Download The Endocrine System - FW Johnson Collegiate

The Endocrine System
The endocrine system, like the nervous system is responsible for allowing communication
between the cells of the body. Unlike the nervous system, the endocrine system does not rely
on a complex system of cells and support, just the existing circulatory system to transport the
chemical messengers of the endocrine system – hormones. The time required for a hormonal
response is much longer than that of the nervous response, and the effect is much longer
lasting.
The endocrine and nervous systems overlap in the brain – the pituitary and hypothalamus. The
hypothalamus stimulates the pituitary gland via a nerve, and the pituitary affects the
hypothalamus with hormones!
Hormones
- Chemical regulators produced by cells in one part of the body that affect cells in another
part of the body
Endocrine Hormones
- chemicals produced in glands and secreted directly into the blood
- carried by the blood
Two Types of Endocrine Hormones:
1. Target Hormones
- affect specific cells in the body (Ex: “gastrin” stimulates stomach cells to make gastric acid)
2. Nontarget Hormones
- have broad effects in the body (Ex: growth hormone – affects the growth of long bones)
Types of Nontarget Hormones:
1. Steroid Hormones
- include both male and female sex hormones, and cortisol
- made from cholesterol
- composed of complex rings of C, H, and O
- insoluble in H2O, soluble in fat
- diffuse into the cell and cause a protein to be made
2. Protein Related Hormones
- include insulin, growth hormone, and epinephrine (adrenalin)
- contain chains of amino acids, soluble in H2O
- combine with receptors on the cell membrane and increase the rate of cell function
Cells in the Islets of Langerhans (where insulin is produced in the pancreas) secrete glycogen
and insulin, which function to keep blood glucose levels relatively constant. Glucagon increases
blood glucose levels and insulin speeds the absorption of glucose by cells.
FACTS:
- The effect of hormones has been studied in animals by removing a gland or organ and then
analyzing the effects. Removal of the testicles in cattle produces less tough meat, and removal
of the pancreas in dogs lead to what we now identify as symptoms of diabetes. Although this
shed some light on the endocrine system, many glands produce more than one hormone, and
levels of some hormones affect the level of other hormones.
- To study hormones today, scientists inject radioactive tracers into the organ and follow the
organ’s products throughout the body.
- In the brain there is an area called the hypothalamus, which regulates the pituitary gland.
- Most hormones are found in very small amounts, the concentration of hormones varies
throughout the day.
- Hormones do not affect all cells. Cells may have receptors for one hormone but not another.
Pituitary Gland – the “master gland”
- controls the rest of the endocrine glands
- connected to the hypothalamus
The hypothalamus regulates the release of hormones from the anterior pituitary. Hormones
are secreted from the nerve ends of the cells of the hypothalamus and transported in the blood
to the pituitary gland.
Thyroid Gland
- located in the neck, in front of the trachea or windpipe
- 2 hormones (thyroxin and triiodothyronine) regulate body metabolism and the growth and
differentiation of tissues
- individuals who secrete higher levels of thyroxine oxidize sugars and other nutrients at a
faster rate
- individuals who have lower levels of thyroxine do not oxidize nutrients as quickly, and
therefore tend not to break down sugars as quickly
o excess blood sugar is converted into glycogen, which, when glycogen stores are
filled, is converted into fat
o people with low levels tend to be less active, intolerant of cold, and have skin that
tends to dry out quickly
o known as hypothyroidism
Thyroid Disorders
- Thyroid disorders are sometimes indicated by the presence of a “goiter” (enlarged
thyroid – in the neck)
- This causes problems with swallowing and causes the patient to cough
-
Blood tests can also determine a Thyroid Disorder
Overview of the Endocrine System
