Endocrine System Lecture Notes PDF

1  At the end of this chapter, students should be able to :  Define a hormone & state the functions of hormones.  Describe the mode of action of the hormones.  Name the major endocrine glands, their locations, their hormones and their functions. 2  The Endocrine System &...

1  At the end of this chapter, students should be able to :  Define a hormone & state the functions of hormones.  Describe the mode of action of the hormones.  Name the major endocrine glands, their locations, their hormones and their functions. 2  The Endocrine System & Hormone Function - Introduction 3  Definition of hormone........ Hormones = chemical substances, secreted by endocrine cells into the extracellular fluids, & affect the behaviour of other glands or tissues. What is the simple definition of hormones? Hormones are your body's chemical messengers. They travel in your bloodstream to tissues or organs. They work slowly, over time, and affect many different processes. 4  Steroids Peptides Hormones from proteins, glycoproteins & lipids/cholesterol, adrenal modified amino acids. cortex & sex hormones Classification of hormones 5  Mechanisms of Hormone Action - General ▪ Hormone affects only certain tissue cells or organs, referred as target cells / target organs ▪ Target cells must have specific protein receptors (so that hormone can attach) ▪ Hormone binding influences the working of the cells ▪ Effects cause by hormones: i. changes in plasma membrane permeability or electrical state ii. synthesis of proteins/enzymes in the cell iii. activation/inactivation of enzymes iv. stimulation of mitosis 6 7  Direct Gene Activation: The Steroid Hormone Mechanism Steroid Cytoplasm Nucleus hormone Plasma membrane of target 8 cell  Steroid Cytoplasm Nucleus hormone Plasma membrane of target cell 9  Steroid Cytoplasm Nucleus hormone Receptor protein Hormone-receptor complex Plasma membrane of target cell 10  Steroid Cytoplasm Nucleus hormone Receptor protein Hormone-receptor complex DNA Plasma membrane of target cell 11  Steroid Cytoplasm Nucleus hormone Receptor protein Hormone-receptor complex DNA mRNA Plasma membrane of target cell 12  Steroid Cytoplasm Nucleus hormone Receptor protein Hormone-receptor complex DNA mRNA New protein Plasma membrane of target cell 13  Direct Gene Activation: The Steroid Hormone Mechanism 1. Diffuse through the plasma membrane of target cells 2. Enter the nucleus 3. Bind to a specific protein within the nucleus 4. Bind to specific sites on the cell’s DNA 5. Activate genes that result in synthesis of new proteins 14  A Second Messenger System: The Amino Acid-based @ Peptide Hormone Mechanism Nonsteroid Cytoplasm hormone (first messenger) Receptor protein Plasma membrane 15 of target cell  Nonsteroid Cytoplasm hormone (first messenger) Enzyme Receptor protein Plasma membrane of target cell 16  Nonsteroid Cytoplasm hormone (first messenger) Enzyme ATP Second cAMP messenger Receptor protein Plasma membrane of target cell 17  Nonsteroid Cytoplasm hormone (first messenger) Enzyme ATP Second cAMP messenger Receptor protein Effect on cellular function, such as glycogen Plasma breakdown membrane of target cell 18  A Second Messenger System: The Amino Acid-based/Peptide Hormone Mechanism 1) Hormone binds to a membrane receptor ** Hormone does not enter the cell 2) The activated receptor sets off a series of reactions that activates an enzyme 3) The enzymes catalyzes a reaction that produces a second-messenger molecule (cAMP) 4) Oversees additional intracellular changes to promote a specific response 19 Variety of possible second messengers – cGMP & calcium ions  Control of Hormone Release Endocrine gland stimuli Hormonal Neural stimuli stimuli Humoral stimuli 20  Hormonal Stimuli of Endocrine Glands Endocrine glands are activated by other hormones 21  Humoral Stimuli of Endocrine Glands Changing blood levels of certain ions stimulate hormone release 22  Neural Stimuli of Endocrine Glands Nerve impulses stimulate hormone release Most are under control of the sympathetic nervous system Eg: under stress 23 SNS: sympathetic nervous system  The Major Endocrine Organs 24 Location of Major Endocrine Glands/Orga 25  PITUITARY GLAND 26  Pituitary Gland Size of a pea Hangs by a stalk from the hypothalamus Protected by the sphenoid bone Has two functional lobes Anterior pituitary – Posterior pituitary – 27  Posterior Pituitary 28  Hormones of the Posterior Pituitary Antidiuretic hormone Oxytocin (ADH) Stimulates Can inhibit urine contractions of the production; by uterus during labor reabsorb more water Causes milk ejection in from the forming nursing women urine – urine volume decrease & blood volume increase 29  Hormones of the Anterior Pituitary Six anterior pituitary hormones: Two affect non-endocrine targets (GH & prolactin) Four stimulate other endocrine glands (tropic hormones) Characteristics of all anterior pituitary hormones: Proteins (or peptides) / Non-steroid  Act through second-messenger systems  Regulated by hormonal stimuli, mostly negative feedback 30  Hormones of the Anterior Pituitary non-endocrine targets 31  Growth Hormone (GH) / Somatotropic Hormone  2 main functions:  stimulates protein synthesis – in cartilage, bone & muscle.  promotes fat metabolism (break down fat as a source of energy).  The amount of GH produced = affects the individual’s height.  