Hormones Flashcards
What is the endocrine system?
Works alongside the neuronal system ro react to changes in the body or environment and bring about the most appropriate response
What is a hormone?
Any member of a class of signalling molecules produced by glands
What are the two types of hormone?
- Amino acid based hormones
- Steroid based hormones
Examples of amino acid based hormones:
- Proteins (insulin)
- Glycoproteins (FSH)
- Polypeptides (ADH)
- Amines
What are steroid based hormones?
- Based on cholesterol
- Examples are sex hormones oestrogen and testosterone
Mechanism for action of steroid based hormones:
- Lipid soluble so can dissolve through cell surface membrane
1) Entering a cell through phospholipid bilayer
2) Binding to receptor protein in nucleus
3) mRNA synthesis, which is the first step of protein synthesis
Mechanism for action of non-steroid based hormones:
Water soluble so cannot pass through cell surface membrane
1) Binding with receptors
2) Cell signalling using secondary messengers
3) Transcription factors activated in nucleus and protein synthesis begins
Differences between hormonal and neuronal communication:
- Hormones not directly released into their target cells
- Hormones not broken down as quickly as neurotransmitters
- Hormones stay in bloodstream for minutes to hours
- Hormones have relatively slow response
- Hormonal response is widespread
- Hormones transported by bloodstream
What are the adrenal glands?
- Glands located at the top of each kidney, covered by a capsule
- Adrenal cortex (outside layer)
- Adrenal medulla (inside layer)
What does the adrenal cortex do?
- Produce hormones vital to life
- Produces steroid based hormones
- Under control of hormones secreted by pituitary gland
- Releases three groups of horomones
What three groups of hormones does the adrenal cortex release?
- Glucocorticoids
- Mineralocorticoids
- Androgens
What do glucocorticoids do?
- Includes cortisol
- Regulates metabolism, controlling how body coverts fats, proteins and carbs to energy
- Help regulate blood pressure and cardiovascular functions in response to stress
- Regulates immune response and suppress inflammatory responses
- Release of these hormones controlled by hypothalamus
What do mineralocorticoids do?
- Main one is aldosterone
- Helps control blood pressure by maintaining balance between salt and water concentrations in blood and body fluids
- Release mediated by signals triggered by the kidney
What are androgens?
- Small amount of male and female sex hormones released
- Impact relatively small compared with larger amounts of hormones like oestrogen and testosterone
- important especially in women after menopause
What does the adrenal medulla do?
- Produces non essential hormones
- Produces amine based hormones
- Hormones released when body is under stress
- Under control of sympathetic nervous system
- Releases adrenaline and noradrenaline
What does adrenaline do?
- Increases heart rate
- Sends blood quickly to muscles and brain
- Rapidly raises blood glucose concentration
- Increases glycolysis
What does noradrenaline do?
- Works with adrenaline in response to stress
- Increases heart rate
- Dilates pupils
- Air passage in lungs widens
- Blood vessels narrow in non-essential organs
What does the pituitary glands do?
- Produces growth hormones
- Controls growth of bones and muscles
- Releases ADH
- Increases reabsorption of water in kidneys
- Controls development of ovaries and testes
What does the thyroid gland do?
- Produces thyroxine
- Control rate of metabolism and rate that glucose is used up in respiration
What does the pineal gland do?
Produces melatonin, which affects reproductive developments and daily cycles
What does the thymus do?
Produces thymosin, which promotes production and maturation of white blood cells
What does the pancreas do?
- Produces insulin
- Converts glucose to glycogen in liver
- Produces glucagon
- Converts glycogen to glucose in liver
What does the ovaries do?
- Produces oestrogen and progesterone
- Control ovulation and secondary sexual characteristics
- Prepares uterus lining for receiving an embyro
What does the testes do?
-Produces testosterone which controls sperm production and secondary sexual characteristics
What is the endocrine function of the pancreas?
Production of hormones insulin and glucagon and release of these directly into the blood
What is the exocrine function of the pancreas?
