BIO224: Chapter 16, Endocrine System (Day 1, NO DIAGRAMS)

Endocrine system

synthesize and secrete chemical messengers

hormones

chemical messengers that interact with specific target cells to influence their function

Endocrine functions

1.) MAINTAIN fluid, electrolyte, and acid-base homeostasis

2.) GROWTH

3.) REGULATE metabolic reactions

4.) EFFECT FUNCTION of cell immediately to several days

Three types of signaling pathways

Endocrine, paracrine, autocrine

Endocrine

secrete into blood; DISTANT targets

Paracrine

chemicals secreted by cells into extracellular space; near by but different types of cells

Autocrine

chemicals secreted by cells into interstitial fluid; elicit effects from same cell or cell type

Ductless glandular epithelial cells

secrete hormones into extracellular fluid for transport by bloodstream

Three groups of endocrine organs

primary organs, secondary organs, neuroendocrine

primary organs

organs only have endocrine functions

secondary organs

endocrine functions and many other non-endocrine functions

neuroendocrine

nervous tissue chemicals that have hormonal function, in the brain

Primary endocrine organs

1.) Hypothalamus

2.) Pituitary gland

3.) Pineal gland

4.) Thyroid gland

5.) Parathyroid gland

6.) Thymus

7.) Adrenal gland

8.) Pancreas

Secondary endocrine organs

1.) heart

2.) kidneys

3.) small intestines

4.) gonads

Classes of hormones by structure

Amino-acid hormones, steroid hormones

Amino-acid hormones

Hydrophilic hormones binding to plasma membrane receptors, DO NOT ENTER.

- free, travels independently through blood

- breakdown quickly, quick response; seconds to minutes

Steroid hormones

derived from cholesterol; hydrophobic hormones that bind to receptors in cytosol or nucleus

- usually bound to protein

- can survive for weeks

Paraneoplastic Syndrome

Hormones produced by lung and intestinal cancel cells cause imbalance of electrolyte and fluid; most common inappropriate ADH secretion

How can Paraneoplastic Syndrome lead to early cancer diagnosis?

Cancer cells secrete hormone that mimic ADH

Hormone transport through blood classification

physiological classification; free hormones, bound hormones

free hormones

hydrophilic, quick breakdown for use

Does hydrophilic hormones always make them free?

No, some are protein bound, such as growth hormone

Bound hormones

hydrophobic, bound to plasma proteins and released when needed; extends lifespan of hormone in blood

Hydrophilic hormones

cannot readily cross plasma membrane; interact with receptors in target cell's plasma membrane

Hydrophobic hormones

can cross through plasma membrane; interact with receptors in cytosol or nucleus

Second messenger

relays a signal from a hormone (the first messenger) that cannot enter the cell directly to target molecules inside the cell

g-protein

molecular switch inside cells that transmits signals from outside the cell to its interior

adenylate cyclase

enzyme activated by g-protein that uses ATP to make cAMP

cAMP function

second messenger; carries the signal inside the cell

- activates PKA (protein kinase A)

Phosphorylation

when PKA adds phosphate groups to specific proteins in the cell

Function of phosphorylated proteins

trigger the actual cellular response

- speeding up a reaction, changing gene activity, or controlling cell functions

7 Effects of hormone actions

1.) stimulate secretion

2.) activate/inhibit enzymes

3.) stimulate/inhibit mitosis/meiosis

4.) ion channels

5.) transcription; gene expression

6.) fluid electrolyte balance

7.) homeostasis

Hormone interactions

maintenance of homeostasis, needs synergist and antagonist

Antagonist

act on same target cells for opposite effects

Synergist

act on same target cells for same STRONGER effect with interaction of multiple hormones instead of just one

Humoral stimulation origin

non-neurological

Neural stimulation origin

neuron causes epinephrine and norepinephrine

Hypothalamus

Vital to many homeostatic functions; direct and indirect

Direct

hormone controls certain body functions

Tropic

control secretion of hormones from other endocrine glands

Hormones of hypothalamus

ADH and oxytocin

ADH

Antidiuretic hormone; increases water reabsorption (intake)

Oxytocin function

uterine contractions and milk ejection

Hormones of Anterior Pituitary

1.) Tropic Hormones

2.) Somatotropin or growth hormone

3.) Adrenocorticotropic hormone

4.) Thyroid stimulating hormone

5.) Follicle stimulating hormone

5.) Luteinizing hormone

Hypothalamus controls many functions of ____. Such as....

anterior pituitary

- stimulating or inhibiting release of hormones from anterior pituitary

Hypothalamus produces and releases ___ hormones.

