The Endocrine System:the human body system that is responsible for our

raging teenage hormones and homeostasis

Jasmine Han, Inam Sakinah, & Kirstin Nygaard

The Endocrine System: Overview

The overall goal of this body system is to maintain homeostasis.• Hormones are chemicals released by one or more cells that

affects cells in other parts of the organism. They assist by carrying messages through the bloodstream to target cells throughout the bloodstream.

• These hormones have different jobs, such as: growth & development, reproduction; they also regulate things like metabolism, biological clock, extracellular fluids , and glandular secretion.

• Although this system is slower than the nervous system's communication systems, hormones have a powerful influence on the body.

Where is the Endocrine System? The Pituitary Gland is

considered the MASTER GLAND since it controls the

other glands.

GLANDS & HORMONES

Pineal Gland

• Stimulated by nerves in the eyes• Produces melatonin at night• Melatonin – involved in circadian rhythm.

Levels rise at night (makes you sleepy) and drop in the morning (wakes you up)– Affects reproductive functions in the gonads– Affects thyroid and adrenal cortex functions

Hypothalamic-pituitary axis

• Forms two distinct systems – the hypothalamus and the pituitary gland

• The axis is the functional interaction between these two systems

Hypothalamus

• Maintains the body’s internal environment by regulating the autonomic nervous system, endocrine system, body temperature, water balance, and appetite

• The neurons in the hypothalamus influence the two sections of the pituitary gland

• Neurosecretory cells produce and release hormones into the bloodstream

Hypothalamus hormones

• Growth-hormone-releasing hormone– Stimulates the synthesis and release of growth hormone (GH)

• Corticotropin-releasing hormone (CRH)– Secreted in response to stress

• Thyroid-releasing hormone– Stimulates the release of thyrotropin (TSH)

• Gonadotropin-releasing hormone (GnRH)• Stimulates the release of Follicle-stimulating hormone

(FSH) and Luteinizing hormone (LH)• Antidiuretic hormone (ADH)• Oxytocin

Pituitary Gland

• Located below the hypothalamus• Secretes growth hormones• 1930 experiment– Biologists removed the pituitary gland from rats– The rats stopped growing, couldn’t maintain a normal

body temperature, and their genitals, thyroid glands, and adrenal cortexes shrunk

– Suggests that the pituitary gland secretes hormones that regulates the production of other hormones

• Two types – posterior and anterior

Posterior pituitary

• Extension of the brain• Stores antidiuretic hormones (ADH) and

oxytocin which are produced from the neurosecretory cells in the hypothalamus

Antidiuretic Hormone• Released when someone is dehydrated (prevents you from peeing)• Helps the kidneys reabsorb water• Triggers the insertion of aquaporins into the apical membrane -> cells

become more permeable to water -> large amounts of water are reabsorbed

• Increases permeability to urea -> increases osmolarity of surrounding fluid -> water loss from the filtrate

• Defective forms of ADH produces an abundance of urine. May suffer from diabetes insipidus

• Negative feedback –Maintains stable conditions and homeostasis– The effect of the hormone causes the hormone to not be released

Oxytocin

• Causes uterine contractions during childbirth and milk release when a baby is being nursed

• More contractions -> more nerve impulses to the hypothalamus -> release of oxytocin

• Positive feedback – the stimulus brings about an effect

• Stimulates affiliative behaviors in both sexes

Anterior pituitary

• Develops from cells in an embryo’s mouth and throat lining (not directly connected to the hypothalamus)

• Neurosecretory cells secrete stimulatory or inhibitory signals into blood vessels. The signals are carried to the anterior pituitary -> the anterior pituitary alters the secretion of hormones that enter the bloodstream and act on target tissues or glands

• Hormones produced stimulate the production of other hormones

Anterior Pituitary Hormones Affecting Other Glands

• Adrenocorticotropic hormone (ACTH)– When injected into humans, cortisol levels in their blood rises

• Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)– Involved in producing sex hormones and regulating the

menstrual cycle

• Thyroid-stimulating hormone (TSH)– Triggers the production of thyroid hormones

• Gonadotropic hormones– Stimulates the testes and ovaries to produce gametes and sex

hormones

Anterior Pituitary HormonesNot Affecting Other Glands

• Growth hormone (GH)– Promotes lengthening of the long bones in children and

muscle growth, tissue repair, and lactation in adults

• Prolactin– Stimulates mammary gland growth and milk production

• Melanocyte-stimulating hormone (MSH)– Skin-color changes in fish, amphibians, and reptiles

