Endocrine system

Organs of the endocrine system

Hypothalamus, thymus, pancreas, adipose tissue, ovaries, testes

Glands of the endocrine system

Thyroid, pituitary, pineal, parathyroid, adrenal (and pancreas, which is itself an exocrine gland)

Difference between endocrine and exocrine glands

• Endocrine glands release hormones directly into the bloodstream (ductless)

• Exocrine glands use ducts to release substances onto body surfaces or into cavities

Organ with both endocrine and exocrine functions (and those functions)

• The pancreas

• Endocrine: releases insulin to lower blood sugar, and glucagon to raise blood sugar (through conversion and release of hepatic glycogen in the liver)

• Exocrine: releases digestive enzymes like amylase (carbs), lipase (fats), and trypsin and chymotrypsin (proteins) through pancreatic duct and into the small intestine/duodenum

Homeostasis

The maintenance of a constant, stable internal environment; using feedback systems to regulate

How is glucose concentration maintained in the blood?

• Pancreatic beta cells detect high levels of glucose and secrete insulin, which enables sugar to move into cells and out of the bloodstream

• Pancreatic alpha cells detect low levels of glucose and secrete glucagon, which triggers the liver to convert hepatic glycogen stores into glucose and release that glucose into the bloodstream

Hypothalamus (location and function)

• Structure/gland located in the brain that integrates the endocrine and nervous systems

• Produces releasing and inhibiting hormones and sends to the pituitary

• Makes some hormones (oxytocin, ADH) and stores in the posterior pituitary

Example of a positive feedback loop in the endocrine system

• Oxytocin and childbirth

• The hypothalamus produces oxytocin and stores it in the posterior pituitary

• During childbirth, cervical stretching (from fetal pressure) triggers the release of oxytocin

• Oxytocin stimulates uterine contractions, which causes the fetus to push against and stretch the cervix more, triggering continued oxytocin release

• This loop continues until the fetus is expelled (triggering event ends, rather than a certain level of hormone reached)

Steroid hormones

• Fat-soluble hormones, made from cholesterol

• Can pass through cell and nuclear membranes due to their lipid construction

• Effect DNA transcription/the expression of specific genes

• Example: testosterone and estrogen influence patterns of gene expression such as distribution of fat and hair

Non-steroid hormones

• Water-soluble, most common

• Bind to receptor proteins on the cell membrane (cannot pass through phospholipid membrane itself)

• Binding then turns on an enzyme that creates molecules (second messengers/G-proteins) within the cell, leading to a network of chemical reactions which have specific metabolic effects

Testosterone (secreting gland and example of effect)

• Secreting gland: testes

• Steroid hormone (fat-soluble)

• Effect ex: promotes development of male sex characteristics

Estrogen (secreting gland and example of effect)

• Secreting gland: ovaries

• Steroid hormone (fat-soluble)

• Effect ex: promotes development of female sex characteristics

Epinephrine (secreting gland and example of effect)

• Secreting gland: adrenal

• Effect ex: regulates heart rate, blood pressure

Follicle-stimulating hormone (FSH) (secreting gland and example of effect)

• Secreting gland: anterior pituitary

• Effect ex: stimulates development of eggs in ovaries and sperm in testes

Glucagon (secreting gland and example of effect)

• Secreting gland: pancreas

• Effect ex: triggers liver to convert hepatic glycogen into glucose and release into the bloodstream (raises blood sugar)

Growth hormone (HGH) (secreting gland and example of effect)

• Secreting gland: anterior pituitary

• Effect ex: stimulates tissue growth (growth plates in children, maintains metabolism in adults)

Inhibiting hormones (secreting gland and example of effect)

• Secreting gland: hypothalamus

• Effect ex: restrict production of certain hormones (somatostatin/growth hormone-inhibiting hormone restricts production of growth hormone)

Melatonin (secreting gland and example of effect)

• Secreting gland: pineal

• Effect ex: plays role in maintaining circadian rhythm

Oxytocin (secreting gland and example of effect)

• Secreting gland: posterior pituitary

• Effect ex: stimulates uterine contractions and milk ejection

Parathyroid hormone (secreting gland and example of effect)

• Secreting gland: parathyroid

• Effect ex: elevates plasma calcium level

Releasing hormones (secreting gland and example of effect)

• Secreting gland: hypothalamus

• Effect ex: stimulate production of certain hormones (growth hormone-releasing hormone tells pituitary to release growth hormone)

Thyroid hormone (secreting hormone and example of effect)

• Secreting gland: thyroid

• Effect ex: regulates growth, development, metabolic rate

Pituitary gland

Small gland located just beneath the hypothalamus at the base of the brain, divided into anterior and posterior sections

Anterior makes and releases growth and development hormones (like FSH, GH, LH), while the posterior stores and releases ADH and oxytocin (made by the hypothalamus)

Anterior pituitary gland hormones (7)

• FSH (follicle-stimulating hormone)

• LH (luteinizing hormone)

• ACTH (adrenocorticotropic hormone)

• TSH (thyroid-stimulating hormone)

^ Tropic hormones

• Prolactin

• Endorphins

• GH (growth hormone)

^ Direct hormones

Pineal gland

Tiny pine cone-shaped organ in the center of the brain, responsible for the production of melatonin

Parathyroid

Four small bean-like glands behind the thyroid, responsible for production of parathyroid hormone (PTH) which regulates plasma calcium levels by inhibiting the kidneys’ ability to transfer calcium ions to urine, and indirectly activating osteoclasts (causing reabsorption of calcium from bones)

Thyroid

Butterfly shaped gland in the neck, responsible for producing thyroid hormones (thyroxine/T4 and triiodothyronine/T3) and calcitonin which regulates calcium; regulates metabolism and is influenced by TRH and TSH

Thymus

Small lymphatic gland located behind the sternum in the mediastinum (between the lungs), responsible for creating T-cells which help immune function

Adrenal glands

Two small triangle-shaped organs that sit on top of each kidney, made up of the adrenal cortex (outer layer) and adrenal medulla (inner layer), responsible for producing hormones that effect the metabolism, blood pressure, and stress response (cortisol in cortex, epinephrine and noradrenaline in medulla)