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Transcript of The Endocrine System Copyright © The McGraw-Hill Companies, Inc. Permission required for...
The Endocrine System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lecture Outline
Endocrine Glands
o Endocrine glands are ductless o Secrete hormones
• Chemical signals that influence: Metabolism Growth and development Homeostasis
• Categories of hormones Peptides (proteins, glycoproteins, and
modified amino acids) – most hormones Steroid hormones
Endocrine Glands
o How Hormones Function• Second messenger system
Peptide hormone binds to a receptor protein on the plasma membrane
Peptide hormone (“first messenger”) activates a “second messenger” (cyclic AMP and calcium)
Second messenger sets in motion an enzyme cascade that leads to a cellular response
Change in cellular behavior Formation of an end product that leaves the cell
Endocrine Glands
• Intracellular mechanism of hormone function
Steroid hormones (lipids) diffuse across the plasma membrane
Once inside the cell, steroid hormones bind to receptor proteins
Hormone-receptor complex binds to DNA, activating particular genes
Gene activation leads to production of cellular enzymes that cause cellular changes
Endocrine Glands
o Hormone Control• Many hormones affect concentrations
of certain substances in the blood• Other hormones are involved in
normal function of various organs• Release of hormones controlled by
one or more of the following: The nervous system The action of other hormones Negative feedback mechanisms
Hypothalamus and Pituitary Gland
o Hypothalamus• Controls secretions of the pituitary
gland• Neurosecretory cells produce
Antidiuretic hormone (ADH) Oxytocin
Hypothalamus and Pituitary Gland
o Posterior pituitary• Stores hypothalamic hormones ADH
and oxytocin• ADH
Released when neurons in the hypothalamus detect that the blood is too concentrated with salt
Causes more water to be reabsorbed into kidney capillaries
Raises blood pressure by vasoconstriction of blood vessels
Diabetes insipidus results from the inability to produce ADH
Hypothalamus and Pituitary Gland
• Oxytocin Causes uterine contraction during
childbirth Causes milk letdown when a baby is
nursing Release of oxytocin is controlled by
positive feedback
Hypothalamus and Pituitary Gland
o Anterior pituitary• Controlled by hypothalamic hormones• Hormones that affect other glands
Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Gonadotropic hormones
• Effects of other hormones Prolactin (PRL) Growth hormone (GH)
Hypothalamus and Pituitary Gland
• Effects of growth hormone Affects the height of an individual Pituitary dwarfism results if too little GH is
produced during childhood If too much GH is produced during
childhood, a person can become a giant Acromegaly results when too much GH is
secreted in adulthood
Thyroid and Parathyroid
o Thyroid Gland• Two forms of thyroid hormone
Triiodothyronine (T3) contains 3 iodine atoms
Thyroxine (T4) contains 4 iodine atoms
• Effects of thyroid hormone Increase the metabolic rate Stimulate all cells of the body
Thyroid and Parathyroid
• Simple goiter Caused by a lack of
iodine Thyroid enlarges in
response to constant stimulation by the anterior pituitary
Thyroid and Parathyroid
• Congenital hypothyroidism Thyroid fails to develop
properly Undersecretion of thyroid
hormone Individuals are short and
stocky• Myxedema
Hypothyroidism in adults Characterized by
Lethargy Weight gain Loss of hair Slower pulse rate Lowered body
temperature Thick and puffy skin
Thyroid and Parathyroid
• Hyperthyroidism (Grave’s Disease) Oversecretion of thyroid hormone Exophthalmic goiter forms
Edema in eye socket tissues Swelling of the muscles that move the eyes
Symptoms include Hyperactivity Nervousness and irritability Insomnia
Thyroid and Parathyroid
• Calcitonin Helps control blood calcium levels Secreted when the blood calcium levels
rise Brings about the deposit of calcium in the
bones
Thyroid and Parathyroid
o Parathyroid Glands• Posterior surface of the thyroid gland• Produces parathyroid hormone (PTH)
Causes blood phosphate (HPO42-) level to decrease
Causes blood calcium (Ca2+) level to increase Promotes the release of calcium from the bones Promotes the reabsorption of calcium by the kidneys
Activates vitamin D in the kidneys, which stimulates the reabsorption of calcium from the intestines
Hypocalcemic tetany results when there is insufficient secretion of PTH
Adrenal Glands
o Adrenal Medulla• Inner portion• Under nervous control• Secretes epinephrine (adrenaline) and
norepinephrine (noradrenaline)• Causes “fight or flight” responses• Provide a short-term response to
stress
Adrenal Glands
o Adrenal Cortex• Outer portion – 3 layers, each
