Urinary System Flashcards
1
Q
What are the main functional units of the urinary apparatus?
A
Kidney Urinary bladder Urethra Ureters and calyces Blood supply Neurological control systems
2
Q
What can kidney problems be misdiagnosed as?
A
Chest infections
3
Q
Why is the right kidney not in the same plane as the left?
A
Pushed inferiorly by the liver
4
Q
What is the blood supply of the kidney?
A
Renal artery is a direct branch of the abdominal aorta
Renal veins from each kidney directly drain into inferior vena cava
5
Q
What are the properties of the renal arteries
A
Short and fat therefore allow blood to be delivered at a high pressure which drives the ultrafiltration process
Branch profusely into arcuate arteries which supply each glomerulus
6
Q
What is each kidney surrounded by?
A
Deep dense fibrous capsule
Middle adipose capsule
Suprarenal fascia
7
Q
What are the parenchyma of the kidneys?
A
Renal cortex
Renal pyramids
8
Q
What gives the medulla its striated appearance?
A
The loops of Henle existing in parallel bundles
9
Q
Which part of the nephron does the cortex contain?
A
Glomeruli surrounded by convoluted tubules
10
Q
What is the course of urine?
A
Formed by nephron and passes through renal ducts to renal papilla, to minor then major calyx. Entering the renal pelvis then the ureter to the urinary bladder
11
Q
Why is the renal papilla the most susceptible following trauma?
A
Blood supply comes from supply of the renal cortex, entering capillaries which go into the loop of Henle then supply the papilla
12
Q
Where are the ureters?
A
They run down vertically down the posterior abdominal wall
13
Q
What are the sites of renal colic caused by kidney stones?
A
Uretopelvic junction
Uretovesical junction
Uretal segment near sacroiliac joint
14
Q
How is urine transported along the ureter?
A
Peristalsis of smooth muscle
15
Q
What is vesicouretal reflux?
A
The abnormal movement of urine from the bladder, into the kidneys/uereter.
Urine collects in the pelvis in saces and then drips back into bladder causing incomplete micturition
16
Q
Describe the urothelium
A
3 layers
Slow turnover rate
tight junctions and plaques to prevent leakage
Folded walls can stretch, accommodate urine during peristalsis
Large luminal cells have low permeability which prevents the loss of the urine/plasma gradient
17
Q
What is the capacity of the bladder?
A
450-550 ml
18
Q
Why may there be loss of bladder control during childbirth?
A
Pelvic floor can increase up to 30x which can damage urinary smooth muscle sphincters that control the movement of urine from bladder the urethra
19
Q
How is the internal sphincter controlled?
A
Is under involuntary parasympathetic control. Is a continuation of the detrusor muscle
The reflex opening is due to wall tension in the bladder involving Ach
20
Q
How is loss of bladder control as a result of inappropriate opening of the internal sphincter treated?
A
Anticholinergics
21
Q
How is the external sphincter controlled?
A
(in the perineum)
Voluntary inhibition of the somatic pudendal nerve (S2,S3,S4)
22
Q
How can the external sphincter affect the sphincter vesicae?
A
Prolonged voluntary inhibition can keep the internal sphincter closed which results in reduced bladder tone
23
Q
What prevents sperm in urine?
A
Internal sphincter
24
Q
What are the steps in the production of urine?
A
1) Ultrafiltration in the glomerulus
2) Selective reabsorption in the proximal convoluted tubule
3) Creation of hyper osmotic extracellular fluid by the counter current mechanism in the loop of Henle
4) Adjustment of ion content in the distal convoluted tubule
5) Adjustment of urine concentration in the collecting duct
25
What creates the pressure gradient which drives ultrafiltration?
The afferent arteriole of the arcuate arteries which supply the glomerulus is at a much higher pressure than the efferent arteriole
26
What surrounds the glomerulus?
Bowman's capsule
27
What is the renal corpuscle?
Glomerulus and Bowman's capsule
28
What does the glomerulus consist of?
Capillaries which have podocytes that wrap around capillaries, leaving fenestratrions
29
How is filtration able to occur in the renal corpuscle?
The fenestrations have specialised basal lamina which allow the passage of ions and molecules with a weight of less than 50,000m to pass from the blood
30
Where does the filtrate drain into the proximal convoluted tubule?
The urinary pole of the corpuscle
31
How much material is reabsorbed?
70%
32
What does reabsorbed fluid consist of?
Glucose
Amino Acids
Water
33
What are the methods of uptake in the proximal convoluted tubule?
