kin 132 UR Flashcards
What are the 4 main processes of the urinary system?
- Glomerular filtration
- Glomerulus to capsular space
- Blood turns to filtrate - Tubular reabsorption
- Renal tubule to peritubual capillaries - Tubular secretion
- Peritubual capillaries to renal tubule
4.Urinary excretion
- Combination of the other 3
- Total amount excreted from the body
- Glomerular filtration + Tubular secretion - Tubular reabsorption
What are the main goals of the UR system
- Regulating water, ions, acidity, and blood volume
- eliminating waste from body
What is the principle of filtration
Using pressure to move fluids through a membrane
The glomerulus is very efficient at filtration fluid. Why?
- Large surface area
- Greater permeability: has more pored
- Higher blood pressure forcing the fluid through harder
Explain why the Glomerulus filtration rate is highly regulated
Too high:
- Not enough time for re absorption leading to too much urinary excretion
Too low:
- Nearly all fluid reabsorbed = little exertion
- Some waste not properly excreted
Explain the 4 sterling pressures
4 pressure:
1. Blood osmotic
2. Blood hydrostatic
3. Filtrate hydrostatic
4. Filtrate osmotic
Osmotic pulls towards itself Hydrostatic away
- The combination of (Blood hydrostatic and filtrate osmotic) - (blood osmotic + filtrate hydrostatic) = net filtration pressure
- Net filtration pressure always favours filtration trough the glomerulus
Explain how NFP affects GFR
- Higher Blood pressure = Higher blood hydrostatic pressure = higher net filtration pressure = higher glomerulus filtration rate
- Lower BP = lower blood hydrostatic pressure = lower NFP = lower GFR
Explain why blood pressure change doesn’t affect the GFR a lot
the GFR is highly regulated by 2 processes:
- Myogenic mechanisme
- Tubuloglomerular feedback
Explain myogenic mechanism . explain what happens if blood presure increases
Stimulus: Blood pressure is changes, causing a stretch or shrinking of the arterial
Response: Arterioles detect the stretch or contraction of the arterial walls and either vasocontrict or vasodilate afferent or efferent arterial in order to counteract the change if the arteriole due to blood pressure
eg. Blood pressure increases = arteriole walls stretch = larger blood hydrostatic pressure = larger NFP = Larger GFR
to counter this, the myogenic mechanism:
vasoconstriction of afferent arteriole and or vasodilation of efferent vasodilation = lower blood hydrostatic pressure = lower NFP = lower GFR
Explain tubuloglormerular feedback
- slower to respond than myogenic mechanism
- Stimulus: A increase in blood pressure increases the salt concentration of the blood
- This is detected by the macula dense cells of the juxtaglomerular apparatus, causing a decrease in secretion of nitric oxide
- Less NO available to bind to the beta 2 receptors of the afferent arteriol = decreased vasodilation = decrease in blood hydrostatic pressure = decreased net filtration pressure = decreased GFR
How can GFR be changes?
- GFR is closely regulated by intrinsic renal auto regulation
- External mechanisms that involve neurvous or hormones are strong enough to overcome I=the intrinsic renal auto regulation
Explain how nervous system stimulus can change GFR
a decrease in:
1. venous pressure
- detected by baroreceptors in large vein
- atrial pressure
- Detected by baroreceptors in atriums - arteriole pressure
- detected by baroreceptors in the arterial
These 3 send a signal to the vasomotor center to increase sympathetic firing to the adrenal gland = increased secretion of EP and NorEP = more bind to alfa receptors = vasoconstriction = lower blood hydrostatic pressure = lower NFP = lower GFR
How can GFR be changed directly without changing the sympathetic firing?
