Transcript Endocrine System

Endocrine System
 Endocrine System and the nervous system often work
together to bring about homeostasis
 Both use specific communication methods and affect
specific target organs
 Their methods and effects differ
Endocrine Glands & Hormones
 Excorine glands
 Secretions released into ducts opening onto an epithelial
surface
 Endocrine glands
 Ductless organs that secrete their molecules directly
into the bloodstream
 All endocrine cells are located within highly
vascularised areas to ensure that their products enter
the bloodstream immediately
Overview of Hormones
 Molecules that have an effect on specific organs
 Only cells with specific receptors for the hormone
respond to that hormone
 Called target cells, and the organs that contain them
are called target organs.
 Organs, tissues, or cells lacking the specific receptor
do not respond to the stimulating effects.
Classification of Hormones
 Peptide hormones
 Formed from chains of amino acids
 Most of out body’s hormones are peptide hormones
 Longer chains are called protein hormones
 Example is growth hormone
 Steroid hormones
 Type of lipid derived from cholesterol
 Example is testosterone
 Biogenic amines
 Small molecules produced by altering the structure of a
specific amino acid
 Example is thyroid hormone
Negative Feedback Loop
 A stimulus starts the process, and eventually either the
hormone that is secreted or a product of its effects
causes the process to slow down or turn off
 Many hormonal systems work by negative feedback
mechanisms
 One example is the regulation of the blood glucose level
in the body
Positive Feedback Loop
 Accelerated the original process, either to ensure that
the pathway continues to run or to speed up its
activities.
 Only a few positive feedback loops occur in the human
endocrine system
 one example is the process of milk release form the
mammary glands
Hypothalamic Control of the
Endocrine System
 As the master control center of the endocrine system
the hypothalamus oversees most endocrine activity.
 Special cells in the hypothalamus secrete hotmones that
influence the secretory activity of the anterior pituitary
gland
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Called regulatory hormones because they are secreted into the
blood to regulate secretion of most anterior pituitary
hormones
Releasing hormones (RH)
Inhibiting hormones (IH)
 Hypothalamus has indirect control over these
endocrine organs
Hypothalamic Control of the
Endocrine System
 Hypothalamus produces two hormones that are
transported to and stored in the posterior pituitary
 Oxytocin
 Antidiuretic hormone (ADH)
 Hypothalamus directly oversees the stimulation and
hormone secretion of the adrenal medulla
 An endocrine structure that secretes its hormones in
response to stimulation by the sympathetic nervous
system
 Some endocrine cells are not under direct control of
hypothalamus
Pituitary Gland
 Lies inferior to the hypothalamus
 Small, slightly oval gland housed within the hypophyseal
fossa of the sphenoid bone
 Covered superiorly by the diaphragma sellae, which is one
of the cranial dural septa that ensheathes the stalk of the
infundibulum to restrict pituitary gland movement
 Connected to the hypothalamus by a tiny stalk, the
infundibulum
 Partitioned both structurally and functionally into an
anterior pituitary and posterior pituitary
 Called anterior lobes and posterior lobes
Control of Anterior Pituitary Gland
Secretions
 Anterior pituitary gland is controlled by regulatory
hormones secreted by the hypothalamus
 Hormones reach the anterior pituitary via
hypothalamo-hypophyseal portal system
 Essentially a “shunt” that takes venous blood carrying
regulatory hormones from the hypothalamus directly to
the anterior pituitary before the blood returns to the
heart
Thyroid Gland
 Located immediately inferior to the thyroid cartilage
of the larynx and anterior to the trachea
 Distinctive “butterfly” shape
 highly vascularized, giving it an intense reddish colour
 Regulation of the thyroid hormones secretion depends
upon a complex thyroid gland- pituitary gland
negative feedback process
Hyperthyroidism
 Too much thyroxine
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Enlargement of the thyroid (Goiter)
Muscle weakness
Increased metabolic rate
Excessive heat production (dilation of blood vessels)
Increased appetite
Budging eyes
 Build up of fluid and entry of lymphocytes into orbital
tissue
Hyperthyroidism
 Treatments
 Removal of thyriod
 Thyroid blocking drugs
 Radioactive iodine
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Destyoys overactive thyroid tissue
 Injections of thyroid hormone
Hypothyroidism
 Too little thyroxine
 Caused by iron deficiency
 Disrupts negative feedback loop with the pituitary
 Continuous production of TSH
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Reduced basal metabolic rate
Decreased heat production
Reduced tolerance to cold
Decreased heart rate and output
Weight gain (decreased appetite)
Weakness & fatigue
Parathyroid Glands
 Small, brownish-red glands located on the posterior
surface of the thyroid gland
 Usually four small nodules
 some individuals may have as few as two or as many as six
 Parathoid hormone (PTH)
 Stimulates osteoclasts to reabsorb bone and release calcium
ions from bone into the bloodstream
 Stimulates calcitriol hormone synthesis in the kidney
 Promotes calcium absorption in the small intestine
 Prevents the loss of calcium ions during the formation of
urine
 Calatonin (thyroid Gland)
 Bones uptake Ca+
 Negative Feedback loop for Blood Calcium (Ca+)
Pancreas
 Located near the small intestine
 Exocrine
 Digestive enzymes to duodenum
 Endocrine
 2 non-steriod hormones (produced by islets of
Langerhans
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Insulin
Glucagon
 Negative Feedback loop for Blood Glucose (sugar)
Levels
Type 1 Diabetes
 Immune system attacks the pancrease
 Insulin producing beta cells
 Body’s inability to produce insulin
Type 2 Diabetes
 More Common form of diabetes (adult onset diabetes)
 90% of diabetics are type 2
 Body produces insulin
 Not enough
 Body doesn’t respond to it
 Diet and exercise
 Insulin injections (both type 1 and 2)
Pineal Gland
 Small, pone cone shaped gland
 Located deep ion the center of the brain
 Hormone: Melatonin
 Causes us to feel sleepy
Thymus Gland
 Located between the lungs in the upper chest cavity
 Immune System
 Regulated by pituitary gland
 Thymosin
 Stimulates the production of lymphocytes into T Cells
 Disappears after puberty
 Lymphocytes continue to be produced by spleen and
lymph glands as adults
Adrenal Glands
 2 adrenal glands
 Located on top of each kidney
 2 parts
 Outer Cortex
 Inner Medulla
 Each produces different hormones & acts like different
organs
 Regulated by hypothalamus
 Adrenaline, noradrenalin, & cortisol
Adrenal Medulla (think “middle”)
 Produces epinephrine and
norepinephrine
 link between medulla and
nervous system is that they
both produce adrenaline
 these chemicals are
released during stress
situations
Adrenal Medulla (continued)
 Epinephrine causes: blood sugar to go up, glycogen to
be turned into glucose, heart rate increases, breathing
rate increases, cell metabolism increases, blood vessels
dilate, iris of the eye dilates…
 It’s fight or flight time!
Adrenal Cortex
 Produces three different
types of hormones:
glucocorticoids,
mineralocorticoids, and
small amounts of sex
hormones
 we’re only concerned about
two hormones
Cortisol
 One of the most important glucocoticoids
 helps the body recover from stress by increasing amino
acid levels
 amino acids are either converted in to glucose (cell
recovery) or protein (cell repair)
Aldosterone
 The most important of the mineralocorticoids
 responsible for sodium levels, and therefore water
levels in the body