Physiology (1) 27/3/2018. Hala Nsour

Transcription

1 Physiology (1) 27/3/2018 Hala Nsour

2 This lecture topic is about kidney function, nephron, renal blood flow (RBF), glomerular filtration (Ma fe da3e trj3/e ll slides) The doctor started with anatomy of renal system, which we were supposed to know from anatomy lectures. You can briefly see the renal system in the picture below which is composed of two kidneys, renal arteries & veins, ureter and urinary bladder which collects and stores the urine. The picture below is a section in the kidney, you can see the cortex (outer layer),medulla (inner layer),major and minor calyces,and renal pelvis which will end with ureter.

3 In this picture u can see the urinary bladder, the two ureter, and urethra down from bladder and prostate. There are many functions of the urinary system, some of them we already took in CVS 1. Get rid of waste (ingested or metabolized) 2. Control the volume and composition of B.F 3. Regulation of water and electrolytes balances 4. Regulation of fluid osmolality 5. Regulation of Acid - Base balance 6. Regulation of Arterial pressure

4 7.Secretion of hormones like the angiotensin hemopoietin (also called hematopoietin and erythropoietin ) 8.Gluconeogenesis :formation of glucose particularly happen during starvation 9. Producing erythropoietin & renin. Converting vit. D The doctor explained some of these functions: Water and electrolyte balance Eating and drinking habits salts and other electrolytes might increase 10 fold daily or decrease 1/10 fold daily slight or modest changes in ECF volume or (Plasma Na) Part of what we usually excrete from our body fluid volume done by the kidney, other part is excreted by respiration, skin, vapor. *Anything we get during the day must be execrated at the end of the day *What's not completed today will be completed the next day So there must be a balance between the input and the output, any disturbance, this mean there is pathogenesis, there is some sort of problem (disease) The imbalance occurs if 1) we take too much water 2) too much electrolytes (salts). 3) Shortage of water (starvation) and so on Despite all this, the kidney still keep the change very minimum (including the blood volume, extracellular volume, osmolality and electrolytes) Excretion of metabolic waste and foreign chemicals 1. Urea is the product from amino acids

5 2. Creatinine from muscles 3. Uric acid from nucleic acid 4. Bilirubin from Hb breakdown 5. Pesticides, drugs, food additives(toxic material excreted by kidney ) Regulation of arterial pressure: - As u supposed to remember from the cardiovascular system we have two mechanisms for regulation blood pressure by the kidney: 1_ long term: Excreting Na and water, and if u remember the antidiuretic hormones which depends on increase and decrease of BP *It takes hour or days 2_short term: Renin and angiotensin, again if u remember from CVS angiotensin take about 30 min to be fully active, that's considered to be short term, the doctor mentioned also with short term baroreceptors but without explainnation so to make it easier remember Short term..>> regulation blood vessel diameter, heart rate and contractility. Long term >> regulation of blood volume. Short term regulation mediated by *nervous system (by baroreceptor) *chemicals

6 Regulation of acid-base balance: excreting acid or base urine (Sulfuric & phosphoric acids) (Hydrogen and bicarbonate) Regulation of erythrocyte production: Secrete erythropoietin Any patient with any renal problem (disease) mostly complain from anemia (anemia is considered the main sign to renal diseases),because the kidney can't secrete erythropoietin so formation of RBCs will be reduced and this will lead to anemia. Regulation of 1,25 dihydroxy vitamin D3 production: Kidneys produce active form of vit. D, by hydroxylating this vitamin vit D is absorbed in non-active form, and the activation will be in the kidney. Glucose synthesis: From amino acids and other precursors during prolonged fasting this occur in starvation (prolonged). **Physiological anatomy as we already mentioned: We have 2 kidneys posterior, outside peritoneal cavity. 150 gm, size clenched fist. Outer cortex Inner medulla: renal pyramids papilla renal pelvis major and minor calyces ureter which ends in the urinary bladder. (If u want go and see slides 11/12/13, it s just a pic to kidney and nephron u can google it)

