Ch 11 - Endocrine Glands

endocrine system 

system of endocrine glands and cells that secrete hormones 

• a major physiological control system 

glands

a group of epithelial cells or an organ that synthesizes and secretes chemical substances

endocrine glands

• ductless

• secrete hormones into the bloodstream to travel to target cells

exocrine glands 

have ducts 

hormone

a biologically active molecule that serves as a chemical messenger in the blood

hormones extra

major endocrine glands 

• pitutitary gland

• hypothalamus

• thyroid

• adrenal

• organs 

  • pancreas - hormone secreting cells

  • ovaries

  • testies 

islets of langerhans

cells in the pancrease that secrete insulin and glucagon

amine hormones

derived from tyrosine and tryptophan (AAs)

• ie, thyroid hormones, E and NE, dopamine, melatonin

polypeptide and protein hormones

most hormones, many sites

• ie; anti diuretic (ADH) - pushes out water, growth hormone (GH), insulin, oxytocin, glucagon, adrenicorticotropic hormone (ACTH) 

glycoproteins

bound to carbohydrate

• ie; thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) 

steroids

lipids based on cholersterol

• ie; testosterone, estrogen, progesterone, aldosterone, cortisol

control hormone secretion

three types of input to endocrine cells can stimulate or inhibit hormone secretion, and multiple inputs can be active simutaneously

• concentration of ions or nutrients

• nervous system

• hormones

concerntration of ions or nutrients

A hormone regulates the plasma concentration of an ion or nutrient via negative feedback 

• ie; insulin lowers blood glucose concentration

nervous system

The autonomic NS controls the adrenal medulla and other endocrine glands

• ie, insulin secretion is stimulated by parasympathetic NS and inhibited by sympathetic NS

The hypothalamus and posterior pituitary hormones are directly regulated by neurons of the brain 

hormones 

The secretion of a hormone can be directly regulated by the blood concentration of another hormone, called a tropic or trophic hormone. This is a hormone that stimulates the secretion of another hormone. 

• ie; the gonadotropic hormone LH stimulates secretion of testosterone by the testes

posterior pituitary hormones

• synthesized in the hypothalamus

• Axons of the hypothalamo-hypophyseal tract terminate on capillaries in the posterior pituitary gland, where hormones are released into the bloodstream. 

• two hormones 

  • Oxytocin

  • antidiuretic (ADH or vasopressin

Oxytocin

stimulates smooth muscle in mammary gland and uterus (reproductive)

antidiuretic hormone (ADH) or vasopressin

acts on smooth muscle in blood vessels to increase blood pressure (constriction) and acts on the kidney to retain fluids for blood volume (circulatory, renal) 

posterior pituitary gland

stores and releases hormones that are synthesized in the hypothalamus

• hormones are transported to capillaries in the posterior pituitary via axons in the hypothalamo-hypophyseal tract 

anterior pituitary hormones

• six hormones and their targets

• trophic effect

• 3-hormone sequence 

trophic effect

hormones secreted by anterior pituitary gland stimulate secretion of another hormone 

3 hormone sequence - step 1

A hypothalamic hormone is secreted from a hypothalamic neuron into the hypothalamo-hypophyseal portal system to control secretion of →

3 hormone sequence - step 2

anterior pituitary hormone (tropic hormone) which controls the secretion of →

3 hormone sequence - step 3a

a hormone from another endocrine gland which affects target cells

3 hormone sequence - step 3b

physiological response

• FSH

Anterior pitutary gland - step 1

hypothalamic hormones from the hypothalamus are transported to the anterior pituitary gland via the blood vessels of the hypothalamo-hyphyseal portal system

Anterior pitutary gland - step 2

Upon arrival, the hypothalamic hormones bind to receptors on the anterior pituitary cells to evoke secretion of the anterior pituitary hormones (red, tropic, hormones) into the same capillaries → blood circulation 

hypothalamus pituitary gonad axis

GnRh stimulates the secretion of FSH and LH, which stimulated the secretion of sex sterioid hormones (gonads) 

• negative feedback loops 

finish

stress

real or perceived threat to homeostasis

• emotional stress, pain, physical trauma, prolonged exposure to cold, decreased water intake. sleep deprivation, infection, foreign chemicals. 

cortisol

a glucocorticoid (steroid hormone) secreted by the adrenal cortex

cortisol facts

• differentiation of tissues and glands in fetal and neonatal stages

• helps maintain blood pressure

• antii-inflammatory and anti-immune functions to control overactivity of immune system

• increases blood sugar level, decreases immune response 

epinepherine 

a catecholomine secreted by the adrenal medull

epinepherine facts

• increases heart rate and respiratory rate

• shifts blood flow to skeletal msucels

  • vasoconstricts gut vessels

  • vasodilates skeletal muscel vessels

add steps 

thyroid gland

controls metabolic rate through diverse, widespread actions

• straddles the esophagus just below the larynx, in the neck. has 2 lobes 

thyroid follicles

• numerous microscopic 

• filled with colloid, a protein-rich fluid

• lines with follicular cells that synthesize T3 and T4 

write steps

synthesis of thyroid hormones - step 1

iodide (I-) from ISF enters the colloid, where it is oxidized and attaches to the tyrosine ring of thyroglobulin (TG), a protein

• MIT (monoiodotyrosine) and DIT (diiodotyrosine) 

synthesis of thyroid hormones - step 2

Enzymes modify the structure of MIT and DIT and couple them together

• T3 results from one MIT attached to one DIT ( so there are 3 iodides)

• T4 results from two DITs coupled (so there are 4 iodides)

synthesis of thyroid hormones - step 3

TG containing T3 and T4 enters folliculats cells via pinocytosis (fluid endocytosis)

synthesis of thyroid hormones - step 4

T3 and T4 are released from TG due to enzymes

synthesis of thyroid hormones - step 5

T3 and T4 are secreted via diffusion into ISF

actions of thyroid hormones

• stimulates carbohydrate absoprtion from small intestine = energy for metabolism

• increases fatty acid release from adiopocytes = energy for metabolism

• calorigenic (heat-generating) action for temperature homeostasis 

hypothyroidism

lower than normal plasma concentration of T3 and T4

hypothyroidism symptoms

cold tolerance, weight gain, and lethargy due to decreased metabolic rate and possibly goiter

hypothyroidism causation

can be a result of iodine deficiency in the diet, which reduces the synthesis of T3 and T4 

can be a result of hormone secreting tumors of the thyroid, or an autoimmune disease called graves disease 

decreased T3 and T4 → less negative feedback on the pituitary → increased TSH → enlarged thyroid or goiter due to overstimulation of thyroid gland

write steps

graves disease

antibodies act like TSH, stimulating the thyroid gland to grow and oversecrete T3 and T4