A change in arteriole pressure can directly change GFR
Explain hormonal regulation of GFR with RAAS (Renin Aldosterone Angiotensin System)
- Liver continuously releases angiotensinogen, which is inactive
- A decrease in plasma volume leads to:
- increase in salt concentration detected by macula dense
- decrease in arterial pressure sending signal to vasomotor center = increased renal sympathetic firing - Both of these factors signal to the juxtaglomerular cells telling them to secrete renin
- Renin converts the angiotensinoigen circulating in blood stream into angiotensin 1
- When angiotensin 1 goes through the lungs and kidneys, it comes into contact with Angiotensin converting enzyme which converts it into angiotensin 2
- Angiotensin 2 binds to alpha receptors on the afferent arterioles causing vasoconstriction as well as contracts mesangial cells
- these things lower GFR
Explain hormonal regulation of GFR with Atrial natrieurtic peptide
- A change in plasma volume changes the distention of the atria (stretch of the atria)
- A stretch of the atria causes a release of atrial natriuretic peptide
- Atrial natrieuretic peptide binds to beta 2 receptors causing vasodilation as well as causing the mesangial cells to relax
- these 2 things cause GFR to increase
How does changing the relaxation or contraction of mesangial cells change GFR
- Relaxation: increases the glomerulus filtration surface area increasing the GFR
- Contraction: decreases the glomerulus filtration surface area
Explain what tubular reabsorption and secretion are
Once filtered the body decides what it wants to pick up from the filtrate moving it from renal tubule to peritubular capillaries and what it wants to secrete, moving it from perituibual capillaries to the renal tubule
How to determine how much is excreted
Excreted = filtered + secreted - reabsorbed
Explain the areas of the renal tubule
- Tubular lumen: inner cavity of the renal tubule
- Tubule epithelial cell: cells making up walls of the renal tubule
- Interstitial fluid: fluid surrounding tubule
- Peritubular capillaries: blood vessel that runs along the tubule
- Tight junctions: connection points between adjacent tubular epithelial cells
- Apical membrane: side of epithelial cell and lumen of tubule
- Basolatteral membrane: between epithelial cell and interstitial fluid
What are the two pathways to travel between lumen and interstitial fluid of the renal tubule
Paracellular: through tight junction
Transcellular: through epithelial cells
What are the different types of passive transport? Flows high to low concentration
- Simple diffusion (chemical diffusion): ions move through a membrane
- Facilitated diffusion: Ions move through a membrane protein
- Osmosis: simple diffusion of water
- Electro: movement from a change to its opposite charge
What needs to happen for it to be considered active transport?
At least one ion has to be moving against its gradient
What are the two types of active transport that move two ions?
Co transport: moves two ions the same way, with one moving against its concentration gradient and one moving with its gradient
Counter transport: Moves two ions in opposite directions, one going against its gradient and one going with its gradient
What is the difference between primary and secondary active transport?
Primary: Uses ATP breakdown in order to power the active transport
Secondary: Movement in response to what primary transport does
What are the sections of the renal tubule?
- Glomerulus
- Glomerular capsule
- Proximal tubule
- Depending loop of henley
- Ascending loop of henley
- Distal tubule
- Collecting duct
Explain reabsorption and secretion in the proximal tubule
- ATP breakdown powers the movement of sodium from the renal tubule into the interstitial fluid which also moves K+ into the cell (counter transport)
- Potassium exits the cell back to the interstitial fluid via facilitated diffusion
- The leaving of sodium causes the concentration of sodium in the cell to decrease
- Sodium flows with its gradient from the renal tubule into the cell, carrying with it X(can be amino acid or glucose) as well as moving H+ out into the renal tubule. This is a example of secondary transport as it happens because of primary transport
- Influx of X into the cell causes an increased concentration of X in the cell which is higher than that of the concentration of X in the interstitial fluid. X flows from cell to interstitial fluid
What percents of glucose amino acids and sodium should be reabsorbed from the renal tube in a healthy person? What percent of hydrogen should be secreted?
100% glucose
100% amino acids
65% sodium
Hydrogen amount depends on blood levels
What is obligatory water reabsorbtion? How much of total water reabsorption happens in the proximal tubule?
Water reabsorption due to water following solutes. 65% of water reabsorption occurs in the proximal tubule.
