- Endocrine system is made of endocrine glands which are a group of cells specialised to secrete chemicals (hormones) directly into the bloodstream
- Pituitary gland = growth hormone, ADH, FSH, LH
- Thyroid gland = thyroxine
- Adrenal gland = adrenaline, noradrenaline, aldosterone
- Testis = testosterone
- Ovaries = oestrogen
- Pancreas = insulin, glucagon
- Thymus = thymosin
Hormones
- Secreted directly into the blood
- They then diffuse to bind to specific receptors on target cells or organs
- Once bound they cause the organ to produce a response
- Steroid hormones --> lipid soluble so pass through the cell membrane of the cell and bind to receptors in the cytoplasm or nucleus --> forms a hormone-receptor complex which has a transcription factor attached so a gene is either activated or inhibited as a result
- Non-steroid hormone --> hydrophillic so bind to specific receptors on the cell surface membrane --> triggers cascade reaction in cell involving secondary messengers like cAMP
Adrenal glands
- Adrenal cortex --> outer region of the glands where cortisol and aldosterone are made
- controlled by hormones released from the pituitary gland
- Glucocorticoids (release controlled by hypothalamus) --> cortisol which regulates metabolism and corticosterone which works with cortisol to regulate the immune response and suppress inflammatory reactions
- Mineralcorticoids (release controlled by signals from the kidneys) --> aldosterone which helps control blood pressure and maintain water and mineral balances in the blood
- Andorgens --> small amounts of sex hormones
- Adrenal medulla --> inner region of the gland where adrenaline and noradrenaline are made
- released when the sympathetic nervous system is stimulated
- adrenaline --> increases heart rate, raises blood glucose levels (glycogenolysis and gluconeogenesis)
- noradrenaline --> works with adrenaline to increase the heart rate, dilate the pupils, widen air passages and narrow blood vessels to non-vital organs
Fight or flight response
- Once a threat is detected by the autonomic nervous system, the hypothalamus is stimulated
- Hypothalamus stimulates sympathetic nervous system
- The sympathetic nervous system stimulates the adrenal medulla and smooth muscles to secrete adrenaline and noradrenaline
- Hypothalamus stimulates the pit. gland to release ACTH
- ACTH travels to the adrenal cortex and activates the release of about 30 hormones to help with the response
- heart rate increases to pump more oxygenated blood to the muscles for respiration
- pupils dilate to take in as much light as possible for better vision
- aterioles near skin constrict to send more blood to major muscle groups
- blood glucose rises to increase glucose available for respiration
- smooth muscle in airways relaxes to let the most amount of air into the lungs
- non-essential systems shut down to focus energy to muscles
Action of adrenaline
- Adrenaline is non-steroid based so binds to specific receptors in the cell membrane
- When it has bound, the enzyme adenylyl cyclase inside the cell is activated
- Adenylyl cyclase triggers the conversion of ATP to cyclic AMP or cAMP on the inner surface of the membrane in the cytoplasm
- The increase in cAMP activates protein kinases which phosphorylate and in turn activate other enzymes (e.g. enzymes that break down stored glycogen to glucose)
The pancreas
- Endocrine gland --> produces hormones (insulin and glucagon) that are released into the bloodstream
- Exocrine gland --> produces enzymes (amylases, proteases and lipases) which are released into the duodenum
- Islets of Langerhans have alpha and beta cells
- Alpha cells produce glucagon
- Beta cells produce insulin
- Alpha cells are bigger and more numerous in the islets than the beta cells
- Beta cells are usually stained blue and alpha cells are pink
Controlling blood glucose
- Example of negative feedback loop
- Increased via diet, glycogenolysis and gluconeogenesis
- Decreased via respiration and glycogenesis
- Role of insulin
- high blood glucose is detected by the beta cells and they respond by secreting insulin into the bloodstream
- virtually all body cells have insulin receptors in their plasma membranes
- when insulin binds to its glycoprotein receptor it changes the tertiary structure of the glucose transport channel proteins in the membrane
- this increases the cell's permeability to glucose so more is removed from the blood
- insulin also activates the enzymes that convert glucose to glycogen in the cell (glycogenesis)
- insulin also increases the respiratory rate of cells and inhibits the release of glucagon by the alpha cells
- Role of glucagon
- low blood glucose is detected by the alpha cells and they respond by secreting glucagon into the bloodstream
