Endocrine System—The Pituitary and Adrenal Glands
Lecture 20
Today we’re going to begin the rst of our lectures on the endocrine
system with the study of the pituitary and the adrenal glands. Now in
these lectures we’re going to study anatomy and physiology together
each time so that we don’t get too far away from the many, many glands
that we’re going to look at.
T
his lecture is the rst of three lectures on the endocrine system of
glands that secrete hormones directly into the spaces surrounding
their cells, from which the bloodstream picks up and circulates them.
After distinguishing endocrine from exocrine functions and reviewing the
endocrine system organs, we examine the functional differences between
the endocrine and nervous systems and the basic properties of hormones.
Next, we look at the most important endocrine glands: the pituitary gland
and hypothalamus and the adrenal glands.
Introduction and general de nitions of the endocrine system
Exocrine glands (ex, “out,” krinein, “to secrete”) are glands that
secrete into ducts, which in turn, carry the secretions out of the
glands and into the lumens of certain body cavities.
Endocrine glands (endo, “within”) are glands that secrete directly
into the spaces around the cells and whose products are picked up
and circulated by the bloodstream.
The endocrine system includes some organs that are wholly
endocrine in function. These include the pituitary gland, thyroid
gland, parathyroid gland, adrenal glands, and pineal gland.
Endocrine organs that have other functions as well as endocrine
functions include the pancreas, liver, ovaries, stomach, hypothalamus
of the brain, small intestine, kidneys, testes, and placenta.
119
, There are differences between the functions controlled by the nervous
system and the endocrine system. Both systems coordinate functions of body
systems in general. Both are mutually interconnected.
Endocrine system
The endocrine system releases chemical messengers called hormones
(hormon, “urge on”), which act on other organs in all parts of the body. Some
hormones promote or inhibit nerve impulses, while others (epinephrine and
norepinephrine) may be neurotransmitters themselves. These hormones act
as hormones (rather than as neurotransmitters) in other places. Hormones
may take seconds, minutes, or hours to work their effects, and their duration
of action may be short- or long-lived. Hormones generally regulate growth,
reproduction, and metabolism.
Lecture 20: Endocrine System—The Pituitary and Adrenal Glands
Nervous system
The nervous system acts by the generation of nerve impulses to stimulate or
inhibit effector organs. It may stimulate the release or inhibition of hormones
themselves from the endocrine organs. Nerve impulses have their effect in
milliseconds, in contrast to the slower endocrine system, but the effects are
also short-lived. Nerve impulses primarily cause muscle contraction and the
secretion of uids by certain glands.
Endocrine gland locations
The hypothalamus, pituitary gland, and pineal gland are in the brain. The
thyroid gland is in the neck, with four parathyroid glands behind it. The
thymus is in the chest. The adrenal (suprarenal) glands lie atop the kidneys.
The stomach, ovaries, and testes in the abdominal cavity and lower also have
endocrine functions.
General properties of hormones
Each of the 50+ hormones affect only a few cells, though they may
reach all the cells of the body via the bloodstream. What accounts for the
selectivity? Target cells contain highly speci c receptors, which are surface
glycoproteins. The geometry of the molecules allows only for very speci c
hormones to attach to the receptor in the target cell surface.
120
Lecture 20
Today we’re going to begin the rst of our lectures on the endocrine
system with the study of the pituitary and the adrenal glands. Now in
these lectures we’re going to study anatomy and physiology together
each time so that we don’t get too far away from the many, many glands
that we’re going to look at.
T
his lecture is the rst of three lectures on the endocrine system of
glands that secrete hormones directly into the spaces surrounding
their cells, from which the bloodstream picks up and circulates them.
After distinguishing endocrine from exocrine functions and reviewing the
endocrine system organs, we examine the functional differences between
the endocrine and nervous systems and the basic properties of hormones.
Next, we look at the most important endocrine glands: the pituitary gland
and hypothalamus and the adrenal glands.
Introduction and general de nitions of the endocrine system
Exocrine glands (ex, “out,” krinein, “to secrete”) are glands that
secrete into ducts, which in turn, carry the secretions out of the
glands and into the lumens of certain body cavities.
Endocrine glands (endo, “within”) are glands that secrete directly
into the spaces around the cells and whose products are picked up
and circulated by the bloodstream.
The endocrine system includes some organs that are wholly
endocrine in function. These include the pituitary gland, thyroid
gland, parathyroid gland, adrenal glands, and pineal gland.
Endocrine organs that have other functions as well as endocrine
functions include the pancreas, liver, ovaries, stomach, hypothalamus
of the brain, small intestine, kidneys, testes, and placenta.
119
, There are differences between the functions controlled by the nervous
system and the endocrine system. Both systems coordinate functions of body
systems in general. Both are mutually interconnected.
Endocrine system
The endocrine system releases chemical messengers called hormones
(hormon, “urge on”), which act on other organs in all parts of the body. Some
hormones promote or inhibit nerve impulses, while others (epinephrine and
norepinephrine) may be neurotransmitters themselves. These hormones act
as hormones (rather than as neurotransmitters) in other places. Hormones
may take seconds, minutes, or hours to work their effects, and their duration
of action may be short- or long-lived. Hormones generally regulate growth,
reproduction, and metabolism.
Lecture 20: Endocrine System—The Pituitary and Adrenal Glands
Nervous system
The nervous system acts by the generation of nerve impulses to stimulate or
inhibit effector organs. It may stimulate the release or inhibition of hormones
themselves from the endocrine organs. Nerve impulses have their effect in
milliseconds, in contrast to the slower endocrine system, but the effects are
also short-lived. Nerve impulses primarily cause muscle contraction and the
secretion of uids by certain glands.
Endocrine gland locations
The hypothalamus, pituitary gland, and pineal gland are in the brain. The
thyroid gland is in the neck, with four parathyroid glands behind it. The
thymus is in the chest. The adrenal (suprarenal) glands lie atop the kidneys.
The stomach, ovaries, and testes in the abdominal cavity and lower also have
endocrine functions.
General properties of hormones
Each of the 50+ hormones affect only a few cells, though they may
reach all the cells of the body via the bloodstream. What accounts for the
selectivity? Target cells contain highly speci c receptors, which are surface
glycoproteins. The geometry of the molecules allows only for very speci c
hormones to attach to the receptor in the target cell surface.
120
