Endocrine System

Negative Feedback Control

body adjust if out of range/setpoint until it doesn’t need to

• hormone release triggered by:

  • Endocrine gland stimuli

  • Nervous system

Positive Feedback

Endocrine Gland Stimuli

stimulated to synthesize and release hormones in response to one of three stimuli:

1. Humoral stimuli

2. Neutral stimuli

3. Hormonal stimuli

Gland Locations (study image!)

Humoral Stimuli

• changing blood levels of ions and nutrients directly stimulate secretion of hormones

• Ex. Ca2+ in blood

Neural Stimuli

• nerve fibers stimulate hormone release

  • nervous system fibers stimulate adrenal medulla to secrete catecholamines (epi & norepi)

Hormonal Stimuli

hormones stimulate other endocrine organs to release their hormones:

• Hypothalamic hormones stimulate release of most anterior pituitary hormones

• Anterior pituitary hormones stimulate targets to secrete additional hormones

• Hypothalamic-pituitary-target endocrine organs feedback loop

  • hormones from final target organs inhibit release of anterior pituitary hormones

Nervous System Modulation

adjusts to hormone levels:

• modify stimulation/inhibition of endocrine glands

can override normal endocrine controls

• Ex: severe stress, hypothalamus and nervous system override insulin to allow blood glucose levels to increase (“fight or flight”)

Action of Hormones

• alter plasma membrane permeability and/ore membrane potential (open or close ion channels)

• stimulate synthesis of enzymes or other proteins

• activate or deactivate enzymes

• induce secretory activity

• stimulate mitosis

Second-Messenger Systems

• Cyclic AMP (cAMP) signaling mechanism

• PIP2 - calcium signaling mechanism

Cyclic AMP (cAMP)

1. hormone (first messenger) binds to receptor

2. receptor activates a G protein

3. G protein activities or inhibits effector enzyme adenylate cyclase

4. adenylate cyclase then converts ATP to cAMP (second messenger)

5. cAMP activates protein kinases that phosphorylate(adda phosphate) other proteins

PIP2

1. hormone-activated G protein activates: phospholipase C

2. splits membrane protein, PIP2, into two second messengers:

   • diacylglycerol (DAG) activates protein kinases

   • inositol trisphosphate (IP3) causes Ca2+ release from intracellular storage sites

3. calcium ions act as another second messenger

   • alters enzyme activity and channels, or binds to regulatory protein calmodulin

   • calcium-bound calmodulin activates enzymes that amplify cellular response

Intracellular Receptors and Direct Gene Activation

1. lipid-soluble steroid hormones and TH

2. diffuse into target cells

3. bind with intracellular receptors

4. enters nucleus and binds to region of DNA

5. initiate DNA transcription to produce mRNA

6. mRNA translate into specific protein

Ex.: metabolic activities, structural purposes, or exported from cell

Chemical Messengers

• Hormones: long-distance chemical signals; travel in blood or lymph

• Autocrines: exert effect on the same cells that secrete them

• Paracrines: locally acting, affecting cells other than those that secrete them

Autocrines and paracrines - local chemical messengers; not considered part of the endocrine system

Endocrine System Overview

Controls and integrates:

• reproduction

• growth and development

• maintenance of electrolyte, water and nutrient balance of blood

• regulate cellular metabolism; energy balance

• mobilization of body defensesBlod Sugar Regula

Blood Sugar Regulation (negative feedback loop)

When STIMULUS increase in glucose:

1. pancreases releases insulin

2. insulin acts on cells

3. body cells take up glucose

• Homeostasis

When STIMULUS decrease in glucose:

1. pancreases releases glucagon

2. glucagon acts on cells

3. liver breaks down glycogen

• Homeostasis

Thyroid Regulation (negative feedback loop)

1. low metabolic rate/body temp. (Low T3 & T4)

2. hypothalamus release TRH

3. pituitary releases TSH

4. thyroid release TH

5. TH stimulates cells to increase activities

6. high metabolic rate/body temp. (High T3 & T4)

7. stop release of TSH and TRH

Difference between circulating hormones and an autocrine/paracrines:

A hormone enters the bloodstream or lymph and binds to receptors on a distant tissue. Autocrine/Paracrine is released in fluid but acts on nearby cells or the same cells that secrete

Changes in cellular activity typically produced by hormones:

• Hormones open or close ion channels to change permeability

• increase enzymes synthesis

• activate/deactivate enzymes

• induce secretion

• stimulate mitosis

Best hormone that fits description: regulate the functions of another endocrine organ; four tropic hormones

thyroid stimulating hormone (TSH), follicle-stimulating hormone (FSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH)

Organs & Glands of the Endocrine System

• Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands

• Hypothalamus = neuroendocrine organ

• Some exocrine and endocrine: pancreas, gonads, placenta

• Other tissues & organs that produce hormones: adipose cells, thymus, and cells in walls of small intestine, stomach, kidneys, and heart

Two main classes of hormones:

• Amino acid-based hormones: (water soluble)

• Steroids:

  • synthesized from cholesterol

  • gonadal and adrenocortical hormones

Water-Soluble Hormones (Amino acid-based)

• acts on plasma membrane receptors

• act via G protein second messengers

• cannot enter cell

(Epinephrine, norepinephrine, melatonin, histamine, serotonin, oxytocin, ADH, GH, TSH, ATCH, FSH, LH, PRL, MSH, insulin, glucagon)

Lipid-Soluble Hormones (Steroid Hormones)

• act on intracellular receptors - directly activate genes

• can enter cell

• attaches to plasma proteins when circulating in blood

(aldosterone, cortisol, Androgens, testosterone, calcitriol, estrogen, progesterone, T3, T4, NO)

Target Cells

tissues with receptors for a specific hormone

Factors for Activation of Target Cells

1. Blood levels of hormone

2. Relative number of receptors on/in target cell

3. Affinity (strength) of binding between receptor and hormone

# of Hormones Influence on Target Cell Receptors

• Up-regulation: target cells form more receptors in response to low hormone levels

• Down-regulation: target cells lose receptors in response to high hormones levels

  • desensitizes the target cells to prevent them from overreacting to persistently high levels of hormones

Half-Life

time required for level of hormones in blood level to decrease by half

How to remove Hormones from blood

• degrading enzymes

• kidneys

• liver

Permissiveness

one hormones cannot exert its effects without another hormone being present

• ex. reproductive hormones need TH to have effect

Synergism

more than one hormones produces same effects on target cell, causing amplification

• ex. glucagon and epinephrine both cause liver to release glucose

Antagonism

one or more hormones oppose(s) action of another hormone

• ex. insulin & glucagon

Dwarfism, Gigantism & Acromegaly

Dwarfism: hyposecretion of GH

Gigantism & Acromegaly: hypersecretion of GH (usually caused by anterior pituitary tumor) gigantism = children, acromegaly = adults

Anterior Pituitary

• growth hormone (GH)

• thyroid stimulating hormone (TSH)

• adrenocorticotropic hormone (ACTH)

• follicle-stimulating hormone (FSH)

• luteinizing hormone (LH)

• prolactin (PL)

Growth Hormone (GH)

promotes growth of bones and muscle

Thyroid Stimulating Hormone (TSH)

promotes the release of thyroid hormone from the hyroid

Adrenocorticotropic Hormone (ACTH)

energy metabolism - stimulate your adrenal glands to release cortisol

Follicle-Stimulating Hormone (FSH)

Females: triggers the growth of eggs in the ovaries and gets the eggs ready for ovulation

Males: stimulates sperm production

Luteinizing Hormone (LH)

Sexual development in children fertility in adults: in women who menstruate (have periods). helps control the menstrual cycle & triggers the release of an egg from the ovary (ovulation)

Males: causes the leydig cells of the testes to produce testosterone

Prolactin (PL)

promotes milk production and the development of mammary glands within breast tissues

Posterior Pituitary

• oxytocin

• antidiuretic hormone (ADH)

Oxytocin

Females: stimulate uterine contractions in labor and childbirth and to stimulate contractions of breast tissue to aid in lactation after childbirth,

Males: ontracts the vas deferens to push sperm and semen forward for ejection

Antidiuretic Hormone (ADH)

causes the kidneys to release less water, decreasing the amount of urine produced

