Endocrinology Overview Lecture Notes PDF

Endocrinology overview Unit: AGEP Endocrinology Unit code: VETS10018 Dr Nobue Itasaki Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced...

Endocrinology overview Unit: AGEP Endocrinology Unit code: VETS10018 Dr Nobue Itasaki Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Overview of lecture We will: Recap the endocrine system from our foundation lecture ‘Basic tissues of the body and body organisation’. Then we will give an overview of each main endocrine gland: Pituitary gland Pineal gland Thyroid gland – tomorrows lecture Parathyroid gland – tomorrows lecture Adrenal gland – next lecture Pancreas – next lecture  What is Endocrine? Endocrine: Glands secrete hormones into the blood stream (to the systemic circulation) Autocrine, Endocrine vs Exocrine paracrine vs Example: Endocrine Endocrine cells in the pancreas secrete hormones (insulin and glucagon) into blood vessels Exocrine cells in the pancreas secrete pancreatic enzymes into the pancreatic duct Pancreatic which leads to the GI duct tract  Other ancillary organs The main organs of the endocrine system involved in endocrine system: Brain, liver, thymus, heart and GIT Adrenal glands - Paired & located close to kidneys. Pituitary gland - Consisting of the cortex and - Appendage of the brain. medulla Kidney - Produces several - Cortex produces - produce renin, erythropoietin etc hormones directly mineralocorticoids, glucocorticoids influencing other & sex steroids. Ovary endocrine glands (FSH, LH, - The medulla produces adrenaline - Produce the sex ACTH, TSH, prolactin, STH and noradrenaline hormones oestrogen (GH)). and progesterone. Parathyroid gland Testis - Usually 4 glands near thyroid. - Produce the sex - Secrete parathyroid hormone hormones oestrogen - Regulates calcium metabolism. and testosterone. Thyroid gland - Located over trachea Pancreas - Produces hormones. - Produces insulin and concerned with glucagon. Also secretes metabolism and growth digestive enzymes by T4 & T3 and calcitonin exocrine Endocrine system The endocrine glands secrete hormones into the blood, lymph or tissue fluid to the target organ(s). What can regulate the secretion of hormones? Nerve stimulation Another hormone (often called ‘releasing- or stimulating-hormone) Levels of certain chemicals in the blood Feedback loops Functions of the endocrine system: Homeostasis Growth and maturation Reproduction Adaption to stress and infection Behaviour Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Important concepts Systemic regulation of cells can occur in two ways: Endocrine system Nervous system The endocrine system communicates with cells by chemical messengers, hormones. Hormones circulate in the blood and diffuse through interstitial tissues. Only cells with the receptor for the hormone are influenced by it. The actions of hormones tend to be slower in taking effect but have a longer duration than the nervous system. Endocrine glands Each endocrine gland secretes specific hormones The endocrine system works with the nervous system to regulate and coordinate activities for nearly all other body structures. The processes regulated by the endocrine system can be broadly divided into: 1. Food intake, digestion 2. Metabolism (storage and utilisation of nutrients) 3. Growth and development 4. Electrolyte and fluid balance 5. Reproduction Endocrine organs There are three types of endocrine organs: 1. Organs of a primary endocrine nature e.g. hypophysis (pituitary gland), epiphysis (pineal gland), thyroid, parathyroid, and adrenal glands. 2. Organs that combine endocrine functions with other important functions e.g. pancreas, tests, ovaries, and placenta. 3. Organs with endocrine components but a different primary function e.g. brain, kidneys, liver, thymus, heart, and GIT.  