Transcript Endocrine System

Endocrine System
Chemical Control
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.
Three types of
chemical signals
are used for cellto-cell
communication.
Four methods of cell-to-cell communication are
found in the human body, ranging from direct to
remote communication.
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).
Hormones and Receptors
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.
peptide or amino
acid-derived
hormone
(first messenger)
1 The hormone binds to
a receptor on the plasma
membrane of a target cell
Hormone–receptor binding
2
activates an enzyme that catalyzes
the synthesis of a second messenger,
such as cyclic AMP
cyclic AMPsynthesizing
enzyme
(extracellular
fluid)
receptor
(cytoplasm)
ATP
active
enzyme
product
cyclic AMP
(second messenger)
4 The activated enzymes
catalyze specific reactions
plasma membrane
inactive
enzyme
reactant
The second
3
messenger activates
other enzymes
nuclear
envelope
(nucleus)
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.
steroid hormone
(extracellular
fluid)
2 The hormone binds to a
receptor in the nucleus or to
a receptor in the cytoplasm
that carries it into the nucleus
3 The hormone–receptor
complex binds to DNA and
causes RNA polymerase to
bind to a nearby promoter
site for a specific gene
1 A steroid hormone
diffuses through the
plasma membrane
DNA
plasma
membrane
hormone receptor
ribosome
RNA polymerase
5
The mRNA leaves the
nucleus, then attaches to a
ribosome and directs the
synthesis of a specific protein
product
mRNA
4 RNA polymerase catalyzes
the transcription of DNA into
messenger RNA (mRNA)
gene
new protein
nuclear
envelope
(cytoplasm)
(nucleus)
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.
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.
hypothalamus
1 Neurosecretory cells of
the hypothalamus produce
oxytocin and ADH
1 Neurosecretory cells
of the hypothalamus
produce releasing and
inhibiting hormones
2 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
blood flow
pituitary
(anterior lobe)
endocrine
cell
pituitary
(posterior lobe)
capillary
bed
3 Endocrine cells of the
anterior pituitary secrete
hormones (red squares)
in response to releasing
hormones; the pituitary
hormones enter the
bloodstream
capillary
bed
blood
flow
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 Stimulates synthesis of skin pigments.
hormone
Growth hormone
Stimulates growth during infancy and puberty.
Antidiuretic hormone
Signals the kidney to conserve more water.
Oxytocin
Affects childbirth, lactation, and some behaviors.
Endocrine Hormones
Gland
Thyroid
Hormones
Functions
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.
Melatonin
Sleep cycles, reproductive cycles in many mammals.
Pineal gland
Homeostasis and Hormones
• Examples:
• Thyroid and temperature control
• Thyroid, Parathyroid, and calcium
• Pancreas and glucose control
Temperature Control
Blood Calcium
Blood Sugar Control
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)
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.
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.
Finally…
• Summarize the roles of the pituitary and
other endocrine glands in maintaining
homeostasis in the human body.