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ENDOCRINE SYSTEMMunirah binti Shaban

Department of Basic Health Sciences Kulliyyah of Allied Health Sciences International Islamic University MalaysiaEmail: munirahshaban@gmail.comExt: 264403 January 2010, Wednesday, AHS 1023Introduction to the endocrine system Comparison of the endocrine and nervous systemsComparison of exocrine and endocrine glandsOBJECTIVES

At the end of the session, the student should be able to understand and define:OBJECTIVES

At the end of the session, the student should be able to understand and define:Endocrine glandsPituitary glandPineal glandThyroid glandParathyroid glandsAdrenal glandsPancreas (islets of Langerhans)Gonads (testes and ovaries)Other endocrine glandsIn the slides that follow, we shall examine the endocrine system that controls the human body for the benefit of the human being and that is a manifestation of the wonder of creation, and we shall witness together the creative art of Allah SWT.Introduction to the endocrine system: Comparison of the endocrine and nervous systemsTogether, the nervous and endocrine systems coordinate the functions of all body systems. How does the nervous system achieve this? through the use of nerve impulses and the secretion of neurotransmitter substances that either excite or inhibit the effectors. Introduction to the endocrine system: Comparison of the endocrine and nervous systemsTogether, the nervous and endocrine systems coordinate the functions of all body systems. How does the endocrine system achieve this control? The endocrine system, in contrast, regulates body functions by releasing chemical messengers called hormones (to urge on or to set in motion) into the bloodstream for delivery throughout the body.Introduction to the endocrine system: Comparison of the endocrine and nervous systemsTogether, the nervous and endocrine systems coordinate the functions of all body systems. Compare the types of effectors the two systems utilize to maintain homeostasis.The nervous system causes muscles to contract and glands to secrete. The endocrine system regulates metabolic activities, growth and development, and reproduction.Introduction to the endocrine system: Comparison of the endocrine and nervous systemsTogether, the nervous and endocrine systems coordinate the functions of all body systems. Compare the time frame the two systems need to accomplish their actions.The nervous system tends to act in milliseconds. The endocrine system acts in seconds, minutes, hours, weeks, months, even years, depending upon the hormone.Introduction to the endocrine system: Comparison of the endocrine and nervous systemsTogether, the nervous and endocrine systems coordinate the functions of all body systems. Compare how long the effects of the two systems persist.Nervous effects are brief; Endocrine effects are much longer lasting.Introduction to the endocrine system: Comparison of the endocrine and nervous systems

the study of the interactions between the nervous system and the endocrine systemNeuroendocrinology Introduction to the endocrine system: Comparison of exocrine and endocrine glandsExocrine glands Have ducts (wired) secrete their products into ducts or directly onto epithelial surfacesE.g. sweat gland

Endocrine glands ductless (wireless) secrete the products called hormones, into the extracellular fluid around the secretory cells. The secretion then diffuses into the blood for distribution throughout the body.E.g. thyroid glandIntroduction to the endocrine system: Which organs are endocrine only?There are a number of specific organs whose sole function is endocrine:

Pituitary glandThyroid glandParathyroid glands (4)Adrenal glands (2)Pineal glandThymus glandIntroduction to the endocrine system: Name other organs that have some endocrine functionPancreas Gonads TestesOvaryStomach Small intestineKidneys Heart Liver SkinPlacentaUterusstriated muscleadipose tissue

chemicals secreted by the endocrine system that diffuses from the interstitial fluid into the bloodstream and eventually act on target cellsHormonesEndocrine glandsIntroduction to the endocrine system: HORMONES: I. HORMONE RECEPTORSWhat is an endocrine target cell?Although a given hormone travels throughout the body in the blood and is seen by all cells of the body, it only affects specific cells called target cells.Like neurotransmitters, hormones influence their target cells by chemically combining to protein receptors on the target cell surface.Only target cells for a particular hormone bear receptors for that hormone, bind to it, and respond to it.Receptors, like other cellular proteins, are constantly synthesized and broken down as part of routine cellular maintenance.Introduction to the endocrine system: HORMONES: I. HORMONE RECEPTORSWhat is down-regulation of a target cells hormone receptors?Down-regulation occurs when the hormone is present in excess and the cell reduces the number of available receptors for it. This causes a decrease in cellular responsiveness to the hormone.What is up-regulation of a target cells hormone receptors?Up-regulation occurs when the hormone is present in less than normal amounts and the cell increases the number of available receptors for it. This causes an increase in cellular responsiveness to the hormone.Introduction to the endocrine system: HORMONES: II. CIRCULATING AND LOCAL HORMONESCirculating hormones Hormones that pass into the blood and act on distant target cells are called circulating hormones or endocrines.Local hormones Hormones that act on target cells close to their site of release are called local hormones. They are further subdivided into either paracrine or autocrine.Paracrine hormones Paracrines are local hormones that act on neighboring cells.Autocrine hormonesAutocrines are local hormones that act on the same cell that secreted them.Define each of the following