Other ancillary organs The main organs of the endocrine system involved in endocrine system: Brain (e.g. pineal body), liver, thymus, Adrenal glands - Paired & located close to kidneys. heart and GIT Pituitary gland - Consisting of the cortex and - Appendage of the brain. medulla Kidney - Produces several - Cortex produces - produce renin, erythropoietin etc hormones directly mineralocorticoids, glucocorticoids influencing other & sex steroids. Ovary endocrine glands (FSH, LH, - The medulla produces adrenaline - Produce the sex ACTH, TSH, prolactin, STH and noradrenaline hormones oestrogen (GH)). and progesterone. Parathyroid gland Testis - Usually 4 glands near thyroid. - Produce the sex - Secrete parathyroid hormone hormones oestrogen - Regulates calcium metabolism. and testosterone. Thyroid gland - Located over trachea Pancreas - Produces hormones. - Produces insulin and concerned with glucagon. Also secretes metabolism and growth digestive enzymes by T4 & T3 and calcitonin exocrine Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Pituitary gland The pituitary gland (Hypophysis) Described as the master gland because produces hormones that directly influence the activities of other endocrine glands. The pituitary gland is an appendage of the brain suspended below the hypothalamus. The pituitary and the hypothalamus are two important structures for integrating the endocrine and nervous systems. The hypothalamus regulates the secretory activity of the pituitary gland in response to hormones, sensory information, and emotions. The Hypophysis (pituitary gland) The pituitary gland is divided into two lobes: anterior lobe and posterior lobe. 1. Anterior lobe (Adenohypophysis) Arised from the roof of the mouth epithelium. Is a major endocrine gland that produces several hormones. Secretes FSH, LH, ACTH, TSH, prolactin, STH (GH) The secretion of hormones is controlled by neurohormones produced in the hypothalamus. (e.g., Gonadotropin-releasing hormone (GnRH) for FSH and LH) Neurohormones are released by neurons in the hypothalamus. These neurons are called neuroendocrine cells.  The Hypophysis (pituitary gland) The pituitary gland is divided into two lobes: anterior lobe and posterior lobe. 2. Posterior lobe (Neurohypophysis) Formed as a down-growth of the hypothalamus. Hormones are synthesised in the hypothalamus and transported via the axon that reaches the posterior lobe of the pituitary gland where they are secreted from the nerve terminals Oxytocin and vasopressin (a.k.a. antidiuretic hormone,ADH) The adenohypophysis includes a thin band of tissue called the pars intermedia at its border with the neurohypophysis. cause the neurohypophysis is part of the nervous system, its hormones are called neurohormones or neuro Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Adenohypophysis (anterior pituitary gland) The adenohypophysis produces six hormones: Somatotropic hormone (STH) or growth hormone (GH) Follicle-stimulating hormone (a Gonadotropic hormone) (FSH) Luteinising hormone (a Gonadotropic hormone) (LH) Adrenocorticotropic hormone (ACTH) Thyroid-stimulating hormone (TSH) Prolactin All are peptide hormone Major Hypothalamic hormones acting on anterior pituitary Hormone Effect of anterior Chemical structure pituitary Corticotropin releasing Causes release of ACTH Peptide hormone (CRH) Thyrotropin releasing Stimulates secretion of TSH Peptide hormone (TRH) and prolactin Growth hormone releasing Causes release of growth Peptide hormone (GHRH) hormone Somatostatin or Growth Inhibits the release of Peptide hormone inhibitory hormone growth hormone (GHIH) Gonadotropin releasing Causes release of LH and Peptide hormone (GnRH) FSH Prolactin releasing Causes release of prolactin? ? hormone? Dopamine or Prolactin Inhibits(GH) Growth hormone release of prolactin is aka Amine Somatotropin (STH) and is secreted by  FSH = follicle-stimulating hormone LH = Luteinising hormone Anterior Pituitary Hormones ACTH = Adrenocorticotropic hormone TSH = Thyroid stimulating hormone GH = growth hormone (or somatotrophin Hypothalamus, pituitary, target organ axis The hypothalamus orders the pituitary glands to secrete required hormones by secreting ‘releasing hormone’ The anterior pituitary gland receives the signal and secretes relevant hormones At the same time, sends signals to the hypothalamus to suppress further secretion of the releasing hormone The relevant organs receive the hormone and exert the