Histology Flashcards
Endocrine System Generalizations
No ducts -> secretions enter circulation directly
Rich blood supply -> delivers modulators to gland, caries secretions to other parts of body
Parenchyma -> epithelial cells
Hormones
specific molecules secreted into bloodstream that elicit selective responses from organs/tissues/cells
- require complementary receptor
- effective at low [ ]
- feedback loops
2 general categories of hormones
- AA derived (proteins, peptides, AA) -> pituitary, thyroid, parathyroid, pancreatic (endodermal/ectodermal)
- Steroids (cholesterol derivatives) -> gonads, adrenal cortex (mesodermal)
Hormone Receptors
- Intracellular receptors -> in cytoplasm or nucleus (lipid soluble -> steroids or thyroids)
- Cell-surface receptors -> all AA-derived hormones except thyroids (hydrophilic -> bind specific receptors -> GPCR)
Discrete Endocrine Glands
pituitary, pineal, thyroid, parathyroid, adrenal
Both endocrine and exocrine glands
kidney, pancreas, gonads, placenta
Signaling
Endocrine -> travel through blood to end organ
Paracrine -> signaling to adjacent cell
Autocrine -> signaling on self-cell
Pituitary Embryology
Formation of floor of diencephalon and roof of stomatodeum (pouch of Rathke)
Oral ectoderm -> pars tuberalis, distalis, intermedia
Neural ectoderm -> pars nervosa, infundibulum
Adenohypophysis
Pars distalis - 75% of hypophysis
- anastamosing cords of cells separated from sinusoidal capillaries by CT
Chromophobes
50% of pars distalis cells
- appear in clusters, nuclei surrounded by light cytoplasm
- may be degranulated acidophils and basophils
Chromophils
50% of pars distalis cells
- Acidophils (40%)
- Basophils (10%)
Acidophils
- Somatotrophs -> growth hormone, somatotropin (STH)
2. Mammotrophs -> prolactin (PRL) (cell # increases during pregnancy and lactation)
Basophils
- Thyrotrophs -> thyroid stimulating hormone (TSH)
- Gonadotrophs -> follicle stimulating hormone (FSH), luteinizing hormone (LH) -> interstitial cell stimulating hormone in men
- both contained in secretory vesicles - Corticotrophs -> adrenocorticotropic hormone (ACTH)
Pars intermedia
rudimentary in humans -> produce melanocyte-stimulating hormone
- Rathke’s cysts
Pars tuberalis
highly vascularized area, superior hypophyseal arteries terminate here to form primary plexus of portal system
Neurohypophysis
pars nervosa and infundibulum
- contains 100,000 unmyelinated axons of secretory nerve cells
- cell bodies lie in supraoptic and paraventricular nucleus
- hypothalamo-hypophyseal tract
Paraventricular Nucleus
oxytocin -> secretion induced by suckling
- causes contraction of myoepithelial cells surrounding mammary glands
- promotes contraction of smooth muscle of uterine wall
Supraoptic nucleus
ADH (vasopressin)
- increases water permeability of distal convoluted tubule and collecting tubules –> increases water resorption
- stimuli –> increased plasma osmolality, decreased blood volume
Pituicytes
“supportive” cells found throughout neural lobe
- may be specialized neuroglial cells
Pineal Gland
cone-shaped, attached by stalk to roof of 3rd ventricle
- septa divide it into incomplete lobules
- Pinealocytes -> melatonin production
- suppresses gonadotropin secretion
Thyroid Embryology
endodermal downgrowth at floor of pharynx (between pouches I and II)
C-cells = calcitonin
Adult Thyroid
2 lateral lobes connected by isthmus –> CT capsule
Follicles
structural unit of thyroid, simple epithelium (mostly cuboidal)
- contain colloid (gel like substance that contains precursors to T3 and T4
Follicular Cells
- Apical ends face colloid and have microvilli projecting into colloid, basal ends rest on basement membrane
- Tight Junctions
- Synthesize thyroid hormones
Inactive follicular cells
Low cuboidal/squamous cells, few mito, basal RER
Active follicular cells
columnar cells, numerous mito, increased RER, lipid droplets, apical lysosomes (break down resorbed colloid)
Parafollicular Cells
C-cells (occur in singly or small groups)
- neural crest origin, wedged between principal cells
