Endocrine System = Made of glands that secrete substances into the bloodstream

Exocrine glands secrete substances into ducts and onto body surfaces like skin or stomach (epithelial tissue) (exo = external)

Function:

• Communication and Control

• Same as nervous system but SLOWER

Hormones: Specific chemicals released in small quantities from one part of the body and carried through the bloodstream that affects another part of the body

Target cells receive specific hormones with their receptors

If hormones contact cells with no target cells and receptors = NO EFFECT

When contacting a target cell, hormones produces one or more changes within the cell:

• Alter plasma/cell membrane permeability, potential or both

• Stimulate protein synthesis

• Activate/Deactivate enzymes

• Induce a secretory activity

• Stimulate mitosis

2 MAJOR TYPES OF HORMONES:

Water-soluble hormones (amino acid)

• Not able to pass through cell membrane

• Bind to receptors on outside of target cell which activate a 2nd messenger to mediate the response to the target cell

• Molecular relay!

Lipid-soluble hormones (steroids)

Can pass directly through the target cell membrane, forming a hormone-receptor complex, which alters action of the cell

Glands are activated in 3 ways:

• Hormonal Stimuli - Glands are encouraged by hormones secreted by other glands (Hypothalamus stimulates pituitary)

• Humoral Stimuli - Levels of nutrients and ions in the blood can cause glands to secrete hormones (Blood calcium levels stimulate parathyroid glands)

• Neural Stimuli - Nerve impulses cause glands to secrete hormones (Sympathetic nervous system during stress causes release of epinephrine from adrenal glands)

Endocrine glands

Pituitary Gland:

Small bulb on the underside of brain

2 lobes: anterior pituitary and posterior pituitary

“Master Gland” = controls many other glands in body

Anterior pituitary hormones:

• Thyroid-stimulating hormone (TSH) = causes thyroid to produce thyroxine

• Adrenocorticotropic hormone (ACTH) = stimulates adrenal glands

• Growth Hormone (GH) = Stimulates growth in bones and muscles

• Melanocyte stimulating hormone (MSH) = stimulates melanocytes to produce melanin

• Prolactin (PRL) = stimulates production of breast milk

• Gonadotropins

  Luteinizing hormone - stimulates release of sex hormones

  Follicle stimulating hormone - stimulates egg/sperm production

Posterior Pituitary hormones:

• Antidiuretic hormone (ADH) or vasopressin = increases water retention in kidneys, decreasing urine production

Oxytocin (OT) = stimulates contraction of uterus during childbirth and promotes release of breast milk

Pineal Gland:

Tiny cone shaped gland near the cerebellum

Main secretion is melatonin = sleep and wake cycle

Thyroid Gland:

Located at base of neck

2 distinctive halve - butterfly shape

• Hormones:
  Calcitonin = reduces calcium levels in blood

• Thyroid Hormones (TH)

  Thryoxine + Triiodothyronine = Regulates metabolism+body heat, controls oxygen usage, maintains blood pressure

Parathyroid Gland:

Attached to back of thyroid

Produces parathyroid hormone (PTH) = opposite of calcitonin; brings calcium out of bones into bloodstream to increase calcium levels

Adrenal Glands:

Sits on top of each kidney

Outer layer - Adrenal Cortex

• Glucocorticoids (cortisol and aldosterone) = regulates ion levels for quick energy

Inner layer - Adrenal medulla

• Epinephrine + Nonepinephrine = Fight or flight respones, increases heart rate, blood pressure and flow, intake of oxygen for immediate energy

Pancreas:

Both exocrine and endocrine glands!

Endocrine part is made up of islets of Langerhans which produce insulin and glucagon

• Beta cells = insulin, lowers blood glucose levels

• Alpha cells = glucagon, raise blood glucose levels

Thymus Gland:

Near Sternum

Produces thymopoietin, thymic factor, thymosin = immune system

Gonads:

Reproductive organs that produce sex cells and secrete sex hormones

• Estrogen - Maturation of reproductive organs and secondary sex characteristics

Females = ovaries

• Progesterone - breast development and menstrual cycle

Males = testes

• Maturation of reproductive organs and secondary sex characteristics, sperm dev

Hormone regulation

Control of hormone secretion is required to regulate the amt of hormones released

Control thru feedback loops

EX: If calcium levels are too high, calcitonin is released. If calcium levels get too low, then PTH is released

Improper functioning:

Hyposecretion - not enough hormone released

Hypersecretion - too much hormone released

Disorders are either hyposecretions or hypersecretions of hormones