Chapter 10
The Endocrine System

Announcements
• Senses lab- Due Wed!
• Next Monday- Class cancellation a possibility

Lecture Outline
• Function of Endocrine system
• Hormones and their mechanisms
• Pituitary gland
• Pancreas
• Other glands

The Endocrine system

Epithelial cells can form glands
• A gland- a collection of cells which secrete a product
• Exocrine- release substances through ducts or tubes

• Hormone- a signalling chemical which is released in one part of the body and affects another part of the body
• Examples- Insulin,
Follicle stimulating hormone, testosterone

The Endocrine System
• The endocrine system communicates using chemical messages
• Hormones influence growth, development, metabolism, and behavior
• Other chemical messengers act locally

Endocrine System Communication
• Endocrine glands are made up of secretory cells that release their products called
hormones directly into the adjacent extracellular fluids where they diffuse directly into the bloodstream
• Hormones are one of the chemical messengers of the body

Endocrine System Communication
Figure 10.1

All signals require a receptor

Endocrine System
• Main function of the endocrine system is to coordinate body systems and maintain homeostasis
• The major endocrine glands are
– Pituitary
– Thyroid
– Parathyroid
– Adrenals
– Pineal

Endocrine System
Pineal gland
Melatonin
• Reduces jet lag and promotes sleep
Thymus gland
Thymopoietin, thymosin
• Promote maturation of white blood cells
Parathyroid glands
(two of four)
Parathyroid hormone (PTH)
• Increases blood levels of calcium
Adrenal gland
(one on each kidney)
Adrenal cortex
Glucocorticoids (cortisol, corticosterone,cortisone)
• Stimulate glucose synthesis and conservation
• Inhibit the inflammatory response
Mineralocorticoids (aldosterone)
• Increase sodium reabsorption by kidneys
• Increase potassium excretion by kidneys
Gonadocorticoids (androgens, estrogens)
• Insignificant effects in adulthood, relative to secretion by gonads
Adrenal medulla
Epinephrine
• Fight-or-flight response to stress
Norepinephrine
• Fight-or-flight response to stress
Heart
Kidney
Figure 10.2 (1 of 2)

Stomach
Pancreas
Glucagon
• Increases blood glucose level
Insulin
• Decreases blood glucose level
Testis
(one of a pair)
Androgens (testosterone)
• Develop male secondary sex characteristics
Endocrine System
Thyroid gland
Thyroid hormone (TH)
• Regulates metabolism and heat production
• Promotes development and function of nervous, muscular, skeletal, and reproductive systems
Calcitonin (CT)
• Decreases blood levels of calcium and phosphate
Small intestine
Uterus
(contains the placenta when pregnant)
Ovary
(one of a pair)
Estrogens and progesterone
• Develop female secondary sex characteristics
Figure 10.2 (2 of 2)

Endocrine System Communication
• Hormones circulate throughout the body until they reach target cells
– They respond to the hormone, influencing growth, development, metabolism, and behavior

Target Cells
• Target cells have receptors
– Protein molecules that recognize and bind to specific hormones
• Cells other than target cells lack the correct receptors and are unaffected by the hormone

• The mechanism by which hormones influence target cells depend on the chemical makeup of the hormones

• Two types of hormones
– Lipid-soluble
– Water-soluble

Lipid-soluble Hormones
• Lipid-soluble hormones include steroid hormones
– Derived from cholesterol
• The main organs that secrete steroid hormones are
– Ovaries
– Testes
– Adrenal glands

Step 1:
The steroid hormone diffuses through the plasma membrane of the target cell.
Steroid hormone
Extracellular fluid
Plasma membrane of target cell
(lipid bilayer)
Step 2:
The steroid hormone binds to a receptor in the cytoplasm.
Nuclear envelope
Step 7:
Enzymes alter the activity of the cell.
Cytoplasm
Receptor
Nuclear pore
Step 6:
Proteins, including enzymes, are synthesized.
Step 5:
Certain genes are activated.
Step 3:
The hormonereceptor complex enters the nucleus.
Step 4:
The hormonereceptor complex binds to DNA.
Nucleus