function. At the same time, sends signals to the pituitary gland and hypothalamus to suppress further secretion of the hormone e.g. Hypothalamic-pituitary-adrenal The brain detects the shortage of the organ axis function Hypothalamic-pituitary-thyroid axis and orders the hypothalamus to secrete ‘releasing Hypothalamus, pituitary, ovarian axis Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Neurohypophysis (posterior pituitary gland) The posterior pituitary is simply a storage location for two neurohormones: Anti-diuretic hormone (vasopressin) – promotes fluid reabsorption by the kidneys; stimulates vasoconstriction Oxytocin – stimulates contraction of the uterus and myoepithelial cells of the udder. The neurohormones released by the posterior pituitary are produced in the hypothalamus. Action potentials in the posterior pituitary cause release of the neurohormones into the blood. Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Origin and hypothalamic regulation of the pituitary glands The anterior pituitary arises from the roof of the mouth epithelium as a gland. The posterior pituitary is an extended structure of the hypothalamus The hypothalamus regulates the anterior pituitary through specialised blood vessels (portal system). The hypothalamus regulates the posterior pituitary through nerve impulses https://www.britannica.com/science/hypothalamus Learning Outcomes Describe what a hormone is and the main classifications of hormones in the body. Describe the location and division of the pituitary gland. Describe and explain the main hormones produced by the anterior pituitary and their associated target organs. Describe and explain the main hormones produced by the posterior pituitary and their associated target organs. Contrast the structure and functions of the anterior and posterior pituitary. Briefly describe the structure and function of the pineal gland, thyroid gland, parathyroid gland, adrenal gland, and pancreas. Pineal gland  Don’t confuse melatonin with melanin, melanin is a pigm Pineal gland (epiphysis) The pineal gland is attached by a stalk to the dorsal wall of the third ventricle, at the dorsal side of the thalamus. The pineal gland produces melatonin at night. Melatonin is important for seasonal hormonal fluctuations (biological rhythms) and sleep. Try search on: melatonin implants and sheep breeding Thyroid gland Thyroid gland Thyroid hormones: Triiodothyronine (T3): The active form Thyroxine (T4): The inactive form, converted in the body to T3 Calcitonin The thyroid gland functions for: Growth Metabolism Store iodine Dyce et al.. Textbook of veterinary anatomy Fig. 6.4 Thyroid gland The thyroid gland lies on the trachea directly behind and sometimes overlapping the larynx. The gross anatomy of the thyroid varies greatly between species. In the dog and cat the thyroid has separate masses occasionally connected by an isthmus. In the horse, paired lobes are connected by a small isthmus. In the cow, the lobes are connected by a wide isthmus. Regulation of thyroid hormone Thyrotropin-releasing hormone (TRH) is secreted from the hypothalamus. TRH stimulates the anterior pituitary gland to release thyroid-stimulating hormone (TSH) TSH stimulates the synthesis and secretion of T3 and T4. Excess T3 and T4 suppress the secretion of TSH and TRH  Acinus (pl. acini):a small sac-like cavity in glands formed by secretory Thyroid gland cells. The thyroid gland contains numerous acini whose walls are composed of simple cuboidal epithelial cells. These thyroid follicles contain a gelatinous material composed of the protein thyroglobulin. Thyroglobulin is synthesised and secreted by the epithelial cells lining the follicles. Young et al. Wheater's Functional Histology 6th Ed. Elsevier Thyroglobulin is the precursor to the thyroid hormones. Parathyroid glands The parathyroid hormone (PTH) The parathyroid hormone, PTH, regulates calcium metabolism: In the gut – Increase absorption In bones – Release calcium to blood In the kidney – Suppress calcium release in urine; activate vitamin D => increase the blood calcium level The production of PTH is mainly regulated by the