trophic

First tier

RELEASE: neuroendocrine cells of hypothalamus secrete releasing and inhibiting hormones in response to change

Second tier

tropic hormones' effect on anterior pituitary; stimulates or inhibits

Third tier

actions of anterior pituitary hormones at target tissues; target tissue glands secrete hormones that can affect various homeostatic variables

Thyroid Stimulating Hormone (TSH)

Stimulates thyroid gland to produce thyroid hormones

Adrenocorticotrophic hormone (ACTH)

stimulates adrenal cortex to secrete cortisol and aldosterone

Prolactin (PRL)

Stimulates milk production in mammary glands

Luteinizing Hormone (LH)

stimulate sex hormones; not direct, increase levels

Follicle-stimulating hormone (FSH)

secreted by the pituitary gland to stimulate maturation of the egg and sperm

Growth Hormone (GH)

regulates the growth of the body; usually direct

Gluconeogenesis

Synthesis of glucose from non-carbohydrate sources

Main function of growth hormone

regulation of growth of various tissues such as skeletal, cardiac muscle, adipose, liver, cartilage, and bone

Growth hormone disorders

imbalances in GH secretion resulting in disruptions in growth

Gigantism

hypersecretion of GH BEFORE epiphyseal plate closure; results in extremely height and size of other tissues (heart)

Acromegaly

hypersecretion of GH AFTER epiphyseal plate closure; tissues of head, face, hands, and feet affected, results in distortion and possible heart failure

pituitary dwarfism

GH hyposecretion; short, but proportional limbs and trunk

Does GH promote fat breakdown and protein synthesis? What problems arise?

Yes, but excessive GH can lead to hyperglycemia (elevated blood glucose) and growth of tissues (tongue and bones)

How do you effectively administer GH protein hormone drugs?

injection; oral is ineffective

GH protein hormone

destroyed by acid and enzymatic reactions in stomach

Thyroid gland

secretes thyroid hormone and calcitonin

What is the shape of the thyroid gland?

butterfly

What is the thyroid gland made of on a microscopic level?

multiple follicle cells

Function of follicle cells

follicles cells at the edge of the cell produce and secrete thyroglobulin

Colloid

protein rich gel-like material; has precursor for thyroid hormone and high concentration of iodine- need for thyroid hormone synthesis

Parafollicular cells

large cells in spaces between adjacent thyroid follicles that produce calcitonin

Thyroid hormone is derived from...

amino acid TYROSINE bound to IODINE; hydrophobic qualities

T3

"triiodothyronine"; functional form

T4

"thyroxine"; storage

What cell contains thyroid hormone receptors?

almost every cell

Effects of thyroid hormone

1.) regulation of metabolic rate and thermoregulation

2.) promotion of growth and development

3.) synergism with sympathetic nervous system

"Regulation of metabolic rate and thermoregulation" meaning

set metabolic rate

"promote growth and development" meaning

thyroid hormones needed for normal bone growth, muscle growth, and nervous system development

"Synergism with sympathetic nervous system" meaning

increase thyroid hormone levels, act on target cells of sympathetic nervous system

Hyperthyroidism

T3 and T4 extremely elevated, but hypothalamus does not detect increase; leads to decreased TSH and elevated T3 and T4

Hyperthyroidism symptoms

heat intolerance, weight loss, BP and HR disruptions, goiter, and exophthalmos

goiter

enlargement of the thyroid gland

Exophthalmos

bulging eyes

Graves' disease

common hyperthyroidism; immune produces abnormal proteins that MIMIC TSH actions on thyroid glands

Hypothyroidism

thyroid gland cannot produce more T3 and T4; receptors sense levels are low so cells secrete more TRH and TSH in attempt to stimulate thyroid; results in elevated TSH and decreased T3 and T4

Why do the hypothalamus and anterior pituitary not stimulate the thyroid gland during hypothyroidism?

hypothalamus and anterior pituitary don't know thyroid is not functioning

Symptoms of hypothyroidism

weigh gain, fatigue, slow heart rate and respiration rate, cold intolerance

What are some potential causes of hypothyroidism?

immune system disorder or lack of available iodine

congenital hypothyroidism

occurs when infant is born with INADEQUATE thyroid function; can lead to delayed physical and nervous system development- potential mental retardation if left untreated

Hashimoto's Thyroiditis

autoimmune disorder; immune system attacks thyroid tissue

Hashimoto's Thyroiditis symptoms

Dry skin

tiredness

weight gain,

puffy face

intolerance to cold

mild depression

memory lapses

joint pain and stiffness

hair loss