Endocrine System

• Plays a role in reproduction, growth, and regulation of energy.

• Made up of glands, specialized cells, and hormones.

Glands:

Secrete hormones that affect target tissue and organs

• Thyroid
• Hypothalamus
• Adrenal Glands
• Pituitary
• Parathyroid
• Pancreas        

Hypothalamus

• Integrative center between the nervous and endocrine system.

• Secretes releasing and inhibiting hormones that either stimulate or inhibit the secretion of hormones from the Anterior Pituitary.

Pituitary

Connected to the hypothalamus and divided into:

Anterior

Posterior 

Anterior Pituitary

Stimulated by hormones from the Hypothalamus.

Anterior Pituitary hormones:

• TSH
• ACTH
• FSH
• LH
• GH
• Prolactin

Anterior Pituitary hormone

TSH

stimulates the thyroid to secrete thyroid hormone

Anterior Pituitary hormone

ACTH

stimulates the adrenal cortex to secrete corticosteroids

Anterior Pituitary hormone

FSH

stimulates the secretion of estrogen and development of ova and sperm

Anterior Pituitary hormone

LH

stimulates ovulation and secretion of sex hormones in both sexes.

Anterior Pituitary hormone

GH

affects the growth and development of skeletal muscle and long bones

also plays a role in protein, fat, CHO metabolism

Anterior Pituitary hormone

Prolactin

stimulates breast development for lactation after childbirth

Posterior Pituitary

• stimulated by nerve tracks from the hypothalamus
• Hormones in the posterior pituitary (PP) are produced in the hypothalamus and stored in the PP

Hormones:

• ADH
• Oxytocin

Posterior Pituitary

hormone

ADH (vasopressin)

• regulates fluid volume
• stimulates reabsorption of H₂O at the renal tubules
• acts as a potent vasoconstrictor

Serum osmolality stimulates ADH:

• ↑ osmolality=stimulation and ↑ ADH

Also stimulated by HYPOvolemia, HYPOtension, pain, stress, trauma, use of morphine, tranquilizers, and positive pressure ventilation

Posterior Pituitary

hormone

Oxytocin

stimulates uterine contractions and ejection of milk

Thyroid

• important for normal growth and development
• ↑ metabolic activity and protein synthesis
• regulated by TSH from the Anterior Pituitary

Stimulates 3 hormones:

• Thyroxine (T₄)
• Triiodothyroxine (T₃)
• Calcitonin

Thyroid Hormone

Thyroxine (T₄)

• Most abundant
• Most are bound to plasma- unbound are considered "free" and are active

↑/↓ in BOTH T₃ and T₄ affect:

• metabolic rate
• caloric requirements
• O₂ consumption
• CHO and Lipid metabolism
• growth and development
• brain function

Thyroid Hormone

Triiodothyronine (T₃)

•  more potent, greater metabolic affects

↑/↓ in BOTH T₃ and T₄ affect:

• metabolic rate
• caloric requirements
• O₂ consumption
• CHO and Lipid metabolism
• growth and development
• brain function

Thyroid Hormone

Calcitonin

• Produced by C-cells of the thyroid in response to HIGH circulating Ca+ levels

• Prevents reabsorption of Ca+ from bones (loss)
• ↑ Ca+ storage in the bone
• ↑ renal excretion of Ca+ and Phosphorus

Parathyroid

• 4 pea-size glands
• controlled by feedback system (NOT pituitary or hypothalamus)
• Secretes PTH-- regulates Ca+ blood level
• Bone- stimulates reabsorption and inhibits bone growth
• Kidneys- ↑ Ca+ reabsorption and Phosphorus excretion and stimulates renal conversion of Vit. D which enhances intestinal absorption of Ca+

↓Ca+ → ↑PTH → (↑Ca+ absorption from intestines,  ↑Ca+ reabsorption from bone, ↑ Ca+ reabsorption and ↓ excretion from kidneys) → ↑Ca+ → ↓PTH

(see figure on pg 1203)

Adrenal Glands

• small vascular glands located on top of the kidneys- Medulla & Cortex

Adrenal Glands-

Medulla

• Inner portion
• made of sympathetic neurons

Secretes:

• Epinephrine
• Norepinephrine
• Dopamine

Adrenal Glands-

Cortex

• Outter portion

Secretes more than 50 hormones

• Glucocorticoids
• Mineralocorticoids
• Adrenal androgens

Adrenal Glands-

Cortex

Glucocorticoids

• Named for effects on Glucose
• Also stumilate lipolysis, and have anti-inflammatory effects

Cortisol

• ↑blood glucose through stimulation of hepatic conversion of amino acids to glucose and inhibit protein synthesis
• ↓inflammatory response
• Helps maintain vascular integrity and fluid volume

Adrenal Glands-

Cortex

Mineralocorticoids

Aldosterone-very potent!

• Maintains extracellular fliud volume by acting on the renaltubule to promote renal reabsorption of Na+ and excretion of K+ and H+ ions
• Stimulated by angiotensin II, hyponatremia, and hyperkalemia
• Inhibited by atrial natriuretic peptide and hypokalemia

Adrenal Glands-

Cortex

Adrenal Adrogens

• stimulate pubic and axillary hair growth and sex drive in females
• have no real affect in men

Pancreas

• long tapered, lobular, soft gland
• has both endocrine and exocrine fucntions
• Islets of Langerhans is the hormone secreting part

Islets of Langerhans

• Hormone secreting part of Pancreas

4 types of secreting cells:

• Alpha
• Beta
• Delta
• F

Islets of Langerhans

Alpha Cells

Produce and secrete glucagon

• Synthasized and released in response to low levels of blood glucose

↑ blood glucose by stimulating:

• glycogenolysis (breakdown of glycogen to glucose)
• glyconeogenesis (the formation of glucose from glycerol and proteins rather than CHO)
• ketogenesis (formation of ketone bodies)

Islets of Langerhans

Beta Cells

Produces and secretes insulin and amylin

Insulin

• principal regulator of the metabolism and storage of CHO, fats, and proteins
• Facilitates glucose transport across most cell membranes
• Major stimulus is ↑ blood glucose
• Also stimulated by ↑ amino acid levels and vagal stimulation
• Inhibited by ↓blood glucose, glucagon, somatostatin, hypokalemia, and catecholine (see table 48-4 pg 1207)
• Enhances glucose incorperation into glycogen and triglycerides by altering enzyme activity and inhibiting gluconeogenesis.

Islets of Langerhans

Delta Cells

produce and secrete somatostatin

• inhibits the release of glucagon and insulin

Islets of Langerhans

F Cells

• secretes pancreatic polypeptide