5.1.4 - Hormonal Communication Flashcards
Endocrine system
Works alongside neuronal system to react to changes ; uses hormones to send information about changes in the environment around the body to bring about a designated response
Endocrine glands
Make up the endocrine system ; group of cells which are specialised to secrete chemicals ; they are known as hormones and are secreted directly into the bloodstream (pancreas and adrenal glands for example)
Pituitary gland?
Makes several hormones which in turn control the release of other hormones ; close proximity to the hypothalamus ensures that the nervous and hormonal responses of the body are closely linked and coordinated
Pineal gland
Produces melatonin which affects reproductive development and daily cycles
Thymus
Produces thymosin which promotes production and maturation of white blood cells
Pancreas
Produces insulin which converts excess glucose into glycogen in the liver ; and glucagon, which converts glycogen back to glucose in the liver
Ovary
Produces oestrogen which controls ovulation and secondary sexual characteristics
Progesterone prepares the uterus lining for receiving an embryo
Testis
Produces testosterone which controls sperm production and secondary sexual characteristics
Adrenal gland
Produces adrenaline which increases heart and breathing rate and raises blood sugar level
Thyroid gland
Produces thyroxine which controls rate of metabolism and rate that glucose is used up in respiration and promotes growth
Pituitary gland
Produces growth hormones which control growth of bones and muscles ; ADH (which increases water reabsorption in kidneys) and gonadotrophins which control development of ovaries and testes
Exocrine glands difference
Secrete chemicals through ducts into organs or to the surface of the body
Hormones?
They are chemical messengers because they carry information from one part of the body to another ; they can be steroids, proteins, glycoproteins, polypeptides, amines or tyrosine derivatives
How are hormones secreted directly into the blood?
When a gland is stimulated ; this can occur as a result of a change in concentration of a particular substance such as blood glucose concentration or a nerve impulse/another hormone
Once secreted…?
Hormones are transported in the blood plasma all over the body ; they diffuse out of the blood and bind to specific receptors for that hormone found on the membranes or in the cytoplasm of cells in the target organs - these are known as target cells
What happens once bound to target cells?
Hormones stimulate the target cells to produce a response
Why does the type of hormone matter?
It determines the way it causes it’s effect on a target cell ; steroid and non-steroid hormones
Steroid hormones
Lipid soluble ; pass through the lipid component of the cell membrane and bind to steroid hormone receptors to form a hormone-receptor complex ; the receptors may be in the cytoplasm or the nucleus depending on the hormone
Hormone receptor complex formed acts as a transcription factor which in turn facilitates or inhibits the transcription of a specific gene - oestrogen is an example
Non-steroid hormones
Hydrophilic so cannot pass directly through the cell membrane ; they bind to specific receptors on the cell surface membrane of the target cell - triggers a cascade reaction mediated by chemicals called second messengers (adrenaline is a non-steroid hormone)
Hormones vs neuronal
Hormones are not released directly into their target cells - slower/less specific form of communication than neuronal communication
Hormones are not broken down as quickly as neurotransmitters so they can result in a much longer and widespread effect
Hormone vs nervous communication
Communication is by chemicals called hormones and nervous is by nerve impulses
Hormonal vs nervous transmission
Blood system vs neurones
Speed of transmission hormonal vs nervous
Relatively slow vs very rapid
Travelling around the body - hormonal vs nervous
Hormones travel to all parts of the body but only target organs respond
Nerve impulses travel to specific parts of the body
Area of response? Hormonal vs nervous?
Widespread vs localised
Length of response? Hormonal vs neuronal?
Long-lasting vs short lived
Effect - hormonal vs neuronal?
Permanent and irreversible / temporary and reversible
Adrenal glands
Located on top of each kidney and are made up of two distinct parts surrounded by a capsule
Adrenal cortex?
Outer regions of the glands ; produces hormones that are vital to life (like cortisol and aldosterone)
Adrenal medulla?
Inner regions of the glands ; produces non-essential hormones like adrenaline which help the body react to stress
3 main types of hormones produced by the adrenal cortex?
Glucocorticoids
Mineralocorticoids
Androgens
Glucocorticoids?
