Homeostasis

Front 1

What is negative feedback?

Back 1

When the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off.

Front 2

What is positive feedback?

Back 2

When a deviation from an optimum causes changes that result in an even greater deviation from the normal one.

Front 3

What is homeostasis?

Back 3

The maintenance of a constant internal environment.

Front 4

What are islets of Langerhans?

Back 4

Groups of hormone-producing cells scattered throughout the pancreas.

Front 5

What do alpha cells produce?

Back 5

Glucagon.

Front 6

What do beta cells produce?

Back 6

Insulin.

Front 7

What is glycogenesis?

Back 7

Conversion of glucose into glycogen.

Front 8

What is glycogenolysis?

Back 8

Breakdown of glycogen to glucose.

Front 9

What is gluconeogenesis?

Back 9

Production of glucose from sources other than carbohydrate such as glycerol and amino acids.

Front 10

Why does blood glucose concentration need to be regulated?

Back 10

If the concentration gets too high, the water potential of the blood is lowered which can cause cells to shrink and dehydrate due to osmosis.

If the concentration gets too low, cells won’t be able to respire and would die.

Front 11

What are the three sources that blood glucose comes from?

Back 11

Diet - carbohydrates hydrolysed to glucose.

Glycogenolysis.

Gluconeogenesis.

Front 12

What are the three main hormones that maintain a constant blood glucose concentration?

Back 12

Insulin.

Glucagon.

Adrenaline.

Front 13

How is insulin used to regulate blood glucose concentration?

Back 13

Receptors on the beta cells of the islets of Langerhans in the pancreas detect a rise in blood glucose concentration.

Beta cells secrete insulin directly into the blood plasma.

Insulin binds to glycoprotein receptors on the cell-surface membrane (most body cells have these).

This causes a change in the tertiary structure of the glucose transport carrier protein which causes them to change shape and open which allows more glucose into the cells by facilitated diffusion.

It increases the number of carrier proteins responsible for glucose transport in the cell-surface membrane.

Activates enzymes that convert glucose to glycogen and fat.

Front 14

How is glucagon used to regulate blood glucose concentration?

Back 14

Receptors on the alpha cells of the islets of Langerhans detect a fall in blood glucose concentration.

Alpha cells secrete glucagon.

Glucagon attaches to specific protein receptors on the cell-surface membrane of liver cells.

It activates enzymes that convert glycogen to glucose and activates enzymes that convert amino acids and glycerol to glucose.

Front 15

What is the role of adrenaline in regulating blood glucose concentration?

Back 15

Adrenaline raises the blood glucose concentration by attaching to protein receptors on the cell-surface membrane of target cells and activates enzymes that cause the breakdown of glycogen to glucose in the liver.

Front 16

What is Type 1 Diabetes?

Back 16

Body being unable to produce insulin. Autoimmune response where body attacks beta cells.

Front 17

What is Type 2 Diabetes?

Back 17

Due to glycoprotein receptors on body cells losing their responsiveness to insulin.

Front 18

How is Type 1 diabetes controlled?

Back 18

Injections of insulin as it cannot be taken orally as the hormone (a protein) would be digested.

Front 19

How is Type 2 diabetes controlled?

Back 19

Controlled by regulating intake of carbohydrate in the diet and regular exercise.

Can be supplemented by injections of insulin.

Front 20

What is osmoregulation?

Back 20

Homeostatic control of the water potential of the blood.

Front 21

What are the different components of a kidney?

Back 21

Fibrous capsule - outer membrane that protects the kidney.

Cortex - lighter coloured outer region made up of Bowman's Capsules, convoluted tubules and blood vessels.

Medulla - darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels.

Renal pelvis - funnel-shaped cavity that collects urine into the ureter.

Ureter - tube that carries urine to the bladder.

Renal artery - supplies kidney with blood from the heart via the aorta.

Renal vein - returns blood to the heart via vena cava.

Front 22

What are the different components of a nephron?

Back 22

Each nephron is made up of a:

Bowman's capsule.

Proximal convoluted tubule.

Loop of Henle.

Distal convuleted tubule.

Collecting duct.

Front 23

What is a Bowman's capsule?

Back 23

The closed end at the start of the nephron. It surrounds a glomerulus.

Front 24

What are podocytes?

Back 24

Specialised cells that make up the inner layer of the renal capsule.

Front 25

What is the proximal convoluted tubule?

Back 25

A series of loops surrounded by blood capillaries. Its walls are made of epithelial cells which have microvilli.

Front 26

What is the loop of Henle?

Back 26

A long, hairpin loop that extends from the cortex into the medulla of the kidney and back again. It is surrounded by blood capillaries.

Front 27

What is the distal convoluted tubule?

Back 27

A series of loops surrounded by blood capillaries. Its walls are made of epithelial cells, but it is surrounded by fewer capillaries than the proximal tubule.

Front 28

What is the collecting duct?

Back 28

A tube into which a number of distal convoluted tubules from a number of nephrons empty. It is lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of the kidney.

Front 29

What blood vessels are associated with each nephron?

Back 29

Afferent arteriole.

Glomerulus.

Efferent arteriole.

Blood capillaries.