- Adapted from : http://members.shaw.ca/zsearle/bio20IB/endocrine%20notes.doc
Gland
Hypothalamus
Hormone
Oxytocin
Target
Action
Posterior Stored in the pituitary for
pituitary later release
(Connected
to the
Antidiuretic
Posterior Stored in the pituitary for
pituitary by a
hormone (ADH) pituitary later release
stalk)
Somatostatin
Anterior
pituitary
Inhibits growth hormone
(GH) release
Dopamine
Anterior
pituitary
Inhibits prolactin (PRL)
secretion (stops the prolactin
Mechanism
controlling
secretion
Nervous system
Blood osmolarity
(concentration of
solutes in urine)
Nervous system
from filling the breasts with
milk)
Pituitary –
Anterior
Lobe
(forebrain)
**
considered
the master
gland
** responds
directly to
hypothalamus
Thyroid
stimulating
hormone (TSH)
Thyroid
Stimulates the release of
thyroxine from the
thyroid (regulates cell
metabolism)
as TSH , thyroxine 
- secreted when thyroxine
too low
Adrenocorticot
ropic hormone
(ACTH)
Adrenal
cortex
Stimulates the release of
hormones involved in
stress response
as ACTH, adrenal
cortex hormones
-ve: cortisol level
Growth
hormone (GH)
(HGH)
Most
cells
Promotes growth by
stimulating uptake of
amino acids and fat
metabolism -  mitosis
rate
as HGH , growth  (until
~18yrs)
Hypothalmic releasing
factors
Somatostatin
Pituitary –
Posterior
Lobe
(forebrain)
Adrenal –
Adrenal
Medulla
(inside)
(on top of
kidneys)
AdrenalAdrenal
Cortex
(outside)
(on top of
kidneys)
Follicle
stimulating
hormone (FSH)
Ovaries
Testes
Females – stimulate
follicle dev. & estrogen
release
Males – stimulate sperm
production
Blood estrogen
Hypothalmic releasing
factors (GnRH)
Luteinizing
hormone (LH)
Ovaries
Testes
Females – stimulate
ovulation, corpus luteum
formation, estrogen &
progesterone release
Males – stimulate
testosterone production
Progesteron (or
testosteron) blood
levels
Hypothalmic releasing
factors (GnRH)
Prolactin (PRL)
Mammary
glands
Stimulates and maintains
milk production in females
Hypothalmic releasing
factors
Oxytocin
Uterus
Mammary
glands
Initiates contractions
Triggers milk production
Nervous system
Antidiuretic
hormone (ADH)
Kidney
Epinephrine
(adrenaline)
Many
cells
Increases blood sugar
level, heart rate,
breathing rate, cell
metabolism, dilate blood
vessels and iris of eye
Stimulated by
sympathetic nervous
system during times
of stress
Cortisol
(glucocorticoids)
Liver
Muscles
Converts amino acids into
glucose, reduces
inflammation
ACTH stimulates
release
Aldosterone
Kidney
Increase sodium retention
and water reabsorption
(maintain fluid levels)
Level of sodium and
potassium in the
blood
Norephinephrine
(noradrenaline)
(mineralocorticoids)
Increases water
Concentration of
reabsorption
solutes in the blood
as ADH , urine volume ,
blood pressure 
Pancreas
Islets of
Langerhans
(near
stomach)
Thyroid
Gland (base
of the neck
in front of
the trachea)
Insulin
(β cells)
Liver,
muscles
and
others
Increases glucose usage
by cells
Stimulated by high
blood sugar levels,
inhibited by low blood
sugar levels
Glucagon
( cells)
Liver
Stimulates conversion of
glycogen back to glucose
Stimulated by low
blood sugar levels,
inhibited by high
blood sugar levels
Thyroxine
All cells
Calcitonin
Bones
Triiodothyronine
Regulate cellular
Stimulated by TSH
metabolism – stimulates
(from the pituitary)
increased sugar utilization,
increases heat released
Inhibits calcium (Ca2+) loss
from bones
Ca2+ concentration in
the blood
GI tract, Raises blood Ca2+ levels by
bones
 absorption from the GI
& stimulates Ca2+ release
from bones
Ca2+ concentration in
the blood
Parathyroid
Glands
(either side
of thyroid)
Parathyroid
hormone (PTH)
Placenta
Progesterone,
Estrogen
Chorionic
Gonadotropin
Ovary
Uterus
Maintains uterine lining
during pregnancy
Testis
Testosterone
androgens
Testis,
many
other
cells
Stimulate
spermatogenesis,
development of secondary
(2) sex characteristics,
sex drive, bone growth,
muscle development
FSH, LH
Ovary
Estrogen
(follicle)
Progesterone
(corpus luteum,
follicle)
Uterus,
many
other
cells
E- promotes dev’t of 2
sex characteristics,
thickening of
endometrium, prep. for
pregnancy
P- stimulates
endometrium, prevents
ovulation, prevents uterine
contractions,
FSH, LH