These include cortisol which help regulate metabolism by controlling how the body converts fats, proteins and carbohydrates to energy. It also helps regulate blood pressure and cardiovascular function in response to stress.
Corticosterone is another glucocorticoid which works with cortisol to regulate immune response and suppress inflammatory reactions - this is controlled by the hypothalamus
Mineralocorticoids
Main one produced is aldosterone which helps control blood pressure by maintaining the balance between salt and water concentrations in the blood and body fluids ; release is mediated by signals triggered by the kidney
Androgens
Small amounts of male and female sex hormones are released ; their impact is relatively small compared with the larger amounts of hormones (oestrogen and testosterone) released by the ovaries or testes after puberty - very important in women after menopause
Adrenal medulla?
Hormones here are released when the sympathetic nervous system is stimulated - this occurs when the body is stressed
Hormones secreted by the adrenal medulla?
Adrenaline
Noradrenaline
Adrenaline?
Increases the heart rate sending blood quickly to the muscles and brain ; rapidly raises blood glucose concentration levels by converting glycogen to glucose in the liver
Noradrenaline
Hormone works with adrenaline in response to stress by producing effects such as increased heart rate, widening of the pupils, widening of air passages in the lungs and the narrowing of blood vessels in non-essential organs (leading to increased blood pressure)
Where is the pancreas found?
Upper abdomen - behind the stomach ; a glandular organ which plays a big role in producing and secreting hormones and digestive enzymes
Controls blood glucose concentration and digestion
Functions of the pancreas
Exocrine gland - produces enzymes and releases them via a duct into the duodenum
Endocrine gland - produce hormones and release them into the blood
Role as an exocrine gland?
Most of the pancreas is made up of exocrine glandular tissue ; this is responsible for producing digestive enzymes and an alkaline fluid known as pancreatic juice - they are secreted into ducts which eventually lead to the pancreatic duct and from there they are released into the duodenum (the top part of the small intestine)
Pancreas produces 3 types of important digestive enzymes
Amylases - break down starch into simple sugars (pancreatic amylase)
Proteases - break down proteins into amino acids (trypsin)
Lipases - break down lipids into fatty acids and glycerol (pancreatic lipase)
Role as an endocrine gland
Responsible for producing insulin and glucagon - within the exocrine tissue there are small regions of endocrine tissue called Islets of Langerhans ; these cells are responsible for producing insulin and glucagon and secreting these hormones directly into the bloodstream
Histology of the pancreas - appearance
Islets of Langerhans ; lightly stained
Pancreatic acini ; darker stained
Histology of the pancreas - shape
Islets : large, spherical clusters
Pancreatic acini : small, berry-like clusters
Histology of the pancreas - type of tissue
Islets of Langerhans - endocrine pancreas
Pancreatic acini - exocrine pancreas
Histology of the pancreas - function
Islets of Langerhans : produce and secrete hormones
Pancreatic acini : produce and secrete digestive enzymes
Within the islets of Langerhans?
There are two types of cells
Alpha cells - produce and secrete glucagon
Beta cells - produce and secrete insulin
Alpha cells vs beta cells
Larger and more numerous than beta cells within an islet
Staining of islets?
Very difficult to distinguish between cell types within an islet so differential staining is often used ; beta cells are stained blue and alpha cells are stained pink
Glucagon and insulin
Carried into the bloodstream by granules
Why does blood glucose matter?
Important that concentration of glucose is kept constant - without control it would range from very high levels after a meal to very low levels ; thus wouldn’t have enough glucose for respiration - this is kept constant by insulin and glucagon
Describe glucose
Small and soluble molecule that is carried in the blood plasma ; normally maintained at around 90 mg cm^-3
How does blood glucose concentration increase?
