Download Mary!Familari!

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Mary!Familari!
BIOL10002!Biomolecules!and!Cells!
2!
Tissues!and!Homeostasis!
Tissues!
•! There!are!four!general!types!of!tissue,!which!are!epithelial,!connective,!muscle,!and!
nervous!
•! Organs!are!composed!of!one!or!more!types!of!tissue!
•! Epithelial!tissues!are!sheets!of!tightly!connected!cells!that!cover!the!body!surfaces!and!
line! hollow! organs.! Epithelial! tissues! create! barriers! and! provide! transport! across!
these! barriers.! Epithelial! tissues! may! be! involved! in! secretion! and! absorption.! The!
three! types! of! epithelial! cells! are! squamous! (flat),! columnar! (rectangular),! and!
cuboidal! (square).! Epithelial! tissues! can! be! stratified,! which! means! that! they! are!
layered.!
•! Connective!tissues!support!and!reinforce!other!tissues.!Connective!tissues!generally!
consist!of!dispersed!cells!in!an!extracellular!matrix.!Cartilage,!bone,!blood,!and!adipose!
tissue!(fat)!are!examples!of!connective!tissue.!The!cells!of!a!connective!tissue!produce!
the! proteins! found! in! the! extracellular! matrix! of! the! connective! tissue.! Collagen!
(resistant!to!stretch,!found!in!bone!and!cartilage)!and!elastin!(can!stretch,!found!in!the!
lungs,!arteries,!and!cartilage)!are!proteins!found!in!the!extracellular!matrix!of!many!
connective!tissues.!Bone!is!hardened!by!calcium!phosphate.!!
•! Muscle! tissues! contract.! The! three! types! of! muscle! tissue! are! skeletal! (voluntary!
control,!mostly!attached!to!bone),!cardiac!(involuntary!control,!found!in!the!heart),!
and!smooth!(involuntary!control,!found!in!hollow!organs!such!as!the!stomach).!Muscle!
tissues! contain! actin! and! myosin,! which! are! the! proteins! responsible! for! muscle!
contraction.!
•! Nervous! tissues! process! information.! Nervous! tissue! is! comprised! of! neurons,!
(generate! and! conduct! electrical! signals,! communicate! with! other! cells! via!
neurotransmitters),!and!glial!cells!(support!neurons).!
Internal!Environment!
•! A!stable!internal!environment!of!extracellular!fluid!(interstitial!fluid)!makes!complex!
multicellular!animals!possible!
•! The!components!of!the!interstitial!fluid!are!from!the!liquid!part!of!blood!and!lymph!
•! Cells! exchange! molecules! between! the! interstitial! fluid! and! their! intracellular!
environment!
Homeostasis!
•! Homeostasis!is!the!maintenance!of!stable!conditions!in!the!internal!environment!
•! Homeostasis!depends!on!the!ability!to!control!and!regulate!the!functions!of!organs!
and!organ!systems!
•! The!nervous!system!and!the!endocrine!system!are!regulatory!systems!
•! Regulatory!systems!have!set!points!and!feedback!information!
•! Negative!feedback!reduces!or!reverses!a!response!
•! Positive!feedback!amplifies!a!response!
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•! FeedPforward!information!changes!the!set!point!
Regulation!of!Body!Temperature!
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•! Heat! cramps,! heat! exhaustion,! and! heatstroke! are! forms! of! hyperthermia.!
Hyperthermia! leads! to! reduced! function! of! proteins! and! cell! membranes,! and! can!
result!in!cell!death.!
•! Endotherms!are!animals!that!regulate!their!body!temperature!by!producing!heat!or!
using!active!mechanisms!to!cause!heat!loss!
•! Ectotherms!are!animals!that!do!not!regulate!their!body!temperature!
•! In! cold! conditions,! endotherms! can! maintain! body! temperature! by! shivering,! and!
constricting!blood!vessels!(vasoconstriction)!
•! In!warm!conditions,!endotherms!can!maintain!body!temperature!by!relacing!skeletal!
muscles,!sweating,!panting,!and!dilating!blood!vessels!(vasodilation)!
•! In! mammals,! the! hypothalamus! is! responsible! for! maintaining! body! temperature.!
Cooling!or!warming!the!mammalian!hypothalamus!results!in!metabolic!and!circulatory!
responses.!
•! The!basal!metabolic!rate!is!the!amount!of!energy!expended!while!at!rest!in!a!neutrally!
temperate!environment!per!unit!time!!
•! Fever!is!an!increase!in!body!temperature!that!can!help!the!body!fight!infections!
•! Hypothermia!is!a!condition!involving!an!unregulated!belowPnormal!body!temperature!
•! Hibernation!involves!a!regulated!belowPnormal!body!temperature!
