1. The Endocrine System Major Glands and Associated Functions Hypothalamus- integrates the nervous and vertebrate endocrine systems by receiving information from nerves throughout the body and other parts of the brain Once the hypothalamus receives this info, it works to initiate endocrine systems that are appropriate for environmental conditions The Hypothalamus regulates all other endocrine glands via the pituitary gland Pituitary Gland- the pituitary gland is made up of the anterior and posterior pituitary glands which are found at the base of the brain and surrounded by bone Although known as the “master gland” it obeys hormonal orders from the hypothalamus Posterior Pituitary Gland- an extension of the brain which develops from a small bulge of the hypothalamus and remains an extension of the hypothalamus Stores and secretes antidiuretic hormone (ADH) and oxytocin Anterior Pituitary Gland- develops from a fold of tissue at the roof of the developing embryo’s mouth and grows upward toward the brain, eventually disconnecting from the mouth Consists of endocrine cells that synthesize and secrete several hormones directly into the blood Unlike the posterior, it is not an extension of the brain Main Function The endocrine system is made up of eight major glands that each secrete different types of hormones that regulate metabolism, growth and development, sexual reproduction and mood among other things. Its main function is to establish and keep homeostasis (equilibrium) within the body.

2. Thyroid gland- covers the windpipe from the front, right, and left sides Produces T3 and T4 hormones that stimulate and maintain metabolic processes Regulated by thyroid stimulating hormone (TSH) Secretes calcitonin which lowers blood calcium levels Regulated by calcium in the blood Plays a vital role in homeostasis In adult mammals, thyroid hormones help to maintain a normal blood pressure, heart rate, muscle tone, digestion and reproductive functions Parathyroid gland- small glands located in the neck behind the thyroid Releases parathyroid hormone which raises blood calcium levels Parathyroid hormone(PTH) is regulated by calcium in the blood Pineal gland- small mass of tissue located near the center of the brain Secretes the hormone melatonin which is involved in biological rhythms and is regulated by light/dark cycles Melatonin signals your body that it is nighttime and assists it in sleep Pancreas- This is a gland located in the abdomen, more specifically, below and behind the stomach. Produces a number of essential chemicals such as insulin and glucagon Inulin is responsible for lowereing blood sugar level and is regulated by sugar in the blood

3. Adrenal glands- located on the top of both kidneys and are divided into an outer portion (adrenal cortex) and an inner portion (adrenal medulla) which specialize in different hormone functions Adrenal Cortex- creates glucocorticoids and mineralocorticoids Glucocorticoids- steroids that raise blood sugar levels and are regulated by Adrenocorticotropic hormone (ACTH) Mineralocorticoids- steroids that promote the reabsorption of sodium ions and excretion of potassium ions in kidneys Adrenal Medulla- creates and secretes epinephrine and norepinephrine which are more commonly known as adrenaline and noradrenaline Both of these dictate metabolic response within the body which include oxygen release in muscles, blood vessel dilation and constricting/ raising blood pressure Gonads- These are the glands that produce and secrete hormones necessary for growth and development, sexual behavior, and regulation of reproductive cycles. The ovaries and the testes are the two glands in this category. Ovaries- situated on either side of the uterus and contain egg cells for reproduction as well as produce Estrogens and Progesterone Estrogens- responsible for promotion of development and maintenance of female secondary sex characteristics and also stimulate the growth of the uterine lining Progesterone- a steroid that promotes uterine lining growth Testes- located on the outside of the male body Androgens generally support sperm formation and promote the development and maintenance of male secondary sex characteristics Main androgen hormone is testosterone

4. Feedback Mechanisms Negative feedback system- This mechanism is important for maintaining homeostasis and most endocrine glands are under its control. The way this system’s loop works can be thought of as the way a thermostat works to maintain a desirable temperature in a house. It senses change in our bodies and triggers glands accordingly, as does the thermostat when it switches the air conditioning on and off in an attempt to find an ideal temperature. In the case of our bodies, the ideal that this system works toward is homeostasis. This negative feedback system is constantly working throughout our bodies. To maintain homeostasis within our bodies, the endocrine system uses two important feedback systems. These mechanisms are known as positive and negative feedback.

5. Positive feedback system- This mechanism works to control self- perpetuating changes that do not require continuous adjustment. Unlike negative feedback, positive feedback is rarely used to maintain homeostatic functions. Positive feedback is only needed on occasion rather that continuously as is the case with negative feedback. An example of positive feedback is childbirth. In the above picture, the positive feedback loop is being shown. When an expecting mother is in labor, the head of the baby will push against the cervix sending nerve impulses from the cervix to be transmitted to the brain. From these impulses, the brain stimulates the pituitary gland to secrete oxytocin. Oxytocin is then carried in the bloodstream to the uterus. Oxytocin stimulates uterine contractions and pushes the baby toward the cervix and the baby will then push its head against it. This loop continues until the baby is born and until the mothers body can again reach homeostasis.