7 *The function unit of the kidney is the nephron, structure of the nephron is composed of different parts, one is the glomerulus, as u can see in picture we have inside a network of capillary (arterial capillary), this glomerulus has blood supply from the renal artery which enters as afferent arteriole then a network of capillary then leave as efferent arteriole. Glomerulus surrounded by epithelial cells which are forming bowman s capsule which is the first part of renal tubule then we have proximal tubule, loop of Henle (descending limb then ascending one) then distal tubule which ends with collecting tubules which later will be collecting duct & will go to pelvis then ureter. We can see in the pic (slide 12/13) peritubular capillary which is capillary surrounding the renal tubule, these capillary play a role in the absorption or secretion. Renal blood supply: Renal blood flow is about 22% of C.O (cardiac output) 1200 ml/min and again from anatomy : Renal artery interlobar arteries arcuate arteries interlobular arteries afferent arterioles glomerular capillaries efferent arterioles peritubular capillaries Venous system Interlobular arcuate Interlobar Renal vein

8 This is an actual diagram to the renal blood flow to the kidney, u can see the cortex (red part) and medulla (pink part) The purpose of the blood flow to the kidneys is not for nutrition, its mainly for the regulation of the functions we mentioned before (filtration, secretion, absorption and also controlling of osmolarity and blood volume), but there is a very little amount for nutrition. So regulation is the actual function of the kidney.

9 Nephron: Human body have one million nephron in each kidney, these nephrons will be decreased in function gradually after the age of 40 years so any disease or damage affecting the nephron is permanent, it s not capable to regenerate, so any problem or disease in kidneys will make a permanent damage (not curable) and ends up with renal failure, that s why people with kidney disease or diabetes end up with renal failure. Tubular system 1.Proximal 2.loop of Henle: a. Descending b. Ascending (last part thick segment) 3.Distal tubule collecting tubule cortical collecting tubule 4.cortical collecting duct (8 to 10) ducts join to form single large collecting duct Medullary collecting duct Renal papillae Renal pelvis Ureter Bladder (250 large coll. Ducts/kidney There are two sets of capillaries in the kidney: 1_ Glomerulus: Beginning with afferent arteriole then a network of capillary end with efferent arteriole, this type of capillary is arterial capillary, as we know all capillaries in

10 the body consists of artery and vein networks but in glomerulus of the kidney it is just arterioles. *Pressure in this capillary is very high it s about 60 mmhg, normal capillary pressure is about 37mmhg. Arteriolar capillary is not involved in exchanging process (reabsorption and secretion) they are mainly for filtration (filtrate plasma to nephron) 2_ peritubular capillary: This type of capillary is like other type of capillary in the rest of the body, this type is involved in the exchange process (reabsorption and secretion). We have two type of nephrons (see the pic below) 1_ cortical nephron: Which originates in the upper cortex, the end of loop of Henle in the upper part of medulla near to the cortex so most of it in the cortex and that s the reason of its name 2_ medullary nephron: (juxtamedullary) Starts in the lower end of the cortex, go deep in medulla even reach near the pelvic inlet, so it s going deeper in medulla than cortical type.

11 Cortical Nephrons: (70-80%) Glomerulus in outer cortex, short Juxtamedulary Nephrons (medullary) Gl. In deep cortex Long L - H 20-30% total Vasa recta 70_80% of the nephron that present in our kidneys are cortical the rest 20% are medullary,,,, why?? Kidney produces urine which is not pure water it contains some waste products and electrolytes,

12 normally the kidney uses only cortical nephron, so regulates normal day input and output When there is a shortage of water, the osmolarity of body fluids will be changed in this case other type of nephrons will be involved. So when there is a shortage of water, we need water so anything that is filtrated, most of it must be reabsorbed Increased absorption of water..increasing will get rid of electrolytes so the kidney will form concentrated urine. The principle of forming concentrated urine of diluted one is related to what we call counter balance and we will take about it next time in details. Kidney chooses the type of nephron according to body needs, the principle function of medullary type is mainly to produce concentrated urine when there is a shortage of water. Body needs is the actual stimulus for the regulation of the body fluids. Main function of the kidney is urine formation (regulation is the upper but that's because of the end product of kidney main function process urine) We have four step in urine formation..1.filtration 2.reabsorbtion 3.secretion 4. Excretion (Final step of urine formation)

