Endocrine System

Endocrine System Overview• Endocrine system

• Consists of ductless glands• Secrete hormones

directly into bloodstream

• Affect the function of specific body organs• Regulates many

intricate body functions

Messenger Molecules

• Cells must communicate with one another to coordinate cell processes within tissues and to maintain homeostasis.

• Cell-to-cell communication is carried out via messenger molecules.

Three types of chemical signals are used for cell-to-cell communication.

Four methods of cell-to-cell communication are found in the human body, ranging from direct to remote communication.

Endocrine hormones

• Produced by endocrine (“ductless”) glands and secreted into the bloodstream.

• Endocrine hormones may affect a wide array of target cells to produce multiple effects.

• Two types: peptides (small proteins) and steroids (lipids).

Hormones and Receptors

Peptide Hormones

• Peptide hormones do not enter the cell directly. These hormones bind to receptor proteins in the cell membrane.

• When the hormone binds with the receptor protein, a secondary messenger molecule initiates the cell response.

• Because peptide hormones are water soluble, they often produce fast responses.

(cytoplasm)

(nucleus)

peptide or aminoacid-derivedhormone(first messenger)

(extracellularfluid)

cyclic AMP-synthesizingenzyme

cyclic AMP

ATP

inactiveenzyme

(second messenger)

activeenzyme

reactant

product

plasma membrane

nuclearenvelope

receptor

The hormone binds toa receptor on the plasmamembrane of a target cell

1

The activated enzymescatalyze specific reactions4

The secondmessenger activatesother enzymes

3

Hormone–receptor bindingactivates an enzyme that catalyzesthe synthesis of a second messenger,such as cyclic AMP

2

Steroid Hormones

• Steroid hormones enter through the cell membrane and bind to receptors inside of the target cell.

• These hormones may directly stimulate transcription of genes to make certain proteins.

• Because steroids work by triggering gene activity, the response is slower than peptide hormones.

gene

plasmamembrane

ribosome

hormone receptor

steroid hormone

mRNA

(nucleus)

RNA polymerase

DNA

(cytoplasm)

new protein

(extracellularfluid)

A steroid hormonediffuses through theplasma membrane

The hormone binds to areceptor in the nucleus or toa receptor in the cytoplasmthat carries it into the nucleus

The hormone–receptorcomplex binds to DNA andcauses RNA polymerase tobind to a nearby promotersite for a specific gene

RNA polymerase catalyzesthe transcription of DNA intomessenger RNA (mRNA)

The mRNA leaves thenucleus, then attaches to aribosome and directs thesynthesis of a specific proteinproduct

1

2

3

4

5

nuclearenvelope

Hormones Everywhere!

• Many other organs besides the endocrine glands produce hormones.

• Kidneys produce several hormones that regulate blood pressure, which is essential for kidney function.

• The digestive system produces several hormones that regulate appetite.

Role of the Hypothalamus

• The thalamus receives sensory information, relays some to the hypothalamus.

• Hypothalamus monitors the body for temperature, pH, other conditions.

• Hypothalamus signals pituitary gland if conditions need to be corrected.

Pituitary Gland• Referred to as “master gland”

• Secretes hormones that control functions of other glands

• Known as hypophysis• Has two distinct lobes with specific

functions

Role of the Pituitary

• The pituitary is the “master gland” that signals other glands to produce their hormones when needed.

• The anterior lobe of the pituitary receives signals from the hypothalamus, and responds by sending out the appropriate hormone to other endocrine glands.

• The posterior pituitary receives oxytocin or antidiuretic hormone (ADH) from the hypothalamus, relays them to the body as necessary.

