Endocrine Glands and Their Major Hormones = ees eta anne foi ooeeeee Protein Promotes growth of boy tissues frat) Projacin (PRL) | Peptide Promotas milk production fis — [mmama erst, 2 |Slycomrtein | Stimslates thyroid hormone release Table 17.2 Endocrine Glands and Their Major Hormones Endocrine Associated Chemical gland hormanes class Effect Paiary __[Adreacearicetonle 5 5 Paumary —AdencearieeetP® |pectdo _|Stmalalos hormano roleaso by anal cortox Pautary | Foliele-stmalating Peet, [feces ee 90 | cxcopiain [Stimson gnate production Finitary | Linetizing hormone ee Glyeoeretein | Stimalates and-ogen production by gonads Pauzary _|Aniiuretebarmane 5 elec Peptde | stimalaras water reabsorption by kidneys unary, cin ie jimulates Uterine contractions during chiidbir causa foe Paptde | stimalntas uterine conractons during chisairn Tod [TCA Lamina [tind mal retina Thyrekd Jcaleitonin Peptide Reduces blood Ca?" levels vwatnyraig |Parayrod z 2 Parmtnyroid [fermen cera) —_|Peptde | reases blood Ca" ves Rarenal _ peranal | waveterone steroid | creases blood Nat levels Corts (ane —_[entcostorone, ——|smvrai—_|ncros blood aueoselavots é cotisone ‘Adrenal | Epinephrine, 5 (ay — |rahartrne [Amine | Stmaiae tight o-ig response Fingal Iwelatanin ‘Amina | Regulatansleep eyes Pancreas [insulin Protein | Reduces blood gucose levels Pancreas [Glucagon Protein |ncreases blood glucasa levels ze os a Slimalates developmert of male secomdary sex a _ Steroid | ommacterstics and sperm production 5 Estrogens and [Simalate development offemmale secondary sex Qvarias [progesterone [SH | characterstica and prepare the bady fr chido Table 17.2> ENDOCRINE SYSTEM i stems: All the physiological activities of the body are regulated by two major syst 1. Nervous system 2. Endocrine system. i 11s in secreting cel Endocrine system consists of several ductless glands and many hormone-secreting organs, The nervous and endocrine systems act together to coordinate functions of all body eae Nervous system acts through nerve impulses (action potentials) conducted along axons of heurones. At synapses, nerve impulses trigger the release of mediator (messenger) molecules called neurotransmitters. The endocrine system also control body activities by releasing mediators, called hormones, but the means of control of the two systems are very different. A hormone is a mediator molecule that is released in one part of the body but regulates the activity of cells in other Parts of the body. Most hormones enter intestinal fluid and then & endoctine gi . i i ands, glands secretes their products into ducts that carry the secretions into body ane oe am organ oto outer surface ofthe body. Exocrine glands include geo sebaceous, mucus ete, Endocrine glands secrete their products (hormones) into the interstitial a the secretory cells rather than ducts. Endocrine glands include pituitary thyroid, parathyroid, adrenal & pineal gland, other several organ and tissues that are not exclusively classified nc ict a a, ot hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, sniall insectinn heart, placenta. The science of the anata function of the endocrine glands and the diagnosis and treatment of disorders is endocrinology. fluid surrounding |ENDOCRINE GLANDS Although, a given hormone travels throughout the body in the blood, it affects only specific target cells, hormones influence the target cells by chemically binding to specific protein receptors. Only target cells for a given hormone have receptors that bind and recognize that hormone. If a hormone is present in excess, the number of target cell receptors may decrease, an effect called down-regulation. Down regulation makes a target cell less sensitive to a hormone. In contrast, when a hormone is dificient, the number of receptors may increase. ‘This phenomenon is known as up-regulation, makes a target cell more sensitive to a hormone. General functions of hormone |. Regulates chemical composition and volume of internal environment-ADH-H20, Aldesterone -PH, Na’ and K*-Aldosterone. . Regulates metabolism & energy balance-TH. . Regulates contraction of smooth & cardiac muscle fibers-oxytocin. . Control growth and development-HGH_ . Help regulates operation of reproductive system-LH, FSH etc. . Help establish circadian rhyme-melatonin aueenClassification of hormones based on site of action 7 Based on the site of action, hormones can be classified as circulating hormones and local hormones. Circulating pass from the secretory cells that make them into interstitial fluid and then into the blood, local hormones act locally on neighbouring cells or on the same cell that secretes them without entering the blood stream. Local hormones that act on neighbouring cells are called paracrines and those that act on the same cell that secretes them are called autocrines. One example of a local hormone is interleukin-2 (IL. 2) which is released by helper T cells during immune responses. IL-2 helps activate other nearby immune cells, a paracrine effect. But it also acts as an autocrine by stimulating the same cell that released it to proliferate. This action generates more helper T cells. See example of local hormone is the gas nitric oxide (NO), which is released by endothelial cells lining blood vessels. No causes relaxation of nearby smooth muscle fibers in blood vessels, which in turn cause vasodilation. Endocrine messenger Autocrine messenger | Signaling cell p Transport of oe hogese ‘onsame cel ‘trough blood] Paracrine messenger —juxtacrine messenger Signaling cet ‘through interstitial uid Signaling coll Target call Messenger diffuses through the gap junction ‘Neurocrine messenger — neurotransmitter | Neurocrine messenger —neurchormone " aoe ee ee ‘Transport of neurohormone Neurotransmitter difuses through the syn: musCHEMICAL CLASSIFICATION OF HORMONES Chemically hormones can be divided into lipid soluble and water soluble. Lipid- soluble hormones include