Front 30

What is the afferent arteriole?

Back 30

Tiny vessel that arises from the renal artery and supplies the nephron with blood. It enters the renal capsule of the nephron where it forms the glomerulus.

Front 31

What is the glomerulus?

Back 31

A many-branched knot of capillaries from which fluid is forced out of the blood. The glomerulular capillaries recombine to form the efferent arteriole.

Front 32

What is the efferent arteriole?

Back 32

A tiny vessel that leaves the renal capsule. The efferent arteriole carries blood away from the renal capsule and later branches to form the blood capillaries.

Front 33

What do the blood vessels in the nephron do?

Back 33

They surround the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule. These capillaries merge together into venules that merge together to form the renal vein.

Front 34

What are the different stages carried out by the nephron in its role in osmoregulation?

Back 34

Formation of glomerular filtrate by ultrafiltration.

Reabsorption of glucose and water by the proximal convoluted tubule.

Maintenance of a gradient of sodium ions in the medulla by the loop of Henle.

Reabsorption of water by the distal convoluted tubule and collecting ducts.

Front 35

How is the glomerular filtrate formed?

Back 35

As the diameter of the afferent arteriole is greater than the diameter of the efferent arteriole, there is a build up of hydrostatic pressure within the glomerulus. This forces water, glucose and mineral ions out of the capillary to form the glomerular filtrate. Blood cells and proteins can not pass into the renal capsule as they are too large.

Front 36

What resists the movement of the filtrate out of the glomerulus?

Back 36

Capillary endothelial cells.

Connective tissue.

Epithelial cells of the renal capsule.

Hydrostatic pressure of the fluid in the renal capsule space.

Low water potential of the blood in the glomerulus.

Front 37

How is the flow of filtrate able to overcome this resistance?

Back 37

The inner layer of the renal capsule is made up of podocytes which have spaces beneath them which allow filtrate to pass beneath them and through the gaps beneath their branches.

This is the same for the endothelium of the glomerular capillaries.

Front 38

How are the proximal convoluted tubules adapted to reabsorb substances into the blood?

Back 38

Microvilli to provide a large surface area to reabsorb substances from the filtrate.

Infoldings at their bases to give a large surface area to transfer reabsorbed substances into blood capillaries.

Front 39

How do the proximal convoluted tubules reabsorb substances from the blood?

Back 39

Sodium ions actively transported out cells lining the proximal convoluted tubule into blood capillaries which carry them away. The sodium ion concentration of these cells is lowered.

Sodium ions diffuse down a concentration gradient from the lumen of the proximal convoluted tubule into the epithelial lining cells through carrier proteins by facilitated diffusion.

Each carrier protein carries another molecule,

The molecules have been co-transported into the cells of the proximal convoluted tubule then diffuse into the blood.

Front 40

What are the two regions of the loop of Henle?

Back 40

Descending limb - narrow with thin walls and are highly permeable to water.

Ascending limb - wider with thick walls and are impermeable to water.

Front 41

How does the loop of Henle act as a counter-current multiplier?

Back 41

Sodium ions actively transported out the ascending limb using ATP.

This creates a low water potential in the interstitial region.

Thick walls in ascending limb prevents water passing out by osmosis.

Walls of descending limb are very permeable to water so it passes out the filtrate by osmosis into the interstitial space.

This water enters the blood capillaries by osmosis and is carried away.

The filtrate's water potential lowers as it moves down the descending limb and reaches its lowest water potential at the tip of the hairpin.

Sodium ions diffuse out of the filtrate at the base of the ascending limb.

As the filtrate moves up the ascending limb, these ions are also actively pumped out therefore the filtrate develops a progressively higher water potential.

The collecting duct is permeable to water so the water passes out of it by osmosis.

This lowers the water potential of the filtrate however the water potential is also lowered in the interstitial space so water continues to move out by osmosis down the whole length of the collecting duct.

Front 42

How does the body respond to the fall in water potential of the blood?

Back 42

Osmoreceptors in the hypothalamus detect the fall in water potential.

Water leaves the osmoreceptors by osmosis which causes them to shrink.

This causes the hypothalamus to produce ADH.

ADH passes to the posterior pituitary gland where it is secreted into the capillaries.

ADH passes from the blood to the kidney where it increases the permeability to water of the cells of the walls of the distal convoluted tubule and the collecting duct.

Specific protein receptors on the cell-surface membrane of these cells bind to ADH, activating phosphorylase.

Phosphorylase causes vesicles containing aquaporins to fuse with the cell-surface membrane which makes the membrane more permeable to water.

ADH increases the permeability of the collecting duct to urea, which lowers the water potential of the fluid around the duct.

This means more water leaves the collecting duct by osmosis and re-enters the blood.

Front 43

How does the body respond to the rise in water potential of the blood?

Back 43

Osmoreceptors in the hypothalamus detect the rise in water potential and increase the frequency of the nerve impulses to the pituitary gland to reduce its release of ADH.

Less ADH leads to a decrease in the permeability of the collecting ducts to water and urea.

Less water is reabsorbed into the blood from the collecting duct.

More dilute urine is produced and the water potential of the blood falls.