Endocrine System

Endocrine system

• made of glands that secrete substances into the bloodstream (exocrine glands secrete substances into ducts)

• Function is communication and control

_{^{*same functions as nervous system, but works slower}}

What types of changes do hormones produce in target cells?

• alter plasma membrane permeability and/or potential

• stimulate protein synthesis, mitosis

• activate/deactivate enzymes

• induce a secretory activity

Hormones

• chemicals released from one part of the body and carried thru the bloodstream to affect another part of the body

• released in small quantities and are very specific

• ‘know’ which cells to affect b/c target cells have receptors for specific hormones (no effect if hormones contact cells w/o these target cells)

Lipid-soluble aka steroid hormones

• steroids

• can pass directly thru the target cell membrane forming a hormone-receptor complex, which alters the actions of the cell

Water-soluble aka non-steroid hormones

• amino acid-based molecules

• not able to pass thru the membrane

• bind to receptors on the outside of the target cell, which activate a 2nd messenger to mediate the response to the target cell (like a molecular relay)

3 ways that glands are activated

• Hormonal stimuli

  • glands are encouraged by hormones secreted by other glands (ex: hypothalamus stimulates pituitary)

• Humoral

  • levels of nutrients/ions in the blood can cause glands to secrete hormones (ex: blood calcium levels stimulate parathyroid glands)

• Neural

  • nerve impulses cause glands to secrete hormones (ex: sympathetic nervous system during stress causes release of epinephrine from adrenal glands)

Pituitary gland

• small bulb on underside of brain

• anterior and posterior lobes

• master gland b/c controls many other glands in the body

Hormones secreted by anterior pituitary

• Thyroid-stimulating - causes thyroid to produce thyroxine

• 🏃🏻‍♀️Adrenocorticotropic - stimulates adrenal glands

• 💪🏻🦴Growth - stimulates growth in bones/muscles

• 👩🏽Melanocyte-stimulating - stimulates melanocytes to produce melanin

• 🍼Prolactin - stim. production of breast milk

• ♂️♀️Luteinizing - stim. release of sex hormones

• 🥚Follicle-stimulating - stim. egg or sperm production

Hormones secreted by posterior pituitary

• 💧🚽Antidiuretic - incr water retention in kidneys, decr urine production

• 👶🏻🍼Oxytocin - stim. contraction of uterus during childbirth & promotes release of breast milk

Hypothalamus

• size of almond, just above pituitary gland

• control pituitary gland by hormonal & neural stimulation

• Functions

  • 🧠controls brain stem & spinal cord

  • 🌡️body temp regulation

  • 🍕regulates food intake

  • 💧controls thirst

  • 😴regulates sleep & wake cycles

  • 😢center of emotional response

Pineal gland

• tiny, cone-shaped gland near cerebellum

• secretes melatonin to regulate sleep & wake cycles

Thyroid gland

• base of neck

• 2 distinctive halves, butterfly shape

• calcitonin - decr calcium levels in the blood

• thyroid hormones (TH) (thyroxine (T₄) and triiodothyronine)

  • 🔥regulate metabolism and body heat production

  • 🌬️control cellular oxygen usage

  • 🩸maintain blood pressure

Parathyroid glands

• attached to the back of the thyroid

• produce PTH - brings calcium out of the bones and into the bloodstream for use by cells

Adrenal glands

• atop each kidney

• adrenal cortex (outer layer)

  • epinephrine & norepinephrine - regulate fight or flight response to emergency situations (incr ❤ rate, blood pressure/flow, intake of O2 for immediate energy)

• adrenal medulla (inner layer)

  • glucocorticoids (ex: cortisol, aldosterone) - regulate ion levels for quick energy

Exocrine vs. endocrine glands _{^{(in pancreas)}}

use ducts vs. ductless

Pancreas’ glands

• endocrine part of pancreas made of groups of cells called islets of Langerhans _{^{(look like tiny islands)}}

• beta cells produce insulin - lower blood glucose levels

• alpha cells produce glucagon - raise blood glucose levels

Thymus gland

• small gland near sternum

• produces thymopoietin, thymic factor, and thymosin, which is involved in the development of the immune system

!!! pancreas and thymus are endocrine glands, also have functions w/in other body systems (ex: digestive, immune)

Homeostasis loop (calcium in blood):
Ca²⁺ too low, PTH, osteoclasts break down bone to release calcium, Ca²⁺ level rises
Ca²⁺ too high, calcitonin, calcium from blood absorbed into bones, Ca²⁺ level decr

Gonads

reproductive organs that produce sex cells and secrete sex hormones

females: ovaries

• estrogen - maturation of reproductive organs & secondary sex characteristics

• 🩸progesterone & estrogen - cause breast development and control of menstrual cycle

males: testes

• testosterone - maturation of reproductive organs & secondary sex characteristics, sperm production

How are hormones regulated?

• control hormone secretion w/ feedback mechanisms (ex: thyroid feedback mechanism is a negative feedback loop)

• endocrine system homeostasis:

  • hypothalamus secretes hormones into the pituitary (thyrotropin-releasing hormone)

  • pituitary secretes thyroid-stimulating hormone

  • thyroid secretes thyroxine into the blood, which incr metabolism

  • thyroxine levels too high, triggering hypothalamus to stop the impulse ⟲

Other hormone-producing structures

• ❤️Heart: secretes atrial natriuretic peptide - reduces blood volume & pressure

• Stomach and small intestine: several digestive hormones regulate multiple digestive processes

• Fatty tissue: produces leptin (controls appetite, feel full)

• 👶🏻Placenta: steroid and protein hormones that influence pregnancy

• 🩸Kidneys: erythropoietin - signals bone marrow to produce more red blood cells

• ☀Skin: produces vitamin D - allows digestive system to absorb calcium from food

Improper functioning of an endocrine gland

• hyposecretion - not enough hormone is released

• hypersecretion - too much hormone is released

• all endocrine disorders are caused by either hyposecretion or hypersecretion of hormones