The Tissue and Skin lecture summary
Groups of cells similar in structure and function group and work together in tissues.
Epithelial tissue forms a tightly connected sheet of cells covering all external and internal surfaces of
structures and ducts. Epithelium no direct blood supply but can regenerate quickly when damaged.
Epithelia cells selectively can absorb materials from the apical side to the basal side or secrete
materials from basal to apical side. Squamous epithelium is formed of flattened cells forming a
single thin layer (simple, e.g. endothelium or alveolar epithelium) or multiple layers (stratified, e.g.
epidermis). Cuboid epithelium often forms the lining of ducts and actively secretes (e.g. sweat
glands) or absorbs (kidney tubule) materials. Endocrine glands that release hormones into the blood
stream are also made of cuboid epithelium. Columnar epithelium is formed of tall cells, often
containing cilia (e.g. in bronchi) or involved in absorbing (gut) or secretion of materials (goblet cells).
Nerve tissue is formed of sensory neurons that bring information to the central nervous system,
which sends instructions through motor neurons to activate muscles and control organs.
Cells in muscle tissue can shorten themselves by contractile proteins and muscle tissue comes in
three types: Striated skeletal muscle is formed of elongated cells, contract only when instructed by
motor neurons and produces wilful movement of the body. Cardiac muscle forms a network of
interconnected cardiomyocytes that contract spontaneously, making the heart squeeze out blood.
Smooth muscle is found around blood vessels and tubes in other organs. Smooth muscle is activated
by motor neurons, causing e.g. vaso-constriction, broncho-constriction and gut peristalsis.
Connective tissue is any tissue that is not epithelium, nerve or muscle tissue. Connective tissue is
therefore a wide range of tissues, but they have in common that they consist of cells in a ground
substance, containing fibres. Cartilage consist of chondroblast that produce a gelatinous ground
substance and can be flexible (with elastin fibres) or more stiff (with reticular fibres) or strong (with
collagen fibres). Unfortunately, once generated, cartilage does not regenerate. Bone consist of
osteoblasts that produce a calcium-rich matrix, reinforced by collagen fibres, making it both stif and
strong, like reinforced concrete. Blood is connective tissue, consisting of blood cells in a ground
substance of plasma.
The skin is the organ system that protects the body from various kinds of damage. The main
functions are (in PESTS sequence): 1) Protection: Barrier against infection and impervious to most
microbes. 2) Excretion: Waste products such as urea and lactic acid are lost when we sweat along
with sodium chloride (salt). 3) Sensory Perception: sensory nerve endings in the skin detect
pressure, vibration, temperature and pain and send information to brain. 4) Thermoregulation:
Sympathetic ANS controls blood flow to the surface (radiation of heat) through vasoconstriction or
dilation of arterioles, sweat production (cooling by evaporation) and hair erection (muscle heat and
air trapping). Adipose tissue insulates against cold. 5) Synthesis of vitamin D: Vitamin D starts its
production process in skin exposed to sunlight.
The skin consist of three layers: the epidermis, dermis and hypodermis. The epidermis is epithelial
tissue, growing from the basal cells outwards, the tightly interconnected cells produce keratin.
When epithelial cells die from lack of oxygen (no capillaries in epidermis), the keratin from the dead
cells forms a protective barrier. The dermis is connective tissue: a meshwork of cells like fibroblasts
Groups of cells similar in structure and function group and work together in tissues.
Epithelial tissue forms a tightly connected sheet of cells covering all external and internal surfaces of
structures and ducts. Epithelium no direct blood supply but can regenerate quickly when damaged.
Epithelia cells selectively can absorb materials from the apical side to the basal side or secrete
materials from basal to apical side. Squamous epithelium is formed of flattened cells forming a
single thin layer (simple, e.g. endothelium or alveolar epithelium) or multiple layers (stratified, e.g.
epidermis). Cuboid epithelium often forms the lining of ducts and actively secretes (e.g. sweat
glands) or absorbs (kidney tubule) materials. Endocrine glands that release hormones into the blood
stream are also made of cuboid epithelium. Columnar epithelium is formed of tall cells, often
containing cilia (e.g. in bronchi) or involved in absorbing (gut) or secretion of materials (goblet cells).
Nerve tissue is formed of sensory neurons that bring information to the central nervous system,
which sends instructions through motor neurons to activate muscles and control organs.
Cells in muscle tissue can shorten themselves by contractile proteins and muscle tissue comes in
three types: Striated skeletal muscle is formed of elongated cells, contract only when instructed by
motor neurons and produces wilful movement of the body. Cardiac muscle forms a network of
interconnected cardiomyocytes that contract spontaneously, making the heart squeeze out blood.
Smooth muscle is found around blood vessels and tubes in other organs. Smooth muscle is activated
by motor neurons, causing e.g. vaso-constriction, broncho-constriction and gut peristalsis.
Connective tissue is any tissue that is not epithelium, nerve or muscle tissue. Connective tissue is
therefore a wide range of tissues, but they have in common that they consist of cells in a ground
substance, containing fibres. Cartilage consist of chondroblast that produce a gelatinous ground
substance and can be flexible (with elastin fibres) or more stiff (with reticular fibres) or strong (with
collagen fibres). Unfortunately, once generated, cartilage does not regenerate. Bone consist of
osteoblasts that produce a calcium-rich matrix, reinforced by collagen fibres, making it both stif and
strong, like reinforced concrete. Blood is connective tissue, consisting of blood cells in a ground
substance of plasma.
The skin is the organ system that protects the body from various kinds of damage. The main
functions are (in PESTS sequence): 1) Protection: Barrier against infection and impervious to most
microbes. 2) Excretion: Waste products such as urea and lactic acid are lost when we sweat along
with sodium chloride (salt). 3) Sensory Perception: sensory nerve endings in the skin detect
pressure, vibration, temperature and pain and send information to brain. 4) Thermoregulation:
Sympathetic ANS controls blood flow to the surface (radiation of heat) through vasoconstriction or
dilation of arterioles, sweat production (cooling by evaporation) and hair erection (muscle heat and
air trapping). Adipose tissue insulates against cold. 5) Synthesis of vitamin D: Vitamin D starts its
production process in skin exposed to sunlight.
The skin consist of three layers: the epidermis, dermis and hypodermis. The epidermis is epithelial
tissue, growing from the basal cells outwards, the tightly interconnected cells produce keratin.
When epithelial cells die from lack of oxygen (no capillaries in epidermis), the keratin from the dead
cells forms a protective barrier. The dermis is connective tissue: a meshwork of cells like fibroblasts