Functional groups can radically change the function of a molecule
Estradiol
Female lion
Testosterone
Male lion

Water-soluble hormones
• Water-soluble hormones are made of amino acids
• They cannot pass through the lipid bilayer of the plasma membrane

Water-soluble hormones
• They exert their effects indirectly by binding to receptors on the surface of the target cell
• This stimulates second messengers within the cell that carry out the effect of the hormone
• One common second messenger is cyclic adenosine monophosphate (cAMP)

Figure 10.4

• A) Lipid-soluble
• B) Steroid
• C) Water-soluble
• D) Prostaglandins

Feedback Mechanisms
• Feedback mechanisms regulate the secretion of hormones

Figure 10.18 (1 of 2)

Feedback Mechanisms
• Control is usually by a negative feedback
mechanism whereby the increased blood level of the hormone inhibits its further release

Feedback Mechanisms
• Some hormones are regulated by a positive
feedback mechanism in which the outcome of a process further stimulates the process

Positive and negative feedback systems regulate reproduction
Figure 10.5

The Pituitary gland

• Controls other glands
• Secretes many hormones that affects systems directly

Hormones
• The anterior pituitary is connected to the hypothalamus, which synthesizes and secretes
releasing and inhibiting hormones

Hormones
• The anterior pituitary gland synthesizes and secretes
– Growth hormone (GH)
– Prolactin (PRL)
– Thyroid-stimulating hormone (TSH)
– Adrenocorticotropic hormone (ACTH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)

Nerve cells in the hypothalamus produce antidiuretic hormone
(ADH) and oxytocin (OT).
ADH and OT travel to the ends of the cells in the posterior pituitary, where they are released into the bloodstream to influence target tissues.
Posterior pituitary
Anterior pituitary
Nerve cells in the hypothalamus secrete releasing hormones and inhibiting hormones.
Releasing and inhibiting hormones travel by way of the bloodstream to the anterior pituitary and cause it to modify secretion of its six hormones (FSH, LH, GH,
PRL, ACTH, and TSH).
Antidiuretic hormone (ADH)
Growth hormone (GH)
Follicle-stimulating hormone (FSH) and
Luteinizing hormone
(LH)
Oxytocin (OT)
Kidney tubules
Smooth muscle in uterus
Mammary glands
Thyroidstimulating hormone (TSH)
Thyroid gland
Prolactin (PRL)
Adrenocorticotropic hormone
(ACTH)
Mammary glands
Cortex of adrenal gland
Bones, muscles
Ovaries, testes
Figure 10.6

Human Growth Hormone
• Two hormones of the hypothalamus regulate the synthesis and release of GH
– Growth hormone-releasing hormone (GHRH) stimulates the release of GH
– Growth hormone-inhibitory hormone (GHIH) inhibits the release of GH

Human Growth Hormone
• Growth hormone (GH) stimulates an increase in cell size and the rate of cell division in target cells
• Gigantism
– Abnormally high production of GH in childhood when the bones are still capable of growing in length

Human Growth Hormone
Figure 10.7

Human Growth Hormone
• Acromegaly
– High levels of GH in adulthood when the bones can thicken but not lengthen

Human Growth Hormone

Human Growth Hormone
• Pituitary dwarfism
– Insufficient production of GH in childhood
– A genetic disorder treated with growth hormone produced by recombinant DNA

Human Growth Hormone
Figure 10.9

Prolactin
• Prolactin (PRL)
– Stimulates the mammary glands to produce milk
– Produced during lactation
• Excess may cause infertility and lactation when there is no pregnancy
• In men
– PRL is involved with the production of mature sperm in the testes
– Overproduction can lead to sterility

Tropic Hormones
• TSH, ACTH, FSH, and LH are tropic hormones
– Hormones that influence the secretion of hormones by other glands

