a&p endocrine chap 10
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Endocrine SystemTRANSCRIPT
The Endocrine SystemThe Endocrine SystemChapter 10Chapter 10
“Control system” along with nervous system
Helps maintain homeostasis
Allows for communication among cells
Endocrine System
Comparison of Nervous & EndocrineNervous system
quick response (milliseconds) relatively short duration of effect works via electrical impulses (action potentials) and direct
release of chemicals (neurotransmitters) across interstitial fluid to adjacent cells affects specific sets of cells (neuron, muscle, gland) resulting in
specific responses (eg. muscle contraction or glandular secretion)
Endocrine system slower response (minutes to hours) potentially long duration of effects (hours to days) works via chemical signals (“hormones”) which are released
through interstitial fluid into blood capillaries affects multiple cells throughout the body that have specific
hormone receptors (“target cells”) resulting in change of metabolic activities of cells (eg. affects protein synthesis)
Endocrine system includes all endocrine cells, tissues, and endocrine glands (organs) of the body
Many different organs have some endocrine cells/tissues within their structure, but the organ’s primary function is not endocrine (ie: heart, kidney, digestive organs, pancreas hypothalamus, gonads, thymus)
Some organs are primarily endocrine organs (endocrine glands) (ie. pituitary, thyroid, parathyroid, adrenal, pineal)
Overview of Endocrine System
Structure of HormonesHormones classified based on their chemical structure:
Amino acid derivatives – eg. epinephrine, norepinephrine, thyroid hormones, melatonin
Peptide/protein hormones – eg. ADH, oxytocin, growth hormone, hypothalamic hormones, pancreatic hormones, thymic hormones
Lipid derivatives – include steroid hormones (eg. estrogens, testosterone, adrenal hormones) & eicosanoids (aka cytokines/local hormones) (eg. prostaglandins)
Secretion, Distribution & Effect of Hormones Hormones are released on demand – only when needed
Hormone release is primarily regulated by negative feedback mechanisms
changes in ECF (ISF/plasma) concentration/composition
changes in circulating levels of hormone itself or regulating hormones
neural stimuli
Hormones secreted by endocrine cells into interstitial fluid, and distributed through bloodstream
Only cells that posses receptors for that particular hormone can be affected (“target cell/target organ”)
Effect of hormones is on metabolic activity of cells, via activation/inactivation of specific genes, affecting protein synthesis
Secretion, Distribution & Effect of Hormones
Mechanism of Hormonal Action
Depends on whether hormone can cross cell membrane & enter cell:
Epi, norepi, peptide hormones are not lipid soluble & therefore will bind to receptors on cell membrane (membrane receptors). Eicosanoids also bind to membrane receptors
Steroid hormones & thyroid hormones can enter cell & therefore will bind to receptors within the cell (intracellular receptors)
Mechanism of Hormonal Action
Hormones that bind to membrane receptors work indirectly, via “second messengers”
Most common second messenger is cyclic AMP (cAMP)
Mechanism of Hormonal Action
Hormones that can enter the cell and bind to intracellular receptors can directly affect the structure or function of the cell, via affect on protein synthesis &/or energy production
Pituitary Gland (Hypophysis)
“master gland”
Sits within sella turcica
Attached to hypothalamus via infundibulum
Two regions – anterior pituitary & posterior pituitary
Regulated by hypothalamus
Secretes 9 hormones
Anterior Pituitary Gland Comprised of endocrine cells that produce & secrete 7 hormones: Adrenocorticotropic hormone (ACTH)
Thyroid stimulating hormone (TSH)
Growth Hormone (GH)
Prolactin (PRL)
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Melanocyte-stimulating hormone (MSH)
Controlled by regulatory hormones (releasing hormones &/or inhibiting hormones) from hypothalamus
Hypothalamic regulatory hormones reach anterior pituitary via “hypophyseal portal system”
Effects of Anterior Pituitary HormonesAdrenocorticotropic hormone (ACTH) -
Thyroid stimulating hormone (TSH) -
Growth Hormone (GH) -
Prolactin (PRL) - Follicle stimulating hormone (FSH) -
Luteinizing hormone (LH) -
Melanocyte-stimulating hormone (MSH) -
Targets adrenal cortex to secrete glucocorticoids (cortisol, corticosterone), which affect glucose metabolism
Targets thyroid gland to secrete thyroid hormones (thyroxine (T4), triiodothyronine (T3)), which affect metabolism, growth and development
Targets most body tissues, but especially liver, bone, muscle & cartilage, affecting growth, repair & mobilization of energy reserves. Works indirectly through release of “somatomedins” (hormones) from liver.
