1. Hormones and the Endocrine system
Chapter 45
Hormones and the Endocrine system

2. Overview: The Body’s Long-Distance Regulators
Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body.
Hormones reach all parts of the body, but only target cells are equipped to respond.
Insect metamorphosis and many other processes are regulated by hormones.
P.S. – Plants have hormones too

3. Overview: continued…
Two systems coordinate communication throughout the body: the endocrine system and the nervous system.
The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior.
The nervous system conveys high-speed electrical signals along specialized cells called neurons.

4. Hormones trigger specific responses
Chemical signals bind to receptor proteins on target cells.
Only target cells respond to the signal.

5. Types of Secreted Signaling Molecules
Secreted chemical signals include:
Hormones
Local regulators
Neurotransmitters
Neurohormones
Pheromones

6. What is a Hormone?
Endocrine chemicals secreted into extracellular fluids and travel in the bloodstream.
Endocrine glands are ductless and secrete hormones directly into surrounding fluid.
Hormones mediate responses to environmental stimuli and regulate growth, development, and reproduction.

7. (a) Endocrine signaling
Fig. 45-2a
Blood
vessel
Response
(a) Endocrine signaling
Response
Figure 45.2 Intercellular communication by secreted molecules
(b) Paracrine signaling
Response
(c) Autocrine signaling

8. Not all Glands are Endocrine.
Exocrine glands have ducts and secrete substances onto body surfaces or into body cavities (for example, tear ducts).

9. Local Regulators
Local regulators are chemical signals that travel over short distances by diffusion.
Local regulators help regulate blood pressure, nervous system function, and reproduction.
Local regulators are divided into two types:
Paracrine signals act on cells near the secreting cell
Autocrine signals act on the secreting cell itself

10. (a) Endocrine signaling
Fig. 45-2a
Blood
vessel
Response
(a) Endocrine signaling
Response
Figure 45.2 Intercellular communication by secreted molecules
(b) Paracrine signaling
Response
(c) Autocrine signaling

11. Neurotransmitters and Neurohormones
Neurons (nerve cells) contact target cells at synapses.
Neurons secrete chemical signals called neurotransmitters that diffuse a short distance across the synapse to bind to receptors on the target cell.

12. (d) Synaptic signaling
Fig. 45-2b
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory
cell
Figure 45.2 Intercellular communication by secreted molecules
Blood
vessel
Response
(e) Neuroendocrine signaling

13. Neurohormones:
Are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream.
Endorphins are an example.

14. (d) Synaptic signaling
Fig. 45-2b
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory
cell
Figure 45.2 Intercellular communication by secreted molecules
Blood
vessel
Response
(e) Neuroendocrine signaling

15. Pheromones
Pheromones - chemical signals that are released from the body and used to communicate with other individuals in the species.
Pheromones are “outside” the body.
Pheromones - mark trails to food sources, warn of predators, and attract potential mates.

16. Chemical Classes of Hormones
Three major classes of molecules function as hormones in vertebrates:
Polypeptides (proteins and peptides)
Amines derived from amino acids
Steroid hormones

17. Classes and properties of hormones
The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells.
Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not.

18. Polypeptide: Insulin Amine: Epinephrine Amine: Thyroxine
Fig. 45-3
Water-soluble
Lipid-soluble
0.8 nm
Polypeptide:
Insulin
Steroid:
Cortisol
Figure 45.3 Hormones differ in form and solubility
Amine:
Epinephrine
Amine:
Thyroxine

19. Cellular Response Pathways
Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors.
Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells.

20. Cell Signaling:
Signaling by any of these hormones involves three key events:
Reception
Signal transduction
Response

21. Water- soluble hormone Fat-soluble hormone Transport protein
Fig
Water-
soluble
hormone
Fat-soluble
hormone
Transport
protein
Signal receptor
TARGET
CELL
Signal
receptor
Figure 45.5 Receptor location varies with hormone type
(a)
NUCLEUS
(b)

22. Water- soluble hormone Fat-soluble hormone Transport protein
Fig
Water-
soluble
hormone
Fat-soluble
hormone
Transport
protein
Signal receptor
TARGET
CELL OR
Signal
receptor
Figure 45.5 Receptor location varies with hormone type
Cytoplasmic
response
Gene
regulation
Cytoplasmic
response
Gene
regulation
(a)
NUCLEUS
(b)

23. Water soluble example:
The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress.
Epinephrine binds to receptors on the plasma membrane of liver cells.
This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream.

24. G protein-coupled receptor
Fig
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
Second
messenger
cAMP
Figure 45.6 Cell-surface hormone receptors trigger signal transduction

25. Epinephrine Adenylyl cyclase G protein GTP G protein-coupled receptor
Fig
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
Second
messenger
cAMP
Figure 45.6 Cell-surface hormone receptors trigger signal transduction
Protein
kinase A
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown

26. Pathway for Lipid-Soluble Hormones
The response to a lipid-soluble hormone is usually a change in gene expression.
Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus.
Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes.

27. Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane
Fig
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
Figure 45.7 Steroid hormone receptors directly regulate gene expression

28. Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane
Fig
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
Figure 45.7 Steroid hormone receptors directly regulate gene expression
DNA
Vitellogenin
mRNA
for vitellogenin

29. Multiple Effects of Hormones
The same hormone may have different effects on target cells that have:
Different receptors for the hormone
Different signal transduction pathways
Different proteins for carrying out the response
A hormone can also have different effects in different species.

30. Negative feedback and antagonistic hormone pairs are common features of the endocrine system
Hormones are assembled into regulatory pathways.
Feedback loops are commonly used.
Hormones are often arranged in pairs that work against each other.
Blood sugar regulation and calcium deposition in bones are common test examples.