Lecture 18, The Endocrine System Lecturer: Dr. Barjis Room: P313 Phone: (718) 260-5285 E-Mail: ibarjis@citytech.cuny.edu The Endocrine System

Learning Objectives Compare the major chemical classes and general mechanisms of hormones. Describe the location and structure of the pituitary gland, and explain its structural and functional relationships with the hypothalamus. Describe the location and structure of each of the endocrine glands.

Learning Objectives Identify the hormones produced by each of the endocrine glands and specify the functions of those hormones. Describe the functions of the hormones produced by the kidneys, heart, thymus, testes, ovaries and adipose tissue. Explain how hormones interact to produce coordinated physiological responses.

Intercellular Communication Endocrine versus Nervous system Endocrine System Endocrine system regulates long term ongoing metabolic activity The endocrine system uses chemicals messenger called hormones to “communicate”. Hormones alter metabolic activities of tissues A hormone is secreted by a group of specialized cells called gland Hormones are transported by the blood vessels Paracrine communication involves chemical messengers between cells within one tissue Nervous System Nervous system performs short term crisis management The nervous system sends electrical messages to control and coordinate the body Nerve impulse is delivered by the axon of a nerve cell called neuron

Endocrine system Includes all cells and endocrine tissues that produce hormones or paracrine factors Following are important endocrine glands Hypothalamus Pituitary gland Pineal Gland Thyroid gland Parathyroid gland Thymus Adrenal Gland Gonads (testes/ovaries) Pancreatic Islet Heart Kidney Digestive Tract

The Endocrine System

Hormone structure Based on their chemical structure hormones are classified into three general classes (groups) of hormones. 1) Amino acid derivatives hormones e.g. epinephrine Structurally similar to amino acids 2) Peptide hormones e.g. insulin Chains of amino acids 3) Lipid derivatives hormones e.g. eicosanoids and steroid hormones (prostaglandin is an example of a steroid hormone)

A Structural Classification of Hormones

Hormones Transportation Hormones can be Freely circulating Rapidly removed from bloodstream Bound to transport proteins e.g. albumin or globulin

Mechanisms of hormone action Each hormone’s shape is specific and can be recognized by the corresponding target cells The binding sites on the target cells are called hormone receptors. Receptors for peptide hormones, are located on the surface of cell membranes because they can not cross the membrane to enter the cell Thyroid and steroid hormones can cross the membrane and bind to receptors in the cytoplasm or nucleus

G Proteins and Hormone Activity Hormones that can not cross the membrane (e.g. Peptide hormones) bind to the receptor on the surface of the cell Binding of hormones to the receptor activate secondary messenger (in this figure binding of hormone activates G protein, and activated G protein activates adenylcyclase or activate PDE or activates PLC

Hormone Effects on Gene Activity Hormones that can cross the membrane (e.g. steroid hormones) bind to the receptor inside the cell, at the cytoplasm, or they will enter the nucleus and bind to the receptor at the nucleus and initiate transcription)

Control of endocrine activity Hypothalamus regulates the activity of the nervous and endocrine systems Hypothalamus secrets regulatory hormones (releasing hormones and inhibiting hormones) that control the activity of the pituitary gland Releasing/inhibiting hormones secreted by the hypothalamus either stimulate or inhibit activity of pituitary gland

Three Methods of Hypothalamic Control over the Endocrine System

The Pituitary Gland The pituitary gland is called the “master gland” but it is under the control of the hypothalamus. Hypothalamus and pituitary gland control many other endocrine functions. Pituitary Gland releases nine important peptide hormones All nine bind to membrane receptors and use cyclic AMP as a second messenger Pituitary gland is divided into posterior and anterior lobe

The Anatomy and Orientation of the Pituitary Gland

Hormones of the adenohypophysis The anterior lobe (adenohypophysis) Hormones of the adenohypophysis Anterior lobe of pituitary gland produces 7 hormones 1) Thyroid stimulating hormone (TSH) TSH triggers the release of thyroid hormones by the thyroid glands Thyrotropin releasing hormone promotes the release of TSH 2) Adrenocorticotropic hormone (ACTH) ACTH stimulates the release of glucocorticoids by the adrenal gland Corticotrophin releasing hormone causes the secretion of ACTH 3) Follicle stimulating hormone (FSH) FSH stimulates follicle development and estrogen secretion in females and sperm production in males

The anterior lobe (adenohypophysis) 4) Leutinizing hormone (LH) LH causes ovulation and progestin (progesterone) production in females and androgen (testosterone) production in males Gonadotropin releasing hormone (GNRH) promotes the secretion of FSH and LH 5) Prolactin (PH) PH stimulates the development of mammary glands and milk production 6) Growth hormone (GH or somatotropin) GH stimulates cell growth and replication through release of somatomedins or IGF Growth-hormone releasing hormone (GH-RH) Growth-hormone inhibiting hormone (GH-IH) 7) Melanocyte stimulating hormone (MSH) Stimulates melanocytes to produce melanin

