Docstoc

NERVOUS SYSTEM

Document Sample
NERVOUS SYSTEM Powered By Docstoc
					ENDOCRINE
 SYSTEM
     ENDOCRINE SYSTEM
       COMPONENTS
• Endocrine organs with endocrine glands –
  thyroid, pineal etc
• Endocrine glands – ductless - produce
  hormones
• Hormones – 1. chemical messengers
  secreted into the bloodstream 2. stimulate
  response in target tissues or organs
• Target cells - have receptors for hormones
Endocrine Organs
  ENDOCRINE vs. EXOCRINE
        GLANDS
• Exocrine glands
  – ducts carry secretion to body surface or other
    organ cavity
  – affect extracellular activities - e.g. food
    digestion
• Endocrine glands
  – ductless, release hormones into bloodstream
  – intracellular effects, alter target cell
    metabolism
  ENDOCRINE SYSTEM

• Works with nervous system to
  maintain:
1. Integration
2. Control
   NERVOUS vs. ENDOCRINE SYSTEM

• Means of communication
   – nervous system has both electrical and chemical methods
   – endocrine system has only chemical methods
• Speed and persistence of response
   – nervous system reacts quickly (1 - 10 msec) and stops quickly
   – endocrine system usually reacts slowly
• Adaptation to long-term stimuli
   – nervous system adapts quickly and response declines
   – endocrine system has more persistent responses
• Area of effect
   – nervous system effects are specific (one organ)
   – endocrine system may have effects on many organs
                   NOTES
• Several chemicals function as both hormones and
  neurotransmitters – e.g. norepinephrine, dopamine and
  antidiuretic hormone
• Some hormones are secreted by nerve cells or neurons
  (neuroendocrine cells)
   – oxytocin and catecholamines
• Nervous & endocrine systems have overlapping effects
  on the same target cells
• Nervous & endocrine systems regulate each other
   – neurons trigger hormone secretion
   – hormones stimulate or inhibit neurons
  HYPOTHALAMUS
• Forms floor and walls of the
  third ventricle of brain
• Regulates many functions
• Produces hormones secreted by
  the pituitary gland
PITUITARY GLAND
• Suspended from hypothalamus by
  stalk (infundibulum)
• Located in sella turcica of
  sphenoid bone
• Controls other endocrine glands
Pituitary Gland Anatomy
       ANTERIOR PITUITARY
           HORMONES
• Tropic hormones target other endocrine glands
1. Gonadotropins target gonads
    a) FSH (follicle stimulating hormone)
    b) LH (luteinizing hormone)
2. TSH (thyroid stimulating hormone)
3. ACTH (adrenocorticotropic hormone)
4. Prolactin (PRL)
5. Growth hormone (GH)
    Anterior Pituitary Hormones




• Principle hormones and target organs are shown
• Axes show how endocrine glands interact
      POSTERIOR PITUITARY
          HORMONES
1. Oxytocin (OT)
2. Antidiuretic hormone (ADH)
• Oxytocin and ADH are produced in
   the hypothalamus and transported
   down to the posterior pituitary lobe by
   the hypothalamo-hypophyseal tract
CONTROL OF PITUITARY GLAND

• Releasing and inhibiting hormones of the
  hypothalamus control the anterior pituitary lobe
• Posterior lobe hormones release in response to
  nervous system signals - neuroendocrine reflexes
     • suckling infant stimulates nerve endings 
       hypothalamus  posterior lobe  oxytocin  milk
       ejection
  – hormone release in response to higher brain centers
     • milk ejection reflex can be triggered by a baby's cry
   Control of Pituitary:
Feedback from Target Organs
                • Negative feedback
                  –  target organ
                    hormone levels
                    inhibits release of
                    tropic hormones
                • Positive feedback
                  – stretching of uterus
                     OT release, causes
                    stretching of uterus
                     OT release,
                    until delivery
              PINEAL GLAND
• Greatest secretion occurs in 1-5 yr. olds
• Secretion is 75% lower by puberty
• Produces serotonin by day, converts it to melatonin at
  night
• May regulate timing of puberty in humans
• Melatonin causes depression, sleepiness, irritability and
  carbohydrate craving




