Chapter 45: The Endocrine System

By: Grace Maxwell and Tegan Ayers

What is the Endocrine System?

• All of an organism’s hormone-secreting cells

• Major regulatory system that consists of various glands (called endocrine glands) throughout the body

• These glands secrete chemicals called hormones, which regulate processes such as mood, growth and development, tissue function, metabolism, and sexual function

Hormones

• Secreted by the endocrine glands into the extracellular fluid

• Carried by the circulatory system (in blood or hemolymph)

• Communicate regulatory messages within the body

• Regulatory messages travel to target cells to stimulate a response

Hormones (cont.)

• Only the specific target cells will respond to each secreted hormone Other cells are unaffected

• Create slow, but long-lasting responses Ex. stress, dehydration, low glucose

levels• Regulate long-term development

Ex. reproductive system development

Hormones (cont.)

• Can be classified as proteins/peptides, amines, and steroids Proteins/Peptides: water-soluble Amines: water-soluble Steroids: not water-soluble

Hormonal Control Pathways

• A receptor protein detects a stimulus and sends information to a control center

• Control center compares incoming signals to a set point (desired value)

• The control center sends out an efferent signal (hormone or neurohormone) which directs an effector to respond Induces specific physiological changes

Hormonal Control Pathways (cont.)

• 3 simple hormonal control pathways: Simple Endocrine

Pathway Simple

Neurohormone Pathway

Simple Neuroendocrine Pathway

• Most pathways operate on a negative feedback loop

Inducing a Response: Signal Transduction Pathway

• Reception: Signal molecule binds to receptor

protein in or on a target cell Each signal molecule has a specific

shape that is recognized by the target cell receptors

• Signal Transduction Series of changes in cellular proteins

triggered by the binding of a signal molecule to a target cell receptor protein

Inducing a Response: Signal Transduction Pathway (cont.)

• Response A change in the cell’s behavior such as

the activation of an enzyme, change in the uptake or secretion of certain molecules, or rearrangement of the cytoskeleton

Review of Hormonal Signaling• Hormone receptors

can be located either inside or outside the plasma membrane Water-soluble

hormones bind to receptors in the plasma membrane

Lipid-soluble hormones bind to intracellular receptors and stimulate transcription of specific genes

Paracrine Signaling• Similar to hormonal signaling• Passage of messages between

neighboring cells by local regulators (do not use hormones) Causes a quicker response

• Common local regulators include: Cytokines, growth factors, nitric oxide,

prostaglandins• Major purpose is to help the body

maintain homeostasis

Major Endocrine Glands in Humans

Hypothalamus

• Location: Base of the brain

• Function Overview: Receives information from nerves and

initiates appropriate endocrine signals Directs activity of the posterior pituitary

gland Regulates body temperature, breathing,

sleep, hunger, thirst, excretion, sex drives, and emotions

http://neurosurgery.ucla.edu/images/Pituitary%20Program/pituitary_gland_illust_tumor.jpg

Hypothalamus (Hormones)

• Vasopressin: Reduces water loss in the kidneys

• Oxytocin: Regulates birth processes and milk

production• Somatostatin:

Slows secretion of growth hormone

Pituitary “Master” Gland

• Location: Underneath the hypothalamus, near the

center of the skull• Function Overview:

Controls activity of various other glands (adrenal, thyroids, gonads)

Posterior Pituitary (Hormones)

• Vasopressin: Reduces water loss in the kidneys

• Oxytocin: Regulates birth processes and milk

production

Anterior Pituitary (Hormones)

• Growth Hormone: Stimulates bone growth and metabolic

functions• Prolactin (PRL)

Stimulates milk production and excretion

• Follicle-Stimulating Hormone (FSH) Stimulates production of ova/sperm

• Luteinizing Hormone (LH) Stimulates ovaries/testes

Anterior Pituitary (Hormones)

• Thyroid-Stimulating Hormone (TSH) Stimulates the thyroid glands

• Adrenocorticotropic Hormone (ACTH) Stimulates adrenal cortex

• Melanocyte-Stimulting Hormone (MSH) In mammals, is thought to inhibit hunger

Thyroid Gland• Location:

Front of the neck (below the voice box), ventral surface of the trachea

• Function Overview: Crucial role in development and

maturation Helps regulate homeostatic functions

and metabolism

http://www.natural-supplements-guide.com/images/thyroid_gland.gif

Thyroid (Hormones)

• Triiodothyronine (T3)/Thyroxin (T4): Help maintain metabolic processes Humans mostly produce T4 , however, 1

iodine atom is subsequently removed and T3 brings about a target cell response

• Calcitonin Lowers blood calcium levels

Parathyroid Glands• Location:

Embedded in the surface of the thyroid• Function Overview:

Regulation of bone growth and function Muscle/nerve function Maintenance of calcium levels in the

body

http://uvahealth.com/Plone/ebsco_images/7709.jpg

Parathyroid (Hormones)

