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| - | ==Endocrine histology==
| + | 3MlH0I I`m so grateful that you enlightened me and the most important thing that it happened in time. Just think, I have been using the internet for six years already but it`s the first time I`ve ever heard about it!... |
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| - | ===Describe the structural organization of the endocrine system===
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| - | *The endocrine has several specific characteristics:
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| - | **cells of epithelial origin secrete hormones onto endothelial tracts (that is, the blood stream)
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| - | **hormones act at distance sites defined by having the receptor for the hromone
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| - | **secretory cells are localized to endocrine organs
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| - | **hormones can be classified into one of several grooups: amino acids, peptides, steroids, or proteins / glycoproteins
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| - | *Note that exocrine glands secrete onto an epithelial surface that is usually in the form of a duct whereas endocrine glands secrete into the blood stream.
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| - | **Furthermore, both exocrine glands and endocrine glands are usually on the '''outside of the basement membrane''' relative to the blood.
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| - | **Therefore, exocrine glands do not secrete across the basement membrane.
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| - | **However, '''endocrine glands often must secrete their hormones across the basement membrane'''.
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| - | ===Define components of the endocrine system===
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| - | *There are three types of endocrine components: full endocrine organs, endocrine components as part of other solid organs, and diffuse endocrine components.
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| - | *Full endocrine organs are those organ in which the primary function is to synthesize, store, and secrete hormones.
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| - | **Think pituitary gland.
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| - | *Endocrine components as part of a solid organ are those organs in which there are '''clusters of endocrine cells'''.
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| - | **Think pancreas.
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| - | *Diffuse endocrine components occur when individual endocrine cells are scattered (or clumped) within an extensive epithelium.
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| - | **Think adipose tissue and sabaceous glands.
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| - | ===Describe the embryonic origin, histological organization, and hormone secretion of the endocrine system===
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| - | ====Origin, organization, and secretion of the hypothalamus====
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| - | *The hypothalamus resides in the lower, central part of the brain and houses '''neurosecretory neurons''' that produce hormones.
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| - | *Neurosecretory neurons secrete hormones into the '''hypothalamic-hypophysis portal system''', a double capillary bed that facilitates potent delivery of hormones from the hypothalamus to the hypophysis (pituitary).
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| - | *The hypothalamus releases 5 hormones from three nuclei (dorsal medial, ventral medial, and infundibular nuclei):
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| - | **GnRH (gonadotropin releasing hormone) which stimulates gonadotropes of the anterior pituitary to release LH and FSH.
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| - | **TRH (thryroid releasing hormone) which stimulates thyrotropes and mammotropes (lactotropes) of the anterior pituitary to release TSH and PRL.
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| - | **PIF (prolactin inhibitory factor, dopamine) which inhibits lactotropes ('''mammotropic cells''') of the anterior pituitary from releasing PRL.
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| - | **CRH (corticotropin releasing hormone) which stimulates corticotropes of the anterior pituitary (adenohypophysis) to transcribe POMC and release '''ACTH and beta-LPH'''.
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| - | **GHRH (growth hormone releasing hormone) which stimulates somatotropes of the anterior pituitary.
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| - | **SST (somatostatin) which '''inhibits''' somatotropes and thyrotopes of the anterior pituitary (adenohypophysis) to release GH and TSH.
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| - | *The hypothalamus also contains two more nuclei that produce two other hormones that are delivered directly to the posterior pituitary (neurohypophysis) through the axons of the neuron cells that produce the hormones.
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| - | **The '''supraoptic neucleus''' produces vasopressin (ADH, AVP) which acts on the collecting ducts of the kidney (think AQ2).
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| - | **The '''paraventricular nucleus''' produces oxytocin which acts on the mammary glands (myoepithelial cells) and uterus (smooth muscle cells, contractions).
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| - | ***Oxytocin may be associated with increased generocity.
