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Chapter 18 The Endocrine System

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Chapter 18 The Endocrine System Endocrine and nervous systems work together Endocrine system hormones released into the bloodstream travel throughout the body – PowerPoint PPT presentation

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Title: Chapter 18 The Endocrine System


1
Chapter 18The Endocrine System
  • Endocrine and nervous systems work together
  • Endocrine system
  • hormones released into the bloodstream travel
    throughout the body
  • results may take hours, but last longer
  • Nervous system
  • certain parts release hormones into blood
  • rest releases neurotransmitters excite or inhibit
    nerve, muscle gland cells
  • results in milliseconds, brief duration of
    effects

2
General Functions of Hormones
  • Help regulate
  • extracellular fluid
  • metabolism
  • biological clock
  • contraction of cardiac smooth muscle
  • glandular secretion
  • some immune functions
  • Growth development
  • Reproduction

3
Endocrine Glands Defined
  • Exocrine glands
  • secrete products into ducts which empty into body
    cavities or body surface
  • sweat, oil, mucous, digestive glands
  • Endocrine glands
  • secrete products (hormones) into bloodstream
  • pituitary, thyroid, parathyroid, adrenal, pineal
  • other organs secrete hormones as a 2nd function
  • hypothalamus, thymus, pancreas,ovaries,testes,
    kidneys, stomach, liver, small intestine, skin,
    heart placenta

4
Hormone Receptors
  • Hormones only affect target cells with specific
    membrane proteins called receptors

5
Circulating Local Hormones
  • Circulating hormones
  • act on distant targets
  • travel in blood
  • Local hormones
  • paracrines act on neighboring cells
  • autocrines act on same cell that secreted them

6
Lipid-soluble Hormones
  • Steroids
  • lipids derived from cholesterol on SER
  • different functional groups attached to core of
    structure provide uniqueness
  • Thyroid hormones
  • tyrosine ring plus attached iodines are
    lipid-soluble
  • Nitric oxide is gas

7
Water-soluble Hormones
  • Amine, peptide and protein hormones
  • modified amino acids or amino acids put together
  • serotonin, melatonin, histamine, epinephrine
  • some glycoproteins
  • Eicosanoids
  • derived from arachidonic acid (fatty acid)
  • prostaglandins or leukotrienes

8
Action of Lipid-Soluble Hormones
  • Hormone diffuses through phospholipid bilayer
    into cell
  • Binds to receptor turning on/off specific genes
  • New mRNA is formed directs synthesis of new
    proteins
  • New protein alters cells activity

9
Action of Water-Soluble Hormones
  • Can not diffuse through plasma membrane
  • Hormone receptors are integral membrane proteins
  • act as first messenger
  • Receptor protein activates G-protein in
    membrane
  • G-protein activates adenylate cyclase to convert
    ATP to cAMP in the cytosol
  • Cyclic AMP is the 2nd messenger
  • Activates kinases in the cytosol to speed up/slow
    down physiological responses
  • Phosphodiesterase inactivates cAMP quickly
  • Cell response is turned off unless new hormone
    molecules arrive

10
Hormonal Interactions
  • Synergistic effect
  • a second hormone, strengthens the effects of the
    first
  • two hormones acting together for greater effect
  • thyroid strengthens epinephrines effect upon
    lipolysis
  • Permissive effect
  • you need two hormone present for one hormone to
    work properly
  • estrogen LH are both needed for oocyte
    production
  • Antagonistic effects
  • two hormones with opposite effects
  • insulin promotes glycogen formation glucagon
    stimulates glycogen breakdown

11
Control of Hormone Secretion
  • Regulated by signals from nervous system,
    chemical changes in the blood or by other
    hormones
  • Negative feedback control (most common)
  • decrease/increase in blood level is reversed
  • Positive feedback control
  • the change produced by the hormone causes more
    hormone to be released
  • Disorders involve either hyposecretion or
    hypersecretion of a hormone

12
Hypothalamus and Pituitary Gland
  • Both are master endocrine glands since their
    hormones control other endocrine glands
  • Hypothalamus is a section of brain above where
    pituitary gland is suspended from stalk
  • Hypothalamus receives input from cortex,
    thalamus, limbic system internal organs
  • Hypothalamus controls pituitary gland with 9
    different releasing inhibiting hormones

13
Pituitary Gland
Hormones human growth hormone- hGH thyroid
stimulating - TSH follicle stimulating-
FSH leutinizing hormone - LH prolactin adrenocorti
cotropin - ACTH melanocyte stimulating - MSH
  • 5 types of cells
  • somatotrophs secrete hGH/somatotropin
  • thyrotrophs secrete TSH/thyrotropin
  • gonadotrophs secrete FSH, LH
  • lactotrophs secrete prolactin
  • corticotrophs secrete ACTH/corticotropin MSH
  • Pea-shaped, 1/2 inch gland found in sella turcica
    of sphenoid
  • Infundibulum attaches it to brain
  • Anterior lobe 75 develops from roof of mouth
  • Posterior lobe 25
  • ends of axons of 10,000 neurons found in
    hypothalamus
  • neuroglial cells called pituicytes

14
Human Growth Hormone
  • Produced by somatotrophs
  • induces target cells to make insulin-like growth
    factors (IGFs) that act locally or enter
    bloodstream
  • common target cells of IGFs are liver, skeletal
    muscle, cartilage and bone
  • GH IGFs increase cell growth cell division by
    increasing their uptake of amino acids
    synthesis of proteins
  • stimulate lipolysis in adipose so fatty acids
    used for ATP
  • retard use of glucose for ATP production by cells
  • reduces uptake of glucose by the liver and
    promote breakdown of liver glycogen so blood
    glucose levels stay high enough to supply brain
  • Excess of growth hormone
  • raises blood glucose concentration
  • pancreas releases insulin continually
  • Leads to beta-cell burnout
  • Diabetogenic effect
  • causes diabetes mellitis if no insulin activity
    can occur eventually

15
Regulation of hGH
  • Low blood sugar stimulates release of GNRH from
    hypothalamus
  • anterior pituitary releases more hGH, more
    glycogen broken down into glucose by liver cells
  • High blood sugar stimulates release of GHIH from
    hypothalamus
  • less hGH from anterior pituitary, glycogen does
    not breakdown into glucose

16
Thyroid Stimulating Hormone (TSH)
  • Hypothalamus regulates thyrotroph cells
  • Thyrotroph cells produce TSH
  • TSH stimulates the synthesis secretion of T3
    and T4
  • Metabolic rate stimulated

17
Thyroid Gland
  • comprised of microscopic sacs called follicles
    follicular cells making up the walls, surrounds a
    lumen
  • synthesize T3 T4 (thyroxin)
  • In between follicular cells cells are
    parafollicular cells
  • produce calcitonin
  • On each side of trachea is lobe of thyroid
  • connected by an isthmus
  • Weighs 1 oz has rich blood supply

18
Formation of Thyroid Hormone
  • Iodide trapping follicular cells actively take
    up iodine from blood
  • Synthesis of thyroglobulin (TGB) follicular
    cells make TGB - secreted into the follicle lumen
    as the material colloid
  • Iodination of colloid iodine ions are oxidated
    (I2- -gt I2) by peroxidase within the cell
  • oxidized iodine then binds onto tyrosine residues
    on the TGB within colloid
  • Coupling of T1 and T2 forms T3 T4
  • Uptake of colloid by follicular cells digestion
    cleaves off T3 and T4
  • Secretion of T3 T4 into blood T3 T4 are
    transported in blood bound to thryoxine-binding
    globulin

19
Actions of Thyroid Hormones
  • T3 T4 increases metabolic rate
  • stimulates synthesis of protein
  • stimulates breakdown of fats
  • stimulates cholesterol excretion
  • increases use of glucose oxygen
  • (ATP production)
  • increases body temperature (calorigenic effect)

20
Control of T3 T4 Secretion
  • Low blood levels of hormones stimulate
    hypothalamus -gt TRH
  • It stimulates pituitary to release TSH
  • TSH stimulates gland to raise blood levels
  • T3 and T4 regulate themselves through a negative
    feedback loop

21
Parathyroid Glands
  • Principal cells produce parathyroid hormone (PTH)
  • Oxyphil cell function is unknown
  • 4 pea-sized glands found on back of thyroid gland

22
Parathyroid Hormone
  • Raises blood calcium levels
  • increases activity of osteoclasts (bone degrading
    cells)
  • increases reabsorption of Ca2 by kidney
  • promote formation of calcitriol (vitamin D3) by
    kidney which increases absorption of Ca2 and
    Mg2 by intestinal tract
  • Opposite function of calcitonin (thyroid)
  • High or low blood levels of Ca2 stimulate the
    release of different hormones --- PTH or CT
  • high level of calcium in blood - release of
    calcitonin by parafollicular cells, promotes
    uptake of calcium into bone matrix, lowers blood
    calcium
  • low level of calcium in blood - release of PTH by
    parathyroid glands, promotes release of calcium
    from bone, raises blood calcium

