Transcript The Endocrine System - Catherine Huff's Site

The Endocrine System
Chapter 15
Introduction
• Nervous system and endocrine system share
responsibility for control and coordination of entire
body.
• Homeostasis- balance of the body.
• Systems have similarities and differences:
• Both systems use chemicals to transmit their
messages.
• Endocrine system produces hormones
• Nervous system produces neurotransmitters
• Endocrine system reacts more slowly to
changes but can sustain response longer.
• Nervous system reacts more quickly to changes
but cannot sustain prolonged responses.
Basics
• Endocrine glands- basic units of the
endocrine system.
• Secrete hormones directly into the
bloodstream.
• Circulate throughout body and
produce effects when attach to
receptors in or outside of cells.
• Ductless glands.
• Exocrine glands- units that secrete their
products onto epithelial surfaces through
tiny tubes called ducts.
Endocrine vs. Exocrine Glands
Endocrine Glands
Hormones
• Chemical messengers produced by
endocrine glands and secreted directly
into blood vessels.
• Produce effects when find their receptors
in or on cells.
• Each body cell has specific receptors to
certain hormones (target).
• If body does not have receptor,
hormone will pass by.
• Only certain hormones can fit to
receptors and when it occurs, then it
changes the activity of the cell.
Control of Hormone Secretion
• “Negative Feedback System”
• Endocrine glands will be stimulated to produce
more hormone when it drops below a certain
amount in the body.
• If hormone is of adequate levels, gland will
either slow or stop production of the hormone.
• Direct Stimulation of Nervous System
• Secretion of some hormones is stimulated by
sympathetic nerve impulses when an animal
feels threatened.
• Fight or flight response from
sympathetic nervous system
The Hypothalamus
• Part of diencephalon of brain.
• Has control of pituitary gland.
• This links the conscious
mind with the rest of the
body. This is an important
bridge between the
endocrine and nervous
systems
Hypothalamus and anterior
pituitary gland
• Portal system of blood vessels links
hypothalamus with anterior portion of
pituitary gland.
• Modified neurons in hypothalamus
secrete releasing and inhibiting
hormones into portal blood vessels
• Specific for a particular anterior
pituitary hormone
• Either promote or inhibit the
production of a specific hormone.
Hypothalamus and Posterior
Pituitary
• Hypothalamus produces antidiuretic
hormone (ADH) and Oxytocin
• Are transported to posterior
pituitary where they are stored.
• Released into bloodstream by
nerve impulses from
hypothalamus.
The Pituitary Gland
• Also referred to as the “hypophysis”.
• Master endocrine gland.
• Many hormones direct activity of other
endocrine glands.
• Very small
• Housed in pituitary fossa of skull.
• Actually two separate glands:
• Anterior- adenohypophysis
• Produces seven known hormones
• Posterior-neurohypophysis.
• Does not produce any hormones but
stores and releases ADH and Oxytocin.
Anterior Pituitary Gland
• Hormones:
• 1. Growth Hormone (GH)
• 2. Prolactin
• 3. Thyroid-stimulating Hormone (TSH)
• 4. Adrenocorticotropic Hormone
(ACTH)
• 5. Follicle-stimulating Hormone (FSH)
• 6. Luteinizing Hormone (LH)
• 7. Melanocyte-stimulating Hormone
(MSH).
Growth Hormone (GH)
• Also known as somatotropin and
somatotropic hormone.
• Promotes growth in young animals.
• Helps regulate metabolism of proteins,
carbohydrates, and lipids in body’s cells.
• GH breaks down lipids for energy while
discouraging use of carbs for energy.
Dwarfism
Rare now since GH is commercially available
Giantism
Body proportions normal
Acromegaly
Excessive GH after epiphyseal plates close
Responsive tissues: bones of hands, feet, face
thickened facial features/tongue
Dairy Cows
• Synthetic GH may be used to
increase milk production of dairy
cows.
• Bovine Somatotropin (BST)
• Enhances milk production by
mammary glands.
• Can elevate body temperature.
• Reduce conception rates
• Increases risk of mammary
gland infections
• Increases risk of digestive
disorders.
Prolactin
• Helps to trigger and maintain lactation
• Continues as long stimulation of nipple
continues.
• Mammary glands will shrink to
normal size once stimulation stops.
• Has no known effect in male.
Thyroid-Stimulating Hormone
(TSH)
• Also referred to as thyrotropic hormone.
• Stimulates growth and development of
thyroid gland and causes it to produce
hormones.
• TSH production is regulated by feedback
from Thyroid gland.
Adrenocorticotropic Hormone
(ACTH)
• Stimulates growth and development of the cortex of
adrenal gland.
• Stimulates release of some of adrenal gland’s
hormones
• Can be released in two ways:
• First by feedback system from adrenal glands
• Second during stress, can be released by
stimulation of hypothalamus by other parts of
brain.
