2. Chemical messengers Flashcards
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What is the primary concern of the endocrine system?
Keeping the internal environment of the body constant
What are the two types of glands in the body?
Endocrine and exocrine glands
What are some characteristics of exocrine glands?
- Secrete into a duct that carries the secretion to the body surface or cavity
- sweat glands, mucous glands, salivary glands and glands of the alimentary canal
What are some characteristics of endocrine glands?
- Secrete hormones into the extracellular fluid that surrounds the cells that make up the gland
- Secretion passes into the capillaries to be transported by the blood
- Ductless glands
- Hypothalamus, pituitary gland, pineal gland, thyroid gland, pancreas, adrenal glands, thymus, ovaries/testes
What is a hormone?
A protein, steroid or amine, that is transported in the blood which may affect all the cells of the body, or only target cells/organs
Can hormones become saturated?
Yes, once all receptor molecules are occupied by hormone molecules, the addition of more hormones does not produce a greater effect
What are paracrines (local hormones?
They are used for cells in the same tissue to communicate with each other.
They are chemicals that diffuse to adjacent cells, moving through the extracellular fluid
How do protein and amine hormones work?
They work by attaching to receptor proteins in the membrane of the target cells
The combination of hormone and receptor causes a secondary messenger substance to diffuse through the cell and activate particular enzymes
eg. protein insulin binds to a receptor protein, leading to an increase in glucose absorption by the cell
How do steroid hormones work?
They work by entering target cells and combining with a receptor protein inside the cells
The receptor may be in the mitochondria, on other organelles, or in the nucleus
hormone receptor complex activates the genes controlling the formation of particular proteins
How do enzymes exert their influence by changing the activity or concentration of enzymes?
- Activate certain genes in the nucleus so that a particular enzyme or structural protein is produced
- change the shape or structure of an enzyme to turn it on or off
- Change the rate of production of an enzyme or structural protein by changing the rate of transcription and translation during protein production
What is enzyme amplification?
the process where one hormone molecule has the ability to cause the manufacture or activation of thousands of enzyme molecules.
What is hormone clearance?
After the hormone produced has had its desired effect, hormone molecules are broken down
Some are broken down in the target cells, but most are broken down in the kidneys and liver
How are degraded hormones excreted?
In the bile or urine
What is the hypothalamus?
It is located at the base of the brain
Regulates body temperature, water balance and heart rate
Where is the pituitary gland?
It lies under the hypothalamus and is joined by the infundibulum
What does the hypothalamus do?
It produces many different hormones, some carried by blood to the anterior lobe wehre the stimulate or inhibit the release of anterior hormones
How is the anterior pituitary lobe connected?
it has no vessesls connected to the hypothalamus but it is connected by a complex network of blood vessels
How are secretions controlled in the anterior pituitary lobe?
Secretions are controlled by releasing and inhiiting factors of the hypothalamus (factors are hormones- secreted into extracellular fluid and carried into the blood
What hormones does the anterior pituitary lobe release?
Gonadotropins (FSH LH)- growth of follicles, sperm production, ovulation and maintenance of corpus luteum, testosterone secretion
Growth Hormone (somatotropin)- increases the rate at which amino acids are taken up by cells and built into proteins
Thyrotropin (TSH)- stimulates production of thyroid hormone
Adrenocoticotropin (ACTH)- controls hormones from cortex of adrenal glands
Prolactin (lactogenic hormone)- initiates and maintains milk secretion
Why is the posterior lobe of the pituitary not a true gland?
Because it doesnt secrete substances, but it is joined to the hypothalamus by nerve fibres
What does the posterior lobe of the pituitary release?
Oxytocin and antiduretic hormone produced in the nerve cells of the hypothalamus which have long extensions which pass to the PPG
What does oxytocin do?
It stimulates the contraction of uterine muscles and is released in large quantities during labour
What does antiduretic hormone do?
causes the kidneys to remove water from urine, helps return fluid into the body and can also cause constriction of smaller arteries
What is the pineal gland?
It is found deep inside the brain and gradually decreases in size following puberty
Role is largely unknown but it does secrete melatonin which is involved in sleep patterns
What is the production of melatonin stimulated by?
It is stimulated by darkness and inhibited light
Where is the thyroid gland found and what is the structure like?
It is found in the neck below the larynx
Consists of two lobes, joined by a narrow piece of tissue that lies across the front of the trachea
What is the main hormone secreted by the thyroid gland?
Thyroxine, made from iodine and an amino acid
What does thyroxine do?
It controls body metabolism by regulating reactions in which complex molecules are broken down to release energy, and other reactions in which complex molecules are synthesised from simpler ones
The overall effect is to bring about the release of energy and thus maintain body temperature
Where are the parathyroid glands found?
there are usually four, the size of a small pea
They are embedded in the rear surface of the lobes of the thyroid gland
What does the parathyroid hormone secrete?
Controls calcium and phosphate levels in the blood
Where is the thymus?
It is located in the chest, just above the heart and behind the sternum
The thymus is large in infants and shrinks after puberty
What does the thymus secrete?
Secretes and group of hormones called thymosins which influence the maturation of T-lymphocytes
What does the adrenal medulla secrete?
Adrenaline (epinephrine) which has a similar effect to the sympathetic division of the autonomy nervous system, prepares the body for a threatening situation
noradrenaline which is similar to adrenaline, it raises the rate and force of the heartbeat
Where is the adrenal medulla found
Inside the adrenal glands
Where is the adrenal cortex found?
Inside of the adrenal glands
What does the adrenal cortex produce?
more than 20 hormones, known as corticosteroids
primarily aldosterone which acts on the kidney to reduce sodium and increase potassium in the urine
Cortisol which promotes normal metabolism, helps the body withstand stress and repairs damaged tisuues
What is the pancreas?
It sits along the duodenum
is both an endocrine and exocrine gland
Exocrine part secretes digestive enzymes into the small intestine
Clusters of islets of Langerhans which are the endocrine part
Where are islets of Langerhans found?
In the pancreas
What are the two main hormones that islets of Langerhans secrete?
insulin and glucagon
What does insulin do?
- reduces the amount of glucose in the blood
- promotes the uptake of glucose from the blood by body cells
- in liver, causes conversion of glucose from glycogen and fat
- in skeletal muscles causes glycogen from glucose
- fat storgae tissue: converts glucose into fat
What is the level of secretion of insulin determined by
The amount of sugar in the blood and is controlled by a negative feedback system
What does glucagon do?
-actis in the opposite way to insulin
Increases blood sugar levels, promotes the breakdown of glycogen to glucose in the liver
-stimulates the breakdown of fat in the liver and fat storage tissue
What are the gonads?
They are the testes and ovaries which produce hormones along with sperm and eggs
What are androgens?
Male sex hormones which are repsonsible for the development and manintenence of male sex characteristsics
What are oestrogen and progesterone?
Female sex hormones which stimulate the development of female sex characteristics
Along with gonadotropic hormones of the pituitary, they regulate the menstrual cycle and are involved in pregnancy
What are some other endocrine tissues and what do they secrete?
stomach and small intestine: secrete hormones that coordinate the exocrine glands of the digestive system
kidneys: secrete erythopoietin which stimulate production of red blood cells in the bone marrow
Heart: secretes hormones to reduces blood pressure
Placenta: secretes hormones during pregnancy that help maintain and stimulate foetal development