3!
Cell!to!Cell!Communication!
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•! Membranes!contain!receptor!proteins!that!allow!cells!to!receive!signals.!Membrane!
receptors! have! an! extracellular! region,! transmembrane! region,! and! an! intracellular!
region.!
•! Intracellular! receptors! can! be! cytoplasmic! or! nuclear.! Nuclear! receptors! generally!
cause!gene!expression!when!bound!to!a!signalling!molecule.!
•! The!signal!transduction!pathway!involves!a!signalling!molecule!(ligand),!a!receptor,!
transduction,!and!effector!molecules!that!produce!the!intended!result!
•! In!order!to!respond,!a!cell!must!have!a!specific!receptor!that!can!detect!the!signal!
•! Signals!can!act!locally!(autocrine,!paracrine),!or!throughout!an!organism!(hormonal)!
•! The!ultimate!cell!response!to!a!signal!may!be!the!opening!of!membrane!ion!channels,!
the!alteration!of!enzyme!activities,!or!a!change!in!gene!transcription!
•! Gated!ion!channel!receptors!are!membrane!receptors.!Gated!ion!channel!receptors!
are!involved!in!direct!transduction.!The!binding!of!a!signalling!molecule!to!a!gated!ion!
channel!receptor!causes!the!receptor!to!change!shape!and!allow!ions!to!pass!through.!!
•! Protein! kinase! receptors! are! membrane! receptors.! Protein! kinase! receptors! are!
involved! in! indirect! transduction.! The! binding! of! a! signalling! molecule! causes! the!
receptor!to!change!shape.!The!change!in!shape!of!the!receptor!activates!the!protein!
kinase! domain! of! the! receptor,! which! can! then! phosphorylate! effector! molecules!
within!the!cell!to!produce!a!response.!
•! GPproteinPlinked! receptors! are! membrane! receptors.! The! GPprotein! is! composed! of!
three! polypeptide! units.! The! GPprotein! binds! to! the! receptor! via! GDP.! When! a!
signalling!molecule!binds!to!the!receptor,!the!receptor!converts!the!GDP!to!GTP.!The!
polypeptide!unit!of!the!GPprotein!that!is!bound!to!the!GTP!separates!from!the!other!
polypeptide!units,!and!moves!along!the!membrane!and!binds!to!an!effector!molecule.!
After! activating! the! effector! molecule,! the! GTP! is! converted! back! into! GDP,! and!
remains!bound!to!the!polypeptide!unit!of!the!GPprotein.!The!activation!of!the!effector!
molecules! results! in! a! cascade! of! reactions! that! amplifies! the! signal! and! leads! to! a!
response.!
•! In!a!normal!cell,!the!signal!is!regulated!and!switched!off!after!a!period!of!time.!If!the!
signal!is!not!switched!off!(for!example,!due!to!a!mutation!in!the!signalling!molecule,!
or!due!to!a!lack!of!negative!feedback),!cancer!can!result.!
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The!Endocrine!System!
•! Most! hormones! are! waterPsoluble! peptides,! proteins,! or! amines,! or! lipidPsoluble!
steroids!(synthesised!from!cholesterol)!or!amines!
•! WaterPsoluble!hormones!can!easily!be!transported!around!the!body!in!blood,!and!are!
packaged!within!vesicles!in!cells!and!secreted!by!exocytosis!
•! LipidPsoluble!hormones!bind!to!carrier!molecules!in!blood,!and!can!diffuse!out!of!cells!
•! Insulin!is!a!peptide!hormone,!testosterone!is!a!steroid!hormone,!and!adrenaline!is!an!
amine!hormone!
•! The!receptors!for!waterPsoluble!hormones!are!on!the!cell!surface.!The!receptors!for!
lipidPsoluble!hormones!are!typically!inside!the!cell.!
•! Most! hormones! diffuse! through! the! extracellular! fluid! then! move! into! the! blood,!
which!distributes!them!throughout!the!body
•! Endocrine!glands!secrete!hormones!into!the!blood!(the!pancreas!is!an!endocrine!gland!
because!it!secretes!insulin!and!glucagon!into!the!blood),!while!exocrine!glands!have!
ducts!that!carry!molecules!to!a!specific!location!(the!pancreas!is!also!an!exocrine!gland!
because!it!secretes!enzymes!and!bicarbonate!via!a!duct!into!the!duodenum)
•! Hormones!can!be!secreted!by!tissues!and!organs!that!are!not!part!of!the!endocrine!
system!(for!example,!adipose!tissue!and!the!heart)
•! A!hormone!that!stimulates!a!target!gland!to!secrete!a!different!hormone!is!a!tropic!
hormone
Pituitary!Gland!
•! The!posterior!pituitary!releases!neurohormones!
