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Endocrine System
Types of hormones and homeostasis
Negative feedback
Endocrine glands overview
The pituitary
Posterior pituitary
Anterior pituitary
Thyroxin - metabolism
PTH and Calcitonin - blood calcium
Insulin / glucagon – blood sugar
Adrenal Glands
Other glands
Recap: Homeostasis
• Homeostasis – is a state of equilibrium where
an organism’s internal environment remains
relatively constant, despite ongoing
environmental changes.
Recap: Negative Feedback
• prevents chemical
imbalances in the body.
• Once the body has
responded to a change in
the environment, the
effect is detected,
receptors are activated,
and further response is
inhibited.
Examples of Negative Feedback
Two Categories of Glands
1. Exocrine Glands –products do not enter the
bloodstream, but are released by ducts or tubes
into a body cavity, or out of the body.
1.
2.
Ex) sweat glands, salivary glands, phermones, pancreas
Endocrine Glands –release hormones into
the blood stream
1. Ex. Pituitary glands, Thyroid glands, pancreas
-Some of these hormones have specific target cells/organs/tissue,
others affect any and all cells. Hormones will attach to
specific receptor proteins on the outside of these target
cells which will then cause a change in the cell.
Hormones In the Body
Hormones: chemicals in the blood that
effect many systems
-Once in the blood, hormones circulate
and effect a target organ by bindng to
specific receptor proteins found on the
outer membrane of the cell
Chemical Nature of Hormones:
• 1) Water-soluble hormones: tend to be proteins,
peptides, or amino acid derivatives. These
hormones usually do not enter cells, but rather
bind to receptors on the outside of cells and
cause a cell to change.
– Ex. Insulin, thyroxin
• 2) Fat-soluble hormones: tend to be steroids. These
will diffuse into the inside of the cell and cause
the cell to change from the inside
– Ex. Testosterone, estrogen
Hypothalamus
• Produces Anti-Diuretic Hormone
(ADH) and Oxytocin
-but stored in the posterior pituitary gland
• Produces releasing and inhibiting factors to
control the pituitary gland
Pituitary Hormones
• Pituitary Gland
– the master gland
– has an anterior and
posterior region
A) Posterior Pituitary –stores and releases
hormones ADH and oxytocin
(NO hormones are actually made here!!)
 no capillary bed or hormone making cells
inside this gland, only has hormone storage
sites that release their hormones when
stimulated by neurons from the hypothalamus
Ex) Hormone (ADH) – increases water re-absorption
by the kidneys when the blood becomes too
concentrated with solutes
– Diabetes insipidus – excessive urination,
dehydration and thirst resulting from a lack of
ADH, usually caused by a tumor
Ex) Oxytocin –
stimulates uterine
contractions during
childbirth, and
triggers initial milk
production
– Pitocin – is a
synthetic form of
oxytocin that is
often given to
induce labour.
B) Anterior Pituitary – produces
hormones which are controlled by a
releasing factor secreted by the
hypothalamus.
Made up of capillary beds that surround
gland cells that form, store, and release
hormones
tend to be tropic (release
hormones that cause
other endocrine glands to
release their hormones)
Ex) Thyroid Stimulating Hormone
(TSH) – stimulates the thyroid gland to
release thyroxin (controls metabolism) and
calcitonin (controls blood calcium)
Ex) Adrenocorticotropic Hormone
(ACTH) – in stressful situations (The 4Fs)
stimulates the adrenal cortex to release
aldosterone and cortisol which regulate
the release of fatty acids in the blood and
regulate fat metabolism
Ex) Prolactin Hormone (PRL) –
stimulates milk production in the
mammary glands after birth, suckling or
other stimulation may result in the “let
down” reflex
Ex) Follicle Stimulating Hormone (FSH) –
stimulates the production of gametes (sperm
and egg) in the male and female reproductive
systems
Ex) Luteinizing Hormone (LH) – stimulates
the production of hormones (estrogen,
progesterone and testosterone) in the male and
female reproductive systems
-These are both examples of gonadatrophins=
hormones that stimulate gonads
Ex) human Growth Hormone (hGH) –
regulates the growth of bones and tissues
during childhood by assisting amino acids
across cell membranes for protein
synthesis.
• Gigantism –
overproduction
(hyersecretion) of
growth hormone
during the growth
years, results in very
large individuals (79 ft)
• often have diabetes
and other medical
issues.
• Acromegaly – overproduction of growth
hormone during the adult years, results in
excessive growth of the cartilage of the nose,
hands, feet, jaw, tongue and internal organs.
The World’s tallest woman.
Defen is 34 years old and 7ft 8" tall.
• Dwarfism –
underproduction
(hyposecretion) of
growth hormone
during the growth
years and
adolescence, results in
individuals of short
stature with
proportionate or
disproportionate size.
• Extra: Melanocyte Stimulating
Hormone (MSH) – affects skin
pigmentation
Thyroid Gland
The thyroid gland is responsible for
the secretion of two hormones:
1. Thyroxin – increases the rate of
cellular respiration by increasing
oxygen uptake in cells
-Regulates energy metabolism of fats,
proteins, and carbohydrates. Increase
rate of cellular respiration
-Also helps with development and
organization of cells into tissues
- a synthetic thyroxin drug is called
synthroid
2. Calcitonin – decreases the concentration
of blood calcium
-Decreases the rate that calcium leaves the
bones, reduces intestinal uptake of calcium,
and reduces re-absorption of calcium by
the kidneys. (Works in opposition to
parathyroid hormone)
Thyroid Disorders
• Hyperthyroidism – excessive production of
thyroxin results in nervousness, weight loss,
sweating, tachycardia, hyperactivity (All due
to extra energy in the body!)
