Hormonal Communication 5.4 Flashcards
(34 cards)
What is an endocrine system?
-a communication system using hormones as signalling molecules
What are hormones?
Molecules (proteins or steroids) that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine glands directly into to a specific target organ or tissue
What are target cells?
For non-steroid hormones, cells that possess a specific receptor on their plasma membrane. The shape of the receptor is complementary to the shape of the hormone molecule. Many similar cells together form a target tissue
What are the two types of hormones and how do they work?
-protein hormones (e.g. adrenaline, insulin and glucagon) they are not soluble in the phospholipid membrane and do not enter the cell. Protein hormones need to bind to the cell surface membrane and release a second messenger inside the cell
-steroid hormones (e.g. oestrogen and testosterone) can pass through the membrane and enter the cell and the nucleus to have a direct effect on the DNA in the nucleus
Endocrine glands …
Secrete hormones which are transported in the blood and then bind to their target cell causing a response
What are first messengers and second messengers?
-non-steroid hormones are known as FIRST MESSENGERS. They are signalling molecules outside the cell that bind to the cell surface membrane and initiate an effect inside the cell. They usually cause the release of another signalling molecule in the cell which is called the SECOND MESSENGER. The second messenger stimulates a change in the activity of the cell.
How are second messengers activated?
-many non-steroid hormones act via a G protein in the membrane. The G protein is activated when the hormone binds to the receptor. The G protein in turn activates an effector molecule- usually an enzyme that converts an inactive molecule into the active second messenger. In many cells the effector molecule is the enzyme adenyl cyclase, which converts ATP into cyclic AMP (cAMP)
-cAMP is the second messenger it may act directly on another protein or initiate a cascade of enzyme controlled reactions that alter the activity of the cell
What is the adrenal cortex controlled by?
-controlled by hormones secreted by the pituitary gland
What are the three types of hormones that the adrenal cortex can secrete?
Glucorticoids- e.g. cortisol->regulate carbohydrate metabolism, released in response to stress or as a result of low blood glucose concentration. Stimulates production of glucose from stored compounds in liver
Mineralocorticoids- e.g. aldosterone->controls ion reabsorption in the kidneys and blood pressure
Androgens
->regulate sexual characteristics and cell growth
What is the adrenal medulla controlled by?
-controlled by the nervous system
What hormones does the adrenal medulla release and what are their functions?
-Adrenaline-> increases the heart rate and raises blood glucose concentration
-Noradenaline- increases heart rate, causes pupils to dilate, widens the airways in the lungs and narrows the blood vessels in non-essential organs to create a higher blood pressure
What is the difference between an endocrine gland and an exocrine gland?
Endocrine glands secrete hormones directly into the blood, whereas exocrine glands secrete substance via a duct
What are the two functions of the pancreas?
The exocrine function of the pancreas is to produce pancreatic juice (containing digestive enzymes e.g. pancreatic amylase-a carbohydrase which digests amylose to maltose, trypsinogen- an inactive protease which will be converted into the active form trypsin, lipase-digests lipid molecules) to be delivered to the small intestine where it helps in the digestion of food
The endocrine function of the pancreas is to produce the hormones glucagon and insulin
What are the exocrine cells called in the pancreas?
-acinar cells, the exocrine cells are in small groups surrounding tiny tubules. Each group of cells are called an acinus (plural-acini)
-the acini are grouped together into small lobules separated by connective tissue. The cells of the acini secrete the enzymes they synthesise into the tubule at the centre of the group
-the tubules from the acini join to form intralobular ducts that eventually combine to make the pancreatic duct (which carries fluid containing the enzymes into the duodenum)
What is the name of the cells in the pancreas that carries out the endocrine function?
Islets of Langerhans
What are the two types of cells in the islets of langerhans and what do they secrete?
The islets of Langerhans contain two cell types: alpha cells, which secrete glucagon, and beta cells, which secrete insulin
What happens when there is a decrease in blood glucose concentration?
If a decrease in blood glucose concentration occurs, it is detected by the α and β cells in the pancreas:
The α cells respond by secreting glucagon
The β cells respond by stopping the secretion of insulin
The decrease in blood insulin concentration reduces the use of glucose by liver and muscle cells
Glucagon binds to receptors in the cell surface membranes of liver cells
This binding causes a conformational change in the receptor protein that activates a G protein
This activated G protein activates the enzyme adenylyl cyclase
Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
cAMP (INITIATES AN ENZYME CASCADE) binds to protein kinase A enzymes, activating them
Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose
This process is known as glycogenolysis
How is adrenaline used to increase the concentration of blood glucose?
The hormone adrenaline also increases the concentration of blood glucose
It does this by binding to different receptors on the surface of liver cells that activate the same enzyme cascade and lead to the same end result – the breakdown of glycogen by glycogen phosphorylase
Adrenaline also stimulates the breakdown of glycogen stores in muscle during exercise
The glucose produced remains in the muscle cells where it is needed for respiration
Describe the control of insulin secretion
1- the cell membranes of the beta cells contain both calcium ion channels and potassium ion channels
2-the potassium ion channels are normally open and the calcium ion channels are normally closed. Potassium ions diffuse out of the cell making the inside of the cell more negative (At rest the potential difference is -70mV )
3-when glucose concentrations outside the cell are high, glucose molecules move into the cell
4-the glucose is used to produce ATP
5-the extra ATP causes the potassium channels to close
6-the potassium can no longer diffuse out and this alters the potential difference across the cell membrane- it becomes less negative inside
7-this change in potential difference opens the calcium ion channels
8-calcium ions enter the cell and cause the secretion of insulin by making the vesicles containing insulin to move to the cell surface membrane and fuse with it releasing insulin by exocytosis
What happens when blood glucose concentrations outside the is too high?
Beta cells in the islets of Langerhans detect when blood glucose levels are too high and secrete insulin in response to this. Insulin will decrease blood glucose in the following ways:
1. Attaching to receptors on the surfaces of target cells. This changes the tertiary structure of the channel proteins resulting in more glucose being absorbed by facilitated diffusion.
More glucose transporter protein channels are incorporated into cell membranes, this increases permeability of the cells to glucose so that more glucose is absorbed from the blood into cells.
Activates enzymes involved in the conversion of glucose to glycogen (once glucose has entered a liver cell and enzyme rapidly converts it to glucose phosphate, different enzymes then convert glucose phosphate into glycogen). This results in glycogenesis in the liver.
Insulin stops the use of fat or protein in respiration causing more insulin to be used
What is GLYCOGENESIS?
Glycgogenesis is the synthesis of glycogen from glucose molecules
Insulin triggers this process after it detects an increased blood glucose concentration
The synthesis of glycogen removes glucose molecules from the bloodstream and decreases the blood glucose concentration to within a normal range
Glycogen acts as a compact and efficient carbohydrate storage molecule
What is GLYCOGENOLYSIS?
Glycogenolysis is the breakdown of glycogen to produce glucose molecules
Glucagon triggers this process after it detects a decreased blood glucose concentration
It activates enzymes within the liver that breakdown glycogen molecules into glucose
The breakdown of glycogen releases more glucose molecules to the bloodstream and increases the blood glucose concentration to within the normal range
