Homeostasis

Question 1

Homeostasis

Answer 1

Maintenance of constant internal
environment via physiological
control systems
control temperature, blood pH, blood
glucose concentration and water
potential within limits

Question 2

Negative
feedback

Answer 2

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

Question 3

Islets of
Langerhans

Answer 3

Endocrine region in the pancreas
containing cells involved in
detecting changes in blood glucose
levels
contains endocrine cells (alpha
cells and beta cells) which release
hormones to restore blood glucose
levels

Question 4

Alpha cells

Answer 4

Located in the islets of
Langerhans
release glucagon
when detect blood glucose
concentration is too low

Question 5

Factors affecting
blood glucose
concentration

Answer 5

Eating food containing
carbohydrates -> glucose absorbed
from the intestine to the blood
exercise -> increases rate of
respiration, using glucose

Question 5

Beta cells

Answer 5

Located in the islets of
Langerhans
release insulin
when they detect blood glucose
concentration is too high

Question 6

Action of
insulin

Answer 6

Binds to specific receptors on the
cell membranes of liver cells
increases permeability of cell
membrane (GLUT-4 channels fuse
with membrane)
glucose can enter from blood by
facilitated diffusion
activation of enzymes in liver for
glycogenesis
rate of respiration increases

Question 7

Action of
glucagon

Answer 7

Binds to specific receptors on cell
membranes of liver cells
activates enzymes for
glycogenolysis
activates enzymes for
gluconeogenesis
rate of respiration decreases
blood glucose concentration
increases

Question 8

Role of
adrenaline

Answer 8

Secreted by adrenal glands during

stress or low blood glucose (fight-or-
flight response)

binds to receptors on target cells (e.g.
liver cells)
activates glycogenolysis
stimulates gluconeogenesis
acts via the second messenger model
involving cAMP

blood glucose control

Question 10

Gluconeogenesis

Answer 10

Creating glucose from non-
carbohydrate stores in liver e.g. amino

acids -> glucose
occurs when all glycogen has been
hydrolysed and body requires more
glucose
initiate by glucagon when blood
glucose concentrations are low

Question 11

Glycogenolysis

Answer 11

Hydrolysis of glycogen back into
glucose
occurs due to the action of
glucagon to increase blood
glucose concentration

Question 12

Glycogenesis

Answer 12

Process of glucose being converted
to glycogen when blood glucose is
higher than normal
caused by insulin to lower blood
glucose concentration

Question 13

What is a second
messenger model

Answer 13

Stimulation of a molecule (usually
an enzyme) which can then
stimulate more molecules to bring
about desired response
adrenaline and glucagon
demonstrate this because they
cause glycogenolysis to occur
inside the cell when binding to
receptors on the outside

Question 14

Second
messenger
model process

Answer 14

Adrenaline/glucagon bind to specific
complementary receptors on the cell
membrane
activate adenylate cyclase
converts ATP to cyclic AMP (secondary
messenger)
cAMP activates protein kinase A
(enzyme)
protein kinase A activates a cascade to
break down glycogen to glucose
(glycogenolysis)

Question 15

Diabetes

Answer 15

A disease when blood glucose
concentration cannot be
controlled naturally

Question 17

Type 1 diabetes

Answer 17

Due to body being unable to
produce any/sufficient insulin
starts in childhood
autoimmune disease where beta
cells are attacked
treated by taking insulin

Question 18

Type 2
diabetes

Answer 18

Due to receptors in target cells
losing responsiveness to insulin
usually develops due to obesity
and poor diet
treated by controlling diet and
increasing exercise, in some
cases, insulin injections may be
required.

Question 19

Osmoregulation

Answer 19

Process of controlling the water
potential of the blood
controlled by hormones e.g.,
antidiuretic hormone (affects distal
convoluted tubule and collecting
duct)

Question 20

Nephron

Answer 20

The structure in the kidney where
blood is filtered, and useful
substances are reabsorbed into the
blood

Question 21

Nephron
structure

Answer 21

• Glomerulus : filters small solutes from blood
• proximal convuluted tuble : reabsorbs water, sodium ions, glucose ; removes toxins and adjusts filerate pH
• Descending loop of henle : aquaporins allow water to pass from the filtrate into the intersitial fluid
• Ascending loop of henle : reabosrbs Na+ and Cl- from the filtrate into the intersitial fluid
• Distal convuluted tuble : selectivley secrects and absorbs diffrent ions to maintain blood pH and electrolyte balance
• Collecting duct : reabsorbs solutes and water from the filtrate

Question 22

Formation of
glomerular
filtrate

Answer 22

• Diameter of efferent arteriole is
  smaller than afferent arteriole
• build-up of hydrostatic pressure
• water/glucose/urea/ions forced out
  of the capillary into Bowman’s
  capsule through pores in capillary
  endothelium, basement membrane
  and podocytes
• large proteins are too large to pass

Question 23

Reabsorption of
glucose by
proximal
convoluted tubule

Answer 23

• Co-transport mechanism
• epithelial cells have microvilli to
  provide a large surface area for the
  diffusion of glucose into cells from
  proximal convoluted tubule
• sodium actively transported out cells
  into intercellular space to create a
  concentration gradient
• glucose is reabsorbed into epithelial
  cells by co-transport with sodium ions,
• then diffuses into the blood

Question 24

Counter-current multiplier mechanism

Answer 24

- Describes how to maintain a gradient of Na+ in medulla by the loop of Henle. - Na+ is actively transported out of ascending limb to the medulla to a lower water potential - water moves out descending limb, the distal convoluted tubule and collecting duct by osmosis due to this water potential gradient

Question 25

Reabsorbtion of water by distal convoluted tubule / collecting duct

Answer 25

- Water moves out of distal convoluted tubule and the collecting duct by osmosis down a water potential gradient - controlled by ADH which changes the permeability of membranes to water

Question 26

Role of hypothalamus in osmoregulation

Answer 26

Contains osmoreceptors which detect changes in water potential produces ADH when blood has low water potential, osmoreceptors shrink and stimulate more ADH to be made so more released from the pituitary gland

Question 27

Anti-diuretic hormone

Answer 27

- Produced by the hypothalamus, released by the posterior pituitary - affects the permeability of walls of collecting duct & DCT to water - more ADH means more aquaporins fuse with walls so more water is reabsorbed back to blood- urine more concentrated.

Question 28

Role of posterior pituitary in osmoregulation

Answer 28

- ADH moves to the posterior pituitary from the hypothalamus - releases ADH into capillaries - travels through blood -> kidney

Question 29

Role of the proximal convoluted tubule

Answer 29

- Site of selective reabsorption in the nephron Reabsorbs: - → All glucose and amino acids (by co- transport) - → Most water and ions (by osmosis and active transport) Lined with epithelial cells with microvilli for a large surface area Contains many mitochondria to produce ATP for active transport