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BRS Cell biology and histology (7th edition): Part 2

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(BQ) Continued part 1, part 2 of the document BRS Cell biology and histology presents the following contents: Endocrine system, skin, respiratory system, digestive system - oral cavity and alimentary tract, digestive system - glands, the urinary system, female reproductive system, male reproductive system, special senses.

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Nội dung Text: BRS Cell biology and histology (7th edition): Part 2

  1. Endo crine System I. OVERVIEW-THE ENDOCRINE SYSTEM A. The endocrine system is composed of several ductless glands, cl usters of cells within certain organs, and isolated single endocrine cel ls, known as the diffuse neuroendocrine system (DNES) cells, located in the epithelial lining of the respiratory and gastrointestinal systems (discussed in chapters 15 and 1 6, respectively) . B. Glands of the endocrine system include the pituitary gland (and a region of the brain known as the hypothalamus), as well as the thyro id, parathyroid, adrenal, and pineal glands. Additional components of the endocrine system, such as the Islets of Langerhans, adipose tissue, female gonads, and male gonads, are discussed in the pertinent chapters. C. Function. The endocrine system secretes hormones into nearby capillaries and interacts with the nervous system to modulate and control the body's metabolic activities. Hormones are chemical messengers that are carried via the bloodstream to distant target cells. They include low-molecular-weight water-so luble proteins, polypeptides, and amino acids (e.g., insulin, glucagon, follicle-stimulating hormone [FSH]) and l i pid-soluble substances, principally the steroid hormones (e.g., progesterone, estradiol, and testosterone). A. Water-soluble hormones interact with specific cell surface receptors on target cells, which communicate a message that generates a biological response by the cell. 1. G protein-li nked receptors are used by some hormones (e.g., epinephrine, thyroid-stimulating hormone [TSH], serotonin). Binding of the hormone to the G protein-linked receptor leads to the production of a second messenger that evokes a target-cell response. 2. Catalytic receptors are used by insulin and growth hormone. Binding of the hormone to the catalytic receptor activates protein kinases that phosphorylate target proteins. B. Lipid-soluble hormones diffuse across the plasma membrane of target cells and bind to specific receptors in the cytosol or in the nucleus, forming hormone-receptor complexes that regulate transcription of deoxyribonucleic acid (DNA) . 221
  2. 222 BRS Cell B iology and H istology The pituitary gland lies below the hypothalamus in a bony housing known as the hypophyseal fossa, a depression in the se lla turcica of the sphenoid bone located in the base of the middle cranial fossa of the skull. The hypothalamus is a region of the diencephalon of the brain; it possesses nuclei that are struc­ turally and functionally linked to the pituitary gland. The structural link is via a series of axons whose cell bodies are located in the supraoptic and paraventricular nuclei of the hypothalamus. These axons form the hypothalamo-hypophysea l tract and terminate in the pars nervosa of the pituitary gland, where they store and, when needed, release their hormones. The functional connection is via releas­ ing hormones that are synthesized in the arcuate, pa raventri cular (and medial paraventricular), peri­ ventricular, ventromedial, and dorsal nuclei of the hypothalamus. These hormones are released by the neurons located in these nuclei, enter a capillary bed, and make their way, via the hypophyseal porta l system t o a second capillary b e d i n the anterior lobe of the pituitary gland, leave the capillary bed, and bind to their respective target cells in the anterior pituitary. The pituitary gland is a relatively small gland, weighing only about 0.6 g in men and 1 . 2 g in women who are pregnant or who have given birth to two or more children. The pituitary is divided into two major subdivisions, the adenohypophysis and the neurohypophysis (Figure 1 3 . 1 ) . Each sub­ division is derived from a distinct embryonic analog, which is reflected in its unique cellular constitu­ ents and functions. A. The adenohypophysis is also called the anterior pituitary gland (Figures 1 3 . 1 and 13.2). It originates from an ectodermal diverticulum of the stomodeum (Rathke pouch). The adenohypophysis is subdivided into the pars d ista l is, pars i ntermedia, and pars tuberalis. 1. The pars distalis is supported by a connective tissue capsule and framework. It consists of irregular cords composed of two types of parenchymal cells, chromoph ils and chromophobes, lying adjacent to fenestrated capillaries. a . Chromophils (Figures 1 3 . 1 and 13.3) (1 ) Overview. Chromophils are parenchymal cells that stain intensely because of their hormone-containing secretory granules. They synthesize, store, and release several hormones. They are regulated by specific stimulatory and inhibitory hormones produced by neurons, referred to as neurosecretory cel ls, in the hypothalamus. These hormones are conveyed to the pars distalis via a system of portal blood vessels originating in the median eminence. (2) Types. Chromophils are classified into two types, acidophils and basophils, depending on the dyes they bind using special histological stains. With hematoxylin-eosin stain, the distinction between the two cell types is much less obvious. (a) Acidophils (Tables 1 3 . 1 and 13.2) bind acidic dyes and often stain orange or red. They are small cells of two subtypes: somatotrophs and mammotrophs. 1 . Somatotrophs constitute about 50% of the chromophils and produce somatotropin (g rowth hormone). They are stimulated by somatotropi n-releasing hormone and are inhibited by somatostatin. 2. Mammotrophs (lactotrophs) constitute about 10% of the chromophil population, except in multiparous women, where they may be as high as 30%. Mammotrophs produce prolactin, which is stored in small secretory granules. They are stimulated by prolacti n-releasing hormone and thyrotropi n-releasing hormone (TRH ) and are inhibited by dopamine (until re-identified that it was designated as prolacti n-inhibiting hormone). (b) Basophils (Tables 13.1 and 13.2) bind basic dyes and typically stain blue. They include three subtypes: corticotrophs, thyrotrophs, and gonadotrophs. 1 . Corticotrophs constitute about 10% of the chromophil population. They produce pro-opiomela nocortin (POMC) whose by-products are adrenocorticotropic hormone (ACTH), melanocyte-stimulating hormone (MSH), and lipotropic
  3. l!iitJ'!1tilU Endocrine System 223 Neu rosecretory c e l l s Parave ntricular located i n hypothalamus nuclei secrete releas i n g and i n h i bitory hnnmnr''"' Hypothalamus M uscle Hyper- � glyce m i a , / Adipose JC tissue Elevation of free · � Ovu l at i o n : fatty acids Mammary p rogestero n e gland secretion Milk secretion F I G U R E 13.1 . An i l l u stratio n of the p itu ita ry g l a n d , s h owing its c o n n ecti o n s with the hypoth a l a m u s, the h o r m o n e s it r e l e a ses, a n d th e effe cts of th e s e h o r m o n e s o n o r g a n s a n d tis s u e s of the b o dy. A D H , a ntid i u reti c h o rm o n e ; ACTH, a d re n o c o rtic otro p i c h o r m o n e ; TS H , thyro i d -sti m u lati n g h o r m o n e ; FS H , fo l l i c l e -sti m u lating h o r m o n e ; LH, l ute i n iz i n g h o r m o n e . I From Gartner LP. H iatt JL. Color Atlas o f Histology. 5th ed. Baltimore. M D : Lippincott William & Wilkins; 2009:206.) hormone (LTH ), a precursor of�-endorphin. They are stimulated by corticotropin­ releasing hormone. 2. Thyrotrophs constitute about 5% of the chromophil population, produce TSH, and are stimulated by TRH .