calcium concentration in the plasma. The parathyroid glands The parathyroid glands are located close to or embedded within the thyroid gland. There are usually four parathyroid glands (two on each side). In the dog, cat, and small ruminants, the parathyroid glands generally become recessed or embedded within the thyroid gland. The parathyroid glands are a pale colour compared to the thyroid gland. https://animalendocrine.blogspot.com/ 2012/10/surgical-thyroidectomy-in-cats- Adrenal glands Adrenal glands The paired adrenal glands lie against the roof of the abdomen by the thoracolumbar region. The glands are retroperitoneal, meaning they lie dorsal side of the peritoneum They are located craniomedially to the corresponding kidney. https://veteriankey.com/post-mortem-examination-of-rabb  Adrenal glands The interior of the adrenals glands is divided into outer cortex and inner medulla. The cortex is yellowish and striated. The medulla is much darker in colour. Young et al. Wheater's Functional Histology 6th Ed. Elsevier Cortex Medulla produces; produces; Mineralocorticoi Norepinephrine ds (noradrenaline) Glucocorticoids Epinephrine (adrenaline) Sex steroids Pancreas Pancreas The pancreas has both exocrine and endocrine components. The exocrine component produces digestive juice, which is discharged into the duodenum via one or two Young et al. Wheater's Functional Histology 6th Ed. Elsevier ducts. The juice contains enzymes which break down proteins, carbohydrates and fats. The endocrine portion consists of islets that are the source of insulin, glucagon, and somatostatin + gastrin. Glucagon alpha cell Insulin beta cell Somatostatin, gastrin delta cell  Where was the pancreas in the rabbits you dissecte Pancreas Generally, the pancreas sits between the stomach and the duodenum. Evans and de Lahunta (2010), Guide to the Dissection of the Dog. 7th Edition. Missouri: Elsevier. Page 149.  (slide 4) What is Endocrine? Endocrine: Glands secrete hormones into the blood stream (to the systemic circulation) Autocrine, Endocrine vs Exocrine paracrine vs Example: Endocrine Endocrine cells in the pancreas secrete hormones (insulin and glucagon) into blood vessels Exocrine cells in the pancreas secrete pancreatic enzymes into the pancreatic duct Pancreatic which leads to the GI duct tract How hormones can transfer info to target cells Paracrine Autocrine Endocrine Neuroendocrine cell Neuron(e.g. in the hypothalamus) For your reference only Based on the chemical Hormone classification structure and solubility, hormones can be divided into different classes. Hormones Lipid soluble Water soluble Solubility - Able to diffuse through cell - Unable to diffuse through cell membrane membrane Steroid Fatty Amino acid derivatives Peptide hormone acid (primarily tyrosine) protein Chemic s derivativ hormones al es Thyroid Catecholamines structur hormone (e.g. norepinephrine, e s epinephrine, dopamine) Formed Formed from from cholesterol eicosanoid s Four main groups: Adrenal 1. Prostaglandi Thyroid Adrenal Pituitary gland (all cortex, sex ns gland medull hormones produced by glands and 2. Prostacyclins a pituitary are peptide) References Sjaastad et al (2016). Physiology of domestic animals. (3rd ed.). Oslo, Norway: Scandinavian Veterinary Press. Guyton & Hall (2006). Textbook of medical physiology (11th ed.). Philadelphia: Saunders/Elsevier. Klein (2019) Cunningham’s textbook of veterinary physiology (6th ed.). St Louis, Missouri: Saunders/Elsevier. VanPutte, Regan & Russo (2017) Seeley’s anatomy and physiology (11th ed.). New York, NY: McGraw-Hill Education. Evans and de Lahunta (2010), Guide to the Dissection of the Dog. 7th Edition. Missouri: Elsevier. Page 149. Origin and hypothalamic regulation of the pituitary glands The anterior pituitary arises from the roof of the mouth epithelium as a gland. The posterior pituitary is an extended structure of the hypothalamus The hypothalamus regulates the anterior pituitary through specialised blood vessels (portal system). The hypothalamus regulates the posterior pituitary through nerve impulses https://teachmeanatomy.info/ neuroanatomy/structures/pituitary-