1. Functional Organization of the Endocrine System
Chapter 17:
Functional Organization of the Endocrine System
Pg 586
AP2 Chapter 17

2. Chapter 17 Outline General Characteristics of the Endocrine System
Chemical structure of hormones
Control & secretion rate
Transport & distribution in the body
Metabolism & Excretion
Interaction of hormones with their target tissue
Classes of Receptors
AP2 Chapter 17

3. I. General Characteristics of the Endocrine System
AP2 Chapter 17

4. I. General Char. of the Endocrine Syst.
Greek:
Endo: within
Krino: to secrete
Hormone: to set in motion
Endocrine System:
Composed of endocrine glands that typically secrete chemical signals (a.k.a. hormones) into the cardiovascular system
Exocrine glands  secrete their products onto a surface
Hormones are:
Prod’d in small amounts by a collection of cells
Secreted in interstitial spaces
Enters the cardiovascular system where it is transported some distance
Acts on specific tissues (target tissues) at another site in the body to influence the activity of these tissues in some specific fashion
AP2 Chapter 17

5. I. General Char. of the Endocrine Syst.
Endocrine System
Nervous System
Regulate activities of structures in body but do so differently
Intimate relationship btwn these 2 syst’s is now recognized
Hormones can be described as Amplitude-modulated Signals
 &  in [ ] of hormones in body fluids over periods ranging from minutes to hours
Responses are also  or  based on [ ]
All or none potentials carried along axons can be described as frequency-modulated signals.
These vary in frequency but not amplitude
Low frequency weak stimulus
High frequency  strong stimulus
FX last only 1 to a few milliseconds
Local actions
As always there are exceptions

6. I. General Char. of the Endocrine Syst
I. General Char. of the Endocrine Syst. Intercellular chemical signals (Table 17.1 pg 588)
allows 1 cell to communicate w/ another
Coordinate & regulate the activities of most cells
NT’s & neuromodulators play essential roles in fxn of the NS
Hormones are secreted by the Endocrine System
Autocrine
Paracrine
Hormones
Neurohormones (AKA hormone)
NT/Neuromodulator
Pheromone
AP2 Chapter 17

7. I. General Char. of the Endocrine Syst. Intercellular chemical signals
Autocrine
Secreted by cells in a local area & influences the activity of the same cell type from which it was secreted
Paracrine
Prod’d by a wide variety of tissues & secreted into tissues spaces; usually has a localized effect on others
Hormones
Secreted into the blood by specialized cells; travels some distance to target tissues; influences specific activities
I. General Char. of the Endocrine Syst. Intercellular chemical signals
AP2 Chapter 17

8. I. General Char. of the Endocrine Syst. Intercellular chemical signals
Neurohormones (AKA hormone)
Produ’d by neurons but function as hormones
NT/Neuromodulator
Prod’d by neurons & secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells
Pheromone
Secreted into the environment; modifies the physiology and behavior of other individuals of the same species
I. General Char. of the Endocrine Syst. Intercellular chemical signals
AP2 Chapter 17

9. II. Chemical Structure of Hormones
Pg 589
Table 17.2 (Examples listed)
Figure 17.3
AP2 Chapter 17

10. II. Chemical Structure of Hormones
Proteins
Short sequences of aa’s called polypeptides
Derivatives of aa’s
Lipids
Glycoproteins
AP2 Chapter 17

11. III. Control of Secretion Rate
AP2 Chapter 17

12. III. Control of Secretion Rate
Negative Feedback loops are used to help maintain the body in a state of homeostasis
Positive Feedback loops is also used in a very limited capacity
III. Control of Secretion Rate
Figure 17.7
AP2 Chapter 17

13. III. Control of Secretion Rate 3 major patterns of regulation
Non-hormonal Regulation of hormone secretion
Nervous System regulation of hormone secretion
Hormonal regulation of hormone secretion
As with everything in the body, it can be much more complicated involving multiple mechanisms
Some hormones:
Are in circulatory system at relatively constant levels
D suddenly in response to stimulation
D in a relatively constant cycle
AP2 Chapter 17

14. III. Control of Secretion Rate 3 major patterns of regulation
Non-hormonal Regulation of hormone secretion
Changes in the extracellular [ ] of a substance other than a hormone effect the function of the endocrine gland
AP2 Chapter 17

15. III. Control of Secretion Rate 3 major patterns of regulation
Neural Control of the endocrine gland
Neuron is synapsed with an endocrine gland and the neuron influences the activity of the gland
AP2 Chapter 17

16. III. Control of Secretion Rate 3 major patterns of regulation
3. Hormonal regulation of hormone secretion
Control of the secretory activity of one gland by a hormone or neurohormone secreted by another gland.
AP2 Chapter 17

17. IV. Transport & Distribution in the body
AP2 Chapter 17

18. IV. Transport & Distribution in the body
2 main ways to transport hormones in the blood
1. Unbound Hormones
2. Bound Hormones
Water soluble and travel in the blood
Lipid soluble and do not like the watery environment of the blood thus it must be bound to a transport protein
Pg 594
Fig 17.9
AP2 Chapter 17