Pituitary Gland • Anterior Pituitary Gland = Adenohypophysis

• Secretes Growth Hormone (GH) • Also called Somatotropic Hormone (STH)• Regulates growth of bone, muscle, and other

body tissues

• Secretes Adrenocorticotropic Hormone (ACTH)• Stimulates normal growth and development of

adrenal cortex and secretion of corticosteroids

Pituitary Gland• Anterior Pituitary Gland

• Secretes Thyroid-Stimulating Hormone (TSH)• Promotes and maintains normal growth and

development of the thyroid gland• Stimulates secretions of the thyroid hormones

• Secretes Lactogenic Hormone (LTH) • Also called Prolactin• Promotes development of breasts during

pregnancy• Stimulates secretion of milk from breasts after

delivery of baby

Pituitary Gland• Anterior Pituitary Gland

• Secretes Follicle-Stimulating Hormone (FSH)• Stimulates secretion of estrogen and

production of eggs in the female ovaries• Stimulates production of sperm in the male

testes• Secretes Luteinizing Hormone (LH)

• Stimulates female ovulation and the secretion of testosterone in the male

• Melanocyte-Stimulating Hormone (MSH)• Controls intensity of pigmentation in

pigmented cells of the skin

Pituitary Gland• Posterior Pituitary Gland = Neurohypophysis

• Secretes Antidiuretic Hormone (ADH)• Decreases excretion of large amounts of urine • Increases reabsorption of water by the renal

tubules

• Secretes Oxytocin (OT) • Stimulates contraction of the uterus during

childbirth• Stimulates release of milk from the breasts of

lactating women in response to the suckling reflex of the infant

Hypothalamus

• Located below the thalamus and above the pituitary gland (=epiphysis)

• Regulates the pituitary gland secretions through two different mechanisms

Hypothalamus - neurohypophysis

• 1- Neurons, receiving information from receptors, fire APs which travel down to the post pituitary gland and stimulate the release of stored neurohormones – Oxytocin (OT) and anti-diuretic hormone (ADH)

Hormones of the posterior pituitaryRegulation Hormone Target organ Action Pathology

Reflex Oxytocin - Uterus (smooth muscle)- breast tubules (smooth muscles)

-labor and delivery

- milk-let down

----

Reflex (osmoreceptor) ADH (vasopressin)

- DCT in kidney tubules

- promote H2O reabsorption

- not enough: diabetes insipidus- too much: ↑ BP?

Hypothalamus – adenohypophysis

• 2- Upon stimulation, secretory cells located in the hypothalamus secrete “releasing” hormones which travel down a capillary bed toward the anterior pituitary gland (adenopituitary). Each type of releasing hormones will stimulate the secretion and release of a pituitary hormone.

• Hormones which control the secretion of other hormones are tropic hormones (found in hypothalamus and pituitary gland)

Figure 6.8

Anterior pituitary

Regulation Hormone Target organ Action Pathology

GHRH and GHIH Growth hormone (GH) Many cells (bones..)

Stimulate cell growth and cell division

- not enough: children pituitary dwarfismtoo much: gigantism (children) – acromegaly (adult)

PRH - PIH Prolactin (PL) Breast secretory cells

- milk secretion

--

TRH Thyroid stimulating hormone (TSH)

Thyroid gland - promote thyroid gland secretion (T3 and T4)

- not enough: hypothyroidism (cretinism in children)- too much: hyperthyroidism

CRH Adrenocorticotropic hormone (ACTH)

Adrenal cortex (3 layers)

- stimulates secretion of adrenal cortex

- not enough: Addison's disease- too much: Cushing syndrome

GnRH Gonadotropin- Follicle stimulating hormone (FSH)- Luteinizing hormone (LH)

Stimulate gamete maturation

Stimulate gonadal gland secretion and gamete formation

- infertility

Pituitary HormonesPituitary Hormone Functions

Follicle-stimulating hormone

Stimulates egg maturation in the ovary and release of sex hormones.

Lutenizing hormone Stimulates maturation of egg and of the corpus luteum surrounding the egg, which affects female sex hormones and the menstrual cycle.

Thyroid-stimulating hormone

Stimulates the thyroid to release thyroxine.

Adrenocorticotropic hormone

Causes the adrenal gland to release cortisol.

Melanocyte-stimulating hormone

Stimulates synthesis of skin pigments.

Growth hormone Stimulates growth during infancy and puberty.

Antidiuretic hormone Signals the kidney to conserve more water.

Oxytocin Affects childbirth, lactation, and some behaviors.