Endocrine Glands: HYPOTHALAMUS AND PITUITARY GLAND (HYPOPHYSIS)What is the role of the hypothalamus in endocrine control?The hypothalamus serves as the master control for many of the hormones secreted by the endocrine system, and serves as the major integrator between the nervous and endocrine systems. In particular, the hypothalamus controls the secretions of the pituitary gland, also known as the hypophysis (in Greek).What is the anatomical relationship between the pituitary gland and the hypothalamus?The pituitary gland is a pea-sized organ lying within the sella turcica of the sphenoid bone. It is suspended from the base of the hypothalamus by the infundibulum, a stalk-like structure.

HYPOTHALAMIC HORMONESEndocrine Glands: PITUITARY GLAND (HYPOPHYSIS)Describe the pituitary gland by describing its embryologic formation.

The pituitary gland has two anatomically and functionally distinct portions due to its embryological formation.The anterior pituitary gland (adenohypophysis) (about 75% of the total gland) is derived from an outpouching of the roof of the developing mouth, called Rathkes pouch.Rathkes pouch breaks off from the mouth and migrates as a unit to make contact with the forming posterior pituitary gland associated with the hypothalamus.Endocrine Glands: PITUITARY GLAND (HYPOPHYSIS)Describe the pituitary gland by describing its embryologic formation.

The posterior pituitary gland (neurohypophysis) forms as an outgrowth of the base of the hypothalamus and remains attached to it via the infundibulum.The posterior pituitary gland contains axons and axon terminals of about 5,000 neurons whose cell bodies are located in nuclei in the hypothalamus.The nerve fibers that terminate in the posterior pituitary gland are associated with neuroglial-like support cells called pituicytes, which are secretory.Regardless of origin, both the anterior and posterior pituitary glands are wholly dependent upon the hypothalamus for regulation of hormonal secretion.24Endocrine Glands: Anterior pituitary gland (adenohypophysis)What is adeno?

glandular

many cell types

many hormones***Hypophysis is the master gland of the endocrine system; located at the base of the brain.25Endocrine Glands: Anterior pituitary gland (adenohypophysis)Name the seven hormones secreted by the anterior pituitary gland.growth hormone (GH)/somatotropinthyroid-stimulating hormone (TSH)/thyrotropinfollicle-stimulating hormone (FSH)luteinizing hormone (LH)/lutropinprolactin (PRL)adrenocorticotropic hormone (ACTH)/corticotropinmelanocyte-stimulating hormone (MSH)26Endocrine Glands: Anterior pituitary gland (adenohypophysis)Tropic hormones (tropins) are those hormones that influence other endocrine glands to secrete their hormone (s).

Name them.FSHLHTSHACTHHormones that act on body tissues (non-tropic hormones)Growth hormone (GH)Prolactin hormone (PRL)27

Endocrine Glands: Posterior pituitary gland (neurohypophysis)Describe the posterior pituitary gland and the way it is controlled by the hypothalamus.The posterior pituitary gland (neurohypophysis), in a strict sense, is not an endocrine organ at all since the hormones released from the gland are actually synthesized by neurons in the hypothalamus.In the axon terminals of the neurons that pass down the infundibulum and terminate among the pituicytes are synaptic vesicles filled with one of two hormones: oxytocin and antidiuretic hormone (ADH)/vasopressin.29Endocrine Glands: Posterior pituitary gland (neurohypophysis)Describe the posterior pituitary gland and the way it is controlled by the hypothalamus.An action potential in one of these neurons causes the release of the hormone into the extracellular fluid of the posterior pituitary, where it will diffuse into the blood for distribution throughout the body.These axons passing from the hypothalamus are collected together as the hypothalamo-hypophyseal tract.30OXYTOCINWhat are the functions of oxytocin?Oxytocin stimulates the contraction of uterine smooth muscle during delivery of the baby and placenta. After birth, oxytocin stimulates contraction of the myoepithelial cells of the mammary glands, causing milk ejection (letdown) from the breast.How is oxytocin secretion controlled?What is the role of oxytocin in males and nonpregnant females?31ANTIDIURETIC HORMONE (ADH)What is an antidiuretic?An antidiuretic is any chemical substance that prevents excessive urine formation.

