The endocrine system is composed of glands that secrete hormones directly into the bloodstream to regulate distant target organs and tissues. The major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pancreas, gonads, pineal, and thymus glands. The pituitary gland is located in the brain and regulates other endocrine glands through the hormones it secretes. Other important glands are the thyroid gland in the neck, which regulates metabolism, and the adrenal glands atop the kidneys, which secrete hormones involved in stress response. Together, hormones maintain homeostasis by influencing growth, development, metabolism, and other bodily functions.

1. THE ENDOCRINE SYSTEM
By Abukar salisu fago.

2. Composition of the Endocrine
System
The endocrine system is composed of
organs that produce and secrete hormones.
Because these organs perform mainly a
secretory function, they are also referred to
as glands
Two types of glands:
– EXOCRINE
– ENDOCRINE

3. EXOCRINE glands secrete their products
into ducts.
The ducts transport the products into body
cavities, into the spaces within organs, or
into the body surface.
EXOCRINE glands include oil glands,
sweat glands, mucous glands, and salivary
glands.

4. ENDOCRINE GLANDS
ENDOCRINE glands secrete their
products into the extracellular space
surrounding the secretory cells.
Endocrine glands are sometimes called
ductless glands.
Their products are the HORMONES,
which diffuse from here to enter the
bloodstream.

5. The primary endocrine glands of the body
are the pituitary gland, the thyroid gland,
the parathyroid glands, the adrenal gland,
the pancreas, and the sex glands, or gonads
(the testes in the male and ovaries in the
female).
Endocrine glands that provide a minor role
in body maintenance include the pineal
gland and the thymus gland.

6. The stomach, kidneys, small intestine, and
the placenta, all have a secondary role as
endocrine glands

7. HORMONES
Hormones are the chemical units produced
by endocrine glands.
Hormones are the means by which
endocrine glands provide control of body
activities to maintain homeostasis.

8. HORMONAL ACTION
Hormones are released in very small
quantities, because they are extremely
potent compounds.
Once released by secretory cells into the
extracellular space, they find their way by
diffusion into the bloodstream.
A given hormone will have an effect only
on a particular type of cell. This is called
the target cell.

9. The effect is limited to the target cells
because only they contain special protein
molecules in their plasma membrane that
serve as receptors, which recognize and
bind to specific hormones while rejecting
others.
Cells other than target cells are not affected
by a hormone, because they lack the
appropriate receptors.

10. Once a hormone has united with the
receptor on a target cell, it begins to exert
its effect.
Its effect is to alter the cell’s metabolic
processes.
Examples: a hormone may change the rates
of enzyme activities, the rate of protein
synthesis, the rates of secretion, or the rates
at which materials are transported across the
plasma membrane.

11. Although there are many types of hormones
that differ chemically, hormones may be
grouped into two broad categories on the
basis of their solubility: those that dissolve
in water, or are water-soluble; and those
that dissolve in lipids, or are lipid-soluble.

12. WATER-SOLUBLE
HORMONES
Hormones that are soluble in water
include molecules that are composed of
amino acids.
Because these hormones are soluble
only in water, they cannot pass through
the lipid plasma membrane.

13. Question: how can they produce an effect
on the cell if they cannot penetrate the
membrane?
This is done by passing the signal to a
second-messenger system located within the
cell. One that uses a compound called
cyclic AMP (adenosine monophasphate).

14. The enzymatic cascade activated by
the second-messenger system has an
enormous amplification effect within
the cell.
A single hormone molecule triggers a
single enzyme, which catalyzes
literally hundreds of reactions.

15. Water-soluble hormones that serve as first
messengers in this system include
epinephrine, norepinephrine (NE),
antidiuretic hormone (ADH), oxytocin
(OT), calcitonin (CT), and parathyroid
hormone (PTH).

16. LIPID-SOLUBLE HORMONES
Hormones that dissolve in lipids include
mainly steroid hormones.
Because the plasma membrane is composed
of a bilayer of lipid molecules, steroid
hormones can pass directly through it by
diffusion to enter the target cell quite easily.
(recall that steroids are a type of lipid also;
lipids dissolve in other lipids).

17. Lipid-soluble hormones activate genes to
synthesize new proteins and enzymes.
The protein products that are newly formed
include enzymes that promote the metabolic
activities specified by the hormone.
Lipid-soluble hormones that stimulate
protein synthesis include aldosterone,
cortisol, testosterone, estrogen, and
thyroxine.

18. PROSTAGLANDINS
Prostaglandins are a group of chemicals that
also have regulating effects on cells.
They are lipids that are produced by many
different parts of the body.
Like hormones, they are extremely potent
compounds and are released in very small
quantities.

19. Specifically, prostaglandins stimulate or
inhibit the formation of cyclic AMP,
thereby modulating the effect of hormones
that use cyclic AMP as a second messenger.
Because they do not induce their own effect
but instead modify the effect of a hormone,
prostaglandins as a group are not
considered true hormones.