Figure 6.6

Mechanism of control

Figure 6.5

Hormones of the hypothalamus and anterior pituitary gland

Pineal Gland• Tiny, pinecone-shaped gland

• Located behind dorsal aspect of midbrain region

• Plays a part in supporting body’s biological clock• Regulation of patterns of eating, sleeping, and

reproduction

• Secretes melatonin• Induces sleep

Thyroid Gland• Located in front of the neck just below

the larynx, on either side of the trachea• Consists of a right and left lobe

Thyroid Gland• Secretes Triiodothyronine (T3)

• Helps regulate growth and development of body

• Helps control metabolism and temperature

• Secretes Thyroxine (T4)• Helps maintain normal body metabolism

• Secretes Calcitonin• Helps regulate the level of calcium in the

blood

Figure 6.8a

The thyroid gland

• Located in the neck, just below the larynx

• Secrete 2 types of hormone: - thyroid hormones stimulate cell metabolism,

triiodothyronine (T3) and thyroxine (T4) – iodine is needed to synthesize these hormones

- calcitonin decrease blood calcium

Thyroid hormones

• T3 and T4 secreted by the follicular cells

• Stored as colloid

• Parafollicular cells (C cells) secrete calcitonin

Thyroid Hormones T3 and T4

• Target organs: all cells

• Role: Increase cell metabolism, oxygen consumption

• Permissive role for some other hormones (growth hormone)

Figure 6.7

Thyroid hormone regulation

Parathyroid Glands

• Four tiny rounded bodies located on dorsal aspect of thyroid gland• Secrete Parathyroid Hormone (PTH)

• Also known as parathormone• Regulates level of calcium in blood

Parathyroid glands

• Four nodules located in the back of the thyroid gland

• Secreted parathyroid hormone or parathormone or PTH

• Action of PTH opposes action of calcitonin• Both hormones play a role in calcium

metabolism, regulating the level of calcium in blood.

Roles of calcium

• Most calcium ions are stored in the bones

• Calcium is an important cofactor for enzymatic activity, plays a role in blood coagulation and action potentials.

• Calcitonin and PTH participate in calcium regulation

• Vitamin D helps PTH activity

Calcium regulation:

• Calcitonin promotes blood calcium decrease, by:

- 1. calcium deposition on bone

- 2. calcium dumping by the kidney

• PTH promotes blood calcium increase by:

- 1. bone resorption- 2. calcium

reabsorption by kidney

- 3. increase calcium absorption by intestine

Calcium Metabolism:

Figure 23-20: Calcium balance in the body

Figure 19.20

Thymus

• Single gland located in mediastinum near the middle of the chest, just beneath sternum• Large in fetus and infants, shrinks

with age• Secretes thymosin and thymopoietin

• Stimulates production of T cells that are involved in the immune response

Adrenal Glands

• Two small glands, one positioned atop each kidney

• Also known as suprarenal glands• Consists of an adrenal cortex and an

adrenal medulla• Each has independent functions

Adrenal Glands• Adrenal cortex secretes corticosteroids

• Mineralocorticoids• Regulate how mineral salts (electrolytes) are

processed in the body• Glucocorticoids

• Influence metabolism of carbohydrates, fats, and proteins in the body

• Necessary for maintaining normal blood pressure

• Have an anti-inflammatory effect on the body• Increase glucose available during “fight-or-

flight” responses by the body

Adrenal Glands

• Adrenal cortex secretes • Gonadocorticoids

• Sex hormones secreted in small amounts• Contribute to secondary sex

characteristics in males and females

Adrenal Glands• Adrenal medulla secretes catecholamines

• Epinephrine = adrenaline• Sympathiomimetic agent• Increases heart rate and force of heart muscle

contraction• Dilates bronchioles in the lungs• Decreases peristalsis in the intestines• Raises blood glucose levels by causing the

