1. Endocrine System
Chemical Control

2. Messenger Molecules
Cells must communicate with one another to coordinate cell processes within tissues and to maintain homeostasis.
Cell-to-cell communication is carried out via messenger molecules.

3. Three types of chemical signals are used for cell-to-cell communication.

4. Four methods of cell-to-cell communication are found in the human body, ranging from direct to remote communication.

5. Endocrine hormones
Produced by endocrine (“ductless”) glands and secreted into the bloodstream.
Endocrine hormones may affect a wide array of target cells to produce multiple effects.
Two types: peptides (small proteins) and steroids (lipids).

6. Hormones and Receptors

7. Peptide Hormones
Peptide hormones do not enter the cell directly. These hormones bind to receptor proteins in the cell membrane.
When the hormone binds with the receptor protein, a secondary messenger molecule initiates the cell response.
Because peptide hormones are water soluble, they often produce fast responses.

8. Hormone–receptor binding activates an enzyme that catalyzes
peptide or amino
acid-derived
hormone
(first messenger)
Hormone–receptor binding
activates an enzyme that catalyzes
the synthesis of a second messenger,
such as cyclic AMP 2
The hormone binds to
a receptor on the plasma
membrane of a target cell 1
cyclic AMP-
synthesizing
enzyme
(cytoplasm)
(extracellular
fluid)
ATP
active
enzyme
receptor
product
cyclic AMP
(second messenger) 4
The activated enzymes
catalyze specific reactions
plasma membrane
inactive
enzyme
reactant
The second
messenger activates
other enzymes 3
nuclear
envelope
(nucleus)

9. Steroid Hormones
Steroid hormones enter through the cell membrane and bind to receptors inside of the target cell.
These hormones may directly stimulate transcription of genes to make certain proteins.
Because steroids work by triggering gene activity, the response is slower than peptide hormones.

10. receptor in the nucleus or to a receptor in the cytoplasm
steroid hormone
(extracellular
fluid)
The hormone binds to a
receptor in the nucleus or to
a receptor in the cytoplasm
that carries it into the nucleus 2
The hormone–receptor
complex binds to DNA and
causes RNA polymerase to
bind to a nearby promoter
site for a specific gene 3
A steroid hormone
diffuses through the
plasma membrane 1
DNA
plasma
membrane
hormone receptor
ribosome
RNA polymerase
The mRNA leaves the
nucleus, then attaches to a
ribosome and directs the
synthesis of a specific protein
product 5
RNA polymerase catalyzes
the transcription of DNA into
messenger RNA (mRNA) 4
mRNA
new protein
gene
nuclear
envelope
(cytoplasm)
(nucleus)

11. Role of the Hypothalamus
The thalamus receives sensory information, relays some to the hypothalamus.
Hypothalamus monitors the body for temperature, pH, other conditions.
Hypothalamus signals pituitary gland if conditions need to be corrected.

12. Role of the Pituitary
The pituitary is the “master gland” that signals other glands to produce their hormones when needed.
The anterior lobe of the pituitary receives signals from the hypothalamus, and responds by sending out the appropriate hormone to other endocrine glands.
The posterior pituitary receives oxytocin or antidiuretic hormone (ADH) from the hypothalamus, relays them to the body as necessary.

13. Neurosecretory cells of the hypothalamus produce oxytocin and ADH 1
produce releasing and
inhibiting hormones 1
Releasing or inhibiting hormones
(green circles) are secreted into
capillaries feeding the anterior lobe
of the pituitary 2
Oxytocin and ADH
(blue triangles) are
secreted into the blood
via capillaries in the
posterior pituitary 2
blood flow
pituitary
(anterior lobe)
endocrine
cell
capillary
bed
pituitary
(posterior lobe)
Endocrine cells of the
anterior pituitary secrete
hormones (red squares)
in response to releasing
hormones; the pituitary
hormones enter the
bloodstream 3
capillary
bed
blood
flow

14. Pituitary Hormones Pituitary Hormone Functions
Follicle-stimulating hormone
Stimulates egg maturation in the ovary and release of sex hormones.
Lutenizing hormone
Stimulates maturation of egg and of the corpus luteum surrounding the egg, which affects female sex hormones and the menstrual cycle.
Thyroid-stimulating hormone
Stimulates the thyroid to release thyroxine.
Adrenocorticotropic hormone
Causes the adrenal gland to release cortisol.
Melanocyte-stimulating hormone
Stimulates synthesis of skin pigments.
Growth hormone
Stimulates growth during infancy and puberty.
Antidiuretic hormone
Signals the kidney to conserve more water.
Oxytocin
Affects childbirth, lactation, and some behaviors.

15. Endocrine Hormones Gland Hormones Functions Thyroid Thyroxine
Regulates metabolism
Calcitonin
Inhibits release of calcium from the bones
Parathyroids
Parathyroid hormone
Stimulates the release of calcium from the bones.
Islet cells (in the pancreas)
Insulin
Decreases blood sugar by promoting uptake of glucose by cells.
Glucagon
Increases blood sugar by stimulating breakdown of glycogen in the liver.
Testes
Testosterone
Regulates sperm cell production and secondary sex characteristics.
Ovaries
Estrogen
Stimulates egg maturation, controls secondary sex characteristics.
Progesterone
Prepares the uterus to receive a fertilized egg.
Adrenal cortex
Epinephrine
Stimulates “fight or flight” response.
Adrenal medulla
Glucocorticoids
Part of stress response, increase blood glucose levels and decrease immune response.
Aldosterone
Regulates sodium content in the blood.
Testosterone (in both sexes)
Adult body form (greater muscle mass), libido.
Pineal gland
Melatonin
Sleep cycles, reproductive cycles in many mammals.

16. Homeostasis and Hormones
Examples:
Thyroid and temperature control
Thyroid, Parathyroid, and calcium
Pancreas and glucose control

17. Temperature Control

18. Blood Calcium

19. Blood Sugar Control

20. Other hormone roles Controlling sleep cycles (melatonin)
Controlling reproductive cycles (melatonin, sex hormones)
Growth (growth hormone)
Responding to stress or emergencies (epinephrine and other hormones)

21. Hormones Everywhere!
Many other organs besides the endocrine glands produce hormones.
Kidneys produce several hormones that regulate blood pressure, which is essential for kidney function.
The digestive system produces several hormones that regulate appetite.

22. The obese mouse on the left does not produce enough leptin, a hormone produced by fat cells.
Low body fat stimulates leptin production, which stimulates appetite. The mouse is obese because its low leptin levels give it an enormous appetite. Leptin injections return the mouse’s weight to normal. Humans sometimes have a leptin issue, too, but the problem is a bad leptin receptor on body cells. Alas, leptin injections won’t cure that.

23. Finally…
Summarize the roles of the pituitary and other endocrine glands in maintaining homeostasis in the human body.