THE ENDOCRINE SYSTEM

What is a Gland?

a cell, group of cells, or organ that produces a secretion

• epithelial composition

What is an Exocrine Gland?

a ducted gland

• secretions move through a duct to a specific area of the body (ex, skin, digestive tract)

examples: sudoriferous (sweat) glands, mammary (milk) glands, salivary glands, goblet cells of intestine, and pancreas

What is an Endocrine Gland?

a ductless gland

• secretion is discharged onto interstitial fluid and enters the bloodstream

• examples: pituitary gland, thyroid, edrinal glands, gonads, pancreas (islets of langerhans)

What is a Humoral Stimulus?

hormone release due to a change in levels of ions or nutrients in ECF

• example: parathyroid hormone released when parathyroid glands detect low Ca in plasma

What is a Neural Stimulus?

hormone release by neural input

• example: epinephrine is released when sensory receptors detect stress, causing nervous stimulation of the adrenal gland

What is a Hormonal Stimulus?

Hormone release due to another hormone

• example: test released from testis when stimulated by gonadotrophins from the anterior pit gland

How do we define what a Hormone is?

a chemical messenger released from an endocrine gland

• regulates activity in a specific body area

• receptor is present in target organs for each hormone

• can be protein or lipid based

What are the Six functions of Hormones?

1. stimulate exocrine glands (ex. gastrin)

2. stimulate other endocrine glandes (ex. releasing or stimulating hormones)

3. affect growth, development, and personality (ex. GH)

4. regulate metabolism (ex. insulin)

5. regulate muscle contraction and nervous stimulation (ex. calcitonin)

6. regulate reproductive processes (ex. estrogen or testosterone)

What is a Lipid Soluble Hormone?

dissolves in fats

• has ability to pass through cell membrane

• binds to a receptor and changes how genes work

• slower but longer effects

examples: norepinephrine, oxytocin, growth hormone

What is a Water Soluble Hormone?

is restricted; binds to an external receptor to send signals inside to generate a response

• fast but short-lasting

examples:testosterone and progesterone

What is a Prostaglandins?

• lipid based

• released from cell membranes

• affect cells locally (same or neighbouring cells)

• may travel through ECF to other target cells in some cases

What is the interrelationship between the Hypothalamus and the Posterior Pituitary Gland?

1. hormones synthesized in neuronal cell bodies in hypothalamus

2. transports through infundibulum to posterior pituitary gland through axons

3. released into capillary bed around posterior pituitary

How does ADH function and release in the P. Pituitary Gland for Urine Formation?

• released due to increased blood osmolarity or dehydration

• increases water permeability and reabsorption int he DCT and kidney collecting ducts

• produced by posterior pituitary gland

• water retention, lower urine volume but more concentrated

How does Oxytocin function and release in the P. Pituitary Gland for Milk Ejection?

• suckling results in stimulation and impulse is sent to brain

• oxytocin releases into bloodstream

• causes smooth muscle contraction of milk ducts

• milk is ejected from the breast

What is the interrelationship of the Hypothalamus and the Anterior Pituitary Gland?

1. releasing / inhibiting hormones syntehsized in hypothalamic neurons

2. hormones are released into cpillary bed in infundibulum

3. stimulate/inhibit release of hormones from anterior pituitary

How does Growth Hormone function in the A. Pituitary Gland?

• GHRH release from hypothalamus, stimulating GH release

  • stimulates adipose cells to break down stored fat for energy

  • increases amino acid uptake from blood + reduces apoptosis for growth

  • stimulates liver to break down glycogen into glucose, releasing IGF-1 (insulin growth factor)

• hypothalamus perceives high IGF-1 levels and releasees GHIH to inhibit GH release

How does Prolactin Hormone function in the A. Pituitary Gland?

• PRH released from hypothalamus, stimulating PRL release during pregnancy

  • acts on breast secretory tissue to produce milk

• PIH inhibits release

• NOTE: estrogen also stimulates release

How does Thyroid Stimulating Hormone function in the A. Pituitary Gland?

• TSH acts on thyroid gland for thyroid hormones

• action is stimulated by TRH which is released from hypothalamus

How does Adrenocorticotropic Hormone function in the A. Pituitary Gland?

• ACTH acts on adrenal gland for glucocorticoids and androgens

• action is stimulated by CRH (corticotropin)

How does Follicle Stimulating Hormone and Luteinizing Hormone function in the A. Pituitary Gland?

• FSH/LH act on ovaries and testes for estrogen, progeesterone, and testosterone

• action is stimulated by GnRH (gonadotropin)

How are Thyroid and Parathyroid Hormone release controlled?

thryoid = both humoral and hormonal

parathyroid = only humoral

How does Thyroxin function in the Thryoid?

• TRH from hypothalamus stimultes TSH from anterior pituitary to stimulate thyroxin

  • releases energy and makes proteins

  • promotes growth and development

How does Calcitonin function in the Thyroid?

