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1. The Endocrine System

2. The Endocrine System

3. How the system communicates
 The organs of the endocrine system communicate
with each other and the rest of the body using
hormones.
 Hormones are made and stored in their
originating organ. The place they are sent is
called the target.
 Targets can be anything from all the bones in the
body to another endocrine organ.
 When the hormones reach their target, they
trigger events in that location.

4. Hypothalamus and Pituitary
Hypothalamus
Located in the brain, the
hypothalamus releases
hormones which stimulate or
suppress the production of
other hormones throughout
the body.
Pituitary
The pituitary is a small
body that hangs in the
central area of the brain.
It produces hormones
which help control the
body’s water and
electrolyte levels, help
with childbirth, trigger the
production of sex
hormones, and promote
body growth.

5. Thyroid and Parathyroid
Thyroid
The thyroid is located around
the esophagus. It creates
hormones which control
metabolic processes in all
cells and control blood
calcium levels.
Parathyroid
The parathyroid is a group of
small glands that are found
on the thyroid and emit
hormones which help
regulate calcium throughout
the body. If levels get too low
the bones will be instructed
to release more; if the levels
get too high the bones are
told to absorb the extra
calcium.

6. Adrenal Gland
Kidneys
The adrenal gland is really two
glands, which are situated on
top of either kidney. The
adrenal gland makes hormones
which regulate the body’s water
and electrolyte levels as well as
hormones which control the
metabolism of proteins, lipids,
and carbohydrates. The most
noticeable thing it does is
protect the body from…

7. Pancreas
The pancreas is located
between the two kidneys.
Produces hormones which
adjust carbohydrate
metabolism. When blood
sugar levels rise (after you
eat) insulin lowers the levels;
when blood sugar levels are
low (if you haven’t eaten all
day) glucagons raises the
blood levels.

8. Ovaries and Testes
Testes
Testes are found in the
scrotum of males. They
generate hormones which
facilitate the development of
male reproductive organs and
produce sperm.
Ovaries
Ovaries are found in the
abdomen of women. They
produce hormones which
assist with the development
of the female reproductive
organs and prepare the
uterus for pregnancy.

9. Autocrines and Paracrines
• Autocrines – chemicals that exert their effects on
the same cells that secrete them
• Paracrines – locally acting chemicals that affect
cells other than those that secrete them
• These are not considered hormones since
hormones are long-distance chemical signals

10. Types of Hormones
• Amino acid based – most hormones belong to
this class, including:
• Amines (Tyrosine: Caecholamines and Thyroid
hormones, Tryptophan: Melatonin)
• Polypeptide hormones
• protein hormones
• Steroids – Derived from Cholesterol, gonadal
and adrenocortical hormones
• Fatty acid derived: Eicosanoids, derived from
arachidonic leukotrienes and prostaglandins

11. A Structural Classification of Hormones

12. Circulating Transport Proteins
Specific
Corticosteroid binding globulin
(CBG, transcortin)
Thyroxine binding globulin (TBG)
Sex hormone-binding globulin
(SHBG)
Nonspecific
Albumin
Transthyretin (prealbumin)
Principle Hormone
Transported
Cortisol, aldosterone
Thyroxine, triiodothyronine
Testosterone, estrogen
Most steroids, thyroxine,
triiodothyronine
Thyroxine, some steroids
Transport Protein

13. Determinants of Free Hormone Receptor Binding
Carrier-bound
hormone
Endocrine
cell
Free
Hormone
Hormone
receptor
Hormone
degradation
Biological
effects

14. Hormone Action
• Hormones alter target cell activity by one of
the following mechanisms:
• Ion Channel–Linked Receptors.
• G Protein–Linked Hormone Receptors.
• Enzyme-Linked Hormone Receptors.
• Intracellular Hormone Receptors and
Activation of Genes (steroid and thyroid
hormones)

15. • Hormones circulate to all tissues but only activate
cells referred to as target cells
• Target cells must have specific receptors to
which the hormone binds
Hormone Action

16. Location of receptors:
• 1. In or on the surface of the cell membrane. The
membrane receptors are specific mostly for the
protein, peptide, and catecholamine hormones.
• 2. In the cell cytoplasm. The primary receptors
for the different steroid hormones are found
mainly in the cytoplasm.
• 3. In the cell nucleus. The receptors for the
thyroid hormones are found in the nucleus and
are believed to be located in direct association
with one or more of the chromosomes.

17. • Target cell activation depends on three factors
• Blood levels of the hormone
• Relative number of receptors on the target cell
• The affinity of those receptors for the hormone
• Up-regulation – target cells form more receptors
in response to the hormone
• Down-regulation – target cells lose receptors in
response to the hormone
Target Cell Activation

18. • Hormones circulate in the blood in two forms –
free or bound
• Steroids and thyroid hormone are attached to
plasma proteins
Hormone Concentrations in the Blood

19. • Concentrations of circulating hormone reflect:
• Rate of release
• Speed of inactivation and removal from the
body
• Hormones are removed from the blood by:
• Degrading enzymes
• The kidneys
• Liver enzyme systems
Hormone Concentrations in the Blood

20. • Three types of hormone interaction
• Permissiveness – one hormone cannot exert its
effects without another hormone being present
• Synergism – the total effect of two hormones
together is greater than the sum of their
individual effects
• Antagonism – one or more hormones opposes
the action of another hormone
Interaction of Hormones at Target Cells

21. • Blood levels of hormones:
• Are controlled by negative and positive
feedback systems
• Vary only within a narrow desirable range
• Hormones are synthesized and released in
response to humoral, neural, and hormonal
stimuli
Control of Hormone Release

22. • Negative feedback is most common: for example,
LH from pituitary stimulates the testis to produce
testosterone which in turn feeds back and inhibits
LH secretion
• Positive feedback is less common: examples include
LH stimulation of estrogen which stimulates LH
surge at ovulation
Feedback Control

23. Feedback Mechanisms
Endocrine
cell
Target
cell
_
+
Biological effects
Endocrine
cell
Target
cell
+
+
Biological effects
Negative Feedback Positive Feedback

24. Negative feedback