Human Anatomy and Physiology: Chapter 15: Endocrine System

This chapter provides an overview of the endocrine system. The endocrine system is more like a satellite radio or television signals broadcast widely so that every radio or television set, with its receiver adjusted properly, can receive the signals. It sends information to the cells it controls in the form of chemical signals, called hormones, which are released form the endocrine glands.

Functions of the Endocrine System:
1. Metabolism and tissue maturation
2. Ion regulation
3. Water balance
4. Immune system regulation
5. Heart rate and blood pressure regulation
6. Control of blood glucose and other nutrients
7. Control of reproductive functions
8. Uterine contractions and milk release

First of all you must be familiar with the different glands of the endocrine system

Classes of Receptors

The two major categories of hormone receptors are membrane-bound receptors and intracellular receptors.

Membrane-bound receptors are receptors that extend across the plasma membrane and have their receptor sites exposed to the outer surface of the plasma membrane.

To understand more about this, watch this video below:

Intracellular receptors are receptors in the cytoplasm or in the nucleus of the cell. Hormones that diffuse through the plasma membrane bind to intracellular receptors and the hormone-receptor complex then initiates the cell's response.

Here is a video on how it works:

Before we move on to the next topic, let us first refresh our minds of the different glands in the endocrine system. Here is a link below that will lead you to a review-activity:

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=MEA1104

Pituitary Gland and Hypothalamus

The hypothalamus of the brain regulates the secretory activity of the pituitary gland. Hormones, sensory information that enters the central nervous system, and emotions, in turn, influence the activity of the hypothalamus.

The pituitary gland is divided functionally into two parts: the posterior and anterior pituitary.

The posterior pituitary, or neurohypophysis is formed during embryonic development form an outgrowth of the inferior part of the brain in the area of the hypothalamus.

The posterior pituitary stores and secretes two polypeptide hormones called antidiuretic hormone and oxytocin.

Antidiuretic hormone (ADH) is so named because it prevents the output of large amounts of urine. It is sometimes called Vasopressin.

Oxytocin binds to membrane-bound receptors and causes contraction of smooth muscle cells of the uterus and milk ejection, or milk "let-down", from the breasts in lactating women. It also plays an important role in the expulsion of the fetus from the uterus during delivery.

For more information about ADH, watch this video below:

For more information about Oxytocin, watch this video below:

Anterior pituitary hormones include growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone and related substances, luteinizing hormone, follicle-stimulating hormone, and prolactin.

To have more information about the hormones in the anterior pituitary, watch the video below:

Thyroid Gland

The thyroid gland is composed of small, hollow balls of cells called follicles, which contain thyroglobulin.

Thyroid Hormones are triiodothyronine (T3) and tetraiodothyronine (T4). Another name for T4 is thyroxine.

Here is a video about the physiology of thyroid hormones for you to understand more about it:

Calcitonin
1. An increase in blood calcium levels stimulates calcitonin secretion.
2. Calcitonin decreases blood Ca2+ levels by inhibiting osteoclasts.

Here is a rap or song about calcitonin on how it works on our body:

Parathyroid Glands
1. The parathyroid glands are embedded in the thyroid gland.
2. Parathyroid hormone (PTH) increases blood Ca2+ levels.
3. A decreases in blood calcium levels stimulates PTH secretion

Below is a video on how parathyroid hormone works:

Adrenal Glands
1. The adrenal glands are near the superior poles of the kidneys.
2. The adrenal medulla arises from the same cells that give rise to postganglionic sympathetic neurons.
3. The adrenal cortex is divided into 3 layers: zona glomerulosa, zona fasciculata and the zona reticularis.

Hormones of the Adrenal Medulla
1. Epinephrine accounts for 80% and norepinephrine for 20% of the adrenal medulla hormones.

Hormones of Adrenal Cortex
1. Aldosterone acts on the kidneys to increase Na+ and to decrease K+ and H+ levels in the blood.
2. Cortisol increases fat and protein breakdown, increases glucose synthesis from amino acids, decreases the inflammatory response, and is necessary for the development of some tissues.
3. In females, androgens stimulate axillary and pubic hair growth and sexual drive.

Here is a video on how body works with adrenal glands:

To enhance more our skills, try this link; it is a game show about the different glands. Enjoy and learn at the same time! :)

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=NUR3103

Pancreas

1. The exocrine portion of the pancreas consists of a complex duct system, which ends in small sacs, called acini, that produce pancreatic digestive juices.

2. The endocrine portion consists of the pancreatic islets. Each islets is composed of alpha cell, which secrete glucagon, and beta cells, which secrete insulin.

Within the islets, alpha cells secrete glucagon and beta cells secrete insulin.

Insulin

Insulin is a hormone produced by the pancreas which is central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle.

To understand more on how insulin is produced, you can watch this video below:

Glucagon

Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar (glucose) levels fall too low. Glucagon causes the liver to convert stored glycogen intoglucose, which is released into the bloodstream.

To understand more about glucagon production, watch the video below: