Excretory System and osmoregulation

Question 1

What is hypotonic urine?

Answer 1

Urine less concentrated than the blood plasma

Question 2

What’s isotonic urine?

Answer 2

Urine with the same concentration as the blood plasma

Question 3

What is hypertonic urine?

Answer 3

Urine more concentrated than the blood plasma

Question 4

What are the main functions of the kidneys?

Answer 4

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

Question 5

List the organs in the urinary system

Answer 5

Kidneys, ureters, urinary bladder, urethra

Question 6

What’s the normal concentration of blood plasma?

Answer 6

290 mosmol/l

Question 7

What’s the maximum urine concentration in humans?

Answer 7

1.5 osmol/l

Question 8

What types of urine can all vertebrates produce?

Answer 8

Hypotonic and isotonic urine

Question 9

Which type of urine can only birds and mammals produce, and why?

Answer 9

Hypertonic urine, due to the presence of the Loop of Henle

Question 10

Where are the kidneys located in the body?

Answer 10

The kidneys lie behind the peritoneum on the posterior abdominal wall, one on each side of the vertebral column

Question 11

Name the processes involved in the production of urine

Answer 11

• Filtration of plasma
• Reabsorption of water
• Reabsorption of solutes
• Secretion of solutes

Question 12

Define the term ‘renal fraction’

Answer 12

The portion of the cardiac output that flows through the kidneys (averages about 21%)

Question 13

Where does most of the urine filtration take place?

Answer 13

Glomerulus

Question 14

Describe the make-up of the renal filtrate

Answer 14

Plasma minus blood cells and blood proteins. Small molecules and ions in almost exactly same concentration as in the plasma

Question 15

What is the glomerular filtration rate (GFR)?

Answer 15

How much fluid is filtered per day

Question 16

What do the ureters do?

Answer 16

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.

Question 17

Where does reabsorption occur in the kidneys?

Answer 17

In the proximal tubule

Question 18

What is transcellular transport?

Answer 18

Transcellular transport involves the transportation of solutes by a cell through a cell.

Question 19

What is paracellular transport?

Answer 19

Paracellular transport refers to the transfer of substances across an epithelium by passing through the intercellular space between the cells.

Question 20

Define the term ‘glycosuria’

Answer 20

A condition characterised by an excess of sugar in the urine

Question 21

When is glycosuria most likely to occur?

Answer 21

• transiently in pregnancy
• in diabetes mellitis
• in kidney disease

Question 22

Why is it dangerous to excrete too much glucose?

Answer 22

Glucose excretion leads to excess water loss leading to dehydration and excessive thirst

Question 23

How much of the filtered water is reabsorbed in the proximal tubule?

Answer 23

60-70% is reabsorbed via osmosis

Question 24

Where is urine concentrated?

Answer 24

In the loop of Henle

Question 25

How is the length of the loop of Henle related to the concentration of urine?

Answer 25

Longer loop of Henle = higher maximum urine concentration

Question 26

List three sources of water intake

Answer 26

(1) drinking water
(2) water contained in feed,
(3) water produced by oxidation of organic nutrients

Question 27

List three sources of water output

Answer 27

(1) urine,
(2) faeces
(3) evaporation from the body surface and respiratory tract

Question 28

What happens in the descending limbs of the loop of Henle?

Answer 28

Water leaves via osmosis, thereby reducing the filtrate volume by 15%. The osmolarity increases to 1,200 mOsmol

Question 29

What happens in the ascending limb of the loop of Henle?

Answer 29

Sodium, potassium, and chloride ions are actively transported out of the filtrate. Water remains in the filtrate

Question 30

Why do sodium, potassium, and chloride ions have to be actively transported out of the filtrate?

Answer 30

The thick segment of the ascending limb isn’t permeable to solutes

Question 31

Compared to blood plasma, what’s the urine concentration like at the end of the loop of Henle?

Answer 31

The urine concentration is hypotonic (90 mOsmol) because solutes are pumped out in the ascending loop of Henle.

Question 32

Where is the osmolarity gradient established?

Answer 32

In the renal medulla

Question 33

Describe the function of the vasa recta

Answer 33

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.

Question 34

What is the collecting duct?

Answer 34

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

Question 35

Another name for the collecting duct?

Answer 35

Renal collecting tubule.

Question 36

When does the permeanabilty to water in the collecting duct change?

Answer 36

Permeability of water increases in presence of ADH (also known vasopressin)

Question 37

Osmoreceptors

Answer 37

These are receptors that detect changes in the blood osmolarity.

Question 38

Give an example of something that lowers body fluid osmolarity

Answer 38

Excess fluid

Question 39

Give an example of something that increases body fluid osmolarity

Answer 39

Fluid deprivation

Question 40

An increase in osmolarity leads to…

Answer 40

an increase in circulating levels of ADH → increased water reabsorption

Question 41

A decrease in osmolarity leads to…

Answer 41

a reduction in circulating levels of ADH → decreased water reabsorption

Question 42

What’s another effect of ADH?

Answer 42

Because it increases blood volume, it increases blood pressure.

Question 43

How does an increase in sodium intake lead to higher levels of extra-cellular fluid?

Answer 43

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.