Renal Anatomy PDF

Hey, everyone. This is the urinary system, functional anatomy and your information by the kidneys. Uh, this is Guyton, chapter 26. The kidneys, filter the plasma and remove waste. They regulate water and electrolyte balance. They regulate body fluid osmolality and electrolyte concentrations. They r...

Hey, everyone. This is the urinary system, functional anatomy and your information by the kidneys. Uh, this is Guyton, chapter 26. The kidneys, filter the plasma and remove waste. They regulate water and electrolyte balance. They regulate body fluid osmolality and electrolyte concentrations. They regulate arterial pressure, regulate acid base balance, regulate erythrocyte production, and they secrete, metabolize and excrete hormones. And lastly, they perform gluconeogenesis. The kidneys are the primary means for eliminating most of the waste products of metabolism from the body. These include urea, creatine, uric acid, bilirubin, and hormone metabolites. The intake of water and many electrolytes is governed by a person's eating and drinking habits, and then the kidneys are required to adjust excretion rates to match intake in order to maintain homeostasis. The excretion of water in electrolytes must match intake precisely. This figure shows a ten fold increase in sodium intake from 30 MQ a day to 300 MQ a day. You can see that within just a few days, the excretion of sodium matches intake. A few days later, the kidneys excrete the excess of sodium that was retained. There is a modest increase in cellular fluid volume during this time that is regulated back to normal. The kidney can not only regulate sodium, but also chloride, potassium, calcium, hydrogen, magnesium, and phosphate. By regulating sodium and water. The kidneys are the dominant force in long term arterial blood pressure regulation. They also help manage short term arterial pressure through hormone secretion and the secretion of vaso active factors such as running. The kidneys assist with acid base regulation along with the lungs and the buffer system. As was mentioned a few slides ago. The kidneys are the primary means to eliminate waste products. This includes certain types of acids. The kidneys regulate erythrocyte production by secreting erythropoietin, which stimulates red blood cell production by hematopoietic stem cells in the bone marrow. Hypoxia is normally the stimulus for erythropoietin secretion in people with severe kidney disease. Severe anemia can develop. The kidneys produce 1 to 5 hydroxy vitamin three. Uh, which is the active form of vitamin D, and it's also called calcium roll. It is essential for normal calcium deposition in bone and calcium reabsorption from the GI tract. The kidneys also perform gluconeogenesis, which is synthesizing glucose from amino acids during prolonged fasting. The two kidneys lie on the posterior wall of the abdomen. Outside the peritoneal cavity, they weigh about 150g each and are about the size of a clenched fist. On the medial side, uh, which, as you see them lie here, would. Medial side is here. Um. On the medial side of each kidney contains the hilum, uh, which is where the renal artery vein lymphatics, nerve supply and Joerger pass. So this would be the hilum. The two major regions of the kidney are the outer cortex and inner medulla. So the cortex here. And medulla. Uh, here in the inner side. Uh, the medulla is divided into 8 to 10 renal pyramids. Uh, so renal pyramid. Here. Um. The base of each pyramid originates at the border between the cortex and the medulla and terminates in the papilla. Um. The miner can collect urine from each papilla. So the miner tailings here. So. Um. Which they then coalesce into the major k links, which then form the renal pelvis, and eventually the years or so they're coming together. The minor helixes come together to form the major, and then the renal pelvis and then the other. Um, the walls of the pelvis and the ureters can contract and propel urine towards the bladder. Blood flow to the kidneys is normally about 22% of cardiac output, or 1100 milliliters a minute. The renal artery enters the kidney through the hilum and then branches progressively to form the inter lobular arteries. Acute arteries enter lobelia arteries and afferent arterials, which then lead to the glomerular capillaries. Large amounts of fluid and solutes are filtered in the glomerular capillaries, beginning urine formation. The distal ends of the capillaries coalesce to form the arterial, which then leads to the secondary capillary network that surrounds the renal tubules. So the peri tubular capillaries glomerulus. And then you have that afferent and effect arterials. Uh, renal circulation is unique. And then it has two capillary beds the globe Marilla and Perry. Tubular capillaries. Uh, just underlined. Um, these capillaries are arranged in series and separated by the efferent arterials. So. Here the fairing arterial separating the glomerular capillaries and the peri tubular capillaries. Um. High hydrostatic pressure in the glomerular capillaries causes rapid fluid filtration in the glomerulus. Uh, whereas lower hydrostatic pressure in the tubular capillaries permits fluid reabsorption by adjusting the resistance of the effort and efferent arterials. Hydrostatic pressure can be