = thyrocytes 1. Synthesize thyroglobulin (prohormone) 2. Secrete into colloid -> become iodinated 3. Break down to form thyroid hormone a) Thyroxine (T4) b) Triiodothyronine (T3) Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig. 19.6c) Fibrous Capsule Thyroid Follicle Colloid Thyrocytes Parafollicular cell (C Cell) Locate between the thyroid follicles Fxn: Regulate [Ca2+] in body fluid through secreting calcitonin Calcitonin decreases [Ca2+] by: 1. Inhibit osteoclast activity 2. Stimulate Ca2+ excretion at kidneys Fibrous Capsule Thyroid Follicle Colloid Thyrocytes Antagonistic hormone = parathyroid hormone Parafollicular Cell Histology – Thyroid Gland Fibrous Capsule Thyroid Follicle Follicular Cell (Thyrocyte) Colloid Parafollicular Cell (C Cell) Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig. 19.6c) Hypothalamus-Pituitary-Thyroid (HPT) Axis ↑ Metabolic Rate of Target Cells = ↑ Body Low Body Temperature Temperature Thyroid Releasing Hormone (TRH) Hypothalamus (neurosecretory cells) Thyroid Stimulating Hormone (TSH) Anterior Pituitary (basophils à thyrotropic cells) Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig. 19.7b) Thyroid Hormones (T3 & T4) Homeostasis Restored! Thyroid Gland (Follicular cells) Parathyroid Glands (I) 4 pea-sized glands located on posterior aspect of thyroid gland o Surrounded by CT capsule -> invade deep into the interior of gland -> form irregular lobules Blood supply: Superior pair of parathyroid gland o Superior pair – by superior thyroid arteries o Inferior pair – by inferior thyroid arteries ** Venous drainage same as thyroid gland** Two specialized cell types: a) Parathyroid cells (aka. Chief cells/principal cells) o Produce parathyroid hormone (PTH) b) Oxyphil cells o Immature/inactive parathyroid cells Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Figs. 19.8a) Inferior pair of parathyroid gland Parathyroid Glands (II) Control by humoral stimuli = [Ca2+] in circulation ↓ [Ca2+] in blood -> stimulate parathyroid cell to secrete PTH PTH increase [Ca2+] by: a) stimulate osteoclasts & osteoblast activity b) reduce urinary excretion of Ca2+ c) stimulate production of calcitriol (kidney hormone – promote intestinal absorption of Ca2+) Histology – Parathyroid Glands Parathyroid cells Oxyphil cell Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Figs. 19.8b,c) Pu*ng it all together! High [Ca2+] Calcitonin ↑ Ca2+ release from bone & ↑ Ca2+ retention in kidney = ↑ [Ca2+] Parathyroid Hormone (PTH) ↑ Ca2+ deposition in bone & ↑ Ca2+ excretion in urine = ↓ [Ca2+] Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Figs. 19.8a, 25.14, & 26.3a) Low [Ca2+] Adrenal (Suprarenal) Glands Pyramid-shaped paired glands o One the superior pole of each kidney (retroperitoneal) o Surrounding by CT capsule o Highly vascularized 1 Arterial Supply: o Superior (1) & Middle adrenal arteries (2) – from abdominal aorta o Inferior adrenal arteries (3) – from renal a. 3 Structurally & functionally divided into 2 regions: a) Adrenal Cortex (Superficial) – adrenocortical steroid hormones b) Adrenal Medulla (Deep) - catecholamines Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Figs. 19.9a & b) 2 Adrenal Cortex Three-layered structure o Composed of cells with high lipid content o Cells synthesize and secrete 24 types of steroid hormones > “adrenocortical steroids” 1. Zona Glomerulosa (A) A o Cells arranged in densely packed clusters called ‘glomeruli’ (= little knots) o Produce mineralocorticoids (e.g. aldosterone) 2. Zona Fasciculata (B) B o Cells arranged in radiating cords & separated by fenestrated capillaries o Produce glucocorticoids (e.g. cortisol, corticosterone) 3. Zona Reticularis (C) o Small cells arranged in ‘reticular’ network o Produce androgens (e.g. testosterone) Histology Guide MHS 216 C Adrenal Medulla Primarily composed of chromaffin cells o Cells – large & rounded cells resemble neuron of sympathetic ganglia (= modified postganglionic sympathetic neuron) Innervated by sympathetic preganglionic neurons -> splenic nerve -> target cells Two types of endocrine cells that secrete catecholamines: o Epinephrine/ adrenaline ( ~80%) o Norepinephrine/ nor adrenaline ( ~20%) Fxn: Triggers utilization of cellular energy o Increase muscle strength & endurance Ross, MH & Pawlina, W. (2011) Histology: A Text and Atlas (6th ed.). Lippincott Williams & Wilkins. (Plate 85: Adrenal Gland II) Hypothalamus-Pituitary-Adrenal (HPA) Axis Stress Stress Response Cortisol CorTcotropin Releasing Hormone (CRH) Hypothalamus (neurosecretory cells) Adrenocorticotropic Hormone (ACTH) Anterior Pituitary (basophils à corticotropic cells) Adapted from Mar-ni, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Figs. 19.7b & 19.9b) Adrenal Cortex (Zona fasciculata cells) Endocrine Pancreas Retroperitoneal accessory digestive organ 2. 1. McKinley, M & O’Loughlin, VD. (2008) Human Anatomy (2nd ed.). McGraw-Hill. (Fig. 20.14) 1. Head, 2. body, & 3. tail Blood supply from pancreatic branches of splenic artery & pancreaticoduodenal arteries “Mixed” gland 3. Acini / ducts à exocrine (~99%) Pancreatic islets à endocrine Pancreatic islets (Islet of Langerhans) Surrounded by connective tissue Fenestrated capillaries Autonomic nervous system input (celiac plexus) Pancreatic Islet 1. Alpha cells Glucagon – increase glycogen breakdown 2. Beta cells 3. 4. Insulin – increase glucose uptake 3. Delta cells SomatostaTn – inhibit alpha & beta cell producTon 4. F cells 1. 2. Cell types cannot be distinguished with H&E staining Adapted from Martini, FR, Timmons, MJ, & Tallitsch, RB. (2012) Human Anatomy (7th ed.). Pearson. (Fig. 19.10b) PancreaTc polypepTde – inhibit gall bladder contracTon, regulate pancreaTc enzyme producTon Alpha & beta cells respond to blood glucose conc. High [glucose] à ? Low [glucose] à ? Glycogen Glucose ↑ [Blood Glucose] High [Blood Glucose] Glucagon Pancreas (beta cells) Insulin Low [Blood Glucose] Pancreas (alpha cells) ↑ [Blood Glucose] Glycogen Glucose + stimulates glucose uptake from food Created with BioRender.com Learning Summary 1. Explain the difference between endocrine and exocrine glands 2. Describe similarities & differences between endocrine and neural signalling 3. Explain how negative & positive feedback regulate hormone secretion 4. Explain the relationships between the hypothalamus and the pituitary gland 5. Describe the anatomy and histology of the pituitary gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas 6. Describe the function of the hormones of the endocrine glands & pancreas