23
Follicle Stimulating Hormone (FSH)
  • Releasing hormone from
    hypothalamus controls
    gonadotrophs
  • Gonadotrophs release
    follicle stimulating hormone
  • FSH functions
  • initiates the formation of follicles within the
    ovary
  • stimulates follicle cells to secrete estrogen
  • stimulates sperm production in testes

24
Luteinizing Hormone (LH)
  • Releasing hormones from hypothalamus stimulate
    gonadotrophs
  • Gonadotrophs produce LH
  • In females, LH stimulates
  • secretion of estrogen
  • ovulation of 2nd oocyte from ovary
  • formation of corpus luteum
  • secretion of progesterone
  • In males, stimulates interstitial cells
    to secrete testosterone

25
Ovaries and Testes
  • Ovaries
  • estrogen, progesterone, relaxin inhibin
  • regulate reproductive cycle, maintain pregnancy
    prepare mammary glands for lactation
  • Testes
  • produce testosterone
  • regulate sperm production 2nd sexual
    characteristics

26
Prolactin (PRL)
  • Hypothalamus regulates lactotroph
    cells
  • Lactotrophs produce prolactin
  • Under right conditions, prolactin causes
    milk production
  • Suckling reduces levels of hypothalamic
    inhibition and prolactin levels rise along with
    milk production
  • Nursing ceases milk production slows

27
Melanocyte-Stimulating Hormone
  • Secreted by corticotroph cells
  • Releasing hormone from hypothalamus increases its
    release from the anterior pituitary
  • Function not certain in humans (increase skin
    pigmentation)
  • May have a role in promoting sexual performance

28
Adrenocorticotrophic Hormone
  • Hypothalamus releasing hormones stimulate
    corticotrophs
  • Corticotrophs secrete ACTH ( MSH also)
  • ACTH stimulates cells of the adrenal cortex

29
Adrenal Glands
  • Cortex derived from mesoderm
  • Medulla derived from ectoderm
  • One on top of each kidney
  • 3 x 3 x 1 cm in size and weighs 5 grams
  • Cortex produces 3 different types of hormones
    from 3 zones of cortex mineralcorticoids
    (aldosterone), glucocorticoids (cortisol)
    androgens
  • Medulla produces epinephrine norepinephrine

30
AdrenalGland
  • Cortex
  • 3 zones
  • Medulla

31
Mineralocorticoids
  • 95 of these hormones - aldosterone
  • Functions
  • increase reabsorption of Na with Cl- ,
    bicarbonate and water following it
  • promotes excretion of K and H
  • dehydration, hemorrhage (decrease in blood
    volume) - decreases blood pressure - secretion of
    renin from kidneys which stimulates angiotensin
    II release from lungs - stimulates aldosterone
    release from adrenal cortex - increases water
    uptake from kidneys and increased excretion of K
    into urine

32
Glucocorticoids
  • 95 of hormonal activity is due to cortisol
  • neurosecretory cells secrete corticotropin-releasi
    ng hormone (CRH)
  • CRH promotes the release of ACTH where it
    stimulates the adrenal cortex to secrete corticol
  • Functions helps regulate metabolism
  • increases rate of protein synthesis
  • increases conversion of amino acids to glucose
    energy for protein synthesis
  • stimulates lipolysis for glucose synthesis (for
    energy)
  • increases glucose synthesis ATP production
    provides resistance to stress by making nutrients
    available for ATP
  • raises BP by vasoconstriction (decreases blood
    loss)
  • anti-inflammatory effects reduced (skin cream)
  • reduces release of histamine from mast cells
  • decreases capillary permeability
  • depresses phagocytosis

33
Androgens
  • Small amount of male hormone produced by the zona
    reticularis
  • insignificant in males
  • may contribute to sex drive in females
  • is converted to estrogen in postmenopausal females

34
Adrenal Medulla
  • hormone producing cells Chromaffin cells
    receive direct innervation from sympathetic
    nervous system
  • Produce epinephrine norepinephrine
  • Hormones are sympathomimetic
  • effects mimic those produced by sympathetic NS
  • cause fight-flight behavior
  • sympathetic preganglionic neurons secrete
    acetylcholine - which stimulates secretion by
    the AM

35
Posterior Pituitary Gland (Neurohypophysis)
  • Does not synthesize hormones
  • Consists of axon terminals of hypothalamic
    neurons
  • Neurons release two neurotransmitters that enter
    capillaries
  • antidiuretic hormone
  • oxytocin

