Histology 3 - Endocrine Glands PDF

Endocrine glands Embryogenesis of endocrine glands How cells communicate among each other —> 1. Direct contact 2. Synaptic communications between neurons and other neurons/cells 3. Endocrine secretion in the blood stream —> the glands secrete an hormone which then travels through the blood vessels...

Endocrine glands Embryogenesis of endocrine glands How cells communicate among each other —> 1. Direct contact 2. Synaptic communications between neurons and other neurons/cells 3. Endocrine secretion in the blood stream —> the glands secrete an hormone which then travels through the blood vessels to reach targeted cells (marked by a receptor) 4. Paracrine activity —> product goes up to different close cells without passing through the blood 5. Autocrine activity —> the target organ is the cell itself Endocrine transport allows the communication with DISTANT cells Hormones: Steroid —> deriving from cholesterol —> gonads and adrenal cortex Protein based —> thyroid, pituitary gland and endocrine pancreas (es: insulin) Hormones interact with specific receptors on target cells —> on membrane or on nucleus Peptide hormones bind to membrane receptors —> they don’t enter the cell, they just bind to the receptor proteins on the membrane and then a second messenger molecule initiates the cell response (cascade reaction) Steroid hormones and nuclear receptors —> they enter the cell through the membrane and bind to receptors inside the cell —> they directly stimulate transcription of genes to make specific proteins Secreting-protein hormones cells have a well developed RER and Golgi apparatus for synthesis and modification of proteins. They have many secretion granules and the mitochondria have lamellar cristae In cells producing steroid hormones the SER is more developed (lipid synthesis) and the mitochondria have tubular cristae. They LACK secretion granules but have lipid drops Classification of endocrine glands: Number of cells —> unicellular (one or very small group of isolated cells, like in the islets of Langerhans) or multicellular (more cells together, like the adrenal glands) Arrangement —> shape when aggregated (islets, cords, follicles, interstitial) UNICELLULAR ENDOCRINE GLANDS  DNES (Diffuse Neuro-endocrine System) —> diffuse because cells are sparse, neuro- endocrine because some properties of this epithelia cell resembles those of the neurons C cells of the thyroid —> they are sparse among the follicles of the thyroid, they produce calcitonin DNES —> they are unicellular entero-endocrine glands localised along the gastrointestinal tract (endocrine and paracrine secretion). They present argentaffin and argyrophil which can be stained with salts of silver and chromium. Before they were known as APUD E (Amine Precursor Uptake and Decarboxylation) because they uptake amine precursors that undergo decarboxylation Parts of Crypts of Lieberkühn are entero-endocrine cells —> they are different types of cells and they secrete PEPTIDE hormones —> they stimulate the secretion of other enzymes and are responsible for the motility of the digestive tract Gastrointestinal diffuse endocrine system —> stomach - small intestine: Gastrin and serotonin —> stimulation of gastric secretion and intestine motility Cholecystokinin (CCK)—> stimulation of secretion of pancreatic enzymes and bile Secretin —> stimulation of bicarbonate secretion and of enzymes by the pancreas Motilin —> increase of intestine motility MULTICELLULAR ENDOCRINE GLANDS Morphological arrangement: Cords —> cords or clumps of cells (pituitary, adrenal, pineal glands, parathyroids). Sometimes they are less organised and they look like rows Islets (endocrine pancreas) Interstitial (testis and ovary) Follicles (thyroid) cue Double omer asmany earns PITUITARY GLAND (HYPOPHYSIS) It consists of a posterior lobe (neurohypophysis, neural secretory tissue deriving from neurons) and an anterior lobe (adenohypophysis, glandular epithelial tissue). It is a very small gland secreting negus I The adenohypophysis receives signals from the hypothalamus to secrete or not secret hormones —> a complex system of capillaries (hypophyseal) makes the passage possible The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain connecting the hypothalamus with the anterior pituitary. Its function is that of transporting hormones between the hypothalamus and the adenohypophysis The main hormones transported by the hypophyseal are hormones regulating the secretion of other endocrine glands —> gonadotropin-releasing hormones (GnRH), corticotripin-releasing hormones (CRH), growth hormon-releasing hormones (GHRH) and thyrotropin-releasing hormones (TRH) + inhibiting factors The anterior lobe only secretes REGULATING hormones (they activate other glands which then produce the gwaver needed substance) while the posterior lobe releases hormones which act directly Ffystatection regulating The medulla of adrenal glands is directly controlled by the hypothalamus while the cortex by the anterior lobe Thehypothalamus releaseshaarmon thatregulatetheanterior lobe ctin  hormone growth hormone releasing easinghormone corticoiare thyroid hormones releasing ofbeadpressure regulation The adenohypophysis responds to signals originated in the hypothalamus—> hypothalamus sends hormones that stimulate/inhibit the production of other hormones in the adenohypophysis Adenohypophysis shape —> cells are arranged in clumps or cards separated by fenestrated blood capillaries Nottoknowbyheart I r Different staining properties —> chromophil cells (acidophils and basophils) or chromophobe cells (don’t get stained) Neurohypophysis —> posterior lobe —> neural tissue (deriving form the hypothalamus) with Herring bodies secreting properties terminating in fenestrated blood capillaries —> it contains non-myelinated nerve fibres and glial cells (pituicytes, it differs from the neurons because it doesn’t send electrical piticytes signals) in a connective stroma. It produces hormones which go directly to the organs (ADH or vasopressin and oxytocin). Herring bodies are storages of hormones CLINICAL DROP(s): Hypophyseal dwarfism —> hyposecretion of GH during the