stem cells and cell specialisation

• levels of organisation

  specialised cell -> tissue -> organ -> organ system -> organism
• structure of multicellular organisms:

  • specialised cells = cells with a specific structure related to a specific function
  • tissue = a collection of similar cells carrying out a specific function
  • organ = a collection of several tissues carrying out the same general function
  • organ system = a group of organs that work together to perform one or several common functions
  • multicellular organism
• • digestive system = oesophagus, stomach, intestines plus associated glands, liver, pancreas = nutrition to provide materials for growth, repair, ATP for energy
  • circulatory system = heart, blood vessels = transport to and from cells
  • respiratory system = airways, lungs, diaphragm, intercostal muscles = breathing, gaseous exchange, excretion
  • urinary system = kidneys, ureters and bladder = excretion and osmoregulation
  • integumentary system = skin, hair and nails = waterproofing, protection, temp regulation
  • muscoloskeletal system = skeleton, skeletal muscles = movement, support, protection
• • immune system = bone marrow, thymus gland, skin, stomach acid, blood = protection against pathogens
  • nervous system = brain, psinal cord and nerves = communication, control and coordination
  • endocrine system = glands that make hormones e.g. thyroid, ovaries, testes, adrenals = communication, control and coordination
  • reproductive system = tests, penis, ovaries, uterus, vagina = sexual reproduction
  • lymphatic system = lymph nodes and vessels = transport fluid back to the circulatory system and is also important in resisting infections
• stem cells = unspecialised cells in all multicellular organisms which can undergo cell division and differentiate into (a variety of) specialised cells

  • totipotent = zygote and its first few divisions into the morula
  • pluripotent = inner cell mass of blastocyst
  • multipotent = bone marrow or umbilical cord blood
  • the number of diffeent cell types a stem cell can become or differentiate into depends on its potency
• potency definitions:

  1. totipotent stem cells -> produced from fusion of an egg and sperm cell into a zygote, these cells can differentiate into ALL cell types ofboth embryo and placenta, placenta = extra - embryonic
  2. pluripotent stem cells -> can differentiate into any embryonic tissue/ cell types but not placenta/ extra embryonic tissue, they differentiate into 3 germ layers: the endoderm, mesoderm, ectoderm
• potency definitions (part 2):

  3. multipotent stem cells -> can produce cells of closely related tissues e.g. adult stem cells in bone marrow differentiate into all blood cells

  4. unipotent stem cells -> can produce only one cell type, but have property of self renewed which distinguishes them from non-stem cells e.g. skin cells, cells lining small intestine, hepatocytes (liver cells)
• in plants, stem cells are known as...

  • meristematic cells
  • all totipotent
  • found in many tissues: apical meristems; lateral buds, cambium (forms between xylem and phloem)
• broad categories of human stem cells in research are:

  1. embryonic stem cells: derived from blastocysts (early embryo), obtained after IVF treatment - pluripotent
  2. adult stem cells (bone marrow): multipotent
  3. induced pluripotent cells (iPS): pluripotent cells generated directly from adult non-stem cells - pluripotent
  4. cord blood stem cells: found in umbilical cord - multipotent
  5. foetal stem cells: from amniotic fluid or miscarriage/abortion - pluripotent
• specialised cells and tissues

  animal cells:

  • erythrocytes (red blood cells)
  • neutrophils (white cells)
  • sperm cells

  animal tissues:

  • epithelia = single or multiple sheets of cells covering outer and inner surfaces of teh body and lining cavities of organs, including blood vessels e.g. Squamous epithelia, Ciliated epithelia
  • muscle
  • cartilage

  plant cells:

  • root hair cells
  • leaf cells: palisade cells, guard cells

  plant tissues:

  • tissues of transport system: xylem, phloem
  • epidermal tissue
• red blood cells = erythrocytes

  • biconcave shape - increases S.A. to vol. ratio - essential to transport oxygen
  • no nucleus: increased space for haemoglobin
  • flexible: fit through capillaries

  neutrophil = a phagocytic white blood cells

  • multi-lobed nucleus: easier to squeeze through gaps to get to site of infection
  • cytoplasm contains many lysosomes that contain enzymes to attack pathogens

  sperm cell:

  • tail/flagellum: can move
  • many mitochondria to supply enegry needed to sweim
  • acrosome contains digestive enzymes - digest protective laters around ovum allowing sperm to penetrate
• epithelia

  squamous epithelia

  • forms lining of lungs
  • very thin due to flat/squat cells
  • only one cell thick
  • allows rapid diffusion of oxygen into blood

  ciliated epithelia

  • lines trachea
  • have 'hair-like' structures called cilia that move in a rhythmic manner - sweeps mucus away from lungs
• muscle tissue

  where else is smooth muscle found = walls of hollow visceral organs (such as liver, pancreas and intestines) except heart - eyes and skin

  A) skeletal

  B) cardiac

  C) smooth

  D) smooth

  
• Elastic cartilage:

  • external ears, eustachian tubes (tube that carries sounds from external ear into head), larynx

  hyaline cartilage

  • articular surfaces of movable joints, walls of respiratory tracts (nose, trachea, bronchi)
  • costal cartilages (bars of cartilage that serve to push ribs forward + contribute to elasticity of walls of thorax) ,epiphyseal plates of long bones (flat bony structure located between epiphysis and metaphysis of long bones)

  fibrous cartilage

  • invertabral disks of spine, at insertions of ligament + tendons - cushion within joints - manages compression forces
• root hair cells:

  • root hairs = increases S.A.
  • thin cellulose cell wall - easy movement of molecules across membrane
  • vacuole contains cell sap - solution of ions and sugars- - lower w.p.

  palisade mesophyll cell

  • chlorophyll - to absorb large amounts of light for p/s
  • rectangular in shape closely pushed to form a continuous layer
  • thin cell walls - increased rate of diffusion of CO2
  • large vacuole to maintain turgor pressure
  • chloroplasts can move within cytoplams in order to absorb more light
• stomata

  • when guard cells lose water and become less swollen as a result of osmotic forces, they change shape and stoma closes to avoid furtehr water loss
  • cell wall of guard cell is thicker on one side so cell doesn't change shape symmetrically as volume changes
• xylem

  • elongated dead cells - strengthened with lignin
  • water transport is also accomplished through physical forms and doesn't need energy
  • sealed with lignin

  phloem

  • columns of seive tube cells sperated by perforated walls called seive plates
  • travels through seive tube plates