Thyroid-Stimulating Hormone
• Thyroid-stimulating hormone (TSH)
– Acts on the thyroid gland to stimulate the synthesis and release of thyroid hormones

Adrenocorticotropic Hormone
• Adrenocorticotropic hormone (ACTH)
– Controls the synthesis and secretion of glucocorticoid hormones from the adrenal cortex

Follicle-Stimulating Hormone
• Follicle-stimulating hormone (FSH)
– Promotes development of egg cells and secretion of estrogen in females
• In males
– FSH promotes the production of sperm

Luteininzing Hormone
• Luteinizing hormone (LH)
– Causes ovulation and the secretion of estrogen and progesterone
– Prepares the uterus for implantation of a fertilized ovum and the breasts for the production of milk
• In males
– LH stimulates the production and secretion of testosterone

Posterior Pituitary
• Cells within the posterior lobe of the pituitary do not produce any hormones
– Neurons of the hypothalamus manufacture antidiuretic hormone (ADH) and oxytocin (OT)
– They travel down the nerve cells into the posterior pituitary, where they are stored and released

Posterior Pituitary
Nerve cells in the
Nerve cells in the hypothalamus produce hypothalamus secrete antidiuretic hormone releasing hormones
(ADH) and oxytocin (OT).
and inhibiting hormones.
ADH and OT travel to the ends of the cells in the posterior pituitary, where they are released into the bloodstream to influence target tissues.
Posterior pituitary
Anterior pituitary
Releasing and inhibiting hormones travel by way of the bloodstream to the anterior pituitary and cause it to modify secretion of its six hormones (FSH, LH, GH,
PRL, ACTH, and TSH).
Antidiuretic hormone (ADH)
Growth hormone (GH)
Follicle-stimulating hormone (FSH) and
Luteinizing hormone
(LH)
Oxytocin (OT)
Kidney tubules
Smooth muscle in uterus
Mammary glands
Thyroidstimulating hormone (TSH)
Thyroid gland
Prolactin (PRL)
Adrenocorticotropic hormone
(ACTH)
Mammary glands
Cortex of adrenal gland
Bones, muscles
Ovaries, testes
Figure 10.6

Posterior Pituitary Hormones
• Antidiuretic Hormone (ADH)
– Also called vasopressin
– Causes the kidneys to remove water from the fluid destined to become urine
• A deficiency of ADH results in diabetes insipidus
– Characterized by excessive urine production and dehydration

Posterior Pituitary Hormones
• Oxytocin (OT)
– Stimulates uterine contractions of childbirth and milk ejection from the mammary glands
• In men
– OT may facilitate the transport of sperm and be involved in male sexual behavior

Posterior Pituitary Hormones
Figure 10.5

Posterior Pituitary Hormones
Figure 10.10

Thyroid Gland Hormones
• Hormones secreted by the thyroid gland regulate metabolism and decrease blood calcium
– Thyroxine (T
4
) and triiodothyrinine (T
3
), collectively known as thyroid hormone (TH), regulate metabolic rate
– Calcitonin
• Decreases blood calcium

Thyroid Gland Hormones
Opening to trachea
Larynx
Thyroid gland
Parathyroid glands
Trachea
Front view Back view
(a)
The thyroid gland lies over the trachea, just below the larynx.
Figure 10.11a

Thyroid Gland Hormones
Figure 10.11b

Thyroid Gland Hormones
• Thyroid hormone (TH)
– Produced in the follicular cells
– Stimulates protein synthesis, the breakdown of lipids, and the use of glucose for the production of
ATP

Thyroid Gland Hormones
• Simple goiter
– An enlarged thyroid gland
– May be produced by a diet deficient in iodine, which is needed for the production of TH
– Can be treated by iodine supplements or administration of TH