growing years (infancy) —> slow bone growth and abnormal height (bone epiphyseal plates close before the normal height is reached) Hypophyseal gigantism —> Hypersecretion of GH during childhood —> abnormal increase in bone length and size of other organs —> very tall person but with normal body proportions Acromegaly —> hypersecretion of GH after puberty —> only the extremities respond to the hypersecretion (head and hands) Exactlyatthecentre EPIPHYSIS or PINEAL GLAND ofthebrain It is located near the base of the brain and it is part of the diencephalon. It has a pine-cone shape. It is characterised by aggregates of epithelia cells and calcium concretions. Calcium concretions are visible under the X-rays and they can be taken as a reference to identify all the other parts of the brain Pineal glands are made of cords or clumps of pinealocytes (chief cells producing hormones) and glial or interstitial cells (astrocytes, they just support the small organ) The pineal gland is photosensitive —> endocrine activity linked to light intensity. The hormone it produces is melatonin (produced at dark) which regulates the day-night circadian rhythm and the gonadal hormones (timing of puberty). In the pineal gland there are also other neurotransmitters like serotonin (precursor of melatonin), dopamine (whose receptors are cuboiae epithelium only active during the day) and others THYROID GLAND It is located in the anterior portion of the neck and has a butterfly shape. It’s made of units of follicles (the number of follicles depends on how much colloid is needed—> colloid stores thyroglobulin, the precursor hormone of T3 and T4). The follicles also present C cells which synthesise calcitonin. There are also lots of capillaries (secretion) Follicles are around 0.02-0.9 mm and they are made of follicular cells, parafollicular cells (c cells) and colloid (thyroglobulin filling, it is an inactive storage of hormones) Thyroid stores colloid extra-cellularly and only releases hormones when there is a signal The activity of follicular cells is regulated by TSH (produced in the hypophysis) while that of C cells is independent and it is regulated by blood calcium levels Follicular cells —> T3 (triiodothyronine) and T4 (tetraiodothyronine) —> they increase metabolism, increase oxygen and ATP consumption, increase body temperature and influence body growth and the correct development of nervous systems —> newborns get checked for the production of these cells and if there are abnormalities they have to be addressed immediately. Parafollicular cells (C cells) produce calcitonin (independent of adenohypophysis) —> it regulates calcium metabolism —> it inhibits osteoclast function by mediating bone resorption and it promotes calcium deposition in bones (hypocalcemic - parathyroid antagonist —> these two hormones control the metabolism of calcium in the body) In the thyroid hormones are continuously produced and then stored Cooprecursor protein of and recapture vesicles modigieainthe etinternalisationtdigestion corgi ofcolloid hormonesare repterereneaay vanes wimpreanson er endocytosis hormone becomeactive extanata intothebloodstream and go Parathyroids - independent of adenohypophysis (like C-cells, regulated by the level of calcium in the blood) 4 glands —> chief cells (producing parathyroid hormone, more abundant) and Oxyphil cells (unknown function) few mightbepreansons onageachiegcens The parathyroid hormone stimulates osteoblasts that in turn activate osteoclasts (macrophages), it increases the release of calcium ions in the bones (and phosphate), it inhibits the secretion of calcium ions and the re absorption of phosphates in the kidneys (more calcium available) and it converts vitamin D into its active form. Hypercalcemic calcitonin antagonist PTH —> increases blood calcium levels Calcitonin —> decreases blood calcium levels ADRENAL GLANDS arenaegeends  go kidney The outer cortex of the adrenal gland is made of cords of cells with different arrangements in 3 layers —> different names = different morphologies Glomerulosa layer (outer layer) —> produces mineralcortdicoids Fasciculata layer —> produces glucocorticoids Reticularis layer —> produces sex hormones The medulla produces adrenaline and non- adrenaline awnerowsa ensylatignait Fasawata CORTEX renwares MEDULLA airecteyreguarea yaypotheeamus In the medulla there are Chromaffin cells —> nerve fibres in that send impulses to the chromaffin to release their product ADRENAL GLAND HORMONES  Cortex (steroid hormones) —> mineralcorticoids (regulates sodium content in blood, glomerulosa), glucocorticoids (stress response, increase blood glucose level and regulates immune response, fasciculata) and androgens (precursor for testosterone production, reticularis) Medulla (catecholamine) —> epinephrine (adrenaline) and norepinephrine (non adrenaline). They are not produced continuously, there is a sudden release of catecholemine controlled by nerve fibers. They are involved in the fight-or-flight response (increase of heart rate and output, pulmonary ventilation, blood pressure, energy —> everything useful in case of danger) ENDOCRINE PANCREAS (encased in the organ) Langerhans islets —> islets of endocrine epithelial cells —> hormones produced —> insulin, don't hey amacini roundshape glucagon, somatostatin, pancreatic polypeptide Size —> 0.3-0.7 mm Shape —> heterogeneous Elongatedshape Loadipocytes ISLETS OF LANGERHANS: A cells (20%) —> produce glucagon —> increase glycemia B cells (70%) —> produce insulin —> decreases glycemia (malfunctioning of B cells causes insulin insufficiency—> diabetes) D cells (5-10%) —> produce somatostatin—> affects the secretion of insulin and glucagon (paracrine effect) F or PP cells (1-2%) —> produce pancreatic polypeptide (PP) —> affects the exocrine secretion of pancreas Bceeesostheyeveintheconeoftheiseets Laces moreintheperiphery 0 Laouacsunamaeaby aboiaaeepitheeia vein overt Glucosecontrol intheblood G oose consumption storing SUM MARY go Jinportent andover testes  Ts tu Glucosedoesn't enterauswithout insulin neguereabythe hypothalamus the regulatedby maenohypophysis antiingeammetory Article on diabetes (not part of the program)