WEEK 2 – lecture notes (Cells to tissues)
Organs are made of tissues which are made of specialised cells
There are 4 main types of tissue (plus blood)
o Connective
o Epithelial
o Muscle
o Nervous
Example: The Oesophagus
Has all 4 tissues. The muscle consists of an inner circular layer and an
outer longitudinal layer.
Epithelial
o Epithelia cover surfaces externally and line surfaces internally
o They are mainly involved in absorption (e.g. the intestine),
secretion (e.g. glands), and protection (e.g. skin)
o Sheets of cells held together by a basement membrane
o little non-cellular material
o No blood supply, rely on diffusion for oxygen, nutrients
o Joined by cell-cell junctions
o Always has lumen next to it
Types of Epithelial
o Epithelial types vary according to where they are in the body
and whether they are on a surface that may easily be damaged
o There are three main criteria for classifying epithelia:
• How many layers of cells are there? One layer (simple) or more
than one (stratified)
• What shape is the cell? Flat (squamous), cuboid or columnar
• Are there any specialisations on the free (apical) surface? For
example – cilia, microvilli, keratin
Simple squamous: lines alveoli in lungs
Simple cuboidal: lines ducts
Simple columnar: large surface area for absorption
Pseudostratified columnar – looks like it is made of several layers
but it is only one. Lines respiratory tract.
o Transitional: stretches easily and found in bladder and other
parts of the urinary tract
o Stratified squamous: found where surface is likely to suffer
friction or abrasion e.g. tongue or skin. (skin has a thick layer of
dead cells and keratin)
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Muscle
o Contractile tissue responsible for movement within the body
o 3 types: smooth, striated (skeletal), cardiac
Smooth muscle
o Smooth muscle is made up of cells that contain a single central
nucleus.
o It is not obviously striated
o It is not under voluntary control (autonomic nervous system)
o Long slow contraction – slow to tire
o Found in the walls of the gut, urinary system, blood vessels,
respiratory system, skin, endocrine system
Striated muscle
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Striated muscle is made up of fibres that contain multiple nuclei.
It is clearly striated
It is voluntary (or reflex)
Fast contraction
Found mostly in muscles that move the skeleton (skeletal
muscles) but also the diaphragm and the upper part of the
oesophagus
Cardiac muscle
o Cardiac muscle is made up of cells that usually contain a single
central nucleus.
o Cells are linked by intercalated discs that allow fast conduction.
o It is striated
o It is not under voluntary control Found in the wall of the heart
Connective tissue
o Cells are surrounded by non-cellular tissue (matrix)
o Mostly for support or packing/wrapping
o 3 main types
Loose connective tissue
Bones and cartilage
Ligaments and tendons
Basic loose connective
o tissue is a mesh of thin (flexible)
elastin fibres and thicker stronger
collagen fibres, interspersed with
fibroblast cells that synthesize the
fibres –
o This basic tissue type can be modified
by the inclusion of other types of cells
and by the secretion of further matrix
Example: Adipose tissue – packed around internal organs,
between muscles and in breast tissue
Bones and cartilage
o support tissues – cells, fibres (mainly collagen), matrix
(proteoglycans and, in bone, mainly calcium
hydroxyapatite/calcium phosphate)
o Bone forms in two main ways:
Endochondral bone replaces cartilage (e.g. limb bones,
vertebrae, skull base)
Intramembranous bone forms directly in membranes/skin in the
absence of cartilage (e.g. skull)
Ligaments and tendons
o Tendon: mainly collagen so very strong
o Ligament: high in elastin and so stretches