• This sends releasing factor to anterior
pituitary through blood vessels.
Follicle-Stimulating Hormone
(FSH).
• Stimulates growth and
development of follicles in
ovaries to create ovum.
• Helps produce estrogens as
well.
• Can be used to produce
“superovulation”
• Can then be harvested for
Artificial Insemination.
Luteinizing (LH)
• Completes process of follicle
development that was started by
FSH.
• Surge in LH is what causes
ovulation to occur.
• High LH is maintained to
produce corpus luteum which
produces its own hormones.
• In male, LH stimulates interstitial
cells to produce testosterone.
• Sometimes LH and FSH are
called gonadotropins.
Melanocyte-Stimulating Hormone
(MSH)
• Associated with color changes
in the melanocytes (pigment
cells) of reptiles, fish, and
amphibians.
• Can cause pigment to darken
when administered artificially.
• Other effects are unknown.
Posterior Pituitary Gland
• Does not produce, but stores and releases
ADH and Oxytocin when stimulated.
• ADH
• Where does it act?
• What does it do?
• Lack of can cause what disease?
• Oxytocin
• Two targets are uterus and mammary
glands.
• What does it do in uterus?
• What does it do in mammary glands?
The Thyroid Gland
• Consists of two parts called lobes
located on either side of the larynx.
• Connected by narrow band called
isthmus in some species.
• Composed of tiny follicles, where
thyroid hormone is produced.
• Each follicle consists of globule
surrounding thyroid precursor
called a colloid.
• Only endocrine gland that stores
large amounts of hormone
precursor for use later.
• Produces two hormones:
• Thyroid hormone
• Calcitonin
Thyroid Hormone
• T3(Triiodothyronine)- contains three iodine atoms
per molecule.
• T4(Tetriodothyronine, thyroxine)-contains four
iodine atoms per molecule.
• These hormones are produced when TSH from
anterior pituitary gland reaches the thyroid gland.
• T4 produced in greater abundance than T3 but is
mostly converted to T3 before producing effects on
target cells
• T3 more potent
• Necessary for normal growth and development in
young animals.
• Influences development and maturation of the
central nervous system, muscles and bones.
Thyroid Dysfunction:
Hypothyroidism
• Too little thyroid hormone produced.
• Occurs commonly in dogs.
• Symptoms include:
• Alopecia
• Dry skin
• Lethargy
• Reluctance to exercise
• Weight gain
• Seeking out sources of heat.
• Easily treated with thyroid supplementation
• Usually occur in middle age.
Thyroid Dysfunction:
Hyperthryoidism
• Too much thyroid hormone production.
• Commonly seen in cats.
• Symptoms include:
• Nervousness
• Excitability
• Weight loss
• Increased appetite, but no weight gain
• Tachycardia
• Vomiting
• Diarrhea
• Polyuria
• Polydipsia
• Treated surgically by removing the thyroid gland,
radioactive treatment, or drugs to suppress thyroid
production.
Thyroid Dysfunction: Goiter
• Non-cancerous, non-inflammatory
enlargement of the thyroid gland.
• Results from iodine deficiency which is a
component of thyroid hormone.
• Not enough iodine produced, less
hormone that can be produced.
• Causes hyperplasia of the gland
• Can be treated and prevented with iodine
supplements.
• Iodized salt.
Calcitonin
• Produced by C cells located between the
thyroid follicles.
• Involved with maintaining homeostasis of
the blood calcium levels.
• Will prevent hypercalcemia by
decreasing blood calcium levels if they
go too high.
• Encourages excess calcium to deposit
in bones
Parathyroid Glands
• Small nodules located near, in or on thyroid glands.
• Produce:
• Parathyroid Hormone (PTH)
Parathyroid Hormone (PTH)
• Also called parathormone.
• Opposite effect of calcitonin.
• Prevents hypocalcemia by increasing
blood calcium if gets too low.
• Causes kidneys to retain calcium and
intestines to absorb calcium from food.
• Can take calcium out of storage from
the bones.
Parathyroid Dysfunction:
Hypocalcemia
• Milk fever- when parathormone is
overwhelmed in lactating animals.
• Can cause muscle weakness and
tremors.
• Can progress to seizures and
spasms if left untreated.
• “Downer cows”
• Called Eclampsia in dogs and cats
• Treated by supplementing calcium
rapidly into system
Adrenal Glands
•
•
Located on cranial aspect of kidneys.
Composed of two glands wrapped around one another.
• Outer Adrenal Cortex
• Classic endocrine gland tissue
• Produce under direction of ACTH:
• Glucocorticoid hormones
• Mineralcorticoid hormones
• Sex hormones
• Inner Adrenal Medulla
• Resembles nervous tissue
• Controlled by sympathetic portion of nervous
system
• Produces:
• Epinephrine
• Norepinephrine
Glucocorticoid Hormones
• Hormones produced are:
• Cortisone
• Cortisol
• Corticosterone
• General hyperglycemic effect by causing blood
glucose levels to rise.
