Homeostasis (DP IB Biology)
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Define the term homeostasis.
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Define the term homeostasis.
Homeostasis is the maintenance of a constant internal environment.
True or False?
Homeostasis ensures that conditions inside the body are kept within preset limits.
True.
Homeostasis maintains conditions inside the body within narrow, preset limits.
What physiological factors are controlled by homeostasis in mammals?
Physiological factors that are controlled by homeostasis in mammals include:
body temperature
blood pH
blood glucose concentration
blood osmotic concentration
What is a negative feedback loop?
A negative feedback loop is a mechanism that works to return values to a set point by reversing the effects of any change within a system.
True or False?
Positive feedback mechanisms maintain conditions within set limits.
False.
Positive feedback mechanisms amplify changes within a system.
It is negative feedback that maintains conditions within set limits.
Why does homeostasis involve negative feedback rather than positive feedback?
Negative feedback loops are used in homeostasis because they reverse change and maintain conditions within set limits; this is not the case in positive feedback mechanisms which instead amplify any change.
What are the cells that secrete insulin and glucagon?
The cells that secrete insulin and glucagon are pancreatic endocrine cells known as the islets of Langerhans:
insulin =
cellsglucagon =
cells
How are insulin and glucagon transported to target cells?
Insulin and glucagon are transported to target cells in the blood.
True or False?
Insulin is secreted when blood glucose levels fall.
False.
Insulin is secreted when blood glucose levels increase, such as after a meal containing carbohydrates.
Glucagon is secreted when blood glucose levels fall after fasting or exercise.
Where are the main target cells for insulin?
The main target cells for insulin are in the liver and muscles.
What is the role of insulin in blood glucose regulation?
The role of insulin in blood glucose regulation is to lower blood glucose concentration by:
promoting glucose uptake into cells
converting glucose into glycogen (glycogenesis)
increasing the rate of respiration
converting glucose to fatty acids for fat storage.
What is the effect of glucagon on target cells?
Glucagon affects target cells as follows:
activation of enzymes that convert glycogen into glucose (glycogenolysis)
a decrease in the rate of respiration
amino acids are converted to glucose (gluconeogenesis)
What is diabetes?
Diabetes is a condition in which the homeostatic control of blood glucose has failed or deteriorated.
What is the cause of type 1 diabetes?
Type 1 diabetes occurs when the pancreas fails to produce sufficient insulin. This is the result of an autoimmune response that destroys the β cells of the islets of Langerhans.
True or False?
Type 1 diabetes is usually managed with diet and exercise alone.
False.
Type 1 diabetes is managed with regular blood tests and insulin injections, not just diet and exercise.
What is the difference between type 1 and type 2 diabetes?
Type 1 diabetes occurs when the pancreas fails to produce insulin, while type 2 diabetes occurs when body cells become resistant to insulin.
What are the risk factors for type 2 diabetes?
Risk factors for type 2 diabetes include:
obesity
lack of physical activity
age
ethnicity
family history of diabetes
How is type 2 diabetes managed?
Type 2 diabetes is managed with:
medication to lower blood glucose
a low carbohydrate diet
an exercise regime that lowers blood glucose
What is a peripheral thermoreceptor?
A peripheral thermoreceptor is a receptor in the skin that monitors external body temperature.
What is the role of the hypothalamus in thermoregulation?
The role of the hypothalamus in temperature regulation includes:
monitoring of internal body temperature via internal temperature receptors
regulation of secretion of thyrotropin-releasing hormone
How do the hypothalamus, pituitary gland and thyroid gland interact to regulate body temperature?
The hypothalamus and pituitary gland work together in temperature regulation as follows:
Structure
Role
hypothalamus
detects blood temperature
regulates secretion of thyrotropin-releasing hormone in response to temperature change
pituitary gland
releases thyroid-stimulating hormone in response to thyrotropin-releasing hormone
thyroid gland
releases thyroxin in response to thyrotropin-releasing hormone
thyroxin increases metabolic rate
What is the function of thyroxin in thermoregulation?
The role of thyroxin is to increase metabolic rate, increasing heat generation by cell metabolism. Altering the secretion of thyroxin therefore allows control of heat generation.
True or False?
White adipose tissue generates heat energy in the absence of shivering.
False.
White adipose tissue stores lipids which provide insulation against heat loss.
It is brown adipose tissue that generates heat energy in the absence of shivering; this is non-shivering thermogenesis
What is the role of muscle tissue in thermoregulation?
Muscle tissue contributes to thermoregulation through shivering, which raises the metabolic rate of muscle cells and releases heat energy.
True or False?
Birds and mammals rely on behavioural mechanisms to regulate body temperature.
False.
Birds and mammals use both behavioural and physiological mechanisms to regulate body temperature.
What is vasodilation?
Vasodilation is the widening of arterioles that supply capillaries in the skin. This allow more blood to flow through skin capillaries, increasing heat loss to the environment.
Define the term vasoconstriction.
Vasoconstriction is the narrowing of arterioles that supply capillaries in the skin. This allows less blood to flow through capillaries, reducing heat loss to the environment.
What is the role of sweat glands in thermoregulation?
The role of sweat glands in thermoregulation is to secrete sweat onto the skin surface. Heat energy is lost from the body when the sweat evaporates.
Define the term uncoupled respiration, in the context of thermoregulation.
Uncoupled respiration is respiration that is separated from the production of ATP, meaning that all of the energy released is in the form of heat. This process occurs in brown adipose tissue.
What is the function of hair erector muscles in thermoregulation?
Hair erector muscles in thermoregulation contract to cause hairs on the skin to stand on end. This forms an insulating layer of air over the skin's surface, reducing heat loss by radiation.