Endocrine System

Overview•Endocrine

system includes all cells and tissues that produce hormones or paracrine factors with effects beyond their tissues of origin.

Intercellular Communication

•Direct communication: When cellular activities are coordinated through gap junctions of adjacent cells

•Paracrine communication: chemical messengers from cell to cell within a tissue▫Hormones are chemical

messengers that are released from one tissue & transported in the bloodstream to alter activities in other tissues Cells within those tissues are called target cells.

Intercellular Communication•Endocrine communication: When hormones coordinate cellular activities in distant portions of the body.▫Stimulate synthesis of an

enzyme/protein An enzyme is a protein that synthesizes a specific reaction

▫Increase/decrease rate of synthesis of an enzyme

▫Turn existing enzyme channel “on” or “off”

Chemical Messengers• Amino Acid Derivatives

▫ Small molecules related to amino acids (building blocks of proteins) (by thyroid and pineal gland).

• Peptide Hormones▫Chains of amino acids (diverse visceral organ/brain

release)• Lipid Derivatives

▫Eicosanoids; small molecules with 5-carbon ring (involved in blood clotting)

▫Leukotrienes; eicosanoids released by activated white blood cells (leukocytes). (coordinate tissue response to injury)

• Steroid Hormones▫Lipid (similar to cholesterol) released by the

reproductive organs

Secretion and Distribution•Typically at occurs where the capillaries are

abundant & hormones quickly enter the bloodstream (2 min-hr)▫Inactivation

1. diffuses out of the bloodstream and binds to receptors on target cells

2. its absorbed and broken down by cells in the liver or kidneys

3. its broken down by enzymes in the plasma or interstitial fluid

Mechanisms of Hormone Action•Hormones and cell membrane receptors; in

order to affect a target cell, the hormone must first interact the the appropriate receptor▫Each cell has receptors for several different

hormones▫Lipid based hormones can diffuse across cell

membranes▫Non-lipid based hormones must bind to

receptor proteins to enter the cell

First and Second Messengers•First messenger: (hormone) does something to the appearance of a second messenger in the cytoplasm.

•Second messenger: may act as an enzyme activator, inhibitor, or cofactor.▫Net result is changes in the rates of various

metabolic reactions. Down regulation: process in which the presence of a hormone triggers a decrease in the number of hormone receptors.

Up regulation: process in which abundance of a hormone triggers an increase in the number of hormone receptors

Overview of Endocrine System

•http://www.youtube.com/watch?v=8fh2HmdxQjQ&feature=related

Control of Endocrine Activity•Direct response to:

▫Changes in the extracellular fluid composition

▫Arrival or removal of a specific hormone▫Arrival of specific neurotransmitters

Simple reflexes only involve one hormoneComplex reflexes involves one or more hormones

Patterns of Hormonal Interaction

•Extracellular fluid contains a mixture of hormones and more than one hormone can affect a cell at a time.

•When a cell receives instructions from 2 hormones at the same time 1 of 4 outcomes is possible:

• 1. Antagonistic effect: (the two hormones have opposing effects)

• 2. Synergistic effect: (the two hormones produce the same effect)

• 3. Permissive effect: 1 hormone is needed in order for the other hormone to produce an effect

• 4. Integrative effects: hormones produce different but complementary results

Pituitary Gland•Anterior lobe: contains a variety of endocrine cells▫Extensive capillary network radiates through these regions-gives cells immediate access to the circulatory system

http://www.youtube.com/watch?v=V08dWz5XNBA&feature=related

Hormones of the Anterior LobeThyroid-Stimulating

Hormone▫Triggers the release

of thyroid hormones•Andrenocorticotropic

Hormone▫Stimulates the

release of steroid hormones by the adrenal-targets cells that affect glucose metabolism

Hormones of the Anterior Lobe•Growth hormone

▫Stimulates cell growth and replication by accelerating the rate of protein synthesis (especially skeletal muscle and cartilage)

•Melanocyte-Stimulating Hormone▫Stimulates the

melanocyte of the skin

Hormones of the Anterior Lobe•Gonadotropins

▫Regulate the activities of the gonads (testes and ovaries) Low levels causes hypogonadism-leads to inability to produce sperm/eggs

Follicle-stimulating hormones: promotes follicle development in females and helps stimulate secretion of estrogens

Luteinizing hormone: induces ovulation (production of reproductive cells in females)

•Prolactin▫Works with other hormones to stimulate

mammary gland development

Hormones of the posterior lobe•Antidiuretic hormone▫Released in response to fall in blood volume or blood pressure Decreases water loss, retains electrolytes, causes vasoconstriction (closes) to help raise blood pressure

•Oxytocin▫Stimulates smooth muscle contraction of the uterus in labor.

