BIOL 1344 Lecture 23Outline of Last Lecture I. Osmotic Gradient and DefinitionsII. Urine ReabsorptionIII. GFR Control Outline of Current Lecture IV. Transport Maximums and Thresholds of UrineV. Blood Flow through KidneysVI. MicturitionCurrent LectureTransport Maximum (Tm)- amount of substance reabsorbed per minute. Renal Threshold: physiological limit of reabsorption, if a substance goes over this limit, it spills out with the urine. If a substance is very useful such as glucose, the threshold is high but if it is useless (urea), the threshold is low. There are also variable thresholds which will change based on the body’s current need, substances with this threshold include water and sodium. The Tm for glucose is 320 mg/min. Blood Flow through the kidneys: 1250 ml/min but only plasma gets filtered so this is about 700 ml/min going through glomerulus. Because of GFR about 125 ml/min actually gets filtered which is 16-18%. Tubular Secretion: the pH of urine is 6.0. Flowing into filtrate and then leaving as urine are substances such as potassium, phosphate, toxins, poisons, ammonia, antibiotics, etc. Blood flowgoes opposite of urine flow as a result of counter current mechanism. Micturition: this is the act of passing urine and it is controlled by T11-L2 and the sympathetic nerve fibers. There is the internal urethral sphincter which opens and closes involuntarily through the sympathetic nervous system. Then the external urethral sphincter is voluntary because it is controlled by skeletal muscles and the parasympathetic spinal nerves. When the bladder fills to 300 ml there is a desire to void the urine. If the person does not urinate at this These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.point, the urge passes and the volume can then get up to 600-700 ml through distending the bladder. Any more than this volume results in involuntary
View Full Document
Unlocking...