• Cause catabolism of proteins and lipids
• Products are ultimately converted back to
glucose through gluconeogenesis.
• Also may help to maintain blood pressure and help
body to resist stress.
Glucocorticoid-Related Diseases
•
•
Too much of cortisol in system-Hyperadrenocorticism=Cushing’s
Disease. (Iatrogenic Cushings)
• Symptoms include:
• Polyuria
• Polydipsia
• Polyphagia
• Hair loss
• Muscle wasting
• Slow wound healing
Too little of cortison in the systemHypoadrenocorticism=Addison’s Disease.
• Symptoms include:
• Weakness
• Lethargy
• Vomiting
• Diarrhea
• Can lead to circulatory and kidney failure.
Cushing’s Disease
Excessive amount of glucocorticoids
pot belly
long hair
laminitis
Addison’s Disease
Glucocorticoid-Related Drugs
• Drugs include:
• Hydrocortisone
• Prednisone
• Dexamethasone
• Triamcinolone
• How they act:
• Suppress immune system
• Affect WBC count
• Slow wound healing
• Catabolic effect of proteins
• Premature parturition
• Hyperglycemia
• Suppress adrenal cortex stimulation
Mineralcorticoid Hormones
• Regulate levels of
electrolytes in body.
• Principle hormone:
• Aldosterone
• Affects Sodium,
Potassium, and
Hydrogen Ions in the
body.
• Targets kidney
(why?)
Sex Hormones
• Adrenal cortex produces small amounts of
sex hormones and effects are generally
minimal.
• Male sex hormones- androgens
• Female sex hormones-estrogens.
Adrenal Medulla
• Inner gland of adrenal glands and
resembles nervous tissue.
• Concerned with sympathetic nervous
system.
• Direct stimulation on target tissues.
• Produces:
• Epinephrine
• Norepinephrine
The Pancreas
• Long and flat, located near the
duodenum.
• Has both endocrine and exocrine
functions
• Pancreatic islets (islets of langerhans)
are tiny clumps of cells that produce
hormones
• Produces:
• Insulin- by beta cells
• Glucagon- by alpha cells
• Somatostatin- by delta cells
Insulin
• Controls metabolism and use of glucose.
• Is essential for life
• Causes glucose, amino acids, and fatty
acids to be absorbed from bloodstream
into body’s cells.
• Lowers level of glucose in the blood.
Glucagon
• Opposite effect of insulin
• Raises glucose level in the blood.
• Stimulates liver to convert glycogen to
glucose
• Stimulates gluconeogenesis
• Other hormones do similar things so
deficiency is not as devastating.
Somatostatin
• Inhibits the secretion of insulin and
glucagon and GH and diminishes activity
of the GI tract.
The Gonads
•
Reproductive organs:
• Testes (when LH stimulates testes)
• Testosterone
• What all does this do?
• Where is it produced within the testes?
• Ovaries (when FSH and LH stimulate)
• Estrogens
• Estradiol
• Estrone
• What all do these do?
• Progestins
• Progesterone
• Produced by corpus luteum after ovulation
• Drugs can be used to delay estrus and
synchronize estrous periods in a group.
The Kidneys
• Produce Erythropoietin
• Stimulates red bone marrow to increase
production of red blood cells.
• Production is stimulated by decrease of
oxygen in the blood.
• Lack of production may result in
anemia.
• Synthetic forms are used in cases of
cancer.
• Procrit
The Placenta
• Produces small amounts of estrogen and
progesterone
• Produces chorionic gonadotropin
• What is tested for in pregnancy tests.
The Thymus
• Very important during early development,
will shrink as animal approaches
adulthood.
• Important in immune system development
• Produces:
• Thymosin
• Thymopoietin
• Seem to transform into t-lymphocytes (Tcells) which help to attack foreign invaders
in the body.
Pineal Body
• Influences body’s biological clock
• Produces:
• Melatonin
• hormone-like substance that affects moods and wakesleep cycles
• Also plays a role in timing of seasonal estrous cycles in
some species
Prostaglandins
• Derived from unsaturated fatty acids
• Sometimes called tissue hormones due to the fact
they travel short distances.
• Organized in groups A-I
• Remember PGE and PGI?
• Produced in a variety of body tissues including:
• Skin
• Intestine
• Brain
• Kidney
• Lungs
• Reproductive organs
• Eye
Prostaglandin effects
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•
•
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Influence blood pressure
GI function
Respiratory function
Kidney function
Blood clotting
Inflammation
Reproductive functions
PGE’s initiate inflammation so NSAIDs
inhibit PGE production.