Week 2 Bioscience Flashcards
Generalised cell
- organelles: little organs found within a cell
- each organelle has a specific function
Cytoplasm
- the watery space between plasma membrane and the nucleus
- contains the cellular organelles
- composed of cytosol or Intracellular fluid (ICF)
- contains dissolved proteins and nutrients
The nucleus
- largest organelle
- houses DNA
- DNA contains the instructions which tells the cell what to do, in particular which protein to make
ribosomes
- site of protein synthesis
- free ribosomes: floating in cytosol produce proteins for use inside cell
- membrane bound ribosomes: attached to endoplasmic reticulum proteins for export
Endoplasmic Reticulum
-interconnected tubes continuous with the nuclear envelop
-functions:
synthesis
storage
transport
detoxification
Rough Endoplasmic Reticulum (RER)
-studded with ribosomes
-proteins produced by ribosomes on RER are packaged and exported out of cell
Smooth Endoplasmic Reticulum (SER)
-no ribosomes attached
-synthesis of lipids, cholesterol and steroid based hormones
-involved in detoxification
-storage of calcium ions
Golgi apparatus (“the traffic director”)
- consists of stacks of flattened sacs
- functions:
- modify, concentrate and packages proteins and lipids
- forms vesicles and distributes them:
1. within the cell
2. move and become inserted within the plasma membrane
3. move to the plasma membrane for the content to be exported out of the cell by exocytosis
Lysosomes (“the demolition crew”)
-membrane enclosed spheres
-contains lysosomal enzymes
-functions:
* dispose of invading bacteria and cell debris
* recycle molecules that have been broken down
Mitochondria (“the power house”)
-bean‐shaped organelle
-enzymes on surface of inner membrane
-function: cellular respiration
-releases energy in the form of ATP (adenosine triphosphate)
The cytoskeleton
-skeleton of the cell but not made of bone
-network of rods running through cytoplasm
-acts as cells bones, muscles and ligaments
Cilia and Flagellum
- A flagellum is a single, long tail found on bacteria and sperm
- it whips back and forth to move the sperm along
- cilia are motile cellular extensions on the top of cells
- they sweep in a wave like manner to move materials across the surface of them
Microvilli
- minute fingerlike extensions of the plasma membrane that project from the cell surface
- they increase the surface area of the cell
Plasma membrane
- cell membrane = plasma membrane
- holds the cell together, separating the ICF from ECF
- acts like a zip‐lock bag, however the membrane selects what it lets into and out of the cell
- helps maintain homeostasis (optimal working conditions)
Phospholipid structure
- made of a phospholipid molecules
- hydrophilic (“love water”) phosphate heads point toward water
- hydrophobic (“hate water”) lipid tails point away from water
Plasma membrane structure
- is a double layer (bilayer) phospholipid molecules
- is a thin flexible membrane
- fluid membrane the consistency of olive oil
- selectively permeable: a membrane that allows some substance through and excludes others
Plasma membrane consists of:
- phospholipids
- integral proteins (channel and carrier)
- peripheral proteins
- cholesterol (membrane stability)
- sugars (“name or ID tags”)
Concentration gradients
- substances (atoms, molecules, particles, ions, solutes) are constantly moving
-random movement (Brownian motion) due to kinetic energy
-non‐directional movement that leads to collisions that ricochet the substance off in another direction
Concentration gradient and equilibrium
- concentration: measure of the amount of a substance in an area
- high concentration means there are higher numbers of the substance compared to another area
- concentration gradient: the difference in concentration of a particular substance between 2 different areas
- equilibrium: equal space between substances (state of stable conditions)
Diffusion
*the movement of a substance from an area of high concentration to an area of low concentration
*substances move in a net direction to achieve equilibrium
Factors that affect rate of movement
- concentration gradient: if a larger concentration gradient exists substances will move faster
- size of the substance: smaller substance move faster than larger substance
- temperature: warmer environments increase the rate of movement
