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Endocrine system glands
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Endocrine System
Ductless Glands
Secret Hormones That Bind To Specific
Receptors on Plasmalemma (Cytoplasmic)Hormones Pass Via Blood To DistantTarget Cells.
Interact with CNS Autonomic That SecretNeurotransmitters.
Always Have Rich Blood Supply
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Endocrine Vs CNS
Endocrines
Hormones
Via Blood
Slow Response
Relatively continuous
AN. System
Neurotransmitters
Local Synapse NMJ
Rapid Response
AS Needed.
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Targetcells
Endocrinecells
NeuronNerve impulse
Neurotransmitter
Hormone inbloodstream
Endocrine System vs Autonomic Nervous
System
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Endocrine Organs Hypothalamus- neuroendocrine gland
Anterior pituitary gland- endocrine gland
Posterior pituitary gland- neuroendocrine gland
Thyroid gland- endocrine gland
Parathyroid glands- endocrine gland
Adrenal gland (cortex and medulla)- endocrine/neuroendocrine gland
Pancreatic islets- endocrine/exocrine gland
Gonads- Ovaries in females; Testes in males- endocrine/exocrine glands
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Hormones
Chemicals
Proteins/Polypeptides: Insulin, FSH.
Amino Acid Derivative: Thyroxine.
Steroids: Progesterone, Testosterone.
Binding of Hormone-Receptor Results inActivation of Signal Transduction Cascade.
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Hormones
Hormone-Receptor Complex Initiate
Phosphorylation Chain.
Second Messengers are Released As cAMP,
cGMP.
Feed Back Mechanism (Positive/Negative)
between Target Cells & Glands
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An intracellular
signaling cascade
Fig. 15-7, p. 487
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Three classes of cell-surface receptors (cont'd)
Fig. 15-12, p. 491
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Three classes of cell-surface receptors
Fig. 15-12 a&b, p. 491
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Types of Endocrine Glands
Three types of glands:1. Pure endocrine glandsthyroid, parathyroid,
adrenal cortex, thymus and pineal.
2. Endocrine/exocrine glandspancreas, ovaries and
testes
3. Neuroendocrine glandsadrenal medulla and
hypothalamus (supraoptic nuclei and
paraventricular nuclei) to posterior pituitary.
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Pituitary Gland (Hypophysis)
Measures 1.00-1.5 * 0.5 cm.
Weighs about 5 gm
Lies Below Hypothalamus & Attached to InferiorSurface of Brain by Infundibulum.
Located in Sella Turica of Sphenoid Bone &
Lined By Dura Matter CalledDiaphragma Sellae
Develop From Oral Ectoderm (Adenohypophysis
& Neural Ectoderm (Neurohypophysis)
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Pituitary Relations
Anteriorly: Sphenoid Sinus (Site Access of
Surgical Operations.
Posterior: Basilar Artery &Pons.
Superior: Diaphramma Sellae which
separates it from Optic Chiasma.
Inferior: Body of Sphenoid & Sinus.
Lateral: Cavernous Sinus & its Contents
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Function Pituitary Gland
Its Hormones RegulateGrowth, Metabolism &Reproduction.
Regulated By Signals ORHormones ofHypothalamus
Hypothalamus Monitorshormones level.
Hypothalamus is TheCNS Center of
Homeostasis.
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The Hypothalamus & Pituitary
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Parts of Pituitary Gland or Hypophysis
Location: Sits in the sella turcica of the sphenoid bone Attached to the hypothalamus by the infundibulum
Consists of two lobes:
1. Adenohypophysis
Releases 7 different hormones
Consists of 3 divisions: pars tuberalis, pars intermedia and pars
distalis (anterior lobe).
