URINARY PHYSIOLOGY Flashcards
1
Q
What is the role of kidney?
A
- Excretion of metabolic waste products, inorganic compound and toxins.
- Homeostasis (Regulation of volume and composition of ECF; Renin and erythropoietin hormone production; Acid base balance)
2
Q
What is the major functions in nephron?
A
- Glomerular filtration
- Tubular secretion
- Tubular reabsorption
- Osmoconcentration
3
Q
What are the 3 layers that glomerular filtration pass through? (extracellularly)
A
- Fenestration in capillaries
- Acellular basement membrane
- Slits in podocytes of the glomerulus
4
Q
What makes filtration occur?
A
Pressure.
1. Hydrostatic pressure
2. Plasma colloid osmotic pressure
3. Hydrostatic pressure in capsule
5
Q
What is the effect of:
1. Glomerular capillary blood pressure
- Plasma-Colloid osmotic pressure
- Bowman’s capsule hydrostatic pressure
- Net filtration pressure ?
A
- Favours filtration
- Opposes filtration
- Opposes filtration
- Favours filtration
6
Q
What’s the effect of increasing or decreasing capillary osmotic pressure?
A
An increase will result in lower net filtration pressure (hyperproteinaemia/ dehydration).
A decrease will result in higher net filtration pressure.
7
Q
What gets through the filter?
A
Molecules with molecular radius <4nm.
Filtrate entering the Bowman’s capsule is called ultra-filtrate of plasma.
8
Q
How to regulate glomerular filtration rate (GFR)?
A
This can be achieved through the regulation of capillary pressure (PH) via afferent arterioles.
Capillary pressure is regulated via:
1. Auto-regulation of single nephron (Myogenic reflex/ Tubuloglomerular feedback)
2. Angiotensin II
Sympathetic input
9
Q
How does smooth muscle react under myogenic reflex?
A
- An increase in systemic blood pressure distends the arteriolar wall which responds by constricting.
- A fall in systemic pressure leads to arteriolar dilation thus increasing blood flow.
10
Q
How does tubuloglomerular feedback regulate capillary pressure?
A
- Macula densa cells of the JGA respond to flow of filtrate in that nephron (monitoring the flow rate in the distal convoluted tubule)
- Granular cells: constrict the vessels
- Mesangial cell: give direct feedback to those cells and afferent arteriole effectively to regulate glomerular flow.
11
Q
When will renin be released from juxtaglomerular apparatus?
A
- A fall in renal perfusion as detected by a reduced afferent arteriole stretch
- increased sympathetic tone
- increased K+
12
Q
Why only 50% of urea is excreted?
A
Because urea is lipophilic. It is able to move across epithelium until the concentration on both side is equal
13
Q
What is the 2 passive transport methods?
A
- Paracellular (pass through the zonula occludens zone between one cell and next)
- Transcellular (molecule passes through the cell; *more important)
14
Q
What is the 3 forms of active transport mechanisms?
A
- Uniport
- Cotransport
- Anti-transport
15
Q
Where does active transport usually occur?
A
Basolateral and apical membranes
16
Q
What is the function of descending limb of loop of henle?
A
Main role: water reabsorption
Impermeable to Na but permeable to water
17
Q
What is the role of ascending limb?
A
Pumping Na out to contribute high tonicity in the medulla.
Permeable to Na but impermeable to water
18
Q
What is diluting segment referred to?
A
Thick ascending limb + Distal convoluted tubule
19
Q
Function of diluting segment
A
- Active Na reabsorption through Na+/ K+/ ATPase
- Secondary active co-transport of Na, K and Cl from lumen
- K+ leaves through apical and basolateral membrane via K+ channels
- Cl- diffuses across basolateral membrane through Cl channels
20
Q
What are the 2 types of cells in CD?
A
- Principal cells (short small projections)
- Intercalated cells (extensive complex membrane folds - acid base balance)
21
Q
What hormones are associated with the kidney?
A
- Aldosterone
- Parathyroid hormone
- Calcitonin
- Atrial Natriuretic Peptide (ANP)
- ADH
22
Q
What is the function of aldosterone?
A
- Sodium saver
- Increases Na+ reabsorption at the distal convoluted tubule and the collecting duct
23
Q
Where is aldosterone released from?
