Unit 1 BHS: Primary Tissues Flashcards
Define: ‘tissue’, ‘organ’ and ‘system’
- Tissues: groups of cells that share a common structure and function
- Organ: consists of at least two types of tissues, serve different functions of the the organ
- Systems: organs that are located in different regions of the body and perform related functions
General properties & characteristics of epithelial tissue
- Covers and lines the body’s surfaces and forms functional units of secretory ducts
- Cells are very closely packed together, joined with little space between them - barrier
- Avascular - receives nutrient from underlying connective tissue
- Cells are anchored to a basement membrane. One free surface to the lumen
Other characteristics:
a) functional polarity: have apical and basal portions that have distinct structural properties
b) regenerative: constant loss and renewal by mitosis
c) junctions between cells and basement membrane
d) derived from ectoderm, endoderm, and mesoderm
General classification of epithelium
- Number of layers
- Shape of cells in upper layer
- Surface specialisation
Classify epithelium according to number of layers
- Simple epithelium: 1 cell layer thick, specialised for transport (lungs)
- Stratified epithelium: composed of 2 or more layers, specialised for protection (skin)
- Pseudostratified epithelium: single layer of irregularly shaped cells, nuclei at different levels thus appear multilayered. Specialised for protection and secretion.
Classify epithelium according to shape of cells in upper layer
- Squamous: cells are flattened in shape
- Columnar: taller than wide
- Cuboidal: wide as tall
Types of simple epithelia
- Squamous cells
fn: diffusion & filtration.
Line all blood vessels, pulmonary alveoli - Cuboidal cells
fn: excretion, secretion, absorption
Line kidney tubules, salivary & pancreatic ducts - Columnar cells
fn: excretion, secretion, absorption
Line digestive tract, uterine tubes, respiratory passageways
Types of stratified epithelia
- Squamous Cells
a) Keratinised: protection. Epidermis of skin
b) Non-keratinised: protection & pliability. Linings of nasal and oral cavities, vagina and oral canal - Cuboidal Cells
strengthening of luminal walls. Large ducts of sweat glands, salver glands and pancreas - Transitional Epithelia
numerous layers of rounded cells. Fn in distension. Walls of uterus, urinary bladder
(Pseudostratified) - in the bronchus
Functions of