1. AP Biology Endocrine System and Hormones –
Overall Function and Feedback Mechanisms

2. Signal Transduction Pathway

3. Kinases “turn on” processes Phosphotases “turn off” processes

4. A stimulus is recognized by the body.
Basic Hormone Pattern
Hormone – a chemical produced in one part of the body that travels to another part of the body (target tissue) and elicits a response.
The basic mechanism of the endocrine system can be seen in the diagram to the left:
A stimulus is recognized by the body.
Endocrine cells release a hormone into the blood stream.
The hormone travels throughout the body to the target tissue.
The appropriate response is triggered.
Pathway
Example
Low blood
glucose
Stimulus
Receptor
protein
Pancreas
secretes
glucagon ( )
Endocrine
cell
Blood
vessel
Target
effectors
Liver
Response
Glycogen
breakdown,
glucose release
into blood
Simple endocrine pathway

5. Remember the “hands” on cell membranes? (In GREEN)
Just as we discussed with the nervous system and the immune system, the endocrine system works through interactions between chemicals and protein receptors found on the surface of all cells throughout the body.

6. Hormonal System of Communication
There are three majors parts to the hormonal system of communication:
1. Exocrine: a hormone is secreted by a gland, and the target is the outside of the body.
Ex. Sweat and pheromones
2. Endocrine: a hormone is secreted by a gland, enters the blood stream and targets tissues in the body.
Ex. Insulin, glycogen, ADH, Oxytocin, etc.
3. Neurosecretory: these are specialized neurons that can also secrete hormones.
Ex. Hypothalamus, pituitary

7. LE 45-7 Hypothalamus Neurosecretory cells of the hypothalamus Axon
Posterior
pituitary
Anterior
pituitary
HORMONE
ADH
Oxytocin
TARGET
Kidney tubules
Mammary glands,
uterine muscles

8. Cytokines IL 1 – Helper T to Cytotoxic T Cell IL2 – Helper T to B Cell

9. Different Types of Hormones
The two major types of hormones found in living organisms are steroid hormones and peptide hormones. These work differently when targeting cells.
1. Steroid (lipid-based) hormones – steroid hormones are lipid-based, so they can easily pass through the phospholipid bilayer. Once in the cell, they target receptors deep in the cytoplasm or the nucleus. Ex. Testosterone, estrogen, aldosterone
2. Peptide (protein-based) hormones – peptide hormones are protein-based, so they can not pass directly through the phospholipid bilayer. These hormones must bind to a cell-surface receptor and then transmit their message into the cell. This follows the stereotypical signal transduction pathway.
Ex. Prolactin, HGH, oxytocin, insulin, glucagon

10. Peptide and Monoamine Hormone Binding
SECRETORY
CELL
SECRETORY
CELL
Hormone
molecule
Hormone
molecule
VIA
BLOOD
VIA
BLOOD
Peptide and Monoamine Hormone Binding
Signal receptor
Steroid Hormone Bonding
TARGET
CELL
TARGET
CELL
Signal
transduction
pathway
Signal
receptor OR
Cytoplasmic
response
DNA
Signal
transduction
and response
mRNA
DNA
Nuclear
response
NUCLEUS
Synthesis of
specific proteins
NUCLEUS
Receptor in plasma membrane
Receptor in cell nucleus

11. Many hormones are involved in negative feedback loops
Many hormones are involved in negative feedback loops. The most easily understood examples are insulin and glucagon. When changes in blood sugar are sensed by the body, these hormones are secreted to reverse the change. The secretion of the hormone stops the situation.
TRH
TSH

12. Positive feedback loops are also very important in living organisms
Positive feedback loops are also very important in living organisms. These are the opposite of negative feedback. The production of a hormone causes continued production of a hormone, or the continuation of a behavior. Oxytocin and prolactin are examples of hormones that function through positive feedback.

13. Human Endocrine Glands
Important Human Endocrine Glands:
Hypothalamus – produces hormones that regulate the pituitary
Pituitary Gland – major gland that produces hormones that travel throughout the body
Thyroid Gland – produces hormones that regulate metabolism
Pancreas – produces hormones that regulate blood sugar
Thymus Gland – produces hormones that stimulate production of T-Cells
Adrenal Glands – produces hormones that stimulate “fight or flight” and kidney function
Ovaries – female sex hormones
Testes – male sex hormones

14. Tropic Hormones of the Anterior Pituitary
Tropic Effects Only
FSH, follicle-stimulating hormone
LH, luteinizing hormone
TSH, thyroid-stimulating hormone
ACTH, adrenocorticotropic hormone
Neurosecretory cells
of the hypothalamus
Nontropic Effects Only
Prolactin
MSH, melanocyte-stimulating hormone
Endorphin
Portal vessels
Nontropic and Tropic Effects
Growth hormone
Hypothalamic
releasing
hormones
(red dots)
Endocrine cells of the
anterior pituitary
Pituitary hormones
(blue dots)
HORMONE
FSH and LH
TSH
ACTH
Prolactin
MSH
Endorphin
Growth hormone
TARGET
Testes or
ovaries
Thyroid
Adrenal
cortex
Mammary
glands
Melanocytes
Pain receptors
in the brain
Liver
Bones