Act together to coordinate functions of all body systems

Nervous system

Acts through nerve impulses and “messenger molecules”: neurotransmitters

Faster responses, briefer effects, acts on specific targets in body

Endocrine system

Acts through “messenger” molecule: hormones

Released in one part of the body but regulates activity of cells in other parts of body

Slower responses, effects last longer, broader influence in body

Exocrine Glands

Secrete their products into ducts that carry secretions into body cavities, into the lumen of an organ, or to the outer surface of a body

Exs.: sweat, sebaceous, mucous and digestive glands

Secrete products (hormones) into interstitial fluid which eventually diffuse into blood

Hormones are quite potent – so circulating levels are low in blood

Pituitary

Thyroid

Parathyroid

Adrenal 

Pineal 

Hypothalamus, pancreas, thymus, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta

Several organs and glands are not exclusively classified as endocrine glands but contain cells that secrete hormones:

Hormones bind and thus affect target tissues with specific receptors

Ex.  Thyroid-stimulating hormone only binds to receptors on cells of thyroid gland and not the ovaries (because it does not have TSH receptors)

Receptors for hormones are constantly synthesized and broken down

Down-regulation: Number of target cell receptors decreases if hormone is present in excess

Up-regulation: Number of target cell receptors increases if hormone is deficient

Blocking hormone receptors

RU486: “morning-after” drug; blocks receptor for the hormone, progesterone, which is necessary for implantation of the embryo to take place

Blocking hormone receptors

RU486: “morning-after” drug; blocks receptor for the hormone, progesterone, which is necessary for implantation of the embryo to take place

Response depends on both hormone and target cell

Various target cells may respond differently to same hormone

Insulin stimulates synthesis of glycogen in liver cells and synthesis of triglycerides in adipose cells

Hormone may cause change in permeability  of plasma membrane to a substance in target cell

Hormone may alter the rate of specific metabolic reactions in target cells

Hormone may cause contraction of smooth or cardiac muscle

Hormone’s concentration

Abundance of target cell receptors

Target cells will respond more vigorously the higher the concentration of hormone and the more receptors it has for that particular hormone

Influence exerted by other hormones

Other hormones may enhance or antagonize the effect of a hormone

Responsiveness of target cell depends on: 

Lipid-soluble hormones

Steroid hormones: derived from cholesterol

Aldosterone, testosterone, calcitriol, estrogen, progesterone

Thyroid hormones: T3 and T4

Can generally be taken orally

Water-soluble hormones

Amine: modified amino acids

Epinephrine (E), norepinephrine (NE), melatonin

Peptide (3 - 49 AA)/ protein (50 – 200 AA)

Insulin, human growth hormone, oxytocin, etc. 

Usually given by injection or iv to avoid being broken down by digestive enzymes in GI tract 

Hormones secreted in short bursts

When stimulated, an endocrine gland will release hormone in more frequent bursts, increasing the concentration of the hormone in the blood

Without stimulation, blood level of hormone decreases

Hormones secreted in short bursts

When stimulated, an endocrine gland will release hormone in more frequent bursts, increasing the concentration of the hormone in the blood

Without stimulation, blood level of hormone decreases

Regulated by:

Signals from nervous system

Chemical changes in the blood

Ex.: Blood calcium levels regulates secretion of PTH hormone

Other hormones

Most hormonal regulation by negative feedback 

Few examples of positive feedback such as oxytocin in childbirth

Both secrete hormones involved in growth, reproduction, metabolism and homeostasis

“Grand-master” of the endocrine system

Pituitary gland’s boss

A major link between nervous and endocrine system

Pituitary gland

Pea-shaped structure about 0.5 inches in diameter that lies in sella turcica of sphenoid bone

Attached to hypothalamus by infundibulum (stalk)

Two anatomically and functionally different portions of Pituitary gland

Anterior pituitary 

Posterior pituitary 

blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary

This direct route allows hypothalamic hormones to act immediately on anterior pituitary, without them getting diluted or destroyed in the general circulation

They synthesize hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles

Nerve impulses stimulate the vesicles to undergo exocytosis which then diffuse into the hypophyseal portal system and reach the anterior pituitary gland

Hormones secreted by anterior pituitary gland pass into the hypophyseal portal system and out into the general circulation to travel to target tissues throughout the body

hGH, TSH, FSH, LH, PRL, ACTH, (MSH)

1)  Releasing hormones which stimulate secretion of anterior pituitary hormones and inhibiting hormones which suppress secretion of anterior pituitary hormones from the hypothalamus

2)  Negative feedback loops by hormones produced by target glands of pituitary hormon

Secretion of anterior pituitary hormones is controlled by:

Stimulates secretion of small protein hormones, insulin-like growth factors (IGFs), by tissues such as liver, skeletal muscles, cartilage, and bones. 

