The Endocrine System: Did you know…

1
The Endocrine System Did you know

• adrenal glands produce the greatest number of
  hormones
• smallest endocrine gland parathyroid
• largest pure endocrine gland thyroid
• endocrine gland proportionately largest at birth
  thymus

2
What are hormones?

• Hormon to excite
• troph to nourish, grow, change
• Chemical messengers
• Target most cells in the body
• Note endocrine system is not continuous
• Endocrine glands produce
• Vs. exocrine glands
• Parenchyma (function) vs. stroma (form)

3
What do they do?

• Alter activity (metabolism) of target cell
• Alter PM permeability or voltage
• Stimulates production of proteins/enzymes
• Activates/deactivates enzymes
• Stimulates mitosis
• Induces secretory activity

4
How does the endocrine sys. compare to the
nervous sys.?

• Slow messages
• Prolonged, continued response
• Via blood
• Can continue to adapt/respond to conditions for
  day or even weeks
• Often general, widespread effects on many organs

5
What are the types of hormones?

• Eicosanoids (paracrines)
• Monoamines
• Steroids
• Peptides

6
What are the types of hormones?

• Eicosanoids (paracrines)
• More localized, lipids
• Not true hormones
• Leukotrines (inflammation)
• Prostaglandins
• Inc. bp, dec. uterine contractions, enhance
  clotting, etc.

7
What are the types of hormones?

• Biogenic amines
• AKA monoamines
• From tyrosine (except melatonin from tryptophan)
• Includes some neurotransmitters
• NE, epinephrine, dopamine (catecholamines)
• NE from SNS, E from adrenal medulla
• Also thyroid hormones (TH)

8
What are the types of hormones?

• Steroids
• From cholesterol lipid sol.
• Sex steroids
• Corticosteroids (cortisol, aldosterone, etc.)
• Passes through PM
• travel to cell via transport protein
• proteins extend half-life
• Bind to DNA receptor in nucleus
• Activates transcription
• 3 binding sites on DNA receptor molecule
• Hormone
• Chromatin acceptor site
• DNA activation site
• lipid-soluble hormone animation

9
What are the types of hormones?

• Peptides
• 3 to 200 aas
• ADH, oxytocin
• All releasing/inhibiting from hypothalamus
• Most from anterior pituitary
• Bind to PM receptor
• Cant pass through PM
• Act through secondary messengers
• peptide hormone activity

10
How do secondary messengers work again?

• cAMP
• Hormone binds to G protein
• Activates adenylate cyclase
• causes cAMP production
• cAMP activates/deactivates kinases
• By contrast T3, T4 (direct cell entry, no
  secondary messenger)
• binds to
• mitochondria
• Stimulates oxidative metabolism
• Ribosomes
• Stimulates translation
• Nucleus
• Stimulates transcription
• Na-K pump controlled this way

11
What are the mechanisms of hormonal action?

• Only cells w/ appropriate receptors respond to
  hormone
• These are target cells
• Receptors on PM, nucleus, mitochondria, other
  organelles

12
What are the mechanisms of hormonal action?

• Receptors
• Specificity
• Saturation
• Amplification
• Up-regulation
• More receptors
• Greater sensitivity
• Oxytocin receptors in late pregnancy
• Down-regulation
• Fewer receptors
• Response to high concentrations
• Adipocytes insulin

13
How do hormones interact with each other?

• Synergistic effects
• Greater than sum
• FSH testosterone adequate sperm production
• Permissive effects
• Hormone enhances targets response to second
  hormone
• Estrogen stimulates up regulation of progesterone
  receptors

• Antagonistic effects
• Opposing actions
• Insulin vs. glucagon
• Estrogen vs. prolactin

14
What is the pituitary gland?

• Hypothalamus secretes releasing/inhibiting
  hormones
• Hypophysis _______________
• No nerve connection to adenohypophysis (anterior
  __________)
• Releasing and inhibiting hormones sent via blood
• hypothalamo-hypophyseal portal system