  4. 224 BRS Cell B iology and H istology Source of hypophysiotropic hormones (releasing factors) --------,. Source of ADH and oxytocin -�·�� Wit.li?..----�--'
  5. l!iitJ'!1tilU Endocrine System 225 F I G U R E 1 3.3. A l i g ht m i c ro g r a p h of c e l l s i n the p a rs d ista l i s of th e a d e n o hy p o p hysis. The two typ es of c h ro m o p h i l c e l l s a r e e a s i ly i d e ntifi e d u s i n g th e tri c h ro m e sta i n . B a s o p h i l s ( B ) sta i n b l u e , a n d a c i d o p h i l s (A) sta i n r e d . C h r o m o p h o b e s ( C ) are smaller a n d s h ow l ittle a ffin ity for the sta i n . M a ny e ryth ro cytes (red b l o o d cells [ R B Cs]) a r e present i n th e c a p i l l a ries ( X 300). 2. The pars intermedia lies between the pars distalis and pars nervosa. a. It contains many colloid-containing cysts ( Rathke cysts) that are lined by cuboidal cells. b. It also possesses basoph i l i c cel ls, which sometimes extend into the pars nervosa. These cells secrete the prohormone POMC, which is cleaved to form ACTH, l i potropin, and MSH. I n humans, M S H acts t o induce melanocytes t o produce melanin and may act i n various ways to modulate inflammatory responses throughout the body, and it may play a role in controlling stores of body fat. 3. The pars tubera lis surrounds the cranial part of the infundibulum (hypophyseal stalk). a. It is composed of cuboidal basophilic cel ls, arranged in cords along an abundant capillary network. b. Its cells may secrete FSH and LH, but this has not been confirmed. CLI N I CAL Pituitary adenomas a re common tumors o f the a nte rior p itu ita ry. CONSID ERATIO N S 1 . They e n l a rg e a n d ofte n s u p p ress s e c reti o n s by the re m a i n i n g p a rs d i sta lis c e l l s. 2. These tu m o rs fre q u e ntly d e stroy s u r ro u n d i n g bone and n e u ra l tiss u e s and a r e treated by s u rg i c a l remova l . B. The neurohypophysis (Figures 1 3 . 1 and 13.2; Table 1 3 . 1 ) i s also called the posterior pituitary gland. I t originates from a n evagination o f the hypothalamus and i s divided into the infundibulum, which is continuous with the hypothalamus, and the pars nervosa, or main body of the neurohypophysis. 1. Hypothalamo-hypophyseal tract a. contains the unmyelinated axons of neurosecretory cells whose cell bodies are located in the supraoptic and paraventricular nuclei of the hypothalamus. b. transports oxytocin and antidiuretic hormone (AD H; vasopressin), each bound to neurophysin (a binding protein specific for each hormone) to the pars nervosa (see Table 13.2). Oxytocin binds to neurophysin I, whereas ADH binds to neurophysin II. Additionally, acetylcholine and adenosine triphosphate (ATP) are transported to the pars nervosa by the axons that compose the hypothalamo-hypophyseal tract.
  6. 226 BRS Cell B iology and H istology t a b I e 13.1 Physiolo g i c a l Effects of Pituita ry H o rmones Cell Hormone M a j o r Function Hormones released by the pars distalis Acidophils Som atotrophs Som atotro pin ( g rowth I n c re a s e s m eta bolism in m o st c e l ls; i n d i r e ctly sti m u lates hormone) e p i phys e a l p l ate, g rowth of long bones via p rod u ction of i n s u l i n - l i ke g rowth fa ctors I , I I M a m m otro p h s Prola ctin Deve l o p m e nt o f m a m m a ry g l a n d d u ring p re g n a n cy, m i l k (La ctotro p h s ) synth esis d u ri n g l a ctati o n Basophi/s C o rtic otro p h s P O M C whose ACTH sti m u lates g l u c o c o rti coid s e c reti o n by z o n a by-produ cts are fa s c i c u lata c e l l s of a d r e n a l c o rtex; ACTH, M S H , a n d M S H sti m u l ates m e l a n o cytes to m a n ufa cture m e l a n i n l i p otro p i n p i g m e nts; Lipotro p i n also sti m u l ates m e l a n o cytes to m a n ufacture m e l a nin, but also m o b i l izes l i p i d s by i n d u c i n g l i p o lysis and the fo rmation of ste roids. G o n a d otro p h s FSH Sti m u l ates g rowth of s e c o n d a ry ova rian fo l l i c les, estrog e n s e c retion i n wo m e n ; sti m u l ates s p e rmato g e n esis via produ ction of a n d ro g e n - b i n d i n g p rote i n i n S e rto l i c e l l s in men LH o r i nte rstiti a l Ovulation, fo rmation o f c o r p u s l ute um, a n d progesterone c e l l-sti m u lating s e c retion i n wo m e n ; testoste ro n e synth esis by Leyd ig hormone cells of testis i n men Thyrotro phs TSH Sti m u l ates synth esis a n d release of T3, T4 by fo l l i c u l a r cells Hormones released by the pars nervosa N e u rosec retory c e l l s of Oxyto c i n I n d u c e s c o ntra ction of smooth m u s c l e in wa l l of ute rus at hypoth a l a m u s ( p ri m a rily p a rtu rition and i n myo e p ith e l i a l c e l l s of m a m m a ry g l a n d in the pa raventri c u l a r d u ring n u rsing nucleus) N e u rosec retory c e l l s of AOH R e n d e rs kidney c o l l e cting tu b u l e s p e r m e a b l e to wate r, hypoth a l a m u s ( p rima rily wh ich is resorbed to p ro d u c e a c o n c e ntrated u rine; in the s u p ra o ptic n u c l e u s ) c o n stri cts smooth m u s c l e i n wall of a rte rioles POMC. pro-opiomelanocortin; ACTH. adrenocorticotropic hormone; MSH. melanocyte-stimu lating hormone; FSH. fol l icle-stimu lating hormone; LH. l uteinizing hormone; TSH, thyroid-sti mulating hormone; ADH. antidiuretic hormone. 2. Pars nervosa a. contains the distal ends of the hypothalamo-hypophyseal axons and is the site where the neurosecretory granules in these axons are stored in accumulations known as Herring bodies. b. releases oxytocin and ADH into fenestrated capillaries in response to nerve stimulation. 3. Pituicytes a. occupy approximately 25% of the volume of the pars nervosa. b. are glial-like cells that support axons in this region. c. possess numerous cytoplasmic processes and contain lipid droplets, intermediate filaments, and pigments. D i a b etes Insi p i d us D i a b etes i n s i p i d u s resu lts fro m i n a d e q u ate a m o u nts of AD H ; it is d i s c ussed i n C h a pter 18 V C C l i n i c a l C o n s i d e rati o n s . C. Vascularization o f t h e p ituitary g l a n d 1. Arterial supply is from two pairs of blood vessels derived from the internal carotid artery. a. The right and left superior hypophyseal arteries serve the pars tuberalis, infundibulum, and median eminence. b. The right and left inferior hypophyseal arteries serve mostly the pars nervosa.
