Renal System S2 Cell Bio
What is the main function of the Kidney
It is to concentrate our urine due to highly specialised filtration system to decide what substances are kept and removed from the body in urine
Ensure maintain water balance and regulate CV system to ensure blood pressure not to high or low
Waste production and maintain acid base balance of the blood
Endocrine roles for hormones secretion
What is chronic kidney disease
Lead to insufficient vit D to mean bone fragility and fractures as well as CV disease, mellitus and cancer types
Cna take Vitamin D skeletal fractures to improve 1,24 OH 203 in liver for more Ca2+ reabsorption
Greater PTH sceretion
More phosphate absorption in the intestine
Improve bone mass and quality
How to see if kidney are healthy
Can test urine sample by colour, clarity, smell, froth and taste
Honey urine disease - if there is glucose in the urine and this is indicator of diabetes
How are kidney involved in homeostatic water and ion content control
Regualtion of extracellular fluid volume to help blood pressure
Regulation of osmolaroty to make us thirsty or not
Maintain Na+ K+ Ca2+ and Cl- concentrations by balance dietary intake and urine loss
Regulate H+ and HCO3- to keep acid base ratio
How are kidneys involved in hormone production
There are no endocrine glands but they are important for endocrine pathway
What is the structure of the urinary system
There are the kindeys that pass waste to the ureter that then go to urinary bladder and then the urethra to then be excreted
What is the structure of the Kindey
There is an outer layer called the capsule, then the next layer in is called the cortex and then the medulla is next
The very centre is called the renal pelvis
The cortex will contain the most of the glomerellus system
The kidney have very high vascularisation due to many different vessels and capillaries as well as larger blood vessels
What are the nephrons
These are the filtering unit of the kidneys and each kidney has millions of them
They contain a filter called the glomerellus and a tubule
They work in a 2 stage process first the glomerula will filter the blood and the tubule will retrun the needed substanes back to the blood and remove the waste, this is called selectiove reabsorption and has to happen due to filtration being unselective
What are the stages of kidney filtration
There is glomerula filtration - uktra filtration of plasma in the glomerula and the movement of fluid from blood to the tubule
Tubular reabsoprtion - transport substances out of urine and return t to the capillary id they are needed
Tubular secretion- involves transport of substances into tubular urine and the Movement INTO URINE (Passive or active)
What are the anatomy of the nephron
The afferent arteriole bring blood to the neprhon where filtered in the glomerellus into the bowmans capsule where there is blood filtration
The filtered then enter the proximal tubule where there is reabsorption to the blood and secretion from the blood to lumen
Then enter loop of henle where there is reabsorption to blood in both descending and ascedning limb before then finally enter distal tubule where get reabsorption and secretion before the enter collecting duct where again have both ways molecule movement
What are the key process of nephron
Bowmans Capsule – There will be 180L of fluid per day will be filtered
Proximal tubule – 70% of the fluid is reabsorbed around 54L/ day left in the nephron and the solutes will be reabsorbed and water then also follow osmosis for some reabsorption
Loop of Henle – 90% of fluid has been reabsorbed so only 18L/day left and there is more solutre reabsorption but not as much water
Distal loop and the collecting duct - 99% fluid reabsorbed so only 1.5L/day left, solutes reabsorbed if needed and water reabsorbed if needed
What does the filtrate have to pass through in the glomerulla
It first has to pass through the glomerula capillary endothelium that is the most permeable layer and lets through the biggest material,
Next is the basal lamina in order to seperate the endothelium and epithelium and t this stops some bigger molecules
Finally is the bowmans capsule that is the finest membrane so stops the most stuff at the end
Why should there be no blood in filtrate
This is due to RBC are too big to pass through the capillary endothelium cells in the glomerullus blood vessesl
What can pass through the glomerullus
This is a high pressure filtration system and smaller molecules like water and smaller ions can pass through unlike red blood cells and proteins
The blood vessels in the glomerullus are leaky to allow water and solute to move across and leave blood for the kidney unlike other blood vessels
What is the glomerular filtration rate effected by
Capillary blood pressure - CBS
Osmotic pressure - OB
Fluid pressure - FB
Net filtration pressure = CBS - OP - FB
What is the glomerula filtrate rate
This is the filtration efficieny = 180L per day
The filtration coefficient = Surface area of the glomerullus as well as the permeability of the endothelial cells
The net filtration pressure is effected by blood, osmotic and fluid pressure
Overall rate will go up with pregnancy and get less with older age
How is the GFR kept stable by kidney
If there is a high blood pressure then constrict the afferent arteriole and dilate the efferent arteriole to lower blood pressure in the glomerular and stabilise GFR
If low blood pressure then dilate afferent arteriole and contrsict the efferent to increase hydrostatic pressure and increase blood pressure
The constriction can increase hydrostatic pressure in capillaries due to act like a dam so more blood pressure
How is the GFR regulated
Renal blood flow is determined by renal artery pressure and resistance in the arterioles as well as autoregulation supress change in renal blood flow
Ifd blood pressure drops to low then sympathetic nervous system overide renal autoregulation
This control is mediated by myogenic response or tubulo glomerula feedback
What is the myogenic response
If there is an increase in BP it cause strech ion channels to open so then smooth muscle will depolarise and contract
This then cause vasoconstriction so then more resistance so less blood flow through arteriole so then less filtration pressure in the glomerulus
What is the tubuologlomerular feedback loop
This will involve the NA/Cl absoprtion, NO and adenosine
There are macula densita cells that monitor blood flow through nephron and provide vasoconstrictors or dilators on blood flow to bring back to normal level to boost or lower GFR
What will happen if systemic blood pressure drops
The sympathetically induced vasoconstrictio of arterioles will start driven by the nervous system so then a decrease in renal blood flow and GFR
What does angiotensin and prostaglandins do
They will change the shape of podocytyes and the filtration slits will get wider so then there will be greater surface area for filtration to take place
The efferent and afferent artiole are both highly innervated
How meausure renal function and GFR
Creatine is a waste product from normal muscle breakdown as creatine is produced its filtered through the kidney and excreted In the urine due to no need in the body so all is removed in the urine - Doctors measure the blood creatinine level as a test of kidney function.