15
What is the hypothalamus-hypophysis axis?

• Better question
• What IS an axis?
• Lets look at the portal system

16
What is the hypothalamus-hypophysis axis?
17
What is the hypothalamus-hypophysis axis?

• Neurohypophysisnot a true gland (posterior
  _________)
• Mass of axons from hypothalamus
• Hypothalamo-hypophyseal tract
• Hormones stored in neurohypophysis
• Oxytocin
• ADH
• Nerve signal stimulates release

18
Anterior pituitary hormones
19
Anterior pituitary hormones
20
What does the posterior pituitary secrete?

• ADH--antidiuretic hormone
• AKA vasopressin
• Causes vasoconstriction at very high levels
• Inc. water retention (lower urine vol.)
• Prevent dehydration
• Oxytocin
• Stims uterine contractions
• Stims milk secretion after birth
• Nerve system stimulation controls both
• Nursing stimulus
• Osmoreceptors in blood vessels detect inc.
  osmolarity and stim. ADH
• Stretching of baroreceptors inhibits ADH

21
How do negative feedback loops control secretion?

• Products from target organs often inhibit further
  secretion of hormone
• Example
• Dehydration lowers blood volume and pressure
• Osmoreceptors detect
• Stimulates hypothalamus to secrete ADH via
  posterior pituitary
• Blood volume/pressure increases
• Osmoreceptors detect
• Inhibit further ADH release
• Another example thyroid hormone (see p. 645
  (new) (646, old) if youre interested)

22
What are some pituitary disorders?

• In juveniles
• Hyposecretion (hypopituitarism)
• Pituitary dwarfism
• Hypersecretion gigantism
• In adults
• Hypersecretion acromegaly
• Posterior lobe hyposecretion diabetes insipidus
  (which is ___________)
• WHY?

23
What is the pineal gland?

• Roof of third ventricle
• Produces serotonin
• Converted to melatonin
• Possible sexual maturation control
• Prevent early maturation?

24
What is the thymus?

• Location mediastinum
• Involution after puberty (shrinks like pineal)
• Secretes thymopoietin
• Regulates development of T-lymphocytes

25
What is the thyroid?

• Largest endocrine gland
• Wraps around trachea
• Contains
• Sacs thyroid follicles
• Lined with follicular cells which secrete T3 and
  T4
• Increases BMR, HR and heart contraction
• C cells
• Produce calcitonin
• Stores calcium by stimulating osteoblasts,
  inhibiting osteoclasts
• Antagonistic to parathyroid hormone (PTH)
• Regulation via the hypothalamo-hypophyseal-thyroid
  axis

26
What are some thyroid diseases?

• Hyposecretion
• Congenital hypothyroidism
• facial thickening, low body temp, lethargy, brain
  damage
• Adults myxedema
• Low BMR, sluggish, sleepy, weight gain, cold,
  tissue swelling

From http//www.type2hypothyroidism.com/Type1VsTy
pe2.html
27
What is goiter?

• Another thyroid disorder two types
• Endemic goiter dietary deficiency of iodine
• No TH produced so pituitary receives no neg.
  feedback and more more TSH produced
• Results in hypertrophy
• Toxic goiter (Graves disease)
• Autoimmune disease
• Abnormal antibodies mimic TSH, raising TH levels
• Called thyroid-stimulating immunoglobin
• Causes high BMR HR, sleeplessness, weight loss,
  exophthalmos

From http//www.medstudents.com.br/image/endoc/im
gend1.htm
28
What are the parathyroids?

