2. Overview: The Body’s Long-Distance Regulators
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 to the same.
Hormones convey information via the bloodstream to target cells
throughout the body.
3. Classification of Hormones
1. Proteins and Polypeptides, including hormones secreted by the anterior
and posterior pituitary gland, the pancreas (insulin and glucagon), the
parathyroid gland (parathyroid hormone), and many others.
2. Steroids secreted by the adrenal cortex (cortisol and aldosterone), the
ovaries (estrogen and progesterone), the testes (testosterone), and the
placenta (estrogen and progesterone)
3. Derivatives of the aminoacid tyrosine, secreted by the thyroid (thyroxine
and tri-iodothyronine) and the adrenal medullae (epinephrine and
norepinephrine)
4. Control Pathways and Feedback Loops
• The endocrine systemsecretes hormones that coordinate slower but
longer-acting responses including reproduction, development, energy
metabolism, growth, and behavior
• A common feature is a feedback loop connecting the response to the
initial stimulus
• Negative feedbackregulates many hormonal pathways involvedin
homeostasis
5. • Signaling by any of these hormones involves three key events:
– Reception
– Signal transduction
– Response
6. Transportationof Hormones
1, Endocrine: glands or specialized cells release hormones into the circulating
blood that influence the function of cells at another location in the body
2, Neuroendocrine: neurons secrete substances (neurohormones) that reach
the circulating blood and influence the function of cells at another
location of the body.
3. Paracrine, in which cells secret substances that diffuse into the extracellular
fluid and affect neighboring cells.
7. 1. Mechanisms of Hormonal Action
The first step of a hormone’s action is to bind to specific receptors at
the target cell.
Locations for the different types of hormones:
1) On the surface of the cell membrane.
protein, peptide, and catecholamine hormones
2) In the cell cytoplasm.
steroidhormones
3) In the cell nucleus.
thyroid hormones (T3 and T4)
8. 2.Second MessengerMechanisms for Mediating Intracellular
Hormonal Functions
Hydrophilic hormones (proteins, peptides and catecholamine)
--bind the receptors on the membrane,
--activate some enzyme on the membrane,
-- regulate the concentration of some messengers (second messengers) in the cytoplasm.
There are at least three kinds of second messengers: cAMP, Calciumionsand productsof
membrane phospholipidmetabolism.
3.Hormones That Act Mainlyon the Genetic Machineryof the Cell
a) Steroid hormones increase protein synthesis
b) Thyroid hormonesincrease genetranscription in the cellnucleus
10. • Binding of a hormone to its receptor initiates a signal transduction
pathway leading to responses in the cytoplasm or a change in gene
expression
• The same hormonemay have different effects on target cells that have
– Different receptors for the hormone
– Different signal transductionpathways
– Different proteins for carrying out the response
11. Paracrine Signaling by Local Regulators
• In paracrine signaling, non-hormonal chemical signals called local
regulators elicit responses in nearby target cells
• Types of local regulators:
– Neurotransmitters
– Cytokines and growthfactors
– Prostaglandins help regulate aggregation of platelets, an early step
in formation of blood clots
12. • The hypothalamus and the pituitary gland control much of the endocrine
system
• Tropic hormones, hormones that regulate endocrine organs
• Tropic hormones are secreted into the blood and transported to the
anterior pituitary
The hypothalamus and pituitary integrate many functions
of the vertebrate endocrine system
13. Hormones Secreted by the Hypothalamus and Their Effects on
Anterior Pituitary
Corticotropin-releasing hormone (CRH)– Stimulates secretion of ACTH
(adrenocorticotropic hormone)
Gonadotropin-releasing hormone (GnRH) Stimulates secretion of FSH
(follicle-stimulatinghormone) and LH (luteinizing hormone)
Thyrotropin-releasing hormone(TRH)-stimulates secretion of TSH (thyroid-
stimulation hormone)
Melanocyte-stimulating hormone release inhibiting factor (MIF)-inhibits
secretion of MSH(Melanocyte-stimulating hormone)
16. Neurosecretory cells
of the hypothalamus
Endocrine cells of the
anterior pituitary
Portal vessels
Pituitary hormones
(blue dots)
Pain receptors
in the brain
Endorphin Growth hormone
Bones
Liver
MSH
Melanocytes
Prolactin
Mammary
glands
ACTH
Adrenal
cortex
TSH
Thyroid
Testes or
ovaries
FSH and LH
TARGET
HORMONE
Hypothalamic
releasing
hormones
(red dots)
Tropic Effects Only
FSH, follicle-stimulating hormone
LH, luteinizing hormone
TSH, thyroid-stimulating hormone
ACTH, adrenocorticotropic hormone
Nontropic Effects Only
Prolactin
MSH, melanocyte-stimulating hormone
Endorphin
Nontropic and Tropic Effects
Growth hormone
17. Posterior Pituitary Hormones
• The two hormones released from the posterior pituitary act directly on
non-endocrine tissues
• Oxytocin induces uterine contractions and milk ejection
• Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys
21. Tropic Hormones
• The four strictly tropic hormones are
– Follicle-stimulating hormone(FSH)
– Luteinizing hormone (LH)
– Thyroid-stimulating hormone (TSH)
– Adrenocorticotropichormone (ACTH)
• Each tropic hormone acts on its target endocrine tissue to stimulate
release of hormone(s) with direct metabolic or developmental effects -
(Release hormones)
22. Hypothalamus
Anterior pituitary
Control by hypothalamus
Pituitary gonadotropins
in blood
FSH LH
FSH
LH
GnRH
Inhibited by combination of
estrogen and progesterone
Inhibited by low levels of
estrogen
Stimulated by high levels
of estrogen
LH surge triggers
ovulation
FSH and LH stimulate
follicle to grow
Mature
follicle
Growing follicle
Ovarian cycle
Corpus
luteum
Degenerating
corpus luteum
Follicular phase Ovulation Luteal phase
Progesterone and
estrogen secreted
by corpus luteum
Estrogen secreted
by growing follicle in
increasing amounts
Progesterone and estro-
gen promote thickening
of endometrium
Peak causes
LH surge
Ovarian hormones
in blood
Estrogen level
very low
Progesterone
Estrogen
Endometrium
Uterine (menstrual) cycle
Menstrual flow phase Proliferative phase Secretory phase
Days
28
25
20
15
14
10
5
0
23. Non-tropic Hormones
• Non-tropic hormones produced by the anterior pituitary:
• Prolactin stimulates lactationin mammals but has diverse effects in
different vertebrates
• MSH influences skin pigmentationin some vertebrates and fat
metabolismin mammals
• Endorphins inhibit pain
24. Parathyroid Hormone and Calcitonin: Control of Blood Calcium
• Two antagonistic hormones, parathyroidhormone (PTH)
and calcitonin, play the major role in calcium (Ca2+)
homeostasis in mammals. Calcitonin stimulates Ca2+
deposition in bones and secretion by kidneys, lowering
blood Ca2+ levels
25.
26. STIMULUS:
Rising blood
Ca2+ level
Thyroid gland
releases
calcitonin.
Calcitonin
Stimulates
Ca2+ deposition
in bones
Reduces
Ca2+ uptake
in kidneys
Blood Ca2+
level declines
to set point
Homoeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
STIMULUS:
Falling blood
Ca2+ level
Blood Ca2+
level rises
to set point
Stimulates
Ca2+ release
from bones
PTH
Parathyroid
gland
Stimulates Ca2+
uptake in kidneys
Active
vitamin D
Increases
Ca2+ uptake
in intestines
27. Insulin and Glucagon: Control of Blood Glucose
(Pancreatic hormones)
• The pancreas secretes insulin and glucagon, antagonistic hormones that
help maintainglucose homeostasis
• Glucagon is produced by alpha cells
• Insulin is produced by beta cells
28.
29. Beta cells of
pancreas
release insulin
into the blood.
Insulin
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Rising blood glucose
level (for instance, after
eating a carbohydrate-
rich meal)
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
Liver breaks
down glycogen
and releases
glucose into the
blood.
Body cells
take up more
glucose.
Alpha cells of pancreas
release glucagon into
the blood.
Glucagon
30. Target Tissues for Insulin and Glucagon
• Insulinreduces blood glucoselevels by
– Promoting the cellular uptake of glucose
– Slowing glycogen breakdown in the liver
– Promoting fat storage
31. • Glucagon increases blood glucose levels by
– Stimulating conversion of glycogen to glucose in the liver
– Stimulating breakdown of fat and protein into glucose
STOP THERE!
32.
33. • The adrenal glands are adjacent to the kidneys
• The adrenal medulla secretes epinephrine (adrenaline) and
norepinephrine (noradrenaline)
• They are secreted in response to stress-activated impulses from
the nervous system
• They mediate various fight-or-flight responses
Adrenal Hormones: Response to Stress
34. Different receptors different cell responses
Epinephrine
a receptor
Epinephrine
receptor
Epinephrine
receptor
Vessel
constricts
Vessel
dilates
Intestinal blood
vessel
Skeletal muscle
blood vessel
Liver cell
Different intracellular proteins different cell responses
Glycogen
deposits
Glycogen
breaks down
and glucose
is released
from cell
35.
36. Melatonin and Biorhythms
• The pineal gland, located in the brain, secretes melatonin
• Light/dark cycles control release of melatonin
• Primary functions of melatonin appear to relate to biological
rhythms associated with reproduction
37. Invertebrateregulatory systems also involve endocrine and nervous
systeminteractions
• Diverse hormones regulate homeostasis in invertebrates
• In insects, molting and development are controlled by three main
hormones:
– Brain hormone stimulates release of ecdysone from the prothoracic
glands
– Ecdysone promotes molting and developmentof adult characteristics
– Juvenilehormone promotes retentionof larval characteristics
39. Growth Hormone
• Growth hormone (GH) has tropic and non-tropic actions
• It promotes growth directly and has diverse metabolic
effects
• It stimulates production of growth factors
40. Diabetes Mellitus
• Diabetes mellitus is perhaps the best-known endocrine
disorder
• It is caused by a deficiency of insulin or a decreased
response to insulin in target tissues
• It is marked by elevated blood glucose levels