steroid hormones, the steroids are synthesized from cholesterol. Of the hormones produced by major endocrine organs, only gonadal and adrenocortical hormones are steroids. Most hormones are amino acid based. Molecular sizes vary widely in this group- from simple amino acid derivatives (which include amines and thyroxine constructed from the amino acid tyrosine), to peptides (short chains of amino acids), to proteins(long polymers of amino acids). MECHANISM OF HORMONE ACTION All major hormones circulate to yirtually all tissues, but a given hormone influences the activity of only certain tissue cells, referred to as its target cells. Hormones bring about their characteristic effects on target cells by altering cell activities ie, they increase or decrease the rate of normal cellular processes. The precise response depends on the target cell type. For example, the hormone epinephrine causes smooth muscle cells in the blood vessels wall to contract. while the action in other cells aside the smooth muscle cell-is different, A hormone stimulus typically produces one or more of the following changes; © Alters plasma membrane permeability or membrane potential by opening. or closing ion channels. Stimulates synthesis of proteins or regulatory molecules such as enzymes within the cell. a © Activate or deactivate enzymes © Induces secretory activity «Stimulates mitosis. oll How does hormone communicate with its target cell? © Plasma membrane receptors and second-messenger systems; cyclic AMP signaling mechanism, the PIP,- calcium signaling mechanism, cyclic GMP. © Intracellular receptors and direct gene activation; transcription of DNA to produc mRNA.Thyroid Steroid hormones | hormones | PHEUCER TY ALT Cael hpoP kgs } ss Tie Wpun dihutum qcveches TR Pile MRNA Protein [Pt fun ditatuan ace ff 7 synthesis _/ tte hip>thalemupe ‘Hypothalamus and pituitary gland Hypothalamus and Pituitary gland works together to control many body activities. Pituit ‘land or hy ihysis is about the size of a pea, about 500g in weight and measures =1.5cm in diameter and lies in the hypophyseal fossa of the id bone, below hypothalamus. It has {0_anatomical_and_functional_lobes-Adenchypophysis which Se ; crior Jobe) 75% _and Neuro-hypophysis consists of neural, tissues (posterior Jobe), A stalk like structure (infundibulum) attaches pituitary gland to the hypothalamus. Hypothalamus is the major link between nervous and endocrine system. It is th region of the forebrain, lying below the thalamus and ‘making_up the floor of the third cerebral ventricle. it has wide range of functions. Ie controls temperature, hunger, thirst, and pituitary gland etc. acs cee Some hormones produced and released by hypothalamus include Growth- hormone releasing hormone (GHRH), GHIH (somatostatin), TRH, GoRH, PRH & CRH. Anterior Pituitary = Anterior pituitary synthesizes and s ne that regulate a wide range of body activities from_growth to reproduction, Secretion and_telease of anterior pituitary hormones is stimulated by releasing hormiones and suppressed by inhibin both prduced by-neuro-seeretory cells of the hypothalamus, Release of an antercr jituitary hormone i: iegative feedback mechanism. henSuperior yponatams —| mary Newcnecratony L cote | cagitary Hypophysea ‘iypocsont | poravine ‘sam Poster ptary sotarot Pruitary gland] sty Secondary eapsary plows of portal syst Anvarr / yrs hoa stm — Orrrerteaserormenes Somacestarta — Ht Crier somatovoPria — Er@e Doma mains —1OE Hormones of the anterior pituitary AG tt asia ‘ Fea gan ames (somatotr Soma re in GHRH and GHIH ‘os lH com Se aa hGH stimulates growth _aeids. into cells roduce more decreasinj Tucose uptake which decreases the use 0 most body cells. Thi production in times of glucose scarcity. etal muscles. AGH promote synthesis ecretion of 5! ~~Somatomedins. ueig ‘cause cells to grow and multiply by increasing uptake of amino- - 1GEs alsoeshance-Hoolysis-in_adinase tissue 10 P_ production. adipose tissue to for ATP production, IGFs influence carbohydrate metabolism by production by is action spares glucose so that it’s available to neurones for ATP Hypersecretion of GH causes, Sees con “of ihe body, leading to gigantism. ney of children causes stunted growth,parades Potuny so.” & Bhaman grown nors 2. epote Dnata tom STs, stoma: Ae Goeeins SP topcovesnts fear: ounce core aeeecees | 32g hom, setts Crowne, b-Pdwrsconteotoate i cot cHin GHRH Sune. | | ame tanibits | “stimulates | stimutates | | * Teh fines ee [ag rtne Anterior pituitary T Growth hormone | Liver} Other tissues Somatomedin _}-. ry (3 vw “Regulation of growth hormone Oa 2. Thyroid stimulating hormone (TSH)- thyroid hormones, T3 and T4, both Haan by the thyroid a ~hormones(TRH) from_the_tiypothalamus controls TSH — secrétion, Release of TRH Shearer es TH, Dich Levels of Ts.& Ty inhibit secretion of TRH vig 3r Saeemunes icle com hormone (FSH)- in one the ovaries-are. the targets for follicle stimulating hormone, Each month, al_ovarian Sc i0_stimulat icles secrete_estro; In _males--FSH-stimulates soem production in the testes. GoRH from the hypothalamus stimulates FSH release stimulates FSH rel elease d_by oestrogen in females and testosterone in males through negative feedback systems, 4. Luteinizing hormone- in females, LH triggers ovulation, the release = of a secondary oocyte by an ovary. LH stimulates formation of corpus luteum (Structure formed after Qvulation) in the ovary oe Be ee conan smn FSH & the uterus for implantation of a fertilized ovum and help pre; ami ds for milk secretion, In males, {LH_stilats_insesiil-el in the tates fee of LH is controlled by GnRH. . Secretion of. Agstosterone. ce ne COFFYS UtscsenAdlemacorfeatopoe ea | 5. Prolactin(-PRL)- together with other hormones, initiates and maintains milk production by the mammary glands. Hypothalamus secrets both inhibitory (PIH) and exhitatory PRH) hormone: r actin secretion. Each month, just before menstruation