Chapter 8: Chemical Signals Maintain HomeostasisSection 8.1 pages 372-377

RecapThe last section (7.6) discussed the

following:

•Water Balance •Change in osmolity release of ADH•Change in solute concentration and body

volume release of Aldosterone•Both those systems are examples of

negative feedbacks•pH is regulated by the carbonic

acid/bicarbonate buffer

To clarify

Angiotensinogen ---------------> Angiotensin Renin (enzyme)

Hormones

•Chemicals released by cells in one part of the body that affect another part

•A small amount is required•They serve as regulators, slowing down or

speeding up processes•Endocrine hormone:

▫Chemicals secreted by endocrine glands directly into blood

▫The circulatory system is involved

Endocrine Glands at Work

• Endocrine hormones are chemicals involved with the regulation of growth, development and homeostasis

Hormones are classified based on their activation site

Non-target Hormones Target Hormones• These hormones affect many

cells throughout the body

• Growth Hormone (GH) or Somatotropin (ST)▫ Regulates development of

long bones

• Insulin▫ Regulates blood sugar

levels

• Epinephrine▫ Also known as adrenaline▫ Produced in times of stress

• These hormones affect specific cells or target tissues

• Parathyroid Hormone▫ Regulates calcium levels

in the body

• Gastrin▫ Stimulates cells of the

stomach to produce digestive enzymes

The Location of Endocrine Glands

Growth HormoneGrowth

Hormone

InsulinInsulin

Chemical Messages and Organ ActivityMering and Minkowski (1889)• Removed the pancreas from one

group of dogs

Their observations?• Dogs became fatigued (symptoms

resemble diabetes)• Ants were attracted to the dogs

without pancreas

Why?• Urine contained glucose (sugar)

that ants were attracted to • Pancreas produce insulin to

monitor blood sugar

Chemical Signals

How do hormones signal cells?

•Hormones do not affect all cells•Cells may have receptors for one hormone

but not another•The numbers of receptors found on cells

can vary▫Liver and muscle cells have many receptor

sites for the hormone insulin

There are two types of hormones

These two hormones differ in chemical structure and action

1.Steroid Hormones

2.Protein Hormones

Steroid Hormones

•Are made from cholesterol, a lipid compound

•Includes male and female sex hormones and cortisol

•Composed of complex rings of carbon, hydrogen and oxygen

•Not soluble in water, but are soluble in fat

Steroid Signaling

Hormones diffuse from capillaries

to interstitial fluid

Hormones diffuse from capillaries

to interstitial fluid

Note the target cell attaches to

the receptor in the cytoplasm

Note the target cell attaches to

the receptor in the cytoplasm

Attaches to chromatin that has complementary shapeAttaches to chromatin that has complementary shape

Figure 4. page 374

Protein Hormones

•This includes insulin and growth hormone (GH)

•Contain chains of amino acids in varying length

•Differ from steroid hormones protein hormones ARE soluble in water

Protein Signaling

Figure 5. page 375

Cyclic AMP acts as a secondary messenger to

activate enzymes

Cyclic AMP acts as a secondary messenger to

activate enzymes

Combines with receptor

on the cell membrane.

Combines with receptor

on the cell membrane.

Hormone-receptor complex produces an enzyme called adenylyl cyclase

Hormone-receptor complex produces an enzyme called adenylyl cyclase

The Pituitary Gland: The Master GlandWhy is it called the master gland?•It exercises control over the other

endocrine glands•Connected to the hypothalamus – the area

associated with homeostasis•Produces and stores hormones•Nerves stimulate hypothalamus which

causes the release of hormones by the pituitary gland

The Pituitary Gland: Posterior Lobe

•The pituitary gland consists of two separate lobes: the posterior lobe and the anterior lobe

•Posterior lobe stores and releases▫ADH, oxytocin

•Hormones travel on specialized nerve cells from the hypothalamus to be stored in the pituitary and are released into the blood when needed

Figure 6. Page 376

The Pituitary Gland

The Pituitary Gland: Anterior Lobe

• The anterior lobe of the pituitary gland produces its own hormones.

• The anterior lobe is connected to the hypothalamus by nerves

1.Hormones secreted by nerve ends of the cells of the hypothalamus

2.Hormones transported in the blood to the pituitary gland

3.This causes the release of pituitary hormones4.Pituitary hormones are carried in blood to target

tissues

Figure 6. Page 376

The Pituitary Gland

Pituitary HormonesTable 1. page 377