•! Hypothalamic!neurons!produce!antidiuretic!hormone!(ADH)!and!oxytocin!and!release!
them!into!the!posterior!pituitary.!These!hormones!then!diffuse!into!capillaries.!
•! The!terminals!of!hypothalamic!neurons!release!neurohormones!that!travel!via!portal!
vessels!within!the!stalk!of!the!pituitary!gland!to!the!anterior!pituitary.!These!hormones!
stimulate!or!inhibit!the!release!of!hormones!from!the!cells!of!the!anterior!pituitary.!
The! hormones! released! by! the! cells! of! the! anterior! pituitary! are! released! into! the!
blood.!
•! When! stimulated! by! thyrotropinPreleasing! hormone! (TRH)! from! the! hypothalamus,!
the!anterior!pituitary!secretes!thyroidPstimulating!hormone!(TSH),!which!causes!the!
thyroid!gland!to!release!thyroxine.!TSH!feedbacks!negatively!to!the!hypothalamus.!
•! Hormones!released!by!the!pituitary!gland,!and!the!hormones!released!by!the!target!
endocrine!glands!of!trophic!hormones!from!the!pituitary!gland!feedback!negatively!to!
the!pituitary!gland!and!to!the!hypothalamus.!
Thyroid!Gland!
•! A!thyroid!follicle!consists!of!a!lumen!and!the!epithelial!cells!around!the!lumen!
•! CalcitoninPproducing!cells!are!found!in!the!spaces!between!follicles!
•! The!thyroid!gland!secretes!thyroxine!
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•! The!cells!around!the!lumen!of!a!thyroid!follicle!synthesise!thyroglobulin!from!tyrosine!
and!secrete!it!into!the!lumen,!where!it!is!iodinated!with!iodine!that!passed!through!
the!follicle!cells!from!a!capillary!into!the!lumen.!Follicle!cells!take!up!the!iodinated!
thyroglobulin! by! endocytosis! from! the! lumen.! Lysozymes! break! the! iodinated!
thyroglobulin! into! T3! and! T4.! The! T3! and! T4! molecules! are! then! secreted! into! the!
blood.!!
•! Thyroxine!is!a!lipidPsoluble!hormone!that!binds!to!receptors!in!the!nucleus!of!target!
cells!
•! Thyroxine!increases!the!metabolic!rate!of!target!cells,!and!is!used!to!maintain!body!
temperature.!Thyroxine!is!also!crucial!for!development!and!growth!in!childhood.!Too!
little!thyroxine!during!childhood!causes!a!condition!called!cretinism.!
•! Thyroxine!feedbacks!negatively!to!the!anterior!pituitary!and!to!the!hypothalamus!
•! A! goitre! (a! large! thyroid! gland)! is! associated! with! hypothyroidism! (low! levels! of!
thyroxine)!and!with!hyperthyroidism!(high!levels!of!thyroxine)!
•! Hypothyroidism! is! caused! by! a! diet! with! insufficient! iodine.! This! means! that! the!
thyroid!gland!continues!to!make!thyroglobulin!but!it!is!poorly!iodinated.!Since!there!
are! low! levels! of! thyroxine,! negative! feedback! to! the! hypothalamus! and! anterior!
pituitary!is!greatly!reduced,!so!there!are!high!levels!of!TRH!and!TSH,!resulting!in!an!
enlarged!thyroid!gland.!The!symptoms!of!hypothyroidism!include!an!intolerance!of!
cold,!and!physical!and!mental!lethargy.!Hypothyroidism!is!treated!with!levothyroxine!
(synthetic!form!of!T4).!
•! Hyperthyroidism! is! an! autoimmune! disease! where! an! antibody! binds! to! the! TSH!
receptor!in!the!follicle!cells!of!the!thyroid!gland.!Since!there!is!a!high!level!of!thyroxine,!
there!is!negative!feedback!to!the!hypothalamus!and!anterior!pituitary.!The!symptoms!
of!hyperthyroidism!include!feeling!hot!and!nervous,!and!bulging!eyes.!
Adrenal!Gland!
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•! The!adrenal!gland!has!an!outer!cortex!and!an!inner!medulla!
•! The!adrenal!gland!secretes!adrenaline!and!noradrenaline!from!the!inner!medulla!
•! Adrenaline! and! noradrenaline! are! released! in! response! to! stressful! situations,! and!
causes! an! increased! heart! rate,! increased! blood! pressure,! blood! to! be! diverted! to!
muscles,!fat!cells!to!release!fatty!acids,!and!the!liver!to!breakdown!glycogen!
•! The!release!of!adrenaline!and!noradrenaline!is!very!rapid!because!the!inner!medulla!
is!controlled!by!the!nervous!system!
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