Homeostasis

Question 1

What is homeostasis?

Answer 1

Homeostasis in mammals involves physiological control systems that maintain the internal environment within restricted limits

Question 2

What is the generic term for the corrective mechanisms that enables mammals to maintain a balanced equilibrium in their internal environment?

Answer 2

Negative feedback

Question 3

What does negative feedback do ?

Answer 3

Restores systems to their original level

Question 4

What are the characteristics of hormones ?

Answer 4

Produce by endocrine glands –> secreted directly into the plasma
Carried in blood plasma to the target cell
Binds to receptors on target cell –> complimentary shaped to the hormone- acts on target cells
Produced in small quantities,but have wide spread and long lasting effects

Question 5

Define negative feedback

Answer 5

When there is a deviation from the normal values and
restorative systems are put in place to return this back to the
original level. This involves the nervous system and often
hormones

Question 6

why must the following be kept within set limits in the
body?
Blood glucose:

Answer 6

glucose is needed for respiration, so a lack of glucose in the
blood could result in cell death. If blood glucose levels are
too high, then this will lower the water potential of the blood
and water will leave surrounding cells by osmosis and
prevent normal cell function. If the water potential of the
blood is too low, water will move into cells by osmosis and
can cause them to burst (lyse).

Question 7

Why must the following be kept within set limits in the
body?
Temperature

Answer 7

f body temperature is too low there will be insufficient kinetic
energy for enzyme-controlled reactions, and if body
temperature is too high then enzymes will denature. Either way,
metabolic reactions could slow to the point that cells die.
Alterations in blood pH will also result in enzymes denaturing.

Question 8

What is the role of the pancreas?

Answer 8

Detects changes in the blood glucose levels and contains
endocrine cells in the Islets of Langerhans which release the
hormones insulin and glucagon to bring blood glucose levels
back to normal.

Question 9

Why do type I and type II diabetes result in the body being unable to control blood
glucose?

Answer 9

Type I diabetes is due to the body being unable to produce insulin, it starts in
childhood and could be the result of an autoimmune disease where the beta cells
were attacked. Treatment involves an injection of insulin.
Type II diabetes is due to receptors on the target cells losing their responsiveness to
insulin, which usually develops in adults because of obesity and poor diet. It is
controlled by regulating the intake of carbohydrates, increasing exercise and
insulin injections.

Question 10

Insulin is secreted by the Beta cells when blood glucose
levels are too high. Explain how insulin helps bring this
back within the normal limits.

Answer 10

1. Attaching to receptors on the surfaces of target cells.
   This changes the tertiary structure of the channel
   proteins resulting in more glucose being absorbed by
   facilitated diffusion.
   2.More protein carriers are incorporated into cell
   membranes so that more glucose is absorbed from the
   blood into cells.
   3.Activating enzymes involved in the conversion of
   glucose to glycogen. This results in glycogenesis in the
   liver

Question 11

Glucagon is secreted by the alpha cells when blood
glucose levels are too low. Explain how glucagon
helps bring this back within the normal limits.

Answer 11

1.attaching to receptors on the surfaces of target
cells (liver cells).
2.When glucagon binds, it causes a protein to be
activated into adenylate cyclase which converts ATP
into a molecule called cyclic AMP (cAMP). cAMP
activates an enzyme, protein kinase, that can
hydrolyse glycogen into glucose.
3.Activating enzymes involved in the conversion of
glycerol and amino acids into glucose.

Question 12

Which two hormones can trigger the second messenger model?

Answer 12

Glucagon and adrenaline

Question 13

Adrenaline is secreted by
the adrenal glands when
blood glucose levels are
too low. Explain how
adrenaline helps bring
this back within the
normal limits.

Answer 13

• Adrenaline attaches to
  receptors on the surfaces of
  target cells. This causes a
  protein (G protein) to be
  activated and to convert ATP
  into cAMP.
• cAMP activates an enzyme
  that can hydrolyse glycogen
  into glucose.
• This is known as the second
  messenger model of
  adrenaline and glucagon
  action because the process
  results in the formation of
  cAMP, which acts as a
  second messenger.

Question 14

Describe what occurs at each part of the
nephron:
The Bowman’s (renal) capsule

Answer 14

Ultrafiltration
occurs here as the afferent arteriole (entering the
glomerulus) is wider than the efferent arteriole
(leaving the glomerulus) creating high
hydrostatic pressure. Small molecules and water
are forced out of the capillaries into the renal
capsule creating the glomerular filtrate. Large
proteins and blood cells remain in the blood.

Question 15

Describe what occurs at each part of the
nephron:
proximal convoluted tubule (PCT)

Answer 15

The walls are
made of microvilli epithelial cells to provide a
large surface area for the diffusion of glucose
into the cells from the PCT.

Question 16

Describe what occurs at each part of the
nephron:
Loop of Henle

Answer 16

Sodium ions are actively
transported out of the ascending limb into the
medulla to create a low water potential. Water
moves out of the descending limb and out of the
distal convoluted tubule and collecting duct by
osmosis due to this water potential gradient.

Question 17

Describe what occurs at each part of the
nephron

Answer 17

Glucose is then actively transported out of the
cells into the intercellular space to create a
concentration gradient. Glucose can then
diffuse into the blood again.

Question 18

What happens when blood glucose levels increase?

Answer 18

1.B cells on islets of Langerhans detect the change
2.B cells secrete insulin into blood plasma
3.Liver cells become more permeable to glucose and enzymes are activated to convert glucose to glycogen.
- Rate of respiration increases, glycogenesis occurs, glucose –> adipose
4. Glucose concentration falls

Question 19

What happens when blood glucose concentration falls?

Answer 19

1. Detected by alpha cells in the islets of langerhans (pancreas)
2. alpha cells release glucagon. the adrenal gland releases insulin
3. second messenger model occurs to activate enzymes to hydrolyse glycogen
   4.glycogen is hydrolysed to glucose and more glucose is released in the blood

Question 20

Describe the structure of slow-twitch fibres compared to fast-twitch fibres

Answer 20

Slow-twitch fibres: contains a large store of myoglobin, a rich blood supply and many mitochondria.
Fast-twitch fibres: thicker and more myosin filaments, a large store of glycogen, a store of phosphocreatine to help make ATP from ADP and a high concentration of enzymes involved in anaerobic respiration

Question 21

Where are slow-twitch fibres located ?

Answer 21

calf muscles

Question 22

Where are fast-twitch fibres located?

Answer 22

biceps

Question 23

What are the general properties of slow-twitch fibres ?

Answer 23

contract slower
can respire aerobically for longer periods of time due to the rich blood supply and myoglobin oxygen store
these muscles are adapted for endurance work such as marathons

Question 24

what are the general properties of fast-twitch fibres?

Answer 24

contract faster to provide short burst of powerful contraction
these are adapted for intense exercise such as sprinting or weight lifting