2. NeurohypophysisReleases 2 different hormones
Consists of 3 divisions: median eminence, infundibular stalk and
pars nervosa (posterior lobe)
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Pituitary gland
Adenohypophysis
Pars tuberalis
Pars intermedia
Pars distalis
Neurohypophysis
Median eminence
Infindibular stalkPars nervosa
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Pituitary Gland
2-Lobes:
a. Anterior
(Adenohypophysis)
b. Posterior
(Neurohypophysis)
Anterior
Posterior
Middle
Pituicyte
Nuclei
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Anterior Pituitary Hormones
There are seven anterior pituitary hormones:Thyroid stimulating hormone (TSH)*
Growth hormone (GH)
Adrenocorticotropic hormone (ACTH)*Melanocyte stimulating hormone (MSH)
Follicle stimulating hormone (FSH)*
Luteinizing hormone (LH) = ICSH in males*Prolactin (PRL)
* indicate trophic hormones
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Hypothalamic releasing hormones Release of anterior pituitary hormones is directed by specific
releasing hormones (factors) from the hypothalamic nuclei. All of these are polypeptide molecules.
TRHthyrotropin releasing hormone (TSH and PRL)
GHRHgrowth hormone releasing hormone (GH)
Somatostatininhibits release of growth hormone
CRHcorticotrophin releasing hormone (ACTH)
MRH- melanocyte releasing hormone (MSH)
MIF- inhibits release of MSH
GnRHgonadotropin releasing hormone (FSH/LH)
PRHprolactin releasing hormone (PRL)
PIHprolactin inhibiting hormone (dopamine)
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Anterior/Posterior Pituitary CirculationBlood flow to pituitary gland is via a portal circulation the
hypophyseal portal. Arterial flow is via superior and inferior
hypophyseal artery into capillary beds in series
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Posterior Pituitary HormonesADH an Oxytocin are secreted by neurosecretory cells in the
paraventricular and supraoptic nuclei of the hypothalamus and aretransported to posterior pituitary via hypothalamohypophyseal
tract.
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Neurohypophyseal Hormones Antidiuretic hormone (ADH)produced by supraoptic
nuclei in the hypothalamus.
Consists of 9 amino acids
Reduces the excretion of water by kidney collectingducts; increases cuddling and grooming behavior.
Oxytocinproduced by the paraventricular nuclei in the
hypothalamusConsists of 9 amino acids, but differs from ADH.
Induces smooth muscle contraction; increases cuddlingand grooming behavior.
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Pituitary Histology
Made of Cords of Cells.
Surrounded by
Fenestrated Sinusoids
Two Types of Cells Basedon Affinity to Dyes
Chromophils VsChromophobes.
Chromophils are majorType of Pars Distalis
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Anterior Pituitary
The anterior pituitary
is composed of the
stained-richchromophils and the
clear chromophobes.
Of the chromophils,
acidophils are red andbasophils are blue.
Ant.Post
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Types of Ant.Pituitary Cell
(Distalis) Acidiphils:
Sommatotrophs
Mammotrophs
Basophils:
Corticotrophs.
Thyrotrophs. Gonadotrophs
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Chromophobes
Have Scanty
Cytoplasm Hence No
Stain. Small Cells.
Maybe Degranulated
Chromophils
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Pars Intermedia/Zona Intermedia
Pars Intermedia/ZonaIntermedia
Lies Between Pars
Distalis & Pars Nervosa. Contain Cysts Remnant
of Rathks Pouch
Made of Cuboidal-Cell
Lined Cysts.
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Pars Intermedia/Zona Intermedia
Cells Stain Basophilic& Arranged In Cords.
SynthesizeMelanocyte-Stimulating Hormone.
Stimulate Melanin
Production. May Stimulate
Prolactin Secretion
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Hypthalamo-Hypophyseal
Tract
Unmylinated Axons of
Cells From Supraoptic &
Paraventricular Nuclei of
Hypothalamus EnterPosterior Pituitary &
Terminate Near
Capillaries
These Tracts Constitutethe Bulk of Post. Pituitary.
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Supraoptic & Paraventricular
Cells of Supraoptic &
Paraventricular SecretAnti-diuretic (ADH)
& Oxytocin
Hormones
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Pars Nervosa (Post. Pituitary)
This is Not A True Endocrine Gland But Continuation ofHypothalamohypophy-seal Tract.
