Endocrine System Lecture

Metabolism

The chemical processes occurring within a living cell that hormones help regulate, consisting of both anabolism and catabolism.

Hormonal stimulation

• gland cell releases its hormone into the blood stream which then binds to another gland

• hormones with the word “ trophic” in them (e.g. Adrenocorticotropic hormone)

Humoral stimulation

• Known as “floating around stimulation”

• releases hormones by detecting ions/nutrients that are floating in the blood

• pancreas releases insulin when blood sugar is high and glucagon when blood sugar is low

Nervous system stimulation

• a gland cell releases its hormone when stimulated by a neuron

• e.g. in the sympathetic division, the neuro interacts with the adrenal glands to release norepinephrine and epinephrine

Second messenger

An internal molecule, such as $cAMP$, generated from $ATP$ after a water-soluble hormone binds to a membrane receptor.

Hormone-response element (HRE)

A specific sequence of $DNA$ to which a lipid-soluble hormone-receptor complex binds to initiate transcription of $mRNA$.

Steroids

• bounded

• Lipid-soluble molecules synthesized from cholesterol

• mostly made in the liver and have a longer half-life

Up-regulation

• increases number of receptors

• increases sensitivity to hormone

• sometimes occurs when blood levels of hormone are low
  

Down-regulation

• decreases number of receptors

• decreases sensitivity to hormone

• sometimes occurs when blood levels of hormone are high (e.g. Type 2 diabetes-insulin resistance)

Synergistic interaction

• One hormone reinforces activity of another hormone

• ex. cortisol, glucagon and epinephrine on raising blood sugar

Permissive interaction

• One hormone requires activity of another hormone

• oxytocin’s milk ejection effect requires prolactin’s milk generating effect

Antagonistic interaction

• One hormone opposes activity of another hormone

• glucagon increases blood glucose, insulin lowers it

Infundibulum

A hollow stalk made of blood vessels and nerves that connects the hypothalamus to the pituitary gland.

Antidiuretic hormone

• found in Posterior Pituitary Gland

• Functions: decrease urine production, stimulate thirst, constrict blood vessels, maintain hydration

• Also known as vasopressin

Oxytocin

• found in Posterior Pituitary Gland

• Functions: uterine contraction, milk ejection , emotional bonding( positive and negative)

Growth hormone

• found in anterior pituitary gland

• causes liver to secrete insulin-like growth factors( 1, 2), somatic tissues (muscles and bones)

• Also called somatotropin

Prolactin

• found in anterior pituitary gland

• causes milk production, mammary gland growth in females

Colloid

A viscous, protein-rich fluid housed within the follicle lumen of the thyroid gland

Parafollicular cells

Cells between thyroid follicles producing calcitonin to decrease blood calcium levels

HYPERthyroidism

• results from excessive production of thyroid hormone

• increased metabolic rate, weight loss, hyperactivity, heat intolerance

• caused by T4 ingestion, excessive stimulation by pituitary, or loss of feedback control in thyroid (Graves disease)

• treated by removing the thyroid (then giving hormone supplements)
  

HYPOthyroidism

• results from decreased production of TH

• low metabolic rate, lethargy, cold intolerance, weight gain

• caused by decreased iodine intake, loss of pituitary stimulation of thyroid, postsurgical, or immune system destruction of thyroid (Hashimoto thyroiditis)

• treated with TH replacement

Adrenal medulla

• forms inner core of each adrenal gland

• releases epinephrine and norepinephrine with sympathetic stimulation

• red-brown color due to extensive blood vessels

Zona glomerulosa

The thin, outer cortical layer of the adrenal gland that produces mineralocorticoids such as aldosterone.

Zona fasciculata

The larger, middle cortical layer of the adrenal gland that produces glucocorticoids like cortisol.

Acinar cells

• generate exocrine secretions for digestion

• make pancreatic juices (Proteases, amylase and lipase)

  • essentially Proteins, carbs and fats

Alpha cells

secrete glucagon

Beta cells

secrete insulin

pineal gland

• small unpaired body in the epithalamus of the diencephalon

• secretes melatonin

  • causes drowsiness, regulates circadian rhythm

Chief cells

• also called principal cells

• produce parathyroid hormone (PTH)

• PTH released when calcium levels are low

Atrial natriuretic peptide (ANP)

• hormone that lowers blood pressure

• kidneys increase urine output and blood vessels dilate

kidney

• its endocrine cells release erythropoietin (EPO)

• EPO causes increased red blood cell production (Erythropoiesis)