36
Oxytocin
  • Two target tissues both involved in
    neuroendocrine reflexes
  • During delivery
  • babys head stretches cervix
  • hormone release enhances uterine muscle
    contraction
  • baby placenta are delivered
  • After delivery
  • suckling hearing babys cry stimulates milk
    ejection
  • hormone causes muscle contraction milk ejection

37
Antidiuretic Hormone (ADH)
  • Known as vasopressin
  • Functions
  • decrease urine production
  • decrease sweating
  • increase BP
  • Dehydration
  • ADH released
  • Overhydration
  • ADH inhibited

38
Pancreas
  • Organ (5 inches) consists of head, body tail
  • Cells (99) in acini produce digestive enzymes
  • Endocrine cells in pancreatic islets produce
    hormones
  • Exocrine acinar cells surround a small duct
    digestive enzymes

39
  • Endocrine cells secrete near a capillary
  • 1 to 2 million pancreatic islets
  • Contains 4 types of endocrine cells
  • Alpha cells (20) produce glucagon
  • Beta cells (70) produce insulin
  • Delta cells (5) produce somatostatin
  • F cells produce pancreatic polypeptide

40
Regulation of Glucagon Insulin Secretion
  • Low blood glucose stimulates release of glucagon
  • High blood glucose stimulates secretion of insulin

41
Pineal Gland
  • Melatonin secretion produces sleepiness - occurs
    during darkness due to lack of stimulation from
    sympathetic ganglion
  • Small gland attached to 3rd ventricle of brain
  • Consists of pinealocytes neuroglia
  • Melatonin responsible for setting of biological
    clock
  • Jet lag SAD treatment is bright light
  • light strikes retina and stimulates
  • suprachiasmatic region of
  • hypothalamus
  • stimulates sympathetic ganglion
  • which then stimulates the
  • pineal gland
  • light -gt NE -gt no melatonin
  • dark -gt lack of NE -gt melatonin

42
Thymus Gland
  • Important role in maturation of T cells
  • Hormones produced by gland promote the
    proliferation maturation of T cells
  • thymosin
  • thymic humoral factor
  • thymic factor
  • thymopoietin

43
Eicosanoids
  • Local hormones released by all body cells
    normally and upon trauma
  • synthesized from arachidonic acid (fatty acid)
  • Leukotrienes influence WBCs inflammation
    allergic response
  • Prostaglandins alter
  • smooth muscle contraction, glandular secretion,
    blood flow, platelet function, nerve
    transmission, metabolism etc.
  • Ibuprofen other nonsteroidal anti-inflammatory
    drugs treat pain, fever inflammation by
    inhibiting prostaglandin synthesis
  • PGs are synthesized by an enzyme complex
    containing the enzymes COX1 and COX2
  • Aspirin and ibuprofen can inhibit activity of
    COX1 isoform short term anti-inflammatory
  • Vioxx, Bextra and Celebrex inhibit activity of
    COX2 isoform long term anti-inflammatory

44
Pituitary Gland Disorders
  • Hyposecretion during childhood pituitary
    dwarfism (proportional, childlike body)
  • Hypersecretion during childhood giantism
  • very tall, normal proportions
  • Hypersecretion as adult acromegaly
  • growth of hands, feet, facial features
    thickening of skin

Thyroid Gland Disorders
  • Hyposecretion of TSH during infancy results in
    dwarfism retardation called cretinism
  • Hypothyroidism - undersecretion of T3 and T4
  • Caused by low production of TSH
  • in adults produces sensitivity to cold, low body
    temp. weight gain mental dullness
  • Hyperthyroidism oversecretion of T3 and T4
    (Graves disease)
  • caused by the inability of the thyroid to respond
    to TSH levels
  • weight loss, cardiac complications, increased
    fluid behind the eyes goiter enlarged thyroid

45
Cushings Syndrome
  • Hypersecretion of glucocorticoids
  • Redistribution of fat, spindly arms legs due to
    muscle loss
  • Wound healing is poor, bruise easily

Addisons disease
  • Hyposecretion of glucocorticoids
  • hypoglycemia, muscle weakness, low BP,
    dehydration due to decreased Na in blood
  • mimics skin darkening effects of MSH
  • potential cardiac arrest

46
Diabetes Mellitus Hyperinsulinism
  • Diabetes mellitus marked by hyperglycemia
  • excessive urine production (polyuria)
  • excessive thirst (polydipsia)
  • excessive eating (polyphagia)
  • Type I----deficiency of insulin (under 20)
  • Type II---adult onset
  • drug stimulates secretion of insulin by beta
    cells
  • cells may be less sensitive to hormone
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