Nephron Function

hi in this tutorial I'm going to talk about the function of the nephron in the renal Anatomy series we looked at the structure of the nephron in order to get the most out of this video I suggest that you make sure you've watched the renal Anatomy's series if you haven't you can check it out at hand written tutorials comm so I'll begin by drawing a nephron and this nephron is a little less than anatomically correct but when we talk about the physiology of the nephron it's easiest to draw it out like this so the blood enters the glomerulus through the afferent arteriole here and exits via the efferent arteriole here as the blood flows through here and then on to the Vaser actor and the peritubular capillaries elements of the blood get pulled into and out of this system of tubes filtration is the major way in which stuff gets out of the blood and into the nephron then as this filtrate moves along the nephron stuff can get added to it or removed from it in general more stuff gets removed from it then added to it so I'll just label these arrows F is for filtration r is for reabsorption which is the movement of stuff back into the blood S is for secretion which is the movement of stuff from the blood into the nephron and E is for excretion which is the urine on its way to the bladder let's begin by talking about filtration the filtrate contains a lot of stuff so I'm just going to talk about the most important ones in general the filtrate should not contain any large proteins like albumin or any red blood cells the presence of these suggests a disease process often within the glomerulus normal filtrate contains mainly water and within that water and many different solutes sodium and chloride usually move together so in this video I consider them as one rather than listing them individually there is also potassium and bicarbonate glucose amino acids creatinine and urea creatinine and urea are waste products and one of the main purposes of urine production is to remove products like these from the circulation before they build up and become toxic if everything is working okay with your kidneys then you produce filtrate at about 90 mils per minute per one point seven three meters squared of body surface area note that this is not the same as producing urine because most of the water will get reabsorbed so you don't dehydrate now let's look at what happens in the proximal convoluted tubule here we get reabsorption of potassium sodium chloride water amino acids glucose and bicarbonate and it's important to note that here 65% of the sodium chloride and 65% of the water that was filtered is reabsorbed furthermore about 100% of the amino acids and glucose that were filtered are reabsorbed because these are important nutrients for the body and it would be wasteful to excrete them and also 90% of the bicarbonate gets reabsorbed excreting too much bicarbonate would cause you to become very acidotic and therefore very ill secreted in the proximal tubule are uric acid which is another nitrogenous waste product and also organic acids which include many antibiotics this is the way in which they are removed from the body now the loop of Henle is all about concentration of urine it does this by reabsorbing water in the descending limb which is highly water permeable and then reabsorbing 25% of the filtered sodium chloride in the ascending limb this means that what we are left with is a higher concentration of waste products such as urea in the distal convoluted tubule we reabsorb about 5% of the filtered sodium chloride and some water so you can see that the main way the nephron reabsorbs water is by movement of sodium chloride which the water follows due to the osmotic gradient in the distal tubule some potassium and some hydrogen ions are secreted this means moved back into the nephron so a simple way to think about the nephron is that the proximal tubular does most of the reabsorption and secretion the loop of Henle does the concentration and the distal tubule does the fine-tuning this brings us to the collecting duct and here one last bit of reabsorption occurs some urea about 5% of the filtered sodium chloride and some water are reabsorbed and this leaves us with excretion the components of excretion are mainly water sodium chloride potassium bicarbonate creatinine and urea and know that creatinine is not reabsorbed or secreted along the nephron this is why it is used as a marker of the glomerular filtration rate for example if the level of creatinine in your blood begins to rise it may suggest there is a problem with filtration in the glomerulus one last thing I would like to mention is that there are two major hormones which control the rate of water excretion these are aldosterone which is part of the renin-angiotensin-aldosterone system which you can find out more about in the our AAS handwritten tutorial and this acts on the distal tubules and increases the rate of water reabsorption the other is antidiuretic hormone also known as vasopressin which is released from the posterior pituitary and this causes more water to be reabsorbed by the collecting ducts both these hormones act when the body is in a state of under hydration and needs to retain water and that's an overview of the function of the nephron if you've enjoyed this tutorial please help us produce more by making a donation at WWE and written tutorials calm

Channel: Handwritten Tutorials

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Keywords: Filtration, Reabsorption, Secretion, Excretion, nephron, kidney, function, creatinine, urea, urine, glomerulus, aldosterone, ADH, antidiuretic hormone, vasopressin, medicine, medical, doctor, student, tutorial, lesson, handwritten tutorials, Lessons, Learn, med school, pre-med, USLME, Step 1, USMLE help, USMLE lessons, USMLE tutorials, free USMLE, Animation

Id: vNvZaGcLzEo

Length: 7min 54sec (474 seconds)

Published: Sun Jun 10 2012