Endocrine organs

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Endocrine organs

Transcript of Endocrine organs

Page 1: Endocrine organs

Endocrine organs

Page 2: Endocrine organs

Endocrine organ classification

Central organs: hypothalamus, hypophysis, pineal gland

Peripheral organs: thyroid gland, parathyroid glands, adrenals

Mixed organs: pancreas, gonads, placenta

Diffuse neuroendocrine or APUD system

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Endocrine gland tissue composition Nerves tissue:

hypothalamus neurohypophysis pineal gland adrenal medulla

Epithelial tissue:adenohypophysis thyroid gland parathyroid glands adrenal cortex

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Endocrine organs are ductless glands

Contain rich network of blood sinusoidal fenestrated capillarieslymphatic capillaries

Release hormones into the blood, lymph, and intracellular spaces

Hormone chemistry: steroidsproteins glycoproteins amino acid derivatives

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Endocrine system is regulating and controlling body system

Hormones act on specific target cells interact with cell receptors (surface or nuclear) alter the target cell biological activity

Control mechanisms: (a) endocrine (b) paracrine(c) autocrine

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Hypothalamus

Contains nuclei of neurosecretory cells

Nuclei with large cells: Paraventricular nucleiSupraoptic nuclei

Nuclei with small cells:Dorsomedial nucleiVentromedial nucleiArcuate or Infundibular nuclei

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Neurosecretory cells secrete hormones

Neurosecretory cell axons leave the hypothalamus terminate on blood capillaries form the axovasal synapses in the neurohemal organs

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Neurohemal organs contain axovasal synapses

Pars nervosa Median eminence

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Hypothalamus nuclei with large neurosecretory cells

Paraventricular nuclei oxytocin Supraoptic nuclei ADH

Neurosecretory cell axons pass through the pituitary stalk

(hypothalamohypophysial tract) enter the pars nervosa form axovasal synapses

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Hypothalamus nuclei with small neurosecretory cell

Secrete adenohypophyseal tropic hormones: releasing (liberins) inhibiting (statins)

Neurosecretory cell axons: form axovasal synapses in the median eminenceon capillaries of the primary capillary network

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Hypophysis (pituitary gland)

lies beneath the brain is connected with the hypothalamus

hypothalamohypophysial neuroendocrine system

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Hypophysis anatomical subdivision

Neurohypophysis (nerves tissue) Pars nervosa (posterior lobe) InfundibulumAdenohypophysis (epithelial tissue) Pars distalis (anterior lobe) Pars intermedia Pars tuberalis

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Hypophysis development

Neuroectoderm neurohypophysis Ectodermal epithelium of the oral cavity

adenohypophysis

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Pars nervosa is not endocrine gland is the neurohemal organ stores and releases hormones

from the hypothalamus nuclei

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Pars nervosa histology

unmyelinated nerve fibers glial cells – pituicytes blood capillaries

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Pars nervosa nerve fibers

are axons of the neurosecretory cellsfrom supraoptic and paraventricular nuclei

of the hypothalamus

form hypothalamohypophyseal tract convey hormones to the pars nervosa form axovasal synapses on capillaries

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Herring bodies

are dilated axon terminals accumulate secretory granules release hormones to the bloodstream

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Pars nervosa hormones

ADH Oxytocin

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Adenohypophysis

is true endocrine gland produces and releases hormones

Hormone chemistry:small proteinsglycoproteins

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Adenohypophysis histology

endocrine epithelial cells (glandulocytes) loose connective tissue trabeculae sinusoidal fenestrated capillaries

cells are arranged in adenomeres

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Pars distalis cell types

Acidophils Basophils Chromophobes

acidophils and basophilscontain secretory granules

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Pars distalis cell hormones

Acidophils GH (STG) PL (LTH)

Basophils TSH LH and FSH ACTH

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Pars distalis chromophobes lack secretory granules

are partially degranulated secretory cells

some of them are stem cells

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Adenohypophysis pars intermedia

Endocrine cells surround the colloid-filled cysts pseudofollicles secrete hormones

MSH LPH

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Adenohypophysis vascularization

superior hypophyseal artery

primary capillary network in the median eminence

portal veins

secondary capillary network in the adenohypophysis

hypophyseal veins

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Adenohypophysis portal system

Scanning EM

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Portal system transports hypothalamic hormones

neurosecretory cells release liberins statins

in primary capillary network

portal veins

secondary capillary network of the adenohypophysis

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Adenohypophysis is regulated by hypothalamic hormones

Liberins and statins leave the secondary capillaries stimulate or inhibit adenohypophysis cells