  7. l!iitJ'!1tilU Endocrine System 227 t a b I e 13.2 Hormones of th e Hypoth a l a m u s Hormone Nucleus Primary Functions Oxyto c i n P ri m a ri ly the pa raventri c u l a r I n d u c e s c o ntraction of s m o oth m u s c l e i n wa l l nucleus of ute rus at p a rtu rition a n d i n myo e p ith e l i a l c e l l s o f m a m m a ry g l a n d d u ring n u rs i n g AD H; vasopressin P ri m a rily t h e s u p r a o ptic n u c l e u s R e n d e rs kidney c o l l e cti n g tubules p e r m e a b l e t o wate r, w h i c h is r e s o r b e d t o prod u c e a c o n c e ntrated u rine; c o n stri cts s m o oth m u s c l e i n w a l l of a rterioles CRH Arcu ate, m e d i a l pa rave ntri c u l a r, Induces the release of POMC by the a n d pe riventri c u l a r n u c l e i c o rti c otro p h s of the a nterior pitu ita ry Dopamine Arcu ate n u c l e u s I n h i b its prola ctin release by m a m m otro p h s ( l a ctotro p h s ) of the a nte ri o r pitu ita ry GnRH Arcu ate, d o rsal, p a rave ntri c u l a r, I n d u c e s the release of LH a n d FSH by a n d ve ntro m e d i a l n u c l e i g o n a d otro p h s of the a nterior pitu ita ry Som atostati n Arcu ate n u c l e u s I n h i b its som atotro p i n release by the som atotro phs of the a nterior p itu ita ry S o m atotropin-releasing factor ( S R H ) Arcu ate n u c l e u s I n d u c e s the release of som atotropin ( g rowth ( a l s o kn own a s g rowth h o r m o n e­ h o r m o n e ) by the som atotro p h s of the releasing fa ctor, G H R H ) a nterior p itu ita ry TRH D o rsal, pa rave ntri c u l a r, I n d u c e s the release of TSH by the thyrotro phs a n d ve ntro m e d i a l n u c l e i a s well a s prola ctin by the m a m m otro p h s ( l a ctotrophs) of the a nterior pitu ita ry ADH, antidiuretic hormone; CRH, corticotropi n-releasing hormone; PDMC, pro-opiomelanocortin; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; FSH, fo l l i cle-stimu lating hormone; SRH, somatotropi n-releasing hormone; GHRH, g rowth hormone-releasing hormone; TRH, thyrotropin­ releasing hormone; TSH, thyroid-stimulating hormone. 2. Hypophyseal porta l system (Figures 1 3 . 1 and 13.2) a. The primary capillary p l exus consists of fenestrated capillaries coming off the superior hypophyseal arteries. (1 ) This plexus is located in the median eminence, where stored hypothalamic neurosecretory hormones enter the blood. (2) It is drained by hypophyseal portal vei ns, which descend through the infundibulum into the adenohypophysis. b. The secondary capil lary plexus consists of fenestrated capillaries derived from the hypophyseal portal veins. This plexus is located in the pars distal is, where neurosecretory hormones leave the blood to stimulate or inhibit the parenchymal cells. CLI N I CAL S h e e h a n Synd rome CONSID ERATIO N Sheehan syndrome is n e c rosis of the a nteri o r p itu ita ry g l a n d due to a s u d d e n re d u ctio n i n b l o o d p re s s u re of th e n ewborn as a result of p o st­ p a rtum h e m o rrh a g e . Th e b u l k of the a nte rior p itu ita ry b e c o m e s n e c roti c a n d o n ly th e p e r i p h e r a l p a r e n c hy m a l c e l l s re m a i n h e a lthy a n d vi a b l e . The f u n cti o n a l ity o f the a d e n o hy p o p hysis d e p e n d s o n th e seve rity o f t h e n e c roti c eve nt; the wid e r t h e p a r e n c hym a l d e stru cti o n , the l e s s fun cti o n r e m a i n s . I nte resti n g ly, the n e u rohypop hysis is u s u a lly u n affe cte d b e c a u s e i t h a s a d iffe rent b l o o d s u p p ly. Hemosiderosis Patie nts affl i cted with hemochromatosis ( i ron overl oad), wh eth e r a s a fun cti o n of h e re d ity or a c q u i re d due to m u lti p l e tra n sfusions, p re s e nt with iron d e posits i n the p itu ita ry g l a n d , e s p e c i a l ly i n the g o n a d otro p h s . This c o n d ition is known a s hemosiderosis a n d is fortu n ately tre ata b l e e ith e r b y p h l e b otomy o r by c h e l ati n g th e iron with o n e of the ava i l a b l e c h e lati n g a g e nts i n the p h a rm a c e uti c a l a r m a m e nta ri u m .