Explain obligatory water reabsorption. Explain the primary and secondary processes
Primary process - solute and water
- solute (sodium, glucose, amino acids) movement causes a change in osmotic pressure, low where it left and high to where it goes
- Water flows via osmosis through aquaporins to try and balance the osmotic pressure
Secondary process - other solutes
- The movement of water changes the concentration of ions as when water leaves they become more concentrated and where water moves to becomes less concentrated
- ions now flow from high concentration to low concentrations causing a change in osmotic pressure. Low osmotic pressure where the solutes leave and high where they move to
- Water follows the solutes in order to correct the osmotic pressure
How to calculate osmotic pressure
osmotic pressure = solutes/solution
Explain reabsorption and secretion in the loop of henley
- 15% more water gets reabsorbed back into the proximal tubule as its still moving to correct the osmotic pressure created in the proximal tubule
Aswell…
- 25% of sodium gets absorbed
- 35% of chloride
- 25% of potassium
Explain where obligatory water reabsorption happens and what percent
65% in the proximal tubule
15% in the loop of henley
80% of total water reabsorption is obligatory
Where does water get reabsorbed in the loop of henley?
Only in the defending loop of Henley because the ascending part has no aquaporins
Explain re absorbtion and secretion in the distal collecting duct
- Reabsorbed another 6-9% of sodium
- Reabsorbed a varying amount of water depending on hormones
- Secretes a varying amount of potassium
- Na+ flows from renal tubule into cell via facilitated diffusion
- Active transport moves Na+ against gradient from cell to interstitial fluid and moves K+ against gradient from interstitial fluid into cell
- K+ moves from cell into renal tubule via facilitated diffusion
Explain how aldosterone lowers the excretion amount of water and sodium (RAAS). Facultative water reabsorption.
- Angiotensin 2 is formed
- Angiotensin signals to adrenal gland to secrete aldosterone into the blood
- Aldosterone binds to collecting duct and increases amount of transport proteins allowing more solute reabsorption = more water reabsorption
- this contributes to the amount of facultative water reabsorption
True or false. The body can make it so no water is secreted.
False. 80% of water is reabsorbed via obligatory water reabsorption and up to 19.8% can be added via facultative water reabsorption. At least 0.2% is always excreted
Explain facultative reabsorption via Antidiuretic hormone
- Very little aquaporins in the distal tubule
- ADH causes aquaporins to be inserted into the distal tubule and collecting duct= increase of water reabsorption
- Plasma volume goes down and osmotic pressure increases
- This causes the posterior pituitary gland to secrete more ADH = more aquaporins of distal tubule and collecting duct = increased water reabsorption = decreased water excretion
vise versa with high plasma volume and low osmotic pressure
Explain facultative water reabsorption levels at different states
Normal: 19%
Dehydrated: 19.8%
Overhydrated: as little as 0%
Explain the function of atrial naturetic peptide
- Change in plasma volume will change the stretch of the atria
- Increase in stretch from increased plasma volume = signals for release of ANP
- ANP inhibits mechanisms of reabsorbing Na+ in the collecting ducts = greater water excretion
What does ANP do?
- Inhibits the reabsorption of Na+ so that less water is reabsorbed = increases water excretion = decrease in blood volume and pressure
- Inhibits the release of ADH and aldosterone, further reducing water retention
- Vasodialates afferent arteriol to increase GFR
Explain the pathway of urinary flow
- Urine leaves kidneys into ureters into the bladder propelled by contractions ureter walls and gravity.
- Urine is stored in bladder and is inverted by 3 neural pathways: Sympathetic, parasympathetic, and motor which controls the filling and release on the urine in the bladder
What are the conditions of the bladder during filling?
