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KIN 191
Bruce Matheson

Urinary System Consists of two kidneys; two ureters, which carry urine from the kidneys to the urinary bladder; urinary bladder; urethra, which carries urine from the bladder to the outside of the body. Functions of the urinary system  Excretion: The kidneys filter blood and produce a large volume of filtrate. Large molecules (proteins and blood cells) stay in the blood. Smaller ones (ions) enter the filtrate. The filtrate flows through the kidneys and is modified until it’s converted to urine. Waste products enter the filtrate and useful molecules are reabsorbed.  Regulation of blood volume and pressure: They control the extracellular fluid volume in the body by producing either a large volume of dilute urine or a small volume of concentrated urine. Therefore, the kidneys regulate blood volume and hence blood pressure,  Regulation of the concentration of solutes in the blood: They help regulate the concentration of the major ions.  Regulation of extracellular fluid pH: They secrete variable amounts of H+ to help regulate the extra cellular fluid pH.  Regulation of red blood cell synthesis: they secrete the hormone erythropoietin, which regulates the synthesis of RBCs in bone marrow.  Regulation of vitamin D synthesis: they help control blood levels of Ca by regulating the synthesis of vitamin D. Location and external atatomy of the kidneys Location: behind the peritoneum on the posterior abdominal wall on each side of the vertebral column, extending from the last thoracic to the third lumbar vertebrae, partially protected by the ribcage. The liver is superior to the right kidney therefore the right kidney is slightly lower than the left. External anatomy:  Renal capsule- layer of fibrous connective tissue surrounding each kidney surrounded itself by a dense layer of adipose tissue which cushions the kidneys.  Renal facia- and a thinner layer of connective tissue surrounding the adipose tissue which helps anchor the kidneys and tissue to the abdominal wall  Hilum- is a small area where the renal artery and nerves enter, and the renal vein and ureter exit. It opens into the renal sinus.  Renal sinus- a cavity filled with adipose tissue and connective tissue which is occupied by the major and minor calix. Internal anatomy and histology of the kidneys Outer cortex Inner medulla: composed of renal pyramids, the bases of which form the boundary between the cortex and medulla. The tips of the pyramids are called the renal papillae which point toward the sinus, and the minor calyces are chambers into which the papillae extend draining urine out of the pyramid and into the calyces. The minor calyces merge to form the major calyces which then converge to for the renal pelvis, which is surrounded by the sinus. The renal pelvis narrows into the ureter which exits via the hilum and connects to the urinary bladder. Structure of Nephron: Functional unit of the kidney Consists of: Renal corpuscle- a proximal convoluted tubule, a loop of Henle, and a distal convoluted tubule. The distal convoluted tubule empties into a collecting duct, which carries urine from the cortex of the kidney towards the renal papilla. Near the tip is where several collecting ducts merge into the papillary duct. Papillary duct- empties into the minor calyx. Corpuscles and tubules are located in the cortex. Collecting ducts, parts of loop of Henle, and papillary ducts are in the renal medulla. Glomerular Apparatus: Bowman Capsule and Glomerulus  The wall of the bowman capsule is indented to for a double-walled chamber; within this chamber is the glomerulus, which is a network of capillaries  Fluid is filtered from the glomerulus into the Bowman capsule which then flows to the proximal convoluted tubule and is carried away.  Bowman capsule has an outer layer, the parietal layer, made up of simple squamous epithelium which become cube shaped at the beginning of the proximal convoluted tubule.  And an inner layer called the visceral layer which is constructed of podocytes, which wrap around the glomerular capillaries  In the endothelial cells of the glomerular capillaries are fenestrae  Gaps called filtration slits are between cell processes of the podocytes which make up the visceral layer of the Bowman capsule  A cell membrane is sandwiched between the endothelial cells of the capillaries and visceral layer of the Bowman. These three things form the kidneys filtration membrane.  The slits in the podocytes regulate what will be allowed to be filtered and what will stay in the blood, to regulate the function for pressure filtration out of the apparatus.  A basement membrane selectively blocks plasma proteins & other molecules from leaving capillary. cells, proteins are too big nutrients, waste products and electrolytes can pass The renal tubules: Proximal Convoluted Tubule-  Simple cuboidal epithelium which lies upon a basement membrane which forms the outer layer of the tubule.  