Most GH is secreted during childhood & adolescence:  too little = a person can have pituitary dwarfism  too much = a person can become a giant (giantism) Overproduced of GH in adult = acromegaly 32 33 Prognathism refers to a protruding jaw.  Functions of other Anterior Pituitary Hormones Prolactin (PRL) Stimulates and maintains milk production following childbirth Plays a role in carbohydrate & fat metabolism Adrenocorticotropic hormone (ACTH) Regulates endocrine activity of the adrenal cortex, to produce its hormones Thyroid-stimulating hormone (TSH) Influences growth and activity of the thyroid, to produce thyroid hormones 35  Functions of other Anterior Pituitary Hormones Stimulates follicle development in ovaries Follicle-stimulating hormone (FSH) Stimulates sperm development in testes Gonadotropic hormones Triggers ovulation Luteinizing hormone (LH) Stimulates testosterone production in males 36  THYROID GLAND 37  Thyroid Gland Found at the base of the throat Consists of two lobes and a connecting isthmus Produces two hormones: Thyroid hormone Calcitonin 38  Thyroid Hormone General function: Increase metabolic rate (stimulate all cells to metabolize at a faster rate). Composed of two active iodine-containing hormones: Thyroxine (T4) – contains 4 iodine atoms Triiodothyronine (T3)  contains 3 iodine atoms  have the greatest effect on the body 39  If lack of iodine...... thyroid gland is unable to produce the thyroid hormones lead to “goiters” (enlargement of the thyroid gland due to constant stimulation from anterior pituitary) 40 41  Calcitonin Decreases blood calcium levels by causing its deposition on bone Antagonistic to parathyroid hormone 44  PARATHYROID GLAND 45  Parathyroid Glands Tiny masses on the posterior of the thyroid Secrete parathyroid hormone (PTH): Stimulate osteoclasts to remove calcium from bone Stimulate the kidneys and intestine to absorb more calcium Raise calcium levels in the blood through the action of osteoclasts to break down bones 46  ADRENAL GLAND 47  Adrenal Glands Two glands Cortex – outer glandular region in three layers Medulla – inner neural tissue region Sits on top of the kidneys 48  Hormones of the Adrenal Cortex Mineralocorticoids (mainly aldosterone) – Regulate water & mineral content in blood (esp conc. of Na+ & K+ ions) – When blood levels of aldosterone rise, kidney tubules reabsorb sodium ions and release potassium ions into the urine – Target organ is the kidney 49  Hormones of the Adrenal Cortex Glucocorticoids (including cortisone and cortisol) – Promote normal cell metabolism, by increasing blood glucose levels – “Hyperglycemic hormone” – fat and protein broken down to glucose, which then release to the blood – Control the unpleasant effect of inflammation – Reduce pain by inhibit prostaglandins (pain-causing molecules) 50  Hormones of the Adrenal Cortex Sex hormones – Small amounts are made throughout life – Mostly androgens (male sex hormones) are made but some estrogens (female sex hormones) are also formed 51  Hormones of the Adrenal Medulla Produces two similar hormones (catecholamines) – Epinephrine (adrenaline) – Norepinephrine (noradrenaline) These hormones prepare the body to deal with short-term stress (“fight or flight”) by – Increasing heart rate, blood pressure, blood glucose levels – Dilating small passageways of lungs 52  PANCREAS 53  Pancreatic Islets (islets of Langerhans) The pancreas is a mixed gland and has both endocrine and exocrine functions The pancreatic islets produce hormones – Insulin — allows glucose to cross plasma membranes into cells from beta cells – Glucagon — allows glucose to enter the blood from alpha cells – These hormones are antagonists that maintain blood sugar homeostasis 54 55  Pancreatic Hormones and Blood Sugar 56 Go to fullsize image PINEAL GLAND 57  Pineal Gland / Pineal Body Found on the third ventricle of the brain Secretes melatonin – Helps establish the body’s wake and sleep cycles – Peak levels occurs at night, make us sleepy – The lowest levels occur during daylight 58  Pineal gland 59 Go to fullsize image Go to fullsize image THYMUS GLAND 60  THYMUS GLAND Located in the upper thorax, posterior to the sternum Largest in infants and children (decreases in size throughout adulthood) Produces thymosin Thymus gland – Matures some types of white blood cells – Important in developing the immune system 61  GONADS - OVARIES & TESTES 62  Hormones of the Ovaries Estrogens – Stimulate the development of secondary female characteristics – Mature female reproductive organs With progesterone, estrogens also – Promote breast development – Regulate menstrual cycle Progesterone – Acts with estrogen to bring about the menstrual cycle – Helps in the implantation of an embryo in the uterus – Helps prepare breasts for lactation 63  Hormones of the Testes Produce several androgens Testosterone is the most important androgen – Responsible for adult male secondary sex characteristics – Promotes growth and maturation of male reproductive system – Required for sperm cell production Go to fullsize image 64 HER HORMONE-PRODUCING TISSUES/ORGA ~PLACENTA~ 65  Endocrine Function of the Placenta Produces hormones that maintain the pregnancy Some hormones play a part in the delivery of the baby Produce: – Human chorionic gonadotropin (hCG)- prevent uterus from sloughed off – Human placental lactogen (hPL)- breast lactation – Relaxin – pelvic ligament and pubic symphysis to relax 66 67  THANK YOU 73