Na+ uptake via the Na+ pump on the basolateral membrane. Water and anions will then follow via osmosis
Glucose uptake via the Na+/glucose co-transporter
Amino acids uptake via the Na+/amino acid co-transporter
Protein uptake via endocytosis
34
What are the structural features of the proximal convoluted tubule?
```
Larger diameter lumen than distal convoluted tubule
Cuboidal epithelium with tight junction
Invaginations of basolateral membrane
Large mitochondria
Aquaporins
Brush border at apical surface
```
35
What are the differences between the ascending and descending loop of Henle?
Thin simple epithelium on the ascending
thick cuboidal on descending
Descending has few microvilli and prominent mitochondria
36
What is the purpose of the aquaporins on the apical surface of the ascending loop?
Allows water to continue begin reabsorbed until a passive equilibrium has been reached
37
What causes the hyper osmotic elf?
On the descending loop, NA+ and Cl- are actively transported out of tubular fluid and into the extra cellular fluid.
Further reabsorption of water is not enabled as it cannot get through the tight junctions between epithelial cells which lack aqaporins
38
What is the appearance of the distal convoluted tubule?
Cuboidal epithelium
Few microvilli
Prominent micochondria
Interdiginations of lateral wall will Na+ pumps
39
What controls the adjustment of Na+ H+ and K+ to form urea?
Aldosterone
40
What controls the re-equilibration of the luminal fluid and the extracellular fluid?
Vasopressin
41
How is urine concentration adjusted?
Water goes does osmotic gradient into ECF
42
What is the appearance of the collecting duct?
```
Simple cuboidal epithelium
One cilium per cell
No interdiginations on membranes
Few mitochondria
Secretory organelles are present such as golgi
AQP 2 on apical
AQP 3 on basolateral
```
43
How are the calyces and renal pelvis resistant to urine?
Lines with urothelium which has the ability to stretch
44
What causes cells to appear cuboidal or squamous?
The degree of their stretch
45
What causes renin release?
Juxtaglomerular apparatus
Macula densa in distal convoluted tubule senses Cl- ions
Juxtaglomerular cells of afferent arteriole sense stretch. In response, renin is secreted via renin angiotensin system to control blood pressure
46
What are the functions of the kidney?
```
Excretion of metabolic products
Excretion of foreign substances
Regulation of blood pressure
Secretion of hormones
Homeostasis of cell volume
```
47
What is glomerular filtration?
The formation of an ultra filtrate of plasma formed into glomerulus of a kidney nephron
48
What does reduced glomerular filtration rate indicate?
Kidney failure
| Abnormalities in renal circulation and urine production
49
What is the filtration barrier impermeable to?
Cells
Drugs
Proteins
50
What is primary urine?
The ultra filtrate formed which is free from cells, proteins, blood and contains only electrolytes and water
51
What will happen if the tubules are obstructed?
Hydrostatic pressure will increase and the amount filtered through will decrease
52
What is the normal net ultrafiltration rate pressure?
10-20 mmHg
53
Other than pressure, what factors influence filtration?
Permeability of the tubule membrane
Surface area of membrane for filtration
these factors make up the ultrafiltration coeffectien -Kf
54
How is glomerular filtration calculated?
Puf xKf
| FF x RPF
55
Define glomerular filtration rate?
The amount of fluid from the glomerular capillaries to the Bowman's capsule per unit time
56
What is normal GFR?
120ml/min
57
What is renal blood flow?
It brings oxygen, nutrients and other substances to the kidney for excretion via the renal arteries which are direct branches off the aorta
58
What is the friction fraction?
Ratio between renal plasma flow and the amount of filtrate filtered by the glomerulus
Primary urine volume/Renal plasma volume
59
How are the arterioles altered to increase glomerular filtration rate?
Constrict efferent, dilate afferent
60
What are the mechanisms of auto regulation to keep GFR constant?
Myogenic mechanism
| Tuboglomerular feedback
61
Describe the myogenic mechanism
When arterial pressure rises, the afferent arteriole will stretch, in response it constricts which reduces blood flow and GFR will be kept constant
62
Describe tuboglomerular feedback?
NaCl concentration in the tubular fluid is sensed by the macular densa cells of distal convoluted tubule
They send ATP as a signalling hormone which causes the afferent arteriole to vasocontrict
63
How will severe hemmorhage affect GFR
Decrease as blood pressure decreases
64
How will obstruction in nephron tubule affect GFR
Decrease as increased hydrostatic pressure in tubule which is an opposing force
65
What is clearance?
