Hormonal Communication Flashcards
The endocrine system
A communication system using hormones as signalling molecules
Protein hormones
- derivatives of amino acids
- not soluble in the phospholipid membrane and do not enter the cell
- bind to cell surface membrane and release a second messenger inside the cell
Steroid hormones
enter the cell and have a direct effect on the DNA in the nucleus
Endocrine glands
ductless glands that release hormones directly into the blood in capillaries running through the gland.
Exocrine glands
consist of groups of cells surrounding a small duct. Secrete products (not hormones) into the duct.
Target cells
The cells receiving an endocrine signal. For non steroid hormones, cells possess a specific receptor on their plasma membrane.
First messengers
Non steroid hormones are first messengers. They bind to the cell surface membrane and initiate an effect inside the cell. They cause the release of a second messenger.
Second messengers
Second messengers are released after a first messenger has initiated a response. the G protein is activated when the hormone binds to the receptor and it activates an effector molecule such as the enzyme adenyl cyclase which converts ATP to cAMP. The second messenger may act directly on another protein or may initiate a cascade of enzyme controlled reactions.
Adrenal glands
a pair of glands above the kidneys which release adrenaline and some other hormones known as corticoids.
The outer layer of the adrenal cortex
Is called the zona glomerulosa and secretes mineralocorticoids
The middle layer of the adrenal cortex
Is called the zona fasciculata and secretes glucocorticoids
The innermost layer of the adrenal cortex
Is called the zona reticularis and secretes precursor molecules used to make sex hormones
The action of steroid hormones
- Hormone passes through cell membrane of target cell
- Hormone binds with specific receptor in the cytoplasm
- The receptor-steroid complex enters the nucleus of the target cell and binds to a specific receptor on the chromosomal material
- Binding stimulates the production of mRNA which codes for the production of proteins.
Mineralocorticoids
- from the zona glomerulosa
- helps to control concentrations of potassium and sodium in the blood
- contribute to maintaining blood pressure
Glucocorticoids
- from the zona fasciculata
- helps control metabolism of carbohydrates, fats and proteins in the liver.
Adrenaline
- from the adrenal medulla
- polar molecule so can’t enter plasma membrane
- many cells and tissues have adrenaline receptors so it has a lot of effects on the body
Effects of adrenaline on the body
- relaxing smooth muscle in bronchioles
- increasing stroke volume of the heart
- increasing heart rate
- causes vasoconstriction to raise blood pressure
- stimulates conversion of glycogen to glucose
- dilates pupils
- increases mental awareness
- inhibits the action of the gut
The exocrine function of the pancreas
Pancreatic cells synthesise and release digestive enzymes. The groups of cells are called acini and are grouped into small lobules separated by connective tissue. The enzymes are secreted into a tubule at the centre of the group. The tubules of the acini join to form intralobular ducts that combine to form the pancreatic duct.
Alpha cells secrete…
glucagon
Beta cells secrete…
Insulin
Releasing insulin
- Cell membrane has potassium and calcium ion channels
- The potassium ion channels are normally open so K+ ions diffuse out making the inside more negative
- When blood glucose concentration is high, glucose moves into the cell
- Glucose is metabolised using the enzyme glucokinase to produce ATP
- The ATP closes the K+ ion channels
- [K+] increases altering the potential difference so the inside becomes less negative.
- This change opens calcium ion channels
- Calcium ions entering cause vesicles of insulin to fuse with the membrane and then be released by exocytosis
Low blood glucose concentration is called and can cause…
Hypoglycaemia
tiredness, confusion, seizures, unconsciousness
High blood glucose concentration is called and can cause…
Hyperglycaemia
Organ failure, diabetes
If blood glucose rises too high
- detected by beta cells in the islets of Langerhans
- beta cells secrete insulin into the blood
- Insulin binds to insulin receptors on liver and muscle cells activating the enzyme tyrosine kinase
- Tyrosine kinase causes phosphorylation of inactive enzymes inside the cells activating a cascade of enzyme controlled reactions
- Liver and muscle cells convert glucose to glycogen
Insulin effects on cells
- more transporter proteins specific to glucose placed on plasma membrane
- more glucose enters the cell
- glucose is converted to glycogen for storage (glycogenesis)
- more glucose converted to fats
- more glucose used in respiration
If blood glucose is too low
- detected by alpha cells in islets of Langerhans
2 alpha cells secrete glucagon into the blood - glucagon binds to receptors on hepatocytes stimulating a G protein which activates adenyl cyclase inside the cell
- ATP is converted to cAMP which activates series of ec reactions
- liver cells convert glycogen to glucose
effects of glucagon
- glycogen is converted to glucose (glycogenolysis) by phosphorylase A
- more fatty acids used in respiration
- amino acids and fats converted to glucose by gluconeogenesis
Gluconeogenesis
Amino acids and fats converted to glucose
glycogenesis
conversion of glucose to glycogen for storage
glycogenolysis
glycogen converted to glucose by phosphorylase A
Type 1 diabetes is caused by
An autoimmune response where the immune system attacks and destroys beta cells. Or a viral attack.
Factors increasing chance of type 2 diabetes
- obesity
- lack of regular exercise
- diet high in sugars
- family history
Treating type 1 diabetes
- insulin injections
- insulin pump therapy
- islet cell transplantation
- pancreas transplantation
- stem cells
Treating type 2 diabetes
Usually treated by changes in lifestyle - losing weight, regular exercise, carefully monitoring diet. This may be supplemented by medications.
Advantages of using genetically modified bacteria to make human insulin
- exact copy of human insulin so effective
- Less chance of rejection due to an immune response
- lower risk of infection
- cheaper than extracting from animals
- manufacturing process is adaptable to demand
- Less moral issues using bacteria rather than animals
