Topic 4:7 - Osmoregulation

Question 1

why is water concentration important in the body

Answer 1

vital for life. Water is a major component of blood and quantity affects osmolarity, blood volume and blood pressure (pressure exerted by blood against arterial walls).

it is involved with the following functions:
-transport
-metabolism
-thermoregulation
-movement
-sexual reproduction
-support

Question 2

define osmoregulation

Answer 2

the process by which organisms regulate osmolarity of the blood, maintaining solute concentration between tolerance limits

Question 3

why is osmoregulation important?

Answer 3

osmoregulation is essential for the maintenance of health and life in an organism, and volume of water, or concentration of solutes affects the cells’ ability to function.

Question 4

what is osmolarity?

Answer 4

the total solute concentration of a solution

Question 5

what hormone controls osmoregulation?

Answer 5

Osmoregulation is controlled by antidiuretic hormone (ADH).

Question 6

ADH production, secretion and activity is regulated by what?

Answer 6

changes in osmolarity

Question 7

describe the blood pressure and blood volume associated with low osmolarity

Answer 7

high blood pressure
high blood volume

Question 8

describe the blood pressure and blood volume associated with high osmolarity

Answer 8

low blood pressure
low blood volume

Question 9

describe the water concentration associated with low osmolarity. What is this caused by?

Answer 9

high water concentration.
Causes: Excessive water/fluid intake, low blood sugar/salt level

Question 10

describe the water concentration associated with high osmolarity. What is this caused by?

Answer 10

low water concentration.
Causes: Dehydration, high blood sugar/salt levels

Question 11

Where are nephrons?

Answer 11

Each kidney contains millions of nephrons.

Question 12

What does the fluid in the blood contain?

Answer 12

The fluid in the blood contains dissolved solutes like glucose, amino acids, ions (eg sodium and potassium) and the waste urea.

Question 13

where does filtration occur?

Answer 13

in nephrons in the kidney

Question 14

what is the filtrate?

Answer 14

In each nephron, most of the fluid in blood is pushed across membranes to form a liquid called the filtrate, in a process called filtration.

Question 15

describe the process of filtration (including locations and specific terms)

Answer 15

The fluid in the blood passes from the capillaries in the glomerulus to the filtrate in Bowman’s capsule. The filtrate travels in a winding tubule until finally becoming urine after passing along a collecting duct.

The winding tubule is surrounded by capillaries. As the filtrate moves along the tubule most of the water and solutes are reabsorbed back into blood in a process called reabsorption. Most urea is not reabsorbed so is excreted in urine.

The amount of water reabsorbed is determined by hormones like antidiuretic hormone (ADH).

Question 16

what detects levels of osmolarity? (and where)

Answer 16

osmoreceptors in the hypothalamus (in the brain)

Question 17

where is ADH released from?

Answer 17

the pituary gland

Question 18

is osmoregulation regulated by the nervous system or the endocrine system?

Answer 18

primarily the endocrine system, as osmoregulation is regulated by the antidiuretic hormone, which is produced and secreted by the pituitary gland and transported through the blood.

however, the brain communicates with the pituitary gland to secrete more or less ADH, through a nerve impulse. (nervous communication between brain and pituitary gland).

Question 19

explain the endocrine (osmoregulation) response to high osmolarity

Answer 19

Low water concentration/high osmolarity is detected by osmoreceptors in the hypothalamus which stimulates the release of ADH from the pituitary gland into the blood.

ADH is transported to the kidneys where it increases the water permeability of the distal convoluted tubule and collecting duct (effectors). As a result more water is reabsorbed back into blood (via aquaporins) from the filtrate and less leaves the body in urine.

Water diffuses into the blood from the filtrate which decreases osmolarity of the blood and reduces the volume of water excreted in urine.

Question 20

what are the effectors of the endocrine response to high or low osmolarity?

Answer 20

distal convoluted tubule and collecting duct

Question 21

how is water absorbed back into the blood in the process of reabsorption?

Answer 21

via aquaporins (facilitated transport across the tubule membrane). the permeability of water through the membrane is regulated by ADH

Question 22

how is active transport of solutes in parts of the tubule affect reabsorption?

Answer 22

The active transport of solutes like ions, glucose, amino acids in previous parts of the tubule enable osmosis of water when the membrane permeability permits water movement across the collecting duct.

Question 23

briefly describe the stimulus, Corrective mechanisms initiated by effectors and response of high osmolarity

Answer 23

detected stimulus: Osmolarity above the tolerance limit

ADH production and secretion is increased.
Permeability of the tubule and collecting duct is increased

response: Decrease in osmolarity

Question 24

briefly describe the stimulus, Corrective mechanisms initiated by effectors and response of low osmolarity

Answer 24

detected stimulus: Osmolarity below the tolerance limit

ADH production and secretion is decreased.
Permeability of the tubule and collecting duct is decreased

response: Increase in osmolarity

Question 25

explain the endocrine (osmoregulation) response to low osmolarity

Answer 25

Increase water concentration/low osmolarity is detected by osmoreceptors in the hypothalamus which inhibits the release of ADH from the pituitary gland, into the circulatory system. Less ADH is transported to the kidneys which decreases the permeability of the distal convoluted tubule and collecting duct to water. Less water is reabsorbed into the blood from the filtrate which increases osmolarity and increases the volume of water excreted in urine.

Question 26

how is blood pressure monitored? (where)

Answer 26

baroreceptors/stretch receptors in the blood vessels

Question 27

stimuli that impact water/solute balance can be detected by what receptors?

Answer 27

osmoreceptors in the hypothalamus in the brain or stretch receptors/baroreceptors in the heart and arteries

Question 28

What stimuli can be detected associated with osmoregulation

Answer 28

Increase/decrease in solute concentration Decrease/increase in blood volume Decrease/increase in blood pressure

Question 29

how does increased release of the antidiuretic hormone impact the blood pressure and blood volume.

Answer 29

in response to high osmolarity, more antidiuretic hormone (ADH) is released. Hence more water is reabsorbed in the collecting ducts resulting in INCREASED BLOOD VOLUME, INCREASED BLOOD PRESSURE, (and a decreased solute concentration/osmolarity)

Question 30

how does decreased release of the antidiuretic hormone impact the blood pressure and blood volume.

Answer 30

in response to low osmolarity, less antidiuretic hormone (ADH) is released. Hence less water is reabsorbed in the collecting ducts resulting in DECREASED BLOOD VOLUME, DECREASED BLOOD PRESSURE, (and increased solute concentration/osmolarity)

Question 31

define hypotension

Answer 31

blood pressure decreases below tolerance limit.

Question 32

define hypertension

Answer 32

blood pressure exceeds upper tolerance limit and over time, can lead to diseases of the circulatory system, including heart attack and stroke

Question 33

causes of hypotension

Answer 33

Dehydration Stress/fear Blood loss Pregnancy Some medications

Question 34

causes of hypertension

Answer 34

Genetic factors Obesity Diet high in fat, salt, cholesterol High alcohol consumption Smoking Lack of exercise

Question 35

symptoms of hypotension

Answer 35

Light-headedness Dizziness Blurred vision Fatigue Fainting

Question 36

symptoms of hypertension

Answer 36

rarely any

Question 37

Describe the processes of filtration and reabsorption

Answer 37

In filtration blood fluid is forced through the membranes of the glomerulus and Bowman’s capsule under pressure to form the filtrate and only blood cells and large proteins remain in the blood. In reabsorption, as the filtrate travels through winding tubes surrounded by capillaries all useful necessary materials are reabsorbed from the filtrate back into blood (eg glucose, amino acids).