1Define homeostasis.
The process of maintaining a constant internal environment
2List examples of variables that are maintained by homeostasis by humans.
Core body temperature
Blood pH
Concentration of glucose in the blood
Osmotic concentration of the blood
3Compare consequences of negative and positive feedback.
Negative feedback reverses changes to maintain a stable internal environment (homeostasis), keeping variables close to a set point.
Positive feedback amplifies changes, driving a process to completion and moving the system away from the set point.
4Explain how negative feedback loops maintain homeostasis.
Negative feedback loops maintain homeostasis by detecting deviations from a set point through receptors. The control centre processes this information and activates effectors to reverse the change, restoring the variable to its normal range.
5Explain the control of blood glucose concentration, including the roles of glucagon, insulin and the endocrine cells in the pancreatic islets.
Blood glucose concentration is regulated by negative feedback involving hormones from the pancreatic islets.
β-cells detect high blood glucose and secrete insulin, which stimulates glucose uptake by cells and conversion of glucose to glycogen in the liver (glycogenesis), lowering blood glucose.
α-cells detect low blood glucose and secrete glucagon, which stimulates breakdown of glycogen to glucose in the liver (glycogenolysis), increasing blood glucose.
This antagonistic action maintains blood glucose within a narrow range.
6Distinguish between causes of type I and type II diabetes.
Type I diabetes is caused by an autoimmune destruction of β-cells in the pancreatic islets, resulting in little or no insulin production.
Type II diabetes is caused by insulin resistance, where target cells do not respond effectively to insulin, often associated with obesity and lifestyle factors.
7Distinguish between treatment of type I and type II diabetes.
Type I diabetes is treated with regular insulin injections and monitoring of blood glucose levels.
Type II diabetes is managed through lifestyle changes such as diet and exercise, and sometimes medication to improve insulin sensitivity or increase insulin production.
8Outline symptoms associated with diabetes.
Frequent urination (polyuria)
Excessive thirst (polydipsia)
Fatigue
Unexplained weight loss (more common in Type I)
9Define thermoregulation.
Thermoregulation is the maintenance of a stable internal body temperature despite external environmental changes.
10Outline thermoregulation as a negative feedback loop.
Thermoreceptors detect changes in body temperature. The hypothalamus acts as the control centre and compares the temperature to a set point. It activates effectors (e.g., muscles, sweat glands, blood vessels) to increase or decrease heat production and loss, restoring temperature to normal.
11Explain the process of thermoregulation in humans, including roles of peripheral and central thermoreceptors, the hypothalamus and pituitary gland, thyroxin and muscle and adipose tissue that act as effectors of temperature change.
Peripheral thermoreceptors in the skin detect external temperature changes, while central thermoreceptors in the hypothalamus monitor core body temperature. The hypothalamus acts as the control centre and initiates responses via the nervous and endocrine systems.
It can stimulate the pituitary gland to release TSH, which leads to secretion of thyroxine from the thyroid gland, increasing metabolic rate and heat production.
Effectors include:
Muscle tissue: generates heat through contraction (shivering)
Adipose tissue: provides insulation; brown fat generates heat via uncoupled respiration
These responses help restore body temperature to the set point.
12State that birds and mammals are thermoregulators.
Birds and mammals are thermoregulators that maintain a relatively constant internal body temperature.
13Outline physiological and behavioral responses to cold temperature, including vasoconstriction, shivering, uncoupled respiration and hair erection.
Vasoconstriction: reduces blood flow to the skin, decreasing heat loss
Shivering: muscle contractions generate heat
Uncoupled respiration: heat production in brown adipose tissue
Hair erection: traps insulating air (limited effect in humans)
14Outline physiological and behavioral responses to heat, including vasodilation and sweating.
Vasodilation: increases blood flow to the skin, promoting heat loss
Sweating: evaporation of sweat removes heat from the body