Transcript Chapter 46 - Workforce3One

The Endocrine System
Chapter 46
How chemical messengers regulate body
processes?
• Hormones are regulatory chemicals secreted by
endocrine glands (table 46.1) into extracellular fluid
and carried by blood.
• Pheromones are regulatory chemicals released into
environment to communicate among individuals of a
single species
• Exocrine glands secrete saliva or milk (exocrine
secretions) into a duct for transport to outside
• Hormones must satisfy two characteristics – must be
complex to convey regulatory information to their
targets and must be able to resist destruction
before reaching their target cells
What are the three chemical classes of
hormones?
• Peptides and proteins are composed of chains of amino acids.
Example: Peptide hormones are antidiuretic hormone, insulin
and proteins are glycoproteins – TSH, LH etc
• Amino acid derivatives – are hormones manufactured by
enzymatic modification of specific amino acids. Secreted from
adrenal medulla (catecholamines), thyroid (tyrosine) and
pineal (melatonin) glands
• Steroids – lipids manufactured by enzymatic modification of
cholesterol – like progesterone, testosterone, cortisol etc.
• Steroid hormones can be divided into sex steroids secreted by
testes, ovaries, placenta and corticosteroids secreted by
adrenal cortex
Chemical nature of hormones
• Chemical nature of hormone determines its mode of
transportation and interaction with their targets
• Hormones categorized as lipophilic (nonpolar and fat
soluble) and hydrophilic (polar and water soluble)
• Hydrophilic hormones activate their receptors of
target cells from outside the cell membrane (activity
for minutes to hours). Lipophilic hormones attach
to transport proteins and their lipid solubility allows
them to cross cell membranes and bind to
intracellular receptors (days to weeks)
• Destroyed or deactivated after use and get excreted
via bile or urine
What are the posterior pituitary or
neurohypophysis hormones?
• Pituitary gland (hypophysis) hangs as a stalk from
hypothalamus (a part of central nervous system)
• Pituitary gland is a compound endocrine gland which has two
parts – glandular part called anterior pituitary or
adenohypophysis and fibrous part called posterior
pituitary or neurohypophysis
• Posterior pituitary releases two neurohormones – Antidiuretic
hormone stimulates water reabsorption by kidneys and
inhibits urine production. ii) Oxytocin stimulates milk ejection
reflex and uterine contractions in women during childbirth
• Produced by neuron cell bodies located in hypothalamus----transported along axon tracts from hypothalamus------to
posterior pituitary for storage-----Upon appropriate
stimulation the neurohormones get released into blood
What are the seven hormones produced by
anterior pituitary?
• Anterior pituitary secretes seven hormones that
stimulate growth of their target organs as well as
production and secretion of other hormones from
additional endocrine glands.
• Collective term – tropic hormones or tropins
• Classification of secreted proteins – peptide
hormones (adenocorticotropic hormones,
Melanocyte stimulating hormone), protein
hormones (growth hormone and Prolactin) and
glycoprotein hormones (Thyroid-stimulating
hormone, luteinizing hormone, follicle-stimulating
hormone) – page 930.
How releasing and inhibiting hormones
regulate anterior pituitary?
• Hypothalamus secretes releasers and inhibiters into blood
capillaries at the base of hypothalamus via portal system
• These blood capillaries drain into small veins that run within
stalk of pituitary to a second bed of capillaries in anterior
pituitary – hypothalamohypophysial portal system/portal
system
• Releasing hormones are peptide neurohormones that stimulate
release of other hormones – thyrotropin-releasing hormone,
corticotropin-releasing hormone and gonadotropin-releasing
hormone.
• Inhibitors can inhibit release of anterior pituitary hormones –
Somatostatin or growth-inhibiting factor and prolactininhibiting factor.
What is negative feedback theory?
• Some endocrine organs are not directly
regulated by hypothalamic control system
• The hypothalamus and the anterior pituitary
are partially controlled by the very hormones
whose secretion they stimulate
• This is called negative feedback and is
important to maintain constant levels of target
cell hormone (example thyroxine)
Negative feedback: Thyroid gland control
• Hpothalamus secretes TRH
Portal system
TRH stimulates anterior pituitary to secrete TSH
TSH stimulates thyroid gland to release thyroxine
Contains iodine
Thyroxine acts on hypothalamus and anterior
pituitary to inhibit secretion of TRH and TSH
Less iodine- hypothalamus and anterior
pituitary receive far less negative
feedback inhibition than normal
Consequence is overgrowth
of thyroid gland-GOITER
Metabolism
Negative feedback
keeps thyroxine levels
constant
Results in elevated increase
of TSH and TRH
Stimulates thyroid gland to
produce more thyroxine (iodine)
• Read 46.4 (examples of major peripheral
endocrine glands) and 46.5 (Other
Hormones and their effects)
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