Homeostasis summary and practice

Homeostasis and response • Homeostasis

Flashcards

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Glucagon - main function

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Hormone from the pancreas that raises blood glucose by converting stored glycogen back to glucose in the liver.

Key concepts

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Definition and core variables

Homeostasis is the maintenance of a constant internal environment to allow optimal enzyme action and cellular processes. Core variables commonly regulated include blood glucose, body temperature and water/ion balance. Deviations from normal values cause reduced cellular efficiency or damage.

Control system components

Receptors detect a specific change (stimulus) and generate a signal. Coordination centres (brain, spinal cord, pancreas) interpret the signal and send instructions. Effectors (muscles or glands) produce responses that change the internal condition. The pathway follows stimulus → receptor → coordinator → effector → response.

Negative feedback as the main mechanism

Negative feedback detects a change from a set point and triggers responses that reverse the change until normal levels return. Examples include blood glucose regulation by insulin and glucagon, and water balance controlled by ADH. Hormonal negative feedback often involves glands increasing or decreasing hormone secretion in response to levels. 0filecite_placeholder

Blood glucose regulation (cause → effect)

Rise in blood glucose after a meal → pancreatic beta cells detect increase → insulin secretion increases → liver and muscle convert glucose to glycogen → blood glucose decreases back toward normal. Drop in blood glucose → pancreatic alpha cells detect decrease → glucagon secretion increases → liver breaks down glycogen to release glucose → blood glucose increases. Disruption of insulin production prevents the effect and causes persistently high blood glucose (type 1 diabetes).

Thermoregulation (cause → effect)

Core temperature increase → thermoregulatory centre detects change via receptors in skin and brain → vasodilation and sweating increase heat loss → body temperature falls. Core temperature decrease → thermoregulatory centre triggers vasoconstriction and shivering → heat conservation and production raise temperature. Normal human core temperature is about 37 °C (range ~36.5–37.5 °C).

Water balance and ADH (cause → effect)

Low water intake or dehydration → osmoreceptors detect increased blood osmolarity → pituitary releases more ADH → kidneys increase water reabsorption in nephrons → urine becomes more concentrated and water loss decreases. Excess water intake → ADH release falls → kidneys reduce reabsorption → urine becomes more dilute. Kidney failure prevents effective removal of urea and regulation of water; dialysis or transplant address this failure.

Nervous versus hormonal control (limiting factors)

Nervous control uses rapid electrical impulses for fast, short-lived responses (reflexes); hormonal control uses slower, longer-lasting chemicals carried in the blood. Limiting factors include signal speed (nervous faster than hormonal), availability of target receptors, gland function (e.g., damaged pancreas), and transport limits (impaired circulation reduces hormone delivery).

Key notes

Important points to keep in mind

Homeostasis operates continuously and often unconsciously to maintain optimal conditions for enzymes and cells.

Negative feedback reverses deviations from set points; identify the stimulus, detector, controller and effector in every example.

Nervous responses are fast and short-lived; hormonal responses are slower and longer-lasting.

Insulin lowers blood glucose by storing glucose as glycogen; glucagon raises blood glucose by breaking glycogen down.

ADH alters kidney water reabsorption to control blood water content; dialysis substitutes kidney filtration when kidneys fail.

Failure at any stage (receptor, coordinator, effector) prevents the corrective response and leads to lasting deviation.