ENDOCRINOLOGY

1. Pineal gland

2. Hypothalamus

3. Pituitary gland

4. Thyroid gland

5. Parathyroid gland

6. Thyms

7. Heart 

8. Adrenal gland

9. Kidney

10. Pancreatic islets

11. Digestive tract

12. Testes

13. Ovaries

1. Pineal gland

2. Hypothalamus

3. Pituitary gland

4. Thyroid gland

5. Parathyroid gland

6. Thyms

7. Heart 

8. Adrenal gland

9. Kidney

10. Pancreatic islets

11. Digestive tract

12. Testes

13. Ovaries

What are the ENDOCRINE GLANDS?

Mediator molecules (nervous)

• Neurotransmitters released locally in response to nerve impulses

Site of mediator action (nervous)

Close to the side of the release, at the synapse; binds to receptors in postsynaptic membrane

• Muscle (smooth, cardiac, and skeletal) cells, gland cells, other neurons

what are the types of target cells?

Time to onset of action (nervous)

• Typically within milliseconds (thousandths of a second)

Duration of action (nervous)

Generally briefer (milliseconds)

Mediator molecules (endocrine)

• Hormones delivered to tissues throughout body by blood

Site of mediator action (endocrine)

Far from site of release (usually); binds to receptors on or in target cells

Types of target cells (endocrine)

Cells throughout body

Time to onset of action

seconds to hours or days

Duration of action

Generally longer (seconds to days)

HORMONE ACTIVITY

• Hormones like neurotransmitters, influence their target cells by chemically binding to specific protein receptors.

• Only the target cells for a given hormone have receptors that bind and recognize that hormone.

Downregulation

• If a hormone is present in excess, the number of target-cell receptors may decrease

Upregulation

If a hormone is deficient, the number of receptors may increase

MECHANISMS OF HORMONE ACTION

• The response to a hormone depends on both the hormone itself and the target cell.

• These varied effects of hormones are possible because a single hormone can set in motion several different cellular responses.

1. Changing the permeability of the plasma membrane

2. altering the rate of specific metabolic reactions

3. causing contraction of smooth muscle or cardiac muscle

What are other hormonal effects?

Synergistic effect

• Two hormones acting together has a more extensive effect than when acting alone

Permissive effect

• Actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone.

• In such cases, the second hormone is said to have a permissive effect.

Antagonistic effects

• When one hormone opposes the actions of another hormone, the two hormones are said to have this effect

• ex. insulin and glucagon

• Somatotrophs

• Thyrotrophs

• Gonadotrophs

• Lactotrophs

• Corticotrophs

What are the types of anterior pituitary cells?

Somatotrophs

• human growth hormone

Thyrotrophs

• thyroid-stimulating hormone

Gonadotrophs

• follicle-stimulating hormone and luteinizing hormone

Lactotrophs

Prolactin

Corticotrophs

• Adrenocorticotropic hormone

• Oxytocin

• Antidiuretic (vasopressin) (ADH)

What are the posterior pituitary hormones?

Negative feedback

• A stimulus elicit the release of a substance; once the substance reaches a certain level, it sends a signal that stops the further release of the substance.

• when the original (abnormal) condition has been repaired, or negated, corrective actions decrease or discontinue.

HUMORAL STIMULI

• Control of hormone release in response to changes in extracellular fluids such as blood or the ion concentration in the blood.

HORMONAL STIMULI

• release of a hormone in response to another hormone.

• ex. hypothalamus produces hormones that stimulate the anterior portion of the pituitary gland. The anterior pituitary in turn releases hormones that regulate hormone production by other endocrine glands.

NEURAL STIMULI

• the nervous system directly stimulates endocrine glands to release hormones

• ex. neuronal signaling from the sympathetic nervous system directly stimulates the adrenal medulla to release the hormones epinephrine and norepinephrine in response to stress.

