Week 6: Functions of the Urinary System Flashcards
What are the 5 functions of the kidney?
- Regulates blood volume and blood pressure
- By adjusting water lost in urine
- It does this through releasing erythropoietin and renin - Regulates plasma ion concentrations
- By controlling quantities of sodium, potassium and chloride ions lost in urine - Regulates body fluid pH
- Through controlling the loss of hydrogen ions and bicarbonate ions that are lost in urine - Conserves valuable nutrients
- By preventing excretion of valuable nutrients while excreting organic waste products
- Even though it is filtered out, the kidney helps save the good stuff, the stuff we need - Assists liver
- Through detoxifying poisons
How much of the blood does the kidney receive?
25%
What are the two types of nephrons, where are they located, and what is there abundance?
- Cortical Nephrons
- These make up 85% of all nephrons
- They are located within the superficial cortex of the kidney
- These have a relatively short Loop of Henle
- No Vasa recta, only peritubular capillary network. The efferent arteriole delivers blood to a network of peritubular capillaries - Juxtamedullary Nephrons
- These make up 15% of all nephrons
- Have a long Loop of Henle that extends deep into the medulla
- The peritubular capillaries connect to vasa recta
- These are important for the urine concentration mechanism (thanks to the long loop of Henle and vasa recta)
Describe the order of the filtration of in the filtration barrier of the glomerulus
Blood plasma goes through endothelial cells which have fenestrations. Then through the basement membrane, then through the podocytes which have foot processes
Where is the juxtaglomerular appartus located?
Located where the end of the thick ascending limb of the distal convoluted tubule touches the afferent and efferent arterioles of its parent glomerulus
Describe what the juxtaglomerular appartus consists of and the function of these cells
- In all nephrons, between the afferent and efferent arterioles runs a portion of the distal tubule. Within this part of the distal tubule, within the region that is closest to the glomerular/arterioles are macula densa cells (which act as salt detectors). These play an important role in regulating the tubular fluid and glomerular filtration rate
- Located just outside of the macula densa cells (closer in to the glomerular) are extraglomerular mesangial cells (or Laci’s cells). They are not sure what exactly these cells do, however we do know they play some role in renal auto regulation
- Within the afferent arteriole are granular cells (also known as juxtaglomerular cells) which secrete renin (it is important to note that these cells are also innervated by sympathetic nerves)
What are the 3 layers of the glomerular filtration barrier
- Endothelium of the capillary
- This is fenestrated, with pores of 70 – 90nm
- These also have glycoproteins known as sialproteins which are negatively charged - Basement membrane
- Is referred to as the glomerular basement membrane
- It is also negatively charged as it contains collagen, laminin and fibronectin
- Has pores that are 8nm (this is the layer which stops large substances from passing through) - Epithelial cells
- Large cells known as podocytes (foot processors) that create pores of 20 – 25nm
- Each of these pores, or slits created by the interlocking podocytes are covered by a filtration slit diaphragm (which are full of proteins)
These are also negatively charged – therefore can repel negatively charged particles
Glomerular filtration of any substance through the glomerular membrane is dependent on?
- Size
- Substances up to 4nm are freely filtered
- Substances greater than 8nm are excluded - Electrical charge
- All negative molecules are repelled (due to the barriers being negatively charged) - Binding to plasma proteins
- Due to the size restriction proteins are not filtered
- Thus, for substances that are bound to proteins, they cannot be filtered
- E.g. Calcium, fatty acids
What are some of the substances turned back and some that pass through the filtration barrier?
What are the 3 important renal processes that lead to the formation of urine?
If GFR is too high will you get rapid reabsorption or no reabsorption?
- GFR too high –> rapid movement of fluid through tubules –> insufficient time for reabsorption –> decreased reabsorption
What are the 3 factors governing glomerular filtration rate?
- The size of the capillary bed
- The bigger the capillary bed size, the more filtration that will occur
- The smaller the capillary bed size, the less GFR - The permeability of the capillaries
- If there is more permeability for substances, more filtration will occur
- The less permeability, the less the GFR
The Hydrostatic and osmotic / oncotic pressure gradients across the capillary wall
Does hydrostatic pressure in the glomerular capillaries favour filtration or reabsorption?
filtration
Does hydrostatic pressure in the bowman’s capsular space favour or oppose filtraiton
oppose
Does colloid osmotic pressure of the glomerular capillaries favour or oppose filtration
oppose
If you have constriction of the afferent arteriole will you have increase or decrease of GFR?
- Constriction of the afferent arterioles decreases GFR because less of the arterial pressure is transmitted to the glomerulus
Does dilation of the afferent arteriole increase of decrease GFR?
increases GFR
Does constriction of the efferent arteriole increase of decrease GFR?
Increase but eventually lowers, as build up of blood - backing up, eventually pressure will decrease as the presssure will suck the the blood out
Does dilation of the efferent arteriole increase or decrease GFR?
