Endocrine System

What is considered an endocrine organ?

Any organ which secretes its substances into the bloodstream

What are components of the endocrine system?

Pineal gland, pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, uterus, ovaries, testes

What is the function of the endocrine system?

Release hormones into the bloodstream which will then cause target cells to carry out specific action

What are some things these hormones control?

Metabolism, growth, mood, sleep, reproduction

Regulation by negative feedback

Hormones which act to maintain homeostasis—> regulated by negative feedback mechanisms (keeps concentration of hormone within narrow range)

Regulation by positive feedback

Small number of hormones regulated by positive feedback
Cause an increase in conc. of hormone in body

What are the two main classes of hormones?

Steroid and non-steroidal

Steroid

Made of: lipids
Function: able to diffuse across plasma membrane of cell, affects gene expression in target cell

Non-steroidal

Made of: amino acids
Function: unable to diffuse across plasma membrane, bind to receptor proteins instead on cell membrane—> affecting processes in target cell

Pituitary gland

Function: secretes hormones which inhibit or stimulate hormone secretion of other glands, primary gland in endocrine system

Structure: seperated into anterior (front facing) and posterior (back facing) lobe, pea sized

Location: suspended under brain in pituitary stalk

Anterior lobe and Posterior lobe

Anterior

Composition: glandular epithelial tissue
Function: secretes many hormones

Posterior

Composition: nervous tissue
Function: produces two hormones

Which hormones does the anterior lobe produce?

Adrenocorticotropic hormone, Beta-melanocyte stimulating hormone, Endorphins, Enkephalins, Follicle stimulating hormone, Growth hormone, Luteinizing hormone, Thyroid stimulating hormone

Adrenocorticotropic hormone

directs adrenal glands to produce cortisol

Beta-melanocyte stimulating hormone

increases pigmentation of skin to protect from UV radiation

Endorphins and Enkephalins

parts of reward circuits, related to activities like eating, exercise, pregnancy- also reduce pain

Enkephalins also reduce pain

Follicle stimulating hormone

stimulate gamete production

Growth hormone

regulates growth + physical development in muscles and bones

Luteinizing hormone

stimulates prod. of sex hormones

Thyroid stimulating hormone

stimulates release of hormones from thyroid gland

Which hormones does the posterior lobe produce?

Antidiuretic hormone - helps kidneys regulate amount of water in body

Oxytocin- stimulates release of breast milk and uterine contractions during labour

Thyroid Gland

Function: Regulates breathing, heart rate, body weight, body temp, cholesterol levels

Structure: 5cm wide, two lobes connected by thin strip of tissue, connected to cardio. system via thyroid arteries + veins

Location: base of neck, below larnyx

What is the thyroid gland controlled by?

Autonomic nervous system, via pituitary gland and hypothalamus

Which 3 hormones does the thyroid gland produce?

T4 (tetraiodothyronine)- steroidal hormone

T3 (triiodothyronine)-steroidal hormone derived from T4

Calcitonin-non-steroidal hormone

What do T3 and T4 work together to do?

Regulate metabolism by regulating heart rate and digestion rate, produced in the follicular cells

True or False, T3 is more powerful but less stable than T4?

True, meaning T3 can cause greater changes in cells, but breaks down more quickly

What can T4 be converted to and used as?

T4 —> T3, act as reserve source for less stable hormone

What is calcitonin responsible for?

Reducing blood calcium levels to maintain homeostasis by:

Slowing breakdown of bone tissue
Causing new bone tissue to form
Reducing absorption of calcium in digestive system
Causing more calcium to be exerted in urine

Endocrine system and Homeostasis

Muscular system: pituitary gland secretes growth hormone —> muscles increase in size

Nervous system: Nervous sys controls endo sys via hypothalamus to achieve actions

Reproductive system: pituitary gland secretes FSH, causing prod. of sex hormones to ensure develop. of sex organs during puberty

Skeletal system: thyroid gland secretes calcitonin, stimulates bone growth and reduces bone degeneration