Download 22-Endocrine

Lecture 22
The Endocrine System
Hormones
 A hormone is a chemical signal that is produced in one part of
the body and that acts at a distant site
 Three advantages to using chemical signals
1. Can spread to all tissues via the blood
2. Can persist much longer than electric signals
3. Many can act as hormones
 Different hormones can target different tissues
Major glands of the human endocrine system
 Hormones are produced by
endocrine glands
 These glands do not have
ducts
 Hormones are secreted
directly into the blood
 Hormones are under the control of
the neuroendocrine system
 The hypothalamus is the main
switchboard
 Issues commands to the
nearby pituitary gland
 Pituitary sends
chemical signals to the
various hormoneproducing glands in
body
Hormones
 Hormones are chemicals that circulate in the blood and so
come in contact with all cells in the body
 However, they only interact with specific receptors on or
in their target cells
 The path of communication of a hormone signal
 1. Issuing the command
 By the hypothalamus
 2. Transporting the signal
 By the blood
 3. Hitting the target
 Binding to the receptor
 4. Having an effect
 A change in cell activity
How hormonal communication works
How Hormones Target Cells
 Steroid hormones
 Manufactured from cholesterol
 Lipid-soluble and thus can across the lipid bilayer of the
cell membrane
 Bind to receptors within the nucleus usually the
hormone-receptor complex binds to DNA causing
changes in gene activity
 Anabolic steroids
 Synthetic compounds resembling testosterone
 Cause muscle cells to produce more protein
How steroid hormones work
How peptide hormones work
 Peptide hormones
 Short peptides or full-sized
proteins
 Bind to receptors
embedded in the cell
membrane
Induce a change in
cytoplasmic end of the
receptor protein
Triggers events within
the cytoplasm
 The change in cellular activity is facilitated by second messengers such
as cAMP
Trigger a cascade of enzymatic activation within cell
The Hypothalamus and the Pituitary
The pituitary gland is located in a
bony recess in the brain below the
hypothalamus
It is actually two glands
Posterior lobe
Anterior lobe
It produces nine major hormones
The hypothalamus secretes
hormones into capillaries that
cause the pituitary to release or
inhibit release of its hormones
Hypophyseal portal system
carries these hormones from the
hypothalamus to the pituitary
The Posterior Pituitary
 Stores and releases two short peptide hormones
 Vasopressin (antidiuretic hormone, ADH)
 Regulates water conservation by the kidney
 Oxytocin
 Initiates uterine contractions during childbirth
 Causes milk letdown
 Both synthesized within hypothalamus neurons
 Transported down nerve axons to the
posterior lobe
The Anterior Pituitary
 A complete gland that produces seven major hormones
1.
2.
3.
4.
5.
6.
7.
Thyroid-stimulating hormone (TSH)
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
Adrenocorticotropic hormone (ACTH)
Growth hormone (GH)
Prolactin
Melanocyte-stimulating hormone (MSH)
The role of the pituitary
Control of the Hypothalamus & Pituitary
 Hypothalamus and anterior pituitary are themselves controlled by negative
feedback inhibition
 Regulated by the hormones whose secretion they stimulate!
The Pancreas

The pancreas gland is
located behind the stomach
 Secretes a number of
digestive enzymes into
the small intestine
through a narrow tube

Islets of Langerhans govern
blood glucose levels
 Insulin
 Secreted by beta
cells
 Storage hormone
that promotes
accumulation of
glycogen in liver
and triglycerides in
fat cells
 Glucagon
 Secreted by alpha
cells
 Cause release of
stored glucose and
fat breakdown
Diabetes mellitus
 Affected individuals cannot take up glucose from the blood
 Type I
 ~ 5-10% of diabetics
 Autoimmune disorder in which immune systems attacks
the Islets of Langerhans
 Develops before age 20 (juvenile-onset diabetes)
 Treated by daily injections of insulin
 Type II
 ~ 90-95% of diabetics
 Caused by abnormally low number of insulin receptors
 Develops after age 40 (adult-onset diabetes)
 Typically in obese individuals
 Treated by diet and exercise
The Thyroid, Parathyroid and Adrenal Glands
The thyroid gland lies just below the Adam’s apple in front of the
neck
Its two most important hormones are
Thyroxine
Increases metabolic rate and promotes growth
Contains iodine
Lack of iodine in diet causes goiters
Calcitonin
Stimulates calcium deposition in the bone
The thyroid gland secretes thyroxine
Goiter
The parathyroid glands

The parathyroid glands are
four small glands attached to
the thyroid Produce
parathyroid hormone (PTH)
 One of only two hormones
essential for survival


Acts as a fail-safe mechanism
ensuring that calcium levels
never fall too low
Calcium ions are key to
muscle contractions
 When levels are low, PTH
stimulates osteoclast cells to
break down bone matrix
 This raises calcium levels in
the blood
PTH also acts on kidneys to
reabsorb calcium ions from
the urine
The adrenal glands
The adrenal glands are two glands, one located just above each
kidney
Each composed of two parts
Medulla – Inner core
Adrenaline and norepinephrine
Released in times of stress to stimulate rapid deployment of
body fuel
Cortex – Outer shell
Cortisol – Stimulates carbohydrate metabolism and reduces
inflammation
Aldosterone – Stimulates the kidney to uptake sodium and other
ions from the urine
This is the other hormone that is absolutely essential for
survival
A Host of Other Hormones
 Steroid sex hormones
 Estrogen, progesterone and testosterone
 Produced by gonads to regulate sexual development
 Atrial natriuretic hormone
 Secreted by the right atrium of the heart
 Stimulate kidneys to excrete salts and water in the urine
 Erythropoietin
 Secreted by the kidney
 Stimulates the bone marrow to produce RBC