Physiology Flashcards
When the micturition reflex is powerful enough, where does the signal pass through and what happens?
The reflex passes through the pudendal (somatic) nerves to inhibit external urethral sphincter (composed of skeletal muscle tissue)
What needs to be inhibited in order for urination to occur?
External urinary sphincter
Sensory signals from bladder stretch receptors (detrusor muscles) are sent where?
- sacral region of spinal cord via pelvic nerve
- conducted reflexively back to bladder via parasympathetic nerves
What is the mathematical expression for urinary excretion rate?
Filtration rate - reabsorption rate + secretion rate
Define filtration fraction and express it mathematically
- The fraction of renal plasma flow that is filtered ~0.2 (20% of plasma flowing through the kidney is filtered
- Filtration fraction= GFR/ renal plasma flow
What types of substances are not filtered by the nephron?
-Proteins and some LMW substances (because they are partially bound to proteins). Almost half of the plasma Ca and FAs are bound to proteins, and thus, do not filtered through the glomerular capillary
What are the components of the filtration barrier?
- Endothelium- with fenestrae and negative charge
- Basement membrane- with collagen, proteoglycans and strong negative charge. Has small spaces through which water and small solutes can pass through
- Podocytes- form slit filtration barrier with negative charges
What is the glomerular filtration rate?
125 ml/min = 180 L/day
Water has a filterability of 1.0
Define minimal change nephropathy
Loss of negative charges on the basement membrane. Some LMW proteins, especially albumin, are filtered and appear in urine –> proteinuria
Mathematically express GFR in terms of Starling forces
GFR= (K1) (Pg-Pb-Pig-Pib)
-Pg: glomerular hydrostatic pressure= 60mmHg
-Pb: Bowman’s capsule hydrostatic pressure= 18mmHg
-Pig: glomerular capillary colloid osmotic pressure= 32mmHg
-Pb: colloid osmotic pressure of Bowman’s capsule= 0mmHg
NET FILTRATION PRESSURE: 10mmHg
Explain the effect of the sympathetic system of GFR
- Strong activation of the sympathetic system will constrict renal arterioles which will decrease renal blood flow and GFR
- Moderate sympathetic activation has little effect
Describe the effects of NE and epinephrine of GFR and their source
- Derived from the adrenal medulla
- Constrict renal arterioles, decrease renal blood flow and GFR
What determines renal blood flow and what is the mathematical expression?
- Kidneys have 7x the blood flow of the brain but only 2x the oxygen consumption
- Most of the oxygen consumption by the kidneys is related to the high rate of active sodium reabsorption
- Renal blood flow= (renal artery pressure - renal vein pressure) / (total vascular resistance)
List the effects of endothelin on GFR and its source
- Released by damaged vascular endothelial cells of the kidney and other tissue
- May contribute to renal vasoconstriction leading to reduced GFR
- May contribute to hemostasis when a blood vessel is severed
List the affects of Angiotensin II on GFR and its source
- Formed in the kidneys
- Preferentially constricts the efferent arterioles
- Formed usually in situations associated with decreased arterial pressure or volume depletion- effects on the efferent arterioles will help to increase GFR
List the effects of NO on GFR and its source
- Derived from endothelial cells
- Basic level helps maintain renal vasodilation which decreases renal vascular resistance and increases GFR
- counteracts the effects of angiotensin II on afferent arterioles
List the effects of prostaglandins and bradykinin on GFR
- vasodilators that may offset effects of sympathetics and angiotensin II (especially on afferent arterioles)
- decrease renal vascular resistance which tends to increase GFR
List the three kinds of aquaporins and their specific locations in the renal tubules
- Aquaporin 1: widespread and includes the renal tubules
- Aquaporin 2: present in apical membranes of collecting tubules; is controlled by ADH***
- Aquaporin 3: present in basolateral membranes of collecting tubule cells
List the sodium-glucose co-transporters on the brush border of the proximal tubule cells and their functions
- SGLT2: reabsorbs 90% of glucose in early proximal tubule
- SGLT1: reabsorbs 10% of glucose in late proximal tubule
List substance that are actively secreted into the renal tubules
creatinine
para aminohippuric acid
Define transport maximum and the limiting factor and explain how this relates to glucose reabsorption
- Limit to the rate at which the solute can be transported due to the saturation of a specific transport system
- transport max for glucose: 375 mg/min –> if we exceed this, glucose will not be transported and you will have glucose in your urine
- small amounts of glucose will begin to appear in the urine after plasma [glucose] rises about 200mg/100ml
- filtered load for glucose: 125 mg/min
List reasons as to why some passively reabsorbed substances do not have a transport maximum
- Rate of diffusion is determined by electrochemical gradient of the substance
- Permeability of the membrane for the substance
- Time that the fluid containing the substance remains within the tubule
Describe characteristics of the proximal tubule, specifically that kinds of molecules/ions and direction transported
- Reabsorbs 65% of filtered sodium, chloride, bicarbonate, and potassium.