  8. 228 BRS Cell B iology and H istology D. Regulation of the pars dista lis (Figures 13.1 and 13.2) 1. Neurosecretory cells in the hypothalamus synthesize specific hormones that enter the hypophyseal portal system and stimulate or inhibit the parenchymal cells of the pars distalis (see Table 13.2). 2. The hypothalamic neurosecretory cells in turn are regulated by the level of hormones in the blood (negative feedback) or by other physiological (or psychological) factors. 3. Some hormones (e.g., thyroid hormones, cortisol) exert negative feedback on the pars distalis directly. The thyroid gland is composed of two lobes connected by an isthmus. It is surrounded by a dense irregular collagenous connective tissue capsule, in which (posteriorly) the parathyroid glands are embedded. The thyroid gland is subdivided by capsular septa into lobules containing follicles. These septa also serve as conduits for blood vessels, lymphatic vessels, and nerves. A. Thyroid fol l i cles are spherical structures filled with colloid, a viscous gel consisting mostly of iodinated thyrog lobulin (Figure 13.5) 1. Surrounding the colloid within each follicle is a single layer of epithelial cells, called follicular cel ls. In addition, one or more parafo l l icular cells occasionally lie sandwiched between the follicular cells. Both of these parenchymal cell types rest upon the basal lamina surrounding the follicle, which separates them from the abundant network offenestrated capillaries in the connective tissue. 2. Function. Thyroid follicles synthesize, store, and release thyroid hormones. B. Fol l icular cells (Figure 13.6) 1. Structure a. Follicular cells are normally cuboidal, but they become columnar when stimulated and squamous when inactive. b. They possess a distended rough endoplasmic reticulum (RER) with many ribosome­ free regions, a supranuclear Golgi complex, many lysosomes, and rod-shaped mito chondria. c. Follicular cells also contain many small apical vesi cles, which are involved in the transport and release of thyroglobulin and enzymes into the colloid. d. They possess short, blunt microvilli that extend into the colloid. 2. Synthesis and release of the thyroid hormones thyroxine (T4) and tri iodothyronine (T3) occur by the sequence of events illustrated in Figure 13.7. These processes are evoked by TSH, which binds to G protein-linked receptors on the basal surface of follicular cells. CLI N I CAL G raves disease i s c h a ra cterized by a d iffus e enlargement o f t h e thyroid CONSID ERATI O N S gland and protrusion of the eyeballs ( exo p hth a l m i c g o iter). 1. This d i s e a s e is a s s o c iated with th e prese n c e of c o l u m n a r-sh a p e d thyro i d fo l l i c u l a r c e l ls, exc essive p rod u ction of thyro i d h o r m o n e s, a n d d e c re a s e d a m o u nts of fo l l i c u l a r c o l l o i d . 2. It is c a u s e d b y th e b i n d i n g o f a uto i m m u n e i m m u n o g l o b u l i n G ( l g G ) a nti b o d i e s t o TS H re c e pto rs, w h i c h sti m u l ates th e thyro id fo l l i c u l a r c e lls. Additi o n a l ly, infl a m m ato ry c e lls, s u c h as T c e l ls, n e utro p h i ls, and m a c ro p h a g es, inva d e the c o n n e ctive tissues of th e retro-orbita l r e g i o n a n d r e l e a s e cyto ki n e s that a ctivate fi b ro b l a sts n ot o n ly t o i n c re a s e th e i r prod u ctio n o f p rote o g ly c a n s b ut a l s o t o d iffe re ntiate i nto f a t c e l l s . S i n c e p rote o g ly c a n s re a d i ly attra ct N a + i o n s wh i c h attra ct wate r m o l e c u l es, th e c o n n e ctive tissue vo l u m e i n c re a ses; m o reover, th e a d d itio n a l n u m b e r of fat c e l l s also a cts to i n c re a s e th e vo l u m e of the retro-o rb ita l c o n n e ctive tissue, putti n g i n c re a s e d press u re o n th e b a c k o f the eye b a l l , p u s h i n g i t fo rwa rd, res u lti n g i n p rotru sion of the eye.
  9. l!iitJ'!1tilU Endocrine System 229 Suprarenal Cortex G land Zona reticularis Zona fasciculata :---'i'----- Ne u roglial cell P i nealocytes F I G U R E 1 3.4. A d i a g ra m showing features of th e thyro id, p a rathyro i d , a d re n a l , and p i n e a l g l a n d s . ( From Gartner LP, H iatt JL. Color Atlas of Histology. 5th ed. Baltimore. M D : Lippincott W i l l iam & Wilki ns; 2009:207 ) C. Parafo l l icular cells are also called clear (C) cells because they stain less intensely than thyroid follicular cells (Figures 13.5 and 13.8). 1. Parafollicular cells are present singly or in small clusters of cells between the follicular cells and basal lamina. 2. These cells belong to the population of O N ES cel ls, previously known as amine precursor uptake and d ecarboxylation (APUD) cells, or enteroendocrine cells.
  10. 230 BRS Cell B iology and H istology FIGURE 13.5. A l i g ht m i c ro g r a p h showing fo l l i c l e s with i n the thyro i d g l a n d . Each fo l l i c l e is s u rro u n d e d by a layer of fo l l i c u l a r c e l l s (F) and c o nta i n s a c e ntra l c o l l o i d -fi l l e d re g i o n ( C ) . The fo l l i c u l a r c e l l s synth esize a n d s e c rete thyro i d h o r m o n e s b o u n d with i n a l a rg e p rote i n m o l e c u l e , thyro g l o b u l i n , w h i c h m a kes u p m ost o f the c o l l o i d . A s e c o n d typ e o f e n d o c ri n e c e l l , t h e pa rafo l l i c u l a r c e l l ( P ). i s a l s o p r e s e nt i n th e thyro i d g l a n d . It h a s n o c o ntact with the c o l l o i d a n d is often fo u n d i n s m a l l c l u sters at o r n e a r the b a s a l s u rfa c e s of th e fo l l i c u l a r c e lls. The pa rafo l l i c u l a r c e l l synth esizes c a l c ito n i n a n d re l e a s e s i t i nto the r i c h n etwork of c a p i l l a ries ( arrows) existi n g betw e e n th e fo l l i c l e s ( X 1 50). FIGURE 13.6. E l e ctron m i c ro g r a p h of thyro i d fol l i c u l a r c e l ls. Two l a rg e colloid d r o p l ets ( C D ), a d iste n d e d ro u g h e n d o p l a s m i c reti c u l u m ( R E R ) with m a ny ribosome-free r e g i o n s , a n d a G o l g i a p p a ratu s ( G ) a re o b s e rved. M i c rovilli (MV) exten d i nto th e l u m e n of a fo l l i c l e - c o nta i n i n g c o l l o i d ( C ) . Also present a r e mito c h o n d ri a ( M ), a n u c l e u s ( N ), a n d a d e s m o s o m e ( D ) ( X 7,500).
