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