Functions of IGF’s:

Cause cells to grow and multiply 

Increase protein synthesis in cells

In children and teenagers, increases growth rate of skeleton and skeletal muscles 

In adults, promotes healing of injuries and tissue repair in muscles and bones

Increase lipolysis (breakdown of fatty acids for ATP production) 

Pituitary Dwarfism

Hyposecretion of hGH during childhood slows bone growth

Epiphyseal plates close before normal height is reached

Other organs of body also fail to grow

Body proportions are childlike (person is abnormally short but the body parts are in proportion)

Treatment: administer hGH during childhood before epiphyseal plates close

Caused by hypersecretion of hGH during childhood

Often due to a pituitary tumor 

Condition causes an abnormal increase in length of long bones

Person grows very tall, but body proportions are about normal

Caused by hypersecretion of hGH during adulthood

Epiphyseal plates are closed - so bones can no longer lengthen

Bones of hands, feet, cheeks, jaws thicken and other tissues enlarge

Eyelids, lips, tongue, and nose enlarge, skin thickens

Thyroid-stimulating hormone (TSH)

Stimulates synthesis and secretion of thyroid hormones (T3 and T4) by thyroid gland

Controlled by TRH (thyrotropin releasing hormone) from hypothalamus

Follicle-stimulating hormone (FSH)

In females, stimulates development of oocytes in ovaries

In males, stimulates testes to produce sperm

Luteinizing hormone (LH)

In females, stimulates secretion of estrogen and progesterone, and ovulation (release of ovum)

In males, stimulates testes to produce testosterone 

Prolactin (PRL)

In females, stimulates secretion of estrogen and progesterone, and ovulation (release of ovum)

In males, stimulates testes to produce testosterone 

Adrenocorticotropic hormone (ACTH)

Stimulates secretion of cortisol and other glucocorticoids by adrenal cortex

Regulated by hypothalamus (CRH) and blood levels of glucocorticoids via negative feedback

Does NOT synthesize hormones

Stores and releases two hormones made by the hypothalamus: oxytocin (OT) and antidiuretic hormone (ADH) 

Consists of axons and axon terminals of more than 10,000 hypothalamic neurosecretory cells

Cell bodies of the neuroscretory cells are in hypothalamus 

OT and ADH are produced in hypothalamus, packaged into vesicles and are stored in axon terminals in posterior pituitary until nerve impulses trigger exocytosis and release of the hormone

During and after delivery of baby OT affects mother’s uterus and breasts

During delivery, enhances smooth muscle contraction in wall of uterus (late pregnancy ↑ OT secretion)

After delivery, stimulates milk ejection (‘letdown”) from mammary glands in response to suckling by infant (suckling ↑ OT secretion)

Promotes expulsion of the placenta (afterbirth) and helps uterus to regain smaller size

Synthetic OT (Pitocin): used to induce labor or increase uterine tone and decrease hemorrhage 

In males and non-pregnant females, function of OT is not known – may promote feelings of pleasure during intercourse

conserves body water by causing the kidneys to return more water to the blood, thus decreasing urine volume

also decreases water lost through sweating and constriction of arterioles which increases BP 

is secreted in response to low BP, dehydration, loss of blood volume

is inhibited in response to high BP and high blood volume

Disorder due to defects in ADH receptors on kidneys or an inability to secrete ADH (due to brain tumor or head trauma that damages posterior pituitary or hypothalamus)

Symptom is large excretion of large volumes of urine, with resulting dehydration and thirst

Bed-wetting is common in children

A person with DI may die of dehydration if deprived of water for only a day or so

Treatment: subcutaneous injection or nasal spray of replacement ADH (if its due to inability to secrete ADH)

Thyroid Gland

Located inferior to larynx (voice box) in neck region

Composed of right and left lobes, one on either side of trachea; connected by an isthmus (anterior to trachea)

Highly vascularized

consists of follicular cells which produce thyroid hormones

Thyroxine or tetraiodothyronine (T4)

Triiodothyronine (T3) 

Parafollicular cells produce calcitonin

T4 contains 4 atoms of iodine

T3 contains 3 atoms of iodine

Thyroid gland normally contains most of the iodine in the body

Thyroid gland is only endocrine gland to store its hormones in large quantities (100 day supply)

T4 is normally secreted in greater quantity, but T3 is several times more potent

After T4 enters a body cell, most of it is converted to T3 by removing one iodine molecule

Most cells in body have receptors for T3 &T4 so they exert their effects throughout most of body!

