Excretory System and osmoregulation Flashcards
What is hypotonic urine?
Urine less concentrated than the blood plasma
What’s isotonic urine?
Urine with the same concentration as the blood plasma
What is hypertonic urine?
Urine more concentrated than the blood plasma
What are the main functions of the kidneys?
Excretion Regulation of blood volume and pressure Regulation of blood solute concentrations Regulation of extracellular fluid pH Stimulation of RBC synthesis Activation of Vitamin D
List the organs in the urinary system
Kidneys, ureters, urinary bladder, urethra
What’s the normal concentration of blood plasma?
290 mosmol/l
What’s the maximum urine concentration in humans?
1.5 osmol/l
What types of urine can all vertebrates produce?
Hypotonic and isotonic urine
Which type of urine can only birds and mammals produce, and why?
Hypertonic urine, due to the presence of the Loop of Henle
Where are the kidneys located in the body?
The kidneys lie behind the peritoneum on the posterior abdominal wall, one on each side of the vertebral column
Name the processes involved in the production of urine
- Filtration of plasma
- Reabsorption of water
- Reabsorption of solutes
- Secretion of solutes
Define the term ‘renal fraction’
The portion of the cardiac output that flows through the kidneys (averages about 21%)
Where does most of the urine filtration take place?
Glomerulus
Describe the make-up of the renal filtrate
Plasma minus blood cells and blood proteins. Small molecules and ions in almost exactly same concentration as in the plasma
What is the glomerular filtration rate (GFR)?
How much fluid is filtered per day
What do the ureters do?
The ureters are a pair of small tubes that connect the kidneys to the urinary bladder. They form a vital link in the urinary tract by allowing urine to drain from the kidneys to be stored in the bladder.
Where does reabsorption occur in the kidneys?
In the proximal tubule
What is transcellular transport?
Transcellular transport involves the transportation of solutes by a cell through a cell.
What is paracellular transport?
Paracellular transport refers to the transfer of substances across an epithelium by passing through the intercellular space between the cells.
Define the term ‘glycosuria’
A condition characterised by an excess of sugar in the urine
When is glycosuria most likely to occur?
- transiently in pregnancy
- in diabetes mellitis
- in kidney disease
Why is it dangerous to excrete too much glucose?
Glucose excretion leads to excess water loss leading to dehydration and excessive thirst
How much of the filtered water is reabsorbed in the proximal tubule?
60-70% is reabsorbed via osmosis
Where is urine concentrated?
In the loop of Henle
How is the length of the loop of Henle related to the concentration of urine?
Longer loop of Henle = higher maximum urine concentration
List three sources of water intake
(1) drinking water
(2) water contained in feed,
(3) water produced by oxidation of organic nutrients
List three sources of water output
(1) urine,
(2) faeces
(3) evaporation from the body surface and respiratory tract
What happens in the descending limbs of the loop of Henle?
Water leaves via osmosis, thereby reducing the filtrate volume by 15%. The osmolarity increases to 1,200 mOsmol
What happens in the ascending limb of the loop of Henle?
Sodium, potassium, and chloride ions are actively transported out of the filtrate. Water remains in the filtrate
Why do sodium, potassium, and chloride ions have to be actively transported out of the filtrate?
The thick segment of the ascending limb isn’t permeable to solutes
Compared to blood plasma, what’s the urine concentration like at the end of the loop of Henle?
The urine concentration is hypotonic (90 mOsmol) because solutes are pumped out in the ascending loop of Henle.
Where is the osmolarity gradient established?
In the renal medulla
Describe the function of the vasa recta
The vasa recta are highly permeable to solute and water. Not only do the vasa recta bring nutrients and oxygen to the medullary nephron segments but they also remove the water and solute that is continuously added to the medullary interstitium by these nephron segments. The vasa recta carries away all of the water and salt reabsorbed by the loop.
What is the collecting duct?
The collecting duct is the last part of a long, twisting tube that collects urine from the nephrons and moves it into the renal pelvis and ureters
Another name for the collecting duct?
Renal collecting tubule.
When does the permeanabilty to water in the collecting duct change?
Permeability of water increases in presence of ADH (also known vasopressin)
Osmoreceptors
These are receptors that detect changes in the blood osmolarity.
Give an example of something that lowers body fluid osmolarity
Excess fluid
Give an example of something that increases body fluid osmolarity
Fluid deprivation
An increase in osmolarity leads to…
an increase in circulating levels of ADH → increased water reabsorption
A decrease in osmolarity leads to…
a reduction in circulating levels of ADH → decreased water reabsorption
What’s another effect of ADH?
Because it increases blood volume, it increases blood pressure.
How does an increase in sodium intake lead to higher levels of extra-cellular fluid?
Sodium intake means ↑ osmolarity of ECF, which is detected by osmoreceptors. ↑ ADH leads to water retention. ↑ Thirst leads to ↑ fluid intake. Increased osmolarity also leads to ↑ osmotic withdrawal of water from cells. All of this increases the volume of ECF.
