Chapter 9: Endocrine System and Hormone Activity

Homeostatic Control through Hormone Release

Overview• Coordinates and directs

the activity of cells.• Interacts with the nervous

system.• Uses chemical

messengers called hormones.

• Controls a variety of necessary biological functions such as:*Reproduction*Growth and Development*Defense*Balance of fluids and electrolytes

Mechanism of Action• Hormones only affect certain tissues or

organs:

• Hormones bind only to specific sites on the plasma membrane of those Target cells:

• The Target cell becomes active once the hormone is bound to its specific receptor.

Targets

Receptors

ClassificationsAmine/Peptide• Chemical base is a SINGLE Amino Acid.• Acts by activating an enzyme through

receptor-binding on the cell membrane.• Does NOT enter the cell; remains on the

outside of the cell membrane.

Lipid/Steroid• Chemical base is cholesterol.• Acts by directing gene activation in

the nucleus.• Enters the cell membrane and

nucleus of the Target cell because it is lipid-soluble.

Hormone Action:What can hormones do?

• Change the permeability or electrical state of the cell membrane.

• Synthesize molecules in the cell.

• Activate/Inactive enzymes.

• Stimulating, slowing or stopping mitosis

Control of Hormone Release

Negative Feedback Mechanisms regulate the blood levels of most hormones in 3 ways:

1. Hormonal stimuli

2. Humoral stimuli

3. Neural stimuli

Hormonal Stimulation

• One hormone triggers the release of another hormone.

• These trigger hormones are TROPHIC HORMONES.

• Released by the Pituitary Gland in the brain.

Humoral Stimulation

• Blood levels of chemicals triggers the release of specific hormones.

Neural Stimulation

• Nerve fibers (Autonomic Sensory Receptors) trigger the release of specific hormones.

Pituitary Gland“The Master Gland”

• 2 Functional Lobes

*Anterior Lobe

*Posterior Lobe• Interacts closely with the

Nervous System through the hypothalamus.

• Protected by what structure?

Sphenoid Bone

Anterior Pituitary

• Regulated through humoral stimulation from the hypothalamus.

• Many of the hormones released are Trophic Hormones.

Anterior Pituitary Hormones

• Growth Hormone (GH)• Thyroid Stimulating Hormone (TSH)• Adrenocorticotropin Hormone (ACTH)• Follicle Stimulating Hormone (FSH)• Luteinizing Hormone (LH)• Melanocyte Stimulating Hormone

(MSH)• Endorphins

Too Much Growth Hormone

• Acromegaly is caused by too much growth hormone AFTER puberty has completed.

• Gigantism is caused by too much growth hormone during adolescence and puberty.

Too Little Growth Hormone

• The man on the left is 25 years old. The man on the right is 22 years old.

• The girl below is pictured with her father at the age of 5 years.

Abnormal TSH secretion

• Goiter formation due to inadequate iodine consumption.

• Exopthalmosis (bulging eyes) due to Graves Disease.

Posterior Pituitary

• Regulated through neural stimulation from the hypothalamus.

• Produces 2 hormones in response to nervous system stimulation.– Antidiuretic hormone (ADH)– Oxytocin

Thyroid Gland• Located in the anterior

portion of the neck, just below the throat.

• Releases hormones that act on the metabolic rate.

*T4: thyroxine

*T3: triiodothyronine

• Also produces the calcitonin.

Parathyroid Gland

• Located on the posterior surface of the Thyroid gland.

• Secretes Parathyroid Hormone (PTH)– The MOST important

regulator of blood calcium levels.

Adrenal Glands

• Located on the superior aspect of each kidney.

• 2 functional parts

*Cortex

*Medulla

Each part secretes a specific type of hormone.

Adrenal Gland Divisions

CORTEX• Produces

hormones that control fluid and electrolyte balance.

• Produces sex hormones.

MEDULLA• Produces

hormones for sympathetic/

parasympathetic nervous system.

Pancreas

• Located in

abdominal cavity

close to stomach.

• Produces hormones for the use and storage of glucose– Insulin– Glucagon

Pineal Gland

• Pineal gland is very close to the optic nerve in the brain.

• Produces Melatonin that activates sleep-wake cycles.

Thymus Gland

• Located behind the sternum.

• Decrease in size as you age.

• Produces Thymosin needed for the production of T-lymphocytes.

T-cells are needed for protection against viral infections.

Ovaries and Testes• Hormone producing glands (Gonads) of the

female and male reproductive systems.• Controls fertility, reproduction, and gestation.

• Ovaries produce and release estrogen and progesterone

• Testes produce testosterone and androgens

Other Hormone-Producing Organs• Placenta• Stomach• Intestines• Heart• Striated muscles

• Skin• Adipose/Fat• Liver• Kidneys• Uterus