Zoology 101: Endocrine System - Exam 3

Endocrine System

The collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, mood etc.

Similarities between Nervous System and Endocrine System

Body systems that send messages/communicate

• Help maintain homeostasis

• React to stimuli

Nervous System: Nature of Message

Electrical impulses traveling along nerves

Endocrine System: Nature of Message

Chemical messages, traveling in the bloodstream

Area of Response - Nervous System

Confined to one area of the body - response is localised

Area of Response - Endocrine System

Usually noticed in many organs - response is widespread

Controlled process - Nervous System

Reflexes such as blinking

Movement of the limbs

Controlled Processes - Endocrine System

Growth; development of reproductive system

Hormone

Chemical produced by body cells that circulates throughout the body, acts on target cell, and impacts a wide range of functions

Polypeptide

Water-solubles (hydrophilic) hormones made by the process of translation, go through endomembrane system, and secreted into bloodstreams

Examples of polypeptides

Insulin and glucagon

Steroids

Lipid-soluble (hydrophobic) hormones derived from cholesterol and cortisol, and

Example of steroid hormones

Cortisol, estrogen, and testosterone

Amines

Hormones derived from a single amino acid

Amine Hormones Example

Epinephrine (hydrophilic), Thyroxine (hydrophobic)

What do water-soluble hormones bind to?

Plasma membrane receptors

Lipid-soluble hormones

Bind to intracellular receptors

What occurs when epinephrine binds to the beta receotir in liver cells?

Breakdown of glycogen, release of glucose

Binding of epinephrine to beta receptor cells in skeletal muscles

Causes the vessel to dilate

Binding of epinephrine to alpha cells in intenstinal blood vessels

The vessel constricts

Negative Feedback Loop in Endocrine System

Hormone released

Response produced that reduces the stimulus, bringing system back to homeostasis

Example: Release of glucagon to break down glycogen and release glucosee

Coordination of endocrine and nervous systems

Hypothalamus recieves info from nerves in brain, initiatiing neuroendocrine signaling

Signals from hypothalamus travels to pituitary gland

Posterior Pituitary Gland

Neurosecretory cells of the hypothalamus extend into the posterior pituitary glands

Neurosecretory cells

Nerve cells that translaes neural signals into chemical stimuli

How does the posterior pituitary gland connected to the hypothalamus?

Through neurons

Posterior Pituitary Gland Function

Releases hormones that are made in hypothalamus and transported down axons for storage and secretion

How is the anterior pituitary connected to the hypothalamus?

Through a portal blood system

The hypothalamus controls it by releasing hormones into the bloodstream

Simple neuroendocrine pathway

• Stimulus picked up by a sensory neuron

• Travels to Central Nervous System and hypothalamus

• Neurosecretory cell produces hormone (i.e. oxytocin)

• Released into blood vessels of posterior pituitary

• Hormone is circulated throghout the body

• i.e suckling

Which hormones are released by the anterior pituitary?

FSH and LH

TSH

ACTH

GH

Prolactin

Which hormones are released by the posterior pituitary gland?

Oxytocin - targeting uterus and mammary glands

ADH - Kidneys

Hormone Cascade

Form of regulation in which multiple endocrine organs and hormones act in a series

i.e. anterior pituitary gland releasing LH/FSH

Neurohormones Location

Made in the hypothalamus and stored in posterior pituitary where they are released into the bloodstream

Hypothalamic releasing and inhibiting hormones

Travel through portal vessels to act on anterior pituitary which secretes pituitary hormones that enter circulation to reach target organs

Tropic Hormones

Act on other endocrine glands to trigger the release of additional hormones

Non-tropic hormones

Act directly on target tissues to produce an effect

Simple hormone pathway

One endocrine gland releases a hormone that acts on a target

i.e. prolactin acting on mammary glands

Functions of thyroid gland - Master of Homeostasis

• Regulates bioenergetics

• Maintaining blood pressure, heart rate, and muscle tone

• Regulates digestive and reproductive functions

Four hormones involved in Cascade of Regulating Thyroid Function

TRH

TSH

T3

T4

T3 and T4 contain iodine

Lack of iodine means …

T3 and T4 can’t be produced so TRH and TSH are constantly being released

Elevated TSH increases rate of thyroid cell division

Hypothyroidism

Result of too little T3/T4 circulating in the bloodstream

Symptoms: weight gain, tiredness, sensitivity to cold, etc.

Cause: Hashimoto’s Thyroiditis

Hyperthyroidism

Result of too much T3/T4 circulating in the bloodstream

Cause: Grave’s disease

Symptoms: Weight loss, heat intolerance, rapid pulse, eye protrusion