A
It is released by the adrenal cortex which is stimulated by:
1. Renin-angiotensin-aldosterone system (RAAS)
- Hyperkalaemia - excess K+
24
Q
What is the function of Aldosterone?
A
- Increase K+ permeability of the apical membrane in CD > enhance K+ secretion.
25
What cause the release of parathyroid hormone?
It is released by low level of Ca2+
26
What is the job of Parathyroid hormone?
1. Increase Ca2+ level and decrease the conc of PO4 in the blood
2. Increase Ca2+ by increasing bone reabsorption.
3. Lowers renal threshold of PO4 thereby increasing PO4 loss in urine
27
What dose parathyroid act on?
1. Distal convoluted tubule to increase Ca2+ reabsorption by increasing rate of production of cycle AMP which enhances the reabsorption of Ca2+ and Mg2+.
2.Proximal tubule to decrease PO4 reabsorption.
28
What produces calcitonin?
Parafollicular (or C) cells of thyroid
29
What is the function on calcitonin?
Decreasing rate of Ca2+ reabsorption from bone thereby reducing Ca2+ levels in body fluid.
30
What cells release atrial natriuretic peptide (ANP)?
Cells in atrium
31
What is the function of Atrial Natriuretic Peptide?
**It lowers the BP by increasing Na+ excretion
Stretch receptors in atrial wall detect increase in BP > ANP acts directly on CD to inhibit Na+ reabsorption > Causes vasodilation, increased GFR, Na+ excretion and water excretion > drop in BP.
32
Beyond the PT, what are the 3 features that allow the production of dilute or concentrated urine?
1. Hypertonic medullary interstitium
2. Diluting segments producing a dilute urine irrespective of animals water balance
3. Variability in water permeability CD in response to antidiuretic hormone (ADH)
33
What alter the concentration of filter to create a hypertonic medulla?
Counter current flow through:
1. Juxtagpositioning of ascending and descending loops
2. Differential permeabilities of the walls of the two loops
3. Active pumping in the ascending thick limb
34
Describe the characteristic of descending limb of loop of henle.
- permeable to water and impermeable to Na
- water leaves the lumen via aquaduct
water diffuses from lumen to peritubular fluid
- Helps to keep medulla hypertonic
35
Describe the characteristic of ascending limb of loop of henle.
- Actively pump Na, K and Cl into interstituim
-impermeable to water
-Na+ readily diffuses outwards (increase interstitium tonicity)
36
What is the role of the vas recta?
1. removal excess water from the interstitium. (prevent swelling of the medulla)
2. Permeable to water and solutes
37
Describe the change in osmolarity in vasa recta.
- The plasma in vasa recta has a fairly high oncotic pressure as it enters the medulla so as these blood vessels descend into the inner medullary interstitium.
- As it approaches the hairpin in the vasa recta, the plasma osmolarity rises, then falls as the blood vessels emerge out of the inner medulla.
- When the tonicity in medulla drops and return to normal, some of solutes go back to the medulla > towards the descending part of the blood vessels and counter current flow occurs
38
Why is the filtrate in the CD is hypotonic regardless of the hydration status of the animal?
Hypotonic allow us to draw H2O back into the interstitium.
39
What leads to the low osmolarity in distal convoluted tubule?
The continuation of sucking out sodium
40
Where is the ADH (antidiuretic hormone) released ?
Pituitary in response to high osmolarity of blood in CNS
40
What is the effects of ADH?
1. Increases water permeability of CD (increases reabsorption)
- open channels of CD
2. Decrease blood volume
3. Systemic vasodilation
4. Heart failure
40
Where does ADH work on?
Apical membrane of the collecting duct
41
What is the 4 nitrogenous compounds in urine?
1. urea
2. creatinine
3. uric acid
4. allantoin
42
Why do we worry about nitrogen?
1. Metabolism of protein results in nitrogenous wastes
- amino acids are broken down to produce ATP, CO2, water amd ammonia (NH3)
2. Ammonia binds with H and form ammonium (NH4+)
- Ammonium replaces K+ at Na+/K+ ATPase transporters and disrupts cell function, espectially neurons
- Ammonia and ammonium are converted to less toxic forms in liver (urea and uric acid( which can be excreted in urine.
43
What is creatinine?
End product of general metabolism
44
what form of creatinine can be found in muscle?
Creatinine phosphate
45
What is urea?
1. main nitrogenous compound in urine
2. end product of protein metabolism
3. formed in liver from amino acids and ammonia compounds
4. Blood urinary nitrogen (BUN) is a measure of urea concentration of serum or plasma (can indicate renal function
46
What is uric acid?
1. End product of purine metabolism in primates and reptiles
2. End product of amino acid degradation in birds
3. Slightly reabsorbed
47
What is gout?
it develops if uric acid synthesis increases and excretion through kidney decreases.
48
What is allantoin?
1. It is a crystalline substance that is derived from uric acid oxidation and the removal of CO2 from the purine ring.
2. urinary end product of purine metabolism in non-primate and some reptiles.
49
Describe the process of urine excretion.
- CD opens into renal pelvis then to the ureters
- Peristalsis drives urine along ureters to bladder
- Reflux of urine into ureter is prevented during micturition by closing of the junction of ureters and bladder
50
Where does the colour of urine come from?
It comes from bilirubin which is excreted from the gall bladder to the gut and then is reabsorbed as urobilinogen.
51
1. Where can we find detrusor muscle in the bladder?
2. What nervous control is it under?
1. It is in the bladder wall
2. under parasympathetic control (with Muscarinic receptors, Ach transmitter)
52
What is the correlation of detrusor muscle and the internal sphincter?
Contraction of detrusor muscle closes off ureters and opens the internal sphincter.
*Contraction opens the sphincter
53
Where is the external sphincter?
What nervous control is it under
1. It is located at the base of the bladder and around the urethra
2. it contains skeletal muscle and is under voluntary control
- excitation of neurone causes contraction
54
Innervation of bladder consists of :
1. Hypogastric nerve
- sympathetic nerve fibres (Beta receptors)
-inactivate muscle of bladder neck and sphincter
- prevent urination
2. Pudendal nerve
- voluntary control of external sphincter
- override others
3. Pelvic nerve
- parasympathetic nerves
55
what will happen when external sphincter relax?
Relaxation of external sphincter allows urine to flow and reflexive contraction of bladder occurs
56
Why is acid-base balance so important?
Cell metabolism and enzyme function are heavily dependent on maintain a physiological pH.
H+ concentration has the greatest impact on pH and can also affect ionic composition of all body fluids.
57
pH below 7.4 refers to
acidosis (acidemia)
58
pH above 7.4 refers to
alkalosis (alkalemia)
59
What is the urine pH of vegetarian?
Vegetarian diet with high Na+ and K+ content produce alkaline urine
60
what are the 3 mechanisms that control pH of body fluid?
1. Intracellular and extracellular buffers
2. Lungs (short term response)
3. Kidneys (long term response)
61
What is the feature of buffers?
1. Buffers do not prevent the change in pH but minimize any change
2. Addition of another acid will increase [H+] and push equation to the left (result in more HA)
3. Removal of H+ will decrease [H+] and push equation right (results in more H+)
62
How does intracellular buffering work?
H+ must enter the cell in exchange for Na+, Ca2+, K+.
Once it is inside cells, H+ is buffered by:
(i) amino acids
(ii) peptide
(iii) protein
(iv) organic phosphate
63
What extracellular buffering occurs in blood?
1. haemoglobin (main)
2. bicarbonate (main)
3. Phosphate
4. Plasma protein
64
The pKa of bicarbonate is not close the the blood pH, why is it and important buffer?
1. there is a large quantity of HCO3- in blood
2. The concentration of HCO3- is closely regulated by the kidney
3. The concentration of H2CO3 is regulated by the lungs (via regulation of pCO2)
65
What is carbonic anhydrase (CA)?
CA is an enzyme found in RBC and many other tissues.
Catalyses the formation of bicarbonate from water and CO2 and vice versa.
essential for transport of CO2 from the tissue to the lung.
important in kidney acid base balance.
66
How does respiration help in balancing pH level in blood?
