Download - Chemical signals in Animals
Chemical signals in Animals
Ch 45 – Endocrine system
Human Endocrine system
Both the nervous system & the endocrine system send message to the bodyNervous – messages for quicker, more specific responses Endocrine – messages for broader, more widespread responses
http://www.youtube.com/watch?v=gjmS4_7kvDM
Lactation- example of interaction between nervous & endocrine systems
Chemical Signals
1) endocrine2) paracrine & autocrine3) synaptic & neuroendocrine
- neurosecretory cells secrete molecules (neurohormones) into the blood stream
4) pheromones- chemicals released into external
environment
Local Regulators• Cytokinases – polypeptide regulators, carry
signals locally between cells• Growth factors• Nitric oxide – gas, produced by many cells
causes changes within seconds in target cell & then breaks down
• Prostaglandins- promote fever and inflammation and intensify the sensation of pain, also active in female reproductive system – ie. Inducing labor in childbirth
Hormones – long distance signals• Three classes:• 1) Polypeptides – Water soluble (hydrophilic)
– i.e. insulin• 2) Steroids – Lipid soluble (Hydrophobic)
– i.e. testosterone, estradiol• 3) Amines – most are water soluble
– i.e. thyroxin, epinephrine
• Water soluble hormones – bind to cell-surface receptor cells
• This starts the signal transduction pathway
• Causes changes in cytoplasm, enzyme activation, or changes in gene expression
• Lipid soluble – can pass through cell membrane, bind to receptors in cytoplasm or nucleus
• Cause possible change in gene expression, or cytoplasmic response
Different receptorsSame receptors but differentintracellular proteins (not shown)
Different cellularresponses
Different cellularresponses
Epinephrine Epinephrine Epinephrine
receptor receptor receptor
Glycogendeposits
Vesseldilates.
Vesselconstricts.
Glycogenbreaks downand glucoseis releasedfrom cell.
(a) Liver cell (b) Skeletal muscleblood vessel
Intestinal bloodvessel
(c)
Hypothalamus & Pituitary gland
• The hypothalamus – at the base of the brain • Helps integrate nervous & endocrine systems
– Receives nervous signals– Releases hormones to control the anterior
pituitary
Pituitary GlandAnterior
• Secretes four tropic hormones: • TSH – thyroxin stimulating hormone• LH – luteinizing hormone• FSH – follicle stimulating hormone• ACTH – adrenocorticotropic hormone• Tropic hormones – control other endocrine
glands• Also releases other peptide hormones
(prolactin, growth hormone)
Pituitary Gland Posterior
• Hypothalamic neurons extend into the posterior
• Secretes 2 neurohormones:–ADH – antidiuretic hormone–Oxytocin
Hormone Feedback loops
• Many used to maintain Homeostasis• Negative feedback helps maintain pre-existing
state• Some homeostatic control systems have two
antagonistic negative feedback pathways, that balance each other
Control of Blood Glucose• Pancreas produces 2 hormones that control glucose level:
• Glucagon• Made by alpha cells in
pancreas• Increases glucose
levels by targeting liver cells – stimulates glycogen hydrolysis, release glucose into bloodstream
• Insulin• Made by beta cells in
pancreas• Lowers glucose levels by
stimulating body cells to take up glucose from blood
• Slows glycogen breakdown in liver
Body cellstake up moreglucose.
InsulinBeta cells ofpancreasrelease insulininto the blood.
Liver takesup glucose and stores itas glycogen.
Blood glucoselevel declines.
Blood glucoselevel rises.
Homeostasis:Blood glucose level
(70–110 mg/m100mL)
STIMULUS:Blood glucose level rises
(for instance, after eating acarbohydrate-rich meal).
Liver breaksdown glycogenand releasesglucose intothe blood.
Alpha cells of pancreasrelease glucagon intothe blood.
Glucagon
STIMULUS:Blood glucose level
falls (for instance, afterskipping a meal).
