1. Endocrine System Hormones
Chapter 45.
Endocrine System
Hormones

2. Regulation Why are hormones needed?
chemical messages from one body part to another
communication needed to coordinate whole body
homeostasis & regulation
metabolism
growth
development
maturation
reproduction
growth hormones

3. Regulation & Communication
Animals rely on 2 systems for regulation
endocrine system
ductless gland which secrete chemical signals directly into blood
chemical travels to target tissue
slow, long-lasting response
nervous system
system of neurons, central nerve system
transmits “electrical” signal to target tissue
fast, short-lasting response
Hormones coordinate slower but longer–acting responses to stimuli such as stress, dehydration, and low blood glucose levels. Hormones also regulate long–term developmental processes by informing different parts of the body how fast to grow or when to develop the characteristics that distinguish male from female or juvenile from adult. Hormone–secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid. From there, the chemicals diffuse into the circulation.

4. Regulation by chemical messengers
Neurotransmitters released by neurons
Hormones release by endocrine glands
Endocrine gland
Axon
Neurotransmitter
Hormone
carried
by blood
Receptor
proteins
Target cell

5. Classes of Hormones Protein-based hormones Lipid-based hormones
polypeptides
small proteins: insulin, ADH
glycoproteins
large proteins + carbohydrate: FSH, LH
amines
modified amino acids: epinephrine, melatonin
Lipid-based hormones
steroids
modified cholesterol: sex hormones, aldosterone

6. How do hormones act on target cells
Lipid-based hormones
lipid-soluble
diffuse across membrane & enter cells
bind to receptor proteins in cytoplasm & then this hormone-receptor complex moves into nucleus
bind to receptor proteins in nucleus
bind to DNA as transcription factors

7. Action of steroid (lipid) hormones
Cytoplasm
Blood plasma
Steroid
hormone S S 1
Protein
carrier S 2
Plasma membrane 1
Steroid hormone (S) passes through plasma membrane. 2
Inside target cell, the steroid hormone binds to a specific receptor protein in the cytoplasm or nucleus. 4 S 3
Hormone-receptor complex enters nucleus & binds to DNA, causing gene transcription 3
DNA
mRNA 5
Protein 4
Protein synthesis is induced.
Nucleus 5
Protein is produced.

8. How do hormones act on target cells
Protein-based hormones
hydrophilic & not lipid soluble
can’t diffuse across membrane
trigger secondary (2°) messenger pathway
transmit “signal” across membrane
“signal transduction”
usually activates a series of 2° messengers
multi-step “cascade”
activate cellular response
enzyme action, uptake or secretion of molecules, etc.
Signal molecule
Cell surface receptor
enzyme
cAMP
G protein
ATP
Target protein
Nucleus
Cytoplasm

9. Action of protein hormones1
Protein
hormone
activates enzyme
G protein
Receptor
protein
cAMP 3 2
ATP
activates
enzyme
protein
messenger cascade
GTP
activates
enzyme 4
Cytoplasm
Produces an action

10. Action of epinephrine (adrenalin)
Liver cell 1
Epinephrine
activates adenylyl cyclase
adrenal gland
G protein
Receptor
protein
cAMP 3 2
ATP
activates
protein kinase-A
GTP
activates
phosphorylase 4
released to blood
Cytoplasm
Glycogen
Glucose

11. Benefits of a 2° messenger system1
Receptor protein
Activated adenylyl cyclase
Signal molecule
Not yet
activated 2
Amplification 4
Amplification
cAMP 3 5
GTP
G protein
Protein kinase 6
Amplification
Amplification!
Enzyme 7
Amplification
Enzymatic product

12. Endocrine system Ductless glands release hormones into blood
Duct glands = exocrine
(tears, salivary)

13. Major vertebrate hormones (1)

14. Major vertebrate hormones (2)

15. Endocrine & Nervous system links
Hypothalamus = “master control center”
nervous system
receives information from nerves around body about internal conditions
regulates release of hormones from pituitary
Pituitary gland = “master gland”
endocrine system
secretes broad range of hormones regulating other glands

16. Melanocyte-stimulating hormone
Thyroid gland
Hypothalamus
Anterior
pituitary
Gonadotropic
hormones:
Follicle-
stimulating
hormone (FSH)
& luteinizing
hormone (LH)
Mammary
glands
in mammals
Muscles
of uterus
Kidney
tubules
Posterior
Thyroid-stimulating
Hormone
(TSH)
Antidiuretic
hormone
(ADH)
Adrenal
cortex
Bone
and muscle
Testis
Ovary
Melanocyte
in amphibian
Adrenocorticotropic
hormone (ACTH)
Melanocyte-stimulating hormone
(MSH)
Oxytocin
Prolactin (PRL)
Growth hormone (GH)

17. metamorphosis & maturation
Homology in hormones
What does this tell you about these hormones?
prolactin
same gene family
growth hormone
mammals
birds
fish
amphibians
milk production
fat metabolism
salt & water balance
metamorphosis & maturation
growth & development
The most remarkable characteristic of prolactin (PRL) is the great diversity of effects it produces in different vertebrate species. For example, prolactin stimulates mammary gland growth and milk synthesis in mammals; regulates fat metabolism and reproduction in birds; delays metamorphosis in amphibians, where it may also function as a larval growth hormone; and regulates salt and water balance in freshwater fishes. This list suggests that prolactin is an ancient hormone whose functions have diversified during the evolution of the various vertebrate groups.
Growth hormone (GH) is so similar structurally to prolactin that scientists hypothesize that the genes directing their production evolved from the same ancestral gene. Gene duplication!

18. Hormones & Homeostasis
Negative feedback
stimulus triggers control mechanism that inhibits further change
body temperature
sugar metabolism
Positive feedback
stimulus triggers control mechanism that amplifies effect
lactation
labor contractions
Inhibition
Hypothalamus –
Releasing hormones
(TRH, CRH, GnRH)
Inhibition
Anterior pituitary –
Tropic hormones
(TSH, ACTH, FSH, LH)
Target glands
(thyroid, adrenal cortex, gonads)
Hormones

19. Regulating blood sugar levels
beta islet cells
triggers uptake of glucose by body cells
triggers storage in liver
- depresses appetite
pancreas
- triggers release of glucose by liver
- stimulates appetite
pancreas
alpha islet cells

20. Regulating blood osmolarity
If amount of dissolved material in blood too high, need to dilute blood
Dehydration
Lowers
blood
volume
& pressure
Osmotic concentration
of blood increases
Osmoreceptors
Negative
feedback
Negative
feedback
ADH synthesized in hypothalamus
ADH
ADH released from posterior pituitary into blood
Increased
water
retention
Increased
vasoconstriction
leading to higher
blood pressure
Reduced
urine volume

21. Regulating metabolism
Hypothalamus
TRH = TSH-releasing hormone
Anterior Pituitary
TSH = thyroid stimulating hormone
Thyroid
produces thyroxine hormones
metabolism & development
bone growth
mental development
metabolic use of energy
blood pressure & heart rate
muscle tone
digestion
reproduction
The thyroid gland produces two very similar hormones derived from the amino acid tyrosine: triiodothyronine (T3), which contains three iodine atoms, and tetraiodothyronine, or thyroxine (T4), which contains four iodine atoms. In mammals, the thyroid secretes mainly T4, but target cells convert most of it to T3 by removing one iodine atom. Although both hormones are bound by the same receptor protein located in the cell nucleus, the receptor has greater affinity for T3 than for T4. Thus, it is mostly T3 that brings about responses in target cells.
tyrosine
iodine
thyroxine

22. Goiter
Iodine deficiency causes thyroid to enlarge as it tries to produce thyroxine

23. Homology in hormones Thyroxine stimulates metamorphosis in amphibians
TRH
TSH
Thyroxine
Thyroxine secretion rate
TRH rises
–35
–30
–25
–20
–15
–10 –5 +5
+10
Days from emergence of forelimb

24. Regulating blood calcium levels
Thyroid
Low blood Ca++
Parathyroids –
Parathyroid
hormone (PTH)
Negative
feedback
PTH activates Vitamin D into hormone that enables calcium absorption from intestines. This is why Vitamin D deficiency causes rickets = poor bone formation
Increased absorption
of Ca++ from intestine due to PTH activation of Vitamin D
Reabsorption of Ca++ &
excretion of PO4
Osteoclasts
dissolve CaPO4
crystals in bone, releasing Ca++
Increased blood Ca++

25. Hormonal regulation of insect development
Neurosecretory cells
Brain hormone
Juvenile hormone
Prothoracic
gland
Low amounts
The hormonal regulation of insect development has been studied extensively. Three hormones play major roles in molting and metamorphosis into the adult form.
Brain hormone, produced by neurosecretory cells in the insect brain, stimulates the release of ecdysone from the prothoracic glands, a pair of endocrine glands just behind the head. Ecdysone promotes molting and the development of adult characteristics, as in the change from a caterpillar to a butterfly. Brain hormone and ecdysone are balanced by the third hormone in this system, juvenile hormone. Juvenile hormone is secreted by a pair of small endocrine glands just behind the brain, the corpora allata (singular, corpus allatum), which are somewhat analogous to the anterior pituitary gland in vertebrates. As its name suggests, juvenile hormone promotes the retention of larval (juvenile) characteristics.
In the presence of a relatively high concentration of juvenile hormone, ecdysone can still stimulate molting, but the product is simply a larger larva. Only when the level of juvenile hormone wanes can ecdysone–induced molting produce a developmental stage called a pupa. Within the pupa, metamorphosis replaces larval anatomy with the insect’s adult form. Synthetic versions of juvenile hormone are now being used as insecticides to prevent insects from maturing into reproducing adults.
Molting hormone
Larval molt
Pupal molt
Adult molt

26. Any Questions??