chapter 15: hormones Flashcards
What are hormones?
- 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
What are some examples of exocrine glands?
- 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
Where are hormones produced?
- 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
how is the production of hormones controlled?
- 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
what is the role of the pituitary gland?
(endocrine glands and their hormonal secretions)
- 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)
what is the role of the ovaries?
(endocrine glands and their hormonal secretions)
- in females
> it secretes oestrogen and progesterone
what is the role of testis?
(endocrine glands and their hormonal secretions)
- in males
> secretes testosterones
what is the role of the hypothalamus?
(endocrine glands and their hormonal secretions)
- an endocrine gland that regulates the secretion of some pituitary hormones
what is the role of adrenal gland ( medulla)?
(endocrine glands and their hormonal secretions)
- the adrenal gland secretes adrenaline
what is the role of the pancreas?
(endocrine glands and their hormonal secretions)
- islets of Langerhans in the pancreas secrete insulin and glucagon
what are the effects when a normal amount of insulin is secreted?
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
what are the effects when there is a lack of secretion of insulin?
-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
what are the effects when there is an over-secretion of insulin?
- abnormal decrease in blood glucose concentration
- low blood glucose concentration results in a condition called SHOCK
- coma and death may follow
what is diabetes mellitus?
+ what are the two types of diabetes?
- 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
what are the signs of diabetes mellitus?
- a persistently high blood glucose level
- the presence of glucose in the urine after a meal
- healing of wounds is slow or difficult
how can diabetes mellitus be treated?
(type 1 and type 2)
- 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
what are the effects of glucagon?
- 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
when is adrenaline secreted?
- 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
- stimuli activates the hypothalamus in the brain
- transmission of impulses down the spinal cord
- motor neurone transmits impulses to adrenal gland
- adrenal gland secretes adrenaline into the bloodstream
- blood transports adrenaline to target organs
what are the effects of adrenaline secretions?
- 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