Thyroid Gland•Curves in front of the trachea

▫Contains fluid 3ox higher in iodide (I-) than the blood Iodide is the building blocks of thyroid-stimulating hormones

▫Extensive blood supply Delivers nutrients and gets rid of wastes

Thyroid GlandThyroid hormones effect almost every cell

▫In the cytoplasm they are held in storage▫In mitochondria the increase rate of ATP

production▫In the nucleus they synthesize enzymes that

control energy transformation Increases metabolic rate of the cell

•C cells release calcitonin which helps regulate Ca+ in body fluids▫Responds directly to Ca+ concentrations in

the blood Stimulates bone growth and density

Parathyroid Glands•2 pairs are embedded in the posterior side of the thyroid gland▫Chief cells Produce parathyroid hormones Increases Ca+ in body fluids▫Allows Ca+ to be taken from the bone

Adrenal Glands: One triangle shaped gland sits on top (superior) of each kidney

• Adrenal cortex▫Yellow because of stored lipids

(steroids)▫Collectively called the corticosteroids

vital for life (gene transcription)Outer region Produces hormones that affect the

composition of fluidsInner border towards the medulla Hormones affect glucose

metabolism Anti-inflammatory effectsNarrow band borders the medulla Produces androgens

Adrenal Glands Cont.Adrenal medulla: Secretory activities are

controlled by the sympathetic nervous systemEpinephrine: 75-80%Norepinephrine: 20—25%

In skeletal muscle:Mobilize glycogen reservesAccelerate glucose breakdown into ATPIn adipose tissue:Stored fat is broken down, released into the blood stream

for production of ATPIn the liver:Glycogen is broken down, released into the blood for use

by neural tissueIn the heart:Triggers increase in rate and force of cardiac muscle

contraction

Adrenaline• http://www.youtube.com/w

atch?v=4g25d7_Afmc&feature=related

The Pineal Gland•Inside the epithalamus•Synthesizes the

hormone melatonin▫Made from molecules

of serotonin Inhibits reproductive function may play a role in determining maturation

Protects against free radicals

Sets circadian rhythm

The Pancreas

•Lumpy organ the abdomen between the inferior border of the stomach (bottom) and the proximal (closest) portion of the small intestine.

•Primarily a exocrine organ (99%) but it makes digestive enzymes

•The endocrine pancreas (1%) consists of clusters known as pancreatic islets.▫Surrounded by capillaries that carry

hormones to the blood stream

Glucagon• Released by

Alpha cells:▫raises blood

glucose levels▫Target

primarily the liver

▫Stimulates release of glucose into the blood Typically in

times of energy need after a period of not eating

Insulin

• Peptide hormone released by beta cells when glucose concentrations exceed normal levels▫ Typically after eating,

especially after eating carbohydrates

• Insulin receptors are present in most cells membranes making them insulin dependent▫ Cells that do not need insulin to

utilize glucose are called insulin independent

Insulin• Effects of Insulin on target cells:

▫Acceleration of glucose utilization (all target cells) and enhanced ATP production

▫Stimulation of glycogen formation (skeletal muscle and liver)

▫Stimulation of amino acid absorption and protein synthesis

▫Stimulation of triglyceride formation in adipose tissue

Endocrine Tissues and Other Systems• Intestines

▫Pace of digestion typically controlled by hormones released locally

• Kidneys▫Calcitrol (part of the group of steroids we call

Vitamin D) Steroid Stimulates absorption of Calcium and Phosphate in

the digestive tract▫Erythropoietin

Stimulates production of red blood cell in the marrow when o2 levels in the kidneys are low

▫Renin Restricts salt and water loss in the kidneys when

renal blood flow declines

Endocrine Tissues and Other Systems

•Heart▫When stretched they reduce blood volume

and pressure by reducing thirst and promoting salt and water loss in the kidneys

•Thymus▫Under the sternum▫Important in the immune defense

Thymosinpromotes development of lymphocytes (white blood cells)

Endocrine Tissues and Other Systems• Gonads▫Androgens

Testosterone In embryos effects development of the CNS Effect development of sperm Protein synthesis in muscles Secondary sex traits: hair, voice, build…

▫Estrogens Follicle maturation (for ovulation) Secondary sex traits: hair, voice, build…

▫Progestins Prepare uterus for implantation Prepare mammary glands

Endocrine Tissues and Other Systems• Adipose tissue

▫Leptin Feedback control of appetite, released when

glucose is absorbed by adipose tissue; gives satiation and suppress appetite

▫Found obese people already have increased levels but have defective receptors for the hormone

Must also be present for normal gonadotropin synthesis Explains why decreased fat % can cause

amenorrhea Increased fat % can improve fertility Female maturation is later

▫Resistin Reduces insulin sensitivity

Explains why body fat % can influence type 2 diabetes

Role of Hormones in growth:Normal growth requires many hormones to cooperate

▫Growth Hormone (GH) More important in

children, its role is to produce skeletal muscle and skeletal bones

▫Thyroid hormones If not present in fetal or

1st year development can cause nervous system to fail

▫Insulin Without it energy is

diminished

▫Parathyroid Hormone (PTH) & Calcitrol Without them bone

density and strength are diminished

▫Reproductive hormones Absence would

prevent gender-related differences including skeletal proportions and secondary sex traits

Hormonal Responses to Stress

•Anything that disrupts homeostasis is a form of stress.

•General Adaptation Syndrome (GAS) or Stress Response▫Exposure to a wide variety of stress causing

factors will produce the same general pattern of hormonal and physiological adjustments

▫Divided into three stages:

•1. Alarm Phase: Immediate response to stress▫Directed by the SNS▫Energy reserves are mobilized (glucose)▫“fight or flight” occurs

Epinephrine•2. Resistance Phase: (weeks to months if necessary,

depending on general health and fat stores)▫When efforts of alarm phase do not overcome

imbalance Glucose demands are high Use glucorticiods: mobilize lipid and protein reserves,

conserve glucose for neural tissue, keep blood glucose elevated, conserve water and electrolytes

•3. Exhaustion Phase: when resistance breaks and homeostasis is lost▫Failure of one or more systems-- can be fatal