Increase basal metabolic rate (BMR): rate of oxygen consumption under standard or basal conditions (awake, at rest, or fasting) 

↑BMR = ↑ cellular metabolism of carbohydrates, lipids and proteins

Increase calorigenic effect: the more cells produce and use ATP, the more heat is given off and body temperature rises

Thyroid hormones are important in maintaining body temperature

the more cells produce and use ATP, the more heat is given off and body temperature rises

Thyroid hormones are important in maintaining body temperature

Congenital hypothyroidism (cretinism): hyposecretion of thyroid hormones (T3 & T4) that is present at birth

Causes severe mental retardation and stunted bone growth if not treated promptly

At birth, baby typically is normal because mother’s thyroid hormones can cross placenta during pregnancy and allows normal development

Most states require testing of newborn thyroid function 

Treatment: oral thyroid hormones at birth and continued for life

low blood levels of T3 and/or T4

Occurs 5X more in females than males; ↑ as one ages

Underdiagnosed!!!!!!

Symptoms:

Edema: facial tissues swell and look puffy

Slow heart rate and metabolism

Gains weight easily

Low body temperature

Sensitivity to cold temperatures

Constipation

Lethargy and depression

Treatment: oral thyroid hormones

Occurs 7 – 10X more in females than men 

Autoimmune disease

Person produces antibodies that mimic action of TSH

Treatment:

Surgical removal of all or part of thyroid gland

Radioactive iodine to destroy thyroid gland

edema behind eyes which causes eyes to protrude

*Weight loss, overeating

*Elevated BMR

*Restlessness

Caused by:

Hypothyroidism

Hyperthyroidism

Low dietary intake of iodine

Iodine salts (iodides) to produce T3 and T4 come from foods e.g. iodized salt and absorbed by intestines

Low iodine→low levels of T3 and T4 →high levels of TSH →enlarged thyroid 

lie superior to each kidney 

Flattened, pyramidal shape

Covered with connective tissue capsule and highly vascularized

Located in periphery

80-90% of gland

Secretes steroid hormones essential for life: mineralcorticoids, glucocorticoids, and  androgens 

Located in center of gland

Secretes E and NE

Aldosterone

Helps regulate levels of Na+, K+, and H+ in blood

Helps regulate blood volume and blood pressure

Secretion of aldosterone is regulated by renin-angiotension-aldosterone pathway (RAA) and K+ levels in blood

RAA is a complex pathway involving kidneys, lungs, and liver

Controlled by negative feedback loop

ACTH from anterior pituitary stimulates its release

CRH from hypothalamus promotes release of ACTH due to stress and/or low level of glucocorticoids 

Increase gluconeogenesis

Liver cells produce and secrete glucose from AA or lactic acid to bloodstream for rest of body

Increase resistance to stress 

Additional glucose made by liver cells provides tissue with ready source of ATP to combat a wide range of stresses on the body

Decrease inflammation

Inhibit WBC’s that participate in inflammatory responses

Decrease immune response

High doses of glucocorticoids (prednisone) are used in organ transplant recipients to depress immune system

Increase protein breakdown: (mainly in muscle fibers); release free AA’s into bloodstream

Increase gluconeogenesis

Liver cells produce and secrete glucose from AA or lactic acid to bloodstream for rest of body

Increase resistance to stress 

Additional glucose made by liver cells provides tissue with ready source of ATP to combat a wide range of stresses on the body

Decrease inflammation

Inhibit WBC’s that participate in inflammatory responses

Decrease immune response

High doses of glucocorticoids (prednisone) are used in organ transplant recipients to depress immune system

Androgens (weak ones)

DHEA (dehydroepiandrosterone) is main one

ACTH stimulates secretion

Produced in both males and females

DHEA promotes axillary and pubic hair growth and growth spurt in pre-pubescent boys and girls

After puberty in males, the androgen, testosterone, is released in greater quantities so DHEA becomes insignificant

In women, DHEA promotes libido (sex drive) and can be converted to estrogens in other body tissues

After menopause, when ovarian secretion of estrogen stops, all estrogen comes from conversion of DHEA

ACTH stimulates secretion

are the hormone-producing cells of adrenal medulla

Directly innervated by sympathetic neurons of the ANS

Adrenal medulla secretes epinephrine (E) and norepinephrine (NE)

Not essential for life

Enhance fight-or-flight response during sympathetic response of ANS during exercise or stress

Effects of these hormones resemble those of the sympathetic division neurotransmitters of same name, except they last up to 10X l

Pancreas

Flattened, organ about 4-6 inches in length

Located behind stomach and in the curve of duodenum (first part of small intestine)

Regulation of Insulin and Glucagon Secretion

Blood glucose levels primarily control secretion of glucagon and insulin via negative feedback

Glucagon: increase blood glucose level

Acts on hepatocytes (liver cells)

Insulin: decrease blood glucose level

Helps glucose into adipose, cardiac and resting skeletal muscle cells

Low blood glucose

Increased sympathetic activity of ANS, as occurs during exercise

High blood glucose

Parasympathetic activity of ANS (“Rest and digest”)

With increasing age, insulin is released more slowly 

Most common endocrine disorder

Two types: Type I and Type II diabetes mellitus

4th leading cause of death in U.S. 

