Homeostatic control of water and salts (1.9)

Question 1

To maintain ____, the kidneys continuously regulate the ____ composition of the blood.

Answer 1

Homeostasis Chemical

Question 2

How do molecules or ions move?

Answer 2

When molecules move passively, they will always move from where they are in high concentration to where there are less of them down a concentration gradient.

Question 3

Water/Solutes will always move from an area of high water/solute concentration (____ ____) through a semi-permeable to an area of lower concentration of water/solute (___ ____). This process is called osmosis.

Answer 3

Hypotonic solution Hypertonic solution

Question 4

Water, if allowed, will always follow ___ solution.

Answer 4

Salt

Question 5

What do we call it when fluids have the same concentration?

Answer 5

Isotonic

Question 6

What happens when molecules move actively?

Answer 6

When molecules move actively, they combine with a carrier molecule and may move against the concentration gradient. This process needs to bring it about.

Question 7

Define osmoregulation.

Answer 7

Osmoregulation maintains the correct balance the between the water and solute contents of the body fluids.

Question 8

Osmoregulation is mainly controlled by the ___ and ___.

Answer 8

Kidneys Skin

Question 9

What is necessary for the cells in the body to function properly? (2)

Answer 9

To keep the following constant: -Amount of water: too little water causes dehydration of the cells. Too much water causes the cells to burst -Concentration of solutes: this determines the osmolarity (osmotic pressure) of the body fluid

Question 10

Define osmolarity.

Answer 10

The number of solute particles dissolved in one litre of water.

Question 11

The greater the concentration of ___, the greater the ___ and the greater the tendency for water to move into this strong (hypertonic) solution by osmosis.

Answer 11

Solutes Osmolarity

Question 12

About __ of the body’s water us returned from the kidney’s into the bloodstream. Under normal conditions, most of it is reabsorbed from the ____ tubule and the ____ limb of the loop of ___.

Answer 12

99% Proximal Descending Henle

Question 13

When fluid intake is low, kidney conserves water by forming more concentrated urine in the following way: (3)

Answer 13

-Sodium ions are actively pumped out of the loop of Henle, which creates a very concentration tissue fluid (hypertonic) in the medulla area. -This results in a steep concentration gradient between the hypotonic filtrate in the distal and collecting ducts and the surrounding hypertonic tissue fluid. -This causes water to move by osmosis from the filtrate into the blood in the peritubular capillaries

Question 14

What is ADH?

Answer 14

Antidiuretic hormone (ADH) is a hormone secreted by the hypothalamus (part of the brain) and stored in the posterior pituitary gland at the base of the brain.

Question 15

What do osmoreceptors do?

Answer 15

They are special cells in the hypothalamus monitor the osmolarity of the blood.

Question 16

How are osmoreceptors stimulated?

Answer 16

These cells are stimulated when the osmolarity increases because of dehydration eg. through dehydration.

Question 17

How does the osmoreceptors stimulation lead to? (2)

Answer 17

-Thirst centre in the hypothalamus, causing more water to be drunk. -Pituitary gland, causing it to release ADH.

Question 18

What role does ADH play?

Answer 18

ADH dissolves in the blood plasma and is carried all over the body. When it reaches its target organ, the kidney, it causes the pores of the collecting ducts to enlarge, making them more permeable to water.

Question 19

What does ADH making the pores of the collecting ducts to enlarge, and thus making them more permeable to water result in? (2)

Answer 19

-More water moving by osmosis from the filtrate in the collecting ducts, into the blood in the capillaries and the blood volume and composition returning to normal -Less, but more concentrated urine being excreted

Question 20

What happens when the osmolarity of the blood and body fluid reduces?

Answer 20

The receptors in the hypothalamus are no longer stimulated and less ADH is secreted. The kidneys then start excreting more urine. This is a good example of a negative feedback system.

Question 21

Sum up the role of ADH:

Answer 21

The role of ADH is to help in ‘fine tuning’ osmoregulation by increasing the amount of water being reabsorbed back in the blood.

Question 22

What is aldosterone?

Answer 22

Aldosterone is a steroid hormone produced by the adrenal glands, that are situated on top of each kidney. Aldosterone controls the concentrations of sodium ions in the body.

Question 23

What to the sodium in the body under normal conditions?

Answer 23

Under normal conditions, 65% of the sodium in the renal filtrate is reabsorbed from the proximal tubules and another 25% from the loop of Henle. Chloride ions passively follow sodium ions, forming sodium chloride.

Question 24

What happens if there are too many sodium ions in your blood?

Answer 24

High blood pressure may develop.

Question 25

What is the concentration of sodium ions linked to?

Answer 25

It is linked to the balance of water and to the regulation of blood pressure.

Question 26

When is the secretion of aldosterone triggered? (2)

Answer 26

-Blood levels of sodium are low, causing a drop in osmolarity, and/or -Blood volume is low, creating low blood pressure

Question 27

What does aldosterone cause? (2)

Answer 27

-The reabsorption of sodium ions from the filtrate returning them to the bloodstream. -Water to follow the sodium ions, increasing the blood volume and therefore blood pressure So homeostasis is maintained as the sodium ion balance is restored and blood volume is increased.

Question 28

Explain the negative feedback mechanism kidney.

Answer 28

Question 29

Describe how ADH increases blood water concentration. (5)

Answer 29

1. Drop in water concentration of the blood is detected by the hypothalamus
2. Signals to the pituary gland to increase prdocution of ADH
3. ADH travels via the blood to the kidney
4. More water is reabsorbed from the distal convoluted tubule and collecting ducts
5. This increases blood water concentration

Question 30

Describe how Aldosterone increases blood salt concentration. (5)

Answer 30

1. Drop in salt concentration of the blood is detected by the hypothalamus
2. Signals to the adrenal to increase production of Aldosterone
3. Aldosterone travels via the blood to the kidney
4. More salt is reabsorbed from the distal convoluted tubule and collecting ducts
5. This increases salt water concentration