3.6 Homeostasis Flashcards
Negative Feedback, Control of Blood Glucose and Water Potential
define homeostasis
the maintenance of a constant internal environment despite changes in the surroundings
describe the importance of homeostasis (4 marks)
- Enzymes are sensitive to changes in pH and temperature, any changes could reduce the rate of reaction or denature them, preventing essential biochemical reactions
- Water potential and blood glucose concentration must be maintained because changes could shrink or burst cells
- Allows organism to be more independent of changes in the external environment, greater chance of finding food and shelter
explain the effect of high temperature and pH on enzyme function
High temperature leads to vigorous vibrations which can cause the hydrogen and ionic bonds holding the tertiary structure together to break. This causes a change in the shape of the active site so it is no longer complementary. The enzyme is therefore denatured and cannot catalyse the reaction.
A decrease in pH from increased carbon dioxide concentration disrupts hydrogen and ionic bonds in the tertiary structure of the enzyme, it is no longer complementary so it is denatured.
define negative feedback
when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
define positive feedback
when a deviation from the optimum causes a change that results in even greater deviation from normal
regulation of metabolic rate with TSH
There is a fall in the energy available to cells due to low thyroxine levels which is detected by the hypothalamus
TRH produced by hypothalamus, causing release of TSH from the PG into blood
TSH binds to thyroid gland to produce thyroxine into the blood
Thyroxine causes the metabolic rate to increase, allowing cells to transfer additional energy
The cells now have enough energy due to normal thyroxine levels, detected by the hypothalamus
describe how hormones function (3 marks)
Produced in endocrine glands, secreted directly into the blood
Carried in blood plasma to target cells
Effective in low concentrations, widespread and long-lasting effects
explain the role of adrenaline in the second messenger model
- Adrenaline binds to transmembrane protein receptor within the CSM of a liver cell, activating glucagon associated with the receptor on the inside
- Glucagon activates a G-protein on the inside which activates adenyl cyclase which now converts ATP to cyclic AMP
- cAMP acts a second messenger which binds to the kinase enzymes and initiates a cascade of kinase-controlled reactions on the inside
- These reactions catalyse glycogenolysis which moves glucose out of the liver via facilitated diffusion into the blood through channel proteins
why is the second messenger model useful in terms of the role of adrenaline
glucose produced can be used in respiration to generate ATP for muscle contraction for the organism to return to safety
glycogenesis
the conversion of glucose into glycogen
glycogenolysis
the breakdown of glycogen to glucose
gluconeogenesis
production of glucose from non carbohydrate sources
Describe how a high blood glucose concentration can result in the reduction of function of body cells
Increased glucose concentration in the blood
Water potential of the blood decreases
Water moves from an area of higher water potential in the cells to an area of lower water potential in the blood by osmosis
Body cells therefore shrink/crenate if a large volume of water leaves
Cells experience a decreased surface area, reducing their ability to function
sources of blood glucose
Diet
Glycogenolysis
Gluconeogenesis
describe how the body detects and responds to an increase in the concentration of blood glucose
An increase in blood glucose concentration is detected by receptors in the Islets of Langerhans, causing Beta cells to secrete more insulin into the bloodstream
Insulin travels in the bloodstream and attaches to membrane bound receptors on the CSM of liver cells, activating a cascade of kinase-controlled reactions for glycogenesis
Increases the conversion of glucose into fats by activating necessary enzymes
Insulin then increases the rate of glucose uptake into the blood by initiating a change in the tertiary structure of glucose transport carrier proteins, causing them to change shape and open, increasing glucose absorption into cells via facilitated diffusion and for glucose transporter carrier proteins vesicles to fuse with the liver cell membrane, increasing the number of glucose transport channels
Increases the use of glucose in respiration
Once blood glucose levels are restored, secretion of insulin by the beta cells decreases
describe how the body detects and responds to a decrease in the concentration of blood glucose
Receptors in the Islets of Langerhans detect a decrease and stimulate alpha cells to secrete more glucagon into the blood
Glucagon binds to membrane bound receptors on liver cells, acting as a first messenger to activate a G-protein inside the cell
The protein now activates adenyl cyclase which converts ATP into cAMP as a secondary messenger
cAMP initiates a cascade of protein kinase controlled reactions to perform glycogenolysis
Glucagon also activates enzymes involved in gluconeogenesis
Once blood glucose concentration returns to its optimum concentration, alpha cells reduce their secretion of glucagon
define autoimmune disease
the body’s own white blood cells produce antibodies to destroy their own body cells, B cells of the Islets of Langerhans are destroyed
symptoms of diabetes
High blood glucose concentration
Glucose in urine
Excessive need to urinate
Genital itching
Weight loss
Blurred vision
Tiredness
Increased thirst and hunger
compare type 1 diabetes to type 2 diabetes
autoimmune disease vs linked to obesity
produces insufficient insulin/none at all vs glycoprotein receptors lost or body cells no longer respond to insulin or pancreas fails to produce insulin
controlled by regular injections of insulin vs need to eat a more balanced, lower carbs diet to treat
normally develops in childhood vs normally occurs later in life
balanced diet and regular exercise vs need to lead a more active lifestyle
