Lecture 13: Aqueous Humor PDF

‭Learning Objectives:‬ ‭Quiz 1:‬ ‭‬ ‭List the functions of the aqueous humor‬ ‭○‬ ‭Serves as nutritive fluid (blood substitue) for avascular cornea, lens, and TM; supplies‬ ‭nutrients and oxygen through diffusion‬ ‭○‬ ‭Removes metabolic was...

‭Learning Objectives:‬ ‭Quiz 1:‬ ‭‬ ‭List the functions of the aqueous humor‬ ‭○‬ ‭Serves as nutritive fluid (blood substitue) for avascular cornea, lens, and TM; supplies‬ ‭nutrients and oxygen through diffusion‬ ‭○‬ ‭Removes metabolic wastes of avascular tissues through continuous formation; travels‬ ‭through ocular chambers and drainage from eye to venous blood‬ ‭○‬ ‭Establishes and maintains hydrostatic pressure (IOP) → inflates eye to maintain proper‬ ‭alignment of optical structures‬ ‭○‬ ‭Transports antioxidants into anterior segment‬ ‭○‬ ‭Transports immunoglobulins to defend against invading pathogens‬ ‭‬ ‭List the components of the aqueous humor‬ ‭○‬ ‭Water‬ ‭○‬ ‭Selective transport of solutes from blood plasma → ions, low MW molecules, high MW‬ ‭molecules‬ ‭‬ ‭Ions → maintain AH as isotonic solution (Na+, K+, Cl-, H+, HCO3-, Ca2+, Mg2+)‬ ‭‬ ‭Low MW molecules‬ ‭‬ ‭Initial AH‬ ‭○‬ ‭Nutrients → glucose (energy), citrate (energy), amino acids‬ ‭(protein synthesis)‬ ‭○‬ ‭Antioxidants → ascorbate, glutathione‬ ‭‬ ‭Waste products → lactic acid/lactate (fermentation), urea (protein‬ ‭metabolism)‬ ‭‬ ‭High MW molecules‬ ‭‬ ‭Proteins‬ ‭○‬ ‭LOW conc of protiens in AH compared to blood plasma‬ ‭○‬ ‭Albumin (carrier for hormones, aa, long-chain fatty acids)‬ ‭○‬ ‭Growth factors‬ ‭○‬ ‭Enzymes (carbonic anhydrase → catalyzes formation of carbonic‬ ‭acid; lysozyme)‬ ‭○‬ ‭Signaling molecules → signal transduction (prostaglandins,‬ ‭cAMP, catecholamines, steroid hormones)‬ ‭○‬ ‭Hyaluronic acid (glycosaminoglycan)‬ ‭○‬ ‭Molecules added to/removed from AH as it travels through ant chamber‬ ‭‬ ‭Outline the flow of aqueous humor from production to outflow‬ ‭○‬ ‭AH produced by ciliary epithelium as selective filtrate from capillaries of CB & secreted‬ ‭into posterior chamber‬ ‭○‬ ‭Flows between lens and iris into anterior chamber‬ ‭○‬ ‭AH drainage‬  ‭ ‬ T‭ rabecular meshwork into Schlemm’s canal and into aqueous vein‬ ‭‬ ‭Uveoscleral route, through extraceullular spaces within CM and through‬ ‭suprachoroidal space and into aqueous vein‬ ‭‬ ‭Describe and sketch the characteristics of the ciliary epithelial cells‬ ‭○‬ ‭Nonpigmented epithelial cells (NPE) and pigmented epithelial cells (PE)‬ ‭‬ ‭Interact at apical surfaces‬ ‭‬ ‭Apical surface membranes = extensive inforldings‬ ‭‬ ‭Connect to basal lamina through hemidesmosomes‬ ‭‬ ‭Connected by desmosomes and gap junctions‬ ‭‬ ‭Contain numerous mitochondria and high levels of carbonic anhydrase → high‬ ‭metabolic rates‬ ‭○‬ ‭NPE = tight junctions → form blood-aqueous barrier‬  ‭‬ ‭Describe the process aqueous humor secretion including:‬ ‭○‬ ‭Production of ultrafiltrate from the ciliary capillaries‬ ‭‬ ‭Fenestrated capillary‬ ‭‬ ‭H2O + solutes → passing through/across semipermeable membrane‬ ‭‬ ‭Only some substances are able to pass through → RBC is unable to pass‬ ‭through/exit‬ ‭○‬ ‭Ion transport from the stroma through the ciliary epithelial cells and into the posterior‬ ‭chamber‬ ‭‬ ‭Ions ONLY transported across membranes through specific transport