Endocrine system

1. INTRODUCTION TO
THE ENDOCRINE
SYSTEM

2. INTRODUCTION TO THE
ENDOCRINE SYSTEM
THE ENDOCRINE SYSTEM, ALONG WITH THE NERVOUS
SYSTEM, FUNCTIONS IN THE REGULATION OF BODY
ACTIVITIES. THE NERVOUS SYSTEM ACTS THROUGH
ELECTRICAL IMPULSES AND NEUROTRANSMITTERS TO CAUSE
MUSCLE CONTRACTION AND GLANDULAR SECRETION. THE
EFFECT IS OF SHORT DURATION, MEASURED IN SECONDS, AND
LOCALIZED. THE ENDOCRINE SYSTEM ACTS THROUGH
CHEMICAL MESSENGERS CALLED HORMONES THAT
INFLUENCE GROWTH, DEVELOPMENT, AND METABOLIC
ACTIVITIES. THE ACTION OF THE ENDOCRINE SYSTEM IS
MEASURED IN MINUTES, HOURS, OR WEEKS AND IS MORE
GENERALIZED THAN THE ACTION OF THE NERVOUS SYSTEM.

3. INTRODUCTION TO THE
ENDOCRINE SYSTEM

4. INTRODUCTION TO THE ENDOCRINE SYSTEM
There are two major categories of glands in the body - exocrine and
endocrine.
Exocrine Glands
Exocrine glands have ducts that carry their secretory product to a
surface. These glands include the sweat, sebaceous, and mammary
glands and the glands that secrete digestive enzymes.
Endocrine Glands
The endocrine glands do not have ducts to carry their product to a
surface. They are called ductless glands. The word endocrine is derived
from the Greek terms "endo," meaning within, and "krine," meaning to
separate or secrete. The secretory products of endocrine glands are
called hormones and are secreted directly into the blood and then
carried throughout the body where they influence only those cells that
have receptor sites for that hormone

6. CHARACTERISTICS OF HORMONES
Chemical Nature of Hormones
Chemically, hormones may be classified as either proteins or steroids.
Mechanism of Hormone
Action Hormones are carried by the blood throughout the entire body,
yet they affect only certain cells. The specific cells that respond to a
given hormone have receptor sites for that hormone. This is sort of a
lock-and-key mechanism. If the key fits the lock, then the door will
open. If a hormone fits the receptor site, then there will be an effect. If
a hormone and a receptor site do not match, then there is no reaction
Protein hormones react with receptors on the surface of the cell, and
the sequence of events that results in hormone action is relatively
rapid. Steroid hormones typically react with receptor sites inside a cell.
Because this method of action involves synthesis of proteins, it is

7. CHARACTERISTICS OF HORMONES
Control of Hormone Action
Hormones are very potent substances, which means that very small
amounts of a hormone may have profound effects on metabolic
processes. Because of their potency, hormone secretion must be
regulated within very narrow limits in order to maintain homeostasis
the body.
Many hormones are controlled by some form of a negative feedback
mechanism. In this type of system, a gland is sensitive to the concentration of a
substance that it regulates. A negative feedback system causes a reversal of
increases and decreases in body conditions in order to maintain a state of
stability or homeostasis. Some endocrine glands secrete hormones in response
to other hormones. The hormones that cause secretion of other hormones are
called tropic hormones. A hormone from gland A causes gland B to secrete its
hormone. A third method of regulating hormone secretion is by direct nervous
stimulation. A nerve stimulus causes gland A to secrete its hormone.

8. CHARACTERISTICS OF HORMONES

9. ENDOCRINE GLANDS & THEIR HORMONES
• The endocrine system is made up of the endocrine glands that
secrete hormones. Although there are eight major endocrine
glands scattered throughout the body.
• Some glands also have non-endocrine regions that have
functions other than hormone secretion. For example, the
pancreas has a major exocrine portion that secretes digestive
enzymes and an endocrine portion that secretes hormones.
• Some organs, such as the stomach, intestines, and heart,
produce hormones, but their primary function is not hormone
secretion.

10. Pituitary Glands
Pituitary Gland,
The pituitary gland is an endocrine gland about the size of a pea that sits in
a small, bony cavity at the base of the brain. It is also known as the master
gland. The pituitary gland secretes hormones that stimulate the other
endocrine glands. Located at the base of the brain, it is functionally linked
to the hypothalamus (the main link between the endocrine and nervous
systems). The tiny pituitary is divided into two parts: the anterior lobe and
the posterior lobe. The anterior lobe regulates the activity of the thyroid,
adrenals, and reproductive glands. The posterior lobe releases antidiuretic
hormones, which help control the balance of water in the body. The
pituitary gland helps control the following body processes:
• Growth
• Blood pressure
• Some aspects of pregnancy and childbirth
• Breast milk production
• Sex organ functions in both women and men
• Thyroid gland function
• The conversion of food into energy (metabolism)

11. Pineal Glands
THE PINEAL GLAND:
The pineal body, also called the pineal gland, is in the middle of the brain.
It secretes melatonin , a hormone that may help regulate when you sleep at
night and when you wake in the morning. The pineal gland (also called the
pineal body or epiphysis) is a small endocrine gland in the brain. Its
functions are not yet fully understood. It produces a hormone called
melatonin and is located near the center of the brain. The pineal gland is a
reddish-gray body about the size of a pea (8 mm in humans), The pineal
gland is large in children, but shrinks at puberty. It appears to play a major
role in sexual development.