- Production of digestive enzymes, such as amylase, protease and lipase (for small intestine)
- Production of pancreatic juice
- Products secreted into a branching pattern of ducts
What is insulin?
- Protein based hormone
- Main anabolic hormone of the body
- Regulate metabolism of carbohydrates by promoting absorption of glucose from blood into liver and skeletal muscles cells
What is glucagon?
- Polypeptide based hormone
- Works to raise concentration of glucose in the blood
- Main catabolic hormone in the body
What is the pancreatic acini?
- Exocrine tissue
- Small, berry like collection of cells that drain into a duct
- Darker stain
- Acinus singular
What are the Islets of Langerhans?
- Endocrine tissue
- Spherical clusters of cells
- Lighter stained (island shaped on micrographs)#
- Contain alpha and beta cells
What are alpha cells?
- Produce and secrete glucagon
- Larger and more numerous than beta cells
- Often stained more pink in differential staining
What are beta cells?
- Produce and secrete insulin
- Smaller and less numerous than alpha cells
- Often stained blue in differential staining
What processes increase blood glucose concentrations?
1) Diet
eating and digesting carbohydrates
2) Glycogenolysis
break down of glycogen to glucose by glucagon
3) Gluconeogenesis
production of new glucose from non-carbohydrate sources (glycerol, amino acids)
What processes decrease blood glucose concentration?
1) Respiration
glucose in blood used for cellular respiration to produce ATP
2) Glycogenesis
production of glycogen
glucose converted in glycogen by insulin and stored in muscle and liver cells
Role of insulin:
- Blood glucose levels too high
- Virtually all cells have insulin receptors in their plasma membranes
- Main response comes from liver and skeletal muscle cells
- Glucose transport channel proteins open and glucose enters cells by facilitated diffusion
Role of glucagon:
- Blood glucose levels too low
- Only cells that have glucagon receptors in their plasma membrane are LIVER and ADIPOSE tissue cells
- Rate of glycogenolysis in liver cells increases
- Increase rate of gluconeogenesis
- Inhibit absorption of glucose from blood (glycogenesis)
- Decreases fatty acids synthesis
Why is glucose required for the contraction of skeletal muscle?
- Glucose used to produce ATP
- ATP breaks cross bridges between myosin and actin
- ATP for active transport of calcium ions into sarcoplasmic reticulum
How insulin released?
1) At normal levels of blood glucose, K+ channels in the plasma membrane of b cells are open and K+ diffuses out of cells (resting potential)
2) When blood glucose rises, glucose enters the cell by a glucose transporter
3) Glucose is metabolised inside the mitochondria, resulting in production of ATP
4) ATP binds to potassium ion channels and closes them
5) Membrane depolarises causing voltage gated calcium ion channels to open
6) Calcium ions enter the cell and cause secretory vesicles to release the insulin they contain by exocytosis
What is diabetes?
A group of metabolic disorders in which there is high blood glucose concentration for a prolonged period
What are the symptoms of high blood sugar?
- Frequent urination
- Increased thirst
- Increased hunger
What is type 1 diabetes?
- Inability to produce insulin (beta cells don’t produce it)
- Early onset in childhood
- Cause is unknown but likely to be an autoimmune disease
What is type 2 diabetes?
- Inability to use insulin effectively
- Either beta cells do not produce enough insulin
- Or body cells don’t respond properly to insulin
- Often the insulin receptors do not produce the correct response in the cells metabolism
- Risk factors are excess body mass, lack of exercise, overeating of refined carbohydrates
How is type 1 diabetes treated?
- Controlled by regular injections of insulin
- Insulin dependent
- Regularly test blood glucose
- Machine analyses blood and shows b.g concentration
- From this reading, person can work out how much they need to inject
How is type 2 diabetes treated?
