CHAPTER 9 THE ENDOCRINE SYSTEM

Introduction The ENDOCRINE SYSTEM is the SECOND MESSENGER SYSTEM of the body. Along with the NS, the endocrine system coordinates and directs the activity of the body’s cells. However, the speed of control in these two systems is very different The nervous system is “built for speed.” It uses nerve impulses to force the muscles and glands into immediate action. The endocrine system is a more slowly acting system that uses chemical messengers called HORMONES, that are released into the blood

Introduction Hormones control several major processes: Reproduction Growth and Development Mobilization of body defenses Maintenance of homeostasis Regulation of metabolism

Hormone Function Overview The key to the incredible power of the endocrine glands is the hormones they produce and secrete. These hormones regulate the activity of other cells.

Hormone Function Mechanisms of Hormone Action Hormones affect only certain tissues or organs - TARGET CELLS or TARGET ORGANS In order for target cells to respond to a hormone, target cells must have specific protein receptors to which THAT hormone can attach. When hormone binding occurs, this influences the working of the cells.

Hormone Function Mechanisms of Hormone Action continued… Effects Caused by Hormones The body’s hormones bring about effects on the body’s cells by ALTERING cellular activity. Four major effects: Changes in plasma membrane permeability or electrical state Synthesis of proteins, such as enzymes Activation or inactivation of enzymes Stimulation of mitosis

Hormone Function Control of Hormone Release WHAT PROMPTS THE ENDOCRINE SYSTEM TO RELEASE OR NOT RELEASE HORMONES? Hormone levels in the blood are maintained by NEGATIVE FEEDBACK. A stimulus or low hormone levels in the blood triggers the release of more hormone. Hormone release stops once an appropriate level in the blood is reached.

The Major Endocrine Organs The endocrine glands are DUCTLESS GLANDS. They produce hormones that they release into the blood. (On the other hand, exocrine glands release their products at the body’s surface or into body cavities through ducts.)

The Major Endocrine Organs Pituitary Gland Structure Size of a grape Hangs by a stalk from the hypothalamus Has 2 functional lobes: ANTERIOR PITUITARY - glandular tissue POSTERIOR PITUITARY - nervous tissue

The Major Endocrine Organs Pituitary Gland continued… Hormones of the Anterior Pituitary Growth Hormone (GH) General metabolic hormone Major effects are directed to growth of skeletal muscles and long bones.

Causes amino acids to be built into proteins. Causes fats to be broken down for a source of energy. If there is NOT enough secretion of GH during childhood, it can lead to DWARFISM. The individual is no taller than 4 feet. If there is TOO much secretion of GH during childhood, it can lead to GIGANTISM. The individual is 8-9 feet tall.

The Major Endocrine Organs Pituitary Gland continued… Hormones of the Anterior Pituitary Functions of Other Anterior Pituitary Hormones: Prolactin (PRL) - stimulates and maintains milk production following childbirth Adrenocorticotropic (ACTH) - regulates endocrine activity of the adrenal cortex Thyroid-Stimulating Hormone (TSH) - Influences growth and activity of the thyroid

The Major Endocrine Organs Pituitary Gland continued… Hormones of the Anterior Pituitary Functions of Other Anterior Pituitary Hormones: Gonadotropic Hormone - regulates hormonal activity of the gonads

Follicle-Stimulating Hormone (FSH): *In females - stimulates follicle development in the ovaries *In males - stimulates sperm development Luteinizing Hormone (LH): *In females - triggers ovulation *In males - stimulates testosterone production If there is too much secretion of FSH or LH, it could lead to sterility in both males and females.

The Major Endocrine Organs Pituitary Gland continued… Hormones of the Posterior Pituitary Oxytocin - stimulates contractions of the uterus during labor and causes milk ejection Antidiuretic Hormone (ADH) - can prevent urine production If there is too much secretion of ADH, it could lead to diabetes. This is why people with this problem are extremely thirsty and drink huge amounts of water.

The Major Endocrine Organs Thyroid Gland Characteristics: Found at the base of the throat Consists of 2 lobes and that are connected by a central mass called the Isthmus. Produces 2 hormones: Thyroid Hormone and Calcitonin Thyroid Hormone: The body’s major metabolic hormone - It controls the rate at which glucose is “burned.” Calcitonin: Decreases blood calcium levels by causing calcium to be deposited in the bones.

Thyroid Gland

The Major Endocrine Organs Parathyroid Gland Characteristics: Tiny masses on the posterior of the thyroid There are 2 glands on each thyroid lobe = total of 4 parathyroid glands Secretes Parathyroid Hormone (PTH): Stimulates osteoclasts to remove calcium from bone Stimulates the kidneys and intestine to absorb more calcium Increases calcium levels in the blood

The Major Endocrine Organs Adrenal Gland Characteristics: 2 bean-shaped glands that curve over the top of the kidneys It has a cortex and a medulla - the central medulla is enclosed by the adrenal cortex

The Major Endocrine Organs Adrenal Gland continued… Hormones of the Adrenal Cortex Mineralocorticoids (Aldosterone) Produced by the outermost adrenal cortex Regulates mineral content in blood, water, and electrolyte balance

Hormones of Adrenal Cortex Glucocorticoids (Cortisone) Produced in the middle layer of the adrenal cortex Promotes normal cell metabolism Prescribed as drugs for patients with rheumatoid arthritis to suppress inflammation

Hormones of Adrenal Cortex Sex Hormones Produced in the inner layer of the adrenal cortex Includes androgens in males and estrogens in females

The Major Endocrine Organs Adrenal Gland continued… Hormones of the Adrenal Medulla Epinephrine Norepinephrine These 2 hormones prepare the body to deal with short-term stress.

The Major Endocrine Organs Pancreatic Islets The pancreas is located close to the stomach and is a MIXED gland The pancreatic islets (also known as islets of Langerhans) are scattered among the tissue of the pancreas. The islets of the pancreas produce 2 hormones: Insulin- decreases blood glucose levels Glucagon - allows glucose to enter the blood Both help to maintain blood sugar homeostasis.

The Major Endocrine Organs Pineal Gland Cone-shaped gland found in the brain Secretes the hormone Melatonin - helps establish the body’s wake and sleep cycles

The Major Endocrine Organs Thymus Located posterior to the sternum Largest in infants and children but decrease in size throughout adulthood Secretes the hormone Thymosin - very important in developing the immune system

The Major Endocrine Organs Gonads Hormones of the Ovaries (Female Gonads) Estrogens Produced by the follicles of the ovaries Stimulates the development of secondary female characteristics Matures female reproductive organs Helps prepare the uterus to receive a fertilized egg Helps maintain pregnancy Prepares the breasts to produce milk Progesterone Acts with estrogen to bring about the menstrual cycle Helps in the implantation of an embryo in the uterus

The Major Endocrine Organs Gonads Hormones of the Testes (Male Gonads) Testosterone Responsible for adult male secondary sex characteristics Promotes growth and maturation of male reproductive system Required for sperm cell production

Other Hormone-Producing Tissue Organ = PLACENTA The Placenta is an organ that is formed temporarily in the uterus of pregnant women. It produces hormones that maintain the pregnancy. Some hormones play a part in the delivery of the baby.

Developmental Aspects of the Endocrine System: Most endocrine organs operate smoothly until old age. Menopause is brought about by lack of efficiency of the ovaries. Can lead to osteoporosis, possible mood changes, and increased chance of heart disease Growth hormone production declines with age.