1. very efficient at reducing [H+] in blood by eliminating CO2
2. The rate of removal of CO2 is governed by minute ventilation
3. If lungs give off CO2 as fast as it is produced then there is no net gain of H+ and pH remains constant
67
What detects the changes in CO2 levels in blood?
Chemoreceptors
68
What is the most effective way in returning pH to normal?
Kidney
69
What can kidney control?
1. H+ excretion (if pH is too low)
2. HCO3- excretion
3. NH3/ NH4+ secretion
- when our kidney gets rid of ammonia, it often combines with excreted hydrogen to form ammonium
70
What is the nature of ammonia
Ammonia is fat soluble
71
H+ excretion depends on:
1. Tubular H+ secretion
- secretion via active transport PT, DT and CD
- 2 types of intercalated cells in DT and CD:
(i) Type A H+ secreting
(ii) Type B HCO3- secreting
2. Urinary buffers
72
What are the main urinary buffers of H+?
1. NH3
2. HPO4 ^2-
- is filter out but not reabsorbed
73
Where is NH3 produced?
NH3 is produced in tubular cells from deamination of amino acids and is permeable to enter lumen.
74
What form is NH3 being excreted
- NH4+ is impermeable (to tubular membranes) so H+ is excreted as NH4+.
- The proximal tubule can secrete NH4+ ions into the lumen by substituting NH4+ for H+ ions on the Na+/H+ exchanger.
- NH4+ is reabsorbed from the thick ascending lmb and its accumulation in the medullary interstitium devlops a concentration gradient for NH4+ and ammonia into the medullary collecting duct.
- Ammonia provides buffering for H+
75
Low pH, High pCO2
respiratory acidosis
76
Low pH, Low pCO2
Metabolic acidosis
77
What are the 4 acid base abnormalities?
1. Respiratory acidosis (common)
2. Respiratory alkolosis
3. Metabolic acidosis (common)
4. Metabolic alkolosis
5. Mixed (e.g. respiratory acidosis and metabolic alkalosis)
78
What causes respiratory acidosis?
it is often cause by alveolar hypoventilation due to:
(i) depression of respiratory center
(ii) ventilation pump damage
(iii) severe respiratory disease
79
What is the significant changes in blood during alveolar hypoventilation (respiratory acidosis)?
elevated arterial pCO2 and pH decreases.
[CO2] in blood rises as CO2 is not effectively removed in lungs.
80
How to restore the normal pH in respiratory acidosis?
it can be corrected by the actions of kidneys in increasing H+ and NH3 production and excretion in the urine.
81
what cause respiratory alkalosis?
It is often caused by alveolar hyperventilation due to:
(i) stimulation of the chemoreceptors in response to hypoxia
(ii) stimulation of the intrapulmonary receptor by lung injury or inflammation
(iii) abnormal stimulation of the respiratory centres
(iv) over enthusiastic use of the ventilator can cause hyperventilation in an anesthetized animal
82
What is the significant changes in blood during alveolar hyperventilation (respiratory akalosis)?
pH increases, [HCO3-] decreases, pCO2 in arterial blood decreases
83
How to restore pH in respiratory alkalosis?
1. kidney must eliminate HCO3-
2. when there are insufficient H+ around to capture filtered HCO3- and form carbonic acid, the excess HCO3- spills into the urine
84
What causes the occurrence of metabolic acidosis?
1. failure of kidneys to eliminate H+
2. increase in production of fixed acid (muscles exercise anaerobically causes the build up of lactic acid/ protein catabolism > production of ketone)
3. Diarrhoea causes excess loss of HCO3- in faeces
4. Ruminant: carboydrates overload casues rumen acidosis and H+ absorbed
5. Diabetes mellitus: Involve the production of acetoacetic acid and betahydroxybutyric acid
85
How does metabolic acidosis lead to hyperkalaemia?
During metabolic acidosis, H+ replaces K+ ions in cells and K+ spills from the cell into ECF, causing hyperkalaemia.
86
What cause metabolic alkalosis?
1. Vomiting resulting in loss of HCL from stomach
2. K+ deficiency (most K+ is located in cells, drag K+ out of the cell in exchange of H+ from blood)
3. Ruminants: displaced abomasum traps H+ that cannot enter circulation
