Anatomy - Endocrine System

Endocrine Overview

SLOW coordination of the body (compared to fast Nervous System)

- Homeostasis

- Growth

- Development

- Reproduction

Endocrine glands

Component of the Endocrine system that is stimulated to secrete hormones

Hormones

component of the Endocrine System; chemical substances that travel in the blood

Target tissue/organ

component of the Endocrine system in which hormones bind to its receptors and regulate the organ's functions

How hormone's bind to receptor

Lock and key mechanism; like an enzyme binding to a specific substrate

2 major types of hormones

1) Steroid (cholesterol-based)

- Ex. Estrogen & Testosterone

2) Amino Acid based (nonsteroidal)

- Ex. Epinephrine (adrenaline) derived from Tyrosine

- Ex. Melatonin derived from tryptophan

- Ex. Insulin; 51 amino acids

Steroid Hormone -> Direct Gene Activation

1) Lipid-soluble hormones diffuse directly into the nucleus

2) Nuclear hormone receptor

3) Hormone-receptor complex binds to DNA and regulates specific genes (Turned on or off)

Amino acid -> Second messenger system

Water-soluble hormones cannot diffuse into the cell

- Membrane-bound receptor

- Activated receptor stimulates second-messenger molecule (Ex. activated cycle AMP, cAMP, triggers glycogen breakdown)

Hormonal hormone release

Hormones stimulate other hormones to be released

- most common type of stimulus

Humoral hormone release

Blood ions or nutrients stimulate hormone release

Neural hormone release

Nerve stimulates hormone release

Negative Feedback

hight hormone levels -> effect -> less hormone secretion

example of hormonal stimulus

Hypothalamus hormones -> anterior pituitary gland hormones -> thyroid/adrenal/testes hormones

thyroid/adrenal/testes hormones -> anterior pituitary gland hormones -> Hypothalamus hormones

Example of humoral stimulus

Low blood calcium -> Parathyroid hormone (PTH) -> Activate osteoclasts + Inhibit osteoblasts -> Blood calcium rises

Blood Calcium rises -> Parathyroid hormone (PTH)

Example of neural stimulus

Sympathetic nervous system (fight or flight) -> Adrenal glands release catecholamines (epinephrine & norepinephrine)

Hypothalamus

Regulates the anterior pituitary gland via releasing + inhibiting hormones

- produxes oxytocin and ADH (stored in pineal gland)

Oxytocin

Crucial in labor and breastfeeding

- produced by the hypothalamus

Antidiuretic hormone (ADH) (aka vasopressin)

Inhibits urine production (Diuresis)

Kidneys reabsorb water -> blood volume increases

- produced by hypothalamus

Pituitary gland

Size of a pea; protected by sphenoid bone

Anterior = glandular tissue

- makes pituitary hormones

Posterior = nervous tissue

- storage area for hormones

Growth Hormone (GH)

Growth of Bones + Skeletal muscle

- regulated by hypothalamus

Prolactin (PRL)

stimulates breast milk production

- regulated by hypothalamus

Thyroid-stimulating hormone (TSH)

Stimulates thyroid

- regulated by hypothalamus

Adrenocorticotropic Hormone (ACTH)

Stimulates adrenal glands

- regulated by hypothalamus

Follicle-stimulating hormone (FSH)

Stimulates ovaries (estrogen + eggs)

Stimulates testes (sperm)

- regulated by hypothalamus

Luteinizing Hormone (LH)

stimulates ovaries (estrogen + progesterone)

Stimulates testes (testosterone)

- regulated by hypothalamus

Melatonin

High _____ at night

Low ______ at noon

- regulated by day-night cycling

Thyroid gland

Bottom of the neck

2 important hormone = Thyroid hormon + Calcitonin

Thyroid hormone - T4 + T3

Controls cell metabolism

- requires iodine

- T4 Produced -> converted to T3 (the active form)

- Stimulated by TSH from anterior pituitary

Calcitonin

Stimulates decrease in blood calcium

- triggers deposit of calcium into bone

- Stimulated by blood calcium levels

Parathyroid gland

4 parathyroid glands attached to thyroid

1 hormone = parathyroid hormone

Parathyroid hormone (PTH)

Stimulates increased blood calcium -> activates osteoclasts

Targets bone AND kidneys AND intestines

- to retain and absorb more calcium

- Stimulated by blood calcium levels

Negative feedback with Thyroid / Parathyroid hormones

PTH and Calcitonin are antagonists

PTH = hypercalcemic hormone

Calcitonin = hypocalcemic hormone

Adrenal glands

- Bean-shaped

- 1 on top of each kidney (2 total)

2 sections:

- Adrenal cortex (glandular) - 3 steroid hormones

- Adrenal medulla (nervous tissue)

Aldosterone (mineralocorticoid) - Cortex

Regulates minerals, mainly sodium (Na) + Potassium (K) ions

- also regulates water

- stimulated by kidneys + heart

- Target = kidneys

Cortison & cortisone (glucocorticoids) - Cortex

1) Long-term stress response

2) Regulates blood glucose

- hyperglycemic hormones

3) Reduces inflammation

- Stimulated by ACTH from anterior pituitary

Sex Hormones - Androgen & Estrogen

- Lesser amount than gonads

Epinephrine/Norepinephrine (adrenaline/noadrenaline) - Adrenal medulla

Neural stimulation; sympathetic nervous system (fight or flight)

- Increase Heart rate & blood pressure & blood glucose

- vasoconstriction

Pancreas

Regulates the level of sugar in the blood

Insulin

Hypoglycemic hormone

Increases cell metabolism, systemic, to use up blood glucose

- Stimulated secretion via High blood glucose

Glucagon (antagonist of insulin)

Hyperglycemic hormone

Primary target = liver where glycogen is stored

- Glycogen gets broken down into glucose

- Stimulated secretion via Low blood glucose

Thymus

Large in infants/children

Decreases in size through adulthood

1 hormone = Thymosin

Thymosin

T cell programming

NK cell and dendritic cell activation

- imunoodulation

Estrogen + Progesterone

1) Steroid hormones

2) Stimulated to be released by the anterior pituitary (FCH + LH)

3) Play role in menstrual cycle and breast development

4) Produce ova (exocrine function)

Estrogen = major role in growth development in women

Progesterone = role in maintaining pregnancy

Testes - 2 in scrotum

Testosterone (Androgens)

Growth and Reproduction in men

Continuous production of sperm (exocrine function)

- Stimulated by FCH and LH