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| - | ====Origin, organization, and secretion of the pituitary gland (hypophysis)====
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| - | *The hypophysis (pituitary gland) is located below the brain in the '''sella turcica, a cavity of the sphenoid bone'''.
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| - | *The hypophysis has two regions: the adenohypophysis (anterior pituitary) and the neurohypophysis (posterior pituitary).
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| - | **The adenohypophysis originates from the oral ectoderm.
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| - | ***This makes sense because it has "ad" "deno" which means "toward the teeth".
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| - | **The neurohypophysis originates from the brain.
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| - | ***This makes sense when one recalls that it is the posterior pituitary (neurohypophysis) into which neurons from the hypothalamus directly connect and directly release hormones.
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| - | ***Also, knowing that the neurohypophysis (posterior pituitary) originates from brain tissue makes sense because one of the hormones released by the posterior pituitary (neurohypophysis) has a very neurotransmitter-like role: oxytocin causes muscle contraction.
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| - | *The pituitary gland's two divisions have several components:
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| - | **The anterior pituitary consists of the pars distalis and the pars tuberalis.
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| - | **The pars intermedia separates the two functional units.
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| - | **The posterior pituitary (neurohypophysis) is made up of the pars nervosa and the infundibular stalk.
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| - | *The infundibulum is the combination of the infudibular stalk and the pars tuberalis, from the neurohypophysis and adenohypophysis, respectively.
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| - | http://academic.kellogg.edu/herbrandsonc/bio201_mckinley/f20-4_pituitary_gland_c.jpg
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| - | http://www.ouhsc.edu/histology/Glass%20slides/38_11.jpg
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| - | *Embryology of the pituitary gland
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| - | **Recall that the adenohypophysis arises from the oral ectoderm.
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| - | ***The oral ectoderm (roof of the mouth) grows caudally, forms '''Rathke's pouch''', and eventually separates the pouch from the oral ectoderm.
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| - | ***Recall that this caudal pouching of the oral ectoderm generates the pars tuberalis, the pars distalis, '''and the pars intermedia'''.
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| - | **Recall that the neurohypophysis arises form the brain tissue.
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| - | ***The neuroectoderm (floor of the diencephalon) grows caudally, forms a stalk, and remains attached to the brain tissue of origin.
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| - | ***Recall that this caudal stalk formation generates the pars nervosa, the median eminance, '''and the median eminence'''.
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| - | http://www.cytochemistry.net/endocrine_system/pitdraw2.jpg
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| - | =====Adenohypophysis (anterior pituitary)=====
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| - | *The adenohyophysis is composed of the pars distalis, the pars tuberalis and the pars intermedia.
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| - | **'''The pars distalis is the same as the anterior lobe'''.
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| - | *The pars distalis (anterior lobe):
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| - | **The pars distalis is composed of '''fibroblast generated reticular fibers''' that support hormone-generating epithelial cells and a rich bed of '''fenestrated capillaries'''.
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| - | **Cells of the pars distalis can be classified by the way the stain: basophilic, acidophilic, and chromophobes.
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| - | **Acidophilic cells: somatotropes and mammotropes (lactotropes).
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| - | **Basophilic cells: gonadotropes, croticotropes, and thyrotropes
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| - | **Chromophobic cells: stem cells, degranulated cells that would otherwise be chromophilic (see acidophilic and basophilic).
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| - | **'''Differentiating cell types is not possible with light microscope''', only by trasmission electron microscopy can these hormone producing cells be differentiated.
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| - | http://embryology.med.unsw.edu.au/histology/endocrine/hya40he.jpg
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| - | *The pars tuberalis:
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| - | **This is a funnel shaped structure that surrounds the infudibular stalk of the neurohypophysis.
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| - | **Most cells of the pars tuberalis are '''basophilic'''.
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| - | *The pars intermeida:
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| - | **The pars intermedia the lumenal remnant of the pouch part of Rathke's pouch.