Parathyroid Glands

• Embedded in the thyroid gland• Can be as small as a grain of rice or as big as a

pea• Control how much calcium there is in our

bones and blood• Releases the parathyroid hormone (PTH) to

increase the calcium levels in the blood

Thyroid Gland

• Located in the neck• Releases thyroid hormone and calcitonin• Thyroid hormone – increases metabolic rate• Calcitonin – lowers blood calcium• Two distinct lobes• Follicles filled with triiodothyronine (T3) and

thyroxine (T4)

T3 and T4

• Increases cellular metabolism• In mammals, T3 has a stronger effect than T4

• In mammals, T4 is converted to T3 in the liver

• T4 increases metabolic rate and heart rate. It also promotes growth

• In amphibians, T3 is responsible for most of the changes that occur in metamorphosis

Adrenal Glands• Two small glands that sit on top of

the kidneys. The cortex (outer portion) secretes steroid hormones. The medulla (inner portion) secretes epinephrine and norepinephrine.

Catecholamines

• Small compounds derived from tyrosine (an amino acid) that are used as hormones or neurotransmitters

• Includes epinephrine, norepinephrine, and dopamine

Epinephrine (Adrenaline)• Released when the adrenal medulla is stimulated by action

potentials from your sympathetic nerves• Released during the fight-or-flight response (short term response

to stress)• When humans are injected with epinephrine, there is an increase

in the concentration of free fatty acids and glucose in the blood, pulse rate, blood pressure, and oxygen consumption by the brain and they feel anxiety and excitement

• Redirects blood away from the skin and digestive system and toward the heart, muscles, and brain

• Relaxes smooth muscles -> opens blood vessels -> increases blood delivery to target tissues

Norepinephrine

• Stress hormone• Produced in the adrenal medulla• Released directly onto target cells• Affects the brain (parts where attention and

responding actions are controlled)• Fight-or-flight– Increases heart rate -> triggers the release of

glucose -> more blood to skeletal muscles

Pancreas• Thin organ that is located in the abdomen• Two types of tissue – exocrine and endocrine• Exocrine tissue produces digestive juices which are sent to the small intestines• Endocrine tissue (pancreatic islets) produces and secrete insulin and glucagon

directly into the blood• Pancreatic islets – groups of pancreatic cells (3 types)

– Alpha cells secrete glucagon– Beta cells secrete insulin– Delta cells secrete somatostatin

• Insulin – secreted when there is too much glucose in the blood. Insulin tells the liver to take the extra glucose out of circulation. Regulates blood sugar

• Glucagon – secreted in response to low blood sugar. Forces cells to produce or release glucose. Regulates blood sugar

• Somatostatin – inhibits the release of glucagon and insulin. Helps with carb metabolism

Glands• Endocrine– Secrete products into the bloodstream (instead of

ducts) -> delivered to the rest of the body– Only target cells can respond to certain hormones

• Exocrine– Secretes substances through a duct into a space

Gonads

• Primary function is to produce gametes (a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote)

• Gender specific– Females have ovaries– Males have testes

Ovaries

• Located on both sides of the uterus below the openings of the fallopian tubes

• Secrete sex hormones• Produce estrogen and progesterone• Estrogen – helps maintain sexual organs and

secondary sex characteristics. Necessary for egg maturation

• Progesterone – secreted after ovulation. Causes the uterine lining to thicken

Testes

• Secrete sex hormones• Located outside of the body in the scrotum• Produce androgens (e.g. testosterone)• Testosterone – stimulates sperm production

and reproductive behaviors– Causes the development of male characteristics

such as facial hair, deepening of the voice, and the growth spurt that takes place during puberty

Communication in Endocrine System

Secreted Signaling Molecules

• Stimulate responses by binding to receptors on target cells

• Endocrine Cells secrete hormones into extracellular fluids– Reach target cells through bloodstream (hemolymph)

• Can exist within organs from organ systems or in endocrine glands (ductless organs)

– Travel to all parts of the body• Local Regulators act over short distances and reach

target cells by diffusion– Paracrine signaling – target cells are close to secreting cell– Autocrine signaling – regulators act on secreting cell

Secreted Signaling Molecules

• Neurohormones are secreted by neurosecretory cells through diffusion from nerve cells into bloodstream– Called neuroendocrine signaling– Example: ADH involved in water balance and

kidney function• Pheromones NOT classified as hormones– Communication that occurs in external

environment between other animals

Secreted Signaling Molecules

• Hormones classified into 4 categories or chemical groups– Peptide and Proteins (Polypeptide)

