Martin Ray A. Arcibal
AP Biology
May 7, 2012
Mrs. Delgado
Hormone Free Response
The endocrine system consists of organs regulating the metabolic activities and
maintaining homeostasis within an organism through the production of hormones. This system
works together with the nervous system to stimulate the production of essential regulatory
molecules through either the positive or negative feedback mechanism. Positive feedback
mechanism is the increased production of a certain product when the level of a certain molecule
increases. Negative feedback mechanism, on the other hand, decreases the production of a
product as a certain molecule increases in quantity. The hypothalamus receives signals from the
body and other parts of the brain and initiates a response for each signal. The hormones produced
can affect either a few of an organism’s tissues or the endocrine glands themselves. Six
hormones essential for the proper regulation of the body are insulin and glucagon, parathyroid
hormone and calcitonin, and thyrotropin and thyroxine.
Glucagon and insulin are hormones that regulate the blood glucose level of an organism.
These hormones are produced by the alpha and beta cells of the pancreas, which are 1-2% of its
total mass. The production of these hormones by the pancreas is controlled by negative feedback
mechanism. When the level of glucose in the blood increases beyond the normal point, insulin is
secreted by the pancreas. Insulin is the hormone that lowers the blood glucose level when it rises
above the optimal level of 90 mg/100 mL of blood. It is secreted by the beta cells in the pancreas
and triggers a higher rate of glucose uptake by body cells. It slows down the breakdown of
glycogen, while also decreasing the conversion of amino acids and glycerol into glucose. Once
the blood glucose level decreases below the normal threshold, glucagon is released. Glucagon is
the hormone that raises the blood glucose concentration. It is produced by the alpha cells of the
pancreas and stimulates the hydrolysis of glycogen molecules and glycerol by the liver,
consequently producing glucose.
The parathyroid glands, which secrete the parathyroid hormone and calcitonin, regulate
the amount of calcium ions in the bloodstream. These hormones are produced and released using
the negative feedback mechanism. The parathyroid hormone (PTH) stimulates the release of
calcium ions in the bloodstream when calcium levels decreases below 10 mg/ 100 mL of blood.
PTH can raise the level of Ca2+ both directly and indirectly. It causes the mineralized matrix to
decompose and the reabsorption of Ca2+ from the kidneys through the renal tubules, leading to
the release Ca2+ in the blood, raising its quantity per milliliter of blood. PTH can also cause the
activation of vitamin D from the liver, stimulating the uptake of Ca2+ from the food by the
intestines. Because of this uptake of calcium ions, the production of PTH is stimulated, which in
turn increases the level of calcium ions in the blood. High levels of calcium ions in the blood will
trigger a negative feedback loop, stopping the production of PTH. The thyroid glands can also
maintain homeostasis by decreasing the level of calcium in the blood when it rises beyond the
normal level. When this occurs, they release calcitonin. Calcitonin is a hormone that inhibits
bone resorption and enhances the release of calcium ions by the kidney. This is important for the
maintenance of the proper amount of calcium in the blood, especially during the development of
the skeletal system in the early years of life for humans.
The hypothalamus receives nerve signals that will initiate a hormone that either
stimulates or inhibits the production of other hormonal molecules. One of its targets is the
anterior pituitary gland. One of the products produced by the hypothalamus is the thyrotropinreleasing hormone. This hormone stimulates the production of thyrotropin, or thyroid-stimulating
hormone. This hormone, in turn, stimulates the production of thyroid hormones, which include
both triiodothyronine and thyroxine. These hormones are responsible for the stimulation and
maintenance of metabolic activities. This is an example of a positive feedback loop. The more a
hormone is produced, the more potent and efficient its effect will be on either an endocrine tissue
or a body tissue, often characterized by an increased production of chemical products.
I. Introduction
a. Endocrine System – maintenance of bodily functions through the releasing of
hormones, as directed by the nervous system
b. Positive Feedback Mechanism – increased production of one substance will
increase the production of another
c. Negative Feedback Mechanism – increased production of a one substance will
decrease the production of another
II.
Blood Glucose Level
a. Insulin – lowers blood glucose level by inhibiting the hydrolysis of glycogen and
glycerol and increases cellular uptake of glucose
b. Glucagon – raises blood glucose level by enhanceing the hydrolysis of glycerol
and glycogen
- Both hormones use the negative feedback mechanism.
III.
Calcium Ion-Level
a. Parathyroid Hormone – raises calcium levels by increasing hydrolysis of
mineralized matrix and reabsorption of calcium from urine; increases uptake of
calcium by the kidneys and the intestines
b. Calcitonin – lowers blood calcium levels to maintain homeostasis
- Both hormones make use of the negative feedback mechanism.
IV.
Metabolic Regulation
a. Thyrotropin – stimulates the thyroid glands
b. Thyroxine – regulates metabolic function
- Both hormones function using the positive feedback mechanism.