Unit 4 Homeostasis

Urea vs. ammonia- 1 Mark

Urea: Less toxic, excreted in urine. Formed in liver
Ammonia: Highly Toxic, requires lots of water to excrete. Common in aquatic animals

Hormones: Next 6 slides- Multiple Mark
ADH

Function: Raises blood pressure, controls water retention by kidneys
Disorder: Diabetes
Negative Feedback

PTH

Raises blood calcium, breaking down bone and increasing absorption
Disorder: HPT
Negative Feedback

TSH

Stimulates thyroid to release thyroid hormones
Disorder: Hypothyroidism (Weight Gain), Hyperthyroidism (Weight loss)
Negative Feedback

Calcitonin

Lowers blood calcium by storing it in bones
Disorder: MTC
Negative Feedback

Insulin

Lowers blood glucose by helping cells absorb it
Disorder: Diabetes mellitus
Negative Feedback

Glucagon

Raises blood glucose by stimulating glycogen breakdown
Disorder: Hypoglycemia
Negative Feedback

Oxytocin

Stimulates uterine contractions & milk ejection
Disorder: Problems with labor, milk release
Positive Feedback

Draw feedback loop (Thyroid feedback Loop)- Multiple Mark

Thyroid hormone feedback Loop
1) TRH released by hypothalamus, stimulates release of TSH in pituitary
2) TSH stimulates thyroid, inhibits release of TRH
3) T4 from thyroid inhibits release of TSH

What happens if you don’t get enough iodine?
Repeat step 1 and 2, 3 is then removed
3. Thyroxine (T₄) from thyroid inhibits release of TSH

4) Lack of iodine prevents T₄ formation, loss of negative feedback on TSH
5) TSH continues to stimulate thyroid

Reflex Arcs- 1 Mark

Pathway that a reflex takes in the body
Receptor, sensory neuron, integration center, motor neuron, and effector

Action potential graph (stimulus, resting membrane, threshold potential, depolarization, repolarization, hyperpolarization)- Multiple Mark

1) Resting membrane potential: -70 mV
2) Stimulus: Triggering event, causes small change
3) Threshold Potential: -55mV minimum voltage needed to start an action potential. Once reached, voltage-gated Na⁺ channels open
4) Depolarization: Na⁺ rushes into the cell, making the inside more positive. Rising phase of the graph. (30mV)
5) Repolarization: Na⁺ channels close, K⁺ channels open. K⁺ leaves the cell, making the inside more negative again (Returns to -70mV)
6) Hyperpolarization: Too much K⁺ exits. The membrane becomes more negative than resting potential (-80 mV).
7) Return to Resting Potential: Na⁺/K⁺ pump restores balance, bringing the cell back to -70 mV

CNS: Central Nervous System- 1 Mark

Brain: controls functions, processes information.
Spinal cord: transmits signals, controls reflexes.
Protected by skull, vertebrae, meninges, and cerebrospinal fluid.