homeostasis Flashcards
homeostasis
process of keeping the environment inside fairly constant despite fluctuations in external environment.
- Body needs optimal temp, pH, oxygen, glucose, etc.
- Makes us independent of external environment.
- There is a dynamic equilibrium, input and output need to be balanced
- Nervous and endocrine system are the main sensory and controlling body systems
› Operate through feedback systems
feedback system
responds to stimulus, response alters original stimulus
- Stimulus: change in environment that causes system to operate
- Receptor: detects change
- Modulator: control centre responsible for processing information from receptor and for sending information to effector
- Effector: carries out a response counteracting/enhancing the effect of the stimulus
- Response: original stimulus has been changed. Feedback achieved
- Homeostatic mechanisms controlled by nervous and endocrine systems. Both detect changes, endocrine is slower.
negative feedback
response reduces or eliminates the stimulus that caused feedback loop.
- AKA steady state system: return body back to steady state
- Dynamic equilibrium = fluctuation
- Point around which it fluctuates = set point
- Tolerance limits = upper and lower limits around which levels fluctuate
› If rise/fall exceeds tolerance limits, dysfunctions occur
positive feedback
no role in homeostasis. Response to stimulus reinforces and intensifies the stimulus results in a greater response
- Childbirth:
› Labour initiated by secretion of oxytocin
› Oxytocin creates uterine contractions; contractions push baby’s head against cervix
› Stimulation of cervix sends impulses to brain which secretes more oxytocin.
› Increased oxytocin increasingly intensifies contractions
› Once baby delivered and cervix no longer stretched, positive feedback stops
- Blood clotting is another example
- Can be dangerous if you have a high fever:
› small rise in temp is good when fighting fever, but when body temp exceeds 42ºC, positive feedback loop occurs
› raised body temp increases metabolic rate which makes more heat, so temp increases.
thermoregulation
- Set point is 36.8ºC: optimal temp for cellular activities
- Heat gain = heat loss
- Heat gain: heat from metabolism, heat from surroundings by conduction/radiation
- Heat loss: radiation, convection, conduction to surroundings, evaporation of water from skin and lungs, warm air breathed out, warm urine and faeces excreted
heat production
- Food we eat contains energy in chemical bonds
› Energy released when oxidised
› 60% of energy used for heat production - Metabolic rate: rate at which energy is released by breakdown of food
- Factors effecting metabolic rate
› Exercise
› Body temp
› Stress: stimulation of sympathetic nerves releases noradrenaline from nerve endings: increasing metabolic activity of cells
thermoreceptors
- Peripheral thermoreceptors: detect temp change in external environment, and send info to hypothalamus (skin and mucous membrane)
- Central thermoreceptors: detect temp of internal environment (hypothalamus, spinal cord, abdominal organs)
- Cold receptors: stimulated by temp lower than normal
- Heat receptors: detect temp higher than normal
skin and thermoregulation
- Large SA and location of skin makes it essential. Heat can be lost by:
› Conduction: transfer by direct contact
› Convection: transfer by movement of liquid/gas
› Radiation: transfer by infrared radiation
› Evaporation: liquid forming gas, absorbs heat energy
blood vessels and heat loss
- Blood vessels in dermis carry heat to skin from body core
› Diameter controlled by autonomic nerves - Vasodilation: moves blood to skin and rate of heat loss increases
- Vasoconstriction: less blood to skin, heat loss rate decreases
sweating and heat loss
- When heat must be lost and arterioles are already dilated, sweating occurs
- Sweating: active secretion of fluid by sweat glands and periodic contractions of cells surrounding sweat glands to pump sweat to skin surface
- Stimulated by sympathetic nerves
- Sweat: water and dissolved substances (salt, urea, lactic acid, potassium ions)
- Evaporation of sweat has a cooling effect
› Heat removed from skin as sweat vaporises cooling skin which cools blood in skin
› Also, water evaporated by lungs and respiratory passages
shivering and heat gain
- Shivering due to increased skeletal muscle tone producing rhythmic muscle tremors
› Energy produced by muscles is released as heat
preventing body temp from falling
- Cold receptors send messages to hypothalamus
- Hypothalamus sends impulses to initiate warming processes
› Stimulates sympathetic nerves that cause skin arterioles to constrict. Cooler skin, less heat lost from body surfaces
› Stimulates adrenal medulla by sympathetic nerves to secrete adrenaline and noradrenaline in blood: increases cellular metabolism
› Stimulates parts of brain that cause shivering. Under primal control of hypothalamus, conscious input from cerebral cortex can suppress urge to shiver
› Anterior lobe secretes TSH. Increased metabolic rate which increase bod temp. slower and long lasting.