Many microvilli line the inner layer of the tubule Loops of Henle-  Continuations of the PCT, each loop has two limbs: the descending limb and the ascending limb  the beginning of the descending limb is simple cuboidal epithelium like that of the PCT and then it thins and becomes simple squamous epithelium  the beginning of the ascending limb, therefore, begins with simple squamous and thickens into simple cuboidal epithelium, ending by giving rise to the DCT. Distal convoluted tubule-  shorter than the PCT, and the cells are smaller and do not have many microvilli  The DCT in many neurons connects to the collecting ducts which extend through the medulla towards the tips of the renal pyramids. Blood Supply:  An afferent arterial supplies blood to the glomerulus and an efferent arteriole drains it.  At the point where the afferent arteriole enters the glomerulus, the smooth muscle cells form a cufflike arrangement around the arteriole of juxtaglomerular cells.  Specialized cells called the macular densa and the juxtaglomerular cells, found in part of the distal convoluted tubule adjacent to the glomerular apparatus, make up the juxtaglomerular apparatus  The juxtaglomerular apparatus helps regulate the flow of blood into the Bowman and therefore the amount of filtrate produced. • Paired Renal arteries from the abdominal aorta- branching, arcuate artery (cruved trajectory between cortex and medulla), smaller inter lobular arteries, to afferent arteriole, glomerular capillaries (filtrate ), efferent arteriole, peritubular capillaries (reabsorption process), vasa recta or inter lobular veins, arcuate veins, renal veins, inferior vena cava, heart 1)Renal artery – Red 2) Segmental Artery – socks 3) Interlobular artery – Ingrid 4) Arcuate Artery – And 5) Interlobular Artery – Ivan 6) Afferent arteriole – Are 7) Glomerulus – Going 8) Efferent Arteriole – Every 9)Peritubular Capillaries – Place 10) Vasa recta – (on) Vacation 11) interlobular vein – Inside 12) Arcuate vein – An 13) Interlobular Vein – Indigo 14) Renal vein – Rucksack 15) Inferior vena cava – Very 16) Heart - happily Urine Production There are three processes that determine the volume and composition of urine 1. Filtration in the glomerulus, the more pressure the more filtrate (increase the blood pressure in and you will produce more filtrate). Blood pressure non-selectively forces water and the other small molecules out of glomerular capillaries into the bowman capsule. 2. Reabsorption happens in the medulla, where we retrieve molecules we want to be reabsorbed into the blood 3. Tubular Secretion- when the nephron cells transport solutes from the blood into the filtrate Filtration Pressure There are three different types of pressure in the glomerular capillary: GCP- blood pressure (50 mm Hg) within the glomerulus, outward pressure of blood pressin on the capillary walls. Moves fluid and solutes from the blood into the Bowman capsule to add to filtrate. The efferent arteriole is smaller in diameter that the afferent one so the pressure builds here as resistance against the walls increases. CHP- an inward pressure from the pressure of filtrate accumulation inside the Bowman capsule, (10 mm Hg) which moves fluid from the Bowman capsule into the blood. CHP is comparable to blood pressure in that, as blood pressing on the walls of the capillary creates blood pressure, filtrate pressing on the walls of the Bowman capsule creates CHP. BCOP- because there are a lot of large proteins staying in the capillaries they create an osmotic pressure, the more materials in the blood the higher the cop. Fluid moves from the Bowman capsule to the blood by osmosis. A condition where the cop would go up is when you are dehydrated and blood is concentrated. Net filtration pressure (10 mm Hg) = GCP-CHP-BCOP if we minus the two forces pushing fluid from the Bowman capsule into the blood from the force pushing fluid into the Bowman from the blood then we can calculate the net movement. Tubular Reabsorption:  The return of filtered water and solutes to the blood, nearly 99 % of water and solutes are returned to the blood via the kidney with toxins removed. Reabsorption insures we do not dehydrate.  The filtrate leaves the Bowman capsule and flows through the PCT, the loop of Henle, the DCT and then into the collecting ducts. As it passes through these structures many of the substances in the filtrate are reabsorbed by one or more of several processes. Reabsorption in the PCT - PCT is responsible for the majority or reabsorption and cilia within the tubule increases surface area for this reabsorption. - The cells are what contribute to this; they have an apical surface which makes up the inside surface of the nephron (touches urine); a basal surface which forms the outer
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