Store Secretions of Their Cell-Bodies
Pituicytes are Glia-Like Cells That Support Those Axons. Pituicytes Occupy 25% of Pars Nervousa
Form Sheats Around Axons
Axons Contain Membrane-Bound Granules of ADH &
Oxytocin In Separate Axons. Chrome-Hematoxyline staining Show Blue Black
Distension in Axons Called Herring Bodies.
Are Non-Secretory Granules
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Pars Nervosa (Post. Pituitary)
Herring bodies (arrow) are
the dilated hypothalamic
nerve terminals from the
hypothalamus from whichthe posterior pituitary
actually releases ADH &
Oxytocin. ADH and
Oxytocin are releasedfrom different Herring
bodies reflecting their
separate cells of origin.
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Growth Hormone
Effects of Growth Horme:
Generalized Increase in Cellular Metabolic
Rate.
Induce Somatomedins leading To
Stimulation of Epiphyseal Growth Plate
Length Hence Bone Growth
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Clinical Applications
Pituitary Adenomas are common tumors. Extension of those tumors cause Pressure Effects on
neighboring structure as Optic Chiasma (visual fielddefects would be bitemporal hemianopia).
Tumors can grow up into the 3rd ventricle causinghydrocephalus.
Rapid lateral expansion, perhaps due to hemorrhagemay compress the 3rd, 4th & 6th cranial nerves.
Headache may be present from stretch of the meninges.Surgery to remove pituitary tumors is usuallyperformed through the sphenoidal sinus.
Diabetes Insipidus: ADH supression causing Polyurea
& Dehydration.
Th id Gl d
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Thyroid Gland
Two Lateral lobes connected by an Isthmus.
Each lobe is about 5 cm. long; its greatest width is
about 3 cm
Upper Limit at level offifth or sixth tracheal ring
Lower Limit at level ofjunction of the middle
with the lower third of the thyroid cartilage
It Weighs about 30 grams. It is slightly heavier in
the female, in whom it becomes enlarged during
menstruation and pregnancy.
Isthmus: second and third rings of the trachea
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Thyroid Gland
The only Gland That
Stores inactive
Secreted Hrmones. Secrets Tri-
iodothyronine-T3 &
Thryoxine-T4 &
Calcitonin
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Thyroid Histology
Functional Unit Called
Follicle
Contain HomogenousColloid.
Septi From Inner
Fibro-elastic Capsule
Divides it into Lobules
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Thyroid Follicles
Colloid material is
Thyrogobulin.
Follicles surroundedby Simple Cuboidal
Epithelium.
Active Follicles
Smaller & CuboidalCells Taller
Th id l d
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Thyroid gland
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Follicular Cells
Thyroglobulin synthesized in Follicular cells
Packed & Released into Lumen Via Apical
Plasma Membrane. Basal PM of Follicular cells has Sodium/Iodide
Pumps to import Plasma Iodide inside where its
levels is 20-40 Folds that of Plasma.
Basal PM of Follicular cells also has Receptors forTSH.
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Parafollicular Cells
Within Interfollicular
Spaces
Present As Individual or
in Clumps
Clear Cells.
Secret Calcitonin.
Regulate Serum Calcium
Levels.
Inhibits Rates of
Decalcification of Bones
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Parafollicular Cells
The C-cells secrete calcitoninwhich helps lower calciumlevels by inhibiting osteoclasticactivity of bone resorption .
These C-cells are actuallynamed for being "clear" (as inlighter staining). Notice thatthey are in the interstitium anddo not normally touch the
follicles
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Clinical Application
Levels of thyroxin affect Metabolic Rate.
If increased it increase CHO and Fatty
Acids Metabolism. Decrease Body Weight.
Increase Heart Rate, Respiration, Muscular
Activity leading to Fatigue & Tremors. Impotence in Males & Menstrual
Disturbances in Females.
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Parathyroid gland
Located On The Posterior Lateral Margins of the thyroidgland are 4 to 8 small nodules.