Thyroid Gland Hormones
Figure 10.12a

Thyroid Gland Hormones
• Cretinism
– Too little TH during fetal development or infancy
– Characterized by dwarfism and delayed mental and sexual development
• Myxedema
– Too little TH in adulthood
– Causes a condition in which fluid accumulates in facial tissues and a decrease in alertness, body temperature, and heart rate

Thyroid Gland Hormones
Figure 10.12b

Thyroid Gland Hormones
• Graves’ disease
– Oversecretion of TH
– Results in an autoimmune disorder due to the production of antibodies that mimic the action of
TSH
• Symptoms include
– Increased metabolic rate and heart rate accompanied by sweating, nervousness, and weight loss
– Many also have exopthalmos

Thyroid Gland Hormones
Figure 10.12c

Thyroid Gland Hormones
• Calcitonin (CT)
– Helps regulate calcium concentration in the blood by either
• Stimulating the absorption of calcium by bone
• Increasing the excretion of calcium in the urine

Thyroid Gland Hormones
Figure 10.13

Thyroid Gland Hormones
Figure 10.13 (1 of 2)

Thyroid Gland Hormones
Figure 10.13 (2 of 2)

Parathyroid Gland Hormones
• Parathyroid glands
– Four small round masses lateral to the thyroid gland
– Secrete parathyroid hormone (PTH), or
parathormone, which increases the blood calcium level

Parathyroid Gland Hormones
• PTH
– Stimulates
• Osteoclasts to break down bone-releasing calcium into the blood
• Removal of calcium from the urine, returning it to the blood
• Rate calcium is absorbed from the gastrointestinal tract
– Inhibits
• Osteoblasts

Parathyroid Gland Hormones
• Undersecretion of PTH
– Can result in nervousness and muscle spasms
• Oversecretion
– Pulls calcium from bone tissue, causing weakened bones and elevated blood calcium levels
• Might lead to kidney stones, calcium deposits in the soft tissue, and decreased activity of the nervous system

Adrenal Gland Hormones
• The adrenal glands
– Located at the top of the kidneys
– Composed of two regions
• Adrenal cortex
• Adrenal medulla

Adrenal Gland Hormones
• The adrenal cortex (outer region) secretes
– Gonadocorticoids
– Glucocorticoids
– Mineralcorticoids
• The adrenal medulla (inner region) secretes
– Epinephrine (adrenaline)
– Norepinephrine (noradrenaline)

Adrenal Gland Hormones
Figure 10.14a

Adrenal Gland Hormones gland • Mineralocorticoids
• Gonadocorticoids
• Glucocorticoids
Adrenal medulla
• Epinephrine
• Norepinephrine
(b)
A section through the adrenal gland reveals two regions, the outer adrenal cortex and the inner adrenal medulla. These regions secrete different hormones.
Figure 10.14b

Adrenal Gland Hormones
• Gonadocorticoids
– Androgens and estrogens
– Secreted by the adrenal cortex in both males and females

Adrenal Gland Hormones
• Mineralocorticoids
– Affect mineral homeostasis and water balance
• Aldosterone
– Acts on cells of the kidneys to
• Increase reabsorption of sodium ions into the blood
• Promote the excretion of potassium ions in the urine

Adrenal Gland Hormones
• Addison’s disease
– Caused by the undersecretion of cortisol and aldosterone
– Appears to be an autoimmune disorder in which the cells of the adrenal cortex are perceived as foreign
– Results in bronzing of the skin, weight loss, fatigue, electrolyte imbalance, poor appetite, and resistance to stress
– May be caused by inadequate secretion of ACTH

Adrenal Gland Hormones
Figure 10.15

Adrenal Gland Hormones
• Glucocorticoids
– Affect glucose homeostasis
– Act on the liver to promote the conversion of fat and protein into intermediate substances available to the body’s cells
– Inhibit the inflammatory response

Adrenal Gland Hormones
• Cushing’s syndrome
– May be caused by the oversecretion of glucocorticoids or a tumor on either the adrenal cortex or anterior pituitary
– Results in redistribution of body fat and accumulation of fluid in the face, fatigue, high blood pressure, and elevated glucose levels