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| - | **The pars intermeida separates the pars distalis of the adenohypophysis and the pars nervosa of the neurohypophysis.
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| - | **Colloid-filled cysts fill the pars intermedia.
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| - | =====Neurohypophysis (posterior pituitary)=====
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| - | *The neurohypophysis is derived from the neuroectoderm and contains two major regions: the pars nervosa and the infundibular stalk.
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| - | *The neurohypophysis contains '''nerve cells and glial cells (pituicytes)'''.
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| - | *The pars nervosa:
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| - | **The pars nervosa contains fibroblasts, pituicytes, mast cells and neurons.
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| - | **The neurons arise from the paraventricular and supraoptic neuclei where oxytocin and vasopressin are made, respectively.
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| - | **These neurons are atypical in that they do not synapse at their distal axons.
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| - | **The '''hormones released by these neurons are stored in granules (called Herring bodies or neurosecretory bodies''') at the distal aspect of the axon.
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| - | ***Herring bodies can be identified under light microscopy.
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| - | *The infundibular stalk
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| - | **The infundibular stalk, like the pars nervosa, contains atypical nerve axon endings that release hormones.
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| - | **The neurons of the infundibular stalk release their hormones into the hypothalamus-pituitary portal system and affect the cells of the anterior pituitary.
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| - | =====Pituitary portal system=====
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| - | *There are superior, middle, and inferior hypophyseal arteries that service the adenohypophysis.
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| - | *There are really 4 main components to the portal system: primary and secondary capillary beds, long veins and short veins.
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| - | *The primary capillary bed arises from the superior hypophyseal artery and resides around the median eminance.
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| - | **At the primary capillary bed, neurons of the hypothalamus dump hormones into the blood stream.
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| - | *The long veins connect the primary capillary bed to the secondary capillary bed.
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| - | *The secondary capillary bed resides around the adenohypophysis.
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| - | **At the secondary capillary bed, hormones from the hypothalamus exit to affect the cells of the anterior pituitary and hormones form the anterior pituitary (adenohypophysis) enter the blood stream.
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| - | *The inferior hypophyseal artery forms a capillary mesh at the neurohypophysis.
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| - | *The short veins connect the capillaries of the neurohypophysis to the secondary capillary bed of the adenohypophysis.
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| - | **It is unclear if there is a particular function associated with this connection between the neurohypophysis and adenohypophysis.
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| - | =====Clinical correlate: growth hormone deficiency=====
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| - | *Growth hormone deficiency results in low levels of GH release and therefore low levels of IGF1, IGF2, and IGF-binding protein 3 from the liver.
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| - | *Decreased levels of IGFs results in decreased growth and stature and delayed physical maturation.
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| - | ====Origin, organization, and secretion of the Adrenal glands====
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| - | *The adrenal glands sit atop the kidneys and have an outer shell and two functional compartments.
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| - | **The outer shell is made of dense connective tissue that sends '''septa into the center of the organ as trabechulae'''.
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| - | **The two functional units are the cortex and the medulla.
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| - | ***The cortex and the medulla have different embryological origins and different functions and morphology.
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| - | http://www.histology-world.com/photomicrographs/adrenallabel.jpg
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| - | =====Adrenal cortex=====
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| - | *The adrenal cortex is derived from '''mesoderm''' (connective tissue progenitor).
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| - | *The adrenal cortex has three layers from superficial to deep: glomerulosa, fasciculata, and reticularis.
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| - | **GoFaRe: Glomerulsoa, Fasciculata, Reteicularis
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| - | **GomiFacoRea: glomerulus-mineralocorticoids, fasciculata-corticoids, reticularis-androgens.
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| - | http://ouhsc.edu/histology/Glass%20slides/39_11.jpg
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| - | http://ouhsc.edu/histology/Glass%20slides/39_03.jpg
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| - | *The glomerulosa:
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| - | **The glomerulosa sits just below the adrenal capsule and is responsible for '''mineralocorticoid production'''.
