The Endocrine System

The Endocrine System

• ductless glands

• secrete directly into blood stream

• produce hormones

• action on other tissues/and or organs

→ target cells or target organs

Difference between exocrine and endocrine glands

Exocrine Glands

• release secretions into ducts (tubes) that carry their contents to other organs or outside the body

→ sweat glands (make sweat to cool body temp), salivary glands (produce saliva with enzymes for digestion), the pancreas (produces enzymes for digestion)

Endocrine Glands

• secrete their products directly into the bloodstream

For example…What is TSH?

• thyroid stimulating hormone (tropic hormone)

→ 1 endocrine gland stimulates another endocrine gland

• comes from the anterior pituitary gland and stimulates the thyroid gland to release additional hormones

Positive Feedback

Hormone production results in increased hormone production → increased activity

• suckling on mammary

• oxytocin produced (released by posterior pituitary gland)

• milk ejection

• more suckling

• more oxytocin

• more milk ejection

• stops when baby stops

Negative Feedback

Hormone production results in decreased hormone production → decreased activity

• glucose rises in blood

• insulin produced (produced by pancreas)

• glucose levels fall

• insulin production falls

• glucose level rises

→ lead to homeostasis

Hormone: Steroids

derived from cholesterol; secreted mostly by reproductive organs and adrenal cortex

1. Cholesterol → turn it into Testosterone

2. Cholesterol → turn it into Cortisol

Hormone: Amines

amino acid derivatives (which are small)

• thyroid hormones

→ Tyrosine → turn it into Thyroxine (produced by thyroid gland)

→ iodine is a part of thyroxine, which is necessary and natural (can’t make thyroxine without iodine)

→ lack of iodine: causes goiter (lump in ur throat bc thyroid gland size increases)

• adrenaline

Hormone: Polypeptides (bonds) and Proteins (strings of amino acids) → Peptides

• too large to pass through cell membranes

• most hormones are “peptide hormones”

→ ALL pituitary hormones

How does a peptide hormone act on a cell if its too large to enter?

• most hormones bind to receptors on the surface of cells

• this triggers a chain of reactions that causes the final result: “Cascade effect”

• membrane proteins are involved

The Endocrine glands!

• Hypothalamus

• Pituitary-Anterior and Posterior

• Pineal

• Thyroid

• Parathyroid

• Thymus

• Adrenal Glands

• Pancreas

• Gonads

Hypothalamus: “control center”

Hypothalamus controls in 3 ways…

• hormones from hypothalamus stimulate the anterior pituitary to produce and secrete hormones

• tropic hormone!

Hypothalamus produced hormones are…

• Thyrotropin Releasing hormone: this hormone which is released from the Hypothalamus stimulates the anterior pituitary gland to secrete Thyroid Stimulating Hormone

• Growth Hormone Releasing Hormone (GRH or GHRH): it’s the hormone secreted by the hypothalamus which stimulates the release of Growth Hormone from the anterior pituitary

• Prolactin Releasing Hormone (PRH): it’s secreted by the Hypothalamus which stimulates the secretion of Prolactin from the anterior pituitary gland

Hypothalamus 1st Influence

The hypothalamus hormones stimulate the Anterior Pituitary gland to produce and secrete more hormones + send them to diff parts of the body

• FSH → Follicle-stimulating hormone

• LH → Luteinizing hormone

• ACTH → Adrenocorticotropic hormone

• TSH → Thyroid stimulating hormone

• MSH → Melanocyte stimulating hormone

• PRL → Prolactin

• GH → Growth hormone

Hypothalamus 2nd influence

Posterior pituitary hormones are made up by the hypothalamus

• ADH (Antidiuretic hormone) and Oxytocin

• these hormones travel down the axons in the infundibulum to be released by the Posterior pituitary gland into the bloodstream

Hypothalamus 3rd influence

Hypothalamus stimulates the Adrena Medulla directly through Autonomic Nerv system (sympathetic)→ fight or flight response

• producing Adrenaline/Epinephrine and Noradrenaline/Norepinephrine

• EpiPen→ device used to deliver epinephrine, delivering adrenaline

Pituitary Gland

controlled by the hypothalamus (Nerv and endocrine system combined)

Anterior pituitary gland

• comes from roof of oral cavity and is not connected to brain → endocrine

Posterior pituitary gland

• comes from floor of brain → nervous tissue

Pituitary hormones

sometimes called the “master gland”

Produces many hormones that affect other endocrine glands (tropic hormones)!

• FSH

• LH

• ACTH

• TSH

• MSH

• Prolactin

• GH

• + ADH

• + Oxytocin

FSH: Follicle Stimulating Hormone and LH: Luteinizing Hormone (Anterior pituitary gland)

• act on gonads and stimulate gamete formation

ACTH: Adrenocorticotropic Hormone (Anterior pituitary gland)

• cause release of corticosteroids from adrenal cortex

→ influence on metabolism

TSH: Thyroid Stimulating Hormone (Anterior Pituitary Gland)

• release of thyroid hormones

MSH: Melanocyte Stimulating Hormone (Anterior pituitary gland)

• melanin release = darker skin and hair

Prolactin (Anterior pituitary gland)

• milk production

GH: Growth Hormone (Anterior Pituitary Gland)

• all body tissue growth!

ADH: Antidiuretic Hormone (Posterior Pituitary gland)

• water retention from kidney

• regulates water balance by telling the kidneys to transport water from your urine back into the bloodstream when you are dehydrated

Oxytocin (Posterior pituitary gland)

• milk ejection

• uterine contraction

• causes uterine contractions during childbirth and allows milk to be released during nursing

→ also involved in social bonding, esp mother-infant

Pineal Gland

produces melatonin

• Circadian rhythm — day and night cycle

Thyroid Gland

located in the throat

• produces thyroid hormones → Metabolism

• Calcitonin → Decrease Ca++ in blood, can result in bone growth

Parathyroid Gland

• Parathormone

• Increase Ca++ in the blood

→ bone density decrease

Thymus Gland

Located behind the sternum

• Numerous thymic hormones → immune response (really big in babies)

• as we get older, our thymus gland gets smaller and smaller

Adrenal Gland

Located in the cortex and medulla (fight or flight)!!!

• Adrenaline (epinephrine) 

• Noradrenaline (norepinephrine)

• Corticosteroids

→ Electrolyte hormones

→ Metabolism

→ Gonad stimulation

Pancreas Gland

Located behind the stomach and under the liver

• Produce insulin(lowers blood sugar) + glucagon(increases blood sugar) → glucose balance

• Composed of 2 tissue types: Endocrine and Exocrine cells produce and secrete digestive enzymes and mucus 

Pancreas Endocrine Function

Endocrine cells (Islets of Langerhans) produce and secrete two hormones that regulate blood glucose levels in a NEGATIVE FEEDBACK LOOP!

• Insulin: secreted by pancreatic beta cells when blood glucose is TOO HIGH; stimulates the uptake or storage of glucose by cells (mostly in muscle and liver cells)

• Glucagon: secreted by pancreatic alpha cells when blood glucose is TOO LOW; stimulates the breakdown of glycogen (the storage of polymer of glucose) in the liver and release of glucose into the blood for energy production throughout the body

Gonads Glands

What are they?

• The ovaries and testes

• Produce sex hormones (steroids)

→ Estrogen, Progesterone, Testosterone…