homeostasis - osmo and gas (chapter 6)

intracellular fluid (cytosol): - fluid contained within the cells of an organism, - 2/3 pf total body water extracellular fluid: - plasma (1/4 of extracellular fluid) - intracellular (tissue/interstitual fluid) - (3/4 extracellular fluid, like lymph, cerebrospinal fluid, kidney filtrate etc.)

water: - moves via osmosis (passive transport - from areas of high concentration to low concentrations) nutrients and waste: - products if small enough and lipid soluble move via diffusion (passive) larger/water soluble substances: - cannot directly diffuse and may remain where they are

filtration: - blood enters renal capsule under high pressure selective reabsorption: - mainly in proximal convoluted tubule - some water and salts are reabsorbed in loop of Henle and distal convoluted tubule tubular secretions: - occurs in proximal and distal convoluted tubules

water is continually lost from the body in sweat, urine, faeces and exhaled air - makes plasma more concentrated and hence higher osmotic pressure water moves from interstitual fluid into the plasma via osmosis this results in the interstitual fluid becoming more concentrated water diffuses out of cells and the cells begin to think from dehydration osmoreceptors in the hypothalamus detect the increase in osmotic pressure

the volume and composition of urine produced by kidneys depends on how much water there is in the body fluids: - drink a large volume of water = produced a large volume of urine - drink not enough water = produces a small volume of concentration urine 99% of water filtered through the glomerulus of the kidneys is reabsorbed: - reabsorption occurring at the proximal convoluted tubule and loop of henle = osmosis - reabsorption occurring at the distal convoluted tubule and collecting duct = active reabsorption = levels of active reabsorption is controlled by the hormone ADH

• hypothalamus stimulates posterior pituitary gland to release ADH • after a stimulus of water concentration of blood plasma/osmotic pressure in blood increases • osmoreceptors in hypothalamus detect decrease in water concentration/increase in osmotic pressure • increased amount of eater is reabsorbed into blood/water concentration of blood plasma increases/osmotic pressure of blood decreases

• secreted from adrenal cortex • acts on distal convoluted tubules and collecting ducts to increase concentration of sodium ions in blood • decreases the concentration of potassium ions in blood, more K+ is excreted in urine • water is also reabsorbed from the filtrate with the sodium ions, hence aldosterone causes water content and blood volume to increase • as a result, aldosterone indirectly increases blood pressure due to the increase in blood volume

dehydration: - when 2% or more of body fluid lost, can be due to sweating, vomiting or diarrhoea (in elderly people thirst reflex isn’t as strong) can lead to severe thirst, head aches, low blood pressure and dizziness. intoxication: - body fluids become diluted and cells take in extra water due to osmosis, it can happen if you lose lots of water through sweating and replace with plain water. lightheadedness, vomiting and collapse

stimulus: - water concentration of blood plasma decreases, osmotic pressure of the blood is increased; mouth becomes dry receptors: - osmoreceptors in the thirst centre of the hypothalamus are stimulated modulator: - hypothalamus is stimulated (thirst centre) effector: - CNS develops conscious desire for water - skeletal muscles - voluntary control (reach for water) response: - person responds to the feeling of thirst by drinking - water drunk is absorbed into the blood from the alimentary canal negative response: - water leaves the blood and extracellular & intercellular fluids return to their normal concentrations

stimulus: - water concentration of blood plasma decreases, osmotic pressure of the blood is increased receptors: - osmoreceptors in the Hypothalamus are stimulated modulator: - hypothalamus stimulates the posterior lobe of the pituitary gland to release ADH effector: - permeability to water of the distal convoluted tubules and collecting ducts in the nephron of the kidney is increased. response: - increased reabsorption of water into the blood plasma from the DCT and collecting duct negative response: - water concentration of the blood plasma increases; osmotic pressure of the blood is decreased

• all cells need a constant supply of oxygen to provide energy through the process of cellular respiration • carbon dioxide is a by-product of cellular respiration, is toxic to calls, hence must be removed from the cellular environment • the respiratory system is responsible for taking in oxygen and excreting carbon dioxide • changes to rate and depth of breathing allow regulation of gas levels in blood

diaphragm: - muscles that separate the thorax from the abdomen - stimulated by impulses from the phrenic nerve - phrenic nerve originate from spinal nerves - these have their origin in the spinal cord at the level of the cervical and thoracic regions intercostal muscles: - muscles between the ribs - stimulated by impulses from the intercostal nerves - intercostal nerves originate from spinal nerves - these have their origin in the spinal cord at the level of the cervical and thoracic regions respiratory centre: - nerve impulses that travel to the diaphragm and intercostal muscles via the phrenic nerve and intercostal nerves are controlled by the respiratory centre, located in medulla oblongata of the brain - there are 2 regions within respiratory centre: - 1 controls expiration - 1 controls inspiration

when they are stimulated, they send a nerve impulse to the area of the respiratory centre that regulates breathing. peripheral: - groups of cells within the walls of the aorta and carotid arteries - sensitive to the changes in the concentration of oxygen, carbon dioxide and hydrogen ions in the blood plasma - known as aortic and carotid bodies central: - located in the medulla oblongata - sensitive to changes in the concentration of carbon dioxide in blood and hydrogen ions in the cerebrospinal fluid

• both O2 and CO2 are carried in the blood, their concentrations effect breathing rate • when CO2 dissolves into plasma it forms carbonic acid which readily breaks down into H- and bicarbonate ions • increasing H- concentrations causes a decrease in plasma, pH = more acidic • increasing CO2 concentrations and H- concentrations are main stimuli for increasing breathing rate and depth

• concentration has to fall to very low levels to stimulate an effect • a large decrease in oxygen concentration stimulates chemoreceptors in peripheral (sending an impulse) • sends to diaphragm and intercostal muscles so breathing rate and depth increase

stimulus: - increase CO2 levels - decreased pH/ increased H- levels - decrease in O2 levels receptors: - chemoreceptors (central in medulla oblongata - increase CO2 only) and (peripheral in aortic and carotid bodies - increase CO2 or decrease O2) modulator: - respiratory centre in medulla oblongata (sends message via phrenic and intercostal nerves) effector: - respiratory muscles - diaphragm and intercostal muscles response: - increased rate and depth of breathing negative response: - CO2 and O2 levels return to normal

• consists of: 1. an active inspiratory phase (contractions of diaphragm and intercostal muscles) 2. a passive expiratory phase (these muscles relaxing) • during the inspiratory phase the respiratory centre in medulla oblongata is active and sends out nerve impulses along the phrenic nerve and intercostal nerves to diaphragm, and intercostal muscles (contract) • during this phase the expiratory centre in medulla is suppressed - the inspiratory circuit remains active for approx. 2 seconds, then shuts down and respiratory muscles relax = breathing out • sequence takes 5 secs, normal breathing rate of 12-15 breaths per minute, the cycle continues

• panting after vigorous exercise • combination of 2 muscles contracting is the expulsion of air from lungs with considerable force

• human can control it, important for speaking • its a protective device (prevention of water, irritating gases from entering lungs) • cannot stop breathing indefinitely (build up of CO2 = breath to be taken)

• rapid, deep breaths • reduction of CO2, an increase of O2 • hyperventilation prior to swimming is dangerous because it can lead to drowning • increases breath holding abilities • may increase loss of consciousness due to lack of O2