19. IV. Transport & Distribution in the body 2. Bound Hormones
These are bound in a reversible fashion
Equilibrium is established btwn bound and their unbound counterparts
Bound are also trapped within the confines of the capillary because they are to big to filter thru
These serve as a reservoir. Thus when one in tissue is used there are replacements that only need to be released from the blood stream
These can also remain in the blood longer without being destroyed
Little Ceasars
AP2 Chapter 17

20. IV. Transport & Distribution in the body
Hormones go thru the bld & thus distributed quickly throughout the body
They diffuse thru the capillary wall & enter interstitial spaces and the rate of that movement varies by hormone
a. Lipid soluble hormones
b. Water soluble hormones
Pass thru capillary walls readily
Typically travel bound to binding proteins
Binding prevents their rapid diffusion from the circulatory system into the tissues
Reservoir also gives a relatively constant rate of diffusion of the unbound hormone from circ.systm.
Must go thru the pores of the capillary walls (fenestrae)
The capillaries of the organs regulated by and glands secreting these hormones usually have these large pores.
These usually get into tissue at a slow rate
AP2 Chapter 17

21. V. Metabolism & Excretion
AP2 Chapter 17

22. V. Metabolism & Excretion
Destruction & elimination of hormones limit the time that they are active in the body. The body’s activities can  or  dependent on how long the hormone remains in the body
Half-Life
Ways to lengthen half-life
Length of time it takes for ½ the dose of a substance to be eliminated from the circulatory system. (RATE)
Time to eliminate entire amount isn’t helpful b/c it all depends on what you start with.
Times vary dependent on specific hormone
Binding them to binding proteins
Their structures may also protect the hormone
Example
Glycoproteins: their carb component protects them from proteolytic enzymes in circulatory system
Half life- this regards rate instead of amount. @ 35 MPH the car will burn through the same amount of fuel per mile regardless of whether that car has 10 gallons or 2 gallons in its tank.
AP2 Chapter 17

23. V. Metabolism & Excretion 4 major ways to remove hormones from bld
Excreted into the urine by the kidney or the bile by the liver
Metabolism
Enzymatically degraded in the bld, liver, kidney, lungs, or target tissues
Byproducts are excreted in the bile & urine
Active Transport
Actively transported into cells and used again later as a NT or hormone
Conjugation
Substances are attached to hormones primarily in the liver. These normally make the hormone less active & increase its rate of excretion
AP2 Chapter 17

24. VI. Interactions of hormones with their target tissues
AP2 Chapter 17

25. VI. Interactions of hormones w/their target tissues
Hormones (a.k.a. Ligands)
Bind to receptors (proteins or glycoproteins)
Bind at the receptor site (binding site)
Binding Site:
Chemical characteristics of the site allow only a specific type of chemical signal to bond to it
“Specificity” can’t get growth hormone to bind to insulin site
Hormone receptors have a high affinity for the hormones that bind them, thus only a small [ ] results in a significant # of receptors being bound
Presence or absence of receptor determines wh/cells will react to the hormone’s release, thus it can travel throughout the body, but will only activate the proper cells

26. VI. Interactions of hormones w/their target tissues
Taking advantage of hormone
shape to make drugs
Drugs can be designed to have a similar structure to a natural hormone & may compete for the receptor’s binding site
Agonist:
Chemical that will bond to a receptor & activate it (Histamine)
Antagonist:
Chemical that will bind to a receptor but inhibits its action (antihistamine)
AP2 Chapter 17

27. VI. Interactions of hormones w/their target tissues
Response to Hormone
Can be constant or variable.
Rxns can decrease rapidly with time.
One Explanation:
Fatigue after prolonged stimulation of targeted cells
AP2 Chapter 17

28. VI. Interactions of hormones w/their target tissues
Down-regulation
# of receptors can also decrease over time after exposure
Tissues that down regulate are usually designed to respond to short term hormone increases
Tissues that respond to constant levels of hormones do not exhibit down-regulation
Up-regulation
Periodic increases in sensitivity of some cells to hormones
Results from an increase in rate of receptor molecule synthesis
Figure Pg 596
AP2 Chapter 17

29. VI. Interactions of hormones w/their target tissues Down-regulation continued
2 ways of down regulation
Synthesis rate of the receptor are reduced
Most hormone receptor complexes are degraded over time. If they are not replaced because of no synthesis the ultimate result is less cell surface receptors
Increased rate of receptor degradation
Receptor hormone complexes are sometimes degraded more quickly than the receptor alone
AP2 Chapter 17

30. VII. Classes of Receptors
2 Major Categories of Hormones
2 Major Categories of Receptors
(Figure pg 597)
AP2 Chapter 17

31. VII Classes of Receptors A
VII Classes of Receptors A. Hormones that bind to membrane bound receptors
Include large molecules & water soluble molecules both can’t pass thru the plasma membrane
Examples:
Proteins, glycoproteins, polypeptides, smaller molecules (epi/norepi)
When the receptor is bound it initiates a response inside the cell
Thus they interact w/the outside of the cell with membrane bound receptors
Transmembrane receptors w/their receptor sites exposed to the outer surface of the plasma membrane
AP2 Chapter 17

32. VII Classes of Receptors B. Hormones that bind intracellular receptors
These include lipid-soluble and relatively small hormones.
Examples:
Thyroid hormones, steroid hormones (testosterone, estrogen, progesterone, aldosterone, & cortisol)
Diffuse thru the plasma membrane & bind to Intracellular Receptors.
These are receptors in the cytoplasm or even the nucleus of the cell
Thus the hormone-receptor complex interacts with the DNA directly to prod. a response.