the secretion of PIH diminishes and the blood le tin rises, butnot_ snow ch to stimulate milk production. The function of prolactin is not known in males, but is i ion (i nce) 6. Adrenocorticotropic hormone (ACTH) — corticotropin releasing hormone (CRH) from hypothalamus_stimulates secretion of ACTH. .ACTH controls secretion of cortico- steroids or cortisol (mineralocorticoids and glucocorticoids) by the adrenal cortex of the adrenal gl: 7. Melanocyte- stimulating hormone- MSH increases skin pigmentation in amphibians. Its f Sxact role in humans is unknown, but the ‘SH in_the brain ‘suggests it may. influences brain activity. CRH stimulate MSH release, PIH (Dopamine) inhibits MSH release. ~ | soos Pruteasey Ony 2 Roem. Posterior pituitary Posterior pituitary or neurohypophysis dacs nat synthesize hormones. It does store and release two hormones, (os eS ees whose cell bodies are paraventricular and_suy thalamus. their axons form the hypothalamohypophyseal tract. This tract begins = the hypothalamus and ends near blood capillaries in the posterior pituitary. The neuronal cell bodies in the —-paraventricular nucleus synthesize the hormone oxytocin, and th cells bodies — inthe supragptic nucleus produc ; also called vasopressin. After their production ‘in the supraoptic nucleus produce ADH, also called vasopressin. n= the “cell “bodies_of neurosecretory cells, oxytocin-and~ADH “are“packaged into “secretory vessicles, which move by fast axonal transport tothe axon terminals in the “posterior pituitary, where. they are stored until nerve i Httigser-exocytosig and | eleascofthehormone. Ay rnc ctdggrecte: YeWmore _Bewcytnsis =aPosterior pitultary Oxytocin Vasopressin "1. Oxytocin- has two target organs during and after delivery of a baby which are uterus and breasts Of the ‘mother. During delivery, ste ching of the cervix of the uterus "Stimulates the release of oxytocin which in turn, ‘Suhances contraction “of smooth —- after delivery, it stimulates milk ejection (It 1¢ mechanical stimulus Rel duting labour, sensory is impulses are generated and travel to the hypothalamus stimulating posterior ituitarySpinal cord ree myoapihelial coll cecopiore im MpBIe Pome Sucxing by baby cp ~cotteesing duet Milk ejection reflex (positive feedback mechanism) 2. Antidiuretic hormone: acts on the DCT & CD of the ki i ing their Permeability to water and re-absorption of water” from the-glomerular filterate is increased. is dration, is ii jorece] ‘which-sti *S posterior jituitary gland to release ADH and water is reabsorbed, urine output is reduced. When ‘osmotic pressure of blood is low, inhibition of osmoreceptors stops ADH. ADH can cause contractions of-smooth muscle and vasoconstriction of arteries and then raises __ blood pressure: This is why ADH is called vasopressin, 3 ~ Thyroid gland — \ This is located just belo box) in the neck, at the level of C5-T1 | vertebrae. It is_butterfly-shaped compoalas-of Ga aba ied and right joined by isthmus. It is about 25g, Sem long and Jem wide’ Microscopic sphrical sacs called i “thyroid follicles_make_up_the_th ind. The-walls of each follicle consists | hich roduce hormone thy shine '4) or ‘tetra jodothyroni: iiodathyronis .: Between the ther _cells Valle parafollicular cells (C-cells) which secrete hormone acre 7 | | iFormation & storage of TH Synthesis of T3&T4 occurs as follows: _____i. odie trapping-fotticutar cells rap iodide fons (L)-— ~~ _Synthesis_of thyroglobulin- While follicular cells ate ping T, they also lobulin( ‘GB) containing iodine molecules (1) is is brs (21-1,), they react with tyrosines that are part of TGB molecules. Bi ig of one iodiné“atom yields ~~ “onoiodotyrosine (T)) and as ond iocinatan roduces diodotyrosi iv. Coupling of Ty and Tx {wo Ta molecules join to form Ty or on T, and one 127 join to form Ty. eer — ¥. Secretion of thyroid hormones; because T3 & TY are lnidesoluble, Ayr the blo through the plasma membrane into interstitial fluid and then into # 1d. T4 "normally is secreted in n greater quantity than T3, but 3 is several times more “potent imo active) Transport in the blagd- they “mainly thyroxin binding globulin (TBG) Mechanism of release of TH Thyrotropin-releasing_ho shag tnd thorcla stimulating hormone (TSH) from the anterior pituitary sti £ TH. The actual are as follows. process a in the blood| i Low blood levels of T3 & T4 or low metabolic rate stimulates hypothalamus “seorete TRH. Lhyousonta Releasing War tna) = TRH is carTied to anterior pituitary where it sretion of TSH. ISHst follicular cells to synthesize 2 secrete TH. Tl licular cells release TH into the blood_until metabolic rate returns normal. v. Ek vel of TH inhibits release of T! H (Negative feedback). Hme~ Basa mirarotte eave Functions of TH i. Increase BMR and heat production ~ Regulates met metabolism of carbohydrates, proteins and fats. -~ iii, Accelerate body growth vp gectoyes re pearernynr ion Qver secretion of TH (hyperthyroidism) causes increased heart rate, increase BMR, anxi-_ increased blood pressure. While under secretion effect include decrease BMR, mei retardation and stunted bone growth in infant. Calcio (CT) deceensey Cou Lever Produced icular cre can dectease the level of calci _ Ju Mad bv iahibting the action of axeolas, the cells that break down bone extracellt _ tmatrix, The secretion of CT is controlled by a negative feedback system. ic anna When its blood level is high, CT lowers the amount of blood calcium by inhibit bone resorption by osteoclasts and See eee elcid ail shines BSE extracellular matrix. Parathyroids glands {~eceases Cou AN These are small ound masses of tlandfar tissue that are embedded in the poste surface of the thyroid gland. id is are secretory cell led chief c that release parathyroid hormone (PTH). The ion is regulated by blood calcium lev ‘hen calcium level falls, PTH is increase and vice versa, Whey Sladdl Catedim Uver va PU deceases - Functions : regulates levels