- Reabsorbs all filtered glucose and aa
- sodium reabsorption in the first half is via co-transport along with glucose, aa, and other solutes
- sodium reabsorption in the second half is mainly chloride ions
- H+, organic acids, and bases go back into the lumen
Describe characteristics of the thin descending loop of Henle, specifically the kinds of molecules/ions and direction transported
- highly permeable to water (reabsorbs about 20% of filtered water)
- moderately permeable to most solutes, including urea and sodium
Describe characteristics of the thin ascending loop of Henle
-impermeable to water
Describe the transport characteristics of the thick ascending loop of Henle
- impermeable to water
- about 25% of filtered loads of Na, K, and Cl are reabsorbed here (1 sodium-2chloride-1potassium into the cell)
- is the site of action of powerful “loop” diuretics: lasix, ethacrynic acid, bumetanide
Describe the transport characteristics of the early and late distal tubule
- first portion forms the macula dense (part of the JG complex)
- 5% of filtered load of NaCl is reabsorbed in the early distal tubule
- second part is highly convoluted and has similar characteristics to the thick ascending loop of Henle –> reabsorbs most of the ions but is impermeable to water and urea
Describe the specific function and location of the principal cells
- are part of the late distal tubule and collecting ducts
- reabsorb Na and water from the tubular lumen; secretes K into the tubular lumen
- is the primary site of K sparing diuretics
Describe the function and location of intercalated cells
- part of the late distal tubule and collecting duct (constitues 30-40% of the cells in this area)
- reabsorbs K and bicarbonate ions from the tubular lumen; secretes H into the tubular lumen
Describe the transport characteristics of the medullary collect duct and the kinds of molecules/ions and direction transported
- permeability to water controlled by ADH. if ADH is present, we will reabsorb water
- permeable to urea via urea transporters
- capable of secreting H against a large concentration gradient
List the source, function, site of action, and stimulus for aldosterone
- source: adrenal cortex
- function: increases sodium reabsorption and stimulates potassium secretion
- site of action: principal cells of cortical collecting ducts
- stimulus: increased extracellular potassium; increased levels of angiotensin II
Relate Addison’s disease and Conn’s syndrome to aldosterone secretion
- Addison’s: absence of aldosterone. results in marked loss of sodium and accumulation of potassium
- Conn’s: hyper-secretion of aldosterone. sodium retention and decreased plasma [K], in part due to excessive potassium secretion by the kidneys
Describe function and effects of Angiotensin II and relate to its effects on the proximal tubule
- Function: increased sodium and water reabsorption; returns BP and extracellular volume to normal
- effects: stimulates aldosterone secretion; constricts efferent arterioles; directly stimulates sodium reabsorption in proximal tubules, loops of Henle, distal tubules, and collecting tubules
Describe source, function, and effects of ADH
- source: posterior pituitary
- function: increases water reabsorption
- effects: binds to V2 receptors in late distal tubules, collecting tubules, and collecting ducts; increases formation of cAMP (stimulates movement of aquaporin-2 proteins to luminal side of cell membrane)
Describe source and function of ANP
- source: cardiac atrial cells in response to distention due to plasma volume expansion and increased atrial BP
- function: inhibits reabsorption of sodium and water (especially in the collecting ducts); inhibits renin secretion
Describe source and function of PTH
- source: parathyroid glands
- function: increases calcium reabsorption
How much water can be excreted by the kidneys per day when there is a large excess of water in the body?
as much as 20 L/day with a concentration as low as 50 mOsm/L
-kidneys continue to reabsorb solutes and simultaneously fail to reabsorb large amounts of water
What is the maximum urine concentration that the kidneys can produce?
1200-1400 mOsm/L
Explain why there is an obligatory volume of excreted urine of 0.5 liters per day
A normal 70kg human must excrete 600 mOsm of solute each day in order to get rid of water products of metabolism and ions that are ingested. The maximal urine concentrating ability= 1200 mOsm/L –> half of this must be excreted
Describe the filtration of electrolytes in the proximal tubule
- Reabsorbs about 65% of filtered electrolytes
- Highly permeable to water
Where specifically is ADH formed?
Magnocellular neurons in supraoptic nuclei and paraventricular nuclei
What is the normal extracellular potassium concentration?
4.2mEq/L (+/- 0.3)
Where are the sites for potassium reabsorption and secretion?
