Characteristics of the Endocrine System Composed of glands that secrete hormones into the circulatory system. Hormones are secreted in minute amounts into the interstitial space. Hormones eventually enter the circulatory system and arrive at specific target tissues.

Characteristics of the Endocrine System Functions are similar to the nervous system. Differences; Amplitude-modulated vs. Frequency-modulated Response of target tissue to hormones is usually slower and of longer duration than that to neurons.

Chemical Structure of Hormones Peptides & Proteins: Most hormones are either peptides or proteins and are usually referred to as peptide hormones. Amines: Amine hormones are derivatives of the amino acid tyrosine.  Lipids & Steroids: Steroid hormones are produced by the adrenal cortex and the gonads. 

Control of Secretion Rates Hormones control the rates of many activities in the body. The rate at which each hormone is secreted is controlled by a negative feedback mechanism. Three major patterns of regulation: Non-hormone substance (e.g. insulin)

Control of Secretion Rates Hormones control the rates of many activities in the body. The rate at which each hormone is secreted is controlled by a negative feedback mechanism. Three major patterns of regulation: Non-hormone substance (e.g. insulin) Stimulation by the nervous system (e.g. epinephrine)

Control of Secretion Rates Hormones control the rates of many activities in the body. The rate at which each hormone is secreted is controlled by a negative feedback mechanism. Three major patterns of regulation: Non-hormone substance (e.g. insulin) Stimulation by the nervous system (e.g. epinephrine) Hormone from another endocrine tissue (e.g. TRH, TSH)

Transport and Distribution in the Body Hormones are dissolved in the blood plasma and transported in free form or bound to a protein carrier. As a result, hormones can be distributed throughout the body relatively quickly. Hormones diffuse from the capillary to the interstitial space.

Transport and Distribution in the Body Lipid-soluble hormones diffuse through the walls of all capillaries. Water-soluble hormones must pass through pores.

Metabolism and Excretion Hormones are only active in the body for a certain time because they are destroyed and eliminated shortly after they are secreted. Half-life = length of time that it takes to eliminate half of the total amount of hormone that was secreted.

Metabolism and Excretion Water-soluble hormones have relatively short half-lives because they are rapidly broken down by enzymes. These hormones normally have concentrations that increase and decrease rapidly in the blood. They generally regulate activities that have a quick onset and a short duration.

Metabolism and Excretion Lipid-soluble hormones are usually bound to protein carriers. The rate at which these hormones are broken down is greatly reduced. Therefore, these hormones have longer half-lives.

Metabolism and Excretion Hormones are removed from the blood in four ways. Excretion (kidney, liver) Metabolism (enzymes) Active transport (actively transported into cells and secreted again) Conjugation (attach water-soluble molecules to hormone and then excreted by kidney or liver).

Interaction of Hormones with Their Target Tissues. Hormones only interact with cells that have binding sites that are specific for the particular hormone.

Classes of Hormone Receptors. Hormones can be placed into one of two major categories. Hormones that cannot pass through the plasma membrane. Hormones that can pass through the plasma membrane. As a result, hormone receptors need to be located in different locations.

Membrane-Bound Hormone Receptors. Some receptors are located in the membrane of the target tissue. After a hormone binds to the receptor, the receptor initiates events that lead to a response. Some receptors alter membrane permeability.

Membrane-Bound Hormone Receptors. Some receptors are located in the membrane of the target tissue. After a hormone binds to the receptor, the receptor initiates events that lead to a response. Some receptors alter membrane permeability. Some receptors activate G proteins.

Membrane-Bound Hormone Receptors. Some receptors are located in the membrane of the target tissue. After a hormone binds to the receptor, the receptor initiates events that lead to a response. Some receptors alter membrane permeability. Some receptors activate G proteins. Some receptors alter intracellular enzyme activity.

Intracellular Hormone Receptors. Some receptors are located in the target cell. They are located either in the cytoplasm or in the nucleus of the target cell. Once the hormone binds to the receptor, the effects of the hormone take place.