- Dilation of the efferent arterioles decreases GFR because more of the arterial pressure is transmitted to the glomerulus.
What are some of the hormones which control GFR?
- Epinephrine and Norepinephrine
- Reduces GFR
- Causes vasoconstriction by binding to alpha1-adrenoceptors on afferent arterioles - Endothelin
- Reduces GFR
- Causes vasoconstriction
- Produced by endothelial cells, distal tubular cells etc. - Angiotensin 2
- Reduces GFR and RBF
- Causes constriction of afferent and efferent arterioles (especially efferent) - Adenosine
- Reduces GFR
- Causes vasoconstriction of the afferent arterioles
- Produced within the kidneys - Prostaglandins
- Rise in RBF
- Causes vasodilation (often released during renal ischemia) - ANP and BNP
- Increase GFR
- Causes dilation of afferent and constriction of efferent arteriole
What are the two mechanisms which allow the kidney to autoregulate their blood flow?
- Myogenic mechanism
- Tubuloglomerular feedback mechanism
Explain the myogenic mechanism
This occurs in the afferent arteriole
Explain the tubuloglomerular feedback mechanism
ATP and adenosine in macula densa cells essentially are just signals
What are the two types of transport?
Primary active - uses ATP
secondary active - uses primary active transport to move substances into cell. This establishes a gradient from lumen into cell.
What does the PCT reabsorb and secrete?
- PCT Reabsorbs: Sodium, Glucose, amino acids, chloride, bicarbonate, potassium, proteins, urea and water
- PCT Secretes: Hydrogen ions, organic acids, bases, creatinine, any drugs, catecholamine, oxalate, organic anions, NH4+, Uric Acid
What does the thick ascending limb reabsorb and secrete and what important transporter does it have?
sodium, potassium, magnesium and calcium
secretes potassium and hydrogen
sodium potassium 2 chloride symporter
What does the early DCT reabsorb and what important transporter does it have
similar to thick ascending, impermeable to water and reabsorbs sodium, chloride and calcium
sodium chloride transporter
What is reabsorbed and secreted in the late DCT (remember theres two parts to it) - also name the transporters which faciliate it
- Principal cells
- Help in the reabsorption of sodium and water and bicarbonate
- Help in the secretion of potassium
- Aldosterone mediates Na+ reabsorption through epithelial sodium channels (ENaCs) - Intercalated cells
- Play an important role in renal acid base balance
- There are 2 types; Type A (alpha) and Type B (Beta)
- Alpha: At the apical membrane have Hydrogen-Potassium ATPase and Hydrogen-ATPase. At the Basolateral membrane they have bicarbonate reabsorption
Beta: The opposite happens. The apical membrane has bicarbonate secretion.
What is reabsorbed in the CD
sodium, water, urea and bicarbonate
which sites are urea reabsorbed?
cd and pct
Which sites in the nephron is Na reabsorbed?
PCT, Thick ascending limb, Early and late DCT and CD
Where is chloride reabsorbed in the nephron
Early DCT. thick ascending limb and pct
where is bicarbonate reabsorbed in the nephron
pct, late dct and cd
What is the function of the intraglomerular mesangial cells (x3)?
structual support, regulate blood flow control and keep filtration barrier free of anything
Name the components of the filtration barrier?
Endothelium, basement membrane and epithelial cells (podocytes)
What is the clinical significance of filtration slit proteins?
selective through its negatively charged nature
Describe the effects of a right ureter blockage with kidney stones on filtration pressures and glomerular filtration in the right kidney?
It would increase hydrostatic bowmans capsulre pressure therefore this would not favour filtration
what are the factors regulating glomerular filtration rate?
Renal autoregulation, neural control and hormonal control
What is the effect of high solute concentration in the distal tubule on the glomerular filtration rate? Explain the mechanism
Increased solute will decrease GFR
The macula densa cells will detect the high salt content and therefore trigger tubular glomerular feedback and trigger tubular glomerual feedback and myogenic mechanism (renal autoregulation)
What are the effects of angiotensin 2 receptor antagonists on renal blood flow and glomerular filtration rate?
Prevent constriction of afferent and efferent arterioles which will increase renal blood flow and therefore increase GFR
What aeffect would epinephrin have on renal blood flow and glomerular filtration rate?
Cause vasoconstriction on effect and afferent arteriole which would decrease renal blood flow and decrease GFR
What would be the effect of increase plasma renin on sodium reabsorption?
increase vasoconstriction on arteriole therefore decrease renal plasma flow and decrease GFR –> leads to increase sodium and water reabsorption
What is the role of macula densa in controlling the secretion of renin by juxtaglomerular granular cells?
detects solute concentration in DCT, if its too high, will secrete renin which will decrease GFR
discuss sodium reabsoprtion mechanism in principal cells of the nephron
reabsorbs sodium and excretes potassium through ENaC channels located