  11. l!iitJ'!1tilU Endocrine System 231 Iodinated thyroglobu l i n in colloid Lysosome � 0 coalescing with -� .-------'\ colloid droplet �t • o :::! Apical 0 . . . . ��0 0 Ox1dat1on of 10d1de � vesicle • ' &... �� -·� · � • � 0 0 Galactose # release thyroid I � add1t1on I Mannose incorporation Protein ---� - � � t;? C:? (;J synthesis V -- · . Amino acids Thyroid-stimulating hormone Iodide bound to receptor F I G U R E 1 3.7. Synth esis a n d re l e a s e of T4 a n d T3 by fo l l i c u l a r c e l l s of the thyro i d g l a n d . A. Thyro g l o b u l i n is synth esized l i ke oth e r s e c reto ry p rote i n s . Circ u l ati n g iodide o-l is a ctively tra n s p o rted i nto th e cytos o l via s o d i u m - i o d i d e sym p o rt­ e rs, so that the i o d i d e c o n c e ntrati o n in the folli c u l a r c e l l s b e c o m e s 20 to 30 ti m e s g reater th a n it i s in the b l o o d . I o d i d e l e aves th e fo l l i c u l a r c e l l t o e n t e r t h e c o l l o i d via pendrin, a n i o d i d e- c h l o r i d e tra n s p o rter. A t t h e s a m e ti m e , n o n i o d i n ated thyroglobulin, p a c k a g e d with th e e n zyme thyroid peroxidase i s a l s o b e i n g r e l e a s e d into the c o l l o i d . At th e c o l l o i d fo l l i c u l a r c e l l i nte rfa c e , thyro i d p e roxi d a s e oxidizes th e i o d i d e to f o r m i o d i n e ( I ) a n d i o d i n ates tyros i n e re s i d u e s o n t h e thyro g l o b u l i n m o l e c u l e , form i n g m o n o i o d otyro s i n e a n d d i i o d otyros i n e r e s i d u e s ; the refo re, i o d i n ation o c c u rs m o stly a t the a p i c a l p l a s m a m e m b r a n e . A rearra n g e m e nt, by oxid ative c o u p l i n g , of the n e i g h b o ri n g i o d i n ated tyrosine res i d u e s o f thyro g l o b u l i n i n the c o l l o i d p r o d u c e s tri iodotyrosine (T3) a n d tetraiodotyrosi ne (14, thyroxine). B. B i n d i n g o f thyro id -sti m u l ati n g h o r m o n e t o r e c e ptors o n th e b a s a l s u rfa c e sti m u l ates fol l i c u l a r c e l l s t o b e c o m e c o l u m n a r a n d to form a p i c a l p s e u d o pods, w h i c h e n g ulf c o l l o i d by e n d o cyto sis. Afte r th e c o l l o i d d ro p l ets fuse with lysosomes, c o ntro l l e d hydro­ lysis of i o d i n ated thyro g l o b u l i n l i b e rates T3 and T4 i nto the cyto s o l . These h o r m o n e s m ove b a s a lly and are re l e a s e d b a s a l ly to e nte r the b l o o d stre a m a n d lym p h atic vessels, wh e re they b i n d with the c a rr i e r p rote i n , thyroxi n e - b i n d i n g g l o b u l i n , that ferries the h o r m o n e s to th e i r ta rget c e l l s . ( Adapted with perm ission from Junqueira LC. Carneiro J. Kel l ey R O . Basic Histology. 9th ed. Stamford. CT: Appleton & Lange; 1 998:403, and from Fawcett OW. Bloom and Fawcett. A Textbook of Histology. 1 2th ed. New York, NY: Chapman & Hall; 1 994:496.) 3. They possess elongated mitochondria, substantial amounts of RER, a well-developed Golgi complex, and many membrane-bound dense secretory granules. 4. They synthesize and release calcitonin, a polypeptide hormone, in response to high blood calcium levels. D. Physiological effects of thyroid hormones 1. T4 and T3 act on a variety of target cells. These hormones increase the basa l metabolic rate and thus promote heat production. They have broad effects on gene expression and the induction of protein synthesis. T4 has a much longer half-life (approximately 6 days vs. less than a day) but is much less active than T3. Both hormones have to enter the nucleus to perform their function. 2. Calcitonin functions primarily to lower blood calcium levels by inhibiting bone resorption by osteoclasts. CLI N I CAL Simple goiter (enlargement o f the thyro id g l a n d ) is c a u s e d b y i n s uffi c i e nt CONSID ERATIO N S i o d i n e ( < 1 0 � g/day) in the d i et. 1 . It is u s u a l ly n ot asso c i ated with e ith e r hyp e rthyro i d i s m or hyp othyroi d i s m . 2 . S i m p l e g o iter is treated by a d m i n istratio n of d i eta ry i o d i n e .
  12. 232 BRS Cell B iology and H istology F I G U R E 13.8. E l e ctron m i c ro g r a p h of a p a rafo l l i c u l a r cell ( c l e a r cell, C c e l l ) i n the thyro i d g l a n d . This cell l i e s b etwe e n the fo l l i c u l a r cells (F) with i n the basal l a m i n a ( B L) e n ve l o p i n g the fo l l i c l e . Its n u c l e u s (N) d i s p l ays a n u c l e o l u s ( arrow) , and its cyto p l a s m possesses e l o n g ated m ito c h o n d ria ( M ) . In response to h i g h levels of c a l c i u m in the b l o o d , the p a rafol l i c u l a r c e l l r e l e a s e s the h o r m o n e c a l c ito n i n by exocyto sis of t h e d e n s e g r a n u l e s ( G ) i n its cyto p l a s m . T h e c a l c ito n i n e nters n e a rby fe n e strated c a p i l l a ri e s and l owers b l o o d c a l c i u m levels by i n h i b iti n g o ste o c l a st b o n e reso rpti o n thro u g h o ut the body ( X 7,000). A. Overview 1. The parathyroid glands are four small glands that lie on the posterior surface of the thyroid gland, embedded in its connective tissue capsule. 2. They have a parenchyma composed of two types of cells, ch ief cells and oxyphil cel ls. 3. They are supported by septa from the capsule, which penetrate each gland and also convey blood vessels (Figure 13.4) into its interior. 4. They become infiltrated with fat cells in older persons, and the number of oxyphil cells also increases. B. Chief cells are small basophilic cells arranged in clusters (Figure 13.9). 1. Chief cells form anastomosing cords, surrounded by a rich, fenestrated capillary network. 2. These cells possess a central nucleus, a well-developed Golgi complex, abundant RER, small mitochondria, glycogen, and secretory granules of variable size.