Creatinine is a waste product that is produced continuously during normal muscle breakdown. The kidneys filter creatinine from the blood into the urine, and reabsorb almost none of it.
Normal creatinine clearance is 88–128 mL/min for healthy women and 97–137 mL/min for healthy men.
What is tubular reabsoprtion
The transport of substances out of the tubular urine filtrate to then be returned to the capillary blood
99% of the glomerular filtrate is reabsorbed = 1.5L urine created from the 180L of fluid that is filtered each day
The high filtration rate is good for clearing foreign substances
What is tubular secretion
Transport of substances into the tubular urine for substances In the blood that wasn’t filtered out but isn’t wanted in the blood
Where does most of the reabsorption take place
Most will happen in the proximal convulated tubule as well as high level of secretion also taking place here
In the loop of henle there is solution concentration maintenance taking place as well as tuning of the water balacne so get reabsorption taking place
In the distal convulated tubule there is limited and final reabsorption and secretion taking place as well as in the collecting duct that alters water balance and osmolarity
What do the microvilli in the tubule do
They will increase the surface area to allow greater reabsoprtion and there is also much more mitochondria in cells to allow more ATP to be made to then allow more active reabsorption and secretion
What are renal proximal tubule epithelial cells responsible for
The reabsorption of solutes from glomerular filtrate and extretion of metabolic waste from the peritubular capillaries that then help for renal clearence as well as nephrotoxicity
What is are the general step of reabsorption
The solutes must first be transported across the tubular epithelium to the renal interstitial fluid before then crossin through the peritubular capillary membrane
The concentration gradient determines the transport mechanism used
What is passive transport
Molecules move down their concentration gradient from high to low via diffusion of facilitated diffusion such as for urea
What is active transport
Molecules move against there concentration gradient from low to high with the help of ATP and a carrier molecules
Primary active transport = This will directly use metabolic energy ATP hydrolysis to drive the transport of molecules from low to high
Secondary active transport uses energy from an electrochemical gradient to drive transport
This is used for Na and Na linked glucose reabsorption as well as salts and water into the blood
How is water reabsorbed
This is done by passive osmosis and is unrugkated and coupled to solute reabsorption
During dehydration there is greater ECF osmolarity so more concentrated urine as kidney save water = more reabsorption
Initially need to remove solute like NaCl in order to change the water potential in the tubule to make it higher and make the outside of tubule more concentrated so then water leave the tubule via osmosis down the water potential gradient
The higher the osmolarity number then = less water and more concentrated
Can increase the osmolarity of the interstitium by moving out the solutes from the tubule so then a lower water potential in the interstitium due to more solutes so then water is more likely to pass over from the tubule down the water potential gradient via osmosis
What are sodium transporters
They are loctaed in different segemnt of the nephron with 60-70% in the PCT
They are needed due to the large amount of glucose that is being moved out of lumen into blood and so is a way to control the rate and keep overall osmolarioty balance stable
The Na+K+ ATPase pump will maintain osmotic balance, as Na+ and K+ move againt the concentration gradient due to ATP hydrolysis to maintain a high Na+ in the extracellular and then high K+ in intracellukar areas
How is glucose moved across the cell memrbanes
Due to being very large and polar it cant use simple diffusion to cross lipid bilayers so need related transporters called glucose transporters to move them over membrane
There are 2 types = Sodium glucose linked transporters and faciliated diffusion glucose transporters
The kidneys rebasorb glucose via Na glucose transporters that are localised on the brush border membrane on the PCT with immune detection of their expression in the bowmans capsule
How do sodium glucose transporters work
Glucose is actively transported across the apical membrane by Na linked active transport – This is secondary active transport
Na is kicked out of the interstitial compartment by Na/K ATPase pump to then lower Na+ concentrations so then Na+ enter from tubule via SGLT2 and so brings a glucose molecules from tubule as well that is then taken into the blood through a GLUT 2 transporter via facilitated diffusion
There is a carrier protein that carry the glucose across the basolateral membrane into the peritubular fluid where it will, diffuse to the plasma
In normal person SGLT2 in early proximal tubule reabsorb 97% of the glucose in urine and the final 3% in SGLT1 in the proximal tubule so that urine is free of glucose
How is penecillin secreted in the war and today
The body will add penicillin to the urine to remove it so then have to take large volumes of it to get the desired effect of the penicillin but in ww2 there was shortage
This meant that had to find a molecules to compete with penicillin for the organic transporter responsible for its secretions into the urine so that the penicillin would stay in the urine so can have low usage due to shortage of it = Probenecid
90% secreted from tubular to the urine and 10% from the glomerular filtration to get it into the urine
What is the amount excreted formula
Amount reabsorbed + Amount secreted - Amount filtered = Solute excreted volume
What is excretion
This is the urine containing molecules that were not reabsorbed and were secretd into the nephron to be removed from the body