Adrenal Gland Hormones
Figure 10.16

Adrenal Gland Hormones
• The adrenal medulla
– Produces epinephrine (adrenaline) and
norepinephrine (noradrenaline)
– Both of these hormones are used in our response to danger, preparing us for fight-or-flight

Pancreas Gland Hormones
• Hormones of the pancreas
– Secreted from the pancreatic islets
– Regulate blood glucose levels through glucagon and insulin

Pancreas Gland Hormones
Stomach
Common bile duct
(from gallbladder and liver)
Pancreas
Pancreatic duct
Duodenum
(first part of small intestine)
(a)
Structure of the pancreas and associated ducts. Exocrine cells of the pancreas secrete digestive enzymes into the pancreatic duct, which unites with the common bile duct before entering the small intestine.
Figure 10.17a

Pancreas Gland Hormones
Figure 10.17b

Pancreas Gland Hormones
• Glucagon
– Increases glucose in the blood by converting glycogen to glucose in the liver

Pancreas Gland Hormones
Figure 10.18 (2 of 2)

Pancreas Gland Hormones
• Insulin
– Decreases blood glucose levels
– Stimulates transport of glucose into muscle cells, white blood cells, and connective tissue cells
– Inhibits the breakdown of glycogen to glucose
– Prevents conversion of amino and fatty acids into glucose

Pancreas Gland Hormones
• Diabetes mellitus
– A group of metabolic disorders characterized by an abnormally high level of glucose in the blood

Pancreas Gland Hormones
• Type 1 diabetes mellitus
– Usually develops in people younger than 25 years of age
– An autoimmune disease
– A person’s own immune system attacks the cells of the pancreas responsible for insulin production

Pancreas Gland Hormones
• Type 2 diabetes mellitus
– Usually develops after age 40, but has begun showing up in younger people recently
– Characterized by a decreased sensitivity to insulin
(insulin resistance)

Thymus Gland Hormones
• Thymus gland
– Secretes hormones, such as thymopoietin and
thymosin, which are involved in the maturation of
T lymphocytes
– These hormones and the thymus gland play a very important role in immunity

Pineal Gland Hormones
• The pineal gland
– Contains secretory cells that produce melatonin
– Levels of circulating melatonin are greater at night than during daylight hours
• Due to the input the pineal gland receives from the visual pathways

Skull
Pituitary gland
Figure 10.19

Pineal Gland Hormones
• Melatonin is linked to sleep, fertility, and aging
• Too much melatonin can result in seasonal
affective disorder (SAD), which is associated with winter
• Treatment includes repeated exposure to very bright light

Pineal Gland Hormones
PLAY Animation —The Hypothalamus and the Pituitary

Other Chemicals Act Locally
• Local signaling molecules act very quickly on adjacent cells
– Neurotransmitters
– Growth factors
– Nitric oxide (NO)
– Prostaglandins

Other Chemicals Act Locally
• Prostaglandins
– Lipid molecules continually released by the plasma membranes of most cells
– At least 16 different prostaglandin molecules function within the human body

Other Chemicals Act Locally
• Although they act locally, prostaglandins can have very diverse effects including
– Actions on the reproductive system
– Fertility
– Blood clotting
– Body temperature

Hormonal Response to Stress
• General adaptation syndrome (GAS)
– A series of physiological adjustments made by our bodies in response to extreme stress
– Has three phases
• Alarm
• Resistance
• Exhaustion

Hormonal Response to Stress
• Alarm
– Fight-or-flight response
• Resistance
– Glucocorticoids from adrenal cortex are the main hormones
– Body’s protein and fat reserves mobilized
– Body fluids conserved
• Exhaustion
– Organs are unable to meet the heavy demands of the resistance phase, and they begin to fail

PLAY
Hormonal Response to Stress
| Fighting Stress