33. VII. Classes of Receptors 2 Major Categories
Membrane Bound Receptors
Intracellular Receptors
AP2 Chapter 17

34. VII. Classes of Receptors
Membrane Bound Receptors
2 major categories
Mechanisms for membrane bound receptors
1. Receptors that activate G-proteins
2. Receptors that directly alter the activity of intracellular enzymes
AP2 Chapter 17

35. 1. Receptors that activate G-proteins
These have 3 subunits: a, b, & g
Called G-proteins because a binds to guanine nucleotides
Result #1:
Activated a-subunit can alter the activity of molecules inside the cell prod’ing cellular responses
AP2 Chapter 17
Fig 7.14 pg 599

36. 1. Receptors that activate G-proteins
Result #2:
Activated a-subunit can combine w/ion channels causing them to open & close
Some ions or molecules can act as intracellular modulators
Enter or are synthesized w/in the cell that regulate enz activity in the cell
Fig 7.15 pg 600
AP2 Chapter 17

37. 1. Receptors that activate G-proteins
Fig 7.16 pg 601
Result #3:
Activated a-subunit can also alter the activity of enz’s inside the cell
AP2 Chapter 17

38. 1. Receptors that activate G-proteins
Result #4:
Alter the [ ] of intracellular mediators other than Ca2+ & cAMP
Fig 7.17 pg 602
AP2 Chapter 17

39. VII. Classes of Receptors
Membrane Bound Receptors
Receptors that activate G-proteins
When the hormone separates from the receptor additional G-proteins are no longer activated
Inactivation of a-subunit occurs when phosphate is removed from the GTP-leaving GDP with the a-subunit
Then the subunits of the G-protein recombine
AP2 Chapter 17

40. VII. Classes of Receptors
Membrane Bound Receptors
2 major categories
Mechanisms for membrane bound receptors
1. Receptors that activate G-proteins
2. Receptors that directly alter the activity of intracellular enzymes
AP2 Chapter 17

41. 2. Receptors that directly alter the activity of intracellular enzymes
These receptor when bound directly alter the activity of an intracellular enzymes (mediators) w/no 2nd messenger needed
Altered enz’s can be membrane bound or not
Mediator enz’s act as chemical signals that move from where they are altered into the cytoplasm where they activate processes that prod a cellular response
Fig 7.18 pg 602
AP2 Chapter 17

42. 2. Receptors that directly alter the activity of intracellular enzymes
Altered enzyme activity can:
 or  the activity of intracellular mediator molecules
Results in the phosphorylation of intracellular proteins
Intracellular mediators (Phosphoylated proteins) activate processes that prod the response of the cell
Fig 7.18 pg 602
AP2 Chapter 17

43. 2. Receptors that directly alter the activity of intracellular enzymes
Some are bound & a portion of the receptor on the inner surface of the membrane acts as a phosphorylase enzyme that phosphorylates several specific proteins
Phosphorylated proteins:
Can be part of the membrane bound protein or not
Influence the activity of other enzymes in the cell
Fig 7.19 pg 603
AP2 Chapter 17

44. 2. Receptors that directly alter the activity of intracellular enzymes
Cascade Effect
Most hormones act exponentially causing a pyramid effect that result in rapid responses
Few mediator molecules activate several enz’s & each enz activates several other enz’s that prod a response
An amplification system exists in wh/a few molecules can control the activity of many enz’s w/in the cell
Fig 7.20 pg 604
AP2 Chapter 17

45. VII. Classes of Receptors 2 Major Categories
Membrane Bound Receptors
Intracellular Receptors
AP2 Chapter 17

46. VII. Classes of Receptors
Lipid soluble hormones cross the plasma membrane into the cytoplasm or nucleus & bind to intracellular receptors by the process of diffusion
Thus receptor location is in the cytoplasm or nucleus
Fig 7.21 pg 605
AP2 Chapter 17

47. VII. Classes of Receptors
Fxns of receptor-hormone complex:
Alter the activity of enz’s of the cell
Bind to DNA to prod a response:
Via gene expression
DNA is transcribed into mRNA then translated into a protein
Thus it increases the synthesis of a specific protein.
Fig 7.21 pg 605
AP2 Chapter 17

48. VII. Classes of Receptors
These types of rxns are not instant, they usually take several hours btwn hormone release & response is observed
To make mRNA & protein
Hormone influence is limited via hormone-receptor complex degradation
Fig 7.21 pg 605
AP2 Chapter 17

49. VII. Classes of Receptors
Intracellular Receptors
Fig 7.21 pg 605
AP2 Chapter 17