- only liver and fat cells have receptors for glucagon so they are the only ones that can respond to the hormone
- glucagon causes glycogenolysis, reduced respiration and increased gluconeogenesis
Control of insulin secretion
- Normal glucose levels --> K channels on the beta cells are open and the cell has a potential of -70mV
- When glucose levels rise, the concentration of glucose inside the cell increases too as it moves in via a glucose transporter
- The glucose is metabolised inside the mitochondria resulting in ATP synthesis
- The ATP binds to the K channels and causes them to close as they are ATP-sensitive potassium channels
- As K cannot leave the cell so the potential rises to -30mV and depolarisation occurs
- This causes the voltage-gated calcium channels to open
- The Ca2+ diffuses in and causes the insulin-containing vesicles to move to the membrane and release the insulin via exocytosis
Diabetes
- Type 1 = patients are unable to produce insulin (usually due to an autoimmune disease that attacks the beta cells) --> usually treated with insulin injections
- inject too much and they'll suffer from hypoglycaemia (low blood glucose) and fall unconcious
- inject too little and they'll suffer from hyperglycaemia (high blood glucose) and fall unconcious and possibly die if left untreated
- Type 2 = patients cannot effectively use or make insulin in order to deal with their blood glucose levels, or their insulin receptors have become unresponsive to the hormone (usually due to diet and often associated with obesity) --> treated via diet and exercise, sometimes with injections but they aren't particularly effective
- Pancreas transplants are also effective for type 1 sufferers but transplants come with their own risks (rejection or infection from the surgery) and the waiting list is very long
- Beta cell transplants have also been tried but they're not very effective as the immunosuppressants that must also be taken increase the metabolic demand on the beta cells which exhausts them
- Stem cells have the potential to help but it seems like the best stem cells to use will be embryonic ones which bring their own ethical issues
- donor availability wouldn't be an issue
- reduced likelihood of rejection
- people wouldn't have to inject themselves with insulin anymore
Controlling the heart rate
- Heart rate is controlled by the autonomic nervous system
- The medulla oblongata is responsible for controlling it and making changes
- Two centres of the med. oblongata which are linked to the SAN via motor neurones
- accelerator nerve increases the heart rate by sending impulses along the sympathetic nervous system
- vagus nerve decreases the heart rate by sending impulses along the parasympathetic nervous system
- Two types of receptor that provide information that affects the heart rate
- baroreceptors --> detect blood pressure --> aorta, vena cava and carotid arteries
- chemoreceptors --> detect changes in the levels of chemicals (like carbon dioxide) in the blood --> aorta, carotid artery and medulla
- Chemoreceptors:
- sensitive to changes in the pH of the blood
- CO2 increases --> pH of blood decreases due to more carbonic acid --> centre in med. oblongata increases frequency of impulses via accelerator nerve to SAN (sympathetic nervous system) --> increase in heart rate --> more blood flow to lungs to remove the CO2 quicker
- CO2 decreases --> pH of the blood increases due to less carbonic acid --> centre in med. oblongata decreases frequency of impulses to the SAN --> decreases the heart rate --> less flow to the lungs as its not needed
- Baroreceptors:
- blood pressure too high --> med. oblongata sends impulses along vagus nerve to the SAN (via parasympathetic nervous system) to decrease the heart rate --> puts the pressure back to normal
- blood pressure too low --> med. oblongata sends impulses along accelerator nerve to the SAN (via sympathetic nervous system) to increase the heart rate --> puts pressure back to normal
- Hormones also effect the heart rate --> adrenaline and noradrenaline bind to SAN to affect it in the fight ot flight response
Endotherms and ectotherms
- Ectotherms --> use their surroundings to warm their bodies (reptiles and amphibians)
- behavioural responses --> they bask in the sun, orientating as much surface area toward the sun to absorb the most head by radiation or they can increase their body heat by conduction by pressing their bodies against warm ground or can use some exothermic metabolic reactions
- they shelter from the sun or dig burrows to cool down or they press their bodies against cool rocks or stones or they orientate their bodies so that a small surface area is in the sun
- physiological responses --> they use the fact that dark colours absorb more heat radiation than light and some increase or decrease their heart rate to effect their metabolic activity
