Chemical Signaling. Endocrine System Hormones Chemical signal secreted into body fluid for communication Secreted by neurosecretory cells Received.

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