The transport processes substances use to cross the plasma membrane
- cell needs to transport substances such as nutrients, gases and waste across the plasma membrane to maintain homeostasis
- substances are moved in and out of cells via the following mechanisms:
Diffusion: simple and facilitated diffusion
Osmosis
Active transport
Exocytosis and endocytosis
Transport process depends on the type of substance transporting
- substances are classified as lipid soluble or water soluble
- lipid soluble substance=water insoluble substance
-not repelled by the lipid part of plasma membrane - water soluble substance=lipid insoluble substance
- repelled by the lipid part of plasma membrane
Simple Diffusion
- the unassisted transport of lipid soluble or very small particles across a plasma membrane
- continues until equilibrium is reached then no net movement
- Lipid soluble substances move by simple diffusion: eg O2 CO2
Facilitated Diffusion
- the assisted transport of large or lipid insoluble substances from an area of high concentration to low concentration across a plasma membrane
- requires an integral protein to facilitate the movement
- integral proteins can be channel or carrier proteins
Osmosis
- diffusion is the movement of substances (solutes), osmosis is the movement of water (solvent) across the plasma membrane
- osmosis: water molecules move down their concentration gradient, from an area of high water concentration to low water concentration
- water can move directly through the phospholipid bilayer or through aquaporins
Active Transport
- diffusion and osmosis are examples of passive transport (they don’t require energy)
- when molecules need to move against their concentration gradient (ie from low to high concentrations), the cell uses energy
- called active transport
- active transport moves molecules against their concentration gradients via special protein pumps in the membrane. In order to pump the molecules, the cell uses ATP
Endocytosis and Exocytosis
- transport processes that move large particles into or out of the cell. Both involve vesicles and the plasma membrane
- exocytosis – out of the cell (eg products from golgi)
- endocytosis – into the cell (Phagocytosis = cell eating)
Tonicity
- is the ability of a solution (fluid outside the cell) to affect the shape of a cell by altering the cells internal water volume (ICF)
- the tonicity of the solution that surrounds the cell is determined by its concentration relative to ICF
Isotonic
an isotonic solution has the same concentration as the ICF for both:
- substances/solutes
- water
isotonic solutions cause no change in cell volume or shape (no water shift)
isotonic solutions maintain homeostasis of cell
Hypertonic
- a hypertonic solution has a higher concentration of impermeable solutes than the ICF, therefore a lower amount of water than the cell
- cells in a hypertonic solution will lose water → shrink (crenate)
Hypotonic
- a hypotonic solution has a lower concentration of impermeable solutes than the ICF, therefore a higher amount of water than the cell
- cells in a hypotonic solution will gain water → swell. Cells can swell and burst or lyse (hemolysis in RBC)
Ion concentrations and leakage channels
- ECF: higher concentration of sodium ions (Na+ ) compared to ICF
➢Na+ moves into cell through Na+ leakage channel - ICF: higher concentration of potassium ions (K+ ) compared to ECF
➢K+ moves out of cell through K+ leakage channels - plasma membrane contains many more K+ leakage channels than Na+ so more K+ ions move out of the cell than Na+ moves in.
Resting Membrane Potential
- outside of plasma membrane is slightly positive, inside is slightly negative
- resting potential ranges from –50 mV to –100 mV, depending on cell type
- average voltage
-70mV - means cytosol is 70mV more negative than ECF
Maintenance of Resting Membrane Potential
- to stop the ions from diffusing across the plasma membrane until equilibrium is reached the plasma membrane has the Na+ /K+ ATPase pump:
➢pumps out 3 Na+ ions
➢pumps in 2 K+ ions - active transport: requires ATP
- this maintains concentration gradient for ions to continue to diffuse through the leakage channels
Cell differentiation
- all cells in our body arise from the same fertilised cell
- all cells have the same DNA and genes
- So, how can they look and function differently (eg RBC, neuron, liver cell etc)?
