Cell specialisation and tissues flashcards

cell specialisation & basic tissues of the human body

learning objectives:

understand cell differentiation

:: cell differentiation is the biological process where a less specialised cell becomes a more specialised cell type

:: crucial for the development of multicellular organisms and it allows the cells to take on unique functions that support organisms as a whole

:: e.g. how muscle cells are adapted for contraction whereas nerve cells or neurons may be specialised for cell transmission and epithelial cells have different roles in protection and absorption within the body

:: stem cells = undifferentiated cells which are capable of giving rise to various specialised cell types

:: stem cells can be categorised into two main types:

  1. embryonic - pluripotent and can differentiate into almost any type of cell

  2. adult stem cells - multipotent and can only differentiate into a limited range of cell types e.g hematopoetic stem cells in bone marrow can give rise to various blood cells

identify the four main tissue types

:: a tissue consists of a group of closely associated similar cells that carry out a specific function

  1. epithelium

:: serves as a protective barrier and is involved in absorption, secretion and sensation

:: closely packed together with minimal extracellular matrix - provides an effective barrier

:: connected via specialised junctions known as tight junctions - create a seal between adjacent epithelium cells which prevent the passage of substances between them which is crucial in areas where a barrier is necessary e.g. intestinal lining where it helps to control what enters the blood stream

:: desmosomes - anchoring junctions that provide mechanical stability by connecting the intermediate filaments of adjacent cells; particularly important in tissues subject to stretching and shear-forces e.g. the skin

:: forms a continuous layer which means the cels are arranged tightly together to form a seamless barrier - essential for protecting underlying tissues or organs from physical damage, pathogens and fluid-loss

:: an important characteristic of epithelial tissue is that one surface is typically exposed to the environment e.g. outer layer of skin is exposed to external environment, while the lining of cavity such as gastrointestinal tract faces the internal space

:: additionally, the other surface is attached to an underlying layer of connective tissue by a non-cellular basement membrane - provides support and anchorage to the epithelial layer separating it from the underlying connective tissue

:: basement membrane also plays a role in filtration and serves as a barrier to regulate the movement of molecules between the two tissue types

TYPES OF EPITHELIAL TISSUE

:: can be classified based on their cell shape and the number of layers

:: a simple squamous epithelium is a single layer of flat cells which are found in areas where diffusion occurs e.g. alveoli in the lungs :: cuboidal epithelium is composed of cube shaped cells e.g. found in glandular tissue

:: columnar epithelium consists of tall column-like cells, often involved in absorption and secretion e.g. in the gastrointestinal tract

:: stratified epithelium consists of multiple layers and provides additional protection e.g. the skin

Two types of glands which are commonly associated with epithelial tissues:

  1. endocrine glands - do not have ducts, instead they release their secretions (hormones) directly into the interstitial fluid from where they enter the bloodstream which allows them to communicate with and regulate distant target hormones throughout the body

  2. exocrine glands - characterised by their formation of ducts that transports their secretions to a free epithelial surface i.e. release the products such as sweat, saliva or digestive enzymes directly onto the surface such as skin, lining of digestive tract or another cavity

  3. connective tissue

:: have a significant amount of extracellular matrix which consists of protein fibres and ground substance - matrix provides structural support and elasticity as well as nutrient storage

connective tissue typically contain three types of fibres:

  1. collagen fibres - accounting for about 25% of total protein, tough and high tensile strength

  2. elastic fibres - branch and form networks, composed of the protein elastin

  3. reticular fibres - thing, branched fibres that form delicate networks joining connective tissue to neighbouring tissue, consists of collagen and some glycoproteins

LOOSE CONNECTIVE TISSUE

:: supports and binds to other tissues allowing for a greater degree of flexibility so by filling between body parts it serves as a reservoir for fluid and salts

:: consists of fibres that run in all directions through a semi-fluid matrix

:: its flexibility permits the parts that it is connected to, to move e.g. attach skin to the muscles underneath

DENSE CONNECTIVE TISSUE

:: strong and can provide structural support in areas of the body such as the tendons and ligaments