of calcium ion, Mangnssium ion in the blood by increasing decreasing absorption of ions in the small intestine. pave grondareProcess involved in the production of PTH are: - ~ Higher level of Ca stimulates para-follicular cells to release calcitonin ~ CT inhibits the activity of osteoclasts, decreasing blood Ca" level: Lower level of Ca” stimulates chief cells to release PTH. PTH increases the activity of osteoclases, which the blood. - - PTH stimulate the kidneys to release calcitriol, ~~ Calcitriol stimulates increased desorption of Ca”* increase in blood level of Ca”, breakdown bone and release Ca** into from foods-in GIT, leading to Adrenal glands (suprarenal glands) There are two adrenal glands, one lying ontop of each kidney. Each is about 4em Jong & 3cm thick. The adrenal blood supply is from. a arteries in nal viens, Each a s. The regions a ~——“Adrenal_cortex-consists-o| i are outer adrenal cortex and.inner adrenal medulla. f three _zones, each~ of which_synthesizes and_ secretes ~~different hormones called steroid hormones. Outer zone releases-mineralocorticoids, n¢ releases glucocor and inner zone releases androgens, iis way corticoids( corticosteroids), ites homeostasis of Na* and Ke: Through is lium (Na’) by the The three hormones are collectively i i locorticoids (Aldosterone) res negative feedback system, it sti_renal tubules and excretion of potassium (K")in the urine, Sodium re reabsorplionss | companied by retention of water; hence regulates blood volume and pressure, It sleereeemies cocoon, of Ef in ie tie en acidosis. secretion of tat ldsteone oocurs as pat ofthe RAS. When tenal blood flow is reduce. or fo blood sodium levels falls, the enzyme renin is secreted by Kidneys. Renin : oS L converts angiotensinogen (plasma protein) produced by the liver to angiotensi ngioténsin conv (ACE) formed in the lungs and PCT converts angiotensin | to angiotensin 2, which stimulates aldosterone secretion Blood pressure ries ‘Angiotensin I 1D angiotensin, converting enzyme Angiotensin? T @ 1S penn “Angiotensinogen Blood pressure falls Glucocorticoids- most abundant glucocorticoid is cortisol, others are corticosterone | and cortisone. secretion is controlled through negative feedback stem ' ‘Androgens adrenal cortex secretes_small_ amounts of androgens do? females. In-males-their effects is insignificant, while in females they contribute to ‘libido \| Adrenal medullaSkkbn ws oum nage Remon areayanrave Colpiaet x) i Innermost region of ‘adrenal gland, Two main hormones Ft inephri fephrine (adrenaline and noradrenaline). In stressful stiaioet and during~éxercise, impulses from the hypothalamus stimulate sympatl as preganglionic neurons, which in turn stimulate the cells of adrenal medulla to sect “epinephrine and norepinephrine. Together they increase heart rate, blood pressure, blood flow, dilate airways, increasing metabolic rate and also help the body to resist stress, | 7 Pancreatic islets (islets of Langerhans) Pancreas is a flattened organ located in the curve of the duodenum. It has both endocrine and exocrine functions. Endocrine part has no ducts leading from the islet cells, pancreatic hormones are secreted directly into the bloodstream and circulate throughout the body. Three types of pancreatic islets cells are identified which are (a (alpha) cells, which secrete glucagon (ii) B(beta) cells, which secretes insulin ee ili) 6 (delta) cells, which secrete somatostatin. ety Functions/Actions of Glucagon and Insulin The normal blood glucose level is between 3.5 and 8mmol/litre (63 to 144mg/100ml). Blood glucose levels are controlled by opposing actions insulin and glucagon. Glucagon increase blood glucose level when it falls below normal while insulin decrease blood glucose level when it is high via negative feedback. Processes involved in blood glucose regulation are highlighted below; ~ Low blood glucose level (hypoglycemia) stimulates secretion of glucagon + Glucagon acts on liver cells to promote breakdown of glycogen into glucose and formation of glucose from lactic acid and amino acid (gluconeogenesis) ~ Liver releases glucose into the blood more rapidly and blood glucose level rises ~ High glucose level (hyperglycemia) inhibits release of glucagon by alpha cells (negative feedback) - High blood glucose level stimulates secretion of insulin by beta cells ~ Insulin acts on various cells to promote facilitated diffusion of glucose and amino-acid into cells, increase conversion of glucose to glycogen, derease conversion of glycowen into lucose(alycogenolyss), prevent breaking down of protein & fat, hence stopping gluconeogenesis. = Blood glucose level falls ~ Low blood glucose level below normal inhibits release of insulin by beta cells (negative feedback), Note: Insulin and glucagon release is regulated by ANS. The parasympathetic divi stimulates secretion of insulin e.g, during digestion & absorption symppathetic ai ee stimulates secretion of glucagon e.g during exercise. ne ve 16 Fis Zheononse thao StenSomatostatins(GHRIH) Alsq produced by hypothalamus. It also inhibits secretion of both glucagon & insulin. Ovaries and Testes (Gonads & Placenta) Female gonads (ovaries) are_paired oval bodies located in the pelvic cavity. They roduce the female sex hormones oestrogens and progesterone. Along with FSH a LH from the anterior pituitary, the female sex hormones regulate menstrual cycle, maintain pregnancy and pre; mammary glands for lactation. Male gonads (testes) located_in_extra-abd ominal_skin_pouch called scrotum. they are ‘oval glands that lies in the seéfeitoh? They produce testosterone, that regulates roduction of sperm and stimulates the develo, ment_and maintenance of masculine characteristics such as beard growth, and deepening of the voice. 