- Endotherms --> rely on metabolic processes to heat themselves, usually maintain a steady body temperature regardless of their environment (mammals and birds)
- behavioural responses --> basking in the sun, pressing themselves to warm surfaces, wallowing in water and mud or digging burrows --> humans wear clothes and build houses
- physiological responses --> peripheral temperature receptors, thermoregulatory centres in the hypothalamus, the skin and muscles
- anatomical adaptations --> animals in hot climates have large SA:Vol to increase heat loss (big ears) and pale fur or feathers to reflect the sun but animals in cold climates do the opposite often having a thick insulating layer of blubber
- cooling down
- vasodilation --> vessels near the skin dilate so more heat is lost via radiation through the skin
- increased sweating --> as sweat evaporates from the surface of the skin, heat is lost and the blood below is cooled
- reducing the insulating effect of hair --> erector pili muscles in the skin relax and hairs lay flat to remove the insulating layer of air
- warming up
- vasoconstriction --> vessels near the skin constrict so less heat is lost via radiation through the skin
- decreased sweating --> reduces the cooling provided by the evaporation of water from the surface of the skin
- raising of body hairs or feathers --> erector pili muscles contract to lift the hairs or feathers which traps a layer of air to insulate the body and reduce heat loss
- shivering --> rapid and ivoluntary contracting and relaxing od the large voluntary muscles to increase respiration which releases heat
- Changes to the temperature of the blood are detected in the hypothalamus which sends impulses along motor neurones and the autonomic nervous system to effectors in the skin and muscles to create these ^^^^ responses
The Liver
- Has a very rich blood supply
- Blood supplied by hepatic artery
- Blood removed by hepatic vein
- Blood loaded with products from digestion supplied by the hepatic portal vein
- Hepatocytes (liver cells) have large nuclei, prominent Golgi apparatus and lots of mitochondria
- Blood from hepatic artery and portal vein mixed together in spaces aka sinusoids which are surrounded by hepatocytes
- Mixing increases the oxygen content to satisfy the needs of the hepatocytes
- Sinusoids contain Kupffer cells which act as macrophages
- Hepatocytes secrete bile which drain into the canaliculi that drain into the bile duct to the gall bladder
- Functions of the liver
- carbohydrate metabolism
- hepatocytes are particularly responsive to insulin and glucagon
- they convert glucose to glycogen and store it and reverse this when glucagon is about
- deamination of excess amino acids
- hepatocytes synthesise most of the plasma proteins
- hepatocytes carry out transamination where one amino acid is converted to another
- hepatocytes carry out deamination where the amine group is removed from the molecule
- the amine group is converted to ammonia and then to urea to be removed
- the rest of the amino acid can be used in respiration or the formation of lipids
- ammonia is converted to urea through the ornithine cycle (ornithine --> ammonia added, CO2 added, water produced --> citruline --> ammonia added, water produced --> arginine --> water added, urea produced --> ornithine)
- detoxificiation
- hydrogen peroxide --> by-product of metabolic pathways --> hepatocytes contain catalase which splits it into oxygen and water
- ethanol --> hepatocytes contain alcohol dehydrogenase --> ethanol converted to ethanal --> ethanal converted to ethanoate which can be used to make fatty acids
- carbohydrate metabolism
The kidneys
- Made of millions of nephrons
- Ultimately, urine is made which is taken to the bladder by the ureters and it then leaves the body via the urethra
- Medulla --> contains the tubules of the nephrons and the collecting ducts
- Cortex --> where the blood is filtered through the dense capillary network
- Pelvis --> central chamber where the urine collects before going to the bladder
- Nephrons
- Bowman's capsule --> contains the glomerulus with its afferent and efferent arteriole
- Proximal convoluted tubule --> in the cortex, many of the substances are reabsorbed into the blood
- Loop of Henle --> creates a region of high solute concentration in the medulla to increase water reabsorption
- Distal convoluted tubule --> in the cortex, fine-tuning of water balance, ions and pH, permeability of walls to water controlled by ADH
- Collecting duct --> more fine-tuning of water balance and also controlled by ADH
- Ultrafiltration
- wide afferent arteriole of glomerulus but narrower efferent arteriole
- this means the glomerulus has a high pressure which forces blood out through the capillary wall