• regulated by Ca ion level negative feedback in blood; humoral

  • reduces blood calcium and phosphate levels by storing in bone

  • stimulates osteoblasts /inhibits osteoclasts

How does the Parathyroid Hormone function in the Parathyroid?

• regulated by Ca ion level negative feedback in blood; humoral

  • increases blood calcium levels

  • stimulates osteoclasts / inhibits osteoclasts (opposite of Calcitonin)

  • reabsorption of Ca2+ in kidneys

  • increases absorption of Ca2+ in small intestine

How does Blood Calcium Homeostasis work in the body?

1. blood Ca2+ concentration drops

2. PTH is released from parathyroid gland

   1. inhibits osteoblasts, stimulates osteoclasts, broken bone releases Ca2+ into bloodstream

   2. PTH stims kidney tubule cells to recover waste ca2+ from urine; releases calcitriol

   3. calcitriol stimulates intestines to absorb Ca2+ from food

3. Blood Ca levels increase

4. high Ca concentration causes calcitonin release

5. calcitonin stimulates osteoblasts, inhibits osteoclasts, and Ca is removed from blood to build bone

What are the Hormones in the Pancreas?

• produced by islets of langerhans

• humoral control

• alpha cells produce glucagon (increase blood glucose levels)

• beta cells produce insulin (decrease blood glucose levels by uptaking glucose for metabolism or storage as glycogen)

How does Glucose Homeostasis work during Hyperglycemia?

1. homeostasis at 70-110 mg/dL

2. hyperglycemia

3. beta cells of pancreas release insulin

   1. triggers body cells to utilize glucose from blood in cellular respiration

   2. inhibits glycogenolysis (glucose is stored as glycogen in liver)

   3. inhibits gluconeogenesis (amino acids and free glycerol are not converted to glucose in ER)

4. blood glucose concentration decreases

How does Glucose Homeostasis work during Hypoglycemia?

1. homeostasis at 70-110 mg/dL

2. hypoglycemia

3. alpha cells of pancreas release glucagon

   1. inhibits body cells from utilizing glucose for cellular resipration

   2. stimulates glycogenolyisis (glycogen in liver is broken down + released as glucose)

   3. stimulates gluconeogenesis (amino acids and free glycerol are converted + released as glucose from ER

How does the Outer Zone of the Adrenal Cortex function with Hormones?

• produces mineralocorticoids

• aldosterone is humoral; reabsorption of sodium in kidneys leads to increased water reabsorption

How does the Middle Zone of the Adrenal Cortex function with Hormones?

• produces glucocorticoids

• cortisol is stimulated by anterior pituitary

• cortisol responds to stress, inhibits tissue building and increases catabolism of nutrients to glucose, and increases gluconeogenesis

• hormonal control

How does the Inner Zone of the Adrenal Cortex function with Hormones?

• has cortical sex hormones

• testosterone and estrogen are primary source until puberty and sex glands take over

• hormones are involved in development of secondary sex characteristics

• hormonal control

What role does the Adrenal Medulla play in Hormones?

• produces epinephrine and norepinephrine

  • both are neurotransmitters

  • release stimulated by sympathetic nervous system (nervous control)

What does Epinephrine do in the body?

• increases blood flow to heart and muscles

• increases bronchial dilation

• increases heart rate and blood sugar levels

What does Norepinephrine do in the body?

• decreases blood flow to the gut and skin

What happens during the Alarm in the General Adaptation Syndrome / Stress Response?

• sympathetic N.S. stimulated

• epinephrine and norepinephrine

• prepare body for extreme exertion

What happens during the Resistance in the General Adaptation Syndrome / Stress Response?

• attempt to adapt to stressor

• cortisol released

• maintain energy levels (release glucose and lipids)

• supress immune

What happens during the Exhaustion in the General Adaptation Syndrome / Stress Response?

• resources depleted

• continued release of cortisol

• depression, fatigue, damage to organ systems

note: stress adaptation may not always include exhaustion

How do Hormones in the Ovaries function?

• stimulated by FSH and LH

• produces estrogen and progesterone (also produced by corpus luteum; involved in ovulation and pregnancy)

• leads to development of primary (growth of uterus and vagina) and secondary (body hair, breasts, pelvis) sex characteristics

How do the Hormones in the Testes function?

• stimulated by FSH and LH

• produces testosterone

• leads to development of primary (penis and accessory glands) and secondary (body hair, voice changes) sex characteristics

• also stimulates spermatogenesis

What does the Thymus Gland do Hormone wise?

• secretes thymosin which is involved in the development of immune system and maturation of lymphocutes

• prepares for pathogen exposure

• decreases in size as age increases

What does the Pineal Gland do Hormone wise?

• secretes melatonin which acts on the hypothalamus to inhibit luteinizing hormone

• regulates reproductive cycles

• also responds to light and may be related to daily rhythms

What are the Undercover Endocrine Organs?

• placenta: estrogen and progesterone

• stomach: gastrin to produce gastric juice

• duodenum: secretin and cholecystokinin