0 draag Pineal gland [vires ) 4 2eceetes maarorin Pineal gland is a small body attached to the roof of the third ventricle, It is about LOmm, ea long. Themain hormone secreted by the pineal gland is Melatonin, The secretion is high ight and lowest around midday, The functions of melatonin are not. clearly understood, but it contribute to setting the ’s biological clock and inhibits gro and development of the sex organs before puberty, & . ' ‘Thymus gland r r Ke ‘Thymus ies in the mediastis ind the sternum and extends to the root of the “neckIt weighs about 10 to 15g at birth and grows until puberty when it begins, to, “atrophy.-Thymosin is the hormone secreted by-the thymus-gland and is involved inthe “development of T-lymphocytes for cell mediaced immunity, Other hormones secreting organs Some organs other than those usually classified as endocrine glands have an endderine function and secrete hormones. Table below shows some of the hormones, orgin of production and actions. e 1> ENDOCRINE SYSTEM i stems: All the physiological activities of the body are regulated by two major syst 1. Nervous system 2. Endocrine system. i 11s in secreting cel Endocrine system consists of several ductless glands and many hormone-secreting organs, The nervous and endocrine systems act together to coordinate functions of all body eae Nervous system acts through nerve impulses (action potentials) conducted along axons of heurones. At synapses, nerve impulses trigger the release of mediator (messenger) molecules called neurotransmitters. The endocrine system also control body activities by releasing mediators, called hormones, but the means of control of the two systems are very different. A hormone is a mediator molecule that is released in one part of the body but regulates the activity of cells in other Parts of the body. Most hormones enter intestinal fluid and then & endoctine gi . i i ands, glands secretes their products into ducts that carry the secretions into body ane oe am organ oto outer surface ofthe body. Exocrine glands include geo sebaceous, mucus ete, Endocrine glands secrete their products (hormones) into the interstitial a the secretory cells rather than ducts. Endocrine glands include pituitary thyroid, parathyroid, adrenal & pineal gland, other several organ and tissues that are not exclusively classified nc ict a a, ot hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, sniall insectinn heart, placenta. The science of the anata function of the endocrine glands and the diagnosis and treatment of disorders is endocrinology. fluid surrounding |ENDOCRINE GLANDS Although, a given hormone travels throughout the body in the blood, it affects only specific target cells, hormones influence the target cells by chemically binding to specific protein receptors. Only target cells for a given hormone have receptors that bind and recognize that hormone. If a hormone is present in excess, the number of target cell receptors may decrease, an effect called down-regulation. Down regulation makes a target cell less sensitive to a hormone. In contrast, when a hormone is dificient, the number of receptors may increase. ‘This phenomenon is known as up-regulation, makes a target cell more sensitive to a hormone. General functions of hormone |. Regulates chemical composition and volume of internal environment-ADH-H20, Aldesterone -PH, Na’ and K*-Aldosterone. . Regulates metabolism & energy balance-TH. . Regulates contraction of smooth & cardiac muscle fibers-oxytocin. . Control growth and development-HGH_ . Help regulates operation of reproductive system-LH, FSH etc. . Help establish circadian rhyme-melatonin aueenClassification of hormones based on site of action 7 Based on the site of action, hormones can be classified as circulating hormones and local hormones. Circulating pass from the secretory cells that make them into interstitial fluid and then into the blood, local hormones act locally on neighbouring cells or on the same cell that secretes them without entering the blood stream. Local hormones that act on neighbouring cells are called paracrines and those that act on the same cell that secretes them are called autocrines. One example of a local hormone is interleukin-2 (IL. 2) which is released by helper T cells during immune responses. IL-2 helps activate other nearby immune cells, a paracrine effect. But it also acts as an autocrine by stimulating the same cell that released it to proliferate. This action generates more helper T cells. See example of local hormone is the gas nitric oxide (NO), which is released by endothelial cells lining blood vessels. No causes relaxation of nearby smooth muscle fibers in blood vessels, which in turn cause vasodilation. Endocrine messenger Autocrine messenger | Signaling cell p Transport of oe hogese ‘onsame cel ‘trough blood] Paracrine messenger —juxtacrine messenger Signaling cet ‘through interstitial uid Signaling coll Target call Messenger diffuses through the gap junction ‘Neurocrine messenger — neurotransmitter | Neurocrine messenger —neurchormone " aoe ee ee ‘Transport of neurohormone Neurotransmitter difuses through the syn: musCHEMICAL CLASSIFICATION OF HORMONES Chemically hormones can be divided into lipid soluble and water soluble. Lipid- soluble hormones include steroid hormones, the steroids are synthesized from cholesterol. Of the hormones produced by major endocrine organs, only gonadal and adrenocortical hormones are steroids. Most hormones are amino acid based. Molecular sizes vary widely in this group- from simple amino acid derivatives (which include amines and thyroxine constructed from the amino acid tyrosine), to peptides (short chains of amino acids), to proteins(long polymers of amino acids). MECHANISM OF HORMONE ACTION All major hormones circulate to yirtually all tissues, but a given hormone influences the activity of only certain tissue cells, referred to as its target cells. Hormones bring about their characteristic effects on target cells by altering cell activities ie, they increase or decrease the rate of normal cellular processes. The precise