› Reduce SA of body, remove layers, move closer to heat source (consciously aware of cold conditions)
› Piloerection
preventing body temp from rising
- Vasodilation: greater heat loss by radiation and convection
- Sweating: cooling effect in dry environment
› Humid: sweat cant evaporate so it doesn’t absorb heat from body
› Less thyroxine: decrease in metabolic rate
› Removing layers, reducing physical activity
control of thermoregulation
- Hypothalamus is modulator
› Receives impulses from peripheral thermoreceptors through negative feedback loop, including autonomic nervous system, thermoregulation mechanisms are maintained
temperature tolerance
- Heat stroke: body temp rises and regulating mechanisms cease. Fatal if brain cells effected (42-45ºC)
- Heat exhaustion: results from extreme sweating and vasodilation to lose heat
› Loss of water reduces volume of blood plasma
› vasodilation reduces resistance to blood flow
› low BP and output of blood from heart decreases
› body temp is almost normal - Hypothermia: temp falls below 33ºC
› Metabolic rate is so low that heat production is unable to replace heat lost and temp continues to fall
› Death below 32ºC
glucose regulation
• Sugar in blood in form of glucose
• Blood sugar = amount of glucose in blood
- Glucose is a source of energy
• Source of glucose is food:
- Carbohydrates broken down to glucose and then absorbed by blood through walls of small intestine
- After a meal BGL rise sharply
- Homeostatic mechanisms reduce BGL by storing excess glucose ready for when BGL drops
glucose and glycogen
- Glucose is stored as glycogen
› Glycogen: molecule made of long chains of glucose molecules - Body can store 500g of glycogen (100g in liver, remainder in skeletal muscles)
- Excess glucose to glycogen
- Not enough glucose, glycogen to glucose
role of liver
- Largest gland
- Converts glucose to glycogen or glycogen to glucose
- Liver’s blood supply comes mostly through the hepatic portal vein.
› Brings blood from stomach, spleen, pancreas, small and large intestine
› Liver has first chance to absorb nutrients from digested food - Glucose absorbed by villi in small intestine
› Hepatic portal vein brings glucose to liver - Glucose can:
› Removed from blood by liver to provide energy for liver functioning
› Removed by liver/muscles and converted to glycogen for storing
› Continue to circulate in blood, for other body cells to use as a source of energy
› Be converted into fat for long term storage if it is in excess of that required to maintain both normal blood sugar and tissue glycogen levels - Glycogenesis: when glucose molecules are chemically joined in long chains to make glycogen (stimulated by insulin)
› Glycogen stored in liver is available for conversion to maintain BGL and provide energy for liver functioning
› Glycogen in muscles provide glucose for muscle activity - Glycogenolysis: when glycogen is broken down into glucose
› Stimulate by glucagon
› Glycogen is short term energy supply (6 hours). If more energy is required, body uses energy reserves stored in fat - Gluconeogenesis: conversion of fats or proteins into glucose
role of pancreas
- Clusters of hormone secreting cells (islets of Langerhans)
- Insulin causes a decrease in BGL:
› Accelerates transport of glucose from blood into body cells (especially skeletal muscle)
› Accelerates conversion of glucose into glycogen in liver and skeletal muscles (glycogenesis)
› Stimulation of glucose to protein (protein synthesis)
› Stimulating conversion of glucose into fats in adipose tissue or fats storage tissue (lipogenesis) - BGL regulated by negative feedback loop
- As BGL rises, chemoreceptors in beta cells stimulate those cells to secret insulin
› As BGL decrease the cells are no longer stimulated and production reduced - Glucagon causes an increase in BGL:
› Stimulate glycogenolysis in liver
› Stimulates gluconeogenesis: production of sugar molecules from fats and amino acids in liver. Involves lipolysis
› Have a mild stimulating effect on protein breakdown - When BGL rises, chemoreceptors in alpha cells stimulate secretion of glucagon.
› As BGL rises, cells no longer stimulated, and production reduced
role of adrenal glands
- Glucocorticoids secreted by adrenal cortex
- Secretion of adrenaline/noradrenaline by adrenal medulla
- Adrenal cortex:
› Stimulated to secrete hormones by ACTH from AL of pituitary gland
› Cortisol secreted
› Glucocorticoids regulate carbohydrate metabolism by ensuring enough energy is provided to cells
› Stimulate conversion of glycogen to glucose in glycogenolysis.
