Urinary systems and electrolyte balance Flashcards
1
Q
What primarily causes the shift in equilibrium between the ECF and the ICF?
A
The movement of water, not solutes
2
Q
What is the osmotic pressure of human blood plasma?
A
300 mOsm
only very slightly higher than the osmotic pressure of the ISF
3
Q
What are the components of the ECF?
A
Interstitial fluid (ISF) and blood plasma
4
Q
What are the two major body fluid compartments?
A
Intracellular Fluid (ICF) and Extracellular Fluid (ECF). ECF = Interstitial Fluid + Blood Plasma.
ECF = Interstitial Fluid + Blood Plasma
5
Q
Are blood plasma and interstitial fluid isosmotic?
A
Yes, they differ by only ~0.5% in osmotic pressure and are considered isosmotic.
6
Q
What are the major sites of ion and water exchange in animals?
A
Skin (in some cases), respiratory system, digestive system, and excretory system.
7
Q
What is osmoregulation?
A
The process of maintaining the proper balance of salts and water in bodily fluids.
8
Q
Why is osmoregulation important at the cellular level?
A
Too much water → cells swell and burst; too little water → cells shrink and die.
9
Q
How do freshwater fish manage water intake?
A
They take in large amounts of dilute water via osmosis and must continuously use energy to expel water to maintain balance.
10
Q
What are aquaporins? Where are they found?
A
- Membrane proteins facilitating water transport
- Found in brain, red blood cells, kidneys, and the amphibian skin and bladder.
11
Q
What are two sources of water in animals?
A
- Ingested ‘preformed’ water
- Metabolic water (from catabolism of food).
12
Q
What are obligatory water losses?
A
Water losses that occur as a result of food catabolism—urinary, faecal, and respiratory losses.
They are beyond an animal’s physiological control
13
Q
Which macronutrient’s catabolism causes the most urinary water loss?
A
Protein, due to nitrogenous waste (e.g., urea) production.
14
Q
What determines respiratory water loss in animals?
A
Breathing physiology and air humidity.
15
Q
Why is metabolic water crucial for desert animals?
A
They often have no access to free water, so they rely on metabolic water (e.g., kangaroo rats metabolizing dry barley).
16
Q
How many molecular forms do aquaporins have?
A
12
17
Q
Catabolism of what products does not yield products to be excreted in urine?
A
Carbohydrates and lipids
18
Q
What are the 3 ways in which blood plasma can be regulated?
A
- Osmotic regulation
- Ionic regulation
- Volume regulation
19
Q
Define osmoconformer
A
An organism’s internal osmotic pressure changes to match that of its external environment
20
Q
Define an osmotic regulator
A
An organism that maintains a constant internal osmotic pressure regardless of changes in the external environment
Maintenance of a constant or neraly constant osmotic pressure in the blood plasma
21
Q
What are the three types of water-salt regulation in animals?
A
Osmotic regulation, Ionic regulation, Volume regulation.
22
Q
What is osmotic regulation?
A
Maintaining a constant or nearly constant osmotic pressure in the blood plasma.
23
Q
What is ionic regulation?
A
Maintaining the composition of ions in body fluids.
24
Q
What is volume regulation?
A
Maintaining the overall amount of water (volume) in body fluids.
25
What are the two types of exchanges between an animal and its environment?
(environmental challenges)
Obligatory (not under physiological control r.g. water loss, diffusion of gases) and Regulated (controlled to maintain homeostasis e.g. active water/ion reabsorption).
26
Give an example of an osmoconformer and an osmoregulator.
Mussel – osmotic conformer; Shrimp – osmoregulator.
27
What is the osmoregulatory strategy of crabs in varying salinities?
Osmoregulator in dilute seawater (<1000 mOsm) and in fresh water, osmoconformer in concentrated seawater.
28
How do freshwater crabs regulate their fluids?
They regulate volume; their hemolymph is hyperosmotic to freshwater, and urine is isosmotic to haemolymph.