• PTH stims osteoclasts, inhibits osteoblasts
• Calcium released
• Hypoparathyroidism
• If parathyroid removed
• Decreased calcium levels
• tetany and death without HRT
• Hyperparathyroidism
• Bone softening, fragility, deformity
• Renal calculi formation

29
What are the adrenal glands?

• Adrenal medulla
• Sympathetic neurons innervate
• Secrete catecholamines
• Adrenal cortex
• Makes more than 25 corticoids (AKA
  corticosteroids)
• Small amounts of sex steroids (androgen/estrogen)
• Including DHEA (an androgen) which is converted
  to testosterone

30
What are the adrenal glands?

• Mineralcorticoids
• Mostly aldosterone (retain Na, secrete K)
• Glucocorticoids
• Secreted in response to ACTH
• Cortisol (hydrocortisone) is most important
• Stimulate gluconeogenesis (fat and protein
  catabolism)
• Also glycolysis
• Stress response
• Suppresses immune system

31
What are some adrenal disorders?

• Regulated by hypothalamo-hypophyseal-adrenocortico
  axis
• Cushing syndrome
• Via adrenal tumor or ACTH excess
• Hyperglycemia, hypertension, muscular weakness,
  edema, moon face, buffalo hump

32
What are some adrenal disorders?

• Addison disease
• Hyposecretion of glucocorticoids and
  mineralcorticoids
• Hypoglycemia, Na/K imbalance, loss of stress
  resistance, hypotension,
• Via excess ACTH secretion (b/c no neg. feedback)
• Bronzing b.c ACTH stimulates melanin production
• Fatal if not treated with corticoids

From http//www.historyplace.com/specials/portrai
ts/presidents/
33
What does the pancreas secrete?

• Mostly exocrine digestive tissue
• Some endocrine tissue in pancreatic islets
• Islets of Langerhans

34
What does the pancreas secrete?

• These secrete
• Insulin via beta cells
• A peptide hormone
• Stimulates glycogenesis and inhibits
  glycogenolysis and gluconeogenesis
• Recruits glucose transporter proteins (GLUTs)
• Glucagon via alpha cells
• Stimulates gylcogenolysis (glycogen hydrolysis)
• Somatostatin (GHIH) via delta cells
• Paracrine secretion
• Modulates beta and alpha cell secretions

35
What are some pancreatic disorders?

• Hyperinsulinism
• Sometimes pancreatic tumor causes
• Sometimes accidental over-injection
• Causes hypoglycemia, weakness, hunger,
• Hypoglycemia stimulates E, glucagon, GH secretion
• Anxiety, hi HR, sweating
• Insulin shockbrain deprived of glucose
• Disorientation, convulsions, unconsciousness

36
What are some pancreatic disorders?

• Diabetes mellitus (DM)
• Diabetes to syphon or run through
• Mellitus sweet insipidus tasteless
• Hyposecretion or inaction of insulin
• Three signs
• Polyuria (excessive urine output)
• Polydipsia (intense thirst)
• Polyphagia (intense hunger)
• Tests reveal hyperglycemia, glycosuria, ketonuria

From http//www.bbc.co.uk/health/conditions/urina
rytract2.shtml
37
What types of DM can patients have?

• Type Iinsulin-dependent (IDDM)
• 10 of cases
• Autoimmune destruction of beta cells
• AKA juvenile diabetes (age 12)
• Type IInon-insulin dependent (NIDDM)
• Insulin resistance
• Adipocytes secrete resistin?
• Shortage of insulin receptors?
• Heredity, age, obesity
• AKA adult onset (age 40)

38
What do the gonads secrete?

• Exocrine products egg and sperm
• Endocrine products gonadal hormones
• Well cover this more at the end of the semester

39
What is stress and how do we adapt to it?

• Any stimulus that upset homeostasis
• Body copes via stress response (AKA general
  adaptation syndrome, GAS)
• Alarm reaction
• NE from sympathetic, E from adrenals Fight or
  flight

40
What is stress and how do we adapt to it?

• Stage of resistance
• If stress continues, glycogen reserves drop
• Cortisol dominates to provide fuels for
  metabolism
• Long-term cortisol exposure suppresses immune
  system
• Stage of exhaustion
• Fat reserves exhausted, rely on protein
• Body wasting and weakening
• Rapid decline and death heart/kidney failure,
  infection