D3.3 Homeostasis and Human Physiology

Vocabulary flashcards covering essential terms and definitions related to human homeostasis, negative feedback, glucose regulation, diabetes, and thermoregulation.

Homeostasis

The ability of an organism to maintain a constant internal environment within preset limits despite external fluctuations.

Set Point

The narrow target value around which a homeostatic variable is regulated (e.g., 90 mg glucose / 100 mL blood).

Homeostatic Variable

A physiological parameter kept within limits by homeostasis, such as body temperature, blood pH, or blood glucose concentration.

Negative Feedback

A control mechanism that counteracts deviations from the set point, returning a variable to its normal range.

Positive Feedback

A control mechanism that amplifies a change and drives the system further from its starting state; rare in homeostasis.

Thermoregulation

The homeostatic maintenance of core body temperature near a set point through physiological and behavioural means.

Peripheral Thermoreceptors

Temperature-sensitive nerve endings in the skin that detect external thermal changes and relay signals to the hypothalamus.

Hypothalamus

Brain region that acts as the central thermostat, integrating thermal information and initiating temperature-regulating responses.

Pituitary Gland

Endocrine gland under hypothalamic control; releases TSH to stimulate thyroxin production during thermoregulation.

Thyroxin (T4)

Thyroid hormone that increases metabolic rate and heat production in target tissues such as muscle, liver, and brain.

Thyrotropin-Releasing Hormone (TRH)

Hormone secreted by the hypothalamus that triggers pituitary release of TSH.

Thyroid-Stimulating Hormone (TSH)

Pituitary hormone that prompts the thyroid gland to secrete thyroxin.

Brown Adipose Tissue

Specialised fat tissue rich in mitochondria that generates heat via uncoupled respiration, especially in infants and small mammals.

Vasodilation

Widening of skin blood vessels to increase heat loss when body temperature rises.

Vasoconstriction

Narrowing of skin blood vessels to conserve heat when body temperature falls.

Sweating

Evaporative cooling mechanism where sweat glands release water; heat is lost as the water evaporates.

Shivering

Involuntary rhythmic muscle contractions that generate heat during cold exposure.

Uncoupled Respiration

Metabolic process in brown fat where proton gradient energy is released as heat instead of producing ATP.

Insulin

Pancreatic β-cell hormone that lowers blood glucose by promoting cellular uptake and glycogen synthesis.

Glucagon

Pancreatic α-cell hormone that raises blood glucose by stimulating glycogen breakdown and gluconeogenesis in the liver.

Pancreatic β Cells

Cells in the islets of Langerhans that secrete insulin.

Pancreatic α Cells

Cells in the islets of Langerhans that secrete glucagon.

Islets of Langerhans

Clusters of endocrine cells in the pancreas responsible for insulin and glucagon production.

Endocrine Gland

Gland that releases hormones directly into the bloodstream (e.g., pancreas, thyroid).

Exocrine Gland

Gland that delivers its product via ducts to specific locations (e.g., sweat glands, digestive enzyme-secreting pancreas).

Blood Glucose Concentration

Amount of glucose present in the blood; normally maintained around 90 mg / 100 mL by insulin and glucagon.

Hyperglycemia

Condition of abnormally high blood glucose, often increasing blood pressure and risk of diabetes complications.

Hypoglycemia

Condition of abnormally low blood glucose, leading to dizziness, weakness, and potential loss of consciousness.

Type 1 Diabetes

Early-onset autoimmune disease where β cells are destroyed, eliminating insulin production.

Type 2 Diabetes

Late-onset disorder characterised by insulin resistance or reduced receptor numbers, often linked to obesity and inactivity.

Glucose Tolerance Test

Diagnostic procedure measuring how quickly ingested glucose is cleared from blood to identify diabetic conditions.

Normoglycemia

State of normal blood glucose levels after fasting or regulated by homeostatic mechanisms.

Target Cell

A cell bearing specific receptors that respond to a particular hormone, such as insulin or thyroxin.

Effector

An organ or tissue that carries out responses dictated by a control centre, e.g., sweat glands or skeletal muscles in thermoregulation.

Metabolic Rate

Overall rate at which the body consumes oxygen and produces energy; modulated by hormones like thyroxin.