ANAPHY LECT NOTES.docx

ENDOCRINE SYSTEM

  • Essential for the body to maintain homeostasis
  • From Greek words “endo” meaning “within” and “krino” meaning “to secrete”
  • Composed of endocrine glands and cells
  • The endocrine glands and cells secrete chemical messengers called hormones
  • Chemical messengers allow cells to communicate with each other to regulate body activities
  • Hormones circulate through the bloodstream to sites called target tissues or effectors.
  • Endocrinology is the study of the endocrine system

4 CLASSESS OF CHEMICAL MESSENGERS

(Based on the source of chemical messenger and its mode of transport in the body)

  1. AUTOCRINE CHEMICAL MESSENGERS- (Auto=self) stimulates the cell that originally secreted it. Ex: those secreted by white blood cells during an infection
  2. PARACRINE CHEMICAL MESSENGERS- (para=next) act locally on neighboring cells. It affects surrounding cells. Ex: Histamine
  3. NUEROTRANSMITTERS- secreted by neurons that activate an adjacent cell, whether it is in another neuron, muscle cell, or glandular cell. Secreted into the synaptic cleft not in bloodstream.
  4. ENDOCRINE CHEMICAL MESSENGERS- (Endo=within) secreted into the bloodstream by certain glands and cells, which together constitutes the endocrine system. Travels through the blood stream to the target cells.
  • Nervous system and endocrine system are the two important control system of the body.
  • Hormones of the ES are secreted in response to humoral, neural, or hormonal stimuli to regulate homeostasis.

MAIN FUNCTIONS OF THE ES

 1. REGULATION OF METABOLISM- controls the rate of nutrient utilization and energy production.
 2. CONTROL OF FOOD INTAKE AND DIGESTION- regulates the level of satisfaction/fullness and the breakdown if food into individual nutrients
 3. MODULATION OF TISSUE DEVELOPMENT-influences the development of tissues
 4. REGULATION OF ION LEVELS- helps monitor blood ph, Na+, K+, and Ca2
 5. CONTROL OF WATER BALANCE- regulates water balance by controlling the solute concentration of the blood and the membrane permeability
 6. REGULATION OF CARDIOVASCULAR FUNCTIONS- regulates the heart rate and blood pressure and prepare the body for physical activity
 7. CONTROL OF BLOOD GLUCOSE AND OTHER NUTRIENTS- regulates the level of glucose and other nutrients in the blood
 8. CONTROL OF REPRODUCTIVE FUNCTIONS-controls the development and functions of the reproductive systems of males and females
 9. STIMULATION OF UTERINE CONTRACTIONS AND MILK RELEASE- regulates uterine contractions during delivery and stimulates milk release from breasts in lactating females

  1. MODULATION OF IMMUNE SYSTEM FUNCTION- control the production of immune cells
  • Hormone is from the Greek word “hormone” meaning ‘set into motion’
  • The chemical composition of hormones affects their chemical behaviors

CHEMICAL NATURE 0F HORMONES

  1. LIPID-SOLUBLE HORMONES -nonpolar molecules ; includes, steroid hormones, thyroid hormones, and fatty acid derivative hormones.
  • TRANSPORT OF LIPID-SOLUBLE HORMONES – if these types of hormones circulated in the blood unprotected, they could be removed and would be unable to effectively regulate their targets. Removal happens through (1.) breakdown of enzymes in the liver or lungs, (2.) extraction into urine by kidneys, (3.) breakdown by enzymes in the bloodstreams.
  • TRANSPORT OF LIPID-SOLUBLE HORMONES – lipid-soluble hormones are protected since they travel through the bloodstream bound to “binding proteins” that acts as chaperone. Binding proteins reduces the rate at which lipid-soluble hormones get degraded or removed.
  1. WATER-SOLUBLE HORMONES- polar molecules; includes peptide protein hormones, peptide hormones, amino acid derivative hormones
  • TRANSPORT OF WATER-SOLUBLE HORMONES- since water soluble hormones can dissolve in blood (free hormones), most dissolve directly into the blood and are delivered to the target tissues ; These hormones have short half-lives.

STIMULATION OF HORMONE RELEASE

(3 types of stimuli regulates hormone release: humoral, neural, and hormonal)

  1. CONTROL BY HUMORAL STIMULI- humoral stimuli refers to the molecules and ions in the bloodstream that can directly stimulate the release of some hormones. “humoral” refers to ‘body fluids’ including blood. Cells that secrete these hormones have receptors for certain substances in the blood.
  2. CONTROL BY NEURAL STIMULI- neurons release a neurotransmitter into the synapse with the cells that produce the hormone. The neurotransmitter may also stimulate the cells to increase hormone secretion.
  3. CONTROL BY HORMONAL STIMULI- occurs when hormones are secreted that, in turn, stimulates the secretion of other hormones.

