Introduction to the
Endocrine System
,NursingABC - Module https://student.portagelearning.com/modules/print_view/454/2009
Introduction to the Endocrine System
Notice: To optimize your learning in this course, we advise that you complete the labs and modules as
indicated in the BIOD 151 Lab Schedule.
18:04
The endocrine system, along with the nervous system, coordinates the various activities of body parts by
utilizing chemical messengers to coordinate these activities. In the nervous system, neurons release
neurotransmitters that influence the excitability of the other neurons. In contrast, the endocrine system
(see the figure below) utilizes hormones, chemical messengers that are typically released directly into the
bloodstream.
1 of 18 8/31/17, 9:35 AM
, NursingABC - Module https://student.portagelearning.com/modules/print_view/454/2009
The nervous system reacts quickly to external and internal stimuli, but the endocrine system tends to
react somewhat slower because it takes time for a hormone to travel through the circulatory system to its
target organ. Cells that can react to a hormone have specific receptors, which combine with the hormone
in a lock-and-key manner. Therefore, certain cells respond to one hormone and not to another, depending
on their receptors.
A hormone is defined as an organic chemical produced by one set of cells that affects a different set of
cells. Many vertebrate hormones are proteins or peptides that are coded for by genes and are
synthesized within the cytoplasm at the ribosomes. Eventually, they are packaged into vesicles at the
Golgi apparatus and are secreted at the plasma membrane.
There are other hormones, called catecholamines, that are derived from the amino acid tyrosine. Their
production requires only a series of metabolic reactions within the cytoplasm. From the viewpoint of
hormonal action, we can categorize the proteins, peptides, and catecholamines as peptide hormones.
Other vertebrate hormones, produced by the adrenal cortex, the ovaries, and the testes, are steroids.
Steroid hormones are derived from cholesterol by a series of metabolic reactions. These hormones are
stored in fat droplets in the cell cytoplasm until their release at the plasma membrane. Steroid hormones
do not bind to cell-surface receptors; they can enter the cell and the nucleus freely. Once inside the
2 of 18 8/31/17, 9:35 AM
Endocrine System
,NursingABC - Module https://student.portagelearning.com/modules/print_view/454/2009
Introduction to the Endocrine System
Notice: To optimize your learning in this course, we advise that you complete the labs and modules as
indicated in the BIOD 151 Lab Schedule.
18:04
The endocrine system, along with the nervous system, coordinates the various activities of body parts by
utilizing chemical messengers to coordinate these activities. In the nervous system, neurons release
neurotransmitters that influence the excitability of the other neurons. In contrast, the endocrine system
(see the figure below) utilizes hormones, chemical messengers that are typically released directly into the
bloodstream.
1 of 18 8/31/17, 9:35 AM
, NursingABC - Module https://student.portagelearning.com/modules/print_view/454/2009
The nervous system reacts quickly to external and internal stimuli, but the endocrine system tends to
react somewhat slower because it takes time for a hormone to travel through the circulatory system to its
target organ. Cells that can react to a hormone have specific receptors, which combine with the hormone
in a lock-and-key manner. Therefore, certain cells respond to one hormone and not to another, depending
on their receptors.
A hormone is defined as an organic chemical produced by one set of cells that affects a different set of
cells. Many vertebrate hormones are proteins or peptides that are coded for by genes and are
synthesized within the cytoplasm at the ribosomes. Eventually, they are packaged into vesicles at the
Golgi apparatus and are secreted at the plasma membrane.
There are other hormones, called catecholamines, that are derived from the amino acid tyrosine. Their
production requires only a series of metabolic reactions within the cytoplasm. From the viewpoint of
hormonal action, we can categorize the proteins, peptides, and catecholamines as peptide hormones.
Other vertebrate hormones, produced by the adrenal cortex, the ovaries, and the testes, are steroids.
Steroid hormones are derived from cholesterol by a series of metabolic reactions. These hormones are
stored in fat droplets in the cell cytoplasm until their release at the plasma membrane. Steroid hormones
do not bind to cell-surface receptors; they can enter the cell and the nucleus freely. Once inside the
2 of 18 8/31/17, 9:35 AM