20. Some prostaglandins reduce blood pressure
and open airways by causing smooth
muscles to relax, others have the opposite
effect.
Other types inhibit the secretion of HCL
from the stomach wall, increase intestinal
contractions, stimulate contraction of the
uterus, regulate metabolism, cause
inflammation, and even cause fever.

21. HORMONAL CONTROL
FEEDBACK CONTROL--how does an
endocrine gland “know” how much
hormone to produce and release?
This information, or feedback, is provided
by way of chemical signals that are sent to
the endocrine gland.
There are two systems that operate in this
manner: negative feedback systems and
positive feedback systems.

22. NEGATIVE FEEDBACK
Negative feedback systems control the
amount of hormone released by providing a
response in the opposite direction to that of
the stimulus.
In these systems, the secretion of a hormone
that accelerates a body activity is inhibited
by the negative feedback signal, and the
secretion of a hormone that slows the same
body activity is stimulated yet further.

23. Negative feedback systems are the most
common method of hormone regulation in
the body.

24. POSITIVE FEEDBACK
SYSTEMS
Positive feedback systems regulate
hormone secretion by providing a response
in the same direction as the stimulus.
When the desired response stimulated by
hormone action occurs, a chemical feedback
signal causes the endocrine gland to
increase its rate of hormone release and
more responses are stimulated.

25. Positive feedback systems tend to cause
extreme changes in conditions in the body
and are therefore quite unstable and
uncommon.

26. Example: the production of oxytocin by the
pituitary gland during childbirth. It
stimulates contractions of the uterus. Its
rising levels in the blood cause the
formation of products that stimulate further
oxytocin production, and uterine
contractions respond by gradually
increasing in strength until birth is
accomplished.

27. NERVOUS CONTROL
A second way of controlling hormone
release is by the nervous system.
Nervous control is responsible for
regulating only some endocrine glands,
such as the adrenal medulla and secretory
cells in the hypothalamus of the brain.
These glands secrete hormones when they
receive nerve impulses.

28. THE ENDOCRINE
GLANDS
Some are in the head,
some are in the neck, and
some in the abdominal
cavity.

29. PITUITARY GLAND
The pituitary gland, or hypophysis, is
located at the base of the brain.
It is about the size of a pea and weighs only
0.5 gram (0.02 ounce).
It is attached to the hypothalamus by a
narrow stalk, called the infundibulum, and
lies within a bony cavity formed by the
sella turcica of the sphenoid bone.

30. The pituitary gland produces many
hormones, some of which control the
activities of several other endocrine glands.
It thereby influences a wide range of body
functions.
The pituitary gland consists of two portions:
an anterior lobe and a posterior lobe.

31. ANTERIOR LOBE
Within its epithelium are five different
types of secretory cells that release
seven types of hormones.
The release of these hormones is
controlled by chemical secretions from
the hypothalamus, called regulating
factors.

32. The seven hormones released by the
anterior lobe are:
– growth hormone (GH): mainly bone
– prolactin (PRL): mammary glands
– thyroid-stimulating hormone (TSH)
– adrenocorticotropic hormone (ACTH)
– melanocyte-stimulating hormone (MSH)
– follicle-stimulating hormone
(FSH):ovaries, testis
– luteinizing hormone (LH): ovaries, testis

33. GROWTH HORMONE
Growth hormone (GH) stimulates body
cells to grow and divide.
On a more short-term basis, the nutritional
status of your body affects the release of
GH in order to maintain a relatively
constant blood sugar level.
When sugar levels are low, a condition
called hypoglycemia exists and the
hypothalamus is stimulated to release
regulating factors.

34. Once these factors reach the anterior
lobe, GH is released into the
bloodstream. As a result, blood sugar
levels rise. (convert glycogen into
glucose)
High levels of sugar in the blood, or
hyperglycemia, cause the opposite
effect (GH is inhibited).

35. Thus, your blood sugar
levels are kept relatively
constant by negative
feedback mechanism
involving Gh

36. MELANOCYTE-
STIMULATING HORMONE
MSH--stimulates the
production of melanin in
the skin, causing the skin
to increase in
pigmentation.

37. PROLACTIN
In combination with other hormones,
prolactin (PRL) stimulates and maintains
milk secretion by the mammary glands in
females.
The actual ejection of milk is controlled by
a hormone released by the posterior lobe,
called oxytocin.

38. The combined secretion and
ejection of milk from the
mammary glands is an
activity referred to as
lactation.

39. THYROID-STIMULATING
HORMONE
The production and secretion of hormones
by the thyroid gland are stimulated by TSH.
It is influenced by the body’s metabolic
rate, levels in the blood of a thyroid
hormone called thyroxine, and other
factors.

40. ADRENOCORTICOTROPIC
HORMONE
The production and secretion of
hormones released by the outer
region or, cortex, of the adrenal
gland are controlled by the ACTH.
Its release is also influenced by
various forms of stress.