response depends on the target cell type. For example, the hormone epinephrine causes smooth muscle cells in the blood vessels wall to contract. while the action in other cells aside the smooth muscle cell-is different, A hormone stimulus typically produces one or more of the following changes; © Alters plasma membrane permeability or membrane potential by opening. or closing ion channels. Stimulates synthesis of proteins or regulatory molecules such as enzymes within the cell. a © Activate or deactivate enzymes © Induces secretory activity «Stimulates mitosis. oll How does hormone communicate with its target cell? © Plasma membrane receptors and second-messenger systems; cyclic AMP signaling mechanism, the PIP,- calcium signaling mechanism, cyclic GMP. © Intracellular receptors and direct gene activation; transcription of DNA to produc mRNA.Thyroid Steroid hormones | hormones | PHEUCER TY ALT Cael hpoP kgs } ss Tie Wpun dihutum qcveches TR Pile MRNA Protein [Pt fun ditatuan ace ff 7 synthesis _/ tte hip>thalemupe ‘Hypothalamus and pituitary gland Hypothalamus and Pituitary gland works together to control many body activities. Pituit ‘land or hy ihysis is about the size of a pea, about 500g in weight and measures =1.5cm in diameter and lies in the hypophyseal fossa of the id bone, below hypothalamus. It has {0_anatomical_and_functional_lobes-Adenchypophysis which Se ; crior Jobe) 75% _and Neuro-hypophysis consists of neural, tissues (posterior Jobe), A stalk like structure (infundibulum) attaches pituitary gland to the hypothalamus. Hypothalamus is the major link between nervous and endocrine system. It is th region of the forebrain, lying below the thalamus and ‘making_up the floor of the third cerebral ventricle. it has wide range of functions. Ie controls temperature, hunger, thirst, and pituitary gland etc. acs cee Some hormones produced and released by hypothalamus include Growth- hormone releasing hormone (GHRH), GHIH (somatostatin), TRH, GoRH, PRH & CRH. Anterior Pituitary = Anterior pituitary synthesizes and s ne that regulate a wide range of body activities from_growth to reproduction, Secretion and_telease of anterior pituitary hormones is stimulated by releasing hormiones and suppressed by inhibin both prduced by-neuro-seeretory cells of the hypothalamus, Release of an antercr jituitary hormone i: iegative feedback mechanism. henSuperior yponatams —| mary Newcnecratony L cote | cagitary Hypophysea ‘iypocsont | poravine ‘sam Poster ptary sotarot Pruitary gland] sty Secondary eapsary plows of portal syst Anvarr / yrs hoa stm — Orrrerteaserormenes Somacestarta — Ht Crier somatovoPria — Er@e Doma mains —1OE Hormones of the anterior pituitary AG tt asia ‘ Fea gan ames (somatotr Soma re in GHRH and GHIH ‘os lH com Se aa hGH stimulates growth _aeids. into cells roduce more decreasinj Tucose uptake which decreases the use 0 most body cells. Thi production in times of glucose scarcity. etal muscles. AGH promote synthesis ecretion of 5! ~~Somatomedins. ueig ‘cause cells to grow and multiply by increasing uptake of amino- - 1GEs alsoeshance-Hoolysis-in_adinase tissue 10 P_ production. adipose tissue to for ATP production, IGFs influence carbohydrate metabolism by production by is action spares glucose so that it’s available to neurones for ATP Hypersecretion of GH causes, Sees con “of ihe body, leading to gigantism. ney of children causes stunted growth,parades Potuny so.” & Bhaman grown nors 2. epote Dnata tom STs, stoma: Ae Goeeins SP topcovesnts fear: ounce core aeeecees | 32g hom, setts Crowne, b-Pdwrsconteotoate i cot cHin GHRH Sune. | | ame tanibits | “stimulates | stimutates | | * Teh fines ee [ag rtne Anterior pituitary T Growth hormone | Liver} Other tissues Somatomedin _}-. ry (3 vw “Regulation of growth hormone Oa 2. Thyroid stimulating hormone (TSH)- thyroid hormones, T3 and T4, both Haan by the thyroid a ~hormones(TRH) from_the_tiypothalamus controls TSH — secrétion, Release of TRH Shearer es TH, Dich Levels of Ts.& Ty inhibit secretion of TRH vig 3r Saeemunes icle com hormone (FSH)- in one the ovaries-are. the targets for follicle stimulating hormone, Each month, al_ovarian Sc i0_stimulat icles secrete_estro; In _males--FSH-stimulates soem production in the testes. GoRH from the hypothalamus stimulates FSH release stimulates FSH rel elease d_by oestrogen in females and testosterone in males through negative feedback systems, 4. Luteinizing hormone- in females, LH triggers ovulation, the release = of a secondary oocyte by an ovary. LH stimulates formation of corpus luteum (Structure formed after Qvulation) in the ovary oe Be ee conan smn FSH & the uterus for implantation of a fertilized ovum and help pre; ami ds for milk secretion, In males, {LH_stilats_insesiil-el in the tates fee of LH is controlled by GnRH. . Secretion of. Agstosterone. ce ne COFFYS UtscsenAdlemacorfeatopoe ea | 5. Prolactin(-PRL)- together with other hormones, initiates and maintains milk production by the mammary glands. Hypothalamus secrets both inhibitory (PIH) and exhitatory PRH) hormone: r actin secretion. Each month, just before menstruation the secretion of PIH diminishes and the blood le tin rises, butnot_ snow ch to stimulate milk production. The function of prolactin is not known in males, but is i ion (i nce) 6. Adrenocorticotropic hormone (ACTH) — corticotropin releasing hormone (CRH) from hypothalamus_stimulates secretion of ACTH. .ACTH controls secretion of cortico- steroids or cortisol (mineralocorticoids and glucocorticoids) by the adrenal cortex of the adrenal gl: 7. Melanocyte- stimulating hormone- MSH increases skin pigmentation in amphibians. Its f Sxact role in humans is unknown, but the ‘SH in_the brain ‘suggests it may. influences brain activity. CRH stimulate MSH release, PIH (Dopamine) inhibits MSH release. ~ | soos Pruteasey Ony 2 Roem. Posterior pituitary Posterior pituitary or neurohypophysis dacs nat synthesize hormones. It