This is supposed to be a test to see if my blog still works. I have no idea what to post so here are my notes on the Endocrine system from Bio 12 (Ms. Oak)
Endocrine System
- Made of glands that secrete substances into the blood stream
- Purpose: Communication and control
- Same functions as nervous system but works slower
- Hormones are…
- Chemicals released from one part of the body and carries through the bloodstream to affect another part of the body
- Are released in small quantities and are very specific
- If the hormones contact cells without these target cells, they will have no effect
- Target cells have receptors for specific hormones
- Two types of hormones
- Lipid-soluble
- Steroids
- Can pass directedly through the target cell membrane forming a hormone-receptor complex which halters the actions of the cell
- Water-soluble hormones
- Amino-acid based molecules
- Not able to pass through the membrane
- Bind to the receptors on the outside of the target cell which activates a 2nd messenger to mediate the response to the target cell
- Like a molecular relay
How are glands activated
- 3 ways
- Hormonal stimuli
- Glands are encouraged by hormones secreted by other glands
- Ex. Hypothalamus stimulates the pituitary
- Humoral Stimuli
- Levels of nutrients and ions in the blood can cause glands to secrete hormones
- Ex. Blood calcium levels stimulate parathyroid glands
- Neural Stimuli
- Nerve impulses cause glands to secrete hormones
- Ex. Sympathetic nervous system during stress causes release of epinephrine from adrenal glands
SUMMARY
When an endocrine gland is stimulated by another gland, ions or nerves, chemicals called hormones are released. These hormones alter target cells either directly or by using a second messenger depending on their ability to cross the cell membrane.
Pituitary gland
- Small bulb found on the underside of the brain
- It has 2 lobes: Anterior pituitary and posterior pituitary
- Called the “master gland” because it controls many other glands in the body
- Anterior:
- Thyroid-Stimulating gland (thyroxine)
- Growth Hormone (caused bone and muscle growth)
- Prolactin (produced breast milk)
- Gonadotropin (releases sex hormones, egg/sperm production), ETC
- Posterior:
- Antidiuretic hormone or vasopressin (increases water retention in kidneys and decreases urine production)
- Oxytocin (Stimulates contractions during childbirth and breast milk production)
Functions of the hypothalamus
- Hypothalamus is located just above the pituitary gland and is about the size of an almond
- Main function is to control the pituitary gland by hormonal and neural stimulation
- Allows for functions like:
- Conrtol of brain stem and spinal cord
- Center of emotional response
- Body temperature regulations
- Regulation of food intake
- Controls thirst
- Regulates sleep and wake cycles
Function of the Pineal gland
- Pineal gland is a tiny cone-shaped gland near the cerebellum
- Main secretion of the pineal gland is melatonin (controls sleep/wake cycles)
SUMMARY
The glands within the brain include the pineal gland which regulates sleep cycles and the pituitary and hypothalamus which work cooperatively to control many body functions. The pituitary is divided into anterior and posterior lobes.
Thyroid gland
- Located at the base of the neck
- Has 2 distinctive halves resulting in a butterfly shape
- Stimulates the hormones:
- Calcitonin (reduced the calcium levels in blood)
- Thyroxine (T4) and Triiodothyronine (T3) (regulates metabolism and body heat production, controls cellular oxygen use and maintains blood pressure)
Function of the Parathyroid glands
- Attached to the back of the thyroid
- Produces:
- Parathyroid hormone which has the opposite function from calcitonin
- (Parathyroid hormone brings calcium out of the bones and into the bloodstream for use by cells)
Functions of the Adrenal glands
- Sit atop each kidney
- Each gland has an outer layer (adrenal cortex) and an inner layer (adrenal medulla) that have different functions
- Adrenal medulla
- Epinephrine and norepinephrine: Regulates the “flight or fight” response to emergency situation by increasing the heart rate, blood pressure, blood flow and intake of oxygen for immediate energy
- Adrenal cortex
- Glucocorticoids: Regulate ion level for quick energy
Functions of the Pancreas
- Pancreas has both exocrine (using ducts) and endocrine (ductless) glands
- The endocrine part is made of groups of cells called the ISLETS OF LANGERHANS that look like islands
- Islet of Langerhans produces insulin and glucagon
- Beta cells
- Insulin: Lower blood glucose level
- Alpha cells
- Glucagon: Raise blood glucose levels
Thymus gland
- Located near the sternum
- Produces thymopoietin thymic factor and thymosin which in involved in the development of the immune system
SUMMARY
The thyroid, parathyroid and adrenal glands have wide-reaching effects on teh body. The pancreas and thymus are endocrine glands but also function in other body systems (digestive and immune).
What are the endocrine functions of the gonads
- Gonads = Reproductive organs that produce sex cells and secrete sex hormones
- Femals: Ovaries
- Estrogen: Maturation of reproductive organs and secondary sex characteristics
- Progesterone (and estrogen): Causes breast development and control of menstrual cycle
- Males: Testes
- Testosterone: Maturation of reproductive organs and secondary sex characteristics, production of sperm
How are hormones regulated
- Control of hormone secretuon requires to regulate the amount hormones released into body
- Often this control comes from FEEDBACK MECHANISMS
- Negative or positive feedback loops
- One gland secretes a hormone triggering another gland and won’t stop secreting certain hormones until a change in body is detected
When the endocrine glands function improperly
- Improper functioning of an endocrine gland may cause
- Hyposecretion: not enough hormones are released
- Hypersecretion: Too many hormones are released
- All endocrine disorders are caused by these two reasons
SUMMARY
The endocrine system is controlled by feedback loops, like that of the hypothalamus – pituitary – thyroid system. If the glands of the endocrine system malfunction, it often results in the hyposecretion or hypersecreting of hormones.