› Also increases rate at which AA are removed by cells (mainly muscle) and transported to the liver - Some AA to glucose by liver during gluconeogenesis if glycogen and fat are low
› Promote metabolism of fatty acids from adipose tissue, allowing muscle cells to shift from using to glucose to FA for much of their metabolic energy - Adrenal medulla:
› Synthesis of adrenaline and noradrenaline make same effects as sympathetic nervous system
› Effect is increase of BGL: adrenaline elevates BGL through glycogenolysis and counteracts effects of insulin - Stimulates production of lactic acid from glycogen in muscle cells, can be used by liver to manufacture glucose
blood glucose homeostasis
- 4-6 millimoles/L
- 5mmol/L = 90mg/100ml
osmoregulation
• Water makes up large portion of human body
- 75% infants
- 50% females
- 60% males
- 45% old age
• Fluid inside cell: intracellular fluid/cytosol
• Fluid outside cell: extracellular:
- Blood plasma located within blood vessels (intravascular)
- Fluid between cells (interstitial, intercellular, tissue)
- Fluid in specific body regions (transcellular)
› Brain, spinal cord, eyes, joints, surrounding heart
• Different body fluids aren’t isolated from one another. Continuous exchange of materials between them
• If imbalance in osmotic concentration (conc of solutes) does occur, osmosis normally restores balance
- Osmotic pressure: tendency of a solution to take in water
› Greater difference in osmotic conc, the greater the osmotic pressure
› Osmosis tends to occur
maintaining fluid balance
- Fluid gain = fluid loss › Keeps composition of body fluid constant - Water intake: › Food › Metabolic water (by-product) › Drink - Water loss: › Lungs › Skin › Kidneys (urine) › Alimentary canal (faeces)
excretion
- Removal of waste products of metabolism from the body
› Toxic, so harmful if it accumulates - Lungs excrete water (vapour) and carbon dioxide
- Sweat glands: secret water containing by-products of metabolism
- Alimentary canal: passes out bile pigments that entered small intestine with bile
› Bile pigments are breakdown products of Hgb from RBC
› Bulk of faeces is undigested food (not excretory producst as it isn’t produced by cells) - Kidneys: principle excretory organ
› Maintain constant conc of materials in body fluids
› Maintain waste in urea
kidneys
- Only place where water loss can be regulated for osmoregulation
› Sweat glands regulated by thermoregulation - Regulated to achieve a constant conc of dissolved substances in body fluids
- Reddish brown, abdomen, wither side of vertebral column, 11cm lon, due to presence of liver: right is usually lower
- Embedded in and held in position by a mass of fatty tissue
- Ureter leaves each kidney, to bladder, to urethra
- Each kidney has ~1.2 million nephrons
› Nephrons: functional unit, carry out role in excretion and water regulation
› 1. Blood enters glomerulus under high pressure
› 2. Filtration: high BP forces water and small dissolved molecules out of blood and into capsule. Large molecules stay in blood
› 3. Filtrate collected by glomerular capsule
› 4. Reabsorption: filtrate passes PCT, LOH, DCT, CD. Water and other useful substances reabsorbed into peritubular capillaries
› 5. Secretion: some materials that need to be removed from body are secreted into kidney tubule from peritubular capillaries
› 6. Urine: water and dissolved substances make up urine. Carried by collecting ducts to ureter to bladder
controlling water levels
- As water is lost, plasma becomes more concentrated and has higher osmotic pressure.