  13. l!iitJ'!1tilU Endocrine System 233 F I G U R E 1 3.9. A l i g ht m i c ro g r a p h of the p a rathyroid g l a n d . C h i ef c e l l s ( C ) a re s m a l l b a s o p h i l i c c e l l s a r r a n g e d in c o rd s a l o n g c a p i l l a ri e s . T h e y synth esize a n d s e c rete pa rathyro i d h o r m o n e t h a t r a i s e s b l o o d c a l c i u m l e v e l s prima rily by m o b i l izing c a l c i u m from the bone. Oxy p h i l cells ( 0 ) a r e a l s o present i n the p a rathyroid g l a n d . They a re a c i d o p h i l i c , much l a rg e r th a n t h e c h ief c e lls, a n d few i n n u m b e r, b u t they i n c re a s e i n n u m b e r with a g e . Oxy p h i l s c o nta i n m a ny l a rg e e l o n g ated m ito c h o n d ri a , but the fun cti o n of th e s e c e l l s is not known (X 1 50). 3. Function. They synthesize and secrete parathyroid hormone (PTH, or parathormone), which raises blood calcium levels. High blood calcium levels inhibit the production of PTH. The hormone acts on osteoclasts (see Chapter 7 II C 4 and II J) and also induces the decrease in calcium excretion by the thick ascending limb of Henle loop. 4. Mechan ism. The cell membrane of chief cells possesses a transmembrane Ca2 + receptor (CaSR) that binds calcium ions. In the presence of calcium ions, CaSR activates G proteins that shut off the release of parathormone, whereas if calcium ions do not bind to CaSR, the inhibitory activity of the G protein is suppressed and the chief cell releases parathormone. C. Oxyph i l cells are large, eosinophilic cells that are present singly or in small clusters within the parenchyma of the gland (Figure 13.9). 1. Oxyphil cells possess many large, elongated mitochondria, a poorly developed Golgi complex, and only a limited amount of RER. 2. Their function is not known. D. PTH functions primarily to increase blood calcium levels by indirectly stimulating osteoclasts to resorb bone. In concert with calcitonin, the hormone produced and released by the C cells of the thyroid gland, PTH provides a dual mechanism for regulating blood calcium levels. A near absence of PTH (hypoparathyroidism) may be caused by accidental surgical removal of the parathyroid glands, which leads to tetany, characterized by hyperexcitability and spastic skeletal muscle contractions throughout the body. CLI N I CAL Hyperparathyroid ism is overa ctivity o f the p a rathyroid g l a n d s, CONSID ERATIO N S resulti n g in excess s e c retio n of PTH a n d c o n s e q u e nt b o n e reso rpti o n ( s e e C h a pte r 7 II J 1 ) . 1 . Hyperpa rathyro i d i s m is a s s o c i ated with high blood calcium l evels, wh i c h m ay l e a d to d e position of c a l c i u m s a lts in the k i d n eys a n d the w a l l s of b l o o d vessels. 2. It may b e c a u s e d by a benign t u m o r of th e p a rathyroid g l a n d s .
  14. 234 BRS Cell B iology and H istology Adrenal glands lie embedded in fat at the superior pole of each kidney. They are derived from two embryonic sources : the ectodermal neural crest, which gives rise to the adrenal medulla, and the mesoderm, which gives rise to the adrenal cortex. The adrenal glands are invested by their own collagenous capsule. A. The adrenal cortex ( Table 13.3) contains parenchymal cells that synthesize and secrete but do not store various steroid hormones. The production of steroid hormones is dependent on a specific protein, steroidogenic acute reg ulatory protei n (StAR) that facilitates the transport of cholesterol across the outer membranes of mitochondria. The adrenal cortex is divided into three concentric histologically recognizable regions: the zona g lomerulosa, zona fasciculata, and zona reticularis ( Figure 13. 10) . 1 . Zona glomerulosa a. synthesizes and secretes mi neralocorticoids, mostly aldosterone and some deoxycortico­ sterone. Hormone production is stimulated by angiotensin II and ACTH. b. is composed of small cells arranged in arch-like cords and clusters. These cells have a few small lipid droplets, an extensive network of smooth endoplasmic reticulum (SER), and mitochondria with shelf-like cristae. 2. Zona fasciculata a. synthesizes and secretes g l ucocorticoids, namely cortisol and corticosterone. Hormone production is stimulated by ACTH ( Figure 13. 1 1) . b. is composed o f columns of cells and sinusoidal capillaries oriented perpendicularly t o the capsule. c. cells contain many lipid droplets and ( in tissue sections ) appear so vacuolated that they are called spongiocytes ( Figure 13. 12). These cells also possess spherical mitochondria with tubular and vesicular cristae, SER, RER, lysosomes, and l ipofuscin pigment g ranules. 3. Zona reticularis a. synthesizes and secretes weak androgens ( mostly dehydroepiandrosterone and some androstenedione) and perhaps small amounts of glucocorticoids. Hormone production is stimulated by ACTH. b. is composed of cells, arranged in anastomosing cords. Many large lipofusc in pigment g ranules are common in these cells ( Figure 13. 