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Urinary System Functions

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Urinary System Functions Urinary System Functions • Major excretory pathway for wastes transported by blood – Filtration, secretion, and reabsorption by the kidney’s microscopic tubules – Includes wastes from metabolism, excess water and excess solutes, absorbed substances • Collection, transport, exit of urine – product of kidney’s function – Responsive to condition – Role in maintenance of blood volume and pressure • Urine release controlled by reflex actions • Regulation of hemopoesis Organs and Vessels of the Urinary System Hepatic veins (cut) Esophagus (cut) Inferior vena cava Renal artery Adrenal gland Renal hilum Aorta Renal vein Kidney Iliac crest Ureter - peristalsis Rectum (cut) Uterus (part of female reproductive system) Urinary bladder Urethra Figure 25.2 Dissection of urinary system organs (male). Kidney Renal artery Renal hilum Renal vein Ureter Urinary bladder Figure 25.3a Position of the kidneys against the posterior body wall. Three layers of supportive tissue surround kidney Renal fascia outer layer of dense fibrous connective tissue Perirenal fat capsule Fatty cushion Fibrous capsule Transparent capsule Anterior Inferior vena cava Aorta Peritoneum Peritoneal cavity (organs removed) Supportive Renal tissue layers vein • Renal fascia anterior Renal posterior artery • Perirenal fat capsule • Fibrous Body of capsule vertebra L2 Body wall Posterior Kidney Function Maintain the body’s internal environment by: – Regulating total water volume and total solute concentration in water – Regulating ion concentrations in ECF – Ensuring long-term acid-base balance – Excreting metabolic wastes, toxins, drugs – Producing erythropoietin (EPO) and renin – Activating vitamin D – Carrying out gluconeogenesis, if needed Figure 25.4 Internal anatomy of the kidney. Blood flow critical – 25% of each ejection enters kidney vessels. Kidneys monitor and facilitate • Favorable BP Renal hilum • Oxygen carrying ability Renal cortex Renal medulla Major calyx Papilla of pyramid Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Photograph of right kidney, frontal section Diagrammatic view Figure 25.5a Blood vessels of the kidney. Cortical radiate vein Cortical radiate Cortical radiate arteries supply artery the glomerulus – Arcuate vein location of blood filtration Arcuate artery Interlobar vein Glomeruli and Interlobar artery portions of Segmental arteries nephrons are Renal vein located in the renal cortex Renal artery About 8 lobes Renal pelvis (pyramid & surrounding Ureter cortex) per kidney 11 cm x 6 cm x 3 Renal medulla cm 150 g / 5 oz Renal cortex Frontal section illustrating major blood vessels Physiology of Kidney • Values for Average Human • 180 L of fluid processed daily, but only 1.5 L of urine is formed – Kidneys filter body’s entire plasma volume 60 times each day – “Filtrate” is basically blood plasma minus proteins • Urine is produced from filtrate – Urine • <1% of original filtrate • Contains metabolic wastes and unneeded substances • Kidneys consume 20–25% of oxygen used by body at rest Nephrons and Nephron Structure • Structural and functional units that form urine • > 1 million per kidney • Two main parts – Renal corpuscle • Glomerulus – “tuft” of capillaries and visceral layer • Glomerular (or Bowman’s) capsule, parietal layer – Renal tubules • Including tubules, loop, and ducts • Collecting ducts in the thousands, drain nephrons Figure 25.6 Location and structure of nephrons. Renal cortex Renal medulla Renal pelvis Glomerular capsule: parietal layer Ureter Basement membrane Podocyte Kidney Fenestrated Renal corpuscle endothelium of the glomerulus • Glomerular capsule • Glomerulus Glomerular capsule: visceral layer Distal convoluted Apical microvilli tubule Mitochondria Highly Proximal infolded convoluted basolateral tubule membrane Proximal convoluted tubule cells Cortex Apical side Medulla Basolateral side Thick segment Distal convoluted tubule cells Thin segment Nephron loop • Descending limb • Ascending limb Collecting Nephron loop (thin-segment) cells duct Principal cell Intercalated cell Terminates at renal papilla Collecting duct cells Renal corpuscle Proximal • Squamous epithelium convoluted of parietal layer of tubule (fuzzy glomerular capsule lumen due to long microvilli) • Glomerular capsular space Distal convoluted • Glomerulus tubule (clear lumen) Histology of corpuscle and nearby tubules and nearby corpuscle of Histology Figure 25.12a The filtration membrane. Glomerular capsular space Efferent Filtration Membrane: arteriole • Fenestrated capillaries • Visceral layer glomerular capsule with filtration slits • Produce solute rich, virtually protein free filtrate Afferent arteriole Proximal convoluted Glomerular capillary tubule covered by podocytes