Hormonal Communication Flashcards
What is the purpose of the endocrine system
Communication around the body
- Hormones travel round the circulatory system to target cells
2 types of hormone
-
protein/peptide hormone
E.g. adrenaline, insulin, ADH -
steroid hormone
E.g. oestrogen, testosterone
Protein hormones
• not soluble through the phospholipid bilayer
• They bind to receptors on the cell surface membrane and release a second messenger inside the cell
Steroid hormones
• Steroid hormones can pass through the membrane, enter the cell and the nucleus
• They have a direct effect on the DNA in the nucleus.
When are hormones secreted
When the gland is stimulated
- this can be done by a change in concentration or stimulated by electrical impulses
2 types of gland
Endocrine and exocrine
Endocrine gland
Are a group of cells that release a hormone directly into the blood
E.g. thyroid, adrenal, pancreas, pituitary
Exocrine gland
Are a group of cells which surround a duct and secrete their hormones into this
E.g. salivary glands, liver (bile)
The pancreas contains endocrine glands and contains cells that produce digestive enzymes. Why are the cells that produce digestive enzymes described as exocrine?
Because digestive enzymes are released into ducts
Pathway from stimulus to respomse
Stimulus —> receptors —> hormone —> effectors —> response
First messengers
Non steroid hormones
- signalling molecules that bind to receptors (glycoproteins) on the cell surface membranes and initiate an effect
- usually cause the release of another signalling molecule (second messenger)
Second messenger
Stimulates a change in the activity of the cell
What is a G protein
Activated when the hormone binds to the receptor
- the G protein
Example: adrenaline
- Adrenaline is a first messenger.
- It binds to specific receptors on the plasma cell membrane of many cells e.g. hepatocytes
- When adrenaline binds it activates an enzyme in the membrane called adenylyl cyclase.
- Activated adenylyl cyclase catalyses the production of a second messenger called cyclic AMP (cAMP) from ATP.
- cAMP activates a cascade eg: a cascade of enzyme reactions to make more glucose available to the cell by catalysing the breakdown of glycogen into glucose
Adrenaline
- produced in medulla of adrenal gland
- peptide hormone / non steroid hormone
Structure of adrenal gland
Cortex (broken into 2 sections)
Medulla
Blood vessels
Effects of adrenaline / noradrenaline
- increase HR
- increase blood flow
- increase blood pressure
- Glycogenolysis (glycogen broken down into glucose)
- dilating of pupils
Aldosterone (mineralocorticoids)
- produced in cortex (outermost layer)
- steroid hormone
Role: - sodium and potassium ions reabsorption in kidneys
- control of blood pressure
Cortisol (glucocorticoids)
- produced in cortex (middle layer)
- steroid hormone
Roles: - regulating metabolism of carbohydrates, fats and proteins
- released in response to stress and as a result of low BGL
How do steroid hormones work
• Passes through the cell surface membrane of the target cell.
• Binds with a receptor in the cytoplasm.
• The receptor-steroid hormone complex enters the nucleus of the target cells and binds to a receptor on the chromosomal material.
• This binding stimulates the production of mRNA which code for the production of proteins
Androgens
Regulation of sexual characteristics and cell growth
Pancreas
- endocrine tissue in the pancreas is called islets of Langerhans
- they are found in cluster around capillaries
- made up of 2 types of cell: alpha cells and **beta cells*
What do alpha cells secrete
GLUCAGON
What do beta cells secrete
INSULIN
What do ducts always have on a micrograph
White space around it
What do electron micrographs of pancreas cells look like
Islets of Langerhans- largest circle, very pale pink/white
Ducts always have white space around it
Alpha cells are pink
Beta cells are purple
acini are also visible and are just pancreatic cells
What is diabetes
A condition in which the homeostatic control of blood glucose has failed / deteriorated
What happens to the kidneys when someone has diabetes
- their insulin function is disrupted which allows the glucose concentration in the blood to rise
- the kidneys are unable to filter out this excess glucose in the blood and so it often appears in the urine
- the increased glucose conc also causes the kidneys to produce large quantities of urine, making the individual feel thirsty due to dehydratiom
What are the 2 types of diabetes
Type I and Type II
Type I diabetes
- begins in childhood due to an autoimmune response where the body’s immune system (T cells) attacks the **beta cells* of the islets of Langerhans in the pancreas
- the pancreas fails to produce sufficient insulin to control BGL
- the lack of insulin also affects glycogen stores which results in an individual feeling fatigued
- may experience a ‘hypo’- if BGC reaches a dangerously high level after a meal, organ damage can occur
Type II diabetes
- more common than type I
- usually develops in this 40+
- pancreas still produces insulin, but receptors have reduced in numbers or no longer respond to it. This reduced sensitivity to insulin occurs in the liver and fat storage tissues
- lack of response to insulin means there is a reduced glucose uptake which leads to an uncontrolled high blood glucose concentration. This can cause the B cells to produce larger amounts of insulin which ultimately damages them
Risk factors for type II diabetes
- obesity
- physical inactivity
- high BP
- high blood cholesterol
- genetics
- specific ethnic groups are more likely to develop the condition
Diabetes and blood pressure