12) and are believed to represent lipid­ containing residues oflysosomal digestion. t a b I e 13.3 Adrenal G l a n d Cells and H o rmones Cell H ormone Function Adrenal cortex Zona g l o m e ru l osa M i n e r a l o c o rti c o i d s (mostly a l d oste ron e ) R e g u l ate e l e ctro lyte, wate r b a l a n c e via effect on c e l l s of re n a l tu b u l e s Zona fa s c i c u l ata G l u c o c o rti c o i d s ( c o rtisol, c o rti c o ste rone) R e g u late c a rbohyd rate meta b o l i s m b y p romoting g l u c o n e o g e nesis; promote breakd own of proteins, fat; a nti·infl a m m ato ry properties; s u p press i m m u n e response Zona reti c u l a ris We a k a n d ro g e n s ( d e hyd roepiand roste rone, Promote m a s c u l i n e c h a ra cteristi c s a n d roste n e d i o n e ) Adrenal medulla C h rom affi n c e l l s E p i n e p h ri n e Fig ht·o r·fl i g ht response; i n c reases h e a rt rate and fo rce of contra ction; relaxes b ro n c h i o l a r smooth m u s c l e ; promotes glyc o g e n o lysis and l i p o lysis N o r e p i n e p h ri n e Littl e effe ct on c a rd i a c o utp ut, rarely u s e d c l i n i c a l ly
  15. F I G U R E 13.10. A l i g ht m i c ro g r a p h of the a d r e n a l g l a n d s h ow i n g the d iffe re nt regions of the c o rtex ( CTX) a n d a p o rti o n of the m e d u l l a ( M E D ) . C e l l s in the outermost z o n a g l o m e ru l o s a (ZG ) a r e a r r a n g e d in c l u sters a n d s e c rete m i n e ra l o c o rti c o i d s ; c e l l s i n th e m i d d l e z o n a fasc i c u l ata ( Z F ) a r e a rra n g e d i n c o rd s between s i n u s o i d a l c a p i l l a ri e s a n d s e c rete g l u c o c o rti c o i d s a n d a s m a l l a m o unt o f a n d ro g e ns; a n d c e l l s o f the i n n e rm o st z o n a reti c u l a ri s ( Z R ) a re a rr a n g e d i n a n a sto m o s i n g c o rd s a n d s e c rete a n d ro g e n s a n d s m a l l a m o u nts of g l u c o c o rti c o i d s . C e l l s i n the a d r e n a l m e d u l l a ( M ), c a l l e d c h ro m affi n c e l ls, synth esize, sto re, and s e c rete e p i n e p h ri n e and n o r e p i n e p h r i n e ( X 1 6). Gonadal axis Adrenal axis Hypothalamus C P ulsatile c:::::J c:::::J c:::::J GnRH agon ists / Chronic c:=====:-�==� I I I I I I I I �� e: 21 (/J f 01 '/ii i �: I I (] �Testis Ovary Adrenal gland F I G U R E 13.11. R e g u l ati o n of g l u c o c o rti c o i d s e c reti o n by the a d r e n a l c o rtex via sti m u lati o n by c o rtic otro p i n - r e l e a s i n g h o r m o n e a n d a d re n o c o rtic otro p i c h o r m o n e (ACTH ) a n d the n e g ative feed b a c k of c o rtis o l at b oth the p itu ita ry a n d t h e hypoth a l a m i c l e v e l s . G n R H , g o n a d otro p i n - r e l e a s i n g h o r m o n e ; C R F, c o rtic otro p i n - r e l e a s i n g fa cto r; FSH, fo l l i c l e-sti m u l ating hormone; LH, lute i n i z i n g hormone. (Reprinted with permission from Rosenfeld G. Loose D . BRS Pharmacology. 5th ed. Baltimore. M D : Wolters Kl uwer Hea lth/Lippi ncott Williams & Wilkins; 2009:21 8 ) 235
  16. 236 BRS Cell B iology and H istology !' . F.Z::.\ . F I G U R E 13.12. C e l l s of the zona fa s c i c u l ata a n d z o n a reti c u l a ri s a re shown in this very low-power e l e ctron m i c ro g r a p h . Zona fa s c i c u l ata (ZF) c e l l s a re called s p o n g i o cytes b e c a use of their a p p e a ra n c e, wh i c h is c a used by the extra cti o n of the m a ny l i p i d d r o p l ets in th e i r cyto p l a s m that h ave b e e n removed thro u g h the process of fixati o n a n d d e hydrati o n . The s p o n g i o cytes l i e n ext to a rich n etwork of s i n u s o i d a l c a p i l l a ries ( CAP), which have been c l e a red of e rythro cytes by p e rfu s i o n . Zona reti c u l a ris (ZR) cells are a lso o b s e rved, and a few of them a re fi l l e d with l a rg e li pofu s c i n ( LF) p i g m e nt g r a n u l e s (X 1 ,500). CLI N I CAL Addison disease is c h a ra cte rized b y s e c reti o n o f i n a d e q u ate a m o u nts of CONSID ERATIO N S a d re n o c o rti c a l h o r m o n e s d u e to d e structi o n of the a d re n a l c o rtex. 1 . A d d i s o n d i s e a s e is m ost often c a u s e d by an a uto i m m u n e d is e a s e or c a n be a s e q u e l a of tu b e r c u losis. 2. This disease is l ife -th re ate n i n g a n d req u i re s ste roid treatm e nt. B. The adrenal med u l l a ( Table 13.3) is completely invested by the adrenal cortex. It contains two populations of parenchymal cells, called chromaffi n cel ls, which synthesize, store, and secrete the catecholamines epi nephrine ( approximately 80% of chromaffin cells ) and norepinephrine ( approximately 20% of chromaffin cells ) . It also contains scattered sympathetic ganglion cel ls. 1. Chromaffi n cells are large, polyhedral cells containing secretory granules that stain intensely with chromium salts ( chromaffin reaction ) . a. Chromaffin cells are arranged in short, irregular cords surrounded by an extensive capillary network.
