Download Endocrine System

Endocrine System
Definition
• Endocrine system =
– Ductless glands and tissues that
secrete hormones
– Pituitary, Gonads, Pancreas, etc.
• Exocrine gland =
– Secretes substance through a duct
– Gall bladder, Pancreas, etc.
Endocrine Tissues
•
• Parts of:
– Brain
– Heart
– Gastrointestinal Tract
– Pituitary Gland
– Thyroid Gland
– Thymus
– Ultimobranchial Gland
– Parathyroid Gland
Parts of:
– Adrenal gland
– Kidneys
– Pancreas
– Ovary
– Testes
– Bursa of Fabricius
What is a hormone?
•
•
•
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Chemical messenger
Carried in blood
Produced by an endocrine gland
Exerts a specific effect on target
cells/tissues/organs
• Binds to receptor
Categories of hormones:
• Proteinaceous
– Made of proteins or peptides (amino
acids)
• Steroids
– Made of cholesterol
– Anabolic steroids mimic testosterone
How do hormones work?
Proteinaceous
• Work at cell surface
• Not fat soluble -can’t cross cell membrane
• Bind to receptors on cell membrane that
then activate second messengers
• Second messengers may activate enzymes
in the cell to obtain desired response
• Faster response (minutes) than with steroid,
but doesn’t last as long
How do hormones work?
Steroids
• Are fat soluble -can cross cell membrane
• Bind to receptors in cytoplasm and then enter
nucleus:
– Turn DNA on
– Turn DNA off
– Change mRNA – i.e., increase a certain
enzyme
• Slower response than with proteinaceous, but
last long time
Brain
• Hypothalamic-Hypophyseal Region
– At the base of brain just anterior to the hard
palate of mouth
• Composed of:
– Hypophysis or Pituitary Gland (Master
Gland)
• Adenohypophysis
–Par distalis or Anterior Pituitary
• Neurohypophysis
–pars nervosa or Posterior Pituitary
–median eminence or Hypothalamus
Hypothalamus
Posterior Pituitary
3rd
Ventricle
of brain
pars distalis or
Anterior Pituitary
Brain
• Hypophyseal portal vessels
– Supply anterior pituitary with blood
– Route for neurosecretory nerve terminals in
hypothalamus to ant. pit.
– Route of control of the ant. pit. by the
hypothalamus.
• Releasing Factors from the hypothalamus
travel to the Ant. Pit. by way of these
vessels. They are peptides.
Anterior Pituitary Gland
• Hormones:
– Luteinizing hormone (LH)
– Follicle stimulating hormone (FSH)
– Prolactin
– Growth Hormone
– Adrenocorticotropic hormone
(ACTH)
– Thyroid stimulating hormone
Releasing Factors from Hypothalamus
• Gonadotropin releasing hormone (GnRH) also
called Luteinizing hormone – releasing
hormone (LHRH)
– Causes production of Luteinizing Hormone
(LH) by Ant. Pit.
• LH is a Gonadotropin that causes
ovulation and secretion of testosterone
– Causes production of Follicle Stimulating
Hormone (FSH) by Ant. Pit.
• FSH is a Gonadotropin that causes
ovarian follicle growth and sperm
formation.
Releasing Factors from Hypothalamus
• Thyrotropin – releasing hormone (TRH)
– Causes production of Thyrotropin (TSH) by
Ant. Pit.
• TSH causes thyroid to produce Thyroxin
(T4) that regulates metabolism (increases
O2 use) and growth.
Releasing Factors from the
Hypothalamus
• Prolactin – releasing factor (PRF)
– Causes production of Prolactin by Ant. Pit.
• Prolactin causes broodiness, suppression
of gonad activity, fat deposition
• Causes production of crop milk- pigeons
• Increase secretion from Nasal Salt Gland
• Growth hormone – releasing factor (GRF or
GHRH)
– Causes production of Growth Hormone
(GH) or Somatotropin by the Ant. Pit.
• GH increases bone growth
Growth Hormone
– GH increases bone growth by increasing
growth of epiphyseal plate.
Epiphyseal plate
Epiphysis
– If remove Anterior Pituitary you get:
• 30% decrease in growth in chickens
• Total suppression of growth in mammals.
Releasing Factors from the
Hypothalamus
• Somatostatin (GHIH)
– Decreases production of Growth Hormone
by Ant. Pit.
• Corticotrophin releasing factor (CRF)
– Causes production of adrenal
corticotrophic hormone (ACTH) by Ant. Pit.
• ACTH activates adrenal cortical tissue to
produce Corticosterone– stress control
Posterior Pituitary
Hormones
• Arginine vasotocin (AVT)
• Mesotocin (MT)
• Released from neurosecretory
terminals in posterior pituitary gland
Posterior Pituitary Hormones
• Arginine Vasotocin (AVT)
– Antidiuretic hormone
– Uterine contraction for egg laying
– One amino acid different from mammalian
arginine vasopressin
• Mesotocin (MT)
– Uterine contraction for egg laying?
– One amino acid different from mammalian
oxytocin.
Brain
• Pineal Gland:
– Located at the junction of the 2 cerebral
hemispheres and the cerebellum.
– Produces 2 hormones:
• Serotonin – controls behavioral
rhythms
• Melatonin – sleep and body
temperature rhythms
Pancreas
• 99% of pancreatic tissue is devoted to
synthesis and secretion of digestive enzymes
– 2-3 pancreatic ducts carry these enzymes
into the lumen of the duodenum
• 1-2% of pancreas is endocrine
• Synthesizes 3 hormones involved in
regulating blood sugar and growth
»Insulin
»Glucagon
»Somatostatin
Pancreas
• If remove pancreas:
– In grain eating birds they will become
hypoglycemic and die
– In meat eating birds and non ruminant
mammals they will become hyperglycemic
• Blood glucose levels:
– 80-100 mg/100 ml in mammal
– 180-300 mg/100 ml in birds
Pancreas
• Endocrine pancreas - Islets of
Langerhans
• A or alpha cells glucagon
• B or beta cells  insulin
• Delta cells somatostatin