Parietal layer that form the visceral layer of glomerular of glomerular capsule capsule Figure 25.12b The filtration membrane. Cytoplasmic extensions of podocytes Filtration slits Podocyte cell body Fenestrations (pores) Glomerular capillary endothelium (podocyte covering and basement Foot processes membrane removed) of podocyte Glomerular capillary surrounded by podocytes Figure 25.12d The filtration membrane. Capillary Filtration membrane • Capillary endothelium • Basement membrane • Foot processes of podocyte of glomerular capsule Allows molecules smaller than 3 nm to pass: Water, glucose, amino acids, nitrogenous wastes, most solutes *Normally no cells can pass* Plasma proteins remain in Filtration slit plasma to maintain colloid osmotic pressure Slit diaphragm Prevents loss of all water to Plasma Filtrate in capsular space capsular *Proteins in filtrate indicate membrane problem* space Fenestration (pore) Foot processes of podocyte Three layers of the filtration membrane Figure 25.10 Juxtaglomerular complex (JGC) of a nephron. Blood pressure in glomerulus high because: • Afferent arterioles are larger in Glomerular diameter than efferent arterioles capsule • Arterioles are high-resistance vessels Efferent arteriole Glomerulus Parietal layer Foot processes of glomerular of podocytes Podocyte cell body capsule (visceral layer) Capsular Red blood cell space Afferent Efferent arteriole Proximal arteriole tubule cell Juxtaglomerular complex • Macula densa cells of the ascending limb of nephron loop • Extraglomerular Lumens of mesangial cells glomerular • Granular cells capillaries Endothelial cell Afferent arteriole of glomerular capillary Glomerular mesangial cells Juxtaglomerular complex Renal corpuscle Figure 25.9 Blood vessels of the renal cortex. Peritubular capillary bed Afferent arteriole Glomerulus Efferent arteriole Renal Tubules and Collecting Duct Renal tubule is about 3 cm (1.2 in.) long • Single layer of epithelial cells in 3 major parts 1. Proximal convoluted tubule (closest to renal corpuscle) • Cuboidal cells with dense “brush border” microvilli, confined to cortex – high surface area to interact with filtrate – large mitochondria to support active transport functions • Functions in (significant) reabsorption and secretion 2. Nephron loop – formerly ‘loop of Henle’ –thick and thin limbs 3. Distal convoluted tubule • Farthest from renal corpuscle, confined to cortex • Cuboidal cells with very few microvilli • Function more in secretion than reabsorption • drains into collecting duct Cortical nephron Juxtamedullary nephron • 85% of all nephrons • Long nephron loop • Almost entirely in • Glomerulus closer to the cortex Glomerulus Efferent Cortical radiate vein cortex-medulla junction (capillaries) arteriole Cortical radiate artery Renal • Short nephron loop corpuscle Glomerular Afferent arteriole • Efferent arteriole supplies capsule Collecting duct vasa recta • Glomerulus further Proximal Distal convoluted tubule from the cortex- • Long nephron loops deeply medulla junction convoluted Afferent arteriole tubule Efferent invade medulla • Efferent arteriole arteriole supplies peritubular • Important in production of capillaries Peritubular capillaries concentrated urine Ascending limb of nephron loop Cortex-medulla junction Arcuate vein Kidney Vasa recta Arcuate artery Nephron loop Descending limb of nephron loop ‘Thin’ sections - Simple squamous Cuboidal or columnar Renal Tubule and Collecting Duct (cont.) • Collecting ducts – Cells lining ducts participate in fine-tuning of water, sodium ion, and acid-base balance between blood and urine – Receive filtrate from many nephrons – Run through medullary pyramids • Give pyramids their striped appearance – Ducts fuse together to deliver urine through papillae into minor calyces Nephron Capillary Beds • Renal tubules are associated with two capillary beds – Glomerulus – Peritubular capillaries • Low-pressure, porous capillaries adapted for absorption of water and solutes • Arise from efferent arterioles • Cling to adjacent renal tubules in cortex • Empty into venules • Juxtamedullary nephrons are associated with Vasa recta – Long, thin-walled vessels parallel to long nephron loops of juxtamedullary nephrons – Arise from efferent arterioles serving juxtamedullary nephrons • Instead of peritubular capillaries – Function in formation of concentrated urine Juxtaglomerular Complex (JGC) • Each nephron has one • Modified portions of distal portion of distal tubule and Afferent arteriole • Regulates rate of filtrate formation and blood pressure • Three cell populations are seen in JGC: 1. Ascending limb macula densa contains chemoreceptors that sense NaCl content of filtrate 2. Granular cells (or JG cells) act as mechanoreceptors to sense blood pressure in afferent arteriole Enlarged, smooth
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