WEEK 2 BIOSCIENCE - CELLS, TISSUES AND SKIN Flashcards
Cytoplasm
- watery space between the plasma membrane and the nucleus
- composed of cytosol or ICF
- contains cellular organelles
- contains dissolved proteins and nutrients
Nucleus
- largest organelle
- houses DNA
- DNA contains the instructions for the cell, in particular, protein synthesis
Ribosomes
- site of protein synthesis
- free ribosomes: floating in cytosol produce proteins for use inside the cell
- membrane-bound ribosomes: attached to endoplasmic reticulum produce proteins for transport
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 the cell
Smooth endoplasmic reticulum (SER)
- no ribosomes attached
- synthesis of lipids, cholesterol and steroid-based hormones
- involved in detoxification
- storage of calcium ions
Mitochondria
- bean-shaped organelle
- enzymes on the surface of the inner membrane
- function: cellular respiration -> releases energy in the form of ATP
Golgi apparatus
- consists of stacks of flattened sacs
- functions: modify, concentrate and packages proteins and lipids
- forms vesicles and distributes then: within the cell, move and become inserted within the plasma membrane, move to the plasma membrane for the content to be exported out of the cell via exocytosis
Lysosomes
- membrane-enclosed spheres (sacs)
- contains lysosomal enzymes
- functions: digest biological material, disposes of invading bacteria, viruses and toxins, recycles molecules
the plasma membrane
- the thin flexible boundary between the ICF and ECF (not a solid structure)
- selectively permeable: only allows certain substances through
- allows for different chemical compositions between ICF and ECF to maintain homeostasis and create optimal working conditions for the cell
phospholipid molecule
- hydrophillic head points towards the water
- hydrophobic lipid tail points away from the water
additional structures of the plasma membrane
- phospholipids
- proteins (integral and peripheral)
- cholesterol
- carbohydrates
peripheral proteins
- not embedded throughout the plasma membrane
- attach loosely to integral proteins or float free
- functions: plasma membrane support, enzymes or motor functions
integral proteins
- embedded within the plasma membrane and span the entire membrane
- classified as channels or carriers for the transport of substances
- act as enzymes or receptors
- include carrier and channel proteins
- substance specific
- required within the plasma membrane to transport substances that need t pass through the plasma membrane but cannot pass directly through the lipid core b/c they are water-soluble or too large
Channel proteins
- small lipid insoluble substances
- leakage channels: always open at both ends
- gated channels: open at one end and can open and close at the other end -> three types = voltage, mechanical and chemical
Carrier proteins
-transform shape to allow substances to pass
- substances that use carrier protein: lipid insoluble substances too large to use channel proteins
e.g. substances that use carrier proteins: glucose and amino acids
concentration gradient
the difference in concentration of a particular substance between 2 different areas
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 the rate of diffusion
- concentration gradient
- size of the substance
- temperature
passive transport
- requires no energy
- substances move down a concentration gradient
- includes simple diffusion, facilitated diffusion and osmosis
active transport
- requires energy ATP
- substances move up concentration gradient
- includes primary active transport with Na+/K+ ATPase pump
facilitated diffusion
- the assisted transport of large or lipid insoluble substances, from an area of high concentration to low concentration, across a plasma membrane, using an integral protein
- requires an integral protein to facilitate the movement
- large or lipid-insoluble substances
osmosis
the net diffusion of water through a selectively permeable membrane from an area of more water (less solutes) to an area of less water (more solutes) when the solute can not pass through the membrane (impermeable)
tonicity
is the ability of a solution to affect the shape of a cell by altering the cells internal water volume (ICF)
isotonic
an isotonic solution has the same concentration as the ICF for both substances/solutes and water
- isotonic solutions cause no change in cell volume or shape
hypertonic
a solution that has a higher concentration of impermeable solutes than the IFC therefore a lower amount of water in the cell
- cells lose water and shrink (crenate)
hypotonic
a solution that has a lower concentration of impermeable solutes than the ICF therefore a higher amount of water than the cell
- cells gain water and swell and burst or lyse
resting membrane potential
potential energy (called voltage and measured in volts) that
exists across the plasma membrane resulting from
separating oppositely charged ions by the plasma
membrane
ion concentrations with a cell
- 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 the 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.