produces a different set of hormones• Under the control of ACTH• Hormones
Provide a long-term response to stress Mineralcorticoids Glucocorticoids Male and female sex hormones
Adrenal Glands
• Glucocorticoids (cortisol) Raises the blood glucose level in at least
2 ways: Counteracts the inflammatory response and
can relieve swelling and pain Can also make a person susceptible to injury
and infection
Adrenal Glands
• Mineralcorticoids (aldosterone) Targets the kidney Promotes renal absorption of sodium and water Promotes renal excretion of potassium ACTH is not the primary controller for aldosterone
secretion Renin-Angiotensin mechanism stimulates
aldosterone secretion when the blood sodium level and blood pressure are low
Renin-Angiotensin-Aldosterone system raises blood pressure in two ways:
Angiotensin II constricts arterioles Aldosterone causes the kidneys to reabsorb sodium
Atrial natriuretic hormone (ANH) is antagonistic to aldosterone
Adrenal Glands
• Malfunction of the Adrenal Cortex Addison Disease
Hyposecretion of adrenal cortex hormones Excessive (but ineffective) ACTH causes
bronzing of the skin Because glucose cannot be replenished without
cortisol, individuals are susceptible to infection Lack of aldosterone results in the development
of low blood pressure and possibly severe dehydration
Cushing Syndrome Hypersecretion of adrenal cortex hormones Tendency towards diabetes mellitus Excess aldosterone leads to hypertension
Pancreas
o Composed of two types of tissue• Exocrine – secretes digestive juices• Endocrine tissue (pancreatic islets or
islets of Langerhans) produces: Insulin
Secreted when blood glucose level is high Stimulates the uptake of glucose by most body
cells Glucagon
Secreted when blood glucose levels are low Targets liver and adipose tissue Stimulates liver to break down glycogen to
glucose
Pancreas
o Diabetes Mellitus• Insulin-sensitive body cells are unable
to take up and/or metabolize glucose• Blood glucose level is elevated
(hyperglycemia)• Symptoms:
Polyphagia – extreme hunger Glycosuria – glucose in the urine Polyuria – excessive water loss through
urine Polydipsia – extreme thirst
Pancreas
• Two forms of diabetes mellitus Type I – insulin-dependent diabetes
mellitus Pancreas does not produce insulin Immune cells destroy the pancreatic islets
Type II – non-insulin-dependent diabetes mellitus
Normal or elevated amounts of insulin are present in the blood
Receptors on the cells do not respond to insulin
Other Endocrine Glands
o Testes and ovaries• Testes produce androgens
(testosterone)• Ovaries produce estrogens and
progesterone• Secretion is controlled by the
hypothalamus and the pituitary
Other Endocrine Glands
• Androgens Increased testosterone secretion during
puberty stimulates the growth of the penis and the testes
Brings about and maintains the male secondary sex characteristics
Facial, axillary, and pubic hair Enlargement of larynx and the vocal cords Muscular strength
Stimulates oil and sweat glands of the skin
Other Endocrine Glands
• Estrogen and Progesterone Required for breast development Regulation of the uterine cycle Estrogens
Stimulate the growth of the uterus and the vagina during puberty
Necessary for egg maturation Responsible for secondary sex characteristics
Female body hair Fat distribution
Other Endocrine Glands
o Thymus Gland• Most active during childhood• Transforms lymphocytes into thymus-
derived lymphocytes (T-lymphocytes)• Epithelial cells secrete hormones
called thymosinso Pineal Gland
• Located in the brain• Produces the hormone melatonin• Melatonin is involved in daily sleep-
wake cycle
Other Endocrine Glands
o Hormones from Other Tissues• Leptin
Produced by adipose tissue Signals satiety in hypothalamus
• Growth Factors – stimulate cell division and mitosis
Granulocyte and macrophage colony-stimulating factor
Platelet-derived growth factor Epidermal growth factor and nerve growth
factor Tumor angiogenesis factor
Other Endocrine Glands
• Prostaglandins Potent chemical signals Act locally Some effects of prostaglandins include:
Uterine contractions Mediate the effects of pyrogens Reduce gastric secretion Lower blood pressure Inhibit platelet aggregation
The Importance of Chemical Signals
o Cells and organs communicate with one another using chemical signals
o Chemical signals between individuals
• Called pheromones• Humans produce airborne chemicals
from a variety of areas
Effects of Aging
o Thyroid disorders• Hypothyroidism• Hyperthyroidism
o Diabetes
Homeostasis
o The endocrine system and the nervous system work together to maintain homeostasis
o The endocrine system helps regulate the following:
• Digestion• Fuel metabolism• Blood pressure and volume• Calcium balance• Response to the external environment