HORMONAL IMBALANCES

• Occurs when there is too much or too little of a hormone in the bloodstream

• Even small hormonal imbalances can cause side effects throughout the body

HYPOSECRETION

• Inadequate release of a hormone

HYPERSECRETION

Excessive release of hormones

Estrogens

•  Produced by Graafian follicles or the placenta

•  Stimulates the development of secondary female characteristics

•  Matures female reproductive organs

•  Helps prepare the uterus to receive a fertilized egg

•  Helps maintain pregnancy

• Prepares the breasts to produce milk

Progesterone

• Produced by the corpus luteum

•  Acts with estrogen to bring about the menstrual cycle

•  Helps in the implantation of an embryo in the uterus

testosterone

•  Responsible for adult male secondary sex characteristics

•  Promotes growth and maturation of male reproductive system

•  Required for sperm cell production

THYROID

• Found at the base of the throat

• Consists of two lobes and a connecting isthmus

•  Produces two hormones

  •  Thyroid hormone

  •  Calcitonin

Thyroid Hormone

• Major metabolic hormone

• Increase basal metabolic rate; stimulate synthesis of proteins; increase use of glucose and fatty acids for ATP production

• Composed of two active iodine-containing hormones

 Thyroxine (T4)

secreted by thyroid follicles

 Triiodothyronine (T3)

conversion of T4 at target tissues

Calcitonin

• Decreases blood calcium levels by causing its deposition on bone

•  Antagonistic to parathyroid hormone

•  Produced by C (parafollicular) cells

PARATHYROID

• Tiny masses on the posterior of the thyroid

Parathyroid hormone

•  Stimulate osteoclasts to remove calcium from bone

•  Stimulate the kidneys and intestine to absorb more calcium

•  Raise calcium levels in the blood

THYMUS

• Located posterior to the sternum

• Largest in infants and children

Thymosin

•  Matures some types of white blood cells

• Important in developing the immune system

PANCREAS

• The pancreas is a mixed gland

• The islets of the pancreas produce hormones

• These hormones are antagonists that maintain blood sugar homeostasis

Insulin

Allows glucose to cross plasma membranes into cells from beta cells

Glucagon

• Allows glucose to enter the blood from alpha cells

PINEAL GLAND

Found on the third ventricle of the brain

Melatonin

• Helps establish the body’s wake and sleep cycles

•  May have other as-yet-unsubstantiated functions

Erythropoietin

Primary function is to stimulate the production of red blood cells in the bone marrow

Renin

• Part of reaction sequence that raises blood pressure by bringing about vasoconstriction and secretion of aldosterone.

Oxytocin

•  Stimulates contractions of the uterus during labor

• Causes milk ejection

Antidiuretic hormone (ADH)

•  Can inhibit urine production

•  In large amounts, causes vasoconstriction leading to increased blood pressure (vasopressin)

• Two affect non-endocrine targets

Four stimulate other endocrine glands (tropic hormones)

What are the categories of the the anterior pituitary hormones?

• Proteins (or peptides)

•  Act through second-messenger systems

•  Regulated by hormonal stimuli, mostly negative feedback

What are the characteristics of all anterior pituitary hormones?

Growth hormone

• General metabolic hormone

• Major effects are directed to growth of skeletal muscles and long bones

• Causes amino acids to be built into proteins

• Causes fats to be broken down for a source of energy

Prolactin (PRL)

•  Stimulates and maintains milk production following childbirth

•  Function in males is unknown

Adrenocorticotropic hormone (ACTH)

Regulates endocrine activity of the adrenal cortex

Thyroid-stimulating hormone (TSH)

Influences growth and activity of the thyroid

ADRENAL MEDULLA

• Produces two similar hormones (catecholamines)

  •  Epinephrine

  •  Norepinephrine

Epinephrine and norepinephrine

•  These hormones prepare the body to deal with short-term stress/Enhance effects of sympathetic division of autonomic nervous system (ANS) during stress.

Mineralocorticoids

• mainly aldosterone

•  Produced in outer adrenal cortex

•  Regulate mineral content in blood, water, and electrolyte balance

•  Target organ is the kidney

•  Production stimulated by renin and aldosterone

• Production inhibited by atrial natriuretic peptide

renin and aldosterone-

stimulates production in the adrenal cortex

Glucocorticoids

• cortizone and cortisol

• Promote normal cell metabolism

•  Help resist long-term stressors

•  Released in response to increased blood levels of ACTH

Androgens

• (mainly dehydroepiandrosterone, or DHEA)Assist in early growth of axillary and pubic hair in both sexes

•  in females, contribute to libido and are source of estrogens after menopause.

PLACENTA

• Produces hormones that maintain the pregnancy

• Some hormones play a part in the delivery of the baby

• Human chorionic gonadotropin (HCG) in addition to estrogen, progesterone, and other hormones