- Reabsorption: Proximal tubule, ascending limb of Henle
- Secretion: late tubule, collecting duct
What are factors that shift potassium into cells (decreases extracellular concentration)?
- insulin
- aldosterone
- beta adrenergic stimulation
- alkalosis
What are factors that shift potassium out of cells (increase extracellular concentration)?
- insulin deficiency
- aldosterone deficiency
- beta adrenergic blockade
- acidosis
- cell lysis
- strenuous exercise
- increased extracellular fluid osmolarity
What is the overall effect of aldosterone secretion on potassium excretion?
- Increased extracellular potassium stimulates increase in aldosterone secretion –> stimulates active reabsorption of sodium ions by principal cells of the late distal tubules and collecting ducts. This effect is through a Na/K ATPase pump which pumps potassium into the cell
- aldosterone increases the number of potassium channels in the luminal membrane, an therefore increasing the cells permeability to potassium
How does the plasma pH effect the amount of plasma calcium bound to plasma proteins?
- Acidosis: less calcium is bound to plasma proteins
- Alkalosis: more calcium is bound to the plasma proteins
What are the effects of PTH?
- parathyroid glands are stimulated by low calcium levels to promote increased secretion of PTH
1) stimulates bone reabsorption (breaking down the bone matrix)
2) stimulates activation of vitamin D
3) indirectly increases the tubular calcium reabsorption
How much calcium is reabsorbed and where in the kidney tubule does this occur?
- About 99%% of calcium is reabsorbed in the proximal tubule (65% through paracellular route and 20% through transcellular route)
- in the thick ascending loop of henle, 50% is reabsorbed through paracellular route and 50% via transcellular route stimulated by PTH
- in the distal tubule, almost all calcium is reabsorbed via active transport
List the factors that decrease calcium reabsorption
- decreased PTH
- metabolic acidosis
- increased BP
- increased extracellular fluid volume
- decreased plasma phosphate
What is the role of insulin in regulation extracellular potassium?
Stimulates potassium uptake by cells
What is the role of catecholamines in regulating extracellular potassium?
- Beta adrenergic stimulation (epi) –> stimulates potassium uptake by cells
- Beta adrenergic receptor blockers –> hyperkalemia
What are the relationships of Conn’s syndrome and Addison’s disease to aldosterone secretion and potassium levels?
- Hypokalemia: excess secretion of aldosterone (Conn’s syndrome)
- Hyperkalemia: deficiency in aldosterone secretion (Addison’s disease)
Describe the role of principal cells in regards to potassium
- found in late distal tubule and cortical collecting tubules
- secrete potassium via Na/K ATPase pump and passive diffusion of K into tubular lumen
- control potassium secretion
- factors that stimulate K secretion: increased extracellular K concentration, increased aldosterone, increased tubular flow rate
Describe the role of intercalated cells in regards to potassium
-Reabsorbs potassium during potassium depletion; possibly through a H/K ATPase pump –> secrete H into tubular lumen (losing H ions)
What are the normal pH ranges of venous and arterial blood?
- Arterial: 7.37-7.44
- Venous: 7.35-7.45
What is the most important extracellular buffer system?
Bicarbonate buffer system
What is the role of the phosphate buffer system?
Play a major rule in buffering renal tubular fluid and intracellular fluids
Where does most of the HCO3- reabsorption occur?
Proximal tubule
In what types of cells does primary active secretion of hydrogen ions occur?
Intercalated cells
What is the lower limit of pH that can be achieved in normal kidneys?
4.5
What are the inspiratory muscles?
- respiratory diaphragm
- external intercostal muscles
- sternomastoids
- serratus anterior
- scalene muscles
What muscles are used during forced expiration?
- abdominal muscles
- internal intercostals
What is tidal volume and what is the normal value?
- The volume of air that is inspired or expired with each breath at rest
- 500mL
What is inspiratory reserve volume?
- The volume of air that can be inspired in addition to tidal volume with forceful inspiration
- 3000mL
What is expiratory reserve volume and what is the normal value?
- The amount of additional air that can be expired at end of tidal volume by forceful expiration
- 1100mL
What is residual volume and what is the normal value?
- Volume of air remaining in lungs after forceful expiration
- 1200mL
What is vital capacity and what is the normal value?
- The sum of all the volumes that can be inspired or exhaled; inspiration to the maximum extent plus expiration to the maximum extent
- 4600mL
Define total lung capacity and what is the normal value?
- The sum of all volumes: vital capacity plus residual volume
- 5800mL
Define inspiratory capacity and what is the normal value?
- The sum of volumes above resting capacity= tidal volume plus inspiratory reserve volume
- (500 + 3000)= 3500mL
Define functional residual capacity and what is the normal value?
