Chapter 11: Endocrine System

11.11: Introduction

A. The endocrine system works with the nervous system to maintain homeostasis

B. The endocrine system is made up of the cells, tissues, and organs that secrete hormones (steroid or non-steroid) into body fluids.

C. Hormones diffuse into the bloodstream to act on target cells some distance away.

D. The body has two kinds of glands, exocrine (secretes products into ducts) and endocrine (secrete products into body fluids to affect target cells).

E. Other types of cell secretions are paracrine (affect neighboring cells) and autocrine (affect itself)

11.2: General Characteristics of the Endocrine System

A. The nervous system and the endocrine system work closely together.

B. The endocrine system uses hormones.

C. They regulate many metabolic processes.

D. Their actions are precise because of Targe Cells

E. Endocrine glands include the pituitary, thyroid, parathyroids, adrenals, pancreas, pineal, reproductive (ovaries and testes), thymus, and other hormone-secreting tissues.

11.3: Hormone Action

A. Hormones are steroids, amines, peptides, proteins, or glycoproteins; they can influence target cells even if they are present only in minute concentrations.

B. Steroid Hormones

• Steroid Hormones are synthesized from cholesterol, are lipid-soluble, and can pass through cell membranes.

• Receptors for steroid hormones are located in the target cell’s nucleus.

C. Nonsteroid Hormones

• Nonsteroid hormones combine with receptors in target cell membranes; the receptors have a binding site and an activity site.

• The hormone-receptor complex (as first messenger) triggers a cascade of biological activity through the cell membrane to the inside-called signal transduction.

D. Prostaglandins

• Prostaglandins are locally-produced lipids that usually affect the organ in which they are produced.

• Prostaglandins produce a variety of effects: some relax smooth muscle, others contract smooth muscle, some stimulate secretion of other hormones or chemicals, some influence blood pressure, and others affect reproductive physiology.

11.4: Control of Hormonal Secretions

A. Hormone levels are very precisely regulated.

B. Control Mechanisms

1. Release of tropic hormones from the hypothalamus controls secretions of the anterior pituitary.

2. The nervous system influences certain endocrine glands directly.

3. Other glands respond directly to changes in the internal fluid composition.

C. Negative Feedback Systems

1. Commonly, negative feedback mechanisms control hormonal releases.

2. In a negative feedback system a gland is sensitive to the concentration of the substance it regulates or which regulates it.

3. When the concentration of the regulated substance reaches a certain level (high or low), it inhibits the gland from secreting more hormone until the concentration returns to normal.

11.5: Pituitary Gland

A. The Pituitary Gland is attached to the base of the brain and connects to the hypothalamus

1. Anterior Pituitary consists mostly of glandular epithelial tissue.

2. Posterior Pituitary consists of nerve fibers and neurological cells that support nerve fibers arising in the hypothalamus.

B. The hypothalamus controls the activity of the pituitary gland.

1. Releasing and inhibiting hormones from the hypothalamus control the secretions of the anterior pituitary.

   1. These hormones are carried in the bloodstream directly to the anterior pituitary by hypophyseal portal veins.

   2. Specific cells are then stimulated to release or to stop releasing their hormone.

2. The posterior pituitary stores hormones made by the hypothalamus and releases them into the bloodstream in response to nerve impulses from the hypothalamus.

C. Anterior Pituitary Hormones

1. Growth hormone (GH) stimulates body cells to grow and reproduce; it also speeds the rate at which cells use carbohydrates and fats.

   1. Growth hormone-releasing hormone (GHRD) from the hypothalamus increases the amount of GH released, GH release-inhibiting hormone (GHIH) inhibits its release.

   2. Nutritional status affects the release of GH; more is released when nutrients are insufficient.

   3. Imbalances of GH

      1. Pituitary dwarfism-deficiency during growing years.

      2. Gigantism-over secretion during growing years.

      3. Acromegaly-over secretion in adulthood.

2. Prolactin (PRL) promotes milk production following the birth of an infant.

   1. No normal physiological role in males is known.

3. Thyroid-stimulating Hormone (TSH) controls the secretion of hormones from the thyroid gland.

   1. Thyrotropin-releasing hormone (TRH) from the hypothalamus regulates the release of TSH.

4. Adrenocorticotropic Hormone (ACTH) controls the secretion of hormones from the adrenal cortex.

   1. Controlled by the hypothalamus and stress levels.

5. Gonadotropins

   1. Follicle-Stimulating Hormone (FSH) and luteinizing hormone (LH) affect the male and female gonads.

   2. In males, LH is also known as interstitial-cell stimulating hormone (ICSH)

D. Posterior Pituitary Hormones

1. Neurons in the hypothalamus produce hormones that are stored in the posterior pituitary.

2. Antidiuretic Hormone (ADH) produces its effect by causing the kidneys to conserve water.

   1. Regulated by the hypothalamus and amount of water in body fluids.

   2. Osmoreceptors sense changes in osmotic pressure in body fluids.

   3. Diabetes Insipidus-insufficient ADH.

   4. Oxytocin (OT) plays a role in childbirth by contracting muscles in the uterine wall, and in milk letdown by forcing milk into ducts from the milk glands.