29
What is a hyperosmotic regulator?
An animal that maintains blood osmotic pressure higher than that of the surrounding freshwater.
30
What is the average osmotic gradient in marine vs freshwater teleost fishes?
Marine: ~700 mOsm; Freshwater: ~300 mOsm.
31
Why are osmoregulatory challenges greater in marine teleosts?
Larger osmotic gradient and opposite directional ion and water movements.
32
What organs help with ion regulation in elasmobranchs and teleosts?
Rectal gland (elasmobranchs), gills (teleosts).
33
What action do the rectal gland (elasmobranchs) and gill (teleost) perform?
- Remove Na+ via paracellular transport
- Pump out Cl- via membrane transporters
34
What is the kidney's main role in marine fishes?
Excretion of divalent ions (Mg²⁺, Ca²⁺, SO₄²⁻); small amounts of isosmotic urine.
35
Where are Na⁺ and Cl⁻ primarily excreted in marine fishes?
In the gills.
36
What is the function of salt glands in marine reptiles (eureptilia)?
Secretion of sodium and chloride ions.
37
What is the difference between stenohaline and euryhaline animals?
Stenohaline tolerate narrow salinity ranges; euryhaline tolerate wide salinity ranges.
38
What lies directly superior to the kidneys?
Adrenal glands
## Footnote
Sometimes called the surarenal glands
39
What does the cortex of the adrenal cortex release?
- Corticosteroids
- Aldosterone
40
What does the medulla of the adrenal gland release?
- Adrenaline
- Noradrenaline
41
What shape are the left and the right adrenal cortex?
## Footnote
They're different shapes!!
- Right: pyramidal shaped
- Left: crescentic shaped
42
What is the name of the area of the kidneys where structures enter and leave?
The hilum
43
What structures enter/leave at the hilum?
- Ureter
- Renal vein
- Renal artery
44
Where does the kidney lie in relation to the peritoneum?
The kidneys lie behind the parietal peritoneum
45
What are the kidneys surrounded by?
- Renal capsule
- Adipose tissue (perinephric fat)
- Renal fascia
- Ribs 11 and 12
## Footnote
Suspensory fibres run from the renal capsule, through the perinephric fat, extending to the renal fascia - these prevent 'wandering kidney'
46
What is the functional unit of the kidney?
Nephron(s)
47
What part of the nephrons does the renal cortex contain?
- Proximal and distal convoluted tubules
- Part of the collecting ducts (in medullary rays)
48
What part of the nephrons does the renal medulla contain?
- Loop of Henle
- Part of the collecting ducts
49
What is the main function of the urinary system?
Elimination of waste products into the environment.
50
Where are the kidneys located?
Either side of the midline on the posterior abdominal wall, between T12–L3.
51
Why is the left kidney higher than the right?
Because of the position of the liver on the right side.
52
Are the adrenal (suprarenal) glands part of the urinary system?
No, they are endocrine glands located on top of the kidneys.
53
What does the adrenal cortex produce?
Corticosteroids and aldosterone.
54
What does the adrenal medulla produce?
Adrenaline and noradrenaline.
55
What is the hilum of the kidney?
The entry/exit site for structures like blood vessels, nerves, lymphatics, and ureter.
56
What is the renal pelvis?
A funnel-shaped structure that collects urine and leads to the ureter.
57
What are the minor and major calyces? Which is which?
Parts of the renal pelvis. Collect urinre and direct it to the ureters.
- Top part is the minor calyx.
- Bottom part is the major calyx
58
What prevents backflow of urine from bladder into ureters?
Ureters enter the bladder obliquely (diagonally) and are compressed as the bladder fills.
59
What is the average capacity of the bladder?
About 0.75 litres.
60
Where is the bladder located?
In the pelvic cavity, posterior to the pubic symphysis.
61
What is the apex and fundus of the bladder?
Apex points toward pubic symphysis; fundus is the posterior wall.