:: much LESS flexible than the loose connective tissue

ELASTIC CONNECTIVE TISSUE

:: consists mostly of bundles of parallel elastic fibres

:: can be found in lung tissue and in the walls of large arteries

RETICULAR CONNECTIVE TISSUE

:: composed mostly of interlacing reticular fibres

:: forms a supporting internal framework in many organs such as the liver, spleen and lymph nodes

ADIPOSE TISSUE

:: specialised for fat storage, insulation and cushioning

BLOOD

:: although it is a fluid, it is classified as connective tissue due to its origin in the mesoderm and its role in transport and immune functions

BONE

:: provides rigid support and protection for internal organs

  1. muscles

:: responsible for movement throughout the body

:: three types of muscle tissues which play a vital role in movement, circulation and organ function

  • skeletal muscle

:: striated (striped appearance under a microscope)

:: under voluntary control - allows us to perform a conscience movement

:: long (up to 4mm), multi-nucleic, cylindrical cells

:: usually attached to bones via tendons which allows for their movement

  • cardiac muscle

:: found exclusively in the heart (main tissue of the heart)

:: striated

:: involuntary - functions without conscience control needed to pump blood

:: cardiac fibres join end-to-end and contain many branches that rejoin other cardiac cells forming complex networks

:: can contain either one or two nuclei

:: responsible for the heart’s rhythmic contractions to pump blood throughout the body

  • smooth muscle

:: found in the walls of hollow organs e.g.digestive tract, intestines, blood vessels, uterus

:: non-striated

:: involuntary- facilitating various automatic processes e.g. digestion and circulation

:: spindle shaped fibres containing a single nuclei which facilitates functions such as peristalsis in the digestive system and regulating blood vessel diameter

STRUCTURE OF MUSCLE TISSUE

:: each muscle cell is called a muscle fibre

:: muscle fibres contain many thin, longitudinal, parallel , contractile units called microfibrils

:: the chief component of a microfibril is myosin and actin

  1. nervous tissue

:: critical for communication within the body

:: nervous tissue consists primarily of…

(1) neurones - receive and transmit electrical signals, or action potentials

(2) glial cells - support and protect the neurones

UNIQUE STRUCTURE

:: dendriTes which are branched extensions specialised for receiving signals and transmitting them TO the cell body

:: long Axon which transmits the nerve impulse AWAY from the cell body

:: axons can have a range of different lengths from 1/2mm up to 1m in length

:: form synapses where transmission of signals occur

:: a nerve will consist of many neurones bound together by connective tissue

:: glial cells outnumber neurones and play an essential role in maintaining homeostasis

:: they can form myelin which are protective sheaths that wrap around the axon providing support

:: neurones and glial cells together ensure efficient function of the nervous system

consider the role of tissues in health and disease

Cellular Dysfunction

:: when normal cellular processes are disrupted it can lead to pathological conditions

:: e.g. CANCER - arises from uncontrolled cell growth

:: in cancer cells lose their specialisation - do not perform their designated function, instead they proliferate and divide uncontrollably and form a tumour

:: these masses of tissue called tumours can then invade nearby tissues and metastasise

:: different cancers originate from different tissues, i.e. carcinoma may arise from epithelium tissues whereas sarcomas originate from connective tissues

:: understanding the cellular basis of cancer is essential in helping to develop targeted therapies

:: treatments for cancer may include surgery to remove a tumour or chemotherapy to kill rapidly dividing cells

:: there are also newer immunotherapies coming through to help the immune system to recognise and attack specific cancer cells

SUMMARY-

  • stem cells can differentiate into specialised cell types including muscle cells, neurones ad epithelial cells contributing to the body’s diverse functions

  • epithelial tissue- comprised of closely packed cells that form protective layers, epithelial tissue covers body surfaces and lines cavities, plays a role in protection, absorption and secretion

  • connective tissue- provides support and structure throughout the body, encompassing various forms such as bone, blood and adipose tissue

  • muscle tissue- responsible for movement, muscle tissue is classified into 3 types:

skeletal: voluntary and striated, attached to bones via tendons

cardiac: found in the heart, featuring branched fibres that form complex networks and may contain one or two nuclei

smooth: involuntary and unstriated, located in the walls of hollow organs such as the digestive tract and blood vessels

  • nervous tissue- composed of neurones and glial cells, nervous tissue facilitates communication within the body through electrical impulses