Diet
Glycogenolysis
Gluconeogenesis
Diet
When you eat carbohydrate rich foods such as pasta and rice and sweet foods such as cakes and fruit (high levels of sucrose) ; the carbohydrates are broken down to release glucose and this is absorbed into the bloodstream causing blood glucose concentration rises
Glycogenolysis
Glycogen stored in the liver and muscle cells is broken down into glucose which is released into the bloodstream increasing blood sugar concentration
Gluconeogenesis
Production of glucose from non-carbohydrate sources ; liver is able to make glucose from glycerol and amino acids - glucose is released into the bloodstream and causes an increase in blood glucose concentration
Lysis
Splitting
Neo
“New”
Genesis
Means birth;origin
Decreasing blood glucose concentration?
Respiration
Glycogenesis
Respiration
Glucose in the blood is used by cells to release energy : however during exercise more glucose is needed as the body needs to generate more energy in order for muscle cells to contract - higher level of activity = higher demand for glucose = greater the decrease of blood glucose concentration
Glycogenesis
Production of glycogen ; when blood glucose concentration is too high, excess glucose taken in through the diet is converted into glycogen which is stored in the liver
Insulin
Produced by the beta cells of the islets in the pancreas ; if too high then beta cells detect this rise in blood glucose and respond by secreting insulin directly into the bloodstream
Insulin receptors?
All body cells have insulin receptors on their cell surface membrane (except RBCs) ; when insulin binds to its glycoproteins receptor it causes a change in the tertiary structure of the glucose transport protein channels
This causes the channels to open allowing more glucose to enter the cell ; insulin also activates the enzymes within some cells to convert glucose to glycogen and fat
Insulin lowers blood glucose concentration by
Increasing rate of absorption of glucose by cells (skeletal muscle cells in particular)
Increasing respiratory rate of cells ; increases the need for glucose and causes a higher uptake of glucose from the blood
Increasing rate of Glycogenesis ; insulin stimulates the liver to remove glucose from the blood by turning the glucose into glycogen and storing it in the liver and muscle cells
Increasing the rate of glucose to fat conversion
Inhibiting the release of glucagon from the alpha cells of the islets
How is insulins effect maintained?
Insulin is broken down by enzymes in the cells of the liver ; thus to maintain its effect it has to be constantly secreted and it may continue for several hours after eating
As blood glucose concentration returns back to normal this is detected by the beta cells of the pancreas ; when it falls below a set level, the beta cells reduce their secretion of insulin (NEGATIVE FEEDBACK) - ensures changes are reversed and returned back to the set level
Glucagon
Produced by the alpha cells of the islets in the pancreas ; if blood glucose concentration is too low - the alpha cells detect this fall in blood glucose concentration and respond by secreting glucagon directly into the bloodstream
Which two cells in the body have glucagon receptors?
LIVER CELLS AND FAT CELLS ; ONLY CELLS WHICH RESPOND TO GLUCAGON
How does glucagon increase blood glucose concentration?
Glycogenolysis - liver breaks down its glycogen store into glucose and releases it back into the bloodstream
Reducing the amount of glucose absorbed by the liver cells
Increasing Gluconeogenesis - increasing the conversion of amino acids and glycerol into glucose in the liver
As blood glucose concentration returns to normal…
Detected by the alpha cells of the pancreas ; when it rises above a set level the alpha cells reduce their secretion of glucagon - this is another example of negative feedback ; causes the corrective measures to be switched off
Interaction of insulin and glucagon
Work together to maintain a constant blood glucose concentration ; they are antagonistic hormones (they work against each other)
LOOK AT PAGE 390
Looked at diagram 😊
System of maintaining blood glucose concentration?
Said to be self-regulating as it is the level of glucose in the blood that determines the quantity of insulin and glucagon that is released ; blood glucose concentration is not constant but fluctuates around a set point as the result of negative feedback - in time of stress adrenaline is released by the body, one of the effects of this hormone is to raise the blood glucose concentration to allow more respirations tissue occur
Control of insulin secretion
When blood glucose concentration rises above the set level ; detected by beta cells in the islets and insulin is released
Mechanism of insulin secretion
1) Normal blood glucose concentration levels mean potassium channels in plasma membrane of beta cells are open and potassium ions diffuse OUT OF THE CELL ; the inside of the cell is -70mV with respect to the outside of the cell
2) When blood glucose concentration rises ; glucose enters the cell by a glucose transporter and is metabolised inside the mitochondria resulting in the production of ATP
3) ATP binds to potassium channels and causes them to close ; they are known as ATP-sensitive potassium channels
4) As potassium ions cannot diffuse out of the cell anymore, the potential difference is reduced to -30mV and depolarisation occurs
5) Depolarisation means voltage-gated calcium channels open and calcium ions now enter the cell and cause secretory vesicles to release the insulin they contain by excocytosis
Diabetes
Unable to regulate blood glucose concentration ; it is a chronic disease - diabetes mellitus
What can patients not do with diabetes?