- the fluid then pushes through the basement membrane AND podocytes with pedicels into the Bowman's capsule
- the fluid in the Bowman's capsule contains water, ions, glucose and other substances
- Reabsorption
- PCT
- all the glucose, amino acids, vitamins and hormones moved back into the blood via active transport
- Na ions move by active transport and Cl ions follow passively
- PCT cells covered in microvilli and have many mitochondria
- once removed from the nephron, the substances diffuse into the capillary network down steep concentration gradients
- Loop of Henle
- ascending limb is very permeable to sodium and chloride ions
- in the early limb they just diffuse out but further up they are actively transported out
- this makes the region hypertonic compared to the descending limb
- descending limb is very permeable to water and due to the hypertonic region created by the ascending limb the water moves out passively by osmosis
- DCT
- permeability of tubule controlled by ADH
- have many mitochondria for active transport
- if the body lacks salt, the ions are pumped out
- water can also leave if there's ADH and aquaporins
- Collecting duct
- main site that's effected by ADH
- the ion concentration in the surrounding solution increases as you go down meaning water can move at any point --> produced hypertonic urine
- PCT
Osmoregulation
- ADH in produced in the hypothalamus and secreted by the posterior pituitary gland
- ADH increases the permeability of the CD and DCT to water
- The hormone is released into the bloodstream
- It binds to the receptors on the cells and triggers the formation of cAMP
- cAMP causes the vesicles lining the collecting duct to fuse to the surface membranes and insert the aquaporins into these membranes
- This provides a route for water to move via osmosis out of the CD and into the capillaries
- more ADH = more aquaporins so more water is reabsorbed
- When ADH levels fall, the process is reversed --> cAMP levels fall so the aqauporins are removed from the membranes and they are made less permeable
- When water levels are low, the osmoreceptors detect that ion concentration of the blood is high and the water potential of the blood and tissue fluid is more negative --> ADH released
- When water levels are high the blood becomes more dilute and the water potential of the blood and tissue fluid becomes less negative --> the release of ADH is inhibited
Kidney failure
- Shown by protein or blood in the urine
- Results in loss of electrolyte balance, build up of urea, high blood pressure, weakened bones, pain and stiffness in joints and anaemia
- If the levels of creatinine in the blood increase it is a sign that the kidneys are damaged
- Dialysis
- Haemodialysis --> blood taken from an artery, blood thinners are added, it passes over a semi-permeable membrane where nutrients either diffuse in or out to the optimum levels then returns to the body (uses a countercurrent system to maintain the concentration gradients)
- Peritoneal dialysis --> inside the body, used the peritoneum as the membrane, dialysis fluid is introduced through a catheter --> excess urea and ions pass out of the capillaries, into the tissue fluid across the membrane and into the dialysis fluid where its drained off
- Transplants
- risk of rejection --> match between antigens is made as closely as possible
- recipient is treated with immunosuppressants for the rest of their lives --> can't respond effectively to any infections
- transplant doesn't last forever
- waiting lists can be very long
Pregnancy tests
- Work using monoclonal antibodies that complement hCG (human chorionic gonadotrophin) which is made by the development of the placenta
- Main stages:
- Wick is soaked in the first urine passed in the morning
- Test contains mobile monoclonal antibodies that have dye attached that will only bind to hCG
- If she's pregnant, the hCG binds to the antibody making a hCG-antibody complex (with the dye)
- The urine moves up the test by capillary action
- 1st window has immobilised antibodies that only bind to hCG-antibody complex (if they do the dye attached will show the positive shape)
- 2nd window has immobilised antibodies that will bind to the mobilised ones regardless of whether they have a hCG attached --> this proves that the test has worked
Other urine tests
- Anabolic steroids
- tested with gas chromatography and mass spectrometry
- sample is vapourised with a known solvent and passed along a tube
- a lining of the tube absorbs the gases and is analysed to give an image that can be read to show the presence of drugs
- Drug testing
- immunoassay which uses monoclonal antibodies that bind to the drug or its breakdown product
- ^ if this is positive, they use gas chromatography and mass spectrometry to confirm the presence of a drug