• secretion occurs in response to low blood oxygen

converting Angiotensinogen to Angiotensin II

1. liver: circulates angiotensinogen in blood regardless of blood pressure level

2. kidney: secretes renin (enzymes) when blood pressure is low. Angiotensinogen is converted to angiotensin I

3. lungs: secrete ACE and converts angiotensin I to the active form angiotensin II

4. angiotensin II: helps raise blood pressure when it starts to fall

Leptin

• secreted by adipose connective tissue

• controls appetite by binding to neurons in hypothalamus

endocrine system functions

• regulates development, growth, metabolism

• maintains homeostasis of blood composition and volume

• controls digestive processes and reproductive activities

endocrine organs

• performs solely endocrine function

• pituitary, pineal, thyroid, parathyroid, and adrenal glands

endocrine cells

• found in clusters in organs with another function

• hypothalamus, skin, thymus, heart, liver, stomach, pancreas, small intestine, adipose connective tissue, kidneys, and gonads

Water-soluble hormones

• use membrane receptors

• hormones are polar and can’t diffuse through membrane (ex: epinephrine)

Lipid-soluble hormones

• can diffuse across target cell membrane, doesn’t need help

• hormones are small, nonpolar, and lipophilic

proteins

• free floating

• more than 100 amino acids

• majority of hormones released from the pituitary gland

amino acids

• free floating except for thyroid hormone

• derived from tyrosine

• Come from the adrenal medulla (adrenal glands)

• Produces catecholamines (e.g norepinephrine)

Endocrine action

hormone is distributed in blood and binds to distant target cells

Paracrine action

hormone acts locally by diffusing from its source to target cells in the
neighborhood

Autocrine action

hormone acts on the same cell that produced it

hypothalamus

• control center located below thalamus

• manages thirst, hunger, mood, sleep

• sends signal to the pituitary gland to release hormones and these hormones are sent to different regions of the body

thyrotropin

• found in the anterior pituitary gland

• causes release of thyroid hormone (TH) from thyroid gland

corticotropin

• found in the anterior pituitary gland

• causes release of corticosteroids by adrenal cortex

gonadotropin

• found in anterior pituitary gland

• follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

• females: regulate ovarian development and secretion of estrogen and progesterone

• males: sperm development and secretion of testosterone

thyroid gland

• left and right lobes inferior to thyroid cartilage of larynx, anterior to trachea

• composed of follicular cells (Thyrocytes), parafollicular cell, follicle lumen houses colloid

Follicular cells

• aka Thyrocytes

• cuboidal epithelial cells that surround a central lumen

Follicle lumen

• houses colloid

• produce and release thyroid hormone, combination of iodine and thyroglobulin

adrenal cortex

• synthesizes more than 25 corticosteroids

• 3 regions producing different steroid hormones: zona glomerulosa, zona fasciculata, and the inner zona reticularis

• yellow color due to lipids within cells

mineralocorticoids

• hormones that regulate electrolyte levels (moving around minerals)

• made in zona glomerulosa

• Aldosterone

glucocorticoids

• hormones that regulate blood sugar

• made in zona fasciculata

• e.g. cortisol that increases blood sugar

gonadocorticoids

• sex hormones

• made in zona reticularis

• androgens are male sex hormones made by adrenals (estrogen in females)

pancreas

• has endocrine and exocrine functions

• posterior to stomach, between duodenum and spleen

• contains acinar cells, pancreatic islets, alpha, beta, and delta cells

pancreatic islets

contain clusters of endocrine cells

low blood sugar process

• beta cells detect blood glucose rise and secrete insulin

• insulin carried into blood stream to drop off excess

• liver: excess sugar dropped into the liver

• muscles: increased amino acid uptake, protein synthesis stimulated

• adipose cells: decrease fatty acid levels, store fat

parathyroid gland

• small structures on the posterior surface of the left and right thyroid gland

• contain chief cells and oxyphil cells

releasing PTH effects

• causes osteoclast to breakdown bone, releasing calcium and phosphate into the blood

• GI absorbs calcium

• acts on kidneys to reduce amount of calcium lost in urine

thymus

• its epithelial cells secrete thymic hormones

• grows during childhood but shrinks during adulthood

• maturation site for T-lymphocyte white blood cells

• anterior to top of heart

gastrin

• secreted by the stomach

• increases secretion and motility in stomach for digestion

secretin

• secreted by small intestine into blood

• stimulates secretion of bile and pancreatic juice

cholecystokinin (CCK)

• secreted by small intestine into blood

• stimulates release of bile from gall bladder