Endocrine System - Chapter 17

Endocrine System

Composed of endocrine glands located throughout the body. Glands synthesize and secrete hormones

What are hormones?

Chemical messengers made by glands in your body that travel through your blood to tell your organs and tissues what to do. At least 50 different types

What are target cells?

Cells have specific receptors for a hormone. Each type of hormone differs in its target cells and thus, the cellular activities that it regulates

Which system is the complementary body system of control with the endocrine system?

Nervous system.
Both providing information around our corpus - controlling every move

Endocrine System features:

• Communication method: Endocrine glands secrete hormones; transported through the blood

• Target Stimulation: Any cell in the body with the receptor for the hormone

• Response Time: Slow, seconds to minutes to hours

• Range of Effect: Widespread effects

• Duration of response: Long-lasting: minutes to weeks, may continue after stimulus is removed

Nervous System

• Communication method: A neurotransmitter is released from a neuron into a synaptic cleft

• Target Stimulation: Other neurons, muscle cells, and glands

• Response Time: Fast, milliseconds or seconds

• Range of Effect: Localized, specific effects

• Duration of response: Short-term: Milliseconds; terminates with removal or stimulus

Functions of Endocrine System

• Maintains homeostasis of blood composition and volume by regulating concentrations of specific substances in the blood

• Controls reproductive activites

• Digestive process

• Regulates development, growth, and metabolism

Endocrine glands

• Composed of connective tissue framework

• Supports the epithelial tissue that produces and releases hormones from their secretory cells

Distinguish between the two types of organization of endocrine cells

Endocrine cells can be organized as single organ with only endocrine function or as small clusters within other organs

What are the Major Endocrine Organs and their location within the body

• Pituitary - Hypothalamus

• Pineal - Hypothalamus

• Thyroid Glands- Thyroid

• Parathyroid - Thyroid

• Adrenal glands - Above kidneys

What is Hormonal Stimulation?

Release hormones from endocrine gland is the binding of another hormone
ex: thyroid-stimulating hormone bind to thyroid and cause release of thyroid hormone

Humoral Stimulation

Some endocrine glands are stimulated to release hormones in response to changing levels of nutrients within the blood
ex: blood glucose levels increase and the pancreas releases insulin

Nervous system stimulation

A few endocrine glands are stimulated to release hormones by direct stimulation from the nervous system

Categories of Hormones: Steroids

• Lipid-soluble molecules synthesized from cholesterol

• Produced within Gonads:

  • Estrogen and progesterone in ovaries

  • Testosterone in testes

• Synthesized by adrenal cortex (corticosteroids such as cortisol)

• -sterone ending is a steroid hormone

• Calcitriol produced from vitamin D

  • Slightly different molecule because it is a sterol hormone

Categories of Hormones: Biogenic Amines (monoamines)

• Modified amino acids

• Catecholamines (epinephrine& norepinephrine) released from the adrenal medulla

  • Thyroid hormone released from the thyroid gland

  • Melatonin from the pineal gland

• Water-soluble except for thyroid hormone

  • Thyroid hormone is lipid-soluble because it is produced from 2 tyrosine amino acids (nonpolar ring)

Categories of Hormones: Proteins

• Composed of small chains of amino acids (small peptides, large polypeptides, and glycoproteins)

• Water-soluble

Name the three structural categories of circulating hormones and give examples within each category

• Steroid hormones- lipid soluble molecules synthesized from cholesterol

• Protein hormones- most abundant hormones, small, water soluble chains of amino acids

• Biogenic amines- modified amino acids that are water soluble

Local hormones

• Large group of short-lived signaling molecules

• Chemical messenger acts directly on nearby cells in the tissue where it is produced, rather than traveling through the bloodstream to distant organs

• Autocrine stimulation = binds with same cell

• Paracrine stimulation = neighboring cells

How are hormones transported?

Within the blood, to target cells following their release from the endocrine gland that synthesized them

Lipid-soluble hormones

• Steroids, calcitriol, thyroid hormone

• Non-polar molecules that do not dissolve readily within aqueous environment of the blood

• Require transport proteins, which are water-soluble proteins synthesized by the liver

• Some are selective

• Transport protein is beneficial because it protects the hormone and prevents early destruction

What happens between the binding of a lipid-soluble hormone and a transport protein?

• Hormone molecules bind to the transport protein, detach from the transport protein, and float free within the blood

• Reattach to a different transport protein molecule

• Bound hormone = attached to transport protein

  • Readily available source within the blood

• Unbound (free) hormone = unattached hormone

  • Exit blood and bind to cellular receptors of target organs

Water-soluble hormones

• Biogenic amines and proteins

• Readily dissolve within aqueous environment of the blood

• Hormones do not generally require transport proteins

• Generally released directly into the blood and transported to target cells

• Bound to transport proteins, function to prolong biological half-life

Describe water soluble hormones induce change in target cells

signal transduction pathway → water hormone (first messenger) must bind with receptor → G protein binds with the receptor → G protein activated by GDP and GTP → G protein released (second messenger)

Describe the 2 primary factors that affect the concentration level of a circulating hormone

hormone synthesis and hormone elimination

Hormone release

• From the endocrine gland and hormone concentration within the blood are positively correlated

• Increase in release of hormone results in a higher concentration within the blood

• Decrease in hormone results in lower hormone concentration within the blood

Hormone elimination

• Through enzymatic degradation (occurs in liver cells)

• Trough removal of hormone from the blood by its excretion from the kidneys as a component of urine

• By uptake into target cells

• Fast rate of elimination = lower hormone concentration in blood

• Slow rate of elimination = higher hormone concentration in blood

Biological half-life

Time required to reduce substance by one-half of its original quality

Where are lipid-soluble hormone receptors located? What is the general cellular change that occurs with binding of a lipid-soluble hormone?

