endocrine system Flashcards
what other system apart form the nervous system is responsible for communication between different parts of the body?
the endocrine system
what are hormones?
hormones are also molecules that can act as messengers carrying the signal from a gland to a specific target organ or tissue
what is an endocrine gland?
hormones are released directly into the blood from glands called endocrine glands
what is an exocrine gland?
exocrine glands secrete molecules into a duct which carries the molecules to where they are used
Give an example of an exocrine gland?
Salivary glands secrete saliva into a duct
give an example of 10 endocrine and exocrine glands?
- pituitary glands - secrete many hormones e.g. ADH
- thyroid gland - secretes thyroxine
- Adrenal gland - secretes adrenaline
- Islets of Langerhans in pancreas (secrete insulin and glucagon)
- Ovary in female (secretes oestrogen and progesterone)
- Testes in male secretes testosterone
- salivary glands - secrete saliva
- liver secretes bile
- stomach secretes gastric juices
- pancreas - secretes gastric juices
what must the target cells receiving the hormone signal possess?
the cells receiving the hormone signal must posses a specific complementary receptor on their plasma membrane
what 2 structures often act as receptors?
GLYCOPROTEINS
GLYCOLIPIDS
Often act as receptors
What can cause a cellular response inside a target cell?
- If the hormone binds to the receptor it can cause a cellular response inside that cell
define the term target cell?
cells that possess the specific receptor on their cell surface membranes are called target cells
What is a target tissue?
A target tissue is a group of target cells
What does the receptor allow hormone to do?
Hormones can cause a very specific response
how is a nerve controlled response different to a hormone controlled response?
- electrical impulses passed along neurones
- chemical neurotransmitters cross synapses
- rapid transmission
- immediate response
- short lived
- response is very exact
what are the 2 main types of hormones?
- polypeptide/protein hormone
- steroid hormones
why do polypeptide hormones not enter the cell?
- protein hormones are insoluble in the phospholipid membrane thus do not enter the cell
if polypeptide hormones do not enter the cell then how do they trigger a response inside the cell?
specific receptors in plasma membrane trigger response inside the cell
given examples of protein hormones?
- insulin
- adrenaline
can steroid hormones diffuse through the phospholipid membrane?
lipid-soluble so steroid hormones diffuse through the membrane of the target cell
once in a cell what does the steroid hormone do?
- hormone bind with a specific receptor with a complementary shape in the cytoplasm
- the receptor-steroid hormone complex enters the nucleus of the target cell and binds to another specific receptor on chromosomal material
- binding stimulates, the production of mRNA molecules which code for the production of proteins
describe how adrenaline affects liver cells?
- adrenaline binds to the membrane on liver cell - has a complementary shape
- This alters the shape of the receptor, causing it to interact with another protein in the membrane called a G-protein
- this causes the G-protein to split and one part of the G-protein combines with an inactive enzyme called adenylyl cyclase - This binding of the G-protein to the adenylyl cyclase activates the enzyme which converts ATP –> cyclic AMP cAMP
- cAMP then leads to a further cascade of enzyme controlled reactions which eventually leads to the break down of stores of glycogen in the liver cell, converting it to glucose
what is the break down of glycogen to glucose known as?
Glycogenolysis
what does the secretion of adrenaline cause?
the secretion of adrenaline thus brings about the production of glucose in liver cells which can be transported in the blood to muscles so that they can respire quickly and generate ATP needed for contraction
what are first and second messengers in the adrenaline response?
- first messenger = adrenaline
because it transmits the signal around the body - second messenger = cAMP
because it transmits the signal inside the cell
what else does cAMP do?
cAMP causes the inhibition of another enzyme glycogen synthase, this prevents glucose conversion to glycogen
what are the adrenal glands a good example of?
the adrenal glands are a good example of a gland in the body which produces a range of hormones that act in different ways
what type of gland are adrenal glands?
The adrenal glands are a good example of an endocrine gland. They are found lying anterior (just above) the kidneys - one on each side of the body
What is each gland divided into?
- the outer adrenal cortex
- the inner adrenal medulla
what surrounds both regions of the adrenal glands?
- both regions are well supplied with blood and produce hormones which are secreted directly into the blood vessels
describe the structure of the adrenal cortex?
- cortex surrounds three distinct layers of cells
1. zone glomerulosa - the outermost layer which secretes mineralocorticoids such as aldosterone
2. zone fasciculata - the middle layer which secretes glucocorticoids such as cortisol
3. zone reticularis - the innermost layer which is thought to secrete precursor molecules which are then used to make sex hormones
where is the adrenal medulla found?
the adrenal medulla is found at the centre of the adrenal gland
it is the hormone that secretes adrenaline
and noradrenaline
what is adrenaline?
adrenaline is a polypeptide hormone derived from the amino acid tyrosine
What is the role of adrenaline in the body?