Unable to metabolise carbohydrates properly - in particular glucose
What two causes of diabetes?
Does not produce enough insulin or cannot effectively respond to insulin - thus blood glucose concentration remains high
Common effect of uncontrolled diabetes?
Hyperglycaemia - over time this can lead to serious damage to many body systems like nerves/blood vessels
Type 1 Diabetes
Unable to produce insulin and the beta cells in the islets do not work - cause is not known and thus the disease cannot be prevented or cured
Conditions arise as a result of autoimmune response where the own immune system attacks the beta cells (CHILDHOOD - people develop symptoms quickly)
Type 2 Diabetes
Cannot effectively use insulin or do not respond properly to insulin/produce enough insulin - GLYCOPROTEIN insulin receptor on the cell membrane does not work properly and the cells lose their responsiveness to insulin (leave glucose in bloodstream)
Causes for type 2 Diabetes
90% of people have type 2 diabetes and this is largely as a result of excess body weight, physical inactivity and habitual/excessive overeating of carbohydrates - symptoms are less severe
Risk of type 2 diabetes
Increases with age - but nowadays also seen as children
Symptoms of diabetes
High blood glucose concentration
Glucose present in urine
Excessive urination (polyuria)
Excessive thirst (polydipsia)
Constant hunger
Weight loss + blurred version + tiredness
How do symptoms of diabetes arise?
Blood glucose concentration remains high and level of glucose in cells is low
Type 1 Diabetes treatment
Controlled by regular injections of insulin - insulin dependent ; a prick test first determines the blood glucose concentration which allows them to work out the dose of insulin they need to inject
What does insulin administered do?
Increases amount of glucose absorbed by cells and causes Glycogenesis to occur (reduces blood sugar concentration
Too low insulin?
Hyperglycaemia- which can also result in unconsciousness and death ; thus careful monitoring/dose regulation is required
If the person injects themselves with insulin?
Causes blood glucose levels to drop quickly
Control in type 2 diabetes
Regulate carbohydrate intake through their diet and match this to exercise levels - increases exercise levels and weight loss is needed
What else can be done to control type 2 diabetes?
Drugs may also have to be used to stimulate insulin production or slow down the rate at which the body absorbs glucose (slow down breakdown thus less glucose in bloodstream)
Original insulin production
Pancreas of cows and pigs
Disadvantages of early insulin?
Very expensive and could cause allergic reactions as they differed slightly
Advantages of insulin production via GM bacteria?
Less likely to cause allergic reactions
Insulin can be produced in much higher quantities
Cheaper
Religious/ethical concerns are overcome
Stem cell treatment in diabetes
Replace the faulty beta cells in pancreatic islets ; after a year patients have no symptoms BUT demand far outweighs their availability and the risk of having transplantable can also be greater than diabetes itself
What drugs are needed with stem cell treatment?
Immunosuppressant drugs that are required to ensure the body accepts the transplanted pancreas - leaves the person susceptible to infection
Immunosuppressant drugs
Prevent rejection of cells which increases metabolic demand of insulin-producing cells - eventually this exhausts their capacity to produce insulin
What type of stem cells are needed?
Totipotent for potential to grow into any body cell type ; likely they be taken from embryos - destroyed a potential JIA,m life and the embryo are used a source for stem cells - they are spare embryos for infertility treatments/terminated pregnancies
Stem cell advantages
Donor availability - produce an unlimited number of cells
Reduced likelihood of rejection
No longer have to inject themselves with insulin
Disadvantage stem cells
Uncontrolled control over growth/differentiation means they may form tumours
