Download Chapter 17 The Endocrine System and Development Endocrine

Chapter 17
The Endocrine System and Development
Endocrine system
 Mostly comprised of glands
 Other organs and tissues also produce and secrete hormones
 Secretes hormones that move through the bloodstream to target cells
o
Allows communication between different parts of the body
o
Results in a slow but prolonged response
Hormones
 Hormones are chemical signals that promotes communication between cells, body
parts, and even individuals
 Steroid hormones - lipids that enter a cell to affect gene activity and thus protein
synthesis
 Nonsteroid hormones - bind to a receptor in the plasma membrane causing the
formation of cAMP which activates a cascade of enzymes
o
Regardless of whether it is a steroid or nonsteroid hormone, the target
cell must have the proper receptor for the hormone to have an effect
Major glands of the endocrine system
Hypothalamus
 Regulates the internal environment through the autonomic nervous system
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Helps control heartbeat
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Helps control body temperature
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Helps control water balance
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Controls glandular secretions
Posterior pituitary gland
 Stores antidiuretic hormone (ADH) and oxytocin that are produced by the
hypothalamus
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ADH - regulates water balance by reabsorbing water into the bloodstream
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Oxytocin - causes uterine contractions during childbirth and allows milk
to be released during nursing
Anterior pituitary gland
 Controlled by hypothalamic-releasing and hypothalamic-inhibiting hormones
 Hormones produced by the anterior pituitary
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Thyroid-stimulating hormone (TSH) - stimulates the thyroid to produce
thyroid hormones
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Adrenocorticotropic hormone (ACTH) - stimulates the adrenal cortex to
produce cortisol
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Gonadotropic hormones - stimulate the gonads to produce sex cells and
hormones
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Prolactin (PRL) - stimulates the mammary glands to develop and produce
milk after childbirth
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Melanocyte-stimulating hormone (MSH) - causes skin cells to produce
melanin
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Growth hormone (GH) - promotes skeletal and muscular growth
What happens when the body produces too much or too little GH?
 Pituitary dwarfism – too little GH is produced during childhood resulting in small
stature
 Giantism – too much GH is produced during childhood resulting in large stature but
overall poor health
 Acromegaly – overproduction of GH as an adult that results in larger than normal
feet, hands, and face
Adrenal glands
 Glands that sit on top of the kidneys
 2 parts of each gland
o
Adrenal medulla - controlled by the nervous system
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Adrenal cortex - portions are controlled by ACTH from the anterior
pituitary
 Adrenal medulla
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Inner portion of the adrenal glands
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Hypothalamus initiates stimulation of hormone secretion in the adrenal
medulla
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Produces hormones that allow a short-term response to stress (“fight or
flight” response)
 Epinephrine (adrenaline)
 Norepinephrine
 Adrenal cortex
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Outer portion of the adrenal glands
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Produces hormones that provide a longer-term response to stress
o
2 major types of hormones
 Mineralocorticoids
 regulate salt and water balance
 e.g. aldosterone (targets the kidney)
 Glucocorticoids
 regulate carbohydrate, protein, and fat metabolism
 Suppress the body’s inflammatory response
 e.g. cortisol and cortisone
Adrenal glands can malfunction
 Addison’s disease – hyposecretion of glucocorticoids by the adrenal cortex
characterized by bronzing of the skin
 Cushing syndrome – hypersecretion of glucocorticoids by the adrenal cortex
characterized by weight gain in the trunk of the body but not the arms and legs
Thyroid gland
 A large gland located below the larynx
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Iodine is needed in the diet to allow the thyroid gland to produce its
hormones
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Thyroid hormone (TH) - regulates overall metabolism
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Calcitonin - helps lower blood Ca2+ levels by stimulating the deposition of
calcium in the bones
 Thyroid abnormalities
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Simple goiter – thyroid enlarges due to lack of iodine in the diet
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Hypothyroidism – low blood levels of thyroid hormones
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Congenital hypothyroidism - thyroid does not develop properly and is
characterized in a short, stocky person that may be mentally retarded
o
Myxedema - hypothyroidism in adults characterized by lethargy, weight
gain, loss of hair, cold intolerance, and thick, puffy skin
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Hyperthyroidism – excess thyroid hormones in the blood
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Exophthalmic goiter - such as seen in Graves' disease and is characterized
by enlargement of the thyroid gland, protrusion of the eyes, hyperactivity,
and insomnia
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Thyroid tumor - can also cause hyperthyroidism
Parathyroid glands
o Small glands embedded in the surface of the thyroid gland
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Produce parathyroid hormone (PTH)
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Causes blood Ca2+ level to increase by promoting osteoclast activity
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Promotes reabsorption of Ca2+ by the kidneys
Thymus gland
o Lies beneath the sternum
o This gland is largest and most active during childhood
o T lymphocytes mature here
o Secretes hormones called thymosins that aid in differentiation of lymphocytes
Pineal gland
o Located in the brain
o Secretes melatonin that regulates the sleep/wake cycle (circadian rhythm)
o May also regulate sexual development
Pancreas
o Fish-shaped organ behind the stomach
o Composed of 2 tissues
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Exocrine produces and secretes digestive juices
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Endocrine (islets of Langerhans) produces and secretes hormones
 Insulin – secreted when blood glucose is high and stimulates the
uptake of glucose by muscle and liver cells
 Glucagon – secreted when blood glucose is low and stimulates the
breakdown of glycogen in the liver
Diabetes
o Inability to control blood glucose levels
o There are two types: Type 1 and Type 2
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18 million people in the US have diabetes
o General symptoms:
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Frequent urination
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Unusual hunger and/or thirst
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Unexplained change in weight
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Blurred vision
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Sores that heal slowly or not at all
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Excessive fatigue
o Long-term effects are blindness, loss of limbs, nerve deterioration, kidney and
cardiovascular disease
Type 1
o Usually early-onset
o Autoimmune disorder that tends to run in families
o Pancreatic cells are attacked and cannot produce insulin
o Require insulin injections
Type 2
o Usually adult-onset and the most common type
o Tends to occur in obese, sedentary people
o Cells do not respond to insulin
o Usually diet and exercise are important for controlling this and may even prevent
this
Hormones from other tissues
o Erythropoietin - secreted by the kidney to increase red blood cell production
o Leptin - produced by fat cells and acts on the hypothalamus to give a feeling of being
satiated
o Prostaglandins
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A group of potent chemicals that work locally on neighboring cells
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Some cause smooth muscle contraction
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Major impact on reproductive organs
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Many other roles in the body
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Aspirin and ibuprofen block the synthesis of these
Homeostasis
o The nervous and endocrine systems are important in maintaining homeostasis
o The hypothalamus bridges the regulatory functions of both systems
o Both systems are able to respond to changes in the external environment
Development
o Hormones signal and control the sequential growth and maturation from the
neonatal period and infancy, through childhood, adolescence, adulthood, and
senescence
Aging
o There are 3 hypotheses for aging
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Limits on cellular division
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Accumulated cell damage
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Demise of organ systems