The number of litres of plasma that have completely been cleared of a substance per unit time
66
What is the value of clearance if a substance is freely filtered
The rate of clearance will equal glomerular filtration rate
67
What substance is freely filtered?
Inulin
68
How is GFR estimated?
Creatine clearance
69
What is renal plasma flow?
The volume of plasma that reaches the kidneys per unit time
70
Why does PAH equal renal plasma flow?
It is completely removed from the plasma that passes through the kidneys
625ml/min
71
Normal plasma osmolarity?
285-295 mosmol/l
72
Normal urine osmolarity?
50-1200 mosmol/l
73
Which directions to reabsorption and secretion occur?
Reabsorption- Apical- basal ( tubular lumen to capillaries)
| Secretion - basal-apical
74
What determines the rate of lipophilic molecule movement?
It is protein independent so the rate is determined by the concentration of the solute
75
What determined the rate of hydrophilic molecule movement
Protein dependent, so has a maximum, depends on the number of carriers that are present
76
What types of active transport can occur across a cell
Directly coupled to ATP hydrolysis- the energy is used to move a substance into a cell
Indirectly coupled to ATP hydrolysis- energy is used to move a substance out of the cell at the basal membrane which creates a passive gradient where another substance will diffuse into the cell at the apical side
77
What is glycosuria?
Transport system for glucose is overloaded therefore not all glucose is reabsorbed from tubular fluid and is excreted in the urine
78
What are the proportions of substances reabsorbed in the proximal convoluted tubule?
100% glucose
65% sodium
90% bicarbonate
Water and anions follow along concentration gradient
79
Why does the osmolarity of fluid decrease as it moves along the loop?
It absorbed more ions (25% Na) but only the descending loop it permeable to water, NOT the ascending
80
How much ion reabsorption occurs in the early distal convoluted tubule?
8% Na
81
Where are lots of mitochondria present?
Proximal convoluted tubule, ascending loop of Henle and early distal convoluted tubule
Indicates lots of active transport
82
Where is a brush border present
All areas except collecting duct
| Indicates passive reabsorption
83
How are proteins reabsorbed?
Protein binds with protein receptor on apical membrane and complex forms a pit and is internalised creating a vesicle. The complex breaks down the ad the receptor is recycled. The protein is then broken down into amino acids and then enters the blood stream
84
Why is the reabsorption of all solutes affected by metabolic poisons?
Reabsorption is driven by the action of the Na/K pump
85
How does reabsorption take place with regards to the Na/K pump?
The Na/K pump on the basolateral membrane pumps Na out of the cell, keeping intracellular Na low and K high. Negative on the inside. Due to the gradient, Na passively diffuses into the cell. Glucose and water follow
86
Why is secretion important in the proximal convoluted tubule?
Excretion of drugs
| Movement of drugs to move distal parts of the nephron to act there
87
What do loop diuretics block?
The Na/K/Cl transporter
88
Which transporter do thiazides block?
Ca2+ channel
89
What are the differences between the principle cells of the distal convoluted tubule and the principle cells of the cortical collecting duct?
DCT- controlled by aldosterone
| Collecting duct- vasopressin
90
What are intercalated cells?
Exist between principle cells and have an important role in acid base balance mediated by a h+ /atp pump on the apical membrane
91
How do principle cells of the collecting duct control water movement?
They have a tight epithelium
92
What are 3 gene defects that affect tubule dysfunction
Renal tubule acidosis
Barrter's syndrome
Fanconi syndrom
93
What is renal tubular acidosis?
Caused by the inability to acidify the urine below pH 5.5 which leads to a hypercholeamic metabolic acidosis of the blood
94
What are the symptoms of renal tubular acidosis?
Impaired growth
| Hypokalaemia
95
What causes renal tubular acidosis?
Failure of H+ secretion
Problem with bicarbonate secretion from cell, leads to accumulation of product which affects carbonic anhydrase activity
Mutation in carbonic anyhydrase enzyme
96
What is Barrter syndrome?
Excessive electrolyte secretion
97
What causes Barrter syndrome?
Mutation is Na/Cl/K co transporter on loop of Henle of K transporter
98
What are the symptoms of Barrter syndrome?
Hypokalaemia, metabolic alkalosis, aldosterone and renin hypersecretion
99
What is Fanconi syndrome?