- cell differentiation is the development of specific and distinctive features
- cells specialise early in gestation
- cells change from a generalised “all-purpose” state (stem cell) into one suitable for a specific function
Formation of tissues
Cell differentiation from stem cells forms collection of similar types of specialised cells to form 4 primary tissue types:
- epithelium
- connective tissue
- nervous tissue
- muscle
Nervous tissue
- nervous tissue is the main component of the brain, spinal cord and nerves
- composed of neurons and supporting cells
- communication
- nervous tissue transmits electrical signals to regulate and control body functions
Muscle tissue
- composed of muscle cells that contain contractile microfilaments
- specialised for contraction to allow movement
- three types of muscle
- skeletal muscle – voluntary skeletal movement
- cardiac muscle – involuntary and found in heart
- smooth muscle – involuntary in blood vessels, gut, bladder, uterus
Epithelial Tissue
- epithelium is a sheet of cells that can *
- cover the body
- line internal organs
- form glands
- anything that is exposed to the external environment is covered by epithelium so forms boundaries between different environments
Connective tissue (CT)
- is the connecting tissue of the body
- most abundant and widely distributed
1.CT proper
2.Cartilage
3.Bone
4.Blood
Connective Tissue Proper
- broken into 6 subclasses of loose and dense connective tissue (do not need to know the 6 classes)
- contains fibroblasts and fibrocytes
- loose CT characterised by loose arrangement of fibers and large amounts of ground substance
- dense CT characterised by closely packed bundles of fibers, little ground substance and poorly vascularised.
- one class of CT proper is adipose tissue contains adipocytes
- functions: support, binding, storage and insulation
Cartilage
- 3 types: hyaline, elastic and fibrocartilage
- cartilage that has qualities between dense CT and bone
- ECM up to 80% water
- consists of collagen and some elastic fibers so can withstand tension and compression
- contain chondroblasts and chondrocytes
- lacks nerve fibers and is avascular
- functions: support and absorb compression
bone
- consists of abundant collagen fibers
- matrix is hard due to calcium phosphate crystals
- contains osteoblasts to produce organic portion of matrix
- osteocytes resorb bone as needed
- contains blood vessels and nerve fibers
- functions: support, protection and storage
Blood
- fluid within blood vessels
- consists of blood cells surrounded by matrix called plasma
- contains erythrocytes (RBC), leukocytes (WBC) and platelets
- function: transport substances throughout the body
Skin
- is the largest and heaviest organ
- surface area ~2 m2 weighs 4-5 kg
- also called integument which means “covering”
- is part of the integumentary system which also includes other accessory structures – nails and hair
epidermis
- like all epithelium, the epidermis is avascular (it lacks blood vessels)
- oxygen and nutrients diffuse from blood vessels of the dermis
- cells of the epidermis are tightly joined together to create continuous sheets of cells that prevent substances moving through spaces between the cells, providing a formidable barrier to microorganisms
- epidermis is in a dynamic steady state
- cells are constantly dying and being shed from the surface
- dead cells are replaced with new cells which originate from stem cells in the deepest epidermal layer
- constant renewal of cells means that your epidermis is replaced every 25-45 days
- as cells move from the deepest layer of the epidermis to a more superficial layer, they flatten, and eventually die.