• Derived from long protein chains

– Steroids• Derived from cholesterol

– Amines• Derived from single amino acid

– Eicosanoids• Derived from fatty acids

• Divided based on structure and synthesis process– Thus, vary in solubility and therefore, cellular response

pathways

CELLULAR RESPONSE PATHWAYSRefers to how binding of hormones to certain receptors causes changes in cytoplasmic molecules , amplifies signaling, and can sometimes alter gene transcription

Water-Soluble Hormones

• Water-Soluble Hormones secreted by exocytosis– Bind to receptors on cell surface– Travel solo in blood stream

• Pathway– Binding stimulates cellular response through signal

transduction• Converts extracellular chemical signal to an intracellular

response• Occurs through a series of molecular interactions

Example

Stress triggers Adrenal gland to secrete

epinephrine

Epinephrine arrives at liver cell and binds to G

protein-coupled receptor

kinase A activates an enzyme that stimulates

glycogen breakdown and an enzyme that

inhibits glycogen synthesis

cAMP activates protein kinase A

Triggers cascade of molecular

interactions resulting in synthesis

of cyclic AMP (second messenger)

Lipid-Soluble Hormones

• Lipid-soluble hormones are secreted through diffusion– Bind to receptors within cell (intracellular)– Travel in blood stream connected to transport

protein• Pathway– Receptor transduces signal within cell• No intermediate molecular interactions like signal

transduction

• Steroid hormone receptors exist in cytosol before binding– Hormone-receptor complex forms – Receptor interacts with DNA directly or via DNA

binding protein• Allows for gene expression by activating specific genes

• Non-Steroid hormone receptors present in nucleus– Receptor binds to specific locations on DNA to

stimulate gene transcription

Hormone Effects

• Type of receptor and cell location = integral to chemical responses produced by a single hormone

• Different effects allow body to have more effective and intense reactions during emergencies.

• Specialized based on species– Ex: frog

Local Regulators

• Act on target cells (neighboring cells or secreting cells) quicker than hormones despite following similar pathways

• Prostaglandins– Produced by many cell types– Have different effects

• Control of blood pressure• Dilation and constriction of blood vessels• Contraction and relaxation of smooth muscles

• Other Examples: cytokines, growth factors, and nitric oxide

Types of FeedbackPositive Feedback

•  Positive feedback occurs when the rate of a process increases as the concentration of the product increases. It is not a way to maintain stable conditions and homeostasis.

Example: Oxytocin

Negative Feedback• Negative feedback occurs

when the rate of the process decreases as the concentration of the product increases. It controls the rate of a process to avoid accumulation of a product.

Example: Insulin

Negative Feedback

• Process of response limiting the initial stimulus– Results in turning off hormone pathway

• Final and essential step in simple hormone pathways– Prevents excessive pathway activity • MAINTAINS HOMEOSTASIS

Negative Feedback Example• Oxytocin regulation of milk during nursing– Nuerohormone pathway:• 1) Baby suckling stimulates sensory neurons in nipples to

send signals to hypothalamus• 2) Triggers neurosecretory cell (posterior pituitary gland)

to secrete neurohormone (oxytocin)• 3) Oxytocin diffuses and travels to smooth muscles in

breasts prompting milk release• 4) Leads to more suckling increasing release

– Response increasing stimulus = positive feedback– Baby stops suckling and pathway shuts off = negative feedback

– Example of animal responding to environmental changes

Biorhythms and Melatonin

• Melatonin secretion by pineal gland allows for regulation of functions connected to seasons or light– Main target for melatonin = suprchiasmatic

nucleus (biological clock)• Decreases SCN activity

– Amount of secretion depends on length of night• Demonstrates influence of external environment on

hormone behavior

ADH

• ADH pathway responds to changes in internal environment– Osmoreceptors help regulate water balance in

body

Insulin and Glucagon

• Example of a twin hormone pathway– Pathways counterbalance each other

• Optimal blood glucose concentration = 90 mg/100 mL– When glucose concentration rises above this set

point, insulin is released• Stimulates all body cells outside brain to uptake of glucose• Slows glycogen breakdown in liver• Prevents conversion of amino acids and glycerol to glucose

– Decreases glucose concentration

Insulin and Glucagon

–When glucose concentration drops below set point, glucagon is released• Prompts liver cells to increase glycogen

hydrolysis• Converts amino acids and glycerol to

glucose• Releases glucose into bloodstream–Increases glucose concentration

• Production of located in pancreas in endocrine cell clusters called islets of Langerhans– Glucagon produced by alpha cells– Insulin produced by beta cells