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
structure of epithelial tissue
- composed of epithelial cells that are situated close together with little intercellular space to form continuous sheets
- cells of epithelium have one free (unattached) surface and another surface attached to a basement membrane separates the epithelium from underlying connective tissue
- epithelium lacks blood vessels (avascular)
- oxygen and nutrients delivered by diffusion from underlying connective tissue
- epithelium contains nerves (innervated)
- susceptible to damage but can regenerate quickly
functions of epithelial tissue
- protection: skin
- absorption: digestive tract
- excretion: kidney
- filtration: kidney
- secretion: respiratory tract
- transport of mucous: respiratory tract
- sensory function: tounge
connective tissue
- the connecting tissue of the body
- most abundant and widely distributed
4 classes of connective tissue
- CT proper
- cartilage
- bone
- blood
characteristics of connective tissue
- characteristics of all CT:
1. specialised cells
2. ground substance
3. protein fibres - Unlike nervous, muscle and epithelial tissue that is composed of predominately the same type of cell, all classes of CT vary greatly in appearance but all have relatively large amounts of extracellular material with relatively few, widely separated cells
CT extracellular matrix (ECM)
ECM nonliving substance surrounding the cells
* composed of ground substance and protein fibres ground substance: unstructured material that fills space between cells and contains protein fibres
* holds a large volume of water called interstitial fluid
* ranges from liquid to solid
- > CT can bear weight and withstand great tension
CT protein fibres
- collagen fibres: tough fibers with high tensile strength
- elastic fibres: long thin fibers for stretch and recoil
CT specialised cells
- CT proper: fibroblasts and fibrocytes
- cartilage: chondroblasts and chondrocytes
- bone: osteoblasts and osteocytes
- blood: haematopoietic stem cells (“blast” cells), RBC and WBC
connective tissue (CT) 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 the loose arrangement of fibres and large amounts of ground substance
- dense CT characterised by closely packed bundles of fibres, 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 fibres so can withstand tension and compression
- contain chondroblasts and chondrocytes
- lacks nerve fibres and is avascular
- functions: support and absorb compression
Bone
- consists of abundant collagen fibres
- 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 fibres
- functions: support, protection and storage
Blood
- fluid within blood vessels
- consists of blood cells surrounded by a matrix called plasma
- contains erythrocytes (RBC), leukocytes (WBC) and platelets
- function: transport substances throughout the body
skin major regions
epidermis – outer epithelial layer
dermis – a deep supporting layer of connective tissue
hypodermis – subcutaneous layer of connective tissue and adipose tissue
Epidermis
- like all epithelium, the epidermis is avascular -> oxygen and nutrients diffuse from blood vessels of the dermis
- cells are tightly joined together to create continuous sheets of cells that prevent substances from moving through spaces between the cells, providing a barrier to microorganisms
- 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
layers of the epidermis
Stratum corneum (top):
* 20-30 cell layers thick
* dead keratinised flattened keratinocytes
* continuously shed
* protective barrier (abrasion, dehydration, penetration)
Stratum basale (bottom):
* single layer of dividing epidermal stem cells
* produce a new keratinocyte above the stem cell
* push older cells toward the surface
* also contains melanocytes (produces pigment)
cells of the epidermis
- epidermal stem cells: divide to produce keratinocytes
- keratinocytes: predominate cells of skin, produce keratin
- melanocyte: produces melanin
- Merkel/tactile cells: touch receptors
- Langerhans cells/dendritic cells
(macrophages): ingest foreign substances and activate immune system
dermis
consists of connective tissue:
-> cells include macrophages and fibroblasts
-> fibroblasts produce collagen & elastic fibres: 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 skin
- Protection
* Physical
* Chemical
* Biological - Sensation
- Metabolic function
- Excretion
- Blood reservoir
- Temperature regulation
functions: protection
The 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 the skin by lipid-soluble substances: e.g. some drugs
Chemical barrier
* low pH secretions (acid mantle) prevent 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
functions: blood reservoir
Blood reservoir
* can hold up to 5% of the 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 the external environment
Heat input and output are balanced
-> monitored by skin thermoreceptors
-> information sent to the “thermoregulatory centre” in the brain
which compares the current temperature to the set point of 37 C
-> control centre coordinates response via the circulatory system (vasodilation/constriction) and sweat glands (increased sweat) to maintain homeostasis
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 remodelling: 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 cause
inflammation
* signs of inflammation: redness, pain, heat and swelling
* blood vessels become more permeable: fluid released into the area
including:
➢ macrophages: engulf debris/invading microorganisms
➢ clotting proteins: produce a blood clot to stop blood loss, minimise fluid and electrolyte loss, and hold the wound together and prevent any further invasion from microorganisms
* clot on the surface dries and forms a scab
stage 2: organisation or proliferate 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, and bring oxygen and nutrients required for healing
➢fibroblasts → produce collagen fibres 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 remodelling
Function: complete permanent skin repair
* collagen laid down in stage 2 is remodelled 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 the scab and regenerate epithelium → scab falls off and the skin reflects preinjury tissue although will still have an 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
burns classification
- superficial: epidermis
- partial thickness: epidermis and part of dermis
- full-thickness: entire thickness of skin
