Unit 5.4- Hormonal Comunication Flashcards
Endocrine system definition:
A communication system using hormones as signalling molecules
Hormones definition:
Molecules (proteins or steroids) that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue
Target cells definition:
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 types of hormone?
- Steroid hormones (E.g. oestrogen and testosterone)
- Protein and peptide hormones and derivatives of amino acids. These are non-steroid (e.g. adrenaline, insulin and glucagon)
How do protein hormones get their message into a cell?
- Not soluble in the phospholipid membrane so do not enter cell
- They bind to the cell surface membrane and release a second messenger inside the cell
How do steroid hormones get their message into a cell?
- They can pass through the cell membrane
- The enter the nucleus and have a direct effect on the DNA
Where are hormones released from?
Endocrine glands
What are endocrine glands?
- Ductless glands
- Consists of groups of cells that manufacture and release hormones directly into the blood in the capillaries running through the gland
What kind of messenger is a non-steroid hormone?
First messenger
What kind of messenger is the signalling molecule inside a cell which a non-steroid hormone causes the release of?
Second messenger
How does the activation of a second messenger with non-steroid hormones work?
- The hormone binds to a receptor on the cell surface membrane. This activates a G protein
- The G protein activates an effector molecule (usually an enzyme that converts an inactive molecule into the active second messenger
- The second messenger may at directly on another protein or it may initiate a cascade of enzyme-controlled reactions
Adrenal cortex definition:
The outer layer of the adrenal gland
Adrenal gland definition:
One of a pair of glands lying above the kidneys, which release adrenaline and a number of other hormones known as corticoids such as aldosterone
Adrenaline definition:
A hormone released from adrenal glands, which stimulates the body to prepare for fight or flight
Adrenal medulla definition;
The inner layer of the adrenal glands
What type of glands are adrenal glands?
Endocrine glands
What are the three layers of cells surrounding the adrenal gland (between the medulla and cortex)?
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
What is the zona glomerulosa?
- Outer most later, (closest to the cortex of the adrenal glands)
- Secretes mineralocorticoids such as aldosterone
What is the zona fasculata?
- The middle layer (of the three in the adrenal gland)
- Secretes glucocorticoids such as cortisol
What is the zona reitcularis?
- The innermost later, (closest to the adrenal medulla)
- Thought to secrete precursor molecules that are used to make sex hormones
What does the adrenal cortex use to make hormones?
Cholesterol
What type of hormones are made in the adrenal cortex?
Steroid hormones
What is the action of steroid hormones?
- Passes through cell membrane of target cell
- Binds with specific receptor in the cytoplasm
- Receptor-steroid hormone complex enters the nucleus of the target cell and binds to another specific receptor on the chromosomal material
- Binding stimulates the production of mRNA molecules which code for the production of proteins
What effects does adrenaline have on the body?
- Relaxing smooth muscle in the bronchioles
- Increasing stroke volume of the heart
- Increasing heart rate
- Causing general vasoconstriction to raise blood pressure
- Stimulating conversion of glycogen to glucose
- Dilating pupils
- Increasing mental awareness
- Inhibiting the action of the gut
- Causing body hair to stand erect
Beta cells definition:
Cells found in the islets of Langerhans that secrete insulin
Glucagon definition:
A hormone that causes an increase in blood glucose concentration
Insulin definition:
The hormone, released from the pancreas, that causes blood glucose levels to go down
What are the two main secretions from the pancreas?
- Pancreatic juices containing enzymes which are secreted into the small intestine
- Hormones which are secreted from the islets of Langerhans into the blood
What do most cells in the pancreas synthesise and secrete?
Digestive enzymes
Acini definition:
Groups of exocrine cells in the pancreas. They surround tiny tubules. The acini are grouped together into small lobules, separated by connective tissue
Where does the fluid from the pancreatic duct go to?
The first part of the small intestine (duodenum)
What enzymes does the fluid from the pancreatic duct contain?
- Pancreatic amylase
- Trypsinogen
- Lipase
What is pancreatic amylase enzyme?
A carbohydrase which digests amylose to maltose
What is trypsinogen enzyme?
An inactive protease which will be converted to the active form trypsin when it enters the duodenum (first part of the small intestine)
What is lipase enzyme?
Digests lipid molecules
What makes the fluid from the pancreatic duct alkaline?
Sodium hydrocarbonase. This helps to neutralise the contents of the digestive system that have just left the acidic stomach
What do alpha cells secrete?
Glucagon
What do beta cells secrete?
Insulin
How is insulin secreted from beta cells?
- Beta cell membranes contain calcium ion channels (normally close) and potassium ion channels (normally open)
- Potassium ions diffuse out of the cell, making the inside more negative, (-70mV at rest)
- When glucose concentrations outside the cell are high, glucose molecules move into the cell
- The glucose is quickly used to produce ATP (also involves the enzyme glucokinase
- The extra ATP causes the potassium channels to close
- Potassium can no longer diffuse out, making it less negative inside the cell
- Change in potential difference opens calcium ion channels
- Calcium ions enter the cell and cause the secretion of insulin by making vesicles containing insulin move to the cells surface membrane and fuse with it, releasing insulin by exocytosis
Hypoglycemia definition:
When someone’s blood glucose concentration drops and remains too low- below 4mmdm-3
Hyperglycemia definition:
When someone’s blood glucose is too high for long periods- above 7mmoldm-3
Which enzyme is activated when insulin binds too the target receptor when it reaches the cell surface membrane of target cells?
Tyrosine kinase
Effects of insulin on the cell:
- More glucose transporter proteins are places into the cell surface membrane by vesicles
- More glucose enters the cell
- Glucose in the cell is converted to glycogen for storage (glycogenesis)
- More glucose is converted to fats
- More glucose is used in respiration
What does glucagon do when secreted?
- Binds to receptors of hepatocytes
- This stimulates a G protein
- This activates the adenyl cyclase inside the cell
- This converts ATP to cAMP which activates a series of enzyme controlled reactions
Effects of glucagon:
- Glycogen is converted to glucose
- More fatty acids used in respiration
- Amino acids and fats are converted to additional glucose by gluconeogenesis
Diabetes mellitus definition:
A condition in which blood glucose concentrations cannot be controlled effectively
Certain factors that seem to bring an earlier onset of type 2 diabetes:
- Obesity
- Lack of regular exercise
- A diet high in sugars
- Being of Asian or Afro-Caribbean descent
- Family history
Alternatives to insulin injections for type 1 diabetes:
- Insulin pump therapy
- Islet cell transplantation
- A complete pancreas transplant
What is insulin pump therapy?
A small device constantly pumps insulin into the bloodstream, through a needle that is permanently inserted under the skin
What is an islet cell transplantation:
Healthy beta cells from the pancreas of a deceased donor are implanted into the pancreas of someone with type 1 diabetes
How is type 2 diabetes treated?
A change in lifestyle
How might it be possible to treat type 1 diabetes with stem cells?
Stem cells can grow new islets of Langerhans in the pancreas
Advantages of using insulin from genetically modified bacteria rather than pigs:
- Exact copy of human insulin so faster acting and more effective
- Less chance of developing tolerance to insulin
- Less chance of rejection
- Lower risk of infection
- Cheaper
- Manufacturing process is more adaptable to demand
- Ethical reasons