• Target cells = liver– Liver involved in accepting nutrients from small

intestine• Opposing effect of glucagon and insulin within liver

allow for control of fuel (glucose) storage and consumption– Retains homeostasis

Alpha Cells: secrete

glucagon

Beta Cells: secrete insulin

ENDOCRINE SYSTEM DISORDERS

Endocrine Disorders: consequences of malfunction

These disorders develop due to: • Disruptions in the hormone levels that are caused by

feedback systems. A hormone imbalance occurs when the negative feedback system fails to maintain stable conditions and homeostasis.

• Failure of certain glands to stimulate other glands in order to release hormones or release too much of the hormone.

• Injury or tumors found in any of the endocrine glands. Some of these disorders are Autoimmune disorders (or autoimmune related), meaning that the immune system mistakenly attacks and destroys healthy body tissue.

Adrenal insufficiency:Addison Disease

• Occurs when the Adrenal cortex secretes low levels of aldosterone into the bloodstream.– Lack of aldosterone in the blood causes low levels

of sodium and water, potentially leading to low blood pressure• Severe dehydration can also occur.

• ACTH is built up and is ineffective causing one's skin to bronze, leading to a buildup of melanin.

Autoimmune Disorder

Cushing Syndrome• Adrenal cortex secretes an excess

amount of cortisol. – An excess of aldosterone and

reabsorption of sodium and water by the kidneys • Hgh blood pressure and a basic

pH blood level. • Obesity of the midsection occurs due

to muscle protein being metabolized and fat being deposited there.

• Diabetes mellitus can also occur.

Thyroid gland control• The hypothalamus secretes TRH to stimulate the

anterior pituitary gland, causing that gland to secrete TSH (or thyrotropin). TRH then stimulates the thyroid gland to release the hormone thyroxine.

• Thyroxine targets the hypothalamus and the anterior pituitary gland causing NEGATIVE FEEDBACK INHIBITION to occur, inhibiting the secretion of TRH and TSH.

• The negative feedback keeps thyroxine levels constant.• Thyroxine has four iodine molecules attached to its

molecular structure

But hey, why is this kind of important?

• Remember the iodine? Without iodine the thyroid gland cannot produce thyroxine.

• The lack of thyroxine causes the hypothalamus and anterior pituitary to receive little negative feedback inhibition, thus causing high secretion levels of TRH and TSH.

• High levels of TSH causes the thyroid to ENLARGE, creating a goiter.

What is suppose to happen

THIS IS WHY WE HAVE HAVE IODINE IN OUR TABLE SALT. Goiter size can be reduced if iodine is provided in one's diet.

Even Disney knows what a goiter is.

Goiters can get pretty large.

Graves' Disease• A disorder in which the immune system attacks the

thyroid gland, causing it to produce too much thyroxine (T4).

• It is a form and/or cause of hyperthyroidism, a condition in which the thyroid gland produces excessive hormones.

• Exophthalmos or bulging of the eyes also is a sign of Graves' disease. GOITERS, weight loss, and irregular heartbeat are also a few signs of this disease.

Autoimmune Disorder

Growth Hormone EffectsWhich is controlled by the pituitary gland of course!

Pituitary gigantism is caused by the excessive secretion of GH (growth

hormone) during childhood.

Tumors in the pituitary gland can cause gigantism and

dwarfism.

Arcomegaly is a form of gigantism that occurs when there's excessive secretion of GH in ADULTHOOD. In this form, people have

protruding jaws, elongated fingers, and thickening of

the skin.

Pituitary dwarfism is the opposite of gigantism: a

deficiency in GH secretion during childhood causes it.

Diabetes Mellitus: Type I • A virus causes the cytotoxic T cells

(a type of white blood cell that would kill damaged or infected cells) to destroy pancreatic islets, which produce and secrete insulin and glucagon into the bloodstream.

• β cells do not produce enough insulin or none at all.

• The treatment for this type are insulin injections that can control glucose levels.

• Onset is early, found usually in childhood. This type is not as common as Type II.

Diabetes Mellitus: Type II• Type II Diabetes occurs

when not enough insulin is produced by the body for it to function properly, or when the body’s cells do not react to insulin. This is called insulin resistance.

• Patients with this generally have normal or even high levels of insulin in their blood, but their cells have a reduced sensitivity to it.

• Can lead to other health problems such as kidney disease and heart disease.