62
How long is the male urethra?
What are its four parts?
- About 20 cm;
- Pre-prostatic, prostatic, membranous, and penile.
63
Where is the internal urethral sphincter located in males?
At the junction between the bladder and urethra.
64
Where is the external urethral sphincter in males?
Just inferior to the internal sphincter.
65
What are the 4 main processes involved in urine production?
- Filtration
- Reabsorption
- Secretion
- Excretion
66
What is the name given to the bundle of capillaries at the beginning of nephrons? What is special about the walls of the capillaries?
- Glomreulus
- They are charge and size selective
## Footnote
Glomeruli is plural
67
What is the name of the first part of the nephron that recieves filtered blood from the glomeruli?
Bowman's capsule
68
What direction do the afferent and efferent glomeruli carry blood in?
- **A**fferent = **A**pproaching
- **E**fferent = **E**xiting
69
What is the osmotic pressure like at the end of the proximal convoluted tubule (PCT)?
By the end of the PCT, the filtrate will be **isosmotic** to the ISF
70
What are the main fucntions of the PCT?
- Bulk reabsorption of filtrate to the ISF
- Secretion from ISF into filtrate
## Footnote
secretion uses up lots of ATP, therefore the cells in the walls here have lots of mitochondria to provide this
71
What are the cell junctions like in the walls of the PCT? Why?
- Leaky tight junctions
- To allow molecules to diffuse between cells, but preventing paracellular movement
72
What is the ascending limb of the loop of henle (LOH) permeable/permeable to? What specialisations do the cells have for this?
- Highly permable to: ions and urea
- **Impermeable to: water**
- Specialisations: **thick walls**, lots of membrane transporters for active transport of molecules
73
What is the main function of the ascending limb of the LOH?
Ion reabsorption from filtrate into the ISF via active transport
74
What is the main function of the descending limb of the LOH?
Water reabsorption from the filtrate to the ISF
75
What is the descending limb of the loop of henle (LOH) permeable/permeable to?
- **Highly** permeable to **H2O**
- Impermeable to ions and urea
## Footnote
No tight junctions to allow water free passage out of the LOH
76
What is the overall 'story' across the LOH?
1. Filtrate enters the LOH
2. The ascending limb **actively transports ions out of the nephron**. The walls here are too **thick** for water to exit, so the filtrate becomes dilute, and the ISF becomes hyperosmotic
3. **Water** in the descending limb moves out due to the **hyperosmotic ISF**, and the filtrate becomes **more concentrated as it moves down**
4. This creates the multiplied osmotic gradient - the deeper you go into the medulla, the 'saltier' it gets
5. Water is reabsorbed into the medulla in the adjacent collecting duct, ensureing that the urine produced is **concentrated**
77
What is the main function of the DCT?
- Reabsorption of filtrate into ISF
- Secretion from ISF into filtrate
78
Where is the juxtaglomerular apparatus (JGA)?
The JGA forms at the point where the DCT loops back and makes contact with the glomerulus
79
What cells sense changes in blood pressure? Where are they?
- Juxtaglomerular cells sense the change in blood pressure
- They are located in the afferent arteriole of the glomerulus, near the JGA
80
What do the juxtaglomerular cells secrete? What is its function?
- Renin
- It increases blood pressure
81
What do the juxtaglomerular cells secretre renin in response to (in health)?
Low blood pressure
## Footnote
In pathology, renin can be secreted incorrectly, causing high blood pressure
82
How does the RAAS system work?
## Footnote
This is a long one!!
- **Angiotensin** (Ang) is made in the liver
- **Renin** enzymatically turns Ang to Ang 1
- Angiotensin-converting enzyme turns And 1 to Ang 2
- Ang 2 stimulates the hormone **aldosterone** (ALD)
- ALD increases Na+ absorption and K+ secretion in the PCT and DCT
- Na+ reabsorption = **increased H2O reabsorption** = increased blood volume = **increased blood pressure**
83
What is the name of the specialised cells in the walls of the DCT at the JGA?