Structure is small ovoid nodules ~ 2-5 mm x 3-8 mm.
Produces Parathyroid Hormone (PTH) which helps
regulate blood Ca++ levels.
Target organs of PTH are Bone, Kidneys And Intestines.
Histologically it contains numerous small chief cells and
rare large oxyphilic cells.Chief cells secrete PTH.
Oxyphilic cells are probably inactive or immature chief cells.
P th id l d
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Parathyroid glands
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Parathyroid
Embedded Within
Thyroid Capsule.
Septi Divides it into
Lobules.
Has 2-Types of Cells:
Chief (Principal) Cells
&
Oxyphil Cells.
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Parathyroid
Oxyphil Cells:
Less in Number.
Larger in Size. Occur in Clumps.
Dense EosinophilicNuclei.
Number Increase withAge. No HormoneSecretion
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Parathyroid
Cell Arranged asstring-likearrangement of the
parathyroid cells onthe right. The large,clear cells to the leftare oxyphil cells They
are found only inhumans and increasewith age.
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Pancreas
Elongated StructureLies in the Epigastric& Left Hypochondriac
Regions. Retroperitoneal on
Posterior AbdominalWall & CrossesTranspyloric Plane.
Has: Head, Body &Tail
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Pancreas
Both Exocrine (EnzymesHydrolyze Fats, Proteins& CHO)
& Endocrine GlandIslets of LangerhansProduce Insulin &Glucagon HormonesBoth Regulate CHO
Metabolism.
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Pancreas
Pancreas stained
with H&E, serves
both endocrine and
exocrine functions.
The round islets of
Langerhans are the
endocrine portionand serve to identify
pancreatic tissue.
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Pancreas
Islets are distinguished from thesurrounding exocrine tissue by:
a continuous CT capsule and an
extensive microvascular in the
center of the islet. Center is rich in B or beta
(insulin) cells
Periphery where most of the A
or alpha (glucagon) cells arelocated. Within the islet, the
glucagon-secreting alpha cells
stain red while the insulin-
secreting beta cellsstain blue.
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Adrernal Glands
2-Retroperitoneal Glands.Rt one Lies on Upper Poleof Rt-Kidneys, Left oneAlong upper medial border
of Left Kidney. Renal Fascia Surrounds
Them.
Perirenal Fat Separatesthem From Kidney.
Rt. Gland Pyramidal inShape
Lt. Gland is Crescent inShape.
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Adrenals
Adrenal Cortex
Same Origin AsGonads SecretsSteroid Hormones;Mineralocorticoids,Glucuocorticoids &Sex Hormones.
Regulated By PituitaryTrophic HormoneACTH
Adrenal Medulla
Same Origin asSymathetic NervousSystem (SNS)
SecretsCatecholamine;Adrenalin &Noradrenaline
Regulated By SNS
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Adrenals
A Capsulated Organ
Main 2-Layers:
Outer Dense Cortex
&
Inner Pale Medulla
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Layers of AdrenalCortex:
1. Zona Glomerulosa:Cells Arranged inIrregular ClumpsSeparated by Trabeculae
Zona Fasciculata:Widest Layer, CellsArranged in Cords.
Zona Reticularis:Thinner Inner Most,Cells in IrregularBranching Cords
ZG
ZF
ZR
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Adrenal
Zona Glomerulosa: Cells;Round Strongly Stained Nuclei.
Very Little Cytoplasm.
Secrets Mainly Adosterone
Zona Fasciculata: One Cell Thick Cords.
Large Cells & Abundant Poorly
Stained Cytoplasm
Secrets Glucocorticoids MainlyCortisol
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Adrenals
Zona Reticularis
Branching Irregular
Cords of Cells. Cells Smaller & Stain
Strongly.
Secrets Very Little
Androgen &
Glucocorticoids
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Adrenal Medulla
Composed ofClosely Packed Basophilic
Secretory Cells.
Supported By Collagenous CT ContainingNumerous Fenestrated Sinusoids.
Many Venous Channels Draining into
Central Medullary Vein