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24 Cards in this Set
- Front
- Back
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Role of Endocrine System, Structure and Parts
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Regulate metabolic activities in the body
Produce localized or systemic effects via hormones Ductless glands and secretory cells with active RER and SER. Glands are highly vascularized Parts - pituitary, thyroid, parathyroid, suprarental, pineal glands, pancreas, gonads, others |
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Development of glandular epithelium
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BOTH exocrine and endocrine glands develop (AND ARE LINED WITH) epithelium invagination down into connective tissue.
Exocrine develops a secretory portion and a duct, Endocrine loses the ductal cells, cappillaries penetrate into secretory portion for endocrine glands |
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4 Forms of hormone signaling pathways
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a) Contact dependent - membrane-bound signaling molecule on signaling cell contacts target cell to induce effect
b) Paracrine - local mediator released, only affects local cells c) Synaptic - NT released from neuron at axon terminal to target cell d) Endocrine - endocrine cell releases hormones into systemic blood. Hormone diffuses to target cells with receptors |
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Mechanism of Endocrine Signaling
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Specificity between ligand (hormone) and receptor (target cell) and interactions with varying degrees of affinity
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Endocrine hormones properties, types
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Chemical messengers released to blood and delivered to target cells, bind to specific surface or cytoplasmic receptors to elicit short-term and long-term effects via initiation of a signal transduction pathway. Feedback mechanism is generated as well to halt additional hormone secretion (homeostasis)
Types a) Proteins and polypeptides (mostly water-soluble) b) Amino acid derivatives (mostly water-soluble) c) Steroid and fatty acid derivatives (mostly lipid-soluble) |
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Protein hormones vs steroid hormones
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Protein hormones bind to cytoplasmic receptor, initiates cascade with secondary messenger which goes to nucleus and leads to physiologic effects
Steroid hormones brought to cell via carrier protein, released, steroid enters cell, goes to nucleus to bind receptor leading to more mRNA, then proteins and physiologic effects |
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Possible intracellular signaling pathways and relative speeds
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Extracellular signal molecules bind to receptor and lead to intracellular signaling cascade
Effector proteins can be: a) metabolic enzyme - altered metabolism b) gene regulatory protein - altered gene expression c) cytoskeletal protein - altered cell shape or movement Altered protein functions leading to altered cell behavior can be FAST (seconds to minutes) Altered protein synthesis will be SLOW (mins to hours) |
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Feedback Mechanisms for Desensitization of Target Cells to hormones
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Receptor sequestration - into endosome, returned to surface later
Receptor down-regulation - into lysosome, degraded Receptor inactivation - no more intracellular pathway Inactivating of signaling protein - stopping intracellular pathway messenger Production of inhibitory protein - protein made as a result of signaling leading to inhibition of intracellular pathway |
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Hypophysis, role, function, location
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Master organ of endocrine system with two subdivisions in a single gland (adenohypophysis and neurohypophysis).
Location - Suspended from the hypothalamus by hypophyseal stalk (continuous with brain). Sits in sella turcica above SPHENOID SINUS. Function - secrete hormones that regulate adrenal glands, thyroid glands, reproductive organs, kidneys, mammary glands, and growth in muscle bone Release of hormones regulated via neurohormones from hypothalamus (HYPOTHALAMOHYPOPHYSIAL SYSTEM) |
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Hypophysis regions
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Adenohypophysis - Anterior lobe, glandular epithelial tissue. Consists of pars distalis, pars tuberalis, pars intermedia. More cellular
Neurohypophysis (posterior lobe) - NEURAL secretory tissue, consists of pars nervosa and infundibulum Divided by follicles and colloids. NO STORAGE FUNCTION in follicles unlike thyroid. Pars tubaris wraps around stalk. Supraoptic nuclei and paraventricular nucleus project down via hypothalamohypophysial tract to pars nervosa |
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Pituitary Developmental Steps
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Oropharynx ectoderm at Rathke's pouch contacts neuroectoderm
Developing sphenoid bone moves in and surrounds Eventually stick together forming posterior lobe (neruroectoderm) and anterior lobe (oropharynx ectoderm) |
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Pituitary gland hormones in, hormones out, targets and function
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Hormones in: Paraventricular nuclei (oxytocin), supraoptic nuclei (ADH) and other neurosecretory cells feed to posterior pituitary
Posterior pituitary a) ADH - acts on kidney to increase water absorption b) Oxytocin - acts on uterus (contraction) and mammary gland (myoepithelial contraction) Anterior pititary a) Acidophils - Prolactin (mammary glands - milk secretion), GH via somatomedins (adipose tissue - elevation of FFAs, muscle - hyperglycemia, bone - growth) b) Basophils - ACTH (adrenal cortex - secretion), TSH (thyroid - secretion), FSH (testes-spermatogenesis, androgen secretion; ovary - follicular development, estrogen secretion), LH (ovary - ovulation, progresterone secretion) Feedback a) Adrenal cortex acts on pars distalis and hypothalamus |
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Type of portal system in hypophysis, blood supply to hypophysis
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VENOUS