Targets mammary gland for development & lactation. May affect prostate gland in males.
Targets gonads (ovaries/testes) for gamete (egg/sperm) production & development. Also causes secretion of estrogens by ovaries.
Targets ovaries causing ovulation & release of estrogens and progesterone, and testes causing secretion of testosterone
Produced primarily during fetal development; targets melanocytes. No secretion in heathy adults
ACTHAdrenal cortex
Glucocorticoids(cortisol, corticosterone)
TSH
Thyroid gland
Thyroid hormones (T3, T4)
GH
Liver
Somatomedins
Bone, muscle, cartilage, other
PRL
Mammary glands (& prostate)
MSH
Melanocytes (uncertain significance)
Overview of Anterior Pituitary Hormones
Testosterone
LH
Testes
FSH
Ovaries
Estrogen ProgesteroneSperm Egg
Posterior Pituitary Gland
Comprised of axons, telodendria and terminals of neurons that originate in the hypothalamus
2 hormones (antidiuretic hormone (ADH) & oxytocin (OT) are produced by the hypothalamic neurons & transported through the axons running within infundibulum to terminals
Hormone release controlled via AP stimulation
Effects of Posterior Pituitary Hormones Antidiuretic hormone (aka vasopressin) – targets kidneys to decrease amount of urine produced (increased water reabsorption), & blood vessels causing vasoconstriction to increase BP
Oxytocin – targets uterus during childbirth (positive feedback), mammary glands for milk release (“let-down”); In non-pregnant females & in males, may contribute to orgasm
Thyroid Gland Located anterior to trachea, just below thyroid cartilage of larynx
Two lobes connected by isthmus
Lobes contain thyroid follicles
Follicular cells secrete 2 hormones under the influence of TSH – Thyroxine (T4) & Triiodothyronine (T3)
Thyroid Gland Thyroid hormones target almost every body cell
Can enter cells & bind to intracellular receptors on mitochondria & in nucleus
Effects include:
increased ATP production
increased cellular metabolism, energy utilization & oxygen consumption
increased body temperature
growth & development of skeletal, muscular & nervous system in fetus & children
Thyroid DisordersHyperthyroidism – different causes but resulting increased production of thyroid hormones may lead to: increased metabolic rate, increased heart rate & blood pressure, increased body temperature, excitability & nervousness, weight loss, possible goiter, possible exopthalmos
Hypothyroidism – decreased secretion of thyroid hormones may cause: lower metabolic rate, sluggishness, fatigue, decreased heart rate & BP, decreased body temperature, weight gain, possible goiter, subcutaneous swelling (myxedema), hair loss, dry skin
Hypothyroidism during pregnancy or in early childhood may lead to “cretinism” – abnormal skeletal & nervous development
Adrenal (Suprarenal) Glands Lie superior to each kidney
Comprised of two parts – outer adrenal cortex & inner adrenal medulla
Adrenal Cortex Divided into 3 functional zones with each zone producing different types of “corticosteroids”
Middle zone secretes steroid hormones known as “Glucocorticoids” (cortisol (hydrocortisone), corticosterone, cortisone), under the control of ACTH
Glucocorticoids target most body cells, especially liver, muscle, adipose & white blood cells
Effects include: increased glucose synthesis, “gluconeogenesis” & glycogen formation mainly in liver release of fatty acids from adipose tissue & protein breakdown in muscle cells for energy use helps provide resistance to stress due to increase in available energy inhibits activity of WBCs & immune responses – anti-inflammatory effects but slow wound healing & resistance to disease
Adrenal Medulla Comprised of cells that are post-ganglionic sympathetic neurons
Sympathetic stimulation results in release of epinephrine (adrenaline) and norepinephrine (noradrenaline) into bloodstream
Effects are sympathomimetic
Pancreas Endocrine & exocrine (digestive) gland
Endocrine function by cells within pancreatic islets (islets of Langerhans)
Alpha (α) cells secrete glucagon
Beta (β) cells secrete insulin
Both regulate blood glucose levels
Regulation of Blood Glucose
Diabetes Mellitus
Most common endocrine disorder of the pancreas
2 major types:
Type 1 (insulin dependent/ ”juvenile”) – actual deficiency of beta cells; sudden onset; may be autoimmune
Type 2 (non-insulin dependent/ “adult”) – insulin resistance due to decreased sensitivity (or number) of insulin receptors
Initial symptoms include: polydipsia, polyphagia, polyurea, glycosuria, weight loss, fatigue
Long term symptoms: neuropathy, retinopathy, gangrene, kidney failure…
Hormones & Stress – General Adaptation Syndrome (GAS)