Thyroid

• triiodothyronine (T3)

• thyroxine (T4)

• calcitonin

Triiodothyronine (T3)

hydrolyzes ATP and increases energy expenditure

Thyroxine (T4)

increases numerous enzymes that produce energy for the body

Calcitonin

inhibits (blocks) the activity of osteoclasts, which are cells that break down bone, reduces the amount of calcium in your blood

Parathyroid Gland

• parathyroid hormone (PTH): raises your blood calcium, absorb more calcium from intestines from food

Adrenal Cortex

• aldosterone (mineralocorticoids)

• cortisol (glucocorticoids)

• Androgens (gonadocorticoids)

Aldosterone (mineralocorticoids)

regulates the salt and water balance of the body (and blood pressure) by increasing the retention of sodium and water and the excretion of potassium by the kidneys

Cortisol (glucocorticoids)

increases glucose in the bloodstream, enhances the brain's use of glucose and increases the availability of substances in the body that repair tissues

Androgens (gonadocorticoids)

development of secondary sexual characteristics in men, including facial and body hair growth and voice change. Androgens also affect bone and muscle development and metabolism

Adrenal Medulla

• epinephrine

• norepinephrine

Epinephrine

increased vascular smooth muscle contraction, pupillary dilator muscle contraction, and intestinal sphincter muscle contraction. Other significant effects include increased heart rate, myocardial contractility

Norepinephrine

Constricts blood vessels, which helps maintain blood pressure in times of stress

Pancreas

• glucagon (alpha cells)

• insulin (beta cells)

Glucagon (alpha cells)

stimulates the conversion of stored glycogen (stored in the liver) to glucose, which can be released into the bloodstream

Insulin (beta cells)

Insulin is critical for transporting intracellular glucose to insulin-dependent cells/tissues, such as liver, muscle, and adipose tissue, lowering blood sugar levels

Testes Gland

• testosterone: stimulates male secondary sex characteristics (muscle mass, deeper voice, facial hair. Increases bone density

Ovary Gland

• estrogen

• progesterone

Estrogen

Female secondary sex characteristics: breast growth, pubic hair, start menstrual cycles, regulate menstrual cycle thickening of uterine lining.

Men: errectile function

Progesterone

Females: promotes maintenance of embryo and uterus during early pregnancy, stays at high levels during pregnancy to stop menstrual cycles,

Men: builds bone mass

Pineal Gland

• melatonin: timing of your circadian rhythms (24-hour internal clock) and with sleep. Being exposed to light at night can block melatonin production

Thymus Gland

• thymosin: differentiation of T-lymphocytes, which provide cell-mediated immunity, promote the production of antibodies to provide humoral immunity

Diabetes Inspidus

Causes: low ADH levels

Symptoms: excessive urination and thirst

Hypo/Hyperthyroidism (Grave’s Disease)

Causes: thyroid produces too little (hypo) or too much (hyper) hormones)

Symptoms:

• hyper: weight loss, irregular/rapid heartbeat, fatigue, enlarged thyroid gland, nervousness (aka. Grave’s Disease)

• hypo: weight gain, fatigue, intolerance to cold, joint/muscle pain, dry skin, slow heartbeat

Diabetes

Cause: body is unable to either produce or use insulin sufficiently to regulate glucose

Symptoms: urinating often, thirsty, hungry, fatigue, weight loss

Hypo/Hypercalcemia

Cause: calcium levels in blood are too low(hypo) or high (hyper) parathyroid gland

Symptoms:

• Hypo: muscle spasms, cramps, seizures

• Hyper: nausea, thirst, muscle weakness, bone pain/fragile

High/Low Blood Pressure Cause

Cause: adrenal gland failure, too little/much intake of aldosterone cortisol

Symptoms:

• high: headaches, chest pain, nausea, blurred vision

• low: dizzy, fainting, blurred, nausea, sleepy, weak

Child Labor (positive feedback loop)

Gland: Pituitary

Hormones: Oxytocin (stimulates contractions)

1. baby presses on cervix

2. neurons send a signal to the brain to release oxytocin form the pituitary gland

3. oxytocin increases uterine contractions

4. pushes baby closer toward the cervix

repeats until the baby is birthed