13 First step of formation the urine is filtration, 20% of CO coming to kidney in the glomerulus arteriole, the plasma will filtrate then go to Bowman s capsule then to renal tubule So first thing is filtration, there must be a mechanism to regulate this huge amount of filtration increase it or decrease it according to body need Filtrated fluid is same as the plasma component but without protein (so no plasma protein present in filtrated fluid So what will happen to this filtration? Normally the plasma(blood ) is re circulate to kidney the filtrated fluid per day is about 180 liters( passing through the kidney per day ) so you can imagine how big it is (the doctor mean that the person cant loose this big amount of fluid per day, we will die )so part of this 180L which is reabsorbed, all of them absorbed except of 1.5 L which is the urine So most of filtrated fluid (mainly all of it ) is reabsorbed so if there is any imbalance between the output and input any different of even 1 or 2 milliliter per day this will make either edema or dehydration so this is prissy regulated or control each day So infiltrated fluid through the glomerulus per day about 180 L

14 Other possibility that some of the waste product not filtrated and the body don t need them so they are secreted from peritubular capillaries As we mentioned above four functions (steps) in urine formation filtration,absorption, secretion, excretion but the major one is the reabsorption because most of 180L per day is absorbed,so the bulk is the absorption so the mechanism of absorption is the main function part of kidney Urinary excretion rate (urine output)= (filter. Rate )- (reabs. Rate )+ secr. Rate

15 So as we see in the picture below we have four type of substance which run through the nephron and filtrated (A,B,C,D) Type (A) substance : this represent substances that filtrated and excreted,they are not absorbed nor secreted, and these are mainly creatinine and inulin(examples) Type )B) substance : They are filtrated but some of them are absorbed from the tubule to the peritubuler capillaries because the body need it, so not all of the filtrated excreted some of it absorbed, most the electrolytes belong to this type ( Na & k for example or any useful material ) Type (C) substance :

16 Here what is filtrated all of it absorbed, simple example of this is glucose Acc to student question It is clear from the doctor answer to her that these schemes illustrate the normal situation, but what happens in patients is different Where we can find glucose in the urine in patients with diabetes, which is not normal In other word.all of amino acids and glucose absorbed again to blood after filtration so normally we don t find them in urine Type (D) substance : here what filtrated not absorbed but secreted again,so all of it excreted in urine, example of this substance is hydrogen here there is secretion from peritubular capillary add to filtrated that s what is called renal handling A.Freely filtered, not reabs., no secretion excretion rate = filtration rate creatinine, inulin B. Freely filtered, partialy reabs, most electrolytes C. Freely filtered, not excreted completely reabs., a.a, glucose D.Freely filtered, not reabs., but secreted, H The doctor repeated how kidney handle with substances thousands times so I guess its very important ( for exam purposes ) Filtration, Reabs. And secretion Reabs. > secretion : So as we say the major function is for the reabsorption Secretion determines K+ and H+ Concentration

17 But the secretion depend on the body need, if the body need sodium for example keep it, not need it so secrete it and so on IF the Volume of plasma is only 3 L, and the filtration rate is 180, so the doctor ask how many times this 3 L filtrate in the kidney?? 60 time per day the plasma perfuse or filtrate in the kidney So you can imagine why there is huge GFR 1_Most waste product removed rapidly (effective) 2_Allow all body fluids to be filtered and processed by kidneys many times each day (precise & rapid control of volume & composition So again as we said the main blood supply to the kidney not for nutrient, less than 1% for nutrition, main (all) blood supply is for regulation of actual function.. This is everything for today,,,,,, I hope it s clear, and sorry in advance of any mistakes.. Best wishes