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| - | **The glomerulosa layer is characterized by '''closely-packed, arched chords of columnar or pyramidal cells''' surrounded by '''capillaries'''.
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| - | **The glomerulus can be differentiated from the capsule because of increased cellularity, prominent, circular nuclei, prominent arches, less connective tissue (which usually stains bright pink).
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| - | *The fasciculata:
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| - | **The fasciculata sits just below the glomerulosa layer and is responsible for production of '''glucocorticoids''' and a small amount of sex steroids.
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| - | **The fasciculata is characterized by '''long chords of polyhedral cellls''' and '''fenestrated capillaries'''.
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| - | **The fasciculata can be differentiated from the glomerulosa by distinct change in from short, bulbous cellular collections to long chord-like cellular collections.
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| - | *The reticularis:
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| - | **The reticularis deepest (below the fasciculata) and is responsible for production of '''androgens''' which can also be converted to '''estrogens'''.
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| - | ***Note that the reticularis mostly produces '''dehydroepiandosterone''' (a weak androgen) that can be converted into more potent androgens and then on to estrogens.
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| - | **The reticularis can be differentiated from the fasciculata by less organized cellular collections, more eosinophilic staining (pinker, think about the granules of norepi and epi),
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| - | http://www.vet.uga.edu/vpp/clerk/groover/Fig1.jpg
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| - | http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_%26_Physiology/A%26P202/Endocrine_System/histology_jpgs/adrenal_40x_P2252261lbd.JPG
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| - | http://wikis.lib.ncsu.edu/images/7/7a/Adrenalcortex.JPG
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| - | http://www.udel.edu/biology/Wags/histopage/colorpage/cen/cenzgf.GIF
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| - | http://withfriendship.com/images/i/43179/adrenal-medulla-hormones.jpg
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| - | =====Adrenal medulla=====
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| - | *The adrenal meduall is derived from the '''neural crest''' and is responsible for making norepinephrine and epinephrine.
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| - | **This makes sense because norepi and epi are neurotransmitters.
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| - | *The medulla of the adrenal is composed of '''chromaffin cells''' which can be considered like post-ganglionic neurons.
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| - | **That is, preganglionic neurons synapse on chromaffin cells just like a pre-ganglionic neuron would synapse onto a postganglionic neuron.
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| - | *Chromaffin cells can either be '''norepinephrine producing or epinephrine producing''' and will have '''granules full of their labors'''.
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| - | **There is an association between the chromaffin's product and it's tissue location.
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| - | **Norepinephrine-producing neurons are found near medullary arteries.
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| - | **Epinephrine-producing neurons are found near cortical sinuses.
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| - | *Chromaffin cells stain lightly with euchromatin chunks visible in the nucleus.
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| - | *Cell density within the medulla is less than that of the cortex.
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| - | http://wikis.lib.ncsu.edu/images/5/50/Adrenalmedu.jpg
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| - | http://www.deltagen.com/target/histologyatlas/atlas_files/endocrine/adrenal_gland_medulla_40x.jpg
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| - | http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab24/IMAGES/ADMEDULL.jpg
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| - | http://histology-world.com/photoalbum/albums/uploads/normal_medulla40X_lbl.jpg
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| - | ====Origin, organization, and secretion of the Pancreas====
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| - | *Recall that the pancreas is a mixed organ (exocrine and edocrine) with exocrine acinar tissue making up the primary structure.
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| - | **Recall that acinar of the exocrine tissue secrete gastric enzymes onto an epithelial duct system that enters the epithelium of the GI tract.
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| - | *The endocrine portion of the pancreas arises '''from endodermal tissue near the bile duct'''.
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| - | **The notes also say that the endocrine protion arises '''from epithelium of the gut'''.
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| - | *The '''islets of Langerhans are the endocrine portion of the pancreas'''.
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| - | *The islets of langerhans are '''surrounded by a capsule of reticular fibers''' that separate them from the exocrine tissue.
