Endocrine organs
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Transcript of Endocrine organs
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
Endocrine gland tissue composition Nerves tissue:
hypothalamus neurohypophysis pineal gland adrenal medulla
Epithelial tissue:adenohypophysis thyroid gland parathyroid glands adrenal cortex
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
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
Hypothalamus
Contains nuclei of neurosecretory cells
Nuclei with large cells: Paraventricular nucleiSupraoptic nuclei
Nuclei with small cells:Dorsomedial nucleiVentromedial nucleiArcuate or Infundibular nuclei
Neurosecretory cells secrete hormones
Neurosecretory cell axons leave the hypothalamus terminate on blood capillaries form the axovasal synapses in the neurohemal organs
Neurohemal organs contain axovasal synapses
Pars nervosa Median eminence
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
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
Hypophysis (pituitary gland)
lies beneath the brain is connected with the hypothalamus
hypothalamohypophysial neuroendocrine system
Hypophysis anatomical subdivision
Neurohypophysis (nerves tissue) Pars nervosa (posterior lobe) InfundibulumAdenohypophysis (epithelial tissue) Pars distalis (anterior lobe) Pars intermedia Pars tuberalis
Hypophysis development
Neuroectoderm neurohypophysis Ectodermal epithelium of the oral cavity
adenohypophysis
Pars nervosa is not endocrine gland is the neurohemal organ stores and releases hormones
from the hypothalamus nuclei
Pars nervosa histology
unmyelinated nerve fibers glial cells – pituicytes blood capillaries
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
Herring bodies
are dilated axon terminals accumulate secretory granules release hormones to the bloodstream
Pars nervosa hormones
ADH Oxytocin
Adenohypophysis
is true endocrine gland produces and releases hormones
Hormone chemistry:small proteinsglycoproteins
Adenohypophysis histology
endocrine epithelial cells (glandulocytes) loose connective tissue trabeculae sinusoidal fenestrated capillaries
cells are arranged in adenomeres
Pars distalis cell types
Acidophils Basophils Chromophobes
acidophils and basophilscontain secretory granules
Pars distalis cell hormones
Acidophils GH (STG) PL (LTH)
Basophils TSH LH and FSH ACTH
Pars distalis chromophobes lack secretory granules
are partially degranulated secretory cells
some of them are stem cells
Adenohypophysis pars intermedia
Endocrine cells surround the colloid-filled cysts pseudofollicles secrete hormones
MSH LPH
Adenohypophysis vascularization
superior hypophyseal artery
primary capillary network in the median eminence
portal veins
secondary capillary network in the adenohypophysis
hypophyseal veins
Adenohypophysis portal system
Scanning EM
Portal system transports hypothalamic hormones
neurosecretory cells release liberins statins
in primary capillary network
portal veins
secondary capillary network of the adenohypophysis
Adenohypophysis is regulated by hypothalamic hormones
Liberins and statins leave the secondary capillaries stimulate or inhibit adenohypophysis cells
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)
Thyroid histologic composition follicles connective tissue stroma capillaries
Follicles are the thyroid morpho-functional units
are spherical cyst-like compartments consist of
basal lamina epithelial cells - thyrocytes colloid
Thyroid follicles are surrounded by rich capillary network
capillaries arefenestrated sinusoidal
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
Thyrocytes secrete protein hormones
Thyroxine (tetraiodothyronine) – T4
Triiodothyronine – T3
Hormones regulate cell and tissue basal metabolism cell growth and cell differentiation
Colloid takes part in hormone synthesis
Colloid contains thyroglobulin - iodinated glycoprotein several enzymes
Thyroglobulin is inactive storage form of the thyroid hormones
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
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
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
Parafollicular cells or C-cells
arise from the neural crest occur in follicle wall or interfollicular spaces contain numerous secretory granules
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
Parathyroid gland
are two pairs: superior and inferior associated with the thyroid
Parathyroid gland histology
epithelial endocrine cells loose connective tissue sinusoidal fenestrated capillaries
Endocrine cells are arranged in cords
Principal or chief cells parathyroid hormone (PTH) Oxyphil cells (unknown function)
Parathyroid hormone is antagonist to calcitonin increases the blood calcium level
stimulates bone resorption reduces the kidney calcium excretion activates the intestine calcium absorption
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
Adrenal (suprarenal) glands
are paired glands are located at the kidney superior poles
are subdivided in cortex and medulla
Adrenal gland blood vessels
Short cortical arteries
cortical capillaries
medullary capillaries medullary veins
Long cortical arteries
medullary capillaries
medullary veins
Adrenal gland vascularization
Adrenal cortex
arises from the mesoderm consists of epithelial cells secretes steroid hormones is adenohypophysis-dependent
Adrenal cortex zonation
Zona glomerulosa
Zona fasciculata
Zona reticularis
Zona glomerulosa
cells are arranged in ovoid clusters secretes mineralocorticoids (aldosterone) is regulated by renin-angiotensin system
and ACTH
Aldosterone effects
stimulates sodium resorption and potassium excretion in the kidney, salivary glands and sweat glands
Zona fasciculata
cells are arranged in long straight cords
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
Zona fasciculata secretion
secretes glucocorticoids (cortisol, corticosterone) hormone effects:regulate gluconeogenesis and glycogenesisdepress immune and inflammatory response
Regulation of Zona fasciculata activity
is under control of ACTH
Zona reticularis
cells are arranged in anastomosing cords
Zona reticularis secretion
secretes weak androgens (dehydroepiandrosterone)
is under ACTH control
Adrenal medulla
arises from the neural crest consists of modified neural cells secretes catecholamine hormones is adenohypophysis-independent
Adrenal medulla cells
are called chromaffin cells secrete norepinephrine and epinephrine
are regulated by preganglionic sympathetic nerve fibers glucocorticoids induce norepinephrine to epinephrin conversation
Adrenal medulla hormone effects
rise in blood pressure dilation of the coronary vessels increase in the heart rate
The END
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