Homeostasis

Question 1

What is osmoregulation and where does it occur?

Answer 1

The control of water potential in the blood, occurs in kidney.

Question 2

Why is it bad if there’s too little water in the blood?

Answer 2

The blood has a lower water potential than our tissue fluid water will move by osmosis into our blood and this will cause tissues to dehydrate.

Question 3

Why is it bad if there’s too much water in the blood?

Answer 3

Blood will have a high water potential, therefore water will move into the tissue and not return, causing swelling.

Question 4

What happens if water potential increases in the blood?

Answer 4

• Osmoreceptors detect it in the hypothalamus
• Pituitary gland produces less ADP
• More water is excreted as urine

Question 5

What happens if water potential decreases in the blood?

Answer 5

• Osmoreceptors detect it in the hypothalamus
• Pituitary gland produces more ADP
• Lesswater is excreted as urine

Question 6

What structure filters blood?

Answer 6

Kidney nephrons

Question 7

What is ultrafiltration?

Answer 7

Blood enters the kidney through the renal artery which will branch into arterioles. The afferent arteriole will allow blood to enter the renal capsule. The afferent arteriole will then branch into small capillaries which make the glomerulus.

The glomerular capillaries remerge to create the efferent arteriole. This has a smaller diameter than the afferent arteriole, increasing the hydrostatic pressure in the glomerulus.

The high hydro static pressure forces the water, glucose, urea and other ions out of the capillary to create the glomerular filtrate.

Red blood cells and proteins are too large to leave the capillary.

The inner layer of the renal capsule is lined with specialised podocytes, these are adapted to have gaps between them to allow the filtrate to pass into the renal capsule, it must pass through the basement membrane to enter the filtrate. The filtrate then moves into the proximal convoluted tubule

Question 8

How is water and glucose reabsorbed?

Answer 8

1. Sodium ions are actively transported into the capillary, this lowers the sodium ion concentration of the epithelial cells lining the proximal convoluted tubule.
2. This allows sodium ions to move from the lumen of the proximal convoluted tubule via facilitated diffusion using carrier proteins. Along with the sodium ions other molecules can move into the epithelial cells. These maybe glucose, amino acids, chloride ions ect. This is co-transport.
3. The additional molecule that have moved into the epithelial cells via facilitated diffusion into the blood, and therefore is reabsorbed.

Question 9

What are some adaptations of the proximal convoluted tubule cells?

Answer 9

· Many microvilli- to increase surface area.
· Many channel proteins- for facilitated diffusion.
· Many carrier proteins- for active transport.
· Many mitochondria- to respire to provide ATP for active transport.

Question 10

How is the sodium ion conc maintained in the medulla od the kidney by the loop of Henle?

Answer 10

1. As the filtrate enters the descending loop of Henle the number represents the concentration of the filtrate. The filtrate is not very concentrated as there is still a large amount of water in the filtrate.
2. As the filtrate moves down the descending loop of Henle as the walls are thin and permeable water moves out of the lumen of the descending loop, by osmosis, into interstitial space (the space around the nephron). The water will eventually enter the capillary and be carried away.
3. As the filtrate reaches the base of the descending loop of Henle is has lost a great deal of water and therefore the concentration of the filtrate is its highest.
4. Next the filtrate will move through the ascending loop of Henle. Initially sodium ions move of the lumen into the interstitial space via facilitated diffusion, due to the concentration gradient.
5. Once at the top of the ascending loop of Henle, the sodium ions are actively transported out of the lumen. The removal of sodium ions from the filtrate reduces its concentration. The purpose of this is to maintain a low water potential in the interstitial space, in order to ensure water moves out of the descending loop of Henle. The ascending loop of Henle has thick walls impermeable to water; therefore, osmosis cannot occur.