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| - | *There are four cell types in the endocrine islets of langerhans: beta, alpha, delta, and F / pp cells (by abundance).
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| - | *Beta cells make insulin.
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| - | *Alpha cells make glucagon.
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| - | *Delta cells make somatostatin.
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| - | *F / pp cells make pancreatic peptide.
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| - | *Islets of Langerhans are generally easily recognized as they stain a different shade or hue than the exocrine acinar tissue of the exocrine pancreas.
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| - | http://www.daviddarling.info/images/islets_of_Langerhans.gif
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| - | http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/islets.jpg
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| - | http://www.medicalhistology.us/twiki/pub/Main/ChapterThirteenSlides/b36_interlobular_duct_pancreas_10x_labeled.jpg
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| - | http://www.ric.edu/faculty/ptiskus/Stem_Cells/Image3.gif
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| - | ====Origin, organization, and secretion of the Thyroid====
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| - | *The thyroid gland originates from the '''foregut endoderm''', near the base of the tongue.
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| - | *The thyroid gland sits anterior to the larynx in the cervical area.
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| - | *The parenchyma of the thyroid gland is composed of epithelial cell funtional units called follicles.
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| - | **Parenchyma: "the functional part of an organ, as opposed to supporting tissue; the tissue making up most of the non-woody parts of a plant" per [http://en.wiktionary.org/wiki/parenchyma wiktionary]
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| - | **Thyroid follicles have a simple epithelial ring of cells and a lumen within that is filled with colloid.
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| - | *'''Within or between''' the follicles can be found '''C cells (parafollicular cells)''' which produce '''calcitonin'''.
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| - | **Recall that calcitonin regulates serum calcium by decrease absorption at the gut, decreasing reabsorption at the bone, and increase excretion at the kidney.
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| - | *Thyroid hormones are T3 and T4.
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| - | *Iodide is required for production of T3 and T4.
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| - | *Production, storage, and release of thyroid hormones '''involves both endocrine and exocrine functions'''.
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| - | *Synthesis of T3, T4:
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| - | **Thyroglobulin made in RER, glycocylated in RER / golgi, and moved into the lumen.
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| - | **Iodide absorbed at basolateral surface (from blood) and oxidized at apical surface.
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| - | **Tyrosine residues of thyrogobulin iodinated at apical surface of follicular epithelial cells.
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| - | **Thyroglobulin pinocytized by follicular cells, fused with lysosomes, cut up to release T3 and T4.
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| - | **T3 / T4 released into blood at basolateral surface.
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| - | http://img.tfd.com/vet/thumbs/gr387.jpg
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| - | http://legacy.owensboro.kctcs.edu/gcaplan/anat2/histology/thyroid4F.jpg
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| - | http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/Endocrine_System/histology_jpgs/thyroid_400x_P2252255lbd.JPG
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| - | http://ouhsc.edu/histology/Glass%20slides/42_04.jpg
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| - | http://www.drharper.ca/images/HPT%20Axis.gif
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| - | ====Origin, organization, and secretion of the Parathyroid glands====
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| - | *The Parathyroid gland '''arises from the pharyngeal pouches'''.
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| - | *Like the adrenal glands, the parathyroid glands have a '''capsule with septa that run inward'''.
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| - | *The parathyroid gland is composed of two cell populations: chief cells and oxyphil cells.
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| - | *Chief cells:
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| - | **Chief cells produce '''PTH which serves to increase serum''' by increasing absorption at the gut (via increased activation of vitD to 1,25 vitD), increasing reabsorption at the bone, and decreasing loss at the kidney.
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| - | **Chief cells '''contain granules eosinophilic granules of PTH'''.
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| - | **Note that regulation of chief cell PTH release is an '''inhibition of inhibitoin mechanism: when serum Ca levels decrease, fewere Ca-receptors bind Ca (the ligand) causing a decrease in intracellular signaling and an increase of PTH release'''.