Arteriole ends at a capillary, deoxygenates and exits via vein This vein then splits in capillary or sinusoids (hypophysis) before exiting in another vein Blood supply: Internal carotid arteries split to superior hypophyseal arteries leading to primary capillary plexus in infundibulum. Axons of neuroendocrine cells from hypothalamus terminate here (primary capillary plexus) Inferior hypophyseal arteries enter from bottom and supply a capillary plexus in pars nervousa Portal veins drain the primary capillary plexus and deliver blood to secondary capillary plexus. These are linked by portal veins forming hypothalamohypohysial portal system. Drop into hypophyseal portal veins (portal system) and portal system in the PARS DISTALIS (anterior hypophysis) |
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Interaction between hypothalamus, adenohypophysis and thyroid gland
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Feedback loop for TSH secretion
Hypothalamus releases TRH to pars distalis. This releases TSH to thyroid. Thyroid releases T3 and T4. This inhibits pars distalis and hypothalamus |
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6 Hypothalamic derived-hormones that regulate cells of pars distalis
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Thyrotropin-releasing hormone (TRH) -
Stimulates secretion of TSH by thyrotrophs Corticotropin-releasing hormone (CRH) - Stimulates secretion of ACTH hormone by corticotrophs Growth hormone releasing hormone (GHRH) - stimulates secretion of GH by somatotropes Somatostatin - inhibits release of GH by somatotropes Gonadotropin-releasing hormone (GnRH) - stimulates secretion of LH and FSH by gonadotropes Dopamine/Prolactin-inhibiting hormone (PIH) - inhibits secretion of prolactin by lactotropes |
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Adenohypophysis development, structure, parts, Hormones
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Development: from Rathke's pouch, an evagination of the oral ectoderm
Structure: Cords of parenchymal cells surrounded by supportive CT and fenestrated capillaries (part of secondary capillary plexus) Parts: Pars distalis, pars intermedia, pars tuberalis Hormones - GH (also somatotropin, straight chain protein), TSH (2 chain), ACTH (small polypeptide), FSH (2 chain glycoprotein), LH (2 chain glycoprotein), PRL (straight-chain) |
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Cells of pars distalis, classes
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Chromophils or chromophobes based on secretory granule dye absorption. Chromophobes probably are immature or degranulated chromophils
Chromophil Classes a) Acidophils - granules large, stain orange-red with acidic dyes, most abundant b) Basophils - stain blue with basic dyes, PERIPHERAL |
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Types of Acidophils, products, stimulators and inhibitors, effect
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Somatotrophs - secrete somatotropin (GH) upon stimulation by GHRH, inhibited by somatostatin, generally increases metabolic rate, induces liver to produce IGF-1 for bone and muscle growth
Lactotropes (mammotropes) - secrete prolactin, stimulated by PRH and oxytocin, inhibited by DOPAMINE/PIF, promotes mammary gland development and lactatoin. Number increases after birth and drops after nursing stops |
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Types of Basophils, products, stimulators and inhibitors, effect
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Corticotrophs - secrete precursor to ACTH, stimulated by CRH, inhibited by high plasma cortisol. Stimulates synthesis and release of hormones from the adrenal cortex
Thyrotrophs - secrete thyrotropin (TSH), release stimulated by TRH, inhibited by T3 and T4 in blood, stimulated synthesis and release of thyroid hormones Gonadotrophs - secrete FSH and LH, stimulated by GnRH and inhibited by hormones of ovaries and testes. Stimulates ovarian follicle growth and estrogen secretion, steroid hormone production in testes |
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Pars Intermedia and Pars Tuberalis role, location
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Pars Intermedia - region between pars distalis and pars nervosa containing colloid-containing cysts surrounded by cuboidal cells, residual lumen of Rathke's pouch, unclear function, may synthesis prohormones and endorphins
Pars Tuberalis - columns of cells surrounding the hypophyseal (or infundibular) stalk, composed of basophilic cells secreting FSH and LH |
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Neurohypophysis development, structure, role, hormones
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Development - neural ectodermal downgrowth of hypothalamus
Structure - composed of unmyelinated axons of neurosecretory cells arising from hypothalamus forms hypothalamohypophysial tract. Neurohormones produced in hypothalamus stored in HERRING BODIES along axons and released directly to blood from axon terminals Hormones - vasopressin (ADH) and oxytocin NO ENDOCRINE TISSUE, storage site for neurohormones produced in hypothalamus |
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Neurohypophysis hormone production, storage, release, role
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Paraventricular nucleus (OXYTOCIN) and Supraoptic nucleus (ADH)
Sent down axon terminal to neurohypophysis (via infundibular process, median eminence in hypothalamoneurohypophysial tract) at PARS NERVOSA together with carrier protein neurophysin Released at fenestrated capillaries to inferior hypophysial artery ADH - vasopressin, modulates plasma membrane permeability of kidney, increases water resorption to lower urine volume and increase its concentration Oxytocin - stimulates smooth muscle contraction of uterus during orgasm, menstruation and labor. Stimulates myeoepithelial cell contraction for milk ejection |
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Pars nervosa cells and roles
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Region where axons of hypothalamohypophysial tract terminate and store secretory granules (seen as distensions in axons called Herring bodies with vasopressin or oxytocin)
Pituicytes are neuroglial cells that support axons. |
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Hormonal Clinical Correlations at Hypophysis level
a) Gigantism/Acromegaly b) Infertility c) Hypothyroidism d) Cushing's Disease e) Diabetes insipidus |
a) Gigantism (child) or Acromegaly (adult) - due to excessive GH secretion.
b) Infertility - decrease in GnRH (and thus FSH and LH secretion) c) Hypothyroidism - deficiency in TSH secretion, reduced metabolism, temperature, mental lethargy d) Cushing's Disease - increased cortisol, decreased ACTH secretion. Leads to obesity, osteoporosis and muscle wasting e) Diabetes insipidus - decreased ADH production, leads to renal dysfunction, polyuria and dehydration |