- First line of control is to regulate person’s carbohydrate intake through their diet and matching this to exercise levels
- In some cases, exercise and diet not enough so drugs are used
- Drugs can stimulate injection production and slow down the rate at which the body absorbs glucose from the small intestine
- In some severe cases, insulin injections will be used
How is insulin medically produced?
- Isolated pigs or cow insulin used up to late 1970s
- This process was difficult, expensive and caused allergic reactions in some diabetics
- Genetically engineered human insulin from E. coli in 1978
How can stem cells be used to treat diabetes?
- Stem cells can be used to make beta cells in type 1 diabetics
- Likely to come from human embryos or umbilical stem cells
Why is using stem cells better than a pancreas transplant when treating type 1 diabetes?
- Reduce risk of rejection
- Insulin injections become redundant
- No waiting list
Disadvantages of using stem cells to treat type 1 diabetes:
- Destruction of embryo
- Stem cells could become cancerous tumour
What is the fight or flight response?
- Coordination between neuronal and endocrine systems to bring about correct responses to external stimuli
- In this case, the response is to potentially dangerous situations
What is the fight or flight response?
- Autonomic nervous system detects a threat
- Hypothalamus communicates with the sympathetic nervous system and the adrenal cortical system
- Sympathetic nervous system uses nervous impulses to cause the adrenal medulla to release adrenaline and noradrenaline and smooth muscles and glands to respond appropriately
- Hypothalamus communicates with the pituitary gland which secretes ACTH
- ACTH stimulates adrenal cortex to release cortisol and corticosterone
Responses and reasons during fight and flight:
- Cortisol increases blood pressure so more blood is pumped around the body
- Adrenaline increases heart rate so more blood pumped around body
- Noradrenaline widens pupils to take in as much light as possible
- Noradrenaline causes dilation of bronchioles to allow oxygen into the lungs for increased respiration
- Sympathetic nervous system causes tunnel vision so you only focus on what’s in front of you
- Adrenaline increases release of glucose by liver cells so increased respiration can be carried out
- Sympathetic nervous system increases muscle tension to provide body with extra strength and speed
What is the action of adrenaline when promoting glycogenolysis?
1) Adrenaline binds to receptor site in cell surface membrane
2) Binding activates adenylyl cyclase
3) Activated enzyme converts ATP to cyclic AMP, which acts as a second messenger
4) cAMP activates other enzymes that, in turn, convert glycogen to glucose
How heart rate controlled?
- Control of heart rate is involuntary and under control of autonomic nervous system
- Part of autonomic nervous system responsible for heart rate is the medulla oblongata
What is the medulla oblongata?
- Located in the brainstem
- Connects the higher levels of the brain to the spinal cord
- Responsible for autonomic functions ranging from vomiting to sneezing
- Contains cardiac centre
How does the medulla oblongata control heart rate?
Two centres
1) Once centre increases heart rate through the sympathetic nervous system using the accelerator nerve connected to the SAN
2) Once centre decreases heart rate through the parasympathetic nervous system using the vagus nerve connected to the SAN
What are the two sets of receptors in blood vessels?
1) Baroreceptors detect blood pressure (aorta, vena cava, carotid arteries)
2) Chemoreceptors detect blood CO2 concentration by measuring blood pH (aorta, carotid arteries, medulla oblongata)
How does the medulla oblongata control CO2 levels in the blood?
1) Too much CO2
- lower blood pH detected by chemoreceptors
- centre in medulla oblongata increases frequency of impulses to the SAN via sympathetic nervous system
- SAN increases heart rate
- increased blood flow removes CO2 faster
2) Too little CO2
- opposite of above
How does medulla oblongata control blood pressure?
1) Too high
- baroreceptors detect change in blood pressure
- nervous impulses sent to medulla oblongata
- medulla oblongata sends nervous impulses along parasympathetic nervous neurones to SAN
- SAN decreases heart rate
- blood pressure reduced
2) Too low
- opposite of above
How do hormones affect heart rate?
- Hormones that control or influence heart rate do by affecting the SAN directly
- Adrenaline and noradrenaline both increase heart rate
