chapter 15: hormones

Question 1

What are hormones?

Answer 1

• a chemical substance produced in minute quantities by an endocrine gland
• it is transported in the bloodstream to target organs where it exerts its effects
• after hormones have performed their functions, they are eventually destroyed by the liver
• they can influence the growth, development and activity of an organism

Question 2

What are some examples of exocrine glands?

Answer 2

• salivary gland has a salivary duct to carry saliva to the mouth
• the sweat gland has a duct for carrying sweat out of the body

Question 3

Where are hormones produced?

Answer 3

• hormones are produced by ductless glands (endocrine glands)
  > ductless gland does not have a duct to carry away its secretion
• the hormone produced by a ductless gland is secreted directly into the bloodstream
  > which then distributes the hormone around the body
• some glands such as pancreas produce both hormones and other secretions
  > pancreas produces pancreatic juice, which is carried by the pancreatic duct to the duodenum
  > the pancreas also contains special groups of cells known as the islets of Langerhans which secrete hormones insulin and glucagon into the bloodstream

Question 4

how is the production of hormones controlled?

Answer 4

• hormone production must be balanced
  > adequate amounts of each hormone must be produced to ensure that the body functions normally
  > excess production of certain hormones may be harmful
• the hormone production of some endocrine glands in controlled by the nervous system
  > others are regulated by certain chemical substances
  > chemical substances may be hormones from other endocrine glands

Question 5

what is the role of the pituitary gland?
(endocrine glands and their hormonal secretions)

Answer 5

• plays and important role as a ‘controller’
  > secretes a number of hormones, which control the secretion of hormones of several other endocrine glands
  > also referred to as ‘master gland’
• the pituitary gland also secretes antidiuretic hormone (ADH)

Question 6

what is the role of the ovaries?
(endocrine glands and their hormonal secretions)

Answer 6

• in females
  > it secretes oestrogen and progesterone

Question 7

what is the role of testis?
(endocrine glands and their hormonal secretions)

Answer 7

• in males
  > secretes testosterones

Question 8

what is the role of the hypothalamus?
(endocrine glands and their hormonal secretions)

Answer 8

• an endocrine gland that regulates the secretion of some pituitary hormones

Question 9

what is the role of adrenal gland ( medulla)?
(endocrine glands and their hormonal secretions)

Answer 9

• the adrenal gland secretes adrenaline

Question 10

what is the role of the pancreas?
(endocrine glands and their hormonal secretions)

Answer 10

• islets of Langerhans in the pancreas secrete insulin and glucagon

Question 11

what are the effects when a normal amount of insulin is secreted?

Answer 11

decreases the blood glucose concentration by:
- increasing the permeability of cell membranes to glucose
> increasing the rate of glucose uptake by the cells
- stimulating the liver and muscle cells to convert glucose into glycogen for storage
- increasing oxidation of glucose during tissue respiration

Question 12

what are the effects when there is a lack of secretion of insulin?

Answer 12

-glucose cannot be stored or utilised by tissue cells
> blood glucose conc rises and some glucose is lost in the urine
> gives rise to a disease called DIABETES MELLITUS
- since muscle cells have no reserves of glycogen, the body grows weak and continuously loses weight
-the body oxidises fats instead of glucose to produce energy
> results in the production of poisonous substances called ketones which are excreted in the urine

Question 13

what are the effects when there is an over-secretion of insulin?

Answer 13

• abnormal decrease in blood glucose concentration
• low blood glucose concentration results in a condition called SHOCK
• coma and death may follow

Question 14

what is diabetes mellitus?
+ what are the two types of diabetes?

Answer 14

• disease in which the body is unable to control its blood glucose concentration so that it remains within normal limits
  >blood glucose concentration can rise to a level that exceeds the kidney’s ability to completely reabsorb all the glucose
  > glucose not absorbed is secreted in the urine

two type of diabetes:
TYPE 1 DIABETES: juvenile or early-onset diabetes
> develops early in a person’s life
> the islets of Langerhans are unable to produce or secrete sufficient insulin

TYPE 2 DIABETES: late-onset diabetes
> occurs later in a person’s life
> overweight people are more likely to develop type 2 diabetes
> occurs when target cells such as the muscle cells do not respond well to insulin

Question 15

what are the signs of diabetes mellitus?

Answer 15

• a persistently high blood glucose level
• the presence of glucose in the urine after a meal
• healing of wounds is slow or difficult

Question 16

how can diabetes mellitus be treated?
(type 1 and type 2)

Answer 16

• diabetics have to measure their blood glucose concentration and test their urine regularly
  > watch their diet carefully, making sure they do not take in too much carbohydrate
• people with type 1 diabetes have to inject insulin regularly
  > have to ensure that they have a supply of sugary foods such as glucose sweets as their blood glucose can drop too low if they use too much insulin, exercise too much or eat too little
• in severe cases, low blood glucose may cause them to go into coma
• people with type 2 diabetes can
  > control their blood sugar level by carefully regulating the carbohydrate content in their diet and by exercising
• if lifestyle changes fail, they may have to take medication and insulin rejections

Question 17

what are the effects of glucagon?

Answer 17

• when the concentration of blood glucose decreases below normal levels
  > the islets of Langerhans increase the secretion of the hormone glucagon

the main target of glucagon is the liver
- glucagon increases blood glucose concentration by stimulating:
- the conversion of glycogen into glucose
-the conversion of fats and amino acids into glucose

> insulin and glucagon together regulate the blood glucose concentration

Question 18

when is adrenaline secreted?

Answer 18

• when you are afraid, angry, anxious or stressed
  > your adrenal medulla secretes the hormone adrenaline
• adrenaline prepares your body for ‘fight or flight’ or for states of emergency
  > the responses that arise from the secretion of adrenaline is temporary as adrenaline is a short-lived hormone

1. stimuli activates the hypothalamus in the brain
2. transmission of impulses down the spinal cord
3. motor neurone transmits impulses to adrenal gland
4. adrenal gland secretes adrenaline into the bloodstream
5. blood transports adrenaline to target organs

Question 19

what are the effects of adrenaline secretions?

Answer 19

• stimulates the liver to convert to glycogen to glucose so that more glucose is available for muscle contraction
• increases blood glucose level
• increases metabolic rate
  > more energy is released in tissue respiration
• increases the rate of heartbeat
  > causes a rise in blood pressure so that oxygen and glucose are carried faster to the muscles
• increases the rate and depth of ventilation
  > these increase the uptake of oxygen by lungs
• increases the rate of blood clotting
  > eg. when skin is cut, the blood clots faster to prevent excessive loss of blood
• constricts arterioles to the gut, thereby decreases digestive activities
• constricts arterioles in the skin, causing paleness
  > channeling more blood to the muscles
• dilate pupils to enhance vision
• contracts hair muscles, producing ‘goose bumps’ and causing hair to stand on end