- The sum of volumes below resting capacity= expiratory reserve volume + residual volume
- (1100 + 1200)= 2300mL
What is alveolar ventilation and how do you calculate it?
- Total volume of gases that enter spaces participating in gas exchange per minute
- (breaths per minute) * (tidal volume- dead space)
Differentiate between anatomic and physiological dead space. What is the total dead space in a normal individual?
- Anatomic: The portion of the airways which conducts gas to the alveoli, but no gas exchange is possible in these places. In trachea, bronchi, and bronchioles.
- Physiological: Some of the alveoli are nonfunctional or only partially functional because of absent or poor blood flow though the adjacent capillaries
- Total dead space: 150mL
What is pleural pressure and how do the values change during inspiration?
- The pressure of fluid between the parietal and visceral pleura
- Normally -5cm of water at beginning of inspiration and goes to -7.5cm water during inspriation
What is alveolar pressure and what is the change in value during inspiration?
- The pressure of air inside the alveoli
- 0 at the beginning of inspiration and -1cm at the end
- during expiration goes from 0 to +1
What is transpulmonary pressure?
-Difference between the alveolar and pleural pressure
Define compliance. How do you calculate it? What is the normal value?
- The extent (volume) to which lungs will expand for each unit increase in the transpulmonary pressure; a measure of the ease with which a hollow viscus may be distended
- (increase in volume) / (increase in pressure * original volume)
- 200mL
Define elastance
A measure of the tendency of a hollow viscus to recoil towards its original dimensions upon removal of a distending or collapsing force
Differentiate between the pressure in the alveolus with and without surfactant
- With surfactant, the pressure is about 4 cm water
- Without surfactant, pressure increases to 18 cm water
Describe the high pressure, low flow lung circulation system
- supplies systemic arterial blood to the trachea, the bronchial tree, the supporting tissues of the lungs, and the outer coats of the pulmonary arteries and veins
- the bronchial arteries supply most of this systemic arterial blood at a pressure that is only slightly lower than the aortic pressure
Describe the low pressure, high flow circulation of the lungs
- Supplies venous blood from all parts of the body to the alveolar capillaries where oxygen is added and CO2 is removed. Includes pulmonary artery and branches –> alveoli
- the wall thickness of arterial artery is 1/3 that of the aorta. therefore the pulmonary arterial tree has a large compliance. 7 ml/mmHg
- the entire pulmonary circulation is smaller than the systemic circulation, but still has to receive the same amount of blood –> therefore has to be more complaint
What is the pulmonary arterial pressure?
24/9 mmHg
What is the mean pulmonary arterial pressure?
15mmHg
What is the left atrium pressure (diastole)?
8mmHg
List agents that dilate pulmonary arterioles
- isoproterenol
- acetylcholine
List agents that constrict pulmonary venules
- serotonin
- histamine
- E.coli endotoxin
Describe zone 1 blood flow through the lungs
-No blood flow; local alveolar capillary pressure (the hydrostatic pressure in the capillaries that supplies the alveoli) never rises higher than alveolar pressure. If the alveolar pressure is higher, it will block the blood flow. This is pathological and does not normally occur
Describe zone 2 blood distribution through the lungs
-Intermittent blood flow occurs only during the peaks of pulmonary arterial pressure because the systolic pressure is greater than the alveolar air pressure, but the diastolic pressure is less than the alveolar air pressure
List the agents that constrict pulmonary arterioles
- NE
- epinephrine
- angiotensin II
- some prostaglandins
Describe zone 3 blood distribution through the lungs
-continuous blood flow because the alveolar capillary pressure remains greater than the alveolar air pressure during the entire cardiac cycle
List the major components of air and their relative concentrations
- N: 78.09%
- O2: 20.95%
- Ar: 0.93%
- CO2: 0.03%
What is Dalton’s law?
The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases
What is Boyle’s law?
For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional
Henry’s law
At a constant temperature, the amount of a given gas that dissolves in a given type of volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is Dalton’s law?
The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases
What is Boyle’s law?
For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional
Henry’s law
At a constant temperature, the amount of a given gas that dissolves in a given type of volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
List the factors that affect rate of gas diffusion in a fluid
- solubility of gas in the fluid
- cross sectional area of the fluid
- distance through which the gas must diffuse
- molecular weight of gas
- temperature of fluids (remains reasonably constant)
List the factors that affect rate of gas diffusion in a fluid
- solubility of gas in the fluid
- cross sectional area of the fluid
- distance through which the gas must diffuse
- molecular weight of gas
- temperature of fluids (remains reasonably constant)
