Intro to Metabolism RegulationThe Thyroid gland

produces the hormones thyroxine (T4), calcitonin, triiodothyronine (T3).

The parathyroid glands produce parathyroid hormone (PTH).

The pituitary gland produces growth hormone (hGH).

Important Hormones in Metabolism

The two important thyroid hormones are T4 and T3.

They both regulate body metabolism and the growth and differentiation of tissues.

Metabolism Feedback Loop If the metabolic rate

decreases then:1) Hypothalamus sends

thyroid releasing hormone (TRH) to the pituitary.

2) Pituitary sends thyroid stimulating hormone (TSH) to the thyroid

3) Thyroid secretes the iodine packed hormone thyroxine.

4) Thyroxine raises metabolism by increasing sugar usage by the body tissues which increases metabolic rate.

Thyroxine inhibits the release of TRH by the hypothalamus.

TRH

TSH

Body Tissues use more sugar

T4

Metabolism Feedback LoopTriiodothyronine (T3) is

also produced.

It is similar to thyroxine (T4) but with fewer iodine molecules associated with it.

It is the more powerful thyroid hormone and is only released in a small quantity. It has many roles.

It increases the production of RNA polymerase and therefore acts to increase the rate of protein synthesis.

Fast MetabolismIndividuals who secrete

high levels of thyroxine can oxidize sugars and other nutrients at a faster rate.

Approximately 60% of the glucose oxidized is released as heat. The other 40% is transferred to ATP which is consumed during activity and therefore there is no weight gain.

Could be caused by hyperthyroidism.

Slow MetabolismIndividuals who do not

secrete high levels of thyroxine cannot oxidize sugars as quickly and the glucose is converted to glycogen and stored. Once the glycogen stores are filled, excess sugar is stored as fat. These individuals gain weight!

This could be a case of hypothyroidism (low thyroid secretions).

Calcium Level Regulation

Calcium Level Feedback Cycle If Calcium Levels Drop

If blood calcium levels drop, the parathyroid gland acts as the sensor, co-ordinating center and effector.

It senses the level of calcium dropping and releases parathyroid hormone (PTH).

PTH activates vitamin D which increases the amount of calcium absorbed in the intestines.

PTH causes the nephron (distal tubule primarily) to reabsorb more calcium.

PTH also causes bones to release calcium into the bloodstream.

Calcium Level Feedback Cycle If Calcium Levels Rise

If blood calcium levels rise the thyroid gland acts as the sensor, co-ordinating center and effector.

It senses the level of calcium rising and releases calcitonin.

Calcitonin inhibits the nephron from reabsorbing calcium.

Calcitonin also inhibits bones from releasing calcium into the bloodstream.

Homework

p. 387 #3, 6, 7