does store and release two hormones, (os eS ees whose cell bodies are paraventricular and_suy thalamus. their axons form the hypothalamohypophyseal tract. This tract begins = the hypothalamus and ends near blood capillaries in the posterior pituitary. The neuronal cell bodies in the —-paraventricular nucleus synthesize the hormone oxytocin, and th cells bodies — inthe supragptic nucleus produc ; also called vasopressin. After their production ‘in the supraoptic nucleus produce ADH, also called vasopressin. n= the “cell “bodies_of neurosecretory cells, oxytocin-and~ADH “are“packaged into “secretory vessicles, which move by fast axonal transport tothe axon terminals in the “posterior pituitary, where. they are stored until nerve i Httigser-exocytosig and | eleascofthehormone. Ay rnc ctdggrecte: YeWmore _Bewcytnsis =aPosterior pitultary Oxytocin Vasopressin "1. Oxytocin- has two target organs during and after delivery of a baby which are uterus and breasts Of the ‘mother. During delivery, ste ching of the cervix of the uterus "Stimulates the release of oxytocin which in turn, ‘Suhances contraction “of smooth —- after delivery, it stimulates milk ejection (It 1¢ mechanical stimulus Rel duting labour, sensory is impulses are generated and travel to the hypothalamus stimulating posterior ituitarySpinal cord ree myoapihelial coll cecopiore im MpBIe Pome Sucxing by baby cp ~cotteesing duet Milk ejection reflex (positive feedback mechanism) 2. Antidiuretic hormone: acts on the DCT & CD of the ki i ing their Permeability to water and re-absorption of water” from the-glomerular filterate is increased. is dration, is ii jorece] ‘which-sti *S posterior jituitary gland to release ADH and water is reabsorbed, urine output is reduced. When ‘osmotic pressure of blood is low, inhibition of osmoreceptors stops ADH. ADH can cause contractions of-smooth muscle and vasoconstriction of arteries and then raises __ blood pressure: This is why ADH is called vasopressin, 3 ~ Thyroid gland — \ This is located just belo box) in the neck, at the level of C5-T1 | vertebrae. It is_butterfly-shaped compoalas-of Ga aba ied and right joined by isthmus. It is about 25g, Sem long and Jem wide’ Microscopic sphrical sacs called i “thyroid follicles_make_up_the_th ind. The-walls of each follicle consists | hich roduce hormone thy shine '4) or ‘tetra jodothyroni: iiodathyronis .: Between the ther _cells Valle parafollicular cells (C-cells) which secrete hormone acre 7 | | iFormation & storage of TH Synthesis of T3&T4 occurs as follows: _____i. odie trapping-fotticutar cells rap iodide fons (L)-— ~~ _Synthesis_of thyroglobulin- While follicular cells ate ping T, they also lobulin( ‘GB) containing iodine molecules (1) is is brs (21-1,), they react with tyrosines that are part of TGB molecules. Bi ig of one iodiné“atom yields ~~ “onoiodotyrosine (T)) and as ond iocinatan roduces diodotyrosi iv. Coupling of Ty and Tx {wo Ta molecules join to form Ty or on T, and one 127 join to form Ty. eer — ¥. Secretion of thyroid hormones; because T3 & TY are lnidesoluble, Ayr the blo through the plasma membrane into interstitial fluid and then into # 1d. T4 "normally is secreted in n greater quantity than T3, but 3 is several times more “potent imo active) Transport in the blagd- they “mainly thyroxin binding globulin (TBG) Mechanism of release of TH Thyrotropin-releasing_ho shag tnd thorcla stimulating hormone (TSH) from the anterior pituitary sti £ TH. The actual are as follows. process a in the blood| i Low blood levels of T3 & T4 or low metabolic rate stimulates hypothalamus “seorete TRH. Lhyousonta Releasing War tna) = TRH is carTied to anterior pituitary where it sretion of TSH. ISHst follicular cells to synthesize 2 secrete TH. Tl licular cells release TH into the blood_until metabolic rate returns normal. v. Ek vel of TH inhibits release of T! H (Negative feedback). Hme~ Basa mirarotte eave Functions of TH i. Increase BMR and heat production ~ Regulates met metabolism of carbohydrates, proteins and fats. -~ iii, Accelerate body growth vp gectoyes re pearernynr ion Qver secretion of TH (hyperthyroidism) causes increased heart rate, increase BMR, anxi-_ increased blood pressure. While under secretion effect include decrease BMR, mei retardation and stunted bone growth in infant. Calcio (CT) deceensey Cou Lever Produced icular cre can dectease the level of calci _ Ju Mad bv iahibting the action of axeolas, the cells that break down bone extracellt _ tmatrix, The secretion of CT is controlled by a negative feedback system. ic anna When its blood level is high, CT lowers the amount of blood calcium by inhibit bone resorption by osteoclasts and See eee elcid ail shines BSE extracellular matrix. Parathyroids glands {~eceases Cou AN These are small ound masses of tlandfar tissue that are embedded in the poste surface of the thyroid gland. id is are secretory cell led chief c that release parathyroid hormone (PTH). The ion is regulated by blood calcium lev ‘hen calcium level falls, PTH is increase and vice versa, Whey Sladdl Catedim Uver va PU deceases - Functions : regulates levels of calcium ion, Mangnssium ion in the blood by increasing decreasing absorption of ions in the small intestine. pave grondareProcess involved in the production of PTH are: - ~ Higher level of Ca stimulates para-follicular cells to release calcitonin ~ CT inhibits the activity of osteoclasts, decreasing blood Ca" level: Lower level of Ca” stimulates chief cells to release PTH. PTH increases the activity of osteoclases, which the blood. - - PTH stimulate the kidneys to release calcitriol, ~~ Calcitriol stimulates increased desorption of Ca”* increase in blood level of Ca”, breakdown bone and release Ca** into from foods-in GIT, leading to Adrenal glands (suprarenal glands) There are two adrenal glands, one lying ontop of each kidney. Each is about 4em Jong & 3cm thick. The adrenal blood supply is from. a arteries