Excessive excretion of low molecular weight proteins caused by a problem with protein reabsorption
Increased excretion of uric acid and glucose phosphate
100
What is the cause of Fanconi syndrome
Problem with Cl transporter in protein receptor vesicle.
| Reduction in number of protein receptors mean proteins can't be reabsorbed
101
What does extracellular fluid consist of?
Interstitial fluid
Transcellular fluid
Plasma
Lymph
102
How much water do we remove?
Sweat- 450 ml/day
Faeces- 100
Respiration - 350
Urine- 1500
103
How much water passes through the fenestrae of the glomerular capillaries?
125ml/min
104
Which areas are permeable to urea?
Bottom of loop of Henle
| Collecting duct
105
How are aquaporins inserted into the lumenal membrane?
Vasopressin binds with specific receptors on the basolateral membrane
106
What triggers the release of vasopressin?
Hypothalamic osmoreceptors which detect an increase in plasma osmoloarity
Baroreceptors which detect a decrease in blood pressure
107
Why does ethanol lead to dehydration?
Inhibits vasopressin and more urine is produced
108
How does an increased water load lead to an increased volume of urine?
Increased water load
Decreased plasma osmolarity
Detected by hypothalamic osmoreceptors which decrease Vasopressin release
Decreased water permeability of collecting duct
Less reabsorbed
Larger urine flow rate
109
What happens if urea is recycled more
Larger gradient in loop of henle and more water will be reabsorbed
110
What is diabetes insipidus
Disorder of water imbalance
111
What are the causes of diabetes insipidus?
No or insufficient vasopressin production
Mutant vasopressin receptor
Mutant aquaporin doesn't respond to binding
Results in polyuria and polydypsia
112
How does sympathetic activity affect GFR?
Increasing sympathetic activity reduces GFR
113
How does increasing sympathetic activity increase sodium reabsorption?
Stimulates Na channels of proximal convoluted tubule
| Stimulates the juxtaglomerular apparatus which stimulates angiotensin II synthesis
114
How does angiotension II increase sodium reabsorption?
Stimulates Na channels on the proximal convoluted tubules
Drives the synthesis of aldosterone which will increase Na and water reabsorption in the distal convoluted tubule and collecting duct
These mechanisms will cause the sodium concentration in the fluid to decrease once it has reached the juxtaglomerular apparatus which will further stimulate the production of angiotensin II
115
How is sodium reabsorption decreased
ANP - increases GFR by vasodilation of the afferent arteriole
Also, reduces uptake of sodium
116
What is aldosterone released in response to?
Angiotensin II
Reduced blood pressure
Reduced osmolarity of ultrafiltrate
117
What does aldosterone result in?
Increased sodium and water reabsorption
| Increased potassium and hydrogen secretion
118
What can excess aldosterone result in?
Hypokalaemic acidosis
119
What is hypoaldosteronism ?
Reabsorption of sodium in distal tubule decreases so ECF falls and blood pressure falls
Dizziness and salt cravings
Compensatory increase in Angiotensin II, vasopressin and renin release
Palpitations as heart requires salt
120
What are the symptoms of hyperaldosteronism?
Muscle weakness
Hypertension
Polyuria
Thirst
121
What is Liddle's syndrome?
Autosomal dominant disease characterised by early and frequent hypertension. Accompanied by low renin plasma concentration and metabolic alkalosis as a result of hypokalaemia and hypoaldosteronism
122
What causes Liddle's syndrome?
Mutation in the aldosterone activated sodium channel on the distal tubule and collecting duct causing it to permanently be activated leading to excessive sodium retention
123
Where do low pressure baroreceptors exist?
Atria, right ventricle, pulmonary vasculature
124
Where do high pressure baroreceptors exist?
Aortic arch, juxtaglomerular apparatus, carotid sinus
125
What is the response to high pressure?
ANP and BNP Release
126
What are the actions of ANP
Vasodilation of renal blood vessels
Inhibition of renin and aldosterone
Inhibition of sodium reabsorption
Ultimately reducing blood pressure
127
What is the effect of ECF volume expansion on the sympathetic nervous system?
Reduced sympathetic activity increases GFR
128
What is the effect of ECF volume expansion on the brain
Reduced vasopressin release so increased sodium and water excretion from the collecting duct
129
What is the effect of ECF volume expansion on the heart?
Releast of ANP, so decrease in renin release, more na+ excretion from the collecting duct
Effects macular dense cells of JGA - reduced renin
Reduces adrenals- reduced aldosterone
130
What are the different types of diuretics?