• Hypothyroidism – underproduction of
thyroxin results in sluggishness, depression,
weight gain, tiredness, goiter (=swelling of
the Thyroid)
– Goiter is caused by a lack of iodine in the diet.
Iodine makes Thyroxin. If not enough thyroxin is
being formed, the Tyhroid will continue to
stimulated to try and make more and more
thyroxin.
• Cretinism – hypothyroidism in a developing
infant results in permanent and severe
retardation and stunted growth
Thyroid Surgery
Feed back Loop for Thyroid
• Low energy metabolism  Hypothalamus signals the
pituitary  anterior pituitary releases TSH  Thyroid
activated and releases thyroxine increased cellular
respiration in cells high energy and increase in
body temperature (heat is a byproduct)
• Excess thyroxine turns off hypothalamus and pituitary
gland
Parathyroid Gland
• a set of four pea-sized glands embedded in the
posterior portion of the thyroid.
• Parathyroid Hormone (PTH) – increases
blood calcium
– increases removal of calcium ions from bones
and increases re-absorption of calcium ions
from the kidneys.
• Tetany – underproduction of the parathyroid
(low blood calcium) resulting in muscle
spasms, convulsions and nervous twitches
• Osteoporosis – demineralization of the
bones due to overproduction of the parathyroid, or
lack of calcium
– very common after menopause due to lowered
estrogen levels (estrogen counters the effect of
PTH)
The Pancreas- The
‘endocrine/exocrine’ gland anomaly
• Islets of Langerhans – are glandular clusters of
cells in the pancreas that produce insulin and
glucagon
Alpha cells – produce glucagon, which stimulates
the conversion of glycogen to glucose by
the liver raising blood glucose
Beta cells – produce insulin, which stimulates
the uptake of glucose by the body’s cells,
lowering blood glucose
Regulation of Blood Sugar Feedback Loop
High Blood Sugar Feedback
Loop
• High Sugar meal increase blood sugar 
pancreas signaled  beta cells release insulin
into the blood  glucose turned into glycogen
in the liver lower blood sugar
• Insulin and glucagon are ‘antagonistic hormones’ in
that they have opposite affects on their target
cells
Blood Sugar Disorders
• Diabetes Mellitis –sugar diabetes or
hyperglycemia
– blood sugar is very high (while cellular
glucose is too low)
– increased urination, fruity odour on the
breath, weight loss, fatigue, blindness
– Long term problems: blindness and loss of
limbs, heart failure, kidney failure
– 2 Types of Diabetes Mellitus:
– Type I /Juvenile Onset – the inability to produce
insulin, degeneration of beta cells (genetic)
– Type II / Adult Onset – decreased insulin
production or ineffective use of insulin (may be
related to insulinase) (lifestyle: diet & exercise)
• Cures: insulin injections, islet cell
transplants (specifically beta cells)
• Diabetic Coma – slow onset, lack of insulin
that result in the brain being deprived of
glucose, and eventually shutting down (insulin is
required)
• Insulin Shock – sudden excess amount of
insulin causing dizziness, sweating, hunger,
confusion, normal urine output (sugar is
required)
• main
Adrenal Glands
• located just above the kidneys
• composed of outer cortex and an inner
medulla which produce different
hormones.
Adrenal Medulla
Adrenaline/Epinephrine – released to elicit the
fight, fright, flight, sex response during short term
stress, causes:
• increased blood glucose
• increased heart rate
• increased metabolism
• increased blood flow to the skeletal muscles
• decreased rate of digestion
• relaxes smooth muscles in the walls of the
bronchioles (opens them up = better gas transport)
Adrenal Cortex
-stimulated
by Adrenocorticotropic Hormone
Produces three classes of hormones called
corticoids:
1. Sex hormones – small amounts of both male
and female sex hormones are released by the
adrenal cortex. Over-activity causes
masculinization of females and feminization of
males.
2. Cortisol – is a glucocorticoid( steroid that
binds with glucocorticoid receptors)
-long term stress
-breaks down muscle proteins to produce amino
acids which are converted into glucose in
response to stress
- stimulates the metabolism of fatty acids raising
the blood glucose.
- counter the inflammatory response.
- Suppresses the production of ACTH
• Aldosterone – is a mineralocorticoid (steroid
that binds to mineralocorticoid receptor).
– regulates Na+/K+ levels and maintains blood
pressure.
– promotes re-absorption of Na+ ions by the
kidney, drawing in water and thus increasing
blood pressure.
Adrenal Disorders
• Cushing’s
Syndrome – over
activity of the adrenal
cortex resulting in
edema, moonlike face,
masculinization of
females, and high
blood sugar.
• Addison’s Disease – under-activity of the
adrenal cortex resulting in low blood
pressure, acidosis, fainting, increased risk
of infection and bronzing of the skin.
Extra: Other Hormones
• Thymus – secrete thymosin that stimulates
maturation and differentiation of the T-cells in the
immune system (most active in children with
developing immune systems, decreases in size as you
get older)
• Melatonin – secreted by the pineal gland,
regulates circadian rhythms such as sleep/wake
cycles, migration, mating and sexual
development. (‘Clock Hormone’)
• Prostaglandins
– made by tissue not glands
– Not delivered in blood (so not a endocrine
hormone)
– Act on the cells that make them or nearby
tissue
Help cause blood clotting
• Link
• Pheromones – are messengers that act between
individuals of a species, secreted to attract a
mate, mark territory, provide warning of danger.
• Leptin- the first fat cell derived hormone
discovered.
This hormone has been shown to be released by
adipose cells and acts on the hypothalamus to
decrease appetite. When fat storage in adipose
cells is at its maximum, leptin is released to the
brain to decrease hunger urges.
Lots of research with this hormone and helping
obesity.