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