Download IB BIO endocrine system

IB BIOLOGY
ENDOCRINE SYSTEM
The endocrine glands are also known as ductless glands.
They secrete certain chemical substances which guide and
control the various metabolic activities, the growth and
differentiation of various systems and thereby bringing
about a correct physiological balance between them. Such
substances are also referred to as chemical co-ordinators.
Differences between exocrine and endocrine glands.
1) Exocrine glands-: The secretion of these glands are
carried away from them to the site of action by special
ducts. For example The Salivary glands are exocrine
gland . The saliva is carried from them to the mouth by
a duct.
The liver is also an exocrine gland as the bile
manufactured is carried away by bile duct.
2) Endocrine glands:- The secretions of these glands are
not carried away by any duct at all. Instead, they get
mixed in the blood stream directly and are carried away
to all the parts of the body via the blood. Pituitary and
Adrenal glands are good examples . They
manufacture hormones that are spread through the
body by the blood.
Characterisitics of hormones:
1. Hormones themselves do not create biochemical
processes, but it modifies the existing metabolic
processes and change the rate of action.
2. Hormones are secreted in response to specific
stimuli.
3. hormones can be secreted independently of one
another.
4. Hormones have a high degree of target specificity.
5. hormones are believed to be catalytic in their
effects.
The pituitary gland :
It is the chief center of the endocrine system. It forms an
important link between the nervous and endocrine
system. It controls other endocrine glands.
It is located at the base of the brain and connected by
the hypothalamus to the brain.
Hormones secreted by anterior lobe of the brain:
1. Growth hormone.
2. thyroid stimulating hormone (TSH)
3. Adrenocortico trophic hormone (ACTH)
4. Follicle stimulating Hormone (FSH)
5. Interstitial cell stimulating hormone or Luteinizing
hormone (ICSH or LH)
6. Prolactin or Luteotrophic hormone
Hormones secreted by the posterior lobe:
1. Antidiuretic hormone (ADH) or Vasopressin.
2. Oxytocin.
Thyroid gland:
It consists of pair of lobes which lie on either side of the
larynx in the neck region.
Functions of thyroid:
1. It stimulates the normal growth and development,
particularly that of skeletal and nervous system.
2. It controls the rate of cellular oxidation and basic
metabolic activities.
Basal metabolic rate: It is defined as the amount of
heat produced in the body in a given time in complete
state of physical and mental rest at room
temperature.
Hypothyroidism can cause cretinism in children ,
myxedema in adult.
Goitre is caused due to iodine deficiency.
Hyperthyroidism causes Grave’s disease or
Exophthalmic goiter.
Adrenal gland :
Adrenal cortex: Aldosterone – promote the resorption of
sodium ions from the renal glomerular filtrate, and plays an
important role in stress tolerance.
Cortisone stimulates the production of glucose from non
carbohydrate sources such as fats and aminoacids.
Also acts as an anti-inflammatory agent.
Adrenal medulla secretes adrenalin.
Prepares you for emergency situations
Testes – secrete male hormone testosterone.
Ovaries secrete female hormones estrogen, progesterone.
Islets of Langerhans:
)
Alpha cells secrete- glucagons.
Beta cells secrete –insulin
Delta cells secrete –somatostatin (they work to reduce the
rate at which food is absorbed from the contents of the
intestine)