• Located inside target cells such as cytoplasm or nucleus

• The alteration of gene expression (transcription) to synthesize new proteins

How do lipid-soluble hormones reach their target cell receptors, and what type of cellular change do they initiate?

Diffuse across plasma membrane → bind to intracellular receptors located in the cytosol or nucleus to from hormone-receptor complex → binds to a certain DNA sequence within the nucleus called hormone response elements → transcription begins and then the synthesis of specific protein begins → results in either an alteration in cell structure or a shift in the target cells metabolic activities

How water-soluble hormones induce cellular change in their target cells

attaching to receptor proteins on the outer surface of the cell membrane

List the hormones released from the hypothalamus that control the anterior pituitary

• Regulatory hormones

• Can either release hormones that stimulate production and secretion

• Inhibiting hormones that deter the production and secretion

Identify and briefly describe the six tropic hormones produced by the anterior pituitary

• Thyroid hormone (TSH): regulates the release of thyroid hormone from the thyroid gland

• Prolactin (PRL): regulates mammary gland growth and breast milk production in females and may help androgen production in males,

• Follicle-stimulating hormone (FSH)/ luteinizing hormone (LH): production and maturation of gametes

• Adrenocorticotropic hormone (ACTH): stimulates the adrenal cortex to produce and secrete glucocorticoids (cortisol)

• Growth hormone (GH): stimulates cell growth and division and affects most body cell

Explain how the hypothalamus controls the release of hormones from the anterior pituitary and the general function of each

portal veins connect the two, hypothalamus releases either releasing hormones or inhibiting hormones

Describe the thyroid gland location and anatomy

the thyroid gland is a butterfly shaped gland anterior to the trachea and inferior to the larynx

Discuss how thyroid hormones are produced, stored and secreted

• The thyroid gland is composed of spherical thyroid follicles.

• The wall of each follicle is formed by cuboidal epithelial cells, called follicular cells, which surround a central lumen

• That lumen houses a viscous, protein-rich fluid termed colloid.

• Iodine is attached to tyrosine amino acids of thyroglobulin within the colloid of thyroid follicles

• Then pre-T3 and pre-T4 structures are formed. Thyroglobulin with pre-T3 and pre-T4 is later transported into the follicular cells.

• Within lysosomes of follicular cells, thyroid hormone (T3, T4) is cleaved from thyroglobulin and released into the blood by endocytosis.

Explain the homeostatic system involving thyroid hormone

• Decreased levels of thyroid hormone and certain stimuli cause the hypothalamus to secrete thyrotropin-releasing hormone (TRH), which causes release of thyroid-stimulating hormone (TSH) from the anterior pituitary

• TSH reaches the thyroid gland and causes release of thyroid hormone (TH) from a stored precursor

• This interactive sequence is referred to as the hypothalamic-pituitary-thyroid axis

• Thyroid hormone increases metabolism with a subsequent increase in body temperature

• To support the higher metabolic rate additional glucose and fatty acids are released into the blood, heart rate and force of contraction are increased, and breathing rate is increased

Describe the structure and location of the adrenal glands

• The adrenal glands are anchored on the superior surface of each kidney and have both an outer cortex and an inner medulla.

• Each adrenal gland is a two-part gland that secretes stress-related hormones.

• The adrenal cortex produces corticosteroid hormones (e.g., cortisol), and the adrenal medulla produces epinephrine and norepinephrine.

Name the three zones of the adrenal cortex and the hormones produced by each

1. Zona glomerulosa: thin, outer layer composed of spherical cells that synthesize mineralocorticoids (e.g., aldosteroid regulates the ration of Na+ and K+ in our blood and body fluids by altering the amounts excreted by the kidney into the urine), a group of hormones that help regulate the composition and concentration of electrolytes in body fluids.

2. Zona fasciculata: the middle layer and largest region of the adrenal cortex. The primary glucocorticoids synthesized in this region are cortisol and corticosterone.

3. Zona reticularis: the innermost region of the cortex with cells capable of secreting minor amounts of sex hormones called gonadocorticoids (e.g., androgens

Describe how the hypothalamus controls the release of glucocorticoid and the effects of cortisol

• Upon receiving certain stimulation, the hypothalamus secretes corticotropin-releasing hormone (CRH), which causes the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary

• ACTH brings about the release of cortisol by the adrenal cortex.

• This relationship is called the hypothalamic-pituitary-adrenal axis.

• The net effect of cortisol is an increase in blood glucose, release of glycerol and fatty acids into blood, and an increase in protein degradation

identify the primary types of pancreatic islet cells and the hormones they produce

• Scattered among the pancreatic acini are small clusters of endocrine cells called pancreatic islets

• A pancreatic islet cell is composed of two primary types of cells: alpha cells that secrete glucagon, and beta cells that secrete insulin

Describe the action of insulin in lowering blood glucose concentration

The release of insulin into the blood from beta cells results in a decrease in all nutrients in the blood (including glucose) and an increase in the storage of these molecules within body tissues.

Explain the action of glucagon in raising blood glucose concentration

The release of glucagon from alpha cells results in an increase in glucose, glycerol, and fatty acids in the blood; it has no effect on structural and functional protein components of the body