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


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


• Oxytocin Causes uterine contraction during

childbirth Causes milk letdown when a baby is

nursing Release of oxytocin is controlled by

positive feedback


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)


• 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


• Simple goiter Caused by a lack of

iodine Thyroid enlarges in

response to constant stimulation by the anterior pituitary


• 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


• 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


• Calcitonin Helps control blood calcium levels Secreted when the blood calcium levels

rise Brings about the deposit of calcium in the

bones


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


• 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


• 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


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


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


• 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

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