14- Hormonal Communication
14.1 Hormonal system and glands:
The Endocrine system is the use of hormones to send information about changes in the body and
elicit a response.
Endocrine glands are a group of specialised cells which secrete a hormone directly into the
bloodstream.
The Hypothalamus-Pituitary axis:
Neural input -> hypothalamus -> pituitary -> hormonal response
Glands:
Pituitary- produces growth hormone which controls growth of
bones and muscles, ADH which increases reabsorption of water
in kidneys, gonadoptrophins which control development of
ovaries and testes.
Thyroid- produces thyroxine which controls metabolism rate
and rate that glucose is used up in respiration, and promotes
growth
Adrenal- produces adrenaline which increases heart rate and breathing rate and raises blood
sugar level.
Testis- produces testosterone which controls sperm production and secondary sexual
characteristics
Pineal- produces melatonin which a ects reproductive development and daily cycles
Thymus- produces thymosin which promotes production and maturation of white blood cells
Pancreas- produces insulin which converts excess glucose into glycogen in the liver, and
glucagon which converts glycogen back to glucose in the liver.
Ovary- produces oestrogen which controls ovulation and secondary sexual characteristic, and
progesterone, which prepares uterus lining for embryo
Hormones are secreted into the blood stream and bind to receptors found on/in target cells.
Lipophilic- lipid soluble. Di uses through membrane, binds with receptor in cytoplasm, complex
enters nucleus and triggers transcription, mRNA translated into proteins that alter cell activity
Hydrophilic- water soluble. Cannot di use through membrane, binds to membrane receptors,
activate a G protein which activates adenylyl cyclase, which catalyses the conversion of ATP to
cAMP which activates protein kinases. These phosphorylate proteins in the cytoplasm activating
them and allowing them to alter cell activity. e.g. TSH, LH, FSH
Categories of hormones:
1) glucocorticoids- cortisol which regulates the metabolism and blood pressure and immune
response.
2) mineral corticoids- act on mineral balance. Aldosterone controls blood pressure through an
anti-diuretic a ect. Controlled by kidneys.
3) Androgens- small amounts of sex hormones which will have little e ect except after
menopause or due to disease.
Adrenal medulla- links neural and endocrine pathways, controlled by sympathetic nervous
system. Rapid actions and responses. Produces adrenaline (heart rate, glucose) and
noradrenaline (pupils, air passages in lungs, narrowing of blood vessels in non-essential organs)
14.2 The pancreas
Endocrine and exocrine roles.
Exocrine- secretion of digestive enzymes into the duodenum through network of ducts. e.g.
amylase, lipase, protease
Endocrine- secretion of hormones into bloodstream via portal vein, e.g. insulin, glucagon. Islets
of langerhans, made up of alpha and beta cells
Alpha cells produce and secrete glucagon, beta cells produce and secrete insulin.
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14.1 Hormonal system and glands:
The Endocrine system is the use of hormones to send information about changes in the body and
elicit a response.
Endocrine glands are a group of specialised cells which secrete a hormone directly into the
bloodstream.
The Hypothalamus-Pituitary axis:
Neural input -> hypothalamus -> pituitary -> hormonal response
Glands:
Pituitary- produces growth hormone which controls growth of
bones and muscles, ADH which increases reabsorption of water
in kidneys, gonadoptrophins which control development of
ovaries and testes.
Thyroid- produces thyroxine which controls metabolism rate
and rate that glucose is used up in respiration, and promotes
growth
Adrenal- produces adrenaline which increases heart rate and breathing rate and raises blood
sugar level.
Testis- produces testosterone which controls sperm production and secondary sexual
characteristics
Pineal- produces melatonin which a ects reproductive development and daily cycles
Thymus- produces thymosin which promotes production and maturation of white blood cells
Pancreas- produces insulin which converts excess glucose into glycogen in the liver, and
glucagon which converts glycogen back to glucose in the liver.
Ovary- produces oestrogen which controls ovulation and secondary sexual characteristic, and
progesterone, which prepares uterus lining for embryo
Hormones are secreted into the blood stream and bind to receptors found on/in target cells.
Lipophilic- lipid soluble. Di uses through membrane, binds with receptor in cytoplasm, complex
enters nucleus and triggers transcription, mRNA translated into proteins that alter cell activity
Hydrophilic- water soluble. Cannot di use through membrane, binds to membrane receptors,
activate a G protein which activates adenylyl cyclase, which catalyses the conversion of ATP to
cAMP which activates protein kinases. These phosphorylate proteins in the cytoplasm activating
them and allowing them to alter cell activity. e.g. TSH, LH, FSH
Categories of hormones:
1) glucocorticoids- cortisol which regulates the metabolism and blood pressure and immune
response.
2) mineral corticoids- act on mineral balance. Aldosterone controls blood pressure through an
anti-diuretic a ect. Controlled by kidneys.
3) Androgens- small amounts of sex hormones which will have little e ect except after
menopause or due to disease.
Adrenal medulla- links neural and endocrine pathways, controlled by sympathetic nervous
system. Rapid actions and responses. Produces adrenaline (heart rate, glucose) and
noradrenaline (pupils, air passages in lungs, narrowing of blood vessels in non-essential organs)
14.2 The pancreas
Endocrine and exocrine roles.
Exocrine- secretion of digestive enzymes into the duodenum through network of ducts. e.g.
amylase, lipase, protease
Endocrine- secretion of hormones into bloodstream via portal vein, e.g. insulin, glucagon. Islets
of langerhans, made up of alpha and beta cells
Alpha cells produce and secrete glucagon, beta cells produce and secrete insulin.
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