hormonal communication Flashcards
What are endocrine glands?
Group of specialised cells which
secrete hormones
• Hormones are secreted directly
into the bloodstream
List the major endocrine
glands in the body
- Pituitary gland
- Thyroid gland
- Adrenal gland
- Pineal gland
- Thymus
- Pancreas
- Testes
- Ovaries
What does the pituitary gland
produce?
• Growth hormone, which controls growth of bones and muscles • Anti-diuretic hormone, which increases reabsorption of water in the kidneys • Gonadotrophins, which control development of ovaries and testes
What is the purpose of the
pituitary gland?
It makes several hormones which in turn control the release of other hormones • The close proximity of the pituitary gland to the hypothalamus ensures that the nervous and hormonal responses the body are closely linked and coordinated
What does the thyroid gland
produce?
Thyroxine which controls rate of
metabolism and rate that glucose is
used up in respiration, and promotes
growth
What does the adrenal gland
produce?
Adrenaline which increases heart
and breathing rate and raises blood
sugar level
What does the pineal gland
produce?
Melatonin which affects reproductive
development and daily cycles
What does the thymus
produce?
Thymosin which promotes
production and maturation of white
blood cells
What does the pancreas
produce?
• Insulin which converts excess glucose into glycogen in the liver • Glucagon which converts glycogen back into glucose in the live
What do the testes produce?
Testosterone which controls sperm
production and secondary sexual
characteristics
What do the ovaries produce?
Oestrogen which controls ovulation and secondary sexual characteristics • Progesterone which prepares the uterus lining for receiving an embryo
What do exocrine glands do?
• e.g. those in the digestive system
• Secrete chemicals through ducts
into organs or to the surface of the
body
Why are hormones referred to
as chemical messengers?
They carry information from one part of the body to another • Steroids, proteins, glycoproteins, polypeptides, amines, or tyrosine derivatives
When are hormones secreted?
Hormones are secreted directly into the blood when a gland is stimulated • Can occur as a result of a change in concentration of a particular substance • Can also occur as the result of another hormone or a nerve impulse
What happens after hormones
have been secreted?
They are transported in the blood plasma all over the body • The hormones diffuse out of the blood and bind to specific receptors for that hormone, found on the membranes or in the cytoplasm of cells in the target organs • Once bound to their receptors, the hormones stimulate the target cells to produce a response
Describe steroid hormones
• Lipid-soluble • Pass through the lipid component of the cell membrane and bind to steroid hormone receptors to form a hormone-receptor complex • Receptors may be present in the cytoplasm or the nucleus • The hormone-receptor complex formed acts as a transcription factor which in turn facilitates or inhibits the transcription of a specific gene • Oestrogen is an example of a hormone which works in this way
Describe non-steroid
hormones
• Hydrophilic so cannot pass directly though the cell membrane • Bind to specific receptors on the cell surface membrane of the target cell • This triggers a cascade reaction mediated by chemicals called second messengers • Adrenaline is an example of a hormone which works in this way
Summarise the main
differences between the
actions of the normal and
nervous systems:
What are the adrenal glands?
• 2 small glands that measure approximately 3cm in height and 5cm in length • Located on top of each kidney and are made up of two distinct parts surrounded by a capsule
Describe the parts of the
adrenal glands
• The adrenal cortex: The outer region of the glands. This produces hormones that are vital to life, e.g. cortisol and aldosterone • The adrenal medulla: The inner region of the glands. This produces non-essential hormones, e.g. adrenaline which helps the body react to stress
What are the 3 main types of
hormone produced by the
adrenal cortex?
• Glucocorticoids (release of these hormones is controlled by the hypothalamus) • Mineralocorticoids • Androgens
Describe glucocorticoids
Cortisol: • Helps regulate metabolism by controlling how the body converts fats, proteins and carbohydrates into energy • Helps regulate blood pressure and cardiovascular function in response to stress Corticosterone: • Works with cortisol to regulate immune response and suppress inflammatory reactions
Describe mineralocorticoids
Aldosterone: • Helps control blood pressure by maintaining balance between salt and water concentration in the blood and body fluids • Its release is mediated by signals triggered by the kidney
Describe androgens
• Small amounts of male and female sex hormones are released • Their impact is relatively small compared with the larger amount of hormones e.f. oestrogen and testosterone released by the ovaries or testes after puberty • Still important, especially in women after menopause
Describe the hormones
secreted by the adrenal
medulla
Adrenaline: • Increases the heart rate sending blood quickly to the muscles and brain • Rapidly raises blood glucose concentration by converting glycogen to glucose in the liver Noradrenaline: • Works with adrenaline in response to stress, producing effects e.g. increased heart rate, widening of pupils, widening of air passages in the lungs, and the narrowing of blood vessels in the non-essential organs (resulting in higher blood pressure)
How is insulin secreted?
1. At normal blood glucose concentration levels, potassium channels in the plasma membranes of beta cells are open and potassium ions diffuse out of the cell. The inside of the cell is at a potential of -70mV with respect to the outside of the cell 2. When blood glucose concentration rises, glucose enters the cell by a glucose transporter 3. The glucose is metabolised inside the mitochondria, resulting in the production of ATP 4. The ATP binds to the potassium channels and causes them to close. They are known as ATPsensitive potassium channels 5. As potassium ions can no longer diffuse out of the cells, the potential difference reduces to around -30mV, and depolarisation occurs 6. Depolarisation causes the voltage-gated calcium ion canals to open 7. Calcium ions enter the cell and cause secretory vesicles to release the insulin they contain by exocytosis
Describe the action of
adrenaline on liver cells
1. When adrenaline binds to its receptor, the enzyme adenylyl cyclase (also present int he cell membrane) is activated 2. Adenylyl cyclase triggers the conversion of ATP into cyclic adenosine mono-phosphate (cAMP) on the inner surface of the cell membrane in the cytoplasm 3. The increase in cAMP levels activates specific enzymes called protein kinases which phosphorylate and activate other enzymes that trigger the conversion of glycogen into glucos
Why is this model of hormone
action known as the second
messenger model?
• The hormone (adrenaline) is the first messenger • cAMP is the second messenger • One hormone molecule can cause many cAMP molecules to be formed • At each stage, number of molecules involved increases, so the process is said to have a cascade effect