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Thyroid gland

is located in anterior portion of the neckon the thyroid cartilage and upper trachea

consists of two lateral lobesisthmuspyramidal lobe (may or may not be)

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Thyroid histologic composition follicles connective tissue stroma capillaries

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Follicles are the thyroid morpho-functional units

are spherical cyst-like compartments consist of

basal lamina epithelial cells - thyrocytes colloid

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Thyroid follicles are surrounded by rich capillary network

capillaries arefenestrated sinusoidal

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Thyrocytes or follicular cells

are epithelial cells arise from the endoderm are cuboidal in shape rest on the basal membrane are in contact with the colloid

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Thyrocytes secrete protein hormones

Thyroxine (tetraiodothyronine) – T4

Triiodothyronine – T3

Hormones regulate cell and tissue basal metabolism cell growth and cell differentiation

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Colloid takes part in hormone synthesis

Colloid contains thyroglobulin - iodinated glycoprotein several enzymes

Thyroglobulin is inactive storage form of the thyroid hormones

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synthesis and secretion of thyroglobulin concentration of iodide, oxidation to iodine, and release to the colloid formation of T3 and T4 hormones by iodination resorption of colloid by endocytosis release of hormones from cells into circulation

resorption vacuoles

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Hyperfunction and hypofunction of the thyroid gland

Hyperfunction HypofunctionFollicular cell shape Columnar Flat

Follicle diameter Smaller Larger

Colloid volume Decreases Increases

Resorption vacuoles More in number Less in number

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Thyrocytes are the adenohypophysis-dependent cells

are stimulated by TSH from the pars distalis release of T3 and T4 is regulated by

a simple feed-back system

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Parafollicular cells or C-cells

arise from the neural crest occur in follicle wall or interfollicular spaces contain numerous secretory granules

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Parafollicular cells secrete protein hormone calcitonin

lowers the blood calcium level

suppresses bone resorption stimulates bone calcification

are the adenohypiphysis-independent cells are regulated by the blood calcium level

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Parathyroid gland

are two pairs: superior and inferior associated with the thyroid

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Parathyroid gland histology

epithelial endocrine cells loose connective tissue sinusoidal fenestrated capillaries

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Endocrine cells are arranged in cords

Principal or chief cells parathyroid hormone (PTH) Oxyphil cells (unknown function)

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Parathyroid hormone is antagonist to calcitonin increases the blood calcium level

stimulates bone resorption reduces the kidney calcium excretion activates the intestine calcium absorption

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Parathyroid gland is the adenohypophysis-independent is directly regulated by the blood calcium level

Simple feedback system:

low calcium levels

stimulate PTH secretion

high calcium levels

inhibit PTH secretion

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Adrenal (suprarenal) glands

are paired glands are located at the kidney superior poles

are subdivided in cortex and medulla

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Adrenal gland blood vessels

Short cortical arteries

cortical capillaries

medullary capillaries medullary veins

Long cortical arteries

medullary capillaries

medullary veins

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Adrenal gland vascularization

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Adrenal cortex

arises from the mesoderm consists of epithelial cells secretes steroid hormones is adenohypophysis-dependent

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Adrenal cortex zonation

Zona glomerulosa

Zona fasciculata

Zona reticularis

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Zona glomerulosa

cells are arranged in ovoid clusters secretes mineralocorticoids (aldosterone) is regulated by renin-angiotensin system

and ACTH

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Aldosterone effects

stimulates sodium resorption and potassium excretion in the kidney, salivary glands and sweat glands

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Zona fasciculata

cells are arranged in long straight cords

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Zona fasciculata cell ultrastructure

is characteristics of steroid-secreting cells: well-developed SER numerous mitochondria with tubular

and vesicular cristae well-developed Golgi complex numerous lipid droplets

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Zona fasciculata secretion

secretes glucocorticoids (cortisol, corticosterone) hormone effects:regulate gluconeogenesis and glycogenesisdepress immune and inflammatory response

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Regulation of Zona fasciculata activity

is under control of ACTH

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Zona reticularis

cells are arranged in anastomosing cords

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Zona reticularis secretion

secretes weak androgens (dehydroepiandrosterone)

is under ACTH control

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Adrenal medulla

arises from the neural crest consists of modified neural cells secretes catecholamine hormones is adenohypophysis-independent

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Adrenal medulla cells

are called chromaffin cells secrete norepinephrine and epinephrine

are regulated by preganglionic sympathetic nerve fibers glucocorticoids induce norepinephrine to epinephrin conversation

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Adrenal medulla hormone effects

rise in blood pressure dilation of the coronary vessels increase in the heart rate

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The END

Thank you for attention!