Study and Master Life Sciences Grade 12 Teacher\'s Book
A full, very detailed summary of the endocrine system and homeostasis, including negative feedback mechanisms. This PDF was compiled in accordance with the 2021 IEB sags document.
Includes diagrams in colour and textbook definitions.
Topic 7 – Responding to the environment: the human endocrine system
Unit 1 – the endocrine system
Endocrine system: system made up of glands that produce and secrete hormones directly into
the bloodstream
Secrete: to release or give off
Gland: group of cells that are specialised to produce and secrete a specific chemical substance
Endocrine gland: a ductless that secretes its hormone directly into the bloodstream
Exocrine gland: gland that secretes its hormone into a duct
Hormone: chemical substance that is produced and secreted in very small amounts into the
bloodstream by the endocrine glands
Target organ: organ that responds to a hormone secreted by an endocrine gland
The endocrine system is made up of glands that produce and secrete hormones directly into the
blood.
• Role: to control and coordinate the life processes in the body in response to changes in the
internal and external environments in such a way that a constant internal environment is
maintained (homeostasis)
• Controls and coordinates the body’s life processes, including growth, development,
metabolism and osmoregulation.
A gland is a group of cells that is specialised to produce and secrete a specific chemical substance
such as a specific hormone.
• Two types of glands: endocrine glands and exocrine glands
• Endocrine glands secrete hormones directly into the blood. Examples of endocrine glands
are the pituitary gland and the thyroid gland.
• Exocrine glands secrete the chemical substance they produce into a duct which carries it to
where it was needed. Examples: digestive glands, salivary glands and sweat glands.
Hormones are secreted in very small amounts into the bloodstream by endocrine glands.
• They act as chemical messengers.
• They transfer information from one set of body cells to another set of body cells in order to
coordinate the functions of different parts of the body.
,Endocrine glands
• Hypothalamus
• The pituitary gland
• The thyroid gland
• The pancreas
• The adrenal gland
• The gonads
Hypothalamus
Hypothalamus: part of the brain that acts an endocrine gland secreting hormone that either
stimulate or suppress the release of hormones by the pituitary gland
Antidiuretic hormone (ADH): hormone produced by the hypothalamus which is stored in the
pituitary gland, allows more water to be re-absorbed into the blood from the kidneys,
reducing the volume of water lost in urine.
The hypothalamus is a part of the brain. It is located below the cerebrum. The hypothalamus is part
of the CNS and endocrine system and links the two systems together.
• CNS: It activates and controls the autonomic nervous system.
• Endocrine system: produces hormones that either stimulate or inhibit the release of
hormones from the pituitary gland.
, • The hypothalamus produces ADH. ADH moves to the pituitary gland via blood vessels that
connect two glands. The pituitary gland stores ADH and secretes the ADH when needed.
• ADH helps regulate the balance of water and salts in the body --> osmoregulation
• ADH increases the permeability of walls of the nephrons in the kidneys which allows more
water to be re-absorbed into the blood.
Pituitary gland
Pituitary gland: endocrine gland at the base of the brain; known as the master gland because it
produces hormones that regulate the secretion of other hormones.
Growth hormone (GH): hormone secreted by the pituitary gland; stimulates protein synthesis,
growth of muscles and bones and the breakdown of fat for energy
Thyroid stimulating hormone (TSH): hormone secreted by the pituitary gland; stimulates the
thyroid gland to secrete thyroxine
Follicle stimulating hormone (FSH): hormone secreted by the pituitary gland; stimulates the
development of follicles in the ovaries and the production of sperm in the testes
Luteinising hormone (LH): hormone secreted by the pituitary gland; in females it causes the
follicle to mature into the corpus luteum and stimulates the secretion of oestrogen and
progesterone; in males it stimulates the secretion of testosterone
Prolactin: hormone secreted by the pituitary gland; stimulates the production of breast milk in
females.
This gland is a pea-sized gland located at the base of the brain. It is linked to the hypothalamus by a
thin stalk. It consists of 2 lobes: anterior in the front and posterior in the back. The anterior lobe is
controlled by hormones from the hypothalamus. The posterior lobe is controlled by nerve impulses
from the hypothalamus.
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