Detrusor: Parasympathetic inhibited = relaxed
Internal urethral sphincter: sympathetic stimulated = contracted
External urethral sphincter: somatic motor stimulated (contracted)
What are the conditions of the bladder during excretion (micturition)
Detrusor: Parasympathetic stimulated = contracted
Internal urethral sphincter: sympathetic inhibited = relaxed
External urethral sphincter: somatic motor inhibited = relaxed
What types of muscle are the detrusor the internal and external urethral sphincter
Detrusor: Smooth muscle
Internal urethral sphincter: Smooth muscle
External urethral sphincter: Skeletal muscle
How does the body know when the bladder is full
Bladder fills up and stretches as it fills more. At a certain point of stretch, mechanoreceptors send a signal to brain to tell it the bladder is full
Explain the stages of micturition
1st part) mechanoreceptors send a afferent signal to spinal chord and the pons that the bladder is full
2nd part) efferent signal returns from spinal chord to tell the detrusor to contract and both sphincters to relax
3rd part) A completed micturition reflex causes urinary excretion
Explain voluntary override of bladder function
- Have ability to voluntarily initiate and stop micturition
- If wish to stop micturition, a efferent signal comes from the pons to the external urethral sphincter telling it to stay contracted
- Can only override micturition reflex for a limited amount of time
What is diuresis and natriuresis.
Diuresis: elevated urine excretion
- Will be dilute urine
- Diuretic: substances that causes diuresis
Natriuresis: Reduced urine excretion
- Will be highly salty urine
- Natriuretic: substances that causes natriuresis
What can stimulate the thirst center in the hypothalamus?
Mechanoreceptors: detect blood volume changes
Baroreceptors: detect blood pressure changes
Osmoreceptors: detect blood osmotic pressure changes (most important)
Dry mouth
Explain what hyponatremia is
- Large loss of water and solutes from body
- Water is replaced by plain water with no solutes
- Leads to low osmotic pressure
- Water flows from high osmotic pressure in interstitial fluid to low in the cells
- Cells get water intoxication from containing too much water
Explain what alkalosis and acidosis are
Alkalosis: Decrease in H+ and increase in PH, increase in alkalinity
Acidosis: Increase in H+ and decrease in PH, decrease in alkalinity
What are the two types of buffers for the acidity of the blood as well as their sub types
Chemical buffers:
- Bicarbonate buffer system
- Phosphate buffer system
- Protein buffer system
Physiological buffers:
- Respritory buffer
- Renal buffer
Explain chemical buffering
- 1st line of defence, immediate response
Has a general form of:
Buffer(H+) <—> Buffer + H+
- Buffer can be bicorbonate, phosphate or a protein
Explain how a chemical buffer works with a alkalosis vs a acidosis
alkalosis: Buffer releases H+
Acidosis: buffer binds to H+
Explain where the the different types of chemical buffers work
Bicarbonate: extracellular buffer
Phosphate: Intracellular buffer
Protein: Intracellular buffer
Explain the first part of the physiological buffers: respritory buffer
- 2nd line of defence, minutes to respond
- Alters ventilation in order to alter CO2 in body
- Higher CO2 = higher acidity
in response to:
Alkalosis: Decreased ventilation = increased CO2 = increased acidity
Acidosis: Increased ventilation = lower CO2 = Lower acidity
Explain the second part of the physiological buffers: renal buffering
- 3rd line of defence, hours to days
Renal mechanism 1:
1. Water and CO2 produce bicarbonate and H+ in cells
2. H+ crosses into the renal tubule and binds with filtered bicarbonate
3. Bicarbonate gets reabsorbed into peritubalar capillaries
4. For every one filtered bicarbonate a bicarbonate gets reabsorbed
Renal mechanisme 2
1. Exact same as mechanism 1, but instead of bicarbonate that accepts the H+ in renal tubule its (HPO4)2-
Mechanisme 3
1. Glutamine enters the cell from either the renal tubule, the peri tubule capillaries or produced in the epithelial cells
2. Glutamine breaks down into bicarbonate and NH4+
3. NH4+ gets secreted counting as a H+
4. Bicarbonate gets reabsorbed into peritubular capillaries
5. For every one glutamine, 1 bicarbonate gets reabsorbed
Explain what happens in the renal mechanisms in response to alkalosis
Mechanisme 1 and 2: Minimum secretion of H+ and reabsorption of bicarbonate
Mechanisme 3: Minimize secretion of NH4+ and reabsorption of bicarbonate
Explain what happens in the renal mechanisms in response to acidosis
Mechanism 1 and 2: Maximize the secretion of H+ and the reabsorption of bnicarbonate
Mechanisme 3: Maximize the secretion of NH4+ and the reabsorption of bicarbonate
leads to acidic urine
