Endocrine System

SBI4U

Endocrine System

Regulation of Body Temperature

Regulation of Body’s H2O

Content

Regulation of Serum Glucose

Levels

Regulation Ca++

MetabolismRegulation of

Rate of Metabolism

Hormones steroids

peptides(proteins)

prostaglandins

catecholamines

“little ones”

“big ones”

“really big ones”

anteriorpituitary

hypothalamus

posterior pituitary

somatostatin

uterus

breast

kidney

adrenal cortex

adrenal medulla

liver

beta cellsin pancreas

alpha cellsin pancreasbody cells

& musclesblood

ovaries

testes

gut

bones

parathyroid

thyroid

oxytocin

prolactin

oxytocin

ADHHGH (somatotropin)

FSH & LH

FSH & LH

TSH

ACTH

T3 &

T4

calcitonin

PTH

catecholamines

peptides

protein

insulin

glucacon

epinephrine & norepinephrine

epinephrine & norepinephrine

steroids

glucocorticoids

aldosterone

estrogen

testosterone

estrogen & progesterone

glycoproteins

Hormone Interactions in the Human Body

Negative feedback regulates the secretion of the thyroid hormones T3 & T4.

• The hypothalamus secretes TRH which stimulates the anterior pituitary to secrete TSH.

• TSH stimulates the thyroid to synthesize and release T3 and T4.

• Elevated levels of T3 and T4 inhibit TRH secretion

Serum Ca2+ levels are regulated by negative feedback of two antagonistic hormones calcitonin and parathyroid hormone

Serum glucose levels are regulated by negative feedback of two antagonistic hormones glucagon and insulin.

Hormones are chemical messengers that…

are secreted directly into the blood stream

are produced by a specialized gland or a group of cells in minute quantities

effect body parts removed from the source

effect a response in specific target cells

blood stream

target cell

endocrine cell

Hormones signal cells at a distance

Hormones are secreted into the blood stream and reach virtually every cell in the body.

Only cells sensitive to the presence of the hormone respond.

Hormones belong to one of 4 groups

1. Catecholamines are modifications of the amino acid tyrosine.

2. Peptide hormones are polypeptide chains of various size ranging from little ones, big ones, &

really big ones.3. Steroid hormones are either produced by the sex

organs (the sex hormones) or the adrenal cortex (corticosteroids).

4. Prostaglandins are a diverse group of modified fatty acids that are secreted by almost all tissues.

1) The four common catecholamines are derived from the amino acid tyrosine.

CC

NOH

OH

OH

H

H

CH3H

H

epinephrine C

OCHCH2

NH2OH

OH

tyrosine

CC

NOH

OH

OH

H

H

HH

H

norepinephrine

OOH

I

I

I

I

CH2 C C

OH

OH

NH2

thyroxine (T4)

OOH

I I

CH2 C C

OH

OH

NH2

I

tri-iodothyronine (T3)

2) The peptide hormones are amino acid chains of various lengths

met enkephalin: tyr-gly-gly-phe-met

leu enkaphalin: tyr-gly-gly-phe-leu

Three Examples of “little ones”:

• Enkephalins are pentapeptides consisting of the 5 amino acids.

• Enkephalins are the body’s natural pain killers:

The primary structures of oxytocin and vasopressin: two nonapeptides.

Oxytocincysteinetyrosine

isoleucineglutamine

asparganinecysteineprolineleucineglycine

Vasopressin (ADH)cysteinetyrosine

phenylalanineglutamine

asparaginecysteineproline

arginineglycine

Four Examples of Peptide Hormones that are “Big Ones”

• Endorphins are natural pain killers having 30 amino acids.

• Glucagon is a hyperglycemic having 29 amino acids.

• Insulin is a hypoglycemic with 51 amino acids in two polypeptide chains.

• Parathormone elevates serum Ca+2 has 84 amino acids.

Examples of “Really Big” peptide hormones

• Human growth hormone (HGH) is a protein having 191 amino acids and a molar mass of 22 124 g.

• Prolactin is a polypeptide with a molar mass around 24 000 g.

3. The Steroid Hormones

Since the steroid hormones are derived from cholesterol, they have structural formulas similar to cholesterol.

OH

CH3

CH3CH3

CH3

CH3

The three steroid sex hormones

OH

CH3OH

estrogen (estradiol)O

CH3

CH3

CH3

O

progesterone

O

CH3

CH3OH

testosterone

Aldosterone is a mineralocorticoid.

• stimulates the active transport of Na+ from the kidney into the blood stream

• reduces Na+ content of the urine

• produced by the adrenal cortex

• 400 μg secreted per day

O

CH3

CH

H2C

OO

OHOH

aldosterone

Cortisol & cortisone are glucocorticoids

O

CH3

CH3

H2C

OO

OH

OH

cortisoneO

CH3

CH3

H2C

OOH

OH

OH

cortisol

• Glucocorticoids raise blood glucose levels by stimulating the conversion of amino acids into glucose in the liver.

• Elevated glucose levels speed cell recovery.

4. The Prostaglandins

• Prostaglandins are modified fatty acids.

• Localized effect.

• Chemically each prostaglandin has a 5 carbon ring and a total of 20 carbon atoms.

• Although prostaglandins act as chemical messengers they are rarely classified as hormones.

4. The Prostaglandins cont’d

Prostaglandins have a wide variety of actions because they act on a wide range of cells.

• Contraction of smooth muscle cells• Contraction and relaxation of smooth muscle cells in blood vessels• Clumping of platelets during clotting• Control cell growth• Regulate calcium movement• Sensitize spinal neurons to pain

Prostaglandins are potent but are short lived. They exert only a local influence or act on the same cell from which it is synthesized.

Hormones trigger responses three different ways

1. Signal transduction pathway via a membrane receptor

2. Ligand-gated ion channels

3. Intracellular receptors

1. Cells sensitive to the presence of a hormone have hormone receptors in their cell membranes.

receptor protein

plasmamembrane

extracellularfluid

cytoplasm

hormone(signal molecule)

Hormones fit into protein receptors on the membrane of the target cell.

Reception: The First Step of the Signal Pathway

receptor protein

plasmamembrane

extracellular fluid

cytoplasm

hormone(signal molecule)

The hormone binds to the receptor protein. Reception of the hormone is the first step of a signal pathway.

Transduction: The Second Step of the Signal Pathway

Reception of the hormone triggers the formation of series of chemical compounds in the cytoplasm of the cell. This series of compounds comprise the signal transduction pathway.

signal transduction pathway

Response:The third step of the signal pathway

The relayed signal triggers a metabolic response. For example, the hormone epinephrine triggers the hydrolysis of glycogen by way of a signal transduction pathway.

glycogen

2. Ligand-Gated Ion Channel

ions (Na+ & Ca++)

ion channel protein

extra cellular fluid

plasma membrane

cytoplasm

hormone(ligand)

The hormone (ligand) binds to the receptor protein, the protein changes shape, the channel opens and ions diffuse into the cytoplasm. The change in ion concentration in the cell triggers metabolic changes.

2. Ligand-Gated Ion Channel

The ligand dissociates and the channel closes. Neurotransmitters trigger the nerve impulse in this manner.

2. Ligand-Gated Ion Channel

Steroid hormones interact with intracellular receptors.

• The hormone testosterone diffuses through the cell membrane.

• Testosterone binds to a receptor protein in the cytoplasm.

• The receptor-hormone complex enters the nucleus and binds to a specific gene or genes that control male characteristics.

• The receptor-hormone complex stimulates transcription of the gene into mRNA.

• The mRNA is translated into protein.