Endocrine System

Major processes of the endocrine system

Reproduction, growth and development, maintenance, regulation of cellular metabolism, mobilization of body defenses

What organs contain endocrine tissue?

Pancreas, gonads, placenta

Cephalic region

Pineal gland, hypothalamus, pituitary gland

Cervical

Thyroid, parathyroid

Thoracic

Thymus

Body

Adrenal glands, pancreas

Gonads

Ovaries and testes

Hormones

long-distance chemical signals of the endocrine system and travel in the blood to reach target cells

Autocrines

Effect exerted on the same cells that secrete them

Paracrines

Locally acting chemicals affecting neighbor cells

Permissiveness

One hormone can’t get in its full effect without another one

Two main second-messenger system

1) Cyclic AMP

2) PIP2+

Amino-acid based hormones

Most hormones, these are water soluble. With the exception of thyroid hormones, they exert their effects through the second-messenger systems

Steps of cAMP signaling

1) Hormone binds to receptor

2) Receptor activates a G protein

3) G protein activates/inhibits effector enzyme (adenylate cyclase)

4) Adcyc converts ATP to cAMP

5) cAMP activates kinase (phosphorylating protein). Effect on the cell determined by kinase prote Afterwards, cAMP is very quickly degraded by the enzyme phosphodiesterase. Produces massive cascade effect.

Oxytocin and ADH

These are small peptide hormones

Oxytocin

Released during childbirth and breast feeding, strong positive feedback loop hormone. It uses the PIP2+ secondary messenger system. It is inhibited by stress and lack of appropriate stimuli.

ADH

Secreted by high blood osmolarity

What three factors determine the degree of target cell activation?

1) The level of the hormone in the blood

2) Relative numbers of receptors for the hormone

3) Affinity of the binding

Hypophyseal portal system

The mechanism of transportation from hypothalamus to anterior pituitary gland

What produces calcitonin?

The parafollicular cells

What is the major hormone produced by the thyroid?

Thyroxine and triodothyronine

What is the main regulator of blood calcium levels?

Parathyroid hormone

Hormonal stimuli

• Hormones stimulate other endocrine organs to release their hormones

Nervous system overrides

The nervous system can override normal endocrine controls (for fight flight)

Up-regulation

This is where target cells add receptors for that hormone

Down-regulation

This is where cells remove receptors in response to persistent stimuli

Half-life of a horrmone

Time for half of the hormone to be removed from the blood

Permissiveness

One hormone can’t create full effect without another hormone being present

Synergism

More than one hormone produces same effects at target cell, and the combined effects are amplified (glucagon and epinephrine with liver blood glucose)

Antagonism

One or more hormone does not allow the other to function

Posterior pituitary is composed of…

Neural tissue

Anterior pituitary consists of…

Glandular tissue

Six tropic hormones

1.) Growth hormone

2.) Thyroid-stimulating hormone

3.) Adrenocorticotropic

4.) Follicle stimulating hormone

5.) Luteinizing hormone

6.) Prolactin

Growth hormone

This is also called somatotropin (has direct actions on

Somatostatins

Growth hormone-releasing hormone and growth hormone-inhibiting hormone

Acrogamely

Excessive thickening of bones, remedied with surgery

Thyroid stimulating hormone

This is also called thyrotropin and is produced by thyrotropic cells. It is triggered by the secretion of TRH

Adrenocorticotropic hormone (ACTH)

• Also called corticotropin (secreted by corticotropin cells)

• The precursor to pro-opiomelanocortin

• Secretion is triggered by hypothalamic CRH

• Secretion of CRH and ACTH is inhibited

Gonadotropins

• Follicle-stimulating hormone (FSH) and luteinizing hormone: secreted by gonadotropic hormone

Prolactin

Prolactin is secreted by the anterior pituitary, PRL stimulates milk production, and is regulated by PIH, which is dopamine. Hypersecretion: galactorrhea

Thyroid gland

T3 and T4: two forms of thyroid gland hormone