regulated, therefore changing the rate of filtration, tubular reabsorption, or both as needed. Each kidney contains about 800,000 to 1 million nephrons, each of which is capable of forming urine. The kidney cannot regenerate new nephrons. Therefore, with renal injury, disease, or aging, the number of nephrons gradually decreases after about 40. It decreases 10% every ten years by and by 80. Many people have lost 40% of their functioning nephrons. Although this is not life threatening. Each nephron contains the glomerulus, which is a cluster of capillaries through which large amounts of fluid are filtered, and a long tubule in which this filtered fluid is converted into urine on its way to the renal, uh, pelvis. The glomerular capillaries have a high. Here's the goal. Married capillaries have a high hydrostatic pressure compared to others. The glomerulus is encased in Bowman's capsule. So Bowman's capsule around the glomerulus. Uh, fluid filtered from the glomerulus flows into Bowman's capsule. So fluid is flowing into Bowman's capsule. Um, then to the proximal tubule. Then into the loop of Henley. Um, of course, the loop of Henley has its descending and ascending limbs. Um. The walls of the descending limb and the lower portion of the ascending limb are very thin and called the thin segment of the loop of Henley, so you can see the thin segment represented on the picture here. Uh, then beginning the thick segment, uh, at the end of the thick ascending limb is a region of specialized epithelial cells known as the macula. Denser. So you can see it labeled here. But this is the area here. Macula denser. Um. After this, the distal tubule is followed by the connecting tubule and the cortical collecting tubule, which lead to the, uh cortical collecting duct. You can see it progressed here. Distal tubule. Connecting tubule. Uh. 8 to 10 cortical collecting duck join to form the gallery collecting duck. These magically collecting ducks merge to eventually empty into the renal pelvis. In each kidney, there are about 250 of these large collecting ducks, collecting urine from 4000 nephrons. Each nephron has all the components that were just described. Although there are some differences depending on how deep the nephron lives within the kidney mass, cortical nephrons are located in the outer cortex. They have short loops of Hindley that only penetrate a short distance in the medulla, while juxtaposed nephrons have long loops of Hindley that travel deeply into the medulla. These long loops of Hindley have specialized vascular structure called the vasa recta, which play a special role in the formation of concentrated urine. The urinary bladder fills progressively until tensions in the walls rise above a threshold level, which then initiates a nervous reflex called the attrition reflex. Uh, this either empties the bladder or causes a conscious desire to urinate. Amatriciana reflexes and autonomic spinal cord reflex, but can also be inhibited or facilitated by centers in the cerebral cortex or brainstem. Urinary bladder is a smooth muscle chamber made up of the body in the neck. The body is the major part of the bladder where urine collects while the neck connects with the urethra. A smooth muscle, the bladder is called the true muscle contraction. This muscle is a major part of emptying the bladder, because its contraction can increase pressure up to 40 to 60mm of mercury. These smooth muscle cells, uh, fuse with each other, creating a low resistance electrical pathway that allows action potentials to spread quickly throughout, causing contraction of the entire bladder at once. The two girders enter the bladder in the triangle. The bladder neck is 2 to 3cm long, composed of the same the true same muscle and large amounts of elastic tissue and muscle in the neck area is called the internal sphincter. It prevents emptying of the bladder until the pressure in the main part of the bladder rises above a critical threshold. After the neck or posterior urethra. The urethra passes through the urogenital diaphragm, which contains the external sphincter of the bladder. This is the voluntary skeletal muscle which can be used to prevent urination, as opposed to the smooth muscle of the bladder, body, and neck. Parasympathetic. Parasympathetic. Involuntary skeletal muscle. Innovation to the bladder. Innovation to the bladder is principally through the pelvic nerves, which connect through the cycle plexus, mainly through S2 and S3. These nerves contain both sensory and motor fibers. Stretch of the bladder wall, particularly the posterior urethra. Since signals that initiate the attrition reflex. These nerves are parasympathetic fibers. The skeletal motor fibers for the external sphincter are transmitted through the pretended nerve. This is, uh, and the sympathetic innovation is through the hypo gastric nerve that connects to L2 of the spinal cord. The synthetic fibers, uh, mainly connect to blood vessels and have little to do with bladder contraction. Urine composition does not change after it flows into the renal Keeling system, as it flows through these K links as it stretches them and increases their inherent pacemaker activity, initiating peristaltic contractions that force urine from the renal pelvis towards the bladder. Ureters are normally 25 to 