U3 Homeostasis: Osmoregulation

Question 1

Distinguish between the two types of body fluids

Answer 1

Intracellular fluid: fluid inside of cells (the cytosol)

Extracellular fluid: fluid outside of cells

• intravascular fluid: blood plasma in blood vessels
• transcellular fluid: fluid in specific body regions (lymph, cerebrospinal fluid)
• tissue/intracellular/interstitial fluid: fluid between cells

Question 2

What is the level of water in the blood plasma and tissue fluid regulated by?

Answer 2

• The varying amount of water taken into the body
• The amount reabsorbed from the filtrate in the nephron tubules

Question 3

What are the ways body fluid is obtained and lost?

Answer 3

Body fluid is obtained from:

• water taken in as a liquid or in food that’s eaten
• chemical processes occurring within cells, creating a by-product called metabolic waster

Body fluid is lost from:
- kidneys (remove urea from the breakdown of proteins in the liver, fluid is lost in urine)

• skin (sweat glands secrete water containing by-productions of metabolism)
• lungs (carbon dioxide and water produced by body cells during cellular respiration is excreted as we exhale in form of water vapour)
• alimentary canal (bile pigments in the feces which entered the small intestine with the bile are excrete)

Question 4

What is excretion and why does it occur?

Answer 4

• Excretion: the removal of the waste products of metabolism form the body
• Many wastes are toxic and would be harmful to a person’s health if left to accumulate in the body fluids

Question 5

What are the kidneys made up of?

Answer 5

Tiny tubules called nephrons, which are the site of filtration and re-absorption of blood

Question 6

How does nephron filtration occur?

Answer 6

• The afferent arteriole leading to the glomerulus of each nephron is wider than the efferent arteriole leading it
• Blood is under high pressure, so the small molecules that form the glomerular filtrate and squeezed into the glomerulus
• The fluid flows towards the ureter where useful substances (water, salts, glucose) are reabsorbed back into the blood

Question 7

Compare the two types of reabsorption into the bloop via nephrons

Answer 7

Proximal convoluted tubules and loop of Henle
- reabsorption occurs by osmosis, so it’s a passive process

Distal convoluted tubules and collecting ducts
- reabsorption requires energy from ATP, so it’s active reabsorption
- the degree of this reabsorption is controlled by antidiuretic hormone (ADH)
- AHD increases the permeability of the distal convoluted tubule and collective ducts to water
- the more ADH released, the greater the reabsoption and the more concentrated the urine is

Question 8

What does the homrone aldoserone do?

Answer 8

• Acts on the kidney to reduce the amount of sodium and increase the amount of potassium in the urine
• It increases the amount of sodium ions reabsorbed into the blood
• It increased the amount of potassium secreted in the urine
• It achieves this trough active transport using a sodium-potassium pump
• For every three sodium ions reabsorbed, two potassium ions are secreted so there’s a net movement of ions into the blood

Question 9

Outline the thirst response

Answer 9

• The water level of the body can be increased by taking in more fluid
• Omsorecpetors are able to stimulate the thirst centre in the hypothalamus, prompting the person to drink water
• This fluid is absorbed across the wall of the alimentary canal into the blood, decreasing the osmotic pressure

Question 10

Dehydration

Answer 10

• Dehydration: when water loss exceeds water intake, and there isn’t enough water in the body to carry out normal functions
• This water may be lost through sweating, vomiting or diarrhea
• Symptoms: sever thirst, low blood pressure, dizziness, headache
• If untreated: delirium, loss of consciousness, death

Question 11

Water intoxication

Answer 11

• Water intoxication: when too much water is consumed when the amount of salt and other electrolytes is too low
• Bodu fluids become dilated and cells take in extra water by osmosis
• May happen if a person loses a lot of water and salt through sweating and replaces the loss with plain water rather than with dissolved substances to help replace the lost salts as well as water
• Symptoms: lightheadedness, headache, vomiting, collapse