INHIBITION OF HORMONE RELEASE

(3 types of stimuli is involved in this process: humoral, neural, and hormonal)

  1. INHIBITION OF HORMONE RELEASE BY HUMORAL STIMULI- when a hormones release is sensitive to the presence of a humoral stimulus, there exists a companion hormone whose release is inhibited by the same humoral stimulus.
  2. INHIBITION OF HORMONE RELEASE BY NUERAL STIMULI- it the neurotransmitter is inhibitory, the target endocrine gland does not secrete its hormone
  3. INHIBTION OF HORMONE RELEASE BY HORMONAL STIMULI- some hormones prevent the release of other hormones, which is a common mode of hormone regulation.

Regulation Of Hormone Levels in Blood

  1. Negative feedback mechanism
  2. Positive feedback mechanism

Hormone Receptors and Mechanism of Action

  • Hormones exert action by binding to target cell proteins called “receptors”
  • The portion of each receptor molecule is called a “receptor site”
  • The tendency for each type of hormone to bind to one type of receptor is called “specificity”

Classes of Receptors

  1. Lipid-soluble hormones bind to nuclear receptors
  2. Water-soluble hormones bind to membrane-bound receptors

ENDOCRINE GLANDS AND THEIR HORMONES

  1. PITUITARY AND HYPOTHALAMUS-
  • Pituitary is also called ‘hypophysis’ (hypo-under ; physis-growth) ; the isze of a pea ; found in the depression in the sphenoid bone inferior to the hypothalamus of the brain ; known as the “master gland”
  1. Anterior pituitary- made up pf epithelial cells derived from the embryonic oral cavity
  2. Posterior pituitary- extension of the brain and composed of neurons
  • Hypothalamus is the control center of the autonomic nervous system as well as the endocrine system. It controls the pituitary gland in 2 ways: (1) hormonal control and (2) direct intervention
  1. Hypothalamic control of the anterior pituitary- the anterior pituitary gland synthesizes hormones whose secretion is controlled by the hypothalamus
  2. Hypothalamic control of the posterior pituitary- the posterior pituitary is a storage location for two hormones synthesized by special neurons in the hypothalamus
  • The pituitary gland is connected to the hypothalamus by a stalk called ‘infundibulum’

Hormones of the Anterior Pituitary

(hormones secreted are proteins ; transported in the blood ; life span is measured in minutes ; binds to membrane bound receptors on their target cells ; each hormone is secreted by a separate cell type ; many are tropic hormones meaning they stimulate the secretion of other hormones from the target tissues )

 1. GROWTH HORMONE- stimulates growth of bones, muscles and other organs by increasing gene expression. It slows protein breakdown during food deprivation and favors lipid breakdown. Part of the effect of GH is influenced by a protein hormones called ‘insulin0like growth factors- IGF’ or ‘somatomedins’
 2. Pituitary dwarf- too little growth hormone secretion can result from the abnormal development of the pituitary gland. This condition happens when a person is suffering from a deficiency of growth hormone.
 3. Giantism- Excess GH secretion can result from hormone secreting tumors of the pituitary gland. This condition happens when exaggerated bone growth occurs and the person becomes abnormally tall.
 4. Acromegaly- if excess hormone is secreted after growth in bone length is completed, growth continues in bone diameter only resulting in facial features and hand becoming abnormally large.
 5. THYROID STIMULATING HORMONE- binds to membrane-bound receptors on cells of the thyroid gland and stimulates the secretion of thyroid hormone. TSH stimulates growth of the thyroid gland, thus, too much TSH enlarges the thyroid gland and makes it secrete too much thyroid hormone, and too little TSH decreases the size of the thyroid gland and its secretion of thyroid hormone.
 6. GONADOTROPINS- bind to membrane-bound receptors on the cells of the gonads (ovaries and testes). Gonadotropins regulate the growth, development, and functions of the gonads.
 7. Luteinizing hormone- It stimulaltes ovulation and promotes the secretion of reproductive hormones, estrogen and progesterone from the ovaries in females. In males, it stimulates interstitial cells of the testes to secrete the reproductive hormone testosterone.
 8. Follicle-stimulating Hormone- In females, it stimulates the development of follicles in the ovary. In males, it stimulates the development of sperm cells in the testes.
 9. PROLACTIN- (pro=precursor , lact=milk) binds to membrane-bound receptors of cells of the breast, where it helps promote the development of breast during pregnancy and stimulates the production of milk

  1. MELANOCYTE-STIMULATING HORMONE- Binds to membrane-bound receptors on melanocytes and causes them to synthesize melanin.

Hormones of the Posterior Pituitary

  1. ANTIDIURETIC HORMONE- (anti=against , uresis=urine volume) binds to membrane-bound receptors and increases water reabsorption by kidney tubules which results in less water lost as urine. ADH is also called ‘vasopressin’
  2. OXYTOCIN- (swift birth) causes contraction of the smooth muscles cells of uterus and milk letdown in breasts of lactating women. ‘Pitocin’ or the commercial preparation of oxytocin os used to assist childbirth.