Functions of the Endocrine System Metabolism and tissue maturation. Ion regulation. Water balance. Immune system regulation. Heart rate and blood pressure regulation. Control of blood glucose and other nutrients. Control of reproductive functions. Uterine contractions and milk release.

Pituitary Gland and Hypothalamus Pituitary gland is responsible for secreting nine hormones. Hypothalamus regulates the pituitary gland’s secretions.

Pituitary Gland Divided into a posterior and anterior portion. Posterior pituitary is also known as the neurohypophysis, because it is continuous with the brain. Anterior pituitary is also known as the adenohypophysis, because it acts more as a gland.

Relationship of the Pituitary Gland to the Brain The hypothalamus and the anterior pituitary are connected to each other via blood vessels. Hypothalamus produces neurohormones that travel to the anterior pituitary via the blood. Neurohormones then leave the blood and act on the cells in the anterior pituitary.

Relationship of the Pituitary Gland to the Brain Some neurohormones acts as releasing hormones and others act as inhibiting hormones. This is how the hypothalamus controls the anterior pituitary gland. See table 18.1 for a complete description of the hormones of the hypothalamus.

Relationship of the Pituitary Gland to the Brain There are no blood vessels that connect the hypothalamus to the posterior pituitary. Instead, neurohormones produced in the hypothalamus travel to the posterior pituitary via axons.

Hormones of the Posterior Pituitary Posterior pituitary stores and secretes two polypeptide hormones: Antidiuretic hormone (ADH) Oxytocin

Antidiuretic Hormone (ADH) ADH is synthesized in the hypothalamus and transported to the posterior pituitary. ADH is then released into the circulatory system and carried to the primary target tissue in the kidney. ADH promotes water retention and reduces urine volume.

Hormones of the Anterior Pituitary Anterior pituitary hormones are called tropic hormones.

Hormones of the Anterior Pituitary Anterior pituitary hormones are called tropic hormones. We will only address one of the many tropic hormones: Thyroid-stimulating hormone

Thyroid-stimulating Hormone (TSH) TSH is also known as thyrotropin. Stimulates the synthesis and secretion of thyroid hormones from the thyroid gland. TSH secretion is controlled by TRH from the hypothalamus.

Thyroid Gland & Hormones Thyroid hormones exist in two forms: Triiodothyronine (T3) Tetraiodothyronine (T4) (also called thyroxine) Approx. 90% T4 and 10% T3 secreted.

Thyroid Gland & Hormones Thyroid hormones are transported in the blood in combination with plasma proteins. Approx. 70-75% of T3 & T4 are bound to thyroxin-binding globulin (TBG). 20-30% are bound to other plasma proteins. Therefore, high half-life.

Thyroid Gland & Hormones Thyroid hormones diffuse through the target cell membrane. Bind to receptors in the nucleus. Thyroid hormones affect nearly every tissue in the body. Factors such as metabolism, growth, and maturation are affected.

Regulation of Thyroid Hormone Secretion TRH & TSH help control thyroid hormone levels. Exposure to stress and cold increases TRH. Prolonged fasting decreases TRH.

Regulation of Thyroid Hormone Secretion TRH & TSH help control thyroid hormone levels. Exposure to stress and cold increases TRH. Prolonged fasting decreases TRH. Abnormal thyroid conditions are listed in Table 18.5

The Adrenal Glands Located atop the kidneys. Composed of an inner medulla and an outer cortex.

The Adrenal Medulla Two major hormones: Epinephrine (80%) Norepinephrine (20%) See Table 18.7 for structure, target tissue, and response.

The Adrenal Cortex All hormones are steroids. Lipid soluble and are carried in the plasma by protein carriers. Three hormone types: Mineralocorticoids (e.g. aldosterone) Glucocorticoids (e.g. cortisol) Androgens

The Adrenal Cortex Adrenocorticotropin-releasing hormone (ACTH) is necessary to maintain the sensory activity of the adrenal cortex. Corticotropin-releasing hormone (CRH) is released from the hypothalamus and stimulates the anterior pituitary to secrete ACTH.