What are the functions of ADH?The principal effect of ADH is to cause the kidneys to remove water from the forming urine and return it to the blood, thus conserving it. ADH also causes decreased perspiration and vasoconstriction of blood vessels. All efforts of ADH are related to maintaining normal blood pressure.32ANTIDIURETIC HORMONE (ADH)How is ADH secretion controlled?What is diabetes insipidus?33

Pituitary gland

Endocrine Glands: PINEAL GLANDLocated at the posterior EPITHALAMUSSecreted hormone:MelatoninAntioxidant effectBiology clock Dimethyltryptamine(speculated role) mystical and dream experiences

Thyroid cartilageEndocrine Glands: THYROID GLANDEndocrine Glands: THYROID GLANDDescribe the thyroid gland.

The thyroid gland is located just below the larynx in the anterior neck, consisting of a right and left lateral lobe, and a central portion called the isthmus. The gland itself consists of microscopic spherical sacs or follicles formed by the follicular cells.Endocrine Glands: THYROID GLANDName the hormones secreted by the follicular cells.

Follicular cells secrete two hormones that are closely related in coordinating basal metabolic rate: triiodothyronine (T3), with three iodine atoms, and tetraiodothyronine (T4 or thyroxine), with four iodine atomsEndocrine Glands: THYROID GLANDWhat are parafollicular cells?

The second major cell population of the thyroid gland.Between the follicles, lying in small nests, are the parafollicular (C) cells that secrete the hormone calcitonin. Calcitonin works antagonistically with parathyroid hormone (PTH) to maintain normal blood calcium levels.Endocrine Glands: THYROID GLANDDescribe the role of calcitonin in calcium homeostasis.

The C-cells have receptors that monitor extracellular fluid calcium concentration. They are stimulated to secrete calcitonin when hyperglycemia occurs.Calcitonin works to decrease serum calcium by:inhibiting osteoclastsstimulating osteogenesisdecreasing calcium reabsorption by the kidneys

Endocrine Glands: THYROID GLAND

Endocrine Glands: PARATHYROID GLANDSEndocrine Glands: PARATHYROID GLANDSDescribe the parathyroid glands and the role of parathyroid hormone (PTH) in calcium homeostasis.

There are four parathyroid glands embedded into the posterior surface of the thyroid gland.The glands consist of two cell types: chief cells that secrete parathyroid hormone (PTH) oxyphil cells function unknownEndocrine Glands: PARATHYROID GLANDSDescribe the parathyroid glands and the role of parathyroid hormone (PTH) in calcium homeostasis.

PTH works antagonistically with calcitonin to regulate the blood concentration of calcium and is secreted by chief cells under conditions of hypocalcemia.PTH works to increase blood calcium levels by:activating osteoclastsincreasing calcium reabsorption by the kidneysincreasing calcium absorption by the gutstimulating secretion of vitamin D

Endocrine Glands: THYMUS GLANDlocated above the heartshrinks with agesecretes thymosinspromotes development of certain lymphocytesimportant in role of immunity

Endocrine Glands: ADRENAL GLANDS

Endocrine Glands: ADRENAL GLANDSDescribe the adrenal glands.The paired adrenal (suprarenal) glands, each lying just superior to each kidney, are structurally and functionally divided into two separate glands: the adrenal cortex and the adrenal medulla.

What are steroids?All hormones secreted by the adrenal cortex are called steroid hormones, lipid molecules whose chemical structure is derived from cholesterol.

Endocrine Glands: ADRENAL GLANDS: I. MEDULLADescribe the adrenal medulla and its hormones.

The adrenal medulla, the inner portion of the gland, consists of chromaffin cells that secrete the catecholamines epinephrine and norepinephrine.These cells receive direct innervation from sympathetic preganglionic neurons. In response, they secrete these catecholamines and add to the fight-or-flight response.Endocrine Glands: ADRENAL GLANDS: I. MEDULLA

Endocrine Glands: ADRENAL GLANDS: II. CORTEXThe adrenal cortex is subdivided into three zones, each of which has a different cellular arrangement and secretes a different class of steroids.MineralocorticoidsGlucocorticoidsGonadocorticoidsEndocrine Glands: ADRENAL GLANDS: II. CORTEXWhat are the mineralocorticoids?

The mineralocorticoids are the class of steroids produced by the outermost zone of the adrenal cortex, the zona glomerulosa.Aldosterone is the primary mineralocorticoid and, like all the steroids of this class, work to control water and electrolyte balance, particularly by controlling sodium and potassium concentrations.Endocrine Glands: ADRENAL GLANDS: II. CORTEXWhat are the mineralocorticoids?

Under normal conditions, aldosterone secretion is in response to high potassium ion concentration in the extracellular fluid.Aldosterone stimulates kidney cells to lose potassium ions into the forming urine, while at the same time conserving sodium ions and, by osmosis, water.Endocrine Glands: ADRENAL GLANDS: II. CORTEXWhat are glucocorticoids? What controls their secretion?

The glucocorticoids are the class of steroids produced by the middle zone of the adrenal cortex, the zona fasciculate. The predominant glucocorticoids are hydrocortisone, cortisone, and corticosterone.Glucocorticoids are secreted in response to ACTH from the anterior pituitary, which is controlled by corticotropic-RF from the hypothalamus.C-RF secretion is in response to stress. Reduction in stress inhibits C-RF and therefore ACTH and the glucocorticoids.Endocrine Glands: ADRENAL GLANDS: II. CORTEXBriefly describe the gonadocorticoids.The gonadocorticoids are the class of steroids produced by the innermost zone of the adrenal cortex, the zona reticularis. These steroids are the male androgens and the female estrogens.During reproductive left, the concentration of these hormones from the adrenal cortex is of little importance because of gonadal secretion. Their secretion during development, childhood, and after menopause does contribute to normal metabolism.Endocrine Glands: ADRENAL GLANDS: II. CORTEX

Endocrine Glands: PANCREAS

Endocrine Glands: PANCREASDescribe the pancreas.

The pancreas is both an exocrine organ related to digestion and an endocrine gland. It is a flattened organ located posterior and just inferior to the stomach. Scattered throughout the exocrine portion of the gland are small islands of cells called the islets of Langerhans.Endocrine Glands: PANCREASDescribe the cell types of the islets of Langerhans?

Islets are composed of four cell types:alpha cells that secrete glucagonbeta cells that secrete insulindelta cells that secrete somatomedin (GH-IF)F-cells that are related to digestionEndocrine Glands: PANCREAS

Endocrine Glands: GONADS: I. OVARYComposed of ovarian follicles (sac-like structures)Structure of an ovarian follicleOocyteFollicular cells

Endocrine Glands: GONADS: I. OVARYSecreted hormone:ProgesteroneSupport pregnancyAnti-inflamatory effectOestrogen (mainly oestradiol)Promote formation of female secondary sex characteristics, coagulation, fluid balanceAndrostenedioneSubstrate for oestrogenInhibin Inhibit production of FSH from anterior pituitaryEndocrine Glands: GONADS: I. OVARY

Endocrine Glands: GONADS: II. TESTES

Coverings of the testes:Tunica albuginea capsule that surrounds each testisSepta extensions of the capsule that extend into the testis and divide it into lobulesInterstitial cells produce androgens such as testosteroneEndocrine Glands: GONADS: II. TESTESSecreted hormone:Androgens (chiefly testosterone) from Leydig cellsgrowth of muscle mass, increased bone density, growth and strengthMaturation of sex organs, promote formation of male secondary sex characteristicsEstradiol from Sertoli cellsPrevent apoptosis of germ cellsInhibin from Sertoli cellsInhibit production of FSH

Endocrine Glands: Life span changesendocrine glands decrease in sizemuscular strength decreases as GH levels decreaseADH levels increase due to slower break down in liver and kidneyscalcitonin levels decrease; increase risk of osteoporosisPTH level changes contribute to risk of osteoporosisinsulin resistance may developchanges in melatonin secretion affect the body clockthymosin production declines increasing risk of infectionsMankind! You are the poor in need of God whereas God is the Rich Beyond Need, the Praiseworthy. (Qur'an, 35: 15)