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homeostasis Flashcards

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1
Q

homeostasis

A

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

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2
Q

feedback system

A

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.
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3
Q

negative feedback

A

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

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4
Q

positive feedback

A

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.

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5
Q

thermoregulation

A
  • 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
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6
Q

heat production

A
  • 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
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7
Q

thermoreceptors

A
  • 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
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8
Q

skin and thermoregulation

A
  • 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
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9
Q

blood vessels and heat loss

A
  • 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
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10
Q

sweating and heat loss

A
  • 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
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11
Q

shivering and heat gain

A
  • Shivering due to increased skeletal muscle tone producing rhythmic muscle tremors
    › Energy produced by muscles is released as heat
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12
Q

preventing body temp from falling

A
  • 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
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13
Q

preventing body temp from rising

A
  • 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
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14
Q

control of thermoregulation

A
  • Hypothalamus is modulator
    › Receives impulses from peripheral thermoreceptors through negative feedback loop, including autonomic nervous system, thermoregulation mechanisms are maintained
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15
Q

temperature tolerance

A
  • 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
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16
Q

glucose regulation

A

• 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

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17
Q

glucose and glycogen

A
  • 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
18
Q

role of liver

A
  • 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
19
Q

role of pancreas

A
  • 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
20
Q

role of adrenal glands

A
  • 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
21
Q

blood glucose homeostasis

A
  • 4-6 millimoles/L

- 5mmol/L = 90mg/100ml

22
Q

osmoregulation

A

• 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

23
Q

maintaining fluid balance

A 
-	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)
24
Q

excretion

A
  • 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
25
Q

kidneys

A
  • 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
26
Q

controlling water levels

A
  • 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
27
Q

kidneys and ADH

A
  • 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
28
Q

kidneys and aldosterone

A
  • 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
29
Q

thirst response

A
  • 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
30
Q

water intoxication

A
  • 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
31
Q

dehydration

A
  • Water loss exceeds intake

- Severe thirst, low BP, dizziness, headache

32
Q

gas regulation

A
  • 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
33
Q

control of breathing

A
  • 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
34
Q

chemicals effecting breathing

A
  • Conc of CO2, O2 affect breathing rate and depth
  • Conc of CO2 in blood plasma affects H+ conc
  • These 3 factors affect breathing
35
Q

chemoreceptors

A
  • 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
36
Q

O2 conc

A
  • 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
37
Q

CO2 conc

A
  • 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
38
Q

H+ conc

A
  • As H+ conc increases, pH decreases
  • Decrease in pH stimulates peripheral chemoreceptors to transmit impulses to respiratory centre
    › Increase breathing rate and depth
39
Q

voluntary control of breathing

holding our breath

A

• 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

40
Q

hyperventilation

exercise and breathing

A

• 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)

Human Biology ATAR (24 decks)

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