liver to convert glycogen into glucose

Adrenal Glands

• Adrenal medulla secretes • Norepinephrine = noradrenaline

• Known as a sympathomimetic agent• Produces a vasoconstrictor effect on the

blood vessels, thereby raising blood pressure

Adrenal gland hormonesRegulation Glands Hormones Target

organsAction Pathology

Reflex Adrenal medulla Epinephrine ANS target organs

Fight/flight Stress

Blood Pressure Adrenal cortex - Mineralocorticoid = aldosterone

DCT from renal tubule

- promote sodium reabsorption

Not enough" Addison disease

CRH ACTH Glucocorticoid = cortisone

Many cells Mobilize fuels – stress adaptation

Excess hormone: Cushing syndrome

GnRH GN Estrogen Testosterone

Sexual organs - Sex organ maintenance- Gamete development

Infertility

Pancreas• Elongated gland located in upper left

quadrant of the abdomen• Behind the stomach

• Extends horizontally across the body• Beginning at first part of small intestines

and ending at edge of spleen• Contains exocrine and endocrine glands• The endocrine function is due to the cells of

the islets of the Langerhans -- α cells glucagon -- β insulin -- δ somatostatin

The pancreas

Pancreas• Islets of Langerhans secrete:

• Glucagon• Increases blood glucose levels by stimulating

liver to convert glycogen into glucose when blood sugar is extremely low

• Insulin• Makes it possible for glucose to pass from

blood through cell membranes to be used for energy

• Promotes conversion of excess glucose into glycogen for storage in the liver for later use

Glucose regulation

• Glucose level controlled by insulin and glucagon

• Insulin promotes a decrease in blood glucose

• Glucagon promotes an increase in blood glucose

Glucose regulation

Figure 3.21

Fate of glucose

Diabetes mellitus

• Type I: autoimmune disease beta cells of the islets of Langerhans are destroyed by antibodies

• Type II: The cells become insulin-resistant glucose does not enter the cells as readily

• http://faculty.weber.edu/nokazaki/Human_Physiology/Class%20notes/diabetes.htm

Ovaries

• Female sex glands = female gonads• Pair of almond shaped glands

• Located in upper pelvic cavity, on either side of lateral wall of uterus

• Near fimbriated ends of the fallopian tubes

• Responsible for producing mature ova and releasing them at monthly intervals during ovulation

Ovaries• Hormones secreted by the ovaries

• Estrogen• Promotes maturation of ovum in the ovary• Stimulates vascularization of uterine lining

each month to prepare for implantation of a fertilized egg

• Contributes to secondary sex characteristic changes in female with onset of puberty

• Progesterone• Primarily responsible for changes within the

uterus in anticipation of a fertilized ovum• Responsible for development of maternal

placenta after implantation of a fertilized ovum

Testes• Testes = male gonads = testicles

• Two small ovoid glands located in scrotum

• Primary organs of male reproductive system

• Responsible for production of sperm and secretion of androgens (male steroid hormones)

• Secrete testosterone• Responsible for secondary sex characteristic

changes that occur in male with onset of puberty

• Responsible for maturation of sperm

Endocrine HormonesGland Hormones Functions

Thyroid Thyroxine Regulates metabolism

Calcitonin Inhibits release of calcium from the bones

Parathyroids Parathyroid hormone Stimulates the release of calcium from the bones.

Islet cells (in the pancreas)

Insulin Decreases blood sugar by promoting uptake of glucose by cells.

Glucagon Increases blood sugar by stimulating breakdown of glycogen in the liver.

Testes Testosterone Regulates sperm cell production and secondary sex characteristics.

Ovaries Estrogen Stimulates egg maturation, controls secondary sex characteristics.

Progesterone Prepares the uterus to receive a fertilized egg.

Adrenal cortex Epinephrine Stimulates “fight or flight” response.

Adrenal medulla

Glucocorticoids Part of stress response, increase blood glucose levels and decrease immune response.

Aldosterone Regulates sodium content in the blood.

Testosterone (in both sexes)

Adult body form (greater muscle mass), libido.

Pineal gland Melatonin Sleep cycles, reproductive cycles in many mammals.

Homeostasis and Hormones

• Examples:• Thyroid and temperature control• Thyroid, Parathyroid, and calcium• Pancreas and glucose control

Temperature Control