Homeostasis and coordination
Homeostasis and coordination tests nervous and hormonal control, feedback, synapses, the kidney and thermoregulation. Expect questions on action potentials, neurotransmitters, blood glucose, ADH and negative feedback.
Nervous coordination
- A stimulus causes sodium ion channels to open; sodium influx depolarises the membrane and generates an action potential. Potassium efflux repolarises it.
- Myelination speeds conduction by saltatory conduction. Synapses use neurotransmitters; transmission is unidirectional because vesicles are presynaptic.
Hormonal control and homeostasis
Negative feedback reverses a change. Insulin lowers blood glucose by increasing uptake and glycogen formation; glucagon raises it by glycogen breakdown. ADH increases water reabsorption in the collecting duct. Thermoregulation uses vasodilation, sweating, shivering and hair erection.
Worked example
After a meal, blood glucose rises. Pancreatic beta cells secrete insulin. Insulin binds liver and muscle cells, increasing glucose uptake and glycogenesis, so blood glucose falls. The fall reduces insulin secretion, demonstrating negative feedback.
Traps
An action potential is not a movement of the whole cell. Depolarisation is mainly sodium influx. Insulin does not raise blood glucose. ADH increases water reabsorption, not urine volume. Negative feedback opposes the initial change.