2. Chemical messengers

Question 1

What is the primary concern of the endocrine system?

Answer 1

Keeping the internal environment of the body constant

Question 2

What are the two types of glands in the body?

Answer 2

Endocrine and exocrine glands

Question 3

What are some characteristics of exocrine glands?

Answer 3

• 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

Question 4

What are some characteristics of endocrine glands?

Answer 4

• 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

Question 5

What is a hormone?

Answer 5

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

Question 6

Can hormones become saturated?

Answer 6

Yes, once all receptor molecules are occupied by hormone molecules, the addition of more hormones does not produce a greater effect

Question 7

What are paracrines (local hormones?

Answer 7

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

Question 8

How do protein and amine hormones work?

Answer 8

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

Question 9

How do steroid hormones work?

Answer 9

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

Question 10

How do enzymes exert their influence by changing the activity or concentration of enzymes?

Answer 10

• 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

Question 11

What is enzyme amplification?

Answer 11

the process where one hormone molecule has the ability to cause the manufacture or activation of thousands of enzyme molecules.

Question 12

What is hormone clearance?

Answer 12

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

Question 13

How are degraded hormones excreted?

Answer 13

In the bile or urine

Question 14

What is the hypothalamus?

Answer 14

It is located at the base of the brain

Regulates body temperature, water balance and heart rate

Question 15

Where is the pituitary gland?

Answer 15

It lies under the hypothalamus and is joined by the infundibulum

Question 16

What does the hypothalamus do?

Answer 16

It produces many different hormones, some carried by blood to the anterior lobe wehre the stimulate or inhibit the release of anterior hormones

Question 17

How is the anterior pituitary lobe connected?

Answer 17

it has no vessesls connected to the hypothalamus but it is connected by a complex network of blood vessels

Question 18

How are secretions controlled in the anterior pituitary lobe?

Answer 18

Secretions are controlled by releasing and inhiiting factors of the hypothalamus (factors are hormones- secreted into extracellular fluid and carried into the blood

Question 19

What hormones does the anterior pituitary lobe release?

Answer 19

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

Question 20

Why is the posterior lobe of the pituitary not a true gland?

Answer 20

Because it doesnt secrete substances, but it is joined to the hypothalamus by nerve fibres

Question 21

What does the posterior lobe of the pituitary release?

Answer 21

Oxytocin and antiduretic hormone produced in the nerve cells of the hypothalamus which have long extensions which pass to the PPG

Question 22

What does oxytocin do?

Answer 22

It stimulates the contraction of uterine muscles and is released in large quantities during labour

Question 23

What does antiduretic hormone do?

Answer 23

causes the kidneys to remove water from urine, helps return fluid into the body and can also cause constriction of smaller arteries

Question 24

What is the pineal gland?

Answer 24

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

Question 25

What is the production of melatonin stimulated by?

Answer 25

It is stimulated by darkness and inhibited light

Question 26

Where is the thyroid gland found and what is the structure like?

Answer 26

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

Question 27

What is the main hormone secreted by the thyroid gland?

Answer 27

Thyroxine, made from iodine and an amino acid

Question 28

What does thyroxine do?

Answer 28

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

Question 29

Where are the parathyroid glands found?

Answer 29

there are usually four, the size of a small pea

They are embedded in the rear surface of the lobes of the thyroid gland

Question 30

What does the parathyroid hormone secrete?

Answer 30

Controls calcium and phosphate levels in the blood

Question 31

Where is the thymus?

Answer 31

It is located in the chest, just above the heart and behind the sternum
The thymus is large in infants and shrinks after puberty

Question 32

What does the thymus secrete?

Answer 32

Secretes and group of hormones called thymosins which influence the maturation of T-lymphocytes

Question 33

What does the adrenal medulla secrete?

Answer 33

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

Question 34

Where is the adrenal medulla found

Answer 34

Inside the adrenal glands

Question 35

Where is the adrenal cortex found?

Answer 35

Inside of the adrenal glands

Question 36

What does the adrenal cortex produce?

Answer 36

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

Question 37

What is the pancreas?

Answer 37

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

Question 38

Where are islets of Langerhans found?

Answer 38

In the pancreas

Question 39

What are the two main hormones that islets of Langerhans secrete?

Answer 39

insulin and glucagon

Question 40

What does insulin do?

Answer 40

• 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

Question 41

What is the level of secretion of insulin determined by

Answer 41

The amount of sugar in the blood and is controlled by a negative feedback system

Question 42

What does glucagon do?

Answer 42

-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

Question 43

What are the gonads?

Answer 43

They are the testes and ovaries which produce hormones along with sperm and eggs

Question 44

What are androgens?

Answer 44

Male sex hormones which are repsonsible for the development and manintenence of male sex characteristsics

Question 45

What are oestrogen and progesterone?

Answer 45

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

Question 46

What are some other endocrine tissues and what do they secrete?

Answer 46

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