Dermis
- consists of connective tissue
- cells include macrophages and fibroblasts
- fibroblasts produce collagen & elastic
fibers: provide strength & flexibility
- contains
- blood vessels
- nerves & sensory receptors
- glands (from epidermis tissue folding in to
produce the gland) - sweat: produce sweat
- sebaceous: produce sebum
- hair follicles
Hypodermis
- consists mostly of adipose tissue
- functions:
- anchors skin to underlying tissue
- stores fat
- shock absorber
- insulator
Functions of the Skin
The skin functions in the following ways:
1. Protection
* Physical
* Chemical
* Biological
2. Sensation
3. Metabolic function
4. Excretion
5. Blood reservoir
6. Temperature regulation
Functions - Protection
Skin protects underlying tissues from damage
Physical/mechanical barriers
* tightly joined epidermal cells, keratin and oily secretions block most water and water- soluble substances leaving or entering the body
* some penetration of skin by lipid-soluble substances: e.g. some drugs
Chemical barrier
* low pH secretions (acid mantle) prevents bacteria from multiplying
* defensins (natural antibiotic) secreted by skin cells to kill bacteria
* melanin protects DNA in underlying cells from UV damage
Biological barriers
* macrophages engulf and dispose of microorganisms that manage to penetrate the epidermis
Functions – Sensation
- dense network of nerves
- control blood flow (vessel diameter)
- control glandular secretion (e.g. sweat)
- collects sensory information:
- pain collected by pain receptors (nociceptors)
- temperature (thermoreceptors)
- touch, pressure & vibration (mechanoreceptors)
Metabolic function - synthesis of vitamin D precursor
Excretion - nitrogenous wastes and salt are excreted in sweat
Blood reservoir
- can hold up to 5% of body’s blood volume
- a dense blood vessel network exists in the dermis
- the amount of blood flow through these blood vessels can be regulated by the diameter of the vessel
- e.g. for temperature control
Functions - Temperature regulation
At elevated temp: dilation of dermal vessels and increased sweat gland activity cool the body.
At low temp: constriction of dermal vessels to minimise heat loss to external environment
Heat input and output are balanced
- monitored by skin thermoreceptors
- information sent to “thermoregulatory centre” in brain which compares current temperature to set point of 37 degrees celcius
- control centre coordinates response via the circulatory system (vasodilation/constriction) and sweat glands (increased sweat) to maintain homeostasis
Tissue repair
occurs differently in different tissues
➢ depends on the ability of the tissue to divide
➢ nutrition
➢ severity of wound
* minor wounds involve just the epidermis
* major wounds involve both epidermis & dermis
*repair of skin generally involves 2 processes: regeneration and fibrosis
Tissue repair: regeneration
- replaces destroyed tissue with the same kind of tissue
- can be restored to normal if:
- damage is minor
- epidermal stem cells present to regenerate lost tissue
Tissue repair: fibrosis
- replaces destroyed tissue with scar tissue
- damage that includes the dermis leads to repair by fibroblasts
- scar tissue does not have any of the same qualities as the tissue before the injury
3 stages of tissue repair
Stage 1. inflammation: includes the formation of a blood clot
Stage 2. organisation or proliferation: includes the formation of granulation tissue
Stage 3. maturation or remodeling: includes regeneration and fibrosis
Stage 1. Inflammation
Function: prepares the wound for repair, eliminates invading microorganisms and removes debris and dead tissue.
- damaged cells release inflammatory chemicals that causes inflammation
- signs of inflammation: redness, pain, heat and swelling
- blood vessels become more permeable: fluid released into area including:
➢ macrophages: engulf debris/invading microorganisms
➢ clotting proteins: produce a blood clot to stop blood loss,
minimise fluid and electrolyte loss, hold wound together and
prevent any further invasion from microorganisms - clot on surface dries and forms a scab
Stage 2. Organisation or proliferative stage
Function: extracellular matrix synthesis including collagen and restore a blood supply
*blood clot is replaced by granulation tissue
*granulation tissue composed of:
➢capillaries that grow across the wound to restore blood supply, bring
oxygen and nutrients required for healing
➢fibroblasts → produce collagen fibers that bridge the gap
➢macrophages → engulf cell debris, invading microorganisms and blood
clot
* epithelial stem cells multiply and migrate over the granulation tissue
Stage 3. Maturation or remodeling
Function: complete permanent skin repair
- collagen laid down in stage 2 is remodeled and contracts to pull wound edges together
- existing blood vessels are compressed, so the scar is avascular and white in appearance
- if epithelial stem cells present near the wound site divide and grow under scab and regenerate epithelium → scab falls off and skin reflects preinjury tissue although will still have underlying area of scar tissue
- if a major wound scar tissue is visible → repair predominantly by fibrosis
- scar tissue → tough but no elasticity or flexibility, no hair, sweat or oil glands
- amount of scar depends on the severity of the wound
