Chemical Signaling
Jan 18, 2016
Chemical Signaling
Endocrine SystemEndocrine SystemHormones
Chemical signal secretedinto body fluid for communication
Secreted by neurosecretory cellsReceived by target cells
SlowLong durationOften “talks” with
nervous system
Endocrine SystemEndocrine System
Local regulators: influence nearby cells
Growth factors: peptides & proteins that stimulate cell growth, division, & development
Prostaglandins (PGs): modified fatty acids act as local regulators, esp. in reproductive & defense systems
Endocrine SystemEndocrine System
Two pathways
1) Hormone binds to receptor on target cell signal transduction pathway response
Response depends on target cell type
Endocrine SystemEndocrine System
2) Hormone enters target cell & nucleus signal transduction pathway (acting as transcription factor) response (change in gene expression through protein synthesis)Steroids,
thyroid hormones
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Overview of hormones, including tropic hormones
Have other endocrine organs as target
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
HypothalamusLower brainReceives info from nerves & brainSends appropriate hormone
response based on environmental conditions
Have two sets of neurosecretory cells Secretions stored in or regulate
activity of pituitary gland
Vertebrate Endocrine Vertebrate Endocrine SystemSystemPituitary gland
Two discrete parts1) Anterior pituitary
(adenohypophysis)Secretes directly into blood“On” if releasing hormones
were secreted from hypothalamus
“Off” if inhibitory hormones were secreted
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Tropic hormones include:
Thyroid-stimulating hormone (TSH)
Follicle-stimulating hormone (FSH)**
Leutinizing hormone (LH)**
Adrenocorticotropic hormone – stimulates adrenal cortex
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
**gonadotropins – stimulate gonad activity
Other hormonesGrowth hormone (GH) – protein;
stimulates liver to produce insulinlike growth factors (IGF), which stimulates bone & cartilage growth
Prolactin (PRL) – protein; mammary growth & milk production in mammals (different in other species)
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Melanocyte-stimulating hormone (MSH) – regulates skin pigment & fat metabolism
Endorphins – inhibit pain perception
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
2) Posterior pituitary (neurohypophysis)Extension of the brainHormones include:
Antidiuretic hormone (ADH) – regulates osmolarity of blood
If osmolarity increases, osmoreceptors in hypothalamus shrink & send impulse to release ADH
Signal-transduction pathway in kidney tubules to increase water permeability, which will stop ADH release (neg feedback)
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Oxytocin – acts on uterus to contract during birth & mammary glands to eject milk during nursing
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Pineal glandCenter of brainSecretes melatonin (amino acid)
Regulates function (mostly reproductive) based on changes in day length
Secreted at nightHas light-sensitive cells or
connections from eyes
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Thyroid glandTwo lobes on ventral surface
of tracheaHormones:
Triiodothyronine (T3) – 3 I atomsThyroxine (T4) – 4 I atoms –
predominant secretion – converted to T3
Calcitonin – lowers Ca2+ in blood
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Embryonic brain development
Vertebrate development & maturation
Homeostasis
Bp, hr, muscle tone, digestion, reproduction
Metabolism
Vertebrate Endocrine Vertebrate Endocrine SystemSystemMalfunctions
HyperthyroidismHypothyroidismCretinism (in infants –
muscular & skeletal retardation)Goiter
Enlarged thyroidIodine deficiency
Vertebrate Endocrine Vertebrate Endocrine SystemSystemParathyroid
4Embedded in thyroidHomeostasis of Ca2+ ionsHormones:
Parathyroid hormone (PTH)Raises blood levels of Ca2+
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Induces osteoclasts to decompose bone minerals and put into blood, increases kidney 7 intestine absorption of calcium
MalfunctionsTetany – convulsive contraction
of skeletal muscles due to lack of PTH
Vertebrate Vertebrate Endocrine SystemEndocrine System
PancreasIslets of Langerhans – endocrine cell
clustersSecrete glucagon (through alpha
cells) & insulin (through beta cells)Regulate glucose in blood (negative
feedback)Insulin lowers blood sugar, slows
glycogen breakdown in liver, inhibits a.a. & glycerol conversion to sugar
Liver is extremely sensitive to glucagon
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
MalfunctionsDiabetes melliuts
High blood sugarExcessive thirst, frequent
urination, sugar in urineUse fat breakdown for cell
respiration instead of sugar – can lower blood pH
Two types
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Type I (insulin-dependent)Immune system attacks
pancreasChildhoodDestroys ability to make insulinInsulin injections
Type II (insulin-independent)Deficiency of insulin or reduced
responsiveness in target cell (change in receptors)
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Adulthood
More than 90% of diabetics
Managed by diet & exercise
Adrenal glands
Sit on top of both kidneys
Two glands
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Adrenal medulla (central portion)Works with nervous systemCells derived from neural crestHormones:
Epinephrine (adrenaline)Norepinephrine (noradrenaline)Both known as
catecholamines, from a.a tyrosine
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Secreted in response to + & - stress
Inc. availability of energy sourcesBoost metabolic rateWork with circ. & resp. systems to
inc. O2 flow & divert blood to heart, brain, & muscles
Works with sympathetic portion of the autonomic nervous system
When nerves stimulated, release acetylcholine in medulla, which causes release of epinephrine
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Norepinephrine works to sustain blood pressure
Adrenal cortex (outer portion)Reacts to stress, but responds to
endocrine rather than nervous system
Hypothalamus secretes anterior pituitary releases ACTH adrenal cortex secretes corticosteroids (glucocorticoids, such as cortisol, & mineralocorticoids, such as aldosterone)
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Glucocorticoids – work on bioenergetics, specifically glucose metabolism
They promote synthesis of glucose from noncarbohydrate sources like muscle proteins
High doses suppress immune system, but are used to fight inflammation
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
Mineralocorticoids – salt & water balance
They stimulate kidney cells to reabsorb sodium & water
Vertebrate Vertebrate Endocrine SystemEndocrine System Gonads
Hormones affect growth, development, reproductive regulation, sexual behavior
Secrete 3 types of steroids (testes of males, ovaries of females)Androgens
Primary steroid of testes (testosterone)
In embryo, development of male organs
Secondary sex characteristics of male
Vertebrate Endocrine Vertebrate Endocrine SystemSystem
EstrogensEstradiolFemale development &
secondary sex charactersticsProgestins
ProgesteronePrepare & maintain uterus
Controlled by gonadotropins, FSH, LH, GnRH of hypothalamus