- synthesize calcitonin –> lowers blood calcuim, decreases osteoclasts, promotes excretion of calcium and phosphate from kidneys (PTH)
Colloid
thyroid only gland to store large quantities of secretory product
- vacuoles appear in active glands
Composition:
1. Thyroglobulin -> synthesized in RER
2. Iodide Uptake -> basal portion of follicle
3. Iodination of thyroglobulin -> tyrosyl residues only, extracellularly, catalyzed by throid peroxidase
T3 and T4 production
occurs in colloid
- TSH stimulation –> follicle height increases, gland hypertrophy, accelerated follicle cell metabolism
- Pinocytosis of thyroglobulin -> fusion of lysosomes, eventual formation and release of T3 and T4
Parathyroid structure
2 pairs located on posterior surface of thyroid
- derived from pharyngeal pouch III and IV
- separate from thyroid by CT capsule
Chief Cells
prominent cell of Parathyroid
- vesicular appearing nucleus, eosinophilic cytoplasm
Resting = sparse RER, abundant glycogen
Active = increased RER, sparse glycogen
- produce PTH - peptide hormone, regulates Ca and PO4 levels = increases blood Ca by stimulating osteoblasts to increase osteoclasts #
Oxyphil Cells
larger than chief cells, smaller and darker
- function unknown
Adrenal Glands
Paired gland on top of kidneys, retroperitoneal
- Cortex = mesoderm
- Medulla = neural crest cells
Thick CT capsule, sympathetic innervation (majority of fibers end in medulla as preganglionic sympathetics)
Cortex
Zona Glomerulosa (outer) Zona fasciculata (middle zone) Zona reticularis (inner zone)
Zona Glomerulosa
relatively narrow zone, cells arranged in ovoid or cords, rich capillary supply
- round cells = intensely basophilic nuceli
- sparse lipid content
- mineralocorticoid production
Zona fasciculata
broadest zone of cortex, cells arranged in parallel cords radiating toward medulla -> each cord enclosed longitudinally in meshwork of capillaries
- cuboidal cells, abundant lipid content, spongy appearance, abundant smooth ER
- primarily glucocorticoid production, some androgens
Zona reticularis
irregular cords of cells form anastomosing network
- few lipid droplets, abundant smooth ER, sex steroid production, some glucocorticoids
Medulla
chromaffin cells surrounded by venules and capillaries
- columnar cells, ovoid, or polyhedral
- nonregenerative, prominent golgi and RER
- fine secretory vesicles (products are stored not produced on demand)
- chromogranin may store catecholamines in vesicles
- regarded as modified post-ganglionic sympathetic neurons (neural crest origin, lack axons, innervated by preganglionic neurons
Blood supply to adrenals
Subcapsular plexus -> 3 sets of capillaries
1. Capsular plexus (empties into veins of capsule)
2. Cortical sinusoidal (drain into veins of medulla)
3. Medullary capillaires (empty into medullary vessels)
Medullary Venules untie to form medullary vein
Paraganglia
Organs of Zuckerland
- similar to cells of adrenal medulla
- secrete epinephrine
- largely retroperitoneal
Pancreatic Islets Structure
spheroidal masses of pale-staining cells embedded in exocrine pancreas
- many islets per gland, surrounded by pancreatic acini (exocrine)
- cords separated by fenestrated capillary networks
- more in tail of pancreas than head
Pancreatic Islet Cell Types
Alpha Cells
Beta cells
Delta Cells
PP (F) cells
Alpha Cells
20% of islet cells, located at periphery of islet
- secretory vesicles have dense core, produce glucagon (polypeptide that raises blood sugar)
Beta Cells
70% of islet cells, located toward center of islet
- secretory vesicles have crystalline appearance, produce insulin (protein that lower blood sugar)
destruction of beta cells = diabetes mellitus
Delta Cells
suppresses secretion of insulin and glucagon
PP (F) Cells
~1% of islet cells
- produce pancreatic polypeptide -> relaxes gall bladder -> decrease bile secretion, inhibits enzyme secretions from exocrine pancreas
Innervation and blood supply of pancreas
sympathetic and parasympathetic supply
rich, fenestrated capillary network
