Ch. 3: Cells & Their Environment

Transcription

1 Ch. 3: Cells & Their Environment OBJECTIVES: 1. To distinguish different cellular (fluid) compartments 2. Understand movement of substances across cell membranes (passive vs active) 3. To recognize different types of cellular transport 4. To understand membrane potential and action potentials 5. To understand different types of cellular signaling See Supplements Page! > Cell Physiology 1 1. Fluid Compartments in the Body Total Body Water (TBW) Intracellular fluid ( cytoplasm )= fluid within the cell. ** Most of your body s water volume (67% of TBW) is located here! Extracellular fluid = fluid outside and in between cells. (33% of TBW) 2 1

2 2. Movement of Substances Across the Plasma Membrane Categorize Substances by how permeable the membrane is to them. 3 B) Categorize by how permeable Membranes are: Permeable Membrane = membrane that allows substances to cross freely. Selectively Permeable Membrane = membrane that only allows some substances to pass (small proteins, non-charged particles, gases, and water) but restricts other things. 2

3 3. Types of Cellular Transport 1. Passive transport = no energy (ATP) required to cross cell membrane. Substances move from high to low concentration (with concentration gradient) 2. Active transport = energy (ATP) required. Substances moving from low to high concentration (against concentration gradient). 3. Bulk transport = Movement of large molecules (endocytosis and exocytosis). 5 1) Passive Transport (3 types) Fig 3.7 ALL involve particles moving high to low concentration! a) Simple Diffusion = Passive movement of particles through membrane with or without need of protein channels, but no binding. Simple Diffusion b) Simple Diffusion with open Channels = Passive movement of particles through membrane with protein channels on cell surface, but no binding. Simple Diffusion - Channels c) Facilitated Diffusion with Carriers = Passive movement of particles through membrane by first binding with protein carrier on cell surface. Facilitated Diffusion 6 3

4 c) Osmosis Fig 3.10 = Passive movement of water across cell membrane from high to low concentration of water. OR From lower to higher concentrations of solutes. 7 Osmosis depends on Tonicity Normal or isotonic, saline Pg 83 Isotonic solution = solute concentration is same on inside & outside of cell membrane. Cell in this soln. won t change shape/size. (ex. Normal or isotonic saline) Hypotonic solution = Solute concentration outside cell is more dilute than inside cell. Water rushes into cell causing it to swell possibly burst. Hypertonic solution = solute concentration outside cell is greater than inside cell. Water leaves cell causing cell to shrink or crenate. 8 4

5 d) Filtration = Passive movement of water & particles through membrane due to fluid pressure. Ex. Filtration of solutes through glomerulus of kidney nephron based on arterial blood pressure entering nephron. 9 Rate of diffusion depends on: > Concentration gradient of solutes > Membrane permeability (see ex of diffusion through a dialysis membrane, Pg 66) - an artificial membrane with fixed pore sizes - small molecules can pass but not large ones. Semipermeable - we will exam diffusion & osmosis through a dialysis membrane in lab! > Surface area of membrane - more surface area the more diffusion occurs. > Temperature of solution - warmer temperature speeds diffusion. 10 5

6 2. Active Transport a) Primary Active Transport = movement of ions with a pump fueled by ATP. i) Calcium (Ca +2 ) Pump keeps Ca +2 concentrations low in cell cytoplasm. (e.g. found on sarcoplasmic reticulum) Fig 6.19 ii) Hydrogen (H+) Pump used to increase acidity. Ex. Parietal cells of stomach have H+ pumps. Nexium targets these cells for those with GERD. iii) Sodium Potassium (Na+/K+) Pump 3 Na+ exit for every 2 K+ that enter cell. Helps maintain cell membrane resting potential. 11 6

7 b) Secondary Active Transport: Coupled transport i) Co-transport ( symport ) = Energy gained from passive transport of one ion fuels the active transport of another ion in the same direction. Ex. Passive transport of Na+ with its concentration gradient helps fuel the active transport of glucose against its concentration gradient in kidney tubules. ii) Counter-transport ( antiport ) = Energy gained from passive transport of one ion fuels the active transport of another ion in the opposite direction BulkTransport = A) Endocytosis = bulk movement of molecules into a cell. i) phagocytosis = entry of solid particles by engulfing. ii) Pinocytosis = entry of fluid particles by engulfing. iii) Receptor-mediated endocytosis = entry of particles by use of a receptor B) Exocytosis = bulk movement of molecules out of a cell. 7

8 Cell Transport - Review Permeability (of substances & membranes) Passive transport = no energy, with concentration gradient ( downhill ) - Simple diffusion - Facilitated diffusion - Osmosis - Filtration Active transport = ATP required, against concentration gradient ( uphill ) - Primary active transport (calcium, hydrogen, & Na+/K+ pumps) - Coupled transport (co-transport & counter-transport) Bulk transport - Endocytosis - Exocytosis Membrane Potential Resting cell membrane potential (MP)= -70 mv inside of cell has fixed number of anions (neg charged particles) > number of K+ ions entering /leaving cell changes intracellular negativity - The more K+ exits, the more neg inside becomes - The more K+ enters, the less neg inside becomes MP maintained by Na+/K+ pump Figs

9 Clinical Application Pg 89 Hyperkalemia & Lethal Injections Lethal injection is potassium chloride. Hyperkalemia = high blood potassium (K+) causes heart to stop. [Heart s pacemaker cells stay relaxed rather than contracting.] 17 Action Potential - Changes In Membrane Potential 4 AP steps: 1. - Stimulus above MP thresh hold opens initial Na+ channels. 2. Opens more Na+ voltage gated channels (Na+ floods inward) - drives MP from -70 to +30 mv = depolarization - Na+ channels close 3. - K+ voltage gated channels open, K+ exits cell. - drives MP back toward -70 mv = repolarization - may overshoot MP & go to -80 mv ( hyperpolarization ) 4. Na+/K+ pump restores normal Resting MP (-70mV) by pumping Na+ out and K+ back in. Fig

10 5. Cell Signaling a) Paracrine Signaling: cells secrete signal that affects neighboring cell. b) Synaptic Signaling: neuronal cells transmit electrical signals (action potentials) that: - involve neurotransmitters - are between two neurons - are between motor neuron and a muscle cell or gland. Fig 3.23 c) Endocrine Signaling: hormones from endocrine gland bind to receptors on cells to exert effect. c) Endocrine signaling = Fig 6.30 Hormones classified as: i) Polar hormones (water soluble) - - Bind to receptor on cell membrane - Receptor binding leads to formation of 2 nd Messengers Ex. Catecholamines (epinephrine, dopamine) Polypepides (insulin, glucagon) ii) Non-Polar hormones (lipid soluble) - - Pass right through cell membrane & bind to nuclear receptor. Ex. Steroids (estrogen, testosterone) Thyroid hormones 20 10

11 Steps to 2 nd messenger endocrine signaling with polar hormones: Fig Hormone binds to cell surface receptor 2. Activates G protein 3. Activates enzyme 4. Activates 2 nd messenger 5. Activates protein kinase cascade & cell response 21 Review Cell membrane potential (MP) - Resting potential - Action potential Cell Signaling - Paracrine signaling - Synaptic signaling - Endocrine signaling - Polar (non-lipid) hormones > catecholamines, polypeptides, glycoproteins - Nonpolar (lipid) hormones > steroids hormones (estrogen, testosterone, progesterone) thyroid hormones (thyroxine & T4) 2 nd messenger system 22 11