› Water moves from interstitial fluid to plasm by osmosis
› Interstitial fluid more concentrated and water diffuses out of cells
› cells start to shrink from dehydration - osmoreceptors in hypothalamus detect increase in osmotic pressure
kidneys and ADH
- Dehydrated = urine is less volume and concentrated
- Reabsorption of water occurring at PCT and LOH is osmosis
- Reabsorption at DCT and CD is active reabsorption controlled by ADH
- When ADH conc is high tubules are very permeable to water
› Water able to leave tubule and re-enter peritubular capillaries
› Outward flow of water from filtrate reduces volume and increases conc of remaining materials - When ADH conc is lower: tubules not very permeable
› Little water reabsorbed into plasma
› Filtrate remains fairly dilute and volume not reduced
kidneys and aldosterone
- Aldosterone helps osmoregulation
- Salt-retaining hormone
- Secreted by adrenal cortex in response to:
› Low sodium in blood
› Low blood volume and pressure
› High potassium in blood - Acts on DCT and CD to increase sodium reabsorbed and amount of potassium secreted in urine
- Uses active transport using a sodium potassium pump
› Every 3 sodium, 2 potassium secreted
› Net movement into blood and subsequent transport of water into blood via osmosis
› So aldosterone has a role in osmoregulation
thirst response
- Osmoreceptors able to stimulate thirst centre in hypothalamus promoting person to drink water
› Fluid absorbed across wall of alimentary canal into blood decreasing osmotic pressure
› Excess fluid in interstitial fluid is collected by lymph system
water intoxication
- Body fluids become diluted and cells take in extra water by osmosis
- Person loses water and salt through sweating and replaces loss with water
- Light-headedness, headache, vomiting
dehydration
- Water loss exceeds intake
- Severe thirst, low BP, dizziness, headache
gas regulation
- Cells need a continuous supply of oxygen and removal of carbon dioxide
- Respiratory system takes in oxygen and removes carbon dioxide, respiratory system transports them
control of breathing
- Muscles that cause air to move in and out are:
› Diaphragm: separates thorax from abdomen
› Intercostal muscles: muscles between ribs - Skeletal muscles require stimulation from nerve impulses to contract
- Phrenic nerve: stimulates diaphragm
- Intercostal nerve: stimulates intercostal muscle
› Spinal nerves have their origin in the spinal cord at the level of the neck and thorax - Nerve impulses controlled by respiratory centre in the medulla oblongata. 2 regions:
› Controls expiration
› Controls inspiration
› To coordinate breathing, messages need to pass between neurons of these regions
chemicals effecting breathing
- Conc of CO2, O2 affect breathing rate and depth
- Conc of CO2 in blood plasma affects H+ conc
- These 3 factors affect breathing
chemoreceptors
- Peripheral chemoreceptors: groups of cells within walls of aorta and carotid arteries
› Sensitive to changes of the 3 factors
› Carotid and aortic bodies - Central chemoreceptors: medulla oblongata sensitive to changes in CO2 and H+ conc in cerebrospinal fluid
› When stimulated send impulse to area of respiratory centre that regulates breathing
O2 conc
- As O2 is consumed by cells, its levels decrease in the blood
› If O2 drops below normal while other factors are constant, breathing increases - Conc has to fall to very low levels before it has a major stimulatory effect
› Under normal circumstances, O2 plays a little roles regulation of breathing - Large decrease in O2 stimulates peripheral chemoreceptors and nerve impulses are sent to respiratory centre
› Stimulates transmission of messages to diaphragm and intercostal muscles so breathing rate and depth increases
CO2 conc
- Small increase in CO2 conc is enough to cause an increase in breathing rate and depth
- Increase in CO2 conc increases H+ conc
› Increase in both stimulates central and peripheral to transmit impulses to respiratory centre to increase breathing rate and depth - Chemoreceptor more sensitive to change in CO2 conc are the ones in medulla oblongata
› Responsible for 70-80% of response form high CO2 conc
› Takes several minutes - Immediate increase in breathing rate that follows an increase in CO2 produced by stimulation of aortic and carotid bodies
H+ conc
- As H+ conc increases, pH decreases
- Decrease in pH stimulates peripheral chemoreceptors to transmit impulses to respiratory centre
› Increase breathing rate and depth
voluntary control of breathing
holding our breath
• Voluntary control of breathing:
- Voluntary control comes via connection from cerebral cortex to descending tracts in spinal cord
› Bypasses respiratory centre
- Protective device: enables us to prevent irritating gases and water from entering lungs
• Holding our breath:
- Cant stop breathing forever
- Build of CO2 in plasma stimulates the inspiratory centre to send impulses to inspiratory muscles
› Forced to breathe
hyperventilation
exercise and breathing
• Hyperventilation:
- Rapid deep breathing
› Provides more O2 and removes more CO2 than needed
› Voluntarily or stimulated by stress
› Usually corrects itself. Reduction in CO2 means chemoreceptors aren’t being stimulated, reduces breathing rate and depth until normal
• Exercise and breathing:
- More O2 required and more CO2 produced
- Respiratory centre increases breathing rate and depth
- Influenced by 3 factors (O2 to a lesser extent)