ENDOCRINE GLANDS AND THEIR HORMONES

  1. THYROID GLAND- (shield-shaped) synthesizes and secrets 3 hormones: (1) triiodothyronine- T3 ; (2) thyroxine- tetraiodothyronine T4 ; (3) Calcitonin.
  • one of the largest endocrine glands and contains numerous thyroid follicles
  • requires iodine to synthesize thyroid hormone
  • GOITER- condition caused by enlarged thyroid gland which is due to the loss of negative feedback that resulted in excess TSH.
  • HYPOTHYROIDISM- lack of thyroid hormones
  • CRETINISM- hypothyroidism in infants ; characterized by developmental delay, short stature, abnormally formed skeletal structures.
  • HYPERTHYROIDISM- elevated rate of thyroid hormone secretion
  • GRAVES DISEASE- autoimmune disease that causes hyperthyroidism. This condition is often accompanied by ‘bulging of eyes’ which is a condition called ‘exophthalmia’
  1. PARATYHROID GLANDS- 4 tiny parathyroid glands are embedded in the posterior wall of the thyroid gland; they secrete hormones called ‘parathyroid hormone (PTH)’ which is essential for regulation of blood calcium levels.
  • HYPERPARATHYROIDISM- abnormally high rate of parathyroid hormone secretion. Can be caused by a tumor in a parathyroid gland.
  • HYPOPARATHYROIDISM- abnormally low rate of PTH secretion. Can result from injury to or removal of thyroid and parathyroid glands.
  1. ADRENAL GLANDS- (near or on the kidneys) 2 small glands located superior to each kidney. Each has an inner part called ‘adrenal medulla’ and outer part called ‘adrenal cortex’
  2. Adrenal Medulla- secretes 2 major hormones, the ‘epinephrine’ and ‘norepinephrine’ which are called the ‘fight-or-flight’ hormones. They prepare the body for intense physical activities.
  3. Adrenal Cortex- secretes 3 classes of steroid hormones: mineralocorticoids, glucocorticoids, and adrenal androgens.
  • Mineralocorticoids- regulate ion balance in the blood. Aldosterone is produced in the greatest amount which helps return blood pressure to its normal range through modulation of kidney function.
  • Glucocorticoids- help to provide energy for cell by stimulating the increased use of lipids and proteins. They decrease the inflammatory and immune responses. Cortisol is primarily secreted, and it is anti-inflammatory.
  • Adrenal Androgens- stimuolates the development of male secondary sex characteristics.
  1. PANCREAS, INSULIN, AND DIABETES
  • The endocrine part of the pancreas consists of ‘pancreatic islets’, and these islets consists of 3 cell types which regulate the blood levels of nutrients, especially glucose:
  1. Alpha cells- secrete glucagon when blood glucose levels are low
  2. Beta cells- secrete insulin in response to elevated blood glucose levels
  3. Delta cells- secrete somatostatin in response to food intake
  • When blood glucose decreases, lipids and proteins are broken down for energy, as lipids are broken down, the liver converts some of the fatty acids to acidic ‘ketones’
  • When the pH of the body fluids are below normal due to release of fatty acids and ketones, ‘acidosis’ occurs
  • Elevated blood glucose levels stimulate beta cells to produce insulin. 2 signals that inhibit insulin secretion are (1) low blood glucose levels and (2) stimulation of the sympathetic nervous system.
  • Diabetes Mellitus- body’s inability to regulate blood glucose levels within the normal range. There are two type of diabetes mellitus: type 1 and type 2
  1. Type 1 diabetes mellitus- occurs when too little insulin is secreted from the pancreas. Tissues cant take up glucose effectively, causing blood glucose levels to become very high which is a condition called ‘hyperglycemia’
  2. Type 2 diabetes mellitus- caused by either too few insulin receptors or defective receptors on target cells.
  • When too much insulin is present, blood glucose levels become very low which causes the brain to malfunction and cause a condition called ‘insulin shock’
  • When blood glucose levels increase, insulin secretion increases and glucagon secretion decreases. When blood glucose levels decrease, the rate of insulin secretion declines and the rate of glucagon secretion increases.
  1. TESTES AND OVARIES- Hormones produced by these organs is important in the development of sexual characteristics, structural and functional difference between males and females, and the ability to reproduce.
  • Testosterone- main reproductive hormone in males secreted by the testes. Regulates the production of sperm cells and is responsible for the development of male reproductive organs and secondary sexual characteristics
  • Progesterone and Estrogen- two main classes of reproductive hormones secreted by the ovaries which are responsible for the development of female reproductive organs and secondary sexual characteristics.
  1. THYMUS- lies in the upper part of thoracic cavity.
  • Important in the function of immune system. If one is born without a thymus, the immune system does not develop normally and the body is less capable of fighting infections
  • Secretes a hormone called ‘thymosin’ which aids the development of white blood cells called T cells
  1. PINEAL GLAND- small, pinecone-shaped structure
  • Produces a hormone called ‘melatonin’ which inhibits the reproductive system