              Pineal gland
                      THYMUS
• Located in mediastinum, superior to heart
• Secretes hormones that regulate development and later
  activation of T-lymphocytes
   – thymopoietin and thymosins
    THYROID GLAND
• Filled with colloid and lined with simple
  cuboidal epithelial (follicular) cells that
  secrete 2 thyroid hormones (T3+T4 )
• C cells (calcitonin or parafollicular cells)
– produce calcitonin that  blood Ca+2,
  promotes Ca+2 deposition and bone
  formation especially in children
    PARATHYROID GLANDS
• Secrete parathyroid hormone
  –  blood Ca+2 levels
  – promotes synthesis of
    calcitriol
     •  absorption of Ca+2
     •  urinary excretion
     •  bone resorption
Adrenal Gland
         ADRENAL MEDULLA
• Sympathetic ganglion innervated by sympathetic
  preganglionic fibers
   – consists of modified neurons called chromaffin cells
   – stimulation causes release of (nor-)epinephrine
• Hormonal effect is long-lasting
   – increases BP and heart rate
   – increases blood flow to skeletal muscle
   – increases pulmonary air flow
   – decreases digestion and urine formation
   – stimulates gluconeogenesis and glycogenolysis
• Stress causes medullary cells to stimulate the cortex
        ADRENAL CORTEX
• Releases corticosteroids
  – mineralocorticoids - control electrolyte
    balance, aldosterone promotes Na+ retention
    and K + excretion
  – glucocorticoids - especially cortisol,
    stimulates fat + protein catabolism,
    gluconeogenesis and release of fatty acids
    and glucose into blood
  – sex steroids - androgen and estrogen
         PANCREATIC ISLET
• Insulin released from beta () cells
  – secreted after meal with carbohydrates raises glucose
    blood levels
  – stimulates glucose and amino acid uptake
  – nutrient storage effect (stimulates glycogen, fat and
    protein synthesis
  – antagonizes glucagon
           PANCREATIC ISLET
• Glucagon released from alpha () cells
   – secreted in very low carbohydrate and high protein diet or
     fasting - stimulates glycogenolysis, fat catabolism, and
     promotes absorption of amino acids for gluconeogenesis
• Somatostatin released from delta () cells)
   – secreted with rise in blood glucose and amino acids after a
     meal - paracrine secretion = modulates secretion of  +  cells
• Hyperglycemic hormones raise blood glucose
   – glucagon, epinephrine, norepinephrine, cortisol &
     corticosterone
• Hypoglycemic hormones lower blood glucose
   – insulin
        Histology of Ovary




Follicles = egg surrounded by granulosa cells
                     OVARY
•  Granulosa cells in wall of ovarian follicle produce
   estradiol
• Corpus luteum: follicle after ovulation produces
   estradiol and progesterone for 12 days or 8-12
   weeks during pregnancy
• Estradiol and progesterone:
1. promote development of female reproductive system
   and physique including bone growth
2. regulate menstrual cycle, sustain pregnancy
3. prepare mammary glands for lactation
• Inhibin release suppresses FSH secretion
      Histology of Testis




Seminiferous tubules produce sperm.
                   TESTES
• Interstitial cells (between seminiferous tubules)
   – produce testosterone and estrogen that:
   1. promote development of male reproductive
     system and physique
   2. sustains sperm production and sex drive
• Sustentacular sertoli cells
   – secrete inhibin that suppresses FSH secretion
     and stabilizes sperm production rates
      TYPES OF HORMONES
• Steroids
  – derived from cholesterol
     • sex steroids, corticosteroids
• Monoamines
  – derived from amino acids
     • catecholamines (norepinephrine, epinephrine, dopamine)
       and thyroid hormones
• Peptides and glycoproteins
  – all releasing and inhibiting hormones of the
    hypothalamus & most anterior pituitary hormones
 HORMONE INTERACTIONS
• Synergistic effects - hormones work together -
  the overall effect that is greater than the sum of
  separate effects e.g. FSH & testosterone during
  sperm production
• Permissive effects - one hormone enhances
  response to a second hormone e.g. estrogen
  stimulates the regulation by progesterone
• Antagonistic effects - one hormone opposes the
  action of another e.g. insulin lowers blood
  glucose level and glucagon raises it
 PARACRINE SECRETIONS
• Chemical messengers that diffuse short
  distances and stimulate nearby cells
   – unlike neurotransmitters not
     produced in neurons
   – unlike hormones not transported in
     blood
                  DISORDERS
• Hypersecretion of growth hormones
  – acromegaly
  – thickening of the bones and soft tissues
  – problems in childhood or adolescence
     • gigantism if oversecretion
     • dwarfism if hyposecretion
THYROID GLAND DISORDERS
• Congenital hypothyroidism ( TH)
• Myxedema (adult hypothyroidism,  TH)
• Endemic goiter (goiter = enlarged thyroid
  gland)
   – dietary iodine deficiency, no TH, no -
     feedback,  TSH
• Toxic goiter (Graves disease)
   – antibodies mimic TSH, TH
Endemic Goiter
                Adrenal Disorders
• Cushing syndrome - due to excess cortical
  secretion
   – causes hyperglycemia, hypertension,
     weakness, edema
   – muscle and bone loss occurs with protein
     catabolism
   – buffalo hump & moon face = fat
     deposition between shoulders or in face
• Adrenogenital syndrome (AGS)
   – adrenal androgen hypersecretion
     accompanies Cushing
   – causes enlargement of external sexual organs
     in children & early onset of puberty
   – masculinizing effects on women (deeper voice
     & beard growth)

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:7/16/2012
language:English
pages:35