 This video will cover the following objective from the urinary system. Describe the structure and function of the major organs of the urinary system, the urethra, urinary bladder, ureters, and the kidneys. The kidneys are a pair of organs located within the abdominal cavity, just posterior to the peritoneal membrane. They're located within the lumbar regions of the abdominal pelvic cavity, just protected on the posterior surface by the floating ribs. The right kidney is a little more inferior than the left kidney because the large right lobe of the liver occupies a large amount of the upper right abdominal quadrant. The functions of the kidneys are to filter the blood and produce urine, and so urine provides a way to excrete waste from the body, such as the ammonia and urea that are nitrogenous waste products from the breakdown of protein. Urochrome is a pigment that gives urine a yellow color, and urochrome is a metabolic waste product from heme within hemoglobin. Another function of the kidneys is to provide a long-term mechanism regulating the blood pressure by regulating the blood volume. The kidneys can regulate the blood pressure. The kidneys also can regulate the chemical composition of the blood, so regulating the concentration of sodium and potassium in the blood, regulating the composition of calcium in the blood, regulating the pH of the blood, and so while the respiratory system provides a more rapid mechanism to help regulate the pH of the blood, the kidneys can excrete hydrogen ions in order to help raise the pH of the blood as a long-term control mechanism. The kidneys produce some hormones. The hormone erythropoietin is produced by the kidneys in order to stimulate the formation of erythropocytes in the red bone marrow. When the kidneys detect hypoxia, a low oxygen concentration, they secrete erythropoietin to stimulate erythropoiesis, or the formation of erythropocytes in the red bone marrow. The kidneys also produce the active form of vitamin D, so this activation of vitamin D is stimulated by another hormone, the parathyroid hormone, from the parathyroid glands in response to hypocalcemia, low blood calcium concentration, stimulates the parathyroid glands to secrete parathyroid hormone, which will have the effects of increasing blood calcium concentration in the kidneys. It will involve increasing the amount of calcium that gets reabsorbed into the blood and reducing the amount of calcium that gets excreted into the urine. But it will also involve stimulating the kidney to make the active form of vitamin D, and then vitamin D will have an action in the small intestine where vitamin D stimulates calcium absorption from the diet. The kidneys are surrounded by an outer capsule of connective tissue. There's adipose tissue surrounding a layer of fibrous connective tissue in the capsule, but then the layer lying deep to the capsule is known as the cortex. So the cortex is the outer region of the kidney that contains renal corpuscles and the tubules of nephrons. We'll see the renal corpuscles are important for initiating the process of urine formation, and then the tubules are important for regulating the composition of that urine, regulating what substances are reabsorbed back into the blood, and then also they're involved in the secretion of substances from the blood into the urine to excrete waste products out of the body. So the cortex is this outer layer within the kidney, and then deep to the cortex is the medulla. So the medulla contains renal columns that are extensions of connective tissue that separate the lobes of the kidney. So within each lobe is a renal pyramid. The renal pyramids contain the collecting ducts that will complete the final process of urine formation and transport the urine into the renal papilla, and so the renal pyramids also contain structures known as the nephron loops or the loops of Henle that are involved in the process of urine formation. So the loops of Henle and the tubules of nephrons and the renal corpuscles are all parts of a structural functional unit known as a nephron. The nephron is the structure in the kidney, the microscopic structure that filters blood and produces urine, and the last part of the nephron drains into the collecting duct that will then carry the liquid out through the renal papilla, and the liquid flowing through the renal papilla is urine at that point has been fully processed to produce the urine, and urine will flow from the renal papilla into minor galaxies, and then the minor calices come together to form major calices, and then the major calices come together to form the renal pelvis that attaches to the ureter. So the ureter is a muscular tube that transports the urine away from the kidney and to the urinary bladder where it will be stored. The ureter, as well as the large blood vessels and nerves attached to the kidney at the concave surface, the medial surface, a region known as the renal hyalum is where the renal pelvis attaches to the ureter. So here we see the histology of a ureter. The ureter is a muscular tube that functions to transport urine from the kidney to the urinary bladder and the smooth muscle in the wall of the ureter can contract involuntary waves of peristalsis that help to propel the urine into the urinary bladder. The outer layer out of antitisha is connective tissue that helps to stabilize the ureter, and then the inner layer is a mucosa with a transitional epithelium that enables stretching as the ureter fills with urine. The ureter is empty into the urinary bladder where urine is stored. There are two ureters coming from one from each kidney and the ureters open into the inferior posterior surface at the ureteral openings. There is a triangular region between the ureteral openings and the exit known as the urethra and that triangular region between the urethra and the ureteral openings is called the trigon. The trigon contains some sensory receptors that are involved in detecting the stretching of the urinary bladder and regulating the process of emptying the urinary bladder. The process of emptying the urinary bladder, commonly called urination, is also known as micturition, so the trigon is involved in regulating the micturition reflex. During micturition, the smooth muscle in the wall of the urinary bladder contracts. The smooth muscle is known as the detrusor muscle. So as the detrusor muscle contracts, this will force the urine out of the urinary bladder. The ureteral openings have one-way valves that prevent the urine from flowing backwards towards the kidneys and so the urine will be squeezed out through the urethra. The opening of the urethra is regulated by urethral sphincters. There's an internal urethral sphincter that consists of smooth muscle that's involuntarily regulated by the autonomic nervous system and then further distally along the urethra just inferior to the internal urethral sphincter is the external urethral sphincter. The external urethral sphincter consists of skeletal muscle surrounding the urethra and so the external urethral sphincter provides voluntary control over micturition and is regulated by somatic efferent fibers that are ultimately controlled by the cerebral cortex to give us the voluntary control over when we empty the urinary bladder when micturition occurs. So the organs of the urinary system are essentially identical in male and female except for the urethra and so the urethra in the female is shorter than the urethra in the male. The male urethra has three major regions that starts off with the prosthetic urethra traveling through the prostate gland then the spongy urethra travels through the penis and in between the spongy urethra and the prosthetic urethra is a very short region known as the membranous urethra.