in nal viens, Each a s. The regions a ~——“Adrenal_cortex-consists-o| i are outer adrenal cortex and.inner adrenal medulla. f three _zones, each~ of which_synthesizes and_ secretes ~~different hormones called steroid hormones. Outer zone releases-mineralocorticoids, n¢ releases glucocor and inner zone releases androgens, iis way corticoids( corticosteroids), ites homeostasis of Na* and Ke: Through is lium (Na’) by the The three hormones are collectively i i locorticoids (Aldosterone) res negative feedback system, it sti_renal tubules and excretion of potassium (K")in the urine, Sodium re reabsorplionss | companied by retention of water; hence regulates blood volume and pressure, It sleereeemies cocoon, of Ef in ie tie en acidosis. secretion of tat ldsteone oocurs as pat ofthe RAS. When tenal blood flow is reduce. or fo blood sodium levels falls, the enzyme renin is secreted by Kidneys. Renin : oS L converts angiotensinogen (plasma protein) produced by the liver to angiotensi ngioténsin conv (ACE) formed in the lungs and PCT converts angiotensin | to angiotensin 2, which stimulates aldosterone secretion Blood pressure ries ‘Angiotensin I 1D angiotensin, converting enzyme Angiotensin? T @ 1S penn “Angiotensinogen Blood pressure falls Glucocorticoids- most abundant glucocorticoid is cortisol, others are corticosterone | and cortisone. secretion is controlled through negative feedback stem ' ‘Androgens adrenal cortex secretes_small_ amounts of androgens do? females. In-males-their effects is insignificant, while in females they contribute to ‘libido \| Adrenal medullaSkkbn ws oum nage Remon areayanrave Colpiaet x) i Innermost region of ‘adrenal gland, Two main hormones Ft inephri fephrine (adrenaline and noradrenaline). In stressful stiaioet and during~éxercise, impulses from the hypothalamus stimulate sympatl as preganglionic neurons, which in turn stimulate the cells of adrenal medulla to sect “epinephrine and norepinephrine. Together they increase heart rate, blood pressure, blood flow, dilate airways, increasing metabolic rate and also help the body to resist stress, | 7 Pancreatic islets (islets of Langerhans) Pancreas is a flattened organ located in the curve of the duodenum. It has both endocrine and exocrine functions. Endocrine part has no ducts leading from the islet cells, pancreatic hormones are secreted directly into the bloodstream and circulate throughout the body. Three types of pancreatic islets cells are identified which are (a (alpha) cells, which secrete glucagon (ii) B(beta) cells, which secretes insulin ee ili) 6 (delta) cells, which secrete somatostatin. ety Functions/Actions of Glucagon and Insulin The normal blood glucose level is between 3.5 and 8mmol/litre (63 to 144mg/100ml). Blood glucose levels are controlled by opposing actions insulin and glucagon. Glucagon increase blood glucose level when it falls below normal while insulin decrease blood glucose level when it is high via negative feedback. Processes involved in blood glucose regulation are highlighted below; ~ Low blood glucose level (hypoglycemia) stimulates secretion of glucagon + Glucagon acts on liver cells to promote breakdown of glycogen into glucose and formation of glucose from lactic acid and amino acid (gluconeogenesis) ~ Liver releases glucose into the blood more rapidly and blood glucose level rises ~ High glucose level (hyperglycemia) inhibits release of glucagon by alpha cells (negative feedback) - High blood glucose level stimulates secretion of insulin by beta cells ~ Insulin acts on various cells to promote facilitated diffusion of glucose and amino-acid into cells, increase conversion of glucose to glycogen, derease conversion of glycowen into lucose(alycogenolyss), prevent breaking down of protein & fat, hence stopping gluconeogenesis. = Blood glucose level falls ~ Low blood glucose level below normal inhibits release of insulin by beta cells (negative feedback), Note: Insulin and glucagon release is regulated by ANS. The parasympathetic divi stimulates secretion of insulin e.g, during digestion & absorption symppathetic ai ee stimulates secretion of glucagon e.g during exercise. ne ve 16 Fis Zheononse thao StenSomatostatins(GHRIH) Alsq produced by hypothalamus. It also inhibits secretion of both glucagon & insulin. Ovaries and Testes (Gonads & Placenta) Female gonads (ovaries) are_paired oval bodies located in the pelvic cavity. They roduce the female sex hormones oestrogens and progesterone. Along with FSH a LH from the anterior pituitary, the female sex hormones regulate menstrual cycle, maintain pregnancy and pre; mammary glands for lactation. Male gonads (testes) located_in_extra-abd ominal_skin_pouch called scrotum. they are ‘oval glands that lies in the seéfeitoh? They produce testosterone, that regulates roduction of sperm and stimulates the develo, ment_and maintenance of masculine characteristics such as beard growth, and deepening of the voice. 0 draag Pineal gland [vires ) 4 2eceetes maarorin Pineal gland is a small body attached to the roof of the third ventricle, It is about LOmm, ea long. Themain hormone secreted by the pineal gland is Melatonin, The secretion is high ight and lowest around midday, The functions of melatonin are not. clearly understood, but it contribute to setting the ’s biological clock and inhibits gro and development of the sex organs before puberty, & . ' ‘Thymus gland r r Ke ‘Thymus ies in the mediastis ind the sternum and extends to the root of the “neckIt weighs about 10 to 15g at birth and grows until puberty when it begins, to, “atrophy.-Thymosin is the hormone secreted by-the thymus-gland and is involved inthe “development of T-lymphocytes for cell mediaced immunity, Other hormones secreting organs Some organs other than those usually classified as endocrine glands have an endderine function and secrete hormones. Table below shows some of the hormones, orgin of production and actions. e 1