Adrenaline helps prepare the body for the fight or flight response
a few examples of the effects of adrenaline:
- targets sino-atrial node in the heart - increase in heart rate
- relaxes smooth muscle in bronchioles
- causes vasoconstriction to raise blood pressure
- inhibit action of gut
- dilate pupils
- stimulate glycogen —> glucose
what is the function of the mineralocorticoid - aldosterone ?
it is main role is to help control the concentration of sodium and potassium ions in the blood which in turn helps control blood pressure
what is the function of the mineralocorticoid - aldosterone ?
it is main role is to help control the concentration of sodium and potassium ions in the blood which in turn helps control blood pressure
what does the cortex use to produce steroid based hormones?
cholesterol
how does the mineralocorticoid - aldosterone work?
Aldosterone helps control blood pressure by acting on the distal tubules and collecting ducts of the nephron increasing/decreasing reabsorption of ions back into the blood
therefore it can indirectly influence water retention or loss
what is the glucocorticoid - cortisol?
cortisol is a steroid hormone in the glucocorticoid class of hormones, and is produced by the zone fasciculata of the adrenal cortex
when is cortisol released?
it is released in response to stress and low blood-glucose concentration
What is the function of cortisol?
it’s main role in the body is to stimulate the production of glucose from stored compounds especially glycogen, fats and proteins in the liver - gluconeogenesis
why can we get ill when we are stressed?
cortisol can also suppress the immune system that is why you can get ill when stressed
describe the pancreas?
the pancreas is a small organ lying below the stomach. It is an unusual organ in that it has both exocrine and endocrine functions
if you looked under a microscope what do the stained sections reveal about the 2 different types of tissue:
- darker-staining cells form ‘acini’ cells which are connected to ducts - these belong to exocrine pancreas
- lighter-staining cells form ‘islets of Langerhans’ which produce hormones - this underlines the endocrine functions of the pancreas
describe the endocrine function of the pancreas?
certain areas of the pancreas are called islets of Langerhans
these contain 2 types of cells
these release hormones directly into the blood
beta cells secrete insulin
alpha cells secrete glucagon
describe the exocrine function of the pancreas?
the majority of cells in the pancreas perform an exocrine function - acinar cells
these secrete pancreatic juices into tubules which join up to make the pancreatic duct which carries the juices to the small intestine
what do pancreatic juices contain?
digestive enzymes - lipase/amylase/trypsin
sodium hydrogencarbonate ions - this helps neutralise stomach acids
what do pancreatic juices contain?
digestive enzymes - lipase/amylase/trypsin
sodium hydrogencarbonate ions - this helps neutralise stomach acids
where are the polypeptide hormones insulin and glucagon synthesised?
insulin and glucagon are both polypeptide hormones synthesised by ribosomes on the RER
how can one differentiate between alpha and beta cells?
the alpha and beta cells in islets of Langerhan look very similar but insulin in beta cells tends to form dark crystalline deposits that are easier to make out than glucagon in alpha cells
what happens in our bodies after we eat foods containing carbohydrates?
after eating food containing carbohydrates, glucose from the digested food is absorbed from the small intestine and passed into the blood
what must happen to the level of glucose in the blood?
the level of glucose in the blood must be kept steady or it can have harmful effects.
what is the normal blood concentration of glucose in a healthy person?
in a healthy person the normal blood concentration of glucose is 90mg 100cm-3
how are glucose levels controlled?
blood glucose levels are controlled as a part of homeostasis
what is homeostasis?
maintaining a relatively stable internal environment
within a narrow range
even though the environment is changing
how does the body know if the blood glucose concentration has risen or fallen away from the acceptable concentration?
if the concentration rises or falls away from the acceptable concentration then the alpha and beta cells in the islets of Langerhan detect a change through receptors and respond by releasing a hormone
define the term hyperglycemia?
if a persons blood glucose concentration is allowed to rise too high > 119 mg 100cm-3 for long periods this is known as hyperglycemia
describe what happens on a cellular level when blood glucose levels rise?
- alpha and beta cell receptors detect an increase in blood glucose concentration
- alpha cells stop secreting glucagon
beta cells secrete more insulin - this is then carried to all parts if the body
describe what happens on a cellular level when blood glucose levels rise?
- alpha and beta cell receptors detect an increase in blood glucose concentration
- alpha cells stop secreting glucagon
- beta cells secrete more insulin - this is then carried to all parts of the body, in the blood
what are the target cells for insulin?
hepatocytes
muscle cells
and some other body cells including some in the brain