- individuals with poorly controlled diabetes often suffer from high blood pressure
- the high blood glucose concentration lowers WP of the blood which causes more water to move from the tissues into the blood vessels by osmosis
- as a result, there is a larger volume of blood within the circulatory system which causes BP to increase
Which of the following is not an endocrine gland or does not contain endocrine tissue:
A- gall bladder
B- ovaries
C- pancreas
D- pituitary
A- gall bladder
3 ways glucose can enter the bloodstream
- Absorption in the gut following carbohydrate digestion
- Hydrolysis of glycogen stores
- Lipids/lactate and amino acids converted into glucose
2 hormones which help regulate BGL
Insulin and glucagon
What do alpha and beta cells act as
Receptors
- detect level of blood glucose
not receptors on cell surface membrane
What happens when BGL are too low
- Alpha cells secrete glucagon, beta cells stop secreting insulin
- Glucagon binds to receptors in the cell surface membranes of liver cells
- This binding causes a conformational change in the receptor protein that activated a G protein
- This activated G protein activated the enzyme adenylyl cyclase
- Active adenylyl cyclase catalyses the conversion of ATP to cAMP (second messenger)
- cAMP binds to Protein Kinase A enzymes, activating them, leading to an enzyme cascade resulting in the breakdown of glycogen to glucose
BGL too low (simplified)
- Glucagon binds to liver cells membrane receptors
- G protein is activated
- Adenylyl cyclase converts ATP to cAMP
- cAMP initiates enzyme cascade
BGL too high
- High BGL detected by beta cells in the pancreas
- Glucose molecules enter B cells by facilitated diffusion
- Cells respire the glucose and produce ATP
- High concentration of ATP causes K+ channels in the B cells to close, causing a change in membrane potential
- Causes voltage gated Ca+ channels to open
- Increase in calcium ions causes B cells to secrete insulin
- Insulin containing vesicles move to cell surface membrane and release insulin into the capillaries by exocytosis
- Insulin (hormone) enters the blood stream and circulates around the body
- BGL returns to normal
Action of insulin
Target cells: muscle cells, fat storage cells, adipose tissue and liver cells
- They have glucose transporter proteins in their surface membranes
- These membrane proteins allow for the uptake of glucose molecules via facilitated diffusion
- The rate of glucose uptake for these cells is limited by the number of glucose transporter proteins present
- Insulin binds to specific receptors on the membranes of target cells, which stimulates them to activate/add more glucose transporter proteins to their cell surface membrane which increases the permeability of the cells to glucose.
Role of the liver
- plays a vital role converting glycogen to glucose
- both insulin and glucagon have specific receptors on the membranes of hepatocytes
Insulin and glucagon result in different responses:
Glycogenesis synthesis of glycogen from glucose
Glycogenolysisthe breakdown of glycogen to glucose
Gluconeogenesis synthesis if glucose from non carbohydrate molecules
What does insulin trigger
Glycogenesis
(Glycogen to glucose)
What does glucagon trigger
Glycogenolysis
(Breakdown of glycogen to glucose)
Gluconeogenesis
(Synthesis of glucose from non-carbohydrate molecules)
What is the function of acini
Secrete digestive enzymes
Type 1 diabetes
- get from early childhood
- pancreas doesn’t produce insulin
- no cure
- must inject insulin
- autoimmune response ee
Type 2 diabetes
- get later in life
- both environmental and genetic
- cells become resistant to insulin
- diet and exercise to help control
- physical inactivity and obesity are risk factors
Type 2 diabetes treatments
Lifestyle changes:
1. Regular exercise
2. Losing weight
3. Healthy diet with less sugary food
Medications:
- metformin- reduces amount of glucose that liver cells release, increases cell sensitivity to insulin
- sulfonylureas- stimulates the pancreas to produce more insulin
Type 1 diabetes treatments: past
Insulin therapy: inject with insulin 4-6 times per day
advantages
- tried and tested method
- effective way of lowering BGL- early treatment kept people alive
disadvantages
- expensive to produce
- doesn’t produce a lot
- needs to be purified
- risk of rejection since pig insulin is different to human insulin
- ethical concerns
Type 1 diabetes treatments: Present
• Insulin injections, monitor BGL levels (made by GM bacteria)
• insulin pump therapy- a small device constantly pumps insulin into the bloodstream through a needle that is permanently inserted under the skin
• Islet cell transplantation- healthy beta cells from the pancreas of a donor are implanted into the pancreas of the person with diabetes
• Complete pancreas transplant
Advantages
- faster to produce
- larger quantities produced
- less likely to trigger allergic response or be rejected
- fewer ethical concerns
- cheaper to produce
disadvantages: transplant
- not enough donors to keep up with demand
- donor must be dead
- risk of rejection
- risks of surgery and infection
Type 1 diabetes treatments: future
Stem cells to grow new islets of Langerhans in the pancreas
Immunotherapy- treatment aims to stop the immune system from attacking the body’s own insulin producing cells
Stem cell therapy: involves using stem cells to create insulin producing cells that can be transplanted into patients
Advantages
- improved quality of life
- no need for injections daily
- reduce risk of hypos
disadvantages
- immunosuppression
- lack of available donors
- ethical issues with stem cells
- high cost