  17. l!iitJ'!1tilU Endocrine System 237 b. They are innervated by pregan g l ionic sympathetic (chol inergic) fibers, making these cells analogous in function to postganglionic sympathetic neurons. c. They possess a well-developed Golgi complex, isolated regions of RER, and numerous mitochondria. d. They also contain large numbers of membrane-bound granules containing one of the catecholamines, ATP, enkephalins, and chromograni ns, which may function as binding proteins for epinephrine and norepinephrine. 2. Catecholamine release occurs in response to intense emotional stimuli and is mediated by the preganglionic sympathetic fibers that innervate the chromaffin cells. CLI N I CAL A pheochromocytoma is a tu m o r a ri s i n g i n cate c h o l a m i n e - s e c reti n g CONSIDERATI O N S c h ro m affi n c e l l s of the a d re n a l m e d u l l a . The tu m o r is r a r e ; i t is fo u n d i n b oth sexes, a n d 90% of the ti m e i t is b e n i g n . H oweve r, its s e c retio n o f excessive a m o u nts o f e p i ­ n e p h ri n e a n d n o re p i n e p h ri n e l e a d s t o hypertension ( e p i s o d i c o r s u sta i n e d ), a lth o u g h the pati e nt m a y r e m a i n a sym pto m ati c . I n c re a s e d levels of c ate c h o l a m i n e s a n d th e i r m eta b o l ites in the u ri n e a re d i a g n osti c o f p h e o c h ro m o cyto m a . If the tu m o r i s d etected e a rly a n d is s u r g i c a l ly removed, t h e hyp e rte n s i o n is c o rre cta b l e , b ut i f n ot, p ro l o n g e d a n d s u sta i n e d hyp e rte n s i o n m a y p rove fata l . C . B l ood supply t o t h e adrenal g l ands i s derived from the superior, middle, and inferior adrenal arteries, which form three groups of vessels : to the capsule, to parenchymal cells of the cortex, and directly to the medulla. 1 . Cortical blood supply a. A fenestrated capillary network bathes cells of the zona glomerulosa. b. Stra ight, disconti nuous, fenestrated capillaries supply the zona fasciculata and zona reticularis. 2. Medullary blood supply a. Venous blood rich in hormones reaches the medulla via the discontinuous fenestrated capillaries that pass through the cortex. b. Arterial blood from direct branches of capsular arteries forms an extensive fenestrated capillary network among the chromaffin cells of the medulla. c. Medullary veins join to form the suprarenal vein, which exits the gland. A. Overview (Figure 13.4) 1. The pineal gland projects from the roof of the diencephalon. 2. Its secretions vary with the light and dark cycles of the day, thereby regulating the individual's circadian rhythm. Although the pineal gland is buried deep within the head, it receives information about the light and dark conditions from special ganglion cells in the retina of the eye. These ganglion cells send their information about the presence of daylight via the retinohypothalamic tract that projects to the suprachiasmatic nucleus of the hypothalamus, from where information reaches the superior cervical sympathetic ganglion whose postganglionic sympathetic fibers reach the pineal gland by riding on the tunica adventitia of blood vessels that supply the pineal. 3. This gland has a capsule formed of the pia mater, from which septa (containing blood vessels and unmyelinated nerve fibers) extend to subdivide it into incomplete lobules. 4. It is composed primarily of pinealocytes, which constitute approximately 95% of the cells, and neuroglial cells (interstitial cells), which constitute about 5% of the cells. 5. It also contains calcified concretions (bra i n sand) in its interstitium. The function of these concretions is unknown, but they increase during short light cycles and decrease during periods of darkness.
  18. 238 BRS Cell B iology and H istology B. Pinealocytes are pale-staining cells with numerous long processes that end in dilations near capillaries. 1. Pinealocytes contain many secretory granules, microtubules, microfilaments, and unusual structures called synaptic ribbons. 2. These cells synthesize and immediately secrete melatonin but almost only at night. During the day, melatonin synthesis is mostly inhibited. 3. Pinealocytes may also produce arginine vasotocin, a peptide that appears to be an antagonist of LH and FSH; they also secrete small quantities of serotonin, histamine, and dopamine. Most of the serotonin manufactured by the pinealocytes is converted to melatonin in a two-step reaction, the first of which is catalyzed by the enzyme N-acetyltransferase. It is the activity of this particular enzyme that is inhibited during daylight conditions, thus preventing the formation of melatonin during daylight. C. Neurog l i a l ( interstitia l ) cells resemble astrocytes, with elongated processes and a small, dense nucleus. They contain microtubules and many microfilaments and intermediate filaments. CLI N I CAL M e l ato n i n is u s e d t o treat j et l a g a n d s e a s o n a l affe ctive d is o rd e r (SAD), CONSID ERATI O N S a n e m oti o n a l response to s h o rte r d a y l i g ht h o u rs d u ri n g the wi nte r.
  19. Review Test D irections: Each of the numbered items or incomplete statements in this section is followed by answers or completions of the statement. Select the ONE lettered answer that is BEST in each case. 1. Protein hormones act initially on target cells by 5. ACTH is produced by which of the following (A) attaching to receptors on the nuclear cells? membrane. (A) Chromophobes in the pars distalis (B) attaching to receptors in the nucleolus. (B) Neurosecretory cells in the median (C) diffusing through the plasma membrane. eminence (D) attaching to receptors on the plasma (C) Basophils in the pars distalis membrane. (D) Neurons of the paraventricular nucleus (E) attaching to receptors on the rough in the hypothalamus endoplasmic reticulum membrane. (E) Basophils in the pars intermedia 2. Which of the following statements concerning 6. The histological appearance of a thyroid adrenal parenchymal cells is true? gland being stimulated by TSH would show (A) Those of the zona fasciculata produce which of the following? androgens. (A) Decreased numbers of follicular cells ( B ) Those of the adrenal medulla produce (B) Increased numbers of parafollicular cells epinephrine and norepinephrine. (C) Column-shaped follicular cells (C) Those of the zona glomerulosa produce (D) An abundance of colloid in the lumen of glucocorticoids. the follicle ( D ) Those of the cortex contain numerous (E) Decreased numbers of parafollicular secretory granules. capillaries (E) Those of the zona reticularis produce mineralocorticoids. 7. A 40-year-old woman is diagnosed with Graves disease. Which of the following 3. Characteristics of pinealocytes include characteristics would be associated with which one of the following? her condition? (A) They produce melatonin. (A) Inadequate levels of iodine in her diet (B) They resemble astrocytes. (B) Weight gain (C) They contain calcified concretions of (C) Flattened thyroid follicular cells unknown function. (D) Excessive production of thyroid hormones (D) They act as postganglionic sympathetic cells. (E) Increased amounts of follicular colloid (E) They are unaffected by dark and light cycles. 8. Which one of the following hormones 4. Prolactin is synthesized and secreted by lowers blood calcium levels by inhibiting which of the following cells? bone resorption? (A) Acidophils in the pars distalis (A) Calcitonin (B) Basophils in the pars tuberalis (B) Epinephrine (C) Somatotrophs in the pars distalis (C) Parathyroid hormone (D) Basophils in the pars intermedia (D) Prolactin (E) Gonadotrophs in the pars distalis (E) T3 239
  20. 240 BRS Cell B iology and H istology 9. A 5 1 -year-old man underwent surgery 10. Which one of the following hormones for removal of a carcinoma on his trachea. plays a role in regulating body temperature by After surgery, he suffered excessive nervous­ promoting heat production? ness, muscle cramps, and spasmodic skeletal (A) Calcitonin muscle contractions in his arms, legs, and feet. (B) Epinephrine Laboratory tests revealed markedly low levels (C) Parathyroid hormone of calcium in his blood. Treatment with intrave­ (D) Prolactin nous calcium and vitamin D led to recovery in (E) Triiodothyronine ( T3 ) a few weeks. Which one of the following condi­ tions is responsible for these symptoms in this patient following surgery? (A) Hypothyroidism (B) Hyperthyroidism (C) Hypoparathyroidism (D) Graves disease (E) Hyperparathyroidism
ADSENSE

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