12. Thyroid & Parathyroid Glands
.
The Thyroid gland is one of the larger endocrine glands in the body. It is a
double-lobed structure located in the neck and produces hormones, principally
thyroxin (T4) and tri- iodothyronine (T3), which regulate the rate of metabolism and
affect the growth and rate of function of many other systems in the body. The
hormone calcitonin is also produced and controls calcium blood levels. Iodine is
necessary to produce both hormones. Hyperthyroidism (overactive thyroid) and
hypothyroidism (under active thyroid) are the most common problems of the
thyroid gland.
The Parathyroid glands are small endocrine glands in the neck, usually located
behind the thyroid gland, which produce the parathyroid hormone. In rare cases,
the parathyroid glands are located within the thyroid glands. Most often there are
four parathyroid glands, but some people have six or even eight.
The parathyroid glands produce the parathyroid hormone, which regulates the
level of calcium in the blood with the help of calcitonin which is produced in the
thyroid and bones. It then stimulates osteoclasts (a type of bone cell) to break
down bone and release calcium into the blood.

13. Thyroid & Parathyroid Glands
.
Diseases of the Thyroid Gland:
Hypothyroidism: It is a disease state in humans and animals caused by insufficient
production of thyroid hormones by the thyroid gland.
Hyperthyroidism: It is due to an ‘overactive thyroid gland’; the clinical syndrome
is caused by an excess of circulating free thyroxine (T4) or free triiodothyronine
(T3), or both.
Goiter: Goiter is a swelling condition in the neck, which is due to an enlarged
thyroid gland.
Note: There are various ways in the yogic system to control the thyroid gland and
keep it healthy with proper secretion of thyroid hormones. Proper application of
yogic exercises and yogic diet can also prevent/cure these diseases.

14. Adrenal Gland
.
The Adrenal Glands:
In mammals, the adrenal glands (also known as suprarenal glands) are the
triangle-shaped endocrine glands that sit atop the kidneys; their name
indicates their position (ad means ‘near’ or ‘at’ and renes means ‘kidneys;).
Anatomically, the adrenal glands are in the abdomen. In humans, the
adrenal glands are found at the level of the 12th thoracic vertebra and
receive their blood supply from the adrenal arteries. An adrenal gland is
made of two parts: the outer region called the adrenal cortex (which
influences or regulates the salt and water balance in the body, the body’s
response to stress, metabolism, the immune system, and sexual
development and function) and the inner region called the adrenal
medulla (increases blood pressure and heart rate when the body
experiences stress) The adrenal glands work interactively with the
hypothalamus and pituitary gland.

15. Pancreas—Islets of Langerhans
.
Pancreas,
The regions of the pancreas that contain its endocrine (i.e.,
hormone-producing) cells. The pancreas works as both the
exocrine and the endocrine glands. The exocrine portion of
pancreas helps in the secretion of digestive juices.
The endocrine portion consists of the pancreatic islets, which
secrete glucagons and insulin.
Alpha cells in the pancreatic islets secrete the hormone glucagons
in response to a low concentration of glucose in the blood. Beta
cells in the pancreatic islets secrete the hormone insulin in
response to a high concentration of glucose in the blood.

16. Gonads
.
The gonads, the primary reproductive organs, are
the testes in the male and the ovaries in the female.
These organs are responsible for producing the
sperm and ova, but they also secrete hormones and
are endocrine glands.

17. OTHER ENDOCRINE GLANDS
.
• THE THYMUS GLAND:
The thymus is an organ located in the upper anterior portion of the chest
cavity, underneath the top of the sternum. It has two lobes which
generally differ in size and are a soft and pinkish-gray color. At birth it is
about 5 cm in length, 4 cm in breadth, and about 6 mm in thickness. The
organ enlarges during childhood. The thymus plays an important role in
the development of the immune system during childhood.
• The lining of the stomach, the gastric mucosa, produces a hormone,
called gastrin, in response to the presence of food in the stomach. This
hormone stimulates the production of hydrochloric acid and the
enzyme pepsin, which are used in the digestion of food.
• The mucosa of the small intestine secretes the hormones secretin and
cholecystokinin. Secreting stimulates the pancreas to produce a
bicarbonate-rich fluid that neutralizes the stomach acid.
Cholecystokinin stimulates contraction of the gallbladder, which
releases bile. It also stimulates the pancreas to secrete digestive
enzyme.

18. .

19. OTHER ENDOCRINE GLANDS
.
• The heart also acts as an endocrine organ in addition to its major role
of pumping blood. Special cells in the wall of the upper chambers of
the heart, called atria, produce a hormone called atrial natriiuretic
hormone, or atriopeptin.
• The placenta develops in the pregnant female as a source of
nourishment and gas exchange for the developing fetus. It also serves
as a temporary endocrine gland.

20. REVIEW: INTRODUCTION TO THE ENDOCRINE SYSTEM
.
Here is what we have learned from Introduction to the Endocrine System:
• Chemical messengers from the endocrine system help regulate body activities. Their effect is of longer
duration and is more generalized than that of the nervous system.
• Neurons are the nerve cells that transmit impulses. Supporting cells are neuroglia.
• Endocrine glands secrete hormones directly into the blood, which transports the hormones through the
body.
• Cells in a target tissue have receptor sites for specific hormones.
• Many hormones are regulated by a negative feedback mechanism; some are controlled by other hormones;
and others are affected by direct nerve stimulation.
• Even though the endocrine glands are scattered throughout the body, they are still considered to be one
system because they have similar functions, similar mechanisms of influence, and many important
interrelationships.
• Major glands include pituitary gland, thyroid gland, parathyroid gland, adrenal (suprarenal) gland, pancreas,
gonads (testes and ovaries), pineal gland, and other endocrine glands.