Flashcards in Renal System Deck (59):
What are the 6 functions of the kidney?
- Regulation of water and electrolyte balance
- Regulation of arterial pressure
- Excretion of metabolic waste products or foreign chemicals from the body
- Regulation of blood pH (e.g. via regulation of H+ and HCO3-)
- Regulation of erythrocyte production
- Regulation of hormone production e.g. calcitriol (vitamin D)
- Regulating blood glucose levels
What are 5 effects that failing kidneys can have on the body?
- High blood pressure
- Shortness of breath
The movement of water through a selectively permeable membrane from an area of lower solute concentration (high water concentration) to an area of higher solute concentration (low water concentration).
What is osmosis pressure?
The pressure required to prevent net water movement.
- A measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane compared to pure water.
- Dependent on the number of particles in solution (but independent of the nature of the particles).
What is meant by hyperosmotic, isosmotic, and hyposmotic? Give examples of each.
- Hyperosmotic: a solution with a higher Osm than another (a 300mM/L NaCl vs 300mM/L urea)
- Isosmostic: two solutions with the same Osm (150mM/L NaCl vs 300mM/L urea)
- Hyposmotic: a solution with a lower Osm than another (150mM/L urea vs 150mM/L NaCl)
What is tonicity?
Takes into account the concentration of a solute and ability of the particle to cross a semi-permeable membrane.
Does NaCl have low or high permeability? What affect does a 150mM solution of NaCl have on a cell?
Cell neither shrinks or swells.
What is the osmolarity of cell cytosol?
Does urea have high or low permeability? What affect does a 300mM urea solution have on a cell?
Cell swells and will eventually burst, because the urea solution is hypotonic.
Distinguish between a hypertonic, isotonic, and hypotonic solution.
- Hypertonic: a solution with a higher POsm than other. Water will leave the cell, causing shrinkage.
- Isotonic: two solutions with the same POsm. No net water movement.
- Hypotonic: a solution with a lower POsm than another. Water will move into the cell causing swelling.
What are the 5 reasons for maintaining osmolarity?
- Setting the membrane potential
- Generating electrical acitivity in nerve and muscle
- Initiation of muscle contraction
- Providing energy for the uptake of nutrients and the expulsion of waste products
- Generation of intracellular signalling cascades
What percentage of a male's mass is fluid? What fraction of the fluid is extracellular? What percentage of that is plasma? What percentage of blood is plasma?
60% fluid = 42 L
1/3 extracellular = 14 L
20% plasma = 2.8 L
Blood is about 55% plasma.
Therefore 2.8 L of plasma = 5 L blood
What contributes to daily intake and output of fluids?
Intake: metabolism (8%), foods (28%), beverages (64%)
Output: faeces (4%), lungs (12%), skin (24%), urine (60%)
What ions have high extracellular concentrations? Which have high intracellular concentrations?
High E: Na+, Cl-, Ca2+
High I: K+
What are the three layers of the external anatomy of the kidneys?
1) Renal capsule: physical barrier, protection against trauma, maintains the shape of the kidneys.
2) Adipose capsule: padding, physical protection, maintains the position of the kidneys.
3) Renal fascia: anchors the kidneys to surrounding structures.
All are connective tissue
What is a lobe of a kidney made up of?
Medullary pyramid, overlapping cortex and half of each column.
What are the ion gradients in the body responsible for?
Responsible for the likes of setting the membrane potential, generating electrical activity in nerves and muscle, providing the energy for the uptake of nutrients and the expulsion of wastes.
What is responsible for the asymmetric distribution of ions between the intracellular and extracellular fluids?
Specialised transport properties of the cell membrane.
What is the equation for excretion?
Excretion = Filtration + Secretion - Reabsorption
What are the three basic processes involved in the formation of urine?
1) Filtration at the glomerulus
2) Tubular reabsorption
3) Tubular secretion
What is the glomerular filtration rate?
125mL/min (25% of the total renal plasma flow) = 180L/day
Describe the contents of glomerular filtrate.
