002/003 Cells & tissues

cells - what, make up & function

• building blocks of all living things

• made up of microscopic organelles that have diff functions (metabolise, digest food, dispose wastes, reproduce, grow, move, respond to stimuli)

• carry out all chemical activities needed to sustain life

3 main things cells need to survive

1. O₂

2. H₂O

3. nutrients (glucose & minerals)

3 basic parts of human cells

1. plasma membrane – flexible outer boundary

2. cytoplasm – intracellular fluid containing organelles

3. nucleus – DNA-containing control centre

cell/plasma membrane

• semi-permeable

• controls what enters & leaves the cell

mitochondria + cellular respiration

• site of cellular respiration

• provides ATP for cellular energy

• C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

nucleus

• control centre – contains DNA

• dictates the kinds & amount of proteins that need to be made by the cell

cell division - what, function, process

• cell replicates itself

• function: produce more cells for growth and repair process

• genetic material in nucleus is duplicated and readies a cell for division into 2 cells

endoplasmic reticulum - smooth & rough

• fluid-filled tunnels that carry substances w/in cell

• smooth – lacks ribosomes; site of lipid synthesis, metabolism & drug detoxification

• rough – studded w/ ribosomes; synthesises proteins; transport vesicles move protein w/in cell

golgi complex

packages and sends proteins within and out of the cell

ribosomes

location of protein synthesis

cytoplasm

gel-like fluid where the cell’s organelles are housed

lysosomes

contain enzymes that digest worn-out or non-usable materials

• if cell is injured or starved of O₂, lysosome membrane ruptures & cell self-digests

cell extensions

1. flagella

• propel the cell

• sperm - only human cell that has flagella

2. cilia

• hair-like organelles that move materials across cell surface

• located in respiratory system - mucus, dust, bacteria

3. microvilli

• finger-like projections that ↑ SA to do its job

• found in intestine (help w/ nutrient absorption) & kidney tubule cells

cells ageing

• larger & less able to divide and multiply

• lose ability to function or function abnormally

• many tissues lose mass – atrophy

• some tissues become lumpy (nodular) or more rigid

neoplasms/tumours - define, types

abnormal mass of tissue that occurs when cells divide more than usual

• benign – not cancerous, slow growth, doesn’t spread, encapsulated

• malignant – cancerous, rapid growth, abnormal cells, metastasises, recurrence common

causes of death with malignant tumours

• infection

• organ failure

• severe physiological disruption

• haemorrhage

solution, solvent & solutes

• solution: liquid mixture of 2 or more components

• solvent: dissolving medium present in larger quantity; body’s main solvent is H₂O

• solutes: components in smaller quantities w/in solution

intracellular fluid

• nucleoplasm & cytosol

• solution containing gases, nutrients & salts dissolved in water

extracellular fluid (interstitial fluid)

• fluid on the exterior of the cell

• contains nutrients, hormones, NTs, salts & waste products

2 basic methods of membrane transport

1. passive process: substances are transported across the membrane w/o input from the cell

• diffusion: simple, osmosis, facilitated

• filtration

2. active process: use energy (ATP) provided by the cell

• active transport

• vesicular transport: exocytosis, endocytosis

diffusion (passive)

• movement of molecules from higher to lower concentration

• occurs b/c of kinetic energy of molecules; no ATP

• particles tend to. distribute themselves evenly within a solution

• size of molecules and temp affect the speed of diffusion

• major e.g. gas exchange at the alveoli & gas exchange for cellular respiration

simple diffusion

• unassisted process

• solutes are lipid-soluble or small enough to pass through membrane pores

• e.g. O₂ and CO₂

osmosis

• simple diffusion of water across a selectively permeable membrane

• highly polar water molecules easily cross the plasma membrane through aquaporin (specific channel protein)

• water moves from a high concentration of water to a lower concentration of water

facilitated diffusion

• transports lipid-insoluble & large substances that cannot simply diffuse

• protein membrane channels or protein molecules that act as carriers are used, e.g. glucose

• small water-soluble material cross through water-filled channels, e.g. Na, K, Ca

filtration

• water and solutes are forced through a membrane (i.e. capillary wall) into a different compartment by fluid or hydrostatic pressure

• the fluid moves from a HIGH to a LOWER-pressure area

• in the body, hydrostatic pressure is usually exerted by the blood, e.g. movement of fluid from capillaries into extracellular fluid

• Unlike simple diffusion (driven by concentration), filtration uses hydrostatic pressure to force fluid across a membrane.

active processes

• when a cell uses ATP to move substances across the membrane

Substances that move actively are usually unable to pass by diffusion:

• too large to pass through membrane channels

• membrane may lack special protein carriers for its transport

• unable to dissolve in the fat core

• move against their concentration gradients

active transport AKA solute pumping

• similar to facilitated – requires protein carriers to transport across the membrane

• difference – facilitated uses kinetic energy of the diffusing molecules, whereas active transport uses ATP to energise its protein carriers (solute pumps)

E.g.

• reabsorption of amino acids, glucose & salts by the kidney (against concentration gradient)

• sodium-potassium pump in cell membranes (esp. nerve cells) – carries Na⁺ ions out of & K⁺ ions into the cell (necessary for transmission of nerve impulses

vesicular transport

• cannot get thru plasma membrane by passive or active transport

• ATP fuses or separates membrane vesicles & cell membrane, to move substances into/out of cell in bulk w/o crossing plasma membrane directly

exocytosis

• actively moves hormones, mucus & other cellular wastes out of the cell

1. Packaged by the Golgi apparatus into a secretory vesicle

2. Vesicle migrates to plasma membrane, fuses w/ it & then ruptures, spilling its content out of the cell

endocytosis

• engulf extracellular substances by enclosing them in a vesicle

1. Vesicle detaches from plasma membrane and moves into cytoplasm, where it usually fuses w/ lysosome & lysosomal enzymes digest its content

2. Vesicle travels to opposite side of cell & releases its contents by exocytosis

• phagocytosis (bacteria or dead cells)

• pinocytosis (solutes)

body tissues - define & types

• tissues: groups of cells that are similar in structure and function