Osmotic diuretics and carbonic anyhdrase inhibitors act on the proximal convoluted tubule
Loop diuretics acts on the thick ascending loop of Henle
Thiazides work on the proximal part of the distal convoluted tubule
K + sparing act on the distal part of the distal convoluted tubule and the cortical collecting ductHow
131
How do osmotic diuretics work?
They are present in the tubular filtrate thus increasing the osmolarity and increasing water retention in the urine
132
How does mannitol work?
it is an osmotic diuretic and is completely filtered by the glomerulus but cannot be reabsorbed which increases the osmolarity of the tubular filtrate and encourages water retention in the urine whereby more water is lost in the urine
133
Where are carbonic anhydrase enzymes present?
Cells of the proximal convoluted tubule
134
What is the mechanism of carbonic anhydrase?
In the tubular fluid, bicarbonate ions bind with protons to form H2c03, carbonic anhydrase converts this into h20 and c03 which can diffuse into the proximal convoluted tubule cell
In the cell, carbonic anhydrase converted this back into h2c03 which will split into h+ which will enter the tubular fluid in exchange for na+ which will enter the cell.
And bicarbonate ions enter the extracellular fluid
135
Give an example of a loop diuretic
Ferosemide
136
Give examples of K+ sparing diuretich?
Spironolactone
| Amiloride
137
Where does potassium secretion occur?
Principle cells of cortical collecting duct
138
What stimulates potassium secretion?
Increased aldosterone
Increase pH
increase plasma potassium concentration
Increased flow rate
139
How does an increase in tubular flow rate increase K+ secretion
Increase detected by cilia which are linked to PDK1 enzyme that cause intracellular movement of calcium leading to the stimulation of the K+luminal channel
140
What is hypokalaemia?
Low potassium levels
141
What is hyperkalaemia?
High potassium levels
142
What causes hypokalaemia?
Diarrhoea
Surreptitious vomiting
Diuretics
Genetics
143
What causes hyperkalaemia?
Ace inhibitors
K+ sparing diuretics
Age
144
What is normal urine pH range?
4-8.5
145
What is the control of pH dependant on?
The dissociation of hydrogen bicarbonate involving carbonic anyhydrase
146
What is the principle buffer in the blood?
H2c03 - h+ + Hc03-
147
What is the principle buffer in the intracellular fluid?
H2p04- ->H+ HP042-
148
How much of the acid load is buffered in metabolic acidosis?
80-85%
149
How much of the oh- ion load is buffered in metabolic alkalosis?
30-35%
150
What is the extracellular buffering system?
h+ + hc03- -> h2c03 -> h20 + c02
151
What are the physiological sources of H+ in the body?
Carbohydrates
Amino Acid
Lysine
Histidine
152
What are the pathological sources of H+ in the body
Ketoacids
Hypoxia
Diabetes
153
What are the non volatile sources of H+ in the body
Metabolism of carbohydrates and fat
154
What are the volatile sources of H+ int he body ?
Metabolism of proteins
155
How are H+ ions secreted into the lumen in the proximal convoluted tubule?
Na/H+ exchanger
156
How are bicarbonate ions returned to the blood in the proximal convoluted tubule?
Na/Hc03 - exchanger
157
In the distal convoluted tubule, how are H+ ions and bicarbonate ions secreted and returned to the blood respectively?
H+/ATPase transporter
| Cl-/Hc03-
158
What are the primary and secondary mechanisms to increase H+ secretion?
Primary- decrease plasma concentration of bicarbonate, increase partial pressure of Co2
Secondary - increase filtered load of bicarbonate, hypokalaemia, increase angiotensin II, increase, increase aldosterone, decrease the volume of extracellular fluid
159
How is the reabsorption of bicarbonate described?
Segmental
160
Why would new bicarbonates need to be formed?
The amount of bicarbonate reabsorbed is less than the amount that is lost during the buffering of non volatile acids
161
How are new bicarbonates formed?
In the liver, amino acids are broken down in glutamine and urea.
In the kidney, urea and glutamine are converted into ammonium ions and alpha ketoglutarate
Alpha ketoglutarate is converted into ammonium ions
162
Why is urea a poor indicator for assessing GFR?
Affected by catabolic state, diet, GI bleeding, drugs and liver function
163
What is creatinine affected by?
Muscle mass
Age
Race
Sex
164
Why is a creatinine sample difficult in elderly patients?
Hard for them to deliver sample
165
What is the problem with radionnuclide studies?
expensive
166
Why do non volatile acids not contribute to pH?
Formed by the metabolism of proteins, the protons formed are excreted by the kidney