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| - | *Oxyphil cells:
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| - | **The function of oxyphil cells is unknown; however it is known that they arise during puberty.
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| - | **Oxyphil cells are '''larger than chief cells''' with an acidophilic cytoplasm and '''abnormally shaped mt'''.
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| - | **Oxyphil cells are often found in clusters at the center of the parathyroid gland or near the perimeter.
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| - | http://www.ouhsc.edu/histology/Glass%20slides/40_06.jpg
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| - | http://www.bu.edu/histology/i/15002loa.jpg
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| - | http://neuromedia.neurobio.ucla.edu/campbell/endocrines/wp_images%5C137_cells.gif
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| - | http://legacy.owensboro.kctcs.edu/gcaplan/anat2/histology/Image514.gif
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| - | =====Primary hyperparathyroidism=====
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| - | *Primary hyperparathyroidism is a defect with the parathyroid itself causing an '''an elevation of PTH'''.
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| - | **Elevated PTH causes increased bone reabsorption, decreased stature, fractures, et cetera.
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| - | *Animals infused with Ca had more trabeculae, increased bone density, and shorter bone length.
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| - | *Giving PTH intermittently to post-menopausal women is associated with decreased risk of bone fracture.
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| - | **This makes sense when you understand that '''continuous administration of PTH causes bone loss yet intermittent PTH administration causes increases in bone mass'''.
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| - | ====Origin, organization, and secretion of the Pineal gland====
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| - | *The pineal gland arises from '''neuroectoderm from the floor of the diencephalon''' (just like the neurohypophysis).
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| - | *The pineal gland is pine-cone shaped and covered with connective tissue.
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| - | **This pine-cone shaped pineal gland is located in the '''posterior aspect of the third ventricle'''.
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| - | http://www.rickrichards.com/chakras/pituitary_brain2a.jpg
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| - | *The pineal gland contains pinealocytes, interstitial glial cells (like astrocytes).
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| - | *The pinealocytes produce '''melatonin''' and thus take part in daily rhythmicity.
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| - | *'''Rene Descarts''' explained human behavior and thought via the pineal gland because of its involvement in sensation, imagination, memory, and bodily movement.
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| - | http://ouhsc.edu/histology/Glass%20slides/41_02.jpg
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| - | http://embryology.med.unsw.edu.au/histology/endocrine/pin42he.jpg
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| - | ====Origin, organization, and secretion of the Diffuse Neuro-endocrine system====
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| - | *We now know that many diffuse organs contain hormone-secreting endocrine cells that are important in physiological regulation of the body.
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| - | *Organs that have diffuse endocrine tissue include the '''heart, kidney, thymus, gut, and gonads'''.
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| - | *We often think of this diffuse set of endocrine cells as having '''primarily paracrine effects''' on nearby cells of the host tissue (like cardiomyocytes in the heart, etc.).
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| - | *An example of these diffuse endocrine cells...
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| - | Get duodenum and cardiac examples form audio.
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| - | =====Bone as an endcrine organ=====
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| - | *We are beginning to understand that bone is an important regulator of aspects of physiology.
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| - | *Two major signals are released by bone to affect physiology: FGF23 and uOCN.
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| - | *FGF23 is released by the bone and causes:
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| - | **Kidneys decrease phosphate (Pi) reabsorption resulting in decreased serium Pi.
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| - | **Kidneys decrease 1,25VitD activation resulting in decreased serum 1,25OH VitD.
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| - | *uOCN is released by the bone and causes:
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| - | **Pancreatic beta cells to increase insulin release resulting in decreased serum glucose.
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| - | **Adipocytes to increase adiponectin resulting in changes to glucose and fatty acid catabolism.
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| - | **Muscle to increase sensitivity to and uptake of glucose resulting in decreased serum glucose.
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| - | *Bone also releases '''osteocalcin''' which has been shown to be associated with poor fertility when deficient.
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