Macula densa cells
84
What do macula densa cells do?
- Sense changes in **Na+ concentration** and the flow rate of the filtrate
- They signal for vasodilation/vasoconstriction of the afferent arterioles **and/or** for the JG cells to secrete renin
85
What things can stimulate renin release/activation of the RAAS?
- Macula densa cells
- Juxtaglomerular cells themselves
- Sympathetic nervous system
- Baroreceptors
86
What are the main functions of the collecting duct?
- Final reabsorption and secretion
- Excretion of the filtrate into the ureters, ready for urination
87
What is the counter-current multiplier? Where is it generated mainly?
The generation of a high osmotic gradient between the cortex and medulla of the kidneys. Mainly generated in the LOH.
88
What do the cells of the CD have in order to maintain the counter-current multiplier?
Cells in the CD have transport proteins that transport urea out of the nephron, allowing 'fine tuning' of the urine composition
## Footnote
Vasopressin (ADH) upregulates the expression of these proteins in the epithelial cells, increasing the rate of urea transport
89
What cells regulate pH in the nephron? Where can they be found?
- Alpha-intercalated cells: acid secreting
- Beta-intercalated cells: base secreting
They are found in the collecting ducts
90
How do alpha and beta intercalated cells regulate pH? How is this controlled?
- They modulate the abundance of H+ / CO2 / HCO3- pumps in the membrane
- This is under hormonal control
91
What is the ideal osmolarity difference between the filtrate and ISF?
The goal is to always have a 200mOsm difference between the ISF and filtrate
92
What is the name given to the capillaries that run parallel to the LOH
The vasa recta
93
What is the main function of the vasa recta?
Maintaining increased osmolarity across the nephron and the counter-current multiplier of the LOH
94
What happens in the descending vasa recta (DVR)?
- DVR comes into contact with the high osmolarity ISF
- Therefore the Na+ diffuses from the ISF into the DVR
- Dilute blood flowing from the cortex to the medulla will lose H2O to the concentrated ISF
95
What happens in the ascending vasa recta (AVR)?
- As the Na+ concentrated blood then moves into the AVR, the ISF adjacent to it has a decreased concentration
- Therefore the Na+ in the upper AVR moves into the ISF
- As the blood is more concentrated in the lower AVR, H2O will move into the ISF due to the increased osmolarity
- Therefore** the blood leaving the vasa recta has low Na+ conc, and high H2O conc** to be carried areound the rest of the body
## Footnote
Remember: blood leaving kidneys has low salt and high water content!!
96
How does water leave the DCT and collecting ducts?
Aquaporins
## Footnote
Also present in the descending limb of the LOH
97
What hormone modulates the expression of aquaporins?
ADH/vasopressin
## Footnote
ADH = Anti Diuretic Hormone
98
What type of aquaporin does vasopressin upregulate? Where is this aquaporin located?
- Aquaporin 2 (AQP-2)
- These are located on the apical (lumen) side of the late DCT and CD
## Footnote
This allows exit of water from the late DCT and CD to be modulated as and when needed
99
Where is ADH/vasopressin synthesised? Where is it released from?
- Synthesised in: Hypothalamus
- Released from: **Posterior** pituitary
100
What causes ADH/vasopressin release?
- **Osmoreceptors** in the hypothalamus sense high osmolarity and secrete it
- **Angiotensin 2** also causes vasopressin release
101
What is the vasopressin mechanism of action?
- When H2O decreases and ISF osmolality increases, osmoreceptors in the hypothalamus sense thisa and vasopressin is secreted from the posterior pituitary gland
- Vasopressin **upregulates AQP-2 **receptors on the **apical** (lumen) side of the **DCT and CD**
- On the basolateral side of the membrane, AQP-3 and AQP-4 are always present
- This allows water to move from the filtrate into the ISF, thereby increasing **blood pressure**
