The Endocrine System

General Characteristics

Hormone Action

Control of Hormonal Secretions

Stress and Health

Introduction

• Endocrine system – includes cells, tissues and organs collectively called endocrine glands.

• Secrete hormones – substances that diffuse from the interstitial fluid into the blood stream and eventually act on cells.– Paracrine hormones = only affect neighboring cells.– Autocrine hormones = affect only the secreting cell

itself.

General Characteristics

• Both the endocrine and nervous systems communicate with cells using chemical signals.

• Hormones are to the endocrine system as neurotransmitters are to the nervous system.

• Endocrine glands and their hormones help regulate metabolic processes.

• They control– Rates of certain chemical reactions– Aid in transport of substances across

membranes– Help regulate water and electrolyte balances.– Play vital roles in reproduction, development,

and growth.

Glands we will look at:

• Pituitary• Thyroid• Parathyroid• Adrenal• Pancreas

Hormones

• Amines – norepinephrine, epinephrine• Peptides – oxytocin, antidiuretic hormone,• Proteins – growth hormone, parathyroid

hormone, prolactin• Glycoproteins – FSH, LH, TSH• *Steroids – Estrogen, testosterone,

aldosterone, cortisol

Steroid Hormonesevents that occur when they enter a target cell

1. Diffuses through the cell membrane2. Combines with a specific protein molecule3. Resulting bound protein binds with a particular

region of the DNA of the nucleus and activates transcription of specific genes into messenger RNA molecules

4. mRNA molecules enter the cytoplasm5. mRNA molecules associate with ribosomes to

direct the synthesis of specific proteins.

Analogy

• Lobbyists in Washington, D.C.(Mr. Pierson story time)

Glands

Pituitary

Thyroid

Parathyroid

Adrenal

Pancreas

Pituitary Gland

• Located at the base of the brain.• About 1 cm in diameter • Consists of an anterior lobe and a posterior

lobe.• ***THE BRAIN CONTROLS MOST OF

THE PITUITARY GLAND’S ACTIVITIES.***

• Growth hormone(GH)- stimulates cell growth in size and frequency.

• Prolactin(PRL)- stimulates a woman’s milk production after the birth of an infant.

• Thyroid-stimulating hormone(TSH)- controls thyroid gland secretion.

• Adrenocorticotropic hormone(ACTH)- controls the manufacture and secretion of certain hormones from the outer layer of the adrenal gland.

• Follicle-stimulating hormone(FSH) and Lutenizing hormone (LH)- also called gonadotropins because they exert their actions on the gonads (reproductive organs.)

Anterior Pituitary Hormones

Posterior Pituitary Hormones

• Antidiuretic hormone (ADH)- diuretics are chemicals that increase urine production, so antidiuretics decrease urine production.

• Oxytosin (OT)- deals mostly with uterine wall contractions for childbirth, but also functions as an antidiuretic.

Thyroid Gland

• Vascular structure that consists of 2 large lobes connected by a broad isthmus.

• Located below the larynx and anterior to the trachea.

Thyroid Hormones

• Thyroxine (T4)• Triiodothyronine (T3)

**These have primarily the same function, except Triiodothyronine is 5 x’s more potent. They help regulate the metabolism of carbohydrates, lipids, and proteins.

• They are the major factors determining how many calories the body must consume at rest in order to maintain life. = Basal Metabolic Rate (BMR)

Parathyroid Glands

• Located on the posterior surface of the thyroid gland.

• 4 lobes: superior and inferior located on each of the 2 lobes of the thyroid.

Parathyroid hormone

• Parathyroid hormone (PTH) – increases blood calcium concentration and decreases blood phosphate ion concentration.

• Affects the bones, kidneys and intestines.

Adrenal Glands

• Closely associated with the kidneys.• A gland sits atop each kidney like a cap.• Consists of 2 parts:

– Adrenal medulla = central portion– Adrenal cortex = outer part

Adrenal Medulla Hormones

• Epinephrine – makes up 80% of adrenal medullary secretion.

• Norepinephrine

**The effects of epinephrine and norepinephrine include increased heart rate, force of cardiac muscle contraction, increased breathing rate, elevated blood pressure, increased blood glucose, and decreased digestive activity.

Hormones of the Adrenal Cortex

• Aldosterone – helps regulate the concentration of mineral electrolytes.– Helps maintain blood volume and blood pressure.

• Cortisol – affects glucose metabolism. Also influences protein and fat metabolism.

• Adrenal sex hormone = androgens and estrogens.– Supplement the supply of sex hormones from the

gondads and stimulate early development of the reproductive organs.

Pancreas

• Flattened, elongated organ posterior to the stomach.

• Consists of 2 major types of secretory tissue = endocrine and exocrine

• Endocrine = Islets of Langerhans• Has a dual function:

– Secretes digestive enzymes – Releases hormones

Hormones of the Islets of Langerhans

• Glucagon – stimulates the liver to break down glycogen into glucose.

• Insulin – stimulates the liver to form glycogen from glucose.