The posterior lobe of the pituitary gland (neurohypophysis) The posterior lobe of the pituitary gland secretes two hormones: Antiduretic Hormone and Oxytocin. 1) Antidiuretic hormone (ADH) Decreases the amount of water lost at the kidneys Elevates blood pressure 2) Oxytocin Stimulates contractile cells in mammary glands Stimulates smooth muscle cells in uterus

The thyroid Thyroid gland is located near the thyroid cartilage of the larynx The two lobes of thyroid gland is connected by an isthmus Microscopically it has 2 distinct population of cells: Flicular Cell (produce thyroid hormone) and C cell (produce calcitonin) Thyroid gland release several hormones such as thyroxine (T4) and triiodothyronine (T3) Thyroid hormones (T4 and T3) are transported by to thyroid binding globulins (TBG), and albumin Functions of Thyroid hormones include: Increasing ATP production, when bound to mitochondria. Activating genes that control energy utilization, when bound to receptors Exert a calorigenic effect C cells of thyroid gland produce calcitonin Calcitonin helps to regulate calcium concentration in body fluids

The Thyroid Gland

Parathyroid glands Four parathyroid glands embedded in the posterior surface of the thyroid gland Chief cells produce parathyroid hormone (PTH) in response to lower than normal calcium concentrations Parathyroid hormones plus calcitriol are primary regulators of calcium levels in healthy adults

The Homeostatic Regulation of Calcium Ion Concentrations When calcium levels decrease in the blood, parathyroid glands produce PTH PTH increase blood calcium level by: Releasing stored calcium from the bones Stimulating production of calcitriol at the kidney. Calcitriol increases absorption of calcium by the digestive system Enhance reabsorption of calcium by the kidneys When calcium levels increase in the blood, thyroid glands produce calcitonin. Calcitonin decreases blood calcium level by: Increasing excretion of calcium by the kidneys Increase calcium deposition in the bones Stop osteoclast

The Adrenal Glands Adrenal cortex Manufactures steroid hormones derived from cholesterol (corticosteroids). Corticosterioid hormones are divided into 3 functional groups Mineralocorticoids (Aldosterone) Regulate mineral and salt balance by renin-angiotensis-aldosterone system Glucocorticoids (cortisol and cortisone) Regulate glucose levels i.e. they increase gluconeogenesis and decrease protein synthesis Decrease inflammation response Androgens also called sex hormones

The Adrenal Glands Adrenal medulla Responsible for flight-or-fight response Produces epinephrine and norepinephrine

Pineal gland Contains pinealocytes Synthesize melatonin Suggested functions include inhibiting reproductive function, protecting against damage by free radicals, setting circadian rhythms (biological clock)

The Pancreas The pancreatic islets Clusters of endocrine cells within the pancreas called Islets of Langerhans or pancreatic islets Alpha cells secrete glucagons Glucagon raises blood glucose by increasing the rates of glycogen breakdown and glucose manufacture by the liver Beta cells secrete insulin Insulin lowers blood glucose by increasing the rate of glucose uptake and utilization Delta cells secrete GH-IH F cells secrete pancreatic polypeptide

Diabetes Type I – Insulin dependent diabetes Caused by autoimmune destruction of beta cells Type II – non insulin dependent diabetes Caused by body resisting the effects of insulin at its receptor. Symptoms: Polyuria (inreased frequency of urination), polydipsia (increased thirst)

The Regulation of Blood Glucose Concentrations

The kidneys Produce calcitriol and erythropoietin (EPO) and the enzyme rennin Calcitriol = stimulates calcium and phosphate ion absorption along the digestive tract EPO stimulates red blood cell production by bone marrow Renin converts angiotensinogen to angiotensin I Angiotensin I is converted to angiotensin II at the lungs Agiotensin II: Stimulates production of aldosterone by the adrenal glands Stimulates release of ADH by the pituitary gland Promotes thirst Elevates blood pressure

Endocrine Functions of the Kidneys

Endocrine Functions of the Kidneys

The heart, The intestines and the Thymus Specialized muscle cells produce natriuretic peptides in response to high blood pressure Natriuretic peptide generally has the opposite actions of angiotensin II The Intestine Produce hormones important to the coordination of digestive activities The Thymus Produces thymosins Help develop and maintain normal immune defenses

The gonads Interstitial cells of the testes produce testosterone Most important sex hormone in males In females, oocytes develop in follicles Follicle cells produce estrogens After ovulation, the follicle cells form corpus luteum. Corpus luteum releases a mixture of estrogens and progesterone

Hormones and growth Normal growth requires the interaction of several endocrine organs Six hormones are important GH Thyroid hormones Insulin PTH Calcitriol Reproductive hormones

Adipose tissues secrete Leptin, a feedback control for appetite Resistin, which reduces insulin sensitivity

Hormones and behavior Many hormones affect the CNS Changes in the normal mixture of hormones significantly alters intellectual capabilities, memory, learning and emotional states