35cm long and contains smooth muscle, which are innervated by sympathetic and parasympathetic nerves. As with other visceral smooth muscle, peristaltic contractions are enhanced by parasympathetic stimulation and inhibited by sympathetic stimulation. The uterus normally course obliquely for several centimeters through the bladder wall, which causes compression and prevents backflow. As the bladder fills, attrition contractions begin to appear, resulting from the stretch receptors in the bladder wall, causing the stretch reflex. Once the reflex begins, it is self regenerative. For example, the bladder contraction causes increased stimulation of the stretch receptors, which causes an increased reflex contraction of the bladder, creating a positive feedback loop. When this reflex becomes powerful, enough signals are sent to inhibit the external sphincter. If these signals are stronger than the signals from the cortex, urination will occur. They make reflex can be inhibited or facilitated by several centres in the cerebral cortex. These higher centres keep the reflex partially inhibited except when tuition is desired. When it is time to urinate. They help by inhibiting the external sphincter. Voluntary urination usually occurs by contraction of the abdominal muscles, which increases pressure in the bladder, which of course stimulates the stretch receptors, exciting the attrition reflex. Inhibiting the external sphincter is usually causes complete emptying of the bladder, rarely more than 5 to 10ml remain. You can see in the graph good that contractions increase as the volume of urine increases. Urine excretion is the result of three renal processes glomerular filtration of substances from the blood, reabsorption of substances from the renal tubules into the blood, and secretion of substances from the blood into the renal tubules. So urinary excretion equals filtration minus reabsorption plus secretion. This begins when protein free fluid is filtered into Bowman's capsule. The fluid is filtered freely, so that concentration in Bowman's capsule is nearly identical to blood concentrations except protein. As his fluid passes through the tubules, is modified by the reabsorption of water and uh, and specific solutes, or by the secretion of other substances from the period tubular capillaries into the tubules. So now we can look at four different ways solutes are handled by the nephron to illustrate this formula. Um one some substances can be freely filtered at the Columbia capillaries, but neither reabsorbed nor secreted. Therefore, the excretion rate is equal to the filtration rate at the glomerulus. Uh, some waste products in the body are handled this way, such as, uh, creatinine. Um, so everything is filtered here at the glomerulus and then it passes through the nephron, uh, with no changes. Um. Here. Right here okay. And then number two substances can be filtered but then partially reabsorbed from the tubules back into the blood. So, uh, some substances are filtered and then partial or just some of them are reabsorbed where some of them are excreted. So their concentration in the urine changes. Uh, next. Uh, number three, some substances are freely filtered in the glomerular capillaries, but not excreted at all in the urine because they are reabsorbed from the tubules back in the blood. Uh, this can occur in the body with nutritional substances such as glucose. So, um. Glucose is filtered, ethical, memoryless, and then all of it is reabsorbed back in to the paired tubule capillaries. So there's none in the urine. Um. And then lastly number four uh, which is substances are freely filtered, ethical capillaries not reabsorbed. And additional quantities are secreted from tubule capillaries into renal tubules. So filtered here at the contrary captures and then more is secreted um from the of tubular capillaries. Uh this occurs in the body with acids uh and it permits a large amount of, of acids to be rapidly excreted if needed. Um. These illustrate the formula. Excretion equals filtration minus reabsorption plus secretion. Tubular reabsorption is much more important than tubular secretion for forming urine. Although secretion plays an important role for certain substances such as potassium and hydrogen ions. As we covered before, uh, some substances are not reabsorbed at all and therefore excreted, whereas other substances are not reabsorbed. Uh, but they are also secreted from the period tubule capillaries. So they're excreted at rates that are even higher. Other substances, such as electrolytes, are highly reabsorbed, so there's only a small amount in the urine. And even further, some nutritional substances are completely reabsorbed and do not appear in the urine at all. For most substances. For most substances, the rate of filtration and reabsorption are much larger than secretion. Therefore, increases in the rate of filtration can lead to large changes in excretion. One large advantage of all this filtration and reabsorption is it allows waste products to be removed rapidly from the body. It also allows all bodily fluids to be filtered and processed by the kidneys many times a day. Since plasma volume is around three liters and the filtration rate is around 180l a day, this allows the plasma to be processed about 60 times a day.