proteins‬ ‭○‬ ‭Transport of water‬ ‭‬ ‭Production of carbon dioxide reacts with water → forms carbonic acid →‬ ‭dissociates into H+ and bicarbonate ions‬ ‭‬ ‭Spontaneous reaction‬ ‭‬ ‭TIGHT JUNCTIONS btwn nonpigmented cells prevents paracellular movement of‬ ‭water and solutes‬ ‭‬ ‭Originate from blood and pass into stroma through fenestrations in capillaries‬ ‭‬ ‭Follows movement of ions‬ ‭‬ ‭Na+/K+ pump =‬‭driving force‬ ‭○‬ ‭Transport of ascorbate, amino acids, glucose, and proteins‬ ‭‬ ‭Ascorbate, amino acids, glucose‬ ‭‬ ‭Active transport from stroma‬ ‭‬ ‭Proteins‬ ‭‬ ‭Active transport from stroma‬ ‭‬ ‭Synthesized and secreted by ciliary epithelial cells‬ ‭‬ ‭Derived from cells of lens, cornea, iris, trabecular meshwork‬ ‭‬ ‭Describe the regulation of aqueous humor secretion‬ ‭○‬ ‭Under adrengergic control‬ ‭‬ ‭High rate of turnover → entire AH replaced every 90-100 min‬ ‭‬ ‭Describe the mechanisms of drugs used to decrease aqueous humor secretion‬ ‭○‬ ‭Beta-blockers block effect of epinephrine → decreases AH production‬ ‭○‬ ‭Norepinephrine stimulation of alpha receptors → decreases AH production‬ ‭○‬ ‭Alpha agonists stimulate alpha receptors → decreases AH production‬ ‭○‬ ‭Carbonic anhydrase inhibitors (CAI) → decreases AH production (reduces intracellular‬ ‭concentration of H+ and HCO3-)‬ ‭Quiz 2:‬ ‭‬ ‭Identify the parts of the trabecular meshwork, and describe the composition of each element‬ ‭○‬ ‭Uveal meshwork‬  ‭‬ C ‭ omprised of endothelial cell-coated collagen beams + large spaced filled‬ ‭loosely with extracellular matrix (ECM)‬ ‭○‬ ‭Corneoscleral meshwork‬ ‭‬ ‭Comprised of endothelial cell-coated collagen beams + large spaced filled‬ ‭loosely with extracellular matrix (ECM)‬ ‭‬ ‭Transitions to JCT → intertabecular spaces decrease in size and lamella become‬ ‭flatter‬ ‭ ‬ ‭Juxtacanaclicular tissue (JCT)‬ ○ ‭‬ ‭Comprised of loosely arranged ECM → sparse number of juxtacanaclicular cells‬ ‭are embedded‬ ‭‬ ‭ECM regulated by MMPs‬ ‭‬ ‭Cells connect through long processes → attach to SC‬ ‭‬ ‭Describe the role of matrix metalloproteinases in adaptation to increased intraocular pressure‬ ‭○‬ ‭Increased IOP = mechanical distortions → upregulation of secretion of MMPs = degrade‬ ‭ECM‬ ‭‬ ‭Describe the process of aqueous humor outflow through the Schlemm’s canal endothelium‬ ‭○‬ ‭Flows from anterior chamber through the TM into SC → passes into collector channels‬ ‭along SC external wal → discharges into episcleral and conjunctival veins on scleral‬ ‭surface‬ ‭‬ ‭Describe the mechanism of drugs used to increase trabecular outflow‬ ‭○‬ ‭Muscarinic agonists‬ ‭‬ ‭Activate muscarinic acetylchpline receptors in CM = contraction of muscle,‬ ‭displacement of SS, widening of spaces in ™‬ ‭‬ ‭Outline the process of the uveoscleral outflow pathway‬ ‭○‬ ‭Chamber angle → uveal layer of trabecular meshwork → CT spaces between muscle‬ ‭bundles of CB → to suprachoroid space → into sclera or perivascular spaces → into‬ ‭episcleral tissue → into venous circulation‬ ‭‬ ‭Describe the mechanism of drugs used to increase uveoscleral outflow‬ ‭○‬ ‭Prostaglandins‬ ‭‬ ‭Bind and activate receptors on CM cells → stimulate increased biosynthesis of‬ ‭MMPs‬ ⇒ ‭‬ ‭Initiate alteration of collagens in CM increase spaces between CM‬ ‭fibers → reduce hydraulic resistance in uveoscleral outflow‬