Chapter 24: Renal System and Long-Term Blood Pressure Regulation24.2: Introduction- Kidneys receive 20% of total cardiac output at rest- Play important endocrine role by producing and secreting hormones involved with BP regulation and blood cell formation, renin and erythropoietin, respectively- Involved in gluconeogenesis and production of calcitriol as final step in vitamin D synthesis- Regulates total water content of body and manage its solute concentration24.3: Anatomy of the Urinary System- Kidneys monitor and process contents of blood supply to form urineo Ureter collects urine from each kidney and delivers it to urinary bladdero Urinary bladder stores urine prior to urinationo Urethra: during urination, urine flows from bladder through urethra to outside of body- Gross Anatomy of Kidneyso Kidneys lie in the retroperitoneal space, extending from T12 to L3 and are protected by floating ribso Each kidney had 3 layers of connective tissue: Renal fascia: dense, fibrous; surrounds both kidneys and adrenal glands Perinephric/perirenal fat capsule: layer of adipose tissue Fibrous/renal capsule: deepest layer covering outer surface of kidneyo Two distinct regions internally Renal Cortex: granular, reddish-brown Renal medulla: composed of series of structures called medullary or renal pyramids  darker and have striped appearance Renal column: separates each renal pyramid Minor calyx: collects urine from renal lobes Major calyx: converged from minor calyx, empties urine into renal pelvis- Structure and Function of Associated Organso Ureters are continuations of renal pelvis that carry urine out of kidneys to the bladdero Capable of peristalsis: involuntary constriction/relaxation of muscles  pushes urine into bladdero Angles of entry create one-way valve, preventing backflow of urineo When bladder fills, it compresses; closes ureter and further preventing backflowo Microscopic histology: Mucosa: deepest layer of its walls; a transitional epithelium- Readily stretches, permitting organ to distend as it fills with urine Muscularis: Middle layer; composed of longitudinally and circularly arranged muscle fibers- Innervated by neurons of autonomic nervous system- Senses distension with urine filling and triggers reflexive peristalsis Adventitia: most superficial; fibrous connective tissue that anchors ureter in placeo Features of the Bladder Trigone: opening for paired ureters and for urethra; triangular area at bottom of bladder Rugae: Series of folds made of transitional epithelium that lines mucosa of the urinary bladder Detrusor: middle layer; longitudinally/circularly arranged smooth muscle fibers that contract during urination Internal urethral sphincter: Thick muscle near the urethra; outermost layer Epithelium transitions to stratified squamous epithelium near urethra’s opening External urethral sphincter: ring of skeletal muscle the urethra passes througho Urethra in females Shorter than males, functions only in transport of urineo Urethra in males Much longer than females, functions to transport urine and semen Can be divided into 3 regions: Prostatic, membranous, and spongyo Kidney Vasculature and Microscopic Anatomy Renal artery: beings to branch into smaller vessels once inside kidney Each vessel gives rise to several segmental arteries- These branch to form interlobar arteries- Interlobar arteries: travel through renal columns and branch into arcuate arteries in the cortex- These branch to form cortical radiate arteries, which give rise to microscopic afferent arterioleso Overall structure of Kidney Nephrons Nephrons: structural and functional unit of urine formation in kidney Consists of two main components:- Renal corpuscle: Located in cortex, composed of a capillary knot called the glomeruluso An afferent arteriole delivers blood to each glomeruluso Filtration occurs when fluid and solutes are forced into space surrounding Bowman’s capsuleo Blood is drained from glomerulus by efferent arterioles- Renal Tubuleo After filtration of nephrons, fluid flows through collecting duct (CD), where two different cells perform different functions: Principal cells: adjust urine in order to maintain body’s water, Na and K balance Intercalated cells: responsible for acid-base balanceo Collecting ducts fuse to form papillary ducts, which empty into minor calyceso Anatomy of the Juxtaglomerular Apparatus (JGA) A portion of DCT that comes in contact with the afferent arteriole Two populations of cells in this area:- Macula densa cells: respond to concentrations of Na and Cl in the filtrate- Juxtaglomerular cells: specialized smooth muscle cells functioning as baroreceptors by responding to changes of BP within the afferent arteriole24.4: Formation of Urine- Includes three processes: filtration, absorption and secretion- Filtration:o Movement of fluid and solutes from blood in the glomerulus to the glomerular capsule space, driven by BPo Must pass through series of layers, known collectively as the filtration barrier: Capillary endothelium: fenestrated cells; very permeable; allows passage of anything smaller than a cell Fused basement membrane: barely permeable; blocks all but smallest proteins Podocytes of glomerular capsule: have pedicels that create filtration slits; prevent passage of most moleculeso Filtration is driven by pressure difference between lumen of glomerular capillaries and the space inside the glomerular capsule GBHP: BP within the glomerulus, which drives filtration CHP: hydrostatic pressure of the fluid inside glomerular capsule; opposes filtration BCOP: osmotic pull of proteins that are not passing through filtration membrane; also opposes filtration NFP: Total driving force of filtration:- NFP = GBHP – (CHP + BCOP)- Typical driving force of filtration is 10mmHg- GFR and Regulation of Filtrationo GFR is the total volume of filtrate formed by all glomeruli of both kidneys each minuteo Normal GFR = 90-120mL/mino Magnitude of NFP is directly proportional to GFR Alteration of GBHP is the mechanism by which NFP and GFR is regulatedo Kidneys need to limit changes to GFR during fluctuating BP Accomplished through changing the radii of afferent and efferent arterioles Vasoconstriction and vasodilation Kidneys perform autoregulation of GFR in two ways:- Tubuloglomerular feedback mechanism: involves relaxation and contraction of the afferent