• Parathyroid Hormone: Raises blood levels of Ca2+ by converting

Vitamin D to its active hormonal form

Pancreas• Location:

Intertwined with the small intestine• Function Overview:

Regulation of glucose in the blood Digestion

http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/image_article_collections/anatomy_pages/Pancreas2.jpg

Pancreas (Hormones)

• Insulin (produced by beta cells): Slows glycogen breakdown in the liver,

lowering blood glucose levels• Glucagon:

Raises blood glucose levels

Adrenal Glands

• Location: One on top of each kidney

• Function Overview: Responses to stress

http://www.nichd.nih.gov/health/topics/images/adrenal_gland.jpg

Adrenal Medulla (Hormones)

Epinephrine/Norepinephrine: Activate fight-or-flight response to stress Raise glucose levels, metabolic

activities, heart rate, and blood pressure

Adrenal Cortex (Hormones)

• Glucocorticoids: Raise blood glucose levels

• Mineralicorticoids: Reabsorb Na+ and excretion of K+ in

kidneys to maintain homeostasis

Gonads

• Location: Testes of males Ovaries of females

• Function Overview: Stimulate growth and development Regulate reproductive cycles and sexual

behavior

Testes (Hormones)

• Androgens: Regulate sperm formation and male sex

characteristics

Ovaries (Hormones)

• Estrogens: Stimulate uterine lining growth and

female sex characteristics• Progesterone:

Stimulates uterine lining growth

Pineal Gland• Location:

Near the center of the brain• General Function:

Regulation of Circadian Rhythms

http://healinghaven.typepad.com/photos/fillmores_12_power/pineal-drawing.jpg

Pineal (Hormones)

• Melatonin: Involved in the regulation of biological

rhythms

Interdependence Between Body Systems

Hormones help to regulate: normal blood pressure, heart rate, muscle tone, digestion, reproductive functions, etc. Therefore, the Endocrine system helps to regulate nearly all other body systems.

Interdependence Between Body Systems

Circulatory System When a hormone is secreted, it is carried

through the circulatory system until it reaches the target cell.

Nervous System The hypothalamus receives information from

nerves throughout the body and then produces an endocrine response.

Ex. Nerve signals send information about the change in weather which triggers the release of reproductive hormones in certain organisms.

Diseases/Disorders - Cretinism

Causes:- Inherited condition of thyroid deficiency

Symptoms:- Slowed skeletal growth, poor mental development- Protruding tongue, choking episodes, constipation and jaundice.

Treatment:- Symptoms can be prevented if treated early in life with the hormone, thyroxine.

Graves’ Disease

Causes:- The Immune system produces antibodies which mimic Thyroid-Stimulating Hormone (TSH) and causes hyperthyroidism (overproduction of thyroid hormones)- Thought to be triggered by genetics or environmental factors

Symptoms:- Protruding eyes, profuse sweating, weight loss, high blood pressure, development of a goiter, change in menstrual cycle.

Graves’ Disease Con’t

Treatment:- Stopping the thyroid’s ability to produce hormones- This can be done through taking radioactive iodine which will destroy cells in the thyroid gland.- Beta-blockers can help treat some effects of Graves’ disease

Diabetes Mellitus

Type I Causes:- The Immune System destroys beta cells in the pancreas which causes an insulin deficiency.- Appears during childhood.

Symptoms: - Dehydration, fatigue, blurry eyesight, weight loss, urinating more often

Treatment:- Insulin injections

Diabetes Mellitus Type II Causes:

- Reduced responsiveness of target cells due to change in insulin receptors.- Due to lack of exercise and poor diet. Can be hereditary.

Symptoms:- Dehydration, bladder, skin or kidney infections, damage to blood vessels and nerves can cause heart attack or stroke.

Treatment:- Healthy diet and exercise, some require drug therapy.

Themes of AP Bio: Regulation

Negative Feedback Reactions Connect response to initial stimulus Prevents system overreaction and

maintains homeostasis Response reduces initial stimulus

Positive Feedback Reactions Response increases initial stimulus

leading to even greater response

Science/Technology/Society

Synthetic Hormone Treatments allow people who lack certain hormones to lead a more normal lifestyle Ex. Growth hormone treatments have

allowed hundreds of children with pituitary dwarfism to reach a normal height

Abuses: steroid treatments have been used by athletes to increase muscle size and improve performance

Works Cited

Campbell, Neil A. and Jane B. Reece. AP Edition Biology. San Francisco: Pearson Education, 2005. Print.

“Cretinism – Symptoms, Causes, Treatment of Cretinism.” Health Issues. Health-Issues.org. 2012. Web. 26 April 2012.

“Type I Diabetes.” MedlinePlus. US National Library of Medicine. 2012. Web. 26 April 2012.

“Type II Diabetes.” MedlinePlus. US National Library of Medicine. 2012. Web. 26 April 2012

“Understanding Graves’ Disease.” WebMD. WebMD, LLC. 2012. Web. 26 April 2012.