Similar solute concentration (glucose, electrolytes etc.) to plasma. Lacks proteins and other high molecular weight compounds, and is free from blood cells.
Which capillary bed is the only one to have arterioles before and after it? What does this allow for?
Allows for tight regulation of pressure gradients to maintain near constant glomerular filtration rate. Increases in arterial pressure can be buffered by vasoconstriction of afferent arteriole whilst decreases in pressure can be buffered by vasoconstriction of efferent arteriole.
Why is glomerular filtration rate relatively constant? What is urine output directly proportional to?
Blood flow to the kidney is tightly regulated, thus glomerular filtration rate is relatively constant.
Urine output is directly proportional to renal pressure.
What does the equation P = QR mean?
Pressure = flow rate x resistance
What is net filtration pressure (NFP)? What is this value usually?
The pressure that determines how much water and small dissolved solutes leaves the blood (10mmHg)
What is glomerular filtration dependent on?
Net filtration pressure.
What is meant by glomerular blood hydrostatic pressure (GBHP)? What is this value usually?
The mechanical pressure between the afferent and efferent arterioles i.e. within the glomerulus: drives the plasma filtrate from the capillaries of the glomerulus into the capsular space (50mmHg).
What is meant by capsular hydrostatic pressure (CHP)? What is this value usually?
The pressure exerted on the plasma filtrate by the elastic recoil of the glomerular capsule (15 mmHg)
What is meant by colloid osmotic pressure (BCOP)? What is this value usually?
The osmotic force of the proteins left in the plasma: the proteins exert an increasing osmotic pull on the water in the plasma filtrate (25 mmHg).
How does NFP, GBHP, CHP, and BCOP relate to one another?
NFP = GBHP - CHP - BCOP
= 55 - 15 - 30 mmHg
= 10 mmHg
What are the three types of regulation of glomerular filtrate?
1) Autoregulation: vasoconstriction
2) Neural: increased sympathetic nerve activity leads to vasoconstriction.
Describe the two ways hormonal regulation occurs.
1) Angiotensin II via vasoconstriction of afferent and efferent arterioles
2) Atrial Naturetic Peptide via relaxation of mesengial cells, increasing SA available for filtration.
What are the two types of nephrons?
1) Cortical nephrons (dilute urine)
2) Juxtamedullary nephrons (important in the production of concentrated urine)
What occurs in the proximal convoluted tubule?
The largest amount of solute and water reabsorption from filtered fluids.
- 60% glomerular filtrate, 60% NaCl and water, 100% glucose (not in diabetes mellitus), amino acids, other organic nutrients and a variable amount of HCO3 are reabsorbed.
What is the proximal convoluted tubule highly active in? What is it characterised by?
- Highly active in membrane transport processes with reabsorption of water, ions, and glucose
- Characterised by the presence of a highly developed brush border increasing the SA.
Describe the process of absorption in the proximal convoluted tubule.
- Na+ gradient maintained by Na+/K+ ATPase on basal surface of epithelial cells.
- Na+ movement into tubule cells occurs via symporters (e.g. Na+/glucose symporter) and antiporters (Na+/H+ allowing H+ to be secreted)
- Glucose and other solutes can then diffuse down their conc. gradient
- Na+ movement then allows water movement via osmosis
- Reabsorption of water increases the concentration of the solutes that are left. These move down their conc. gradients.
- Lipid-soluble substances diffuse by the transcellular route
- Cl-, K+ and urea diffuse by the paracellular route.
What is the osmolarity in the proximal convoluted tubule?
Similar to plasma (290 Osmol/L)
Describe the permeability of the descending loop of Henle, water movement, and the concentration of the filtrate.
- Low permeability to ions and urea
- Highly permeable to water
- Because the interstitial fluid is highly concentrated in the medulla of the kidney, water moves out of the tubule via osmosis
- By the bottom of the loop of Henle, the filtrate is very concentrated (1200 mOsmol/L)
Describe the thick ascending loop of Henle
- Especially thick segment
- Impermeable to water
- Na+, K+, Cl- actively reabsorbed
- By the time, the filtrate gets to the top of the loop of Henle, it is very dilute (100 mOsmol/L)
Describe the countercurrent mechanism of the loop of Henle.