If present trends continue, one in three Americans, and 1 in 2 minorities, born in 2000 will develop diabetes in their lifetime

Caused by inability to produce or use insulin

Because insulin is either unavailable or not able to aid transport of glucose into cells, blood glucose levels become high (hyperglycemia) and “spills” into the urine (glucosuria)

Three “polys” of diabetes mellitus:

Polyuria: excessive urine production

Polydipsia: excessive thirst

Polyphagia: excessive eating

Warning Signs of Diabetes Mellitus

Type I Diabetes

Polyuria: frequent urination 

Polydipsia: unusual thirst 

Polyphagia: extreme hunger 

Unusual weight loss 

Extreme fatigue 

Irritability

Warning Signs of Diabetes Mellitus

Type II Diabetes

Any of the type 1 symptoms 

Frequent infections 

Blurred vision 

Cuts/bruises that are slow to heal 

Tingling/numbness in the hands/feet 

Recurring skin, gum, or bladder infections

Heart Disease and Stroke

High Blood Pressure 

Blindness 

Cataracts: excessive glucose attaches to lens causing cloudiness

Damage to blood vessels of retina (diabetic retinopathy)

Kidney Disease 

Damage to renal blood vessels (diabetic nephropathy)

Nervous System Damage (diabetic neuropathy)

Gangrene/Amputations 

Dental Disease 

Pregnancy Complications 

Sexual Dysfunction 

Insulin-dependent diabetes mellitus

Usually appears before age 20, persists throughout life

Autoimmune disease

Immune system destroys beta cells of pancreas; so patients can’t make insulin

Trigger for autoimmune disease is unknown; combination of genetic factors and environmental exposure

Most common in northern Europe

In U.S., higher prevalence in whites than African or Asian populations

Self-monitoring of blood glucose levels (up to 7X daily)

Regular meals 

Low fat, plant-based diet (vegetables, fruits) can decrease amount of insulin needed

Exercise

Decreases resistance of cells to insulin

Insulin injections

Typically everyday and may be up to 3X a day

Implantable pumps

Replaces repeated injections of insulin

Pancreas transplant

Need to be on immunosuppressive drugs for life 

Non-insulin-dependent diabetes mellitus

Represents more than 90% of cases of diabetes mellitus

Most often occurs in overweight/obese people over age 35

Number of overweight/obese children and teenagers with type II diabetes is increasing

High number of type II diabetes in minority populations (African- and Latino-Americans) in U.S.

Most type II diabetics still produce insulin, but target cells no longer respond to it!

Due to down-regulation of insulin receptors

Type II diabetes is a preventable disease!!!!!!!!!!!!!!

Disease develops primarily from LIFESTYLE FACTORS:

Being overweight/obese 

Poor diet: Too high in refined carbohydrates (white rice, bread, pasta, sugar, etc.) and fat (impedes absorption of glucose into cells)

Lack or not enough exercise 

Diet: Eating more fibrous foods (vegetables, fruits, beans, whole grains) increases satiety and decreases risk of developing diabetes.

High in fresh (cooked and raw) vegetables (especially green leafy vegetables (lettuces, kale, collards, chard, spinach)

Beans/Lentils 

Fruit 

LOWER FAT (fats should come from raw nuts/seeds, avocado) (Max. 15-20% of total calories)

*Some whole grains (brown rice, quinoa, amaranth, slow-cook oatmeal)/starchy vegetables (sweet potatoes, yams, potatoes, winter squash)

Low to no animal products (too high in fat) 

No processed/refined food, soda pop, sugary drinks (fruit juice), oils, sugar, salt

Exercise Everyday (aerobic and weight resistance) 

Increases insulin sensitivity of cells

Helps build lean muscle mass (more insulin-responsive than fat tissue)

Weight loss or maintaining healthy weight

Increases insulin sensitivity of cells

Decrease body fat (adipose tissue) 

Stored body fat has metabolic life of its own (increases appetite, causes inflammation and interferes with insulin action)

Most people are over-fat and under-muscled!

Sleep

People with chronic insomnia or who sleep five hours or less per night have highest rates of diabetes compared with normal sleepers

Sleep deprivation decreases hormone levels of leptin (makes you feel full) and increases ghrelin (makes you feel hungry)

Keep your teeth and gums clean

Moderate gum disease increases risk (2X) of developing diabetes

Bacterial infection can increase inflammation and impair insulin action

Drugs: (Metformin, Avandia, etc.)

They have side effects!!!!!!!