The Adrenal Cortex Table 18.9 outlines the abnormalities associated with hypersecretion and hyposecretion of adrenal hormones.

The Adrenal Cortex Table 18.9 outlines the abnormalities associated with hypersecretion and hyposecretion of adrenal hormones. Predict 7

Predict 7 Cortisone, a drug similar to cortisol, is sometimes given to people who have severe allergies or extensive inflammation or who suffer from autoimmune diseases. Taking this substance chronically can damage the adrenal cortex. Explain how this damage can occur.

The Adrenal Cortex Table 18.9 outlines the abnormalities associated with hypersecretion and hyposecretion of adrenal hormones. Predict 7 Clinical Focus – Stress (page 621; 633)

Effects of Aging What happens to the endocrine system when we get old? Endocrine glands differ in how they respond to the aging process. Some experience a gradual decrease in secretion while others are not affected to a great degree.

Effects of Aging - Growth Hormone - There is a decrease in growth hormone (GH). Decrease is greater in people who do not exercise. Decreases in GH may explain a gradual decrease in lean-body mass in these people.

Effects of Aging - Melatonin - Melatonin decreases in aging people. May influence sleeping patterns. May also affect the patterns of other hormones like GH and testosterone.

Effects of Aging - Thyroid Hormone - Decreases slightly with increasing age. Age-related damage to the thyroid gland may also occur.

Effects of Aging - Insulin - There does not appear to be a age-related decrease in the ability to maintain blood glucose levels. However, there is an age-related tendency to develop Type II diabetes.

Hormonelike Substances Autocrine chemical signals are released from cells in a local area and influence activity of the same cell type. Paracrine chemical signals are produced by a wide variety of tissues and secreted into tissue spaces.

Hormonelike Substances Autocrine and paracrine signals are not like hormone signals. They are not secreted by endocrine glands. They act locally not systemically. They are also not completely understood…

Autocrine Chemical Signals Autocrine chemical signals include the chemical mediators of inflammation. Prostaglandins Thromboxanes Prostacyclins Leukotrienes Collectively known as eicosanoids.

Autocrine Chemical Signals These products are released from injured cells. Responsible for initiating some of the symptoms of inflammation. Pain receptors are stimulated directly by prostaglandins.

Prostaglandins Produced in all cells in the body except for red blood cells. Once prostaglandins enter the circulatory system, they are metabolized rapidly. They are synthesized from essential fatty acids (omega-3, omega-6). Ratio of omega-6:omega-3 seems to be important in the synthesis of prostaglandins.

Prostaglandins Anti-inflammatory drugs like asprin inhibit prostaglandin synthesis. Prostaglandins can both intensify or diminish inflammation and increase or decrease the clotting tendency of the blood. In order for the body to remain healthy, these two potentials must be properly balanced.

Prostaglandins In simple terms; prostaglandins derived from omega-6 fatty acids promote inflammation and blood clotting, while those derived from omega-3 fatty acids oppose those effects. Remember that both are needed to maintain health.

Prostaglandins Evidence suggests that our diet can affect this balance. The Western diet is deficient in omega-3 fatty acids. An ideal omega-6:omega-3 ratio is between 1:1 and 4:1. A typical American diet is between 20:1 and 40:1!

Prostaglandins Essential fatty acid deficiency and omega-6:omega-3 imbalance is linked with the following serious health conditions: Heart attack Cancer Insulin resistance Asthma Lupus Schizophrenia Depression Stroke Obesity Diabetes Arthritis Alzheimer’s Disease

Prostaglandins Omega-3 sources: Flaxseed oil Fish oil Flax seeds, hemp seeds Walnuts, walnut oil Salmon, herring, mackerel, sardines Soybeans, soybean oil

Prostaglandins Omega-6 sources: Corn oil Peanut oil Meat Poultry Safflower oil Sesame oil Sunflower oil