41. FOLLICLE-STIMULATING
HORMONE
FSH has a different effect upon the two
sexes.
In females, FSH stimulates the development
of eggs, or ova, each month within the
ovaries.
It also stimulates the cells in the ovaries to
secrete estrogens, the female sex hormone.

42. In the male, FSH stimulates the production
of sperm by the testes.
FSH production is controlled by regulating
factors released from the hypothalamus in
response to estrogens in the female and to
testerone in the male, in the manner of a
negative feedback system.

43. LUTEINIZING HORMONE
LH also plays a different role in each of the
two sexes.
In females, it works together with estrogens
to stimulate the ovary to release an ovum (a
process called ovulation). and prepare the
uterus for implantation of the fertilized
ovum.

44. In males, LH stimulates cells
within the testes to produce and
secrete testosterone.
LH secretion is controlled by the
hypothalamus by way of negative
feedback.

45. OXYTOCIN
OXYTOCIN (OT) stimulate
contraction of smooth muscle in
the wall of the uterus.
It also stimulates cells around
mammary ducts to contract,
thereby causing milk to eject.

46. ANTIDIURETIC HORMONE
ADH regulates fluid balance
in the body.
ADH causes a decrease in
urine output and an increase
in body fluid volume.

47. THYROID GLAND
The THYROID GLAND is the prominent
organ in the neck.
Located slightly below the larynx in front of
the trachea.
Its follicles contain a clear liquid called
colloid.
The three primary hormones are: thyroxine.
also known as T4; triiodothyronine (T3),
and calcitonin.

48. Thyroxine and
Triiodothyronine play
important roles in
metabolism and growth.

49. CALCITONIN
Calcitonin reduces the calcium and
phosphate levels in the blood.
Calcium concentrations must be kept within
narrow limits for normal nerve and muscle
function, and both ions are essential mineral
components of bone.

50. PARATHYROID GLANDS
The parathyroid glands are four
or five pea-shaped masses of
glandular epithelium.
They secrete one hormone,
called parathyroid hormone
(PTH).

51. Parathyroid Hormone (PTH)
Parathyroid hormone
(PTH) plays an important
role in maintaining the
calcium and phosphate levels
in the blood.

52. ADRENAL GLANDS
The Adrenal Glands are paired,
triangular masses that lie atop each
kidney.
Like the kidneys, they are located
behind the membrane that encloses the
abdominal cavity, which is called the
peritoneum

53. Adrenal Medulla
The adrenal medulla is
composed of modified nerve
tissue.
It secretes two hormones ,
epinephrine and
norepinephrine

54. Adrenal Cortex
It occupies the larger portion of the adrenal
gland.
The secretory cells in each one of the
adrenal cortex secrete steroid hormones.
These hormones are synthesized from
colesterol. They include three classes of
compounds: mineralocorticoids,
glucocorticoids, and sex hormones.

55. Mineralocorticoids
The primary
mineralocorticoid is
aldosterone.
This steroid hormone
maintains body fluid balance.

56. Sex Hormones
The two classes of sex hormones
released by the adrenal cortex are
androgens, which have a
masculinizing effect, and
estrogens, which have feminizing
effects.

57. Pancreas
The pancreas is a soft, oblong organ
located in the abdominal cavity behind the
stomach.
It is actually two body systems, since it
performs two distinct functions.
It is an endocrine gland, since it secretes
two important hormones into the blood
stream.

58. It is also a digestive organ, because of its
secretion of digestive enzymes into ducts
that empty into the small intestine.
The endocrine cells of the pancreas form
clusters called the islets of Langerhans.
The hormones play important roles in
providing body cells with sufficient
amounts of energy. They do this by
regulating the amount of sugar in the blood.

59. GLUCAGON--stimulates the
conversion of glycogen into the simple
sugar glucose.
INSULIN--has the opposite effect to
that of glucagon on liver cells: it
stimulates the formation of glycogen
from glucose.

60. Gonads
The gonads are the sex organs; that is, they
are the organs that produce the sex cells and
secrete the primary sex hormones.
In females, the ovaries , they secrete
estrogens, which are the primary female
sex hormone
In males, the testes secrete testosterone.

61. Pineal Gland
The pinal gland is a small structure within
the cranial cavity associated with the brain.
It is sometimes called the epithalamus
because it is attached to the upper margin of
the thalamus.
It secretes one hormone, melatonin
the pineal gland in reptiles and birds, has
been shown to regulate reproduction cycles,
hibernation cycles, and migration patterns

62. Thymus Gland
The thymus gland is a prominent structure
in infants and young children but
diminishes in size with advancing age.
It is a soft, irregularly shaped structure that
lies in the mediastinum on top of the heart.
It secretes a hormone known as thymosin,
which stimulates the production of certain
white blood cells called T lymphocytes

63. The thymus gland
plays an important role
in immunity.