      1. stretching of the uterus and suckling of an infant at the breast stimulates release after birth.

      2. Positive Feedback loop.

11. 6: Thyroid Gland

A. The Thyroid Gland is located below the larynx and consists of two broad lobes connected by an isthmus.

B. Thyroid Hormones

1. The follicular cells produce two iodine containing hormones, thyroxine (T4) (tetraiodothyronine), and triiodothyronine (T3-the more potent form), that together regulate energy metabolism.

   1. These 2 hormones increase the rate at which cells release energy from carbohydrates, enhance protein synthesis, and stimulate the breakdown and mobilization of lipids.

   2. These hormones are essential for normal growth and development and nervous system maturation.

   3. The hypothalamus and pituitary gland control release of the thyroid hormones

   4. Iodine is needed by the follicular cells to make thyroid hormones.

2. Extrafollicular cells of the thyroid secrete calcitonin, which lowers blood levels of calcium and phosphate ions when they are too high.

   1. Calcitonin increases calcium stored in bones and decreases calcium released in urine.

C. Thyroid Disorders

1. Hypothyroidism-under activity

2. Hyperthyroidism-over activity

11.7: Parathyroid Glands

A. The 4 tiny parathyroids are located on the posterior of the thyroid.

B. Parathyroid Hormone (PTH)

1. Increases blood calcium ion concentration and decreases phosphate ion concentration and decreases phosphate ion concentration

2. PTH releases calcium from bone into blood, conserves calcium in the kidneys, and makes intestines absorb calcium.

3. Calcitonin and PTH exert opposite effects in regulating calcium ion levels in the blood.

4. Parathyroid Hormone Disorders

   1. Hypoparathyroidism-Blood calcium decrease

   2. Hyperparathyroidism-Blood calcium increase

11.8: Adrenal Gland

A. Located atop each kidney

B. Adrenal Medulla and Adrenal Cortex

C. Epinephrine and Norepinephrine increase heart rate, the force of cardiac muscle contraction, breathing rate, and blood glucose level. They also elevate blood pressure and decrease digestive activity.

D. Controlled by sympathetic impulses.

E. Hormones of the Adrenal Cortex

1. Aldosterone

   1. Regulates the concentration of mineral electrolytes.

   2. Causes kidney to conserve sodium ions and excrete potassium ions.

   3. Water retention, maintains blood volume and pressure.

   4. Controlled by concentrations of Calcium and Sodium ions.

2. Cortisol

   1. Inhibits protein synthesis and increases blood concentration of amino acids.

   2. Fatty acid release from adipose tissue. Increases utilization of fatty acids as energy. Decreases use of glucose.

   3. Liver cells synthesize glucose from noncarbohydrates, increases blood glucose concentration.

   4. Negative Feedback Loop

• Disorders

1. Hypersecretion of Cortical Hormones-Cushing Syndrome

   1. Alters carbohydrate and protein metabolism and electrolyte balance.

   2. →Too much sodium, puffy skin, increase in adrenal sex hormones.

2. Hyposecretion of Cortical hormones-Addison Disease

   1. Decrease of blood Sodium concentration, increases blood potassium, decreases blood glucose concentration, dehydration, lower blood pressure, decrease in skin pigmentation.

4. Sex Hormones

   1. Supplement sex hormones from the gonads.

11.9: Pancreas

A. Posterior to stomach and behind the parietal peritoneum.

B. Secretes digestive juice and relaxes hormones.

C. Hormones

1. Glucagon: stimulates the liver to break down glycogen and convert noncarbohydrates into glucose, increases blood sugar concentration.

   1. Regulated by Negative Feedback loop

2. Insulin: Opposite of glucagon. Liver forms glycogen from glucose and inhibits conversion. Promotes facilitated diffusion of Glucose across the cell membranes that have insulin receptors.

   1. Regulated by Negative Feedback loop

D. Disorders

1. Decreased blood glucose causes brain problems.

2. Diabetes mellitus-Insulin deficiency or impaired insulin response disturbs carbohydrate, protein, and fat metabolism. Hampers protein and fat synthesis.

11.10: Other Endocrine Glands

A. Pineal Gland-between hemispheres

1. Melatonin-”biological clock”, regulates circadian rhythms.

B. Thymus-posterior to sternum, between lungs.

1. Thymosin-production of differentiation of certain white blood cells.

C. Placenta

1. Estrogens, progesterone, and gonadotropin.

D. Heart

1. Atrial Natriuretic peptide-urinary sodium excretion.

E. Kidneys

1. Erythropoietin-red blood cell growth

11.11: Stress and Health

A. Factors that serve as stressors to the body produce stress and threaten homeostasis. Stressors increase the activity of the sympathetic nervous system.

1. Stress may be physical, psychological, or some combination of the two.