Diabetes
• Chronic disease where there are high levels of sugar in the blood
• Symptoms: frequent urination, blurred vision
Diabetes
• Type 1– insulin dependent• Beta cells produce little or no insulin, so
glucose builds up in blood• Autoimmune system destroys beta cells
• Type 2 – non insulin dependent • Target cells do not respond to insulin• Suppression of target cells, so pathway
doesn’t function
Thyroid gland
• Helps regulate metabolic rate and body temperature
• Also involved in calcium regulation
Thyroid regulationThyroid produces Thyroxine (T4)
and similar hormone T3(T3 is more active)
(count iodines)
• Thyroxine – lipid soluble• Binds to intracellular receptor that stimulates
transcription of several genes• These genes encode proteins involved in
energy pathways – leads to general increase in cell metabolism
• Important in development and growth – it promotes amino acid uptake & protein synthesis
• Insufficient thyroxine – retards physical and mental development – (cretinism)
• Thyroxine levels are controlled by the hypothalamus and anterior pituitary
• Hypothalamus releases TRH – thyrotropin releasing hormone
• This stimulates the anterior pituitary to release thyroid stimulating hormone
Pathway ExampleStimulus Cold
Sensory neuron
Hypothalamus
Neurosecretory cell
Releasing hormone
Blood vessel
Anterior pituitary
Tropic hormone
Hypothalamus secretesthyrotropin-releasinghormone (TRH ).
Anterior pituitary secretesthyroid-stimulatinghormone (TSH, also knownas thyrotropin ).
Anterior pituitary
Tropic hormone
Endocrine cellHormone
Targetcells
Response
Anterior pituitary secretesthyroid-stimulatinghormone (TSH, also knownas thyrotropin ).
Thyroid gland secretesthyroid hormone(T3 and T4 ).
Body tissues
Increased cellularmetabolism
Pathway Example
Neg
ativ
e fe
edba
ck
Tohypothalamus
Hormone cascade pathway
• Thyroid regulation is an example of a hormone cascade pathway
• One hormone stimulates a series of other hormones, which finally activates a nonendocrine target cell
Thyroid issues
• Too much thyroxine – Hyperthyroidism• - most commonly a result of an autoimmune
disorder, where antibody binds to and activates TSH receptors
• Blood TSH is low due to negative feedback from thyroxine
• - Thyroid gland is always stimulated, so goiter may occur (enlarged thyroid)
• - symptoms: high metabolism, feel hot, nervous, may have eyes bulge (buildup of fat)
• Too little thyroxine – Hypothyroidism
• Most commonly – due to too little dietary iodine, so the thyroid cannot make functional thyroxine
• TSH levels high, stimulates Thyroid to become bigger
• Can lead to Goiter – enlarged thyroid
Adrenal gland
• Adrenal glands sit above the kidneys• Two parts:
– Inner – Adrenal medulla – produces epinephrine and norephinephrine (catecholamines)
– Outer – Adrenal cortex – produces glucocorticoids,mineralcorticoids and sex hormones
Stress response – “fight or flight” • Epinephrine and norepinephrine secreted in
response to positive or negative stress– Trigger the release of glucose and fatty acids into
the blood– Increase oxygen delivery to body cells – Direct blood toward heart, brain, and skeletal
muscles and away from skin, digestive system, and kidneys
• http://www.youtube.com/watch?v=BIfK0L8xDP0• http://www.youtube.com/watch?v=
FBnBTkcr6No
Stress response- longer term
• Glucocorticoids are secreted from adrenal cortex (affect glucose production)– Increased blood glucose
• Mineralcorticoids secreted from adrenal cortex (affect salt & water balance)– Increased blood volume & blood pressure
Spinal cord(cross section)
(a) (b) Long-term stress responseand the adrenal cortex
Short-term stress responseand the adrenal medulla
StressNervesignals
Nervecell
Releasinghormone
Hypothalamus
Anterior pituitary
Blood vesselNerve cell ACTH
Adrenal medullasecretes epinephrineand norepinephrine.
AdrenalglandKidney
Adrenal cortexsecretes mineralo-corticoids andglucocorticoids.
Effects of epinephrine and norepinephrine: Effects of mineralocorticoids:
Effects of glucocorticoids:
• Glycogen broken down to glucose; increased blood glucose
• Increased blood pressure • Increased breathing rate• Increased metabolic rate
• Retention of sodium ions and water by kidneys
• Increased blood volume and blood pressure
• Proteins and fats broken down and converted to glucose, leading to increased blood glucose
• Partial suppression of immune system
Melatonin and Biorhythms
• The pineal gland, located in the brain, secretes melatonin
• Light/dark cycles control release of melatonin– It is secreted at night, amount depends on
length of night• Primary functions of melatonin appear to
relate to biological rhythms associated with reproduction