Ch.26 Hormones and the Endocrine System

WHAT DISEASES CAN THYROID CAUSE?
The thyroid regulates development and metabolism. There are two big types of diseases that can be caused by the thyroid. Hyperthyroidism and hypothyroidism. Hyperthyroidism is when  too much T4 and T3 are in the blood and they lead to high blood pressure, loss of weight, overheating, and irritability. It can produce Graves disease. Hypothyroidism is when too little T4 and T3 are in the blood. It can lead to low blood pressure, overweight, often cold, and lethargy. They are the two opposite diseases.

WHAT IS DIABETES?
Diabetes is a common endocrine disorder. Diabetes mellitus results from a lack of insulin or a failure of cells to respond to it. It affects about 21 million Americans. There are two common types of diabetes mellitus. Type 1 is called insulin-dependent. It is an autoimmune disease and occurs when insulin producing cells are destroyed. Type 2 is called non-insulin dependent. It is deficiency of insulin and more commonly, reduced response to insulin. More than 90% of diabetics are type 2. It is associated with being overweight and underactive.

WHAT ARE THE STEROID SEX HORMONES?
The gonads secrete sex hormones. Steroid sex hormones include estrogens, progestins, and androgens. They are produced by the gonads in response to signals from hypothalamus and pituitary. Estrogens and progestins stimulate the development of female characteristics and they maintain the female reproductive system. Androgens such as testosterone trigger the development of male characteristics.

SUMMARY:
The endocrine system consists of all hormone, which is secreting cell and it works with nervous sytem to regulate body activities. The nervous system also communicates, regulates, and uses electrical signals via nerve cells. Nervous system reacts faster but endocrine system responses last longer. Hormone signaling involves three key events, which are reception, signal transduction, and response. Steroid hormones can diffuse through plasma membranes and they bind to a receptor protein in the cytoplasm or nucleus. The vertebrate endocrine system consists of more than a dozen glands and it secretes more than 50 hormones. The hypothalamus responds by sending out appropriate nervous or endocrine signals and it uses the pituitary gland to exert master control over the endocrine system. Pituitary glands consist of two parts. Posterior pituitary and anterior pituitary. Anterior pituitary is controlled by the hypothalamus.  Thyroid gland hormones are thyroxine and triiodothyronine. They regulate metabolism and development and it is a part of negative feedback. Blood calcium level is regulated by a tightly balanced antagonism between calcitonin from the thyroid and PTH from the parathyroid glands. Pancreatic hormones regulate blood glucose levels. Hormones from the adrenal glands help maintain homeostasis when the body is stressed. Nerve signals from the hypothalamus stimulate the adrenal medulla to secrete epinephrine, and norepinephrine. These hormones quickly trigger the fight-or-flight responses. ACTH from the pituitary causes the adrenal cortex to secrete glucocorticoids, and mineralocorticoids. Prolactin in humans stimulates mammary glands to grow and produce milk during late pregnancy. Sucking by a newborn stimulates further release of prolactin.


KEY TERMS:
- Hormones: chemical signal which cause specific changes in target cells
- Steroid hormones: non-polar lipids made from cholesterol
- Glands: specialized for hormone secretion only but some also do other jobs
- Hypothalamus: receives input from nerves about body conditions
- Posterior pituitary: stores and secretes oxytocin and ADH
- Anterior pituitary: synthesizes and secretes hormones that control the activity of other glands
- Releasing hormones: stimulate the anterior pituitary
- Inhibiting hormones: inhibit the anterior pituitary
- Pancreas: secretes two hormones that control blood glucose
- Insulin: signals cells to use and store glucose

This is a diagram of thymus gland.

Structure: the thymus lies beneath the sternum in the middle of the chest at the same level as the heart. It has a pyramidal shape and is divided into two lobes that separate at the mid-line of the body. It consists of two types of cells, lymphocytes and reticulin fibers, similar to other organs of the lymphatic system.

The thymus helps protect the body from foreign invaders, such as viruses and bacteria. However the thymus doesn’t filter lymphatic fluid to cleanse the body of toxins. Its primary function involves producing an array of highly specialized cells vital to the immune response. Its work involves thymosin, which promotes development of immune-system cells.

The thymus gland produces hormones called thymosins. Thymosins are involved in stimulating the growth of T lymphocytes, which help regulate the immune system. They also stimulate the production of other immune cells.


https://www.youtube.com/watch?feature=player_embedded&v=fPgQE9WgKpM

5 FACTS:
1) Hormones affect target cells by two main signaling mechanisms.
2) The vertebrate endocrine system consists of more than a dozen major glands.
3) The hypothalamus, which is closely tied to the pituitary, connects the nervous and endocrine systems.
4) Diabetes is a common endocrine disorder.
5) The adrenal glands mobilize responses to stress.