Homeostasis & Kidney

Question 1

What is homeostasis

Answer 1

The maintenance of constant or steady conditions within the body

Question 2

Ultimately, why is it so important that conditions such as water potential, pH and temperature remain constant inside our bodies and do not fluctuate too much

Answer 2

It is important that enzymes that control our cell reactions do not denature

Question 3

What are the three main components of homeostatic mechanisms?

Answer 3

->Sensors or receptors-detect the change away from the set point
->Corrective mechanism- effectors bring about responses to return the factor to its set point
->Negative feedback- prevents over correction of the factor by switching off the corrective mechanism

Question 4

What are the two main roles of the kidney

Answer 4

-EXCRETION- the removal of the waste and toxic products of metabolism i.e urea and creatine
-OSMOREGULATION-maintains the body’s water potential at a constant optimal level

Question 5

Name the functional units of the kidney and say where they are found

Answer 5

Nephrons-extend from the cortex into the medulla

Question 6

Label the kidney

Answer 6

See notes

Question 7

Label the nephron

Answer 7

See notes

Question 8

What 2 processes does exertion of the urine involve

Answer 8

Ultrafiltration and reabsorption

Question 9

What is ultrafiltration and where does it occur?

Answer 9

The filtering of small molecules, under pressure, from the blood in the glomerulus into the Bowman’s Capsule

Question 10

What is the significance of the afferent arteriole being wider than the efferent arteriole?

Answer 10

The builds up a HYDROSTATIC PRESSURE to help force the small molecules, such as water, urea, amino acids and glucose from the glomerulus into the Bowman’s Capsule

Question 11

What substances will not be present in the filtrate?

Answer 11

Red blood cells, white blood cells, platelets and plasma proteins which are too large to fit through the basement membrane of the glomerulus

Question 12

Describe the three parts of the filter system

Answer 12

-Squamous endothelium of glomerular capillaries: a porous, coarse filter
-Basement non-porous membrane of glomerular capillaries:is a fine filter so determines what is in the filtrate
-Podocyte cells of Bowman’s Capsule wall: porous’ coarse filter

Question 13

What is the equation for water potential and what is the rule?

Answer 13

Y=Yp + Ys
Water always moves from the higher (or less negative) to the lower (or more negative) water potential

Question 14

How is net filtration force worked out for ultrafiltration?

Answer 14

It is the difference between water potential in the glomerulus and water potential in the Bowman’s Capsule

Question 15

What gets reabsorbed into the vasa recta at the proximal convoluted tubule?

Answer 15

-65% of the water (i.e most of the water absorption)
-all of the glucose, amino acids, salts and vitamins

Question 16

By what means are substances reabsorbed?

Answer 16

-active transport and facilitated diffusion
-pinocytosis for very small proteins
-osmosis for water

Question 17

Which substances are selectively reabsorbed into the vasa recta by active transport?

Answer 17

Salt, glucose and amino acids

Question 18

Some urea ends up diffusing down its concentration gradient from the proximal tubule into the vasa recta. So how are we still able to excrete urea efficiently?

Answer 18

The urea left in the proximal tubule is actually highly concentrated due to the fact that 65% of the water has been osmotically reabsorbed

Question 19

What type of cells line the proximal tubule and give three fractures they have for active uptake and facilitated diffusion

Answer 19

Cuboidal epithelium
-mitochondrial to provide ATP
-microvilli and basal invaginations to increase SA
-close proximity to capillaries

Question 20

What is the key role of the LOOP OF HENLE?

Answer 20

The Loop of Henle is important for creating a high solute concentration or very negative solute potential in the tissues of the medulla

Question 21

What is the significance, especially to land swelling organisms, of the medulla having a high solute concentration and thus providing a salt gradient?

Answer 21

It means that water can be reabsorbed osmotically from the collecting duct, distal convoluted tubule and descending limb of the Loop of Henle, creating a hypertonic urine and thus conserving water.

Question 22

How is having the region of high solute concentration achieved?

Answer 22

Sodium and chloride ions (SALT) are actively pumped out of the ascending limb of the Loop of Henle into the tissues of the medulla

Question 23

What term is used to describe the processes by which water potential and salt potential of body fluids is regulated?

Answer 23

Osmoregulation

Question 24

Name the hormone involved in osmoregulation and say where it acts

Answer 24

ADH (anti diuretic hormone) and it acts on the aquaporin channels of the collecting ducts and distal tubules

Question 25

Where is a change in water potential/solute potential of the body fluids detected?

Answer 25

It is detected by osmoreceptor cells in the hypothalamus of the brain

Question 26

Where is ADH produced?

Answer 26

The hypothalamus of the brain

Question 27

Where is ADH stored?

Answer 27

The pituitary gland in the brain

Question 28

What stimulates ADH release?

Answer 28

A decrease in water potential or solute potential (hypertonic plasma)

Question 29

What effect, exactly, does ADH have on the collecting ducts and distal tubules

Answer 29

ADH makes the membranes of the collecting ducts and distal tubules more permeable (by opening aquaporin channels) allowing more water to be reabsorbed