Endocrinw System Flashcards
T/F endocrine system has ducts
F, ductless glands
Diffuse neuroendocrine system (DNES)
. Single endocrine cells
. Seen in respiratory and GI
Nonepithelial cells w/ endocrine function
. Atrial myocardial cells w/in heart
. Juxtaglomerular apparatus in kidney
Endocrine cell signaling
. secrete hormones distributed to blood to distant target cells
Neuroendocrine signaling
. Neuronal secretory products carried to blood to distant cells
Paracrine cell signaling
. Secreted molecules act locally
. Regulates activity of nearby cells
. Synaptic cell signaling by release of neurotransmitters is specific type of paracrine signaling
Autocrine cell signaling
. Cells regulated by signaling molecules that they produce themselves
Protein and peptide hormones
. Neuropeptides and growth factors . Synthesized as precursors . Stored in secretory vesicles . Water soluble . Circulate in blood as unbound molecules . Bind to surface receptors . Can’t be administered orally
Steroid hormones
... from cholesterol . Bind to intracelllular receptors . Lipid-soluble . Not stored in producing cell . Can be taken orally
Nitric oxide
. Paracrine molecules in circulatory, immune, and nervous system
Eicosanoids
. Arachidonic acid is main precursor
. Include PGEs
. Autocrine and paracrine
. Bind to cell surface receptors
Organs in neuroendocrine system
. Hypothalamus
. Hypophysis
. Pineal gland
Hypothalamus
. Brain region w/ 12 hypothalamic hypophysiotropic nuclei
. Neurosecretory cells release neuropeptides (releasing and inhibitory hormones and factors)
. Hormones carried in blood, have pos. And neg/ effects on hypophysis
. Paraventricular and supraoptic nuclei of hypothalamus have neurons that give rise to axons that form hypothalamic hypophyseal tract
. Terminals of neurons in pars nervosa gf hypophysis
Hypophysis gross anatomy
. Pituitary
. Master endocrine gland
. Pea-sized (500-900 mg in adults, larger in women)
. Below hypothalamus in sella turcica in sphenoid bone in middle cranial fossa
. Suspended from hypothalamus by infundibulum
. Infundibulum contains neural and vascular connections to hypothalamus
Pituitary gland embryology
. Adenohypophysis: from Rathke’s pouch (evagination) of ectodermal lining of primitive oral cavity, extends upwards toward neurohypophysis
. Neurohypophysis: neural tissue from infundibular downgrowth of diencephalon
Parts of adenohypophysis
. Pars distalis: ant. Lobe, main part of gland (75%)
. Pars tuberalis: forms collar around infundibulum
. Pars intermedia: rudimentary in adults, thin wedge separating pars distalis from neurohypophysis, has Rathke’s cysts filled w/ colloid that are remnants for Rathke’s pouch
Parts of neurohypophysis
. Pars nervosa: post. Lobe or neural lobe
. Infundibular stalk: connects pars nervosa to hypothalamus
. Median eminence: funnel-like extension of hypothalamus
Pituitary gland blood supply
. Sup. Hypophyseal aa. From internal carotid enter median eminence and upper part of infundibular stalk forming primary capillary plexus
. Plexus receives products of neurosecretory cells from hypothalamus
. Capillaries give rise to hypophyseal portal system (venule network)
. Portal system drains into pars distalis and forms secondary capillary plexus
. Inf. Hypophyseal aa. Supply pars nervosa and form 3rd capillary plexus
Adenohypophysis structure
. Cords of epithelial cells
. Small amt CT
. Fenestrated capillaries
Hormone pathway in adenohypophysis
. Secreted hormones diffuse into capillaries,
. Drain via hypophyseal vv. Into dural venous sinuses
Adenohypophysis secretory cell classification
. Chromophills (acidophilus and basophils)
. Chromophobes
Acidophils in pituitary
. Cytoplasmic granules
. Somatotrophs: 40-50% of ant. Hypophysis cells, secrete GH (somatotropin) to induce growth, stimulated by somatotropin-releasing hormone, inhibited by somatostatin from hypothalamus
. Mammotrophs: 10-20% ant. Hypophysis cells, secrete prolactin, stimulated by prolactin-releasing hormone and thyrotropin-releasing hormone (TRH), inhibited by dopamine
Basophils in pituitary
. Corticotrophs: 10% ant. Cells, secrete ACTH, stimulated by corticotropin-releasing hormone from hypothalamus, inhibited by cortisol in blood
. Thyrotrophs: 5% ant. Cells, produce TSH, stimulated by TRH, inhibited by inc. concentrations of thyroid hormones
. Gonadotrophs: 10% ant. Cells produce FSH and LH, stimulated by gonadotropin-releasing hormone from hypothalamus
Function of ACTH
, stimulate adrenal cortex
. Inc. skin pigmentation
Follicle-stimulating hormone (FSH) function
. Stimulates development of ovarian follicles or productionof androgen-binding protein by Sertoli cells in males
Luteinizing hormone
. Ovulation and formation of corpus luteum in females
. Controls synthesis of tester one by Leydig cells in males
Chromophobes
. Small cells w/o secretory granules . Could be undifferentiated cells
Cels in pars tuberalis
Gonadotrophs
Cells in pars intima
. Basophils: mostly corticotrophs
. Chromophobes
. Products include melanocyte-stimulating hormone (MSH)
Growth hormone cell adenoma
. If tumor occurs as child gigantism occurs, if adult acromegaly
Prolactinoma
. Causes amenorrhea in females
. Galactorrhea
. Dec. libido
. Headaches
ACTH-secreting adenoma
Cushing’s disease
Neurohypophysis structure
. . Bundles of unmyelinated axons of neurosecretory neurons
. Cell bodies found in paraventricular and supraoptic nuclei of hypothalamus
. Supported by pituicytes (glial-like cells)
. Produces oxytocin and ADH
Oxytocin function
. Contraction of smooth muscle of uterine wall at parturition and myoepithelial cells of mammary gland
ADH function
. Acts on collecting ducts and distal convoluted tubules of kidney
. Inc. H2O permeability
. Inc. bp. By smooth muscle constriction in arterioles
. Inc. osmotic presssure/dec. blood volume stimulates it’s release
Neurophysin I and II
. I: Carrier for oxytocin
. II: binds ADH
. Both hormones transported down axons and stored in nerve terminals in herring bodies
Neurogenic diabetes insipidus
. ADH is dec. or absent from head injury, tumor, or autoimmune damage of ADG secreting neurons
. Polyuria common symptom
Pineal gland
. Endocrine organ w/ neurosecretory cells
. In center of brain behind 3rd ventricle
. Highly vascular
. Pinealocytes and interstitial cells
. Has pineal calcifications (corpora arenacea/brain sand) that inc. w/ age
. Doesn’t have direct connection to brain
. Innervated by postganglionic sympathetic fibers from sup. Cervical ganglion
Pineal gland functions
. Pinealocytes secrete melatonin that is inc. or dec. w/ amt of light
. Melatonin released by passive diffusion into circulation
. Acts on hypothalamus and hypophysis to inhibit gonadotropin and GH secretion
. Melatonin integrates photoperiods and modulates circadian rhythms
. Induces sleepiness
Pineocytomas
. 80% malignant
. Precocious Puberty or delayed onset of sexual maturation seen in 10% males w/ this
Thyroid gross anatomy
. Butterfly shaped, bilobed gland, 15-25g
. 2 lobes connected via thin isthmus
. In ant. Neck inf. To larynx
. Lobes on each side of trachea
Thyroid embryology
. Endodermal downgrowth at base of tongue
. Thyroglossal duct transient structure that connects developing gland to point of origin (foramen cecum)
. Parafollicular cells originate from neural crest
Thyroid gland
. Has follicles formed by single layer cuboidal epithelial follicular cells enclosing central cavity
. CT capsule around gland
. Blood supply from sup. And inf. Thyroid aa.
. Sup., middle, and inf. Thyroid vv. Drain blood from gland
Follicular cells of thyroid
. Rest on basement membrane
. Height depends on activity
. Lumens of follicles filled w/ colloid
. Major component of colloid is thyroglobulin (iodinated glycoprotein)
Parafollicular cells of thyroid
. Called C cells
. Form minor component of gland (0.1% mass, 10% cells)
. Found individually or in small groups at periphery of follicular wall in basement membrane but w/o contact w/ follicular lumen
. C cells separated from interstitium by follicular basal lamina
Thyroid functions
. Store thyroglobulin
. Follicular cells synthesize and secrete thyroid hormone (T3 and 4)
. Regulated by TSH
. Has exocrine and endocrine phases
Exocrine phase of thyroid
. Uptake of inorganic iodide from blood
. Stimulated by TSH
. Synthesis of thyroglobulin
. Oxidation of iodide to iodine w/in colloid
Endocrine phase of thyroid
. TSH-stimulated endocytosis of iodinated thyroglobulin into follicular cell
. Fusion of colloid droplets lysosomes
. Lysosomal degradation of iodothyroglobulin to release T3,T4, and other intermediates
. T3 and T4 released across basal lamina of follicular cells into fenestrated blood capillaries
. T3 has shorter half life and more potent and less abundant than T4
. T4 90% of secreted thyroid hormones
Parafollicular cells (C cells)
. Produce and store calcitonin (or thyrocalcitonin) in small cytoplasmic granules
. Calcitonin lowers blood Ca levels by inhibiting bone resorption and inc. Ca absorption by bone
. Release of calcitonin is directly regulated by blood Ca levels (High Ca stimulates)
. Part of diffuse neuroendocrine system
Goiter
. Hypertrophy of thyroid gland most commonly caused by iodine-deficient diet
Graves’ disease
. Autoimmune disease affecting women
. Caused by antibody that is agonist to TSH receptor
. Binding of autoantibodies to TSH receptors
. Causes unregulated synthesis of thyroid hormone
Hashimoto’s thyroidits
. Autoimmune thyroiditis
. Hypothyroidism
. Accumulation of lymphocytes in stroma of thyroid
. Caused by autoantibodies against thyroglobulin and other molecules in thyroid hormone production
Hypothyroidism in infants
. Results in mental retardation and short stature w/ skeletal abnormalities
. Can be caused by maternal hypothyroidism
Parathyroid glands gross anatomy
. 4 pea-sized glands on post. Surface of thyroid glands
. Btw thyroid CT capsule and surrounding CT of neck
. Distinguished in surgery from other tissue bc they bleed a lot
Parathyroid gland embryology
. Inf. Parathyroid glands from 3rd branchial pouch
. Sup. Parathyroid glands from 4th branchial pouch
Parathyroid gland characteristics
. Chief cells: more of them, round euchromaic nuclei and clear cytoplasm
. Oxyphil: esosinophilic from mitochondria, pyknotic nuclei, not found until puberty, inc. w/ age after that
. Stroma fat cells appear and end of 1st decade of life and inc. w/ age
Parathyroid gland functions
. Chief cells produce PTH: regulate Ca and P levels
. PTH stimulates resorption of mineralized bone by osteoclasts and release of Ca in blood
. PTH activates vit. D production in kidney which when vit. D stimulates intestinal resorption of Ca
What occurs if you accidentally remove parathyroid gland?
. Hypocalcemia
. Muscle cramping, twitching, spasms
. Contractions of muscles in respiration can cause death
Hyperparathyroidism
. Caused by adenoma
. Inc. blood Ca causes renal stones or deposition of Ca in blood vessels
Adrenal gland gross anatomy
. Paired triangular glands located at sup. Pole of kidneys
. Cortex and medulla
. Blood drained from both cortex and medulla by central v.
Adrenal gland embryology
. Cortex from mesoderm
. Medulla from neural crest ectoderm (migrates from sympathetic ganglia into fetal cortex)
. CT capsule forms and envelops adrenal gland during development
Adrenal gland characteristics
. Cortex (0-90% gland) essential for life
. Cortex zones: zona glomerulosa, zona fasciculata, and zona reticularis
. Medulla not essential
. Medulla has chromatin cells: modified postganglionic neurons w/o postganglionic processes, secrete catecholamines (E for 80% cells, NE for rest)
Zona glomerulosa
. 10-15% of adrenal cortex
. Under capsule
. Made of closely packed clusters of parenchyma cells
. Secretes mineralcorticoids (aldosterone)
. Angiotensin II-dependent (stimulates it)
. Aldosterone acts on distal convoluted tubules and collecting ducts in kidney
. Inc. Na reabsorption and K and H excretion (regulates Na and K homeostasis and H2O balance)
How is angiotensin II formed?
.. derived from conversion of angiotensin I in pulmonary circulation by angiotensin-converting enzyme (ACE)
Zona fasciculata
. 75% adrenal cortex
. Middle region
. Radially oriented cords of polyhedral cells (look like steroid cells w/ smooth ER, mitochondria w/ tubular cristae)
. Cords separated by fenestrated capsules
. Secrete glucocorticoids (cortisol)
. Cortisol not stored in cells, synthesis is stimulated by ACTH
Effects of cortisol
. Metabolic: opposite to insulin, stim. Gluconeogenesis
. Anti-inflammatory: suppression of tissue responses to injury and inhibition of cellular and humoral immunity
Zona reticularis
. 5-15% adrenal cortex
. Adjacent to medulla
. Anastomosing network of cords of acidophilic cells separated by fenestrated capillaries
. Secretes androgens (DHEA, androstenedione)
. Under ACTH control
. Major source androgens in women
Adrenal medulla functions
. E and NE stored in granules
. Bind to alpha and beta adrenergic receptors
. Released in response to nerve stimulation by preganglionic sympathetic nerve fibers carried in splanchnic nn.
. Inc. HR, bp, CO
Conn’s syndrome
. Primary hyperaldosteronism from tumor localized in zona glomerulosa
. Causes hypertension, low K levels
. Same as symptoms from inc. renin secretion
Cushing’s disease
. Inc. in aldosterone, cortisol, and adrenal androgen production secondary to ACTH production
. Cushing’s syndrome from adrenocortical adenoma causing overproduction of same hormones
. Causes muscle weakness w/ thin extremities, moon face, buffalo hump, truncates obesity from high insulin, abdominal striae from impaired collagen, osteoporosis, and immunosuppression
Addision’s disease
. Autoimmune disorder
. Destroys adrenal cortex and chronic adrenal insufficiency
. Cortisol insufficiency inc. ACTH
. Inc. skin pigmentation
. Loss of mineralcorticoids causes hypotension and circulatory shock
Exogenous Cushing’s syndrome
. Happens from taking oral corticosteroids for extended period of time