- Descending limb impermeable to NaCl
- Ascending limb impermeable to water
- Interstitial fluid incredibly concentrated in tip of medulla
What happens in the distal convoluted tubule and collecting duct?
- Additional reabsorption of NaCl
- Water permeability dependent on antidiuretic hormone
- In the absence of ADH, urine is dilute
What is another name for ADH?
What does ADH act on? Describe how it leads to concentrated urine.
Acts on the last part of the DCT and collecting duct
Stimulates the insertion of aquaporin-2 containing vesicles into the apical membrane. Aquaporin-2 is a water channel, thus water can now move from the tubule into the cell and because the basolateral membrane is always relatively permeable to water, water is ultimately reabsorbed into the blood. Facilitates the reabsorption of water resulting in very concentrated urine.
What effect does alcohol have on ADH? What are the consequences of this?
Alcohol inhibits ADH. Urine will be very dilute. Despite the fluid intake, you become dehydrated.
Describe the effect that water and and isotonic solution would have on the body.
Water: rapidly equilibrates throughout the ICF and ECF, decreasing osmolarity.
Isotonic solution: will remain in ECF. Has no effect on plasma osmolarity.
Where are precursors for ADH made and stored?
The precursor to ADH is made in the hypothalamus and stored in vesicles in the posterior pituitary.
What do osmoreceptors in the hypothalamus sense? What happens if these things are sensed?
Increase in Na+ concentration
Increase in osmolarity
A signal is sent to the posterior pituitary and ADH is released into the bloodstream
Describe how osmoreceptors work.
- Osmoreceptors have stretch-inhibited cation channels
- When the cell shrinks due to hypertonic stimulus, cation channels open
- Na+ entering the cells triggers action potentials.
What is the Renin-Angiotensin-Aldosterone system important for?
Maintaining sodium balance and blood pressure regulation
Where is the juxtaglomerular apparatus found? What does each component release?
Where distal convoluted tubule abuts the glomerulus.
1) Macula Densa cells respond to a decrease in NaCl content by increasing prostaglandins.
2) Granular cells in the afferent arteriole (juxtaglomerular cells) release renin
3) A decrease in pressure in afferent arteriole also acts on the juxtaglomerular cells cause the release of renin
WHat are the triggers for renin release from granular (juxtaglomerular) cells?
- Low NaCl concentration in the distal tubule (Na+ depletion)
- Decreased perfusion pressure (by granular cells themselves)
- Increased sympathetic activity (e.g. via baroreflex)
i.e. low BP, low BV, or low Na+ content
Describe the renin-angiotensin system.
Angiotensinogen converted to angiotensin I using renin released from JG cells in the kidney (rate-limiting step).
Angiotensin I converted to angiotensin II by angiotensin converting enzyme (ACE) in the lungs.
What are the effects of increased angiotensin II?
- Increase in aldosterone release
- Vasoconstriction so decrease in glomerular filtration
- Increase sodium and water reabsorption in proximal and distal convoluted tubules
- Stimulate thirst and salt intake, release of ADH
What is aldosterone released in response to? What are the effects of aldosterone?
Released from adrenal cortex in response to angiotensin II. Aldosterone acts on distal tubule and collecting ducts to increase transcription of Na+/K+ ATPase pumps, thus increasing Na+ reabsorption and K+ excretion. Water reabsorption also increases via osmosis. Na+ and water retention are the result.
What do ACE inhibitors do?
Reduce the level of angiotensin II which may be causing excess fluid (edema)
What do the separate actions of ADH and renin-angiotensin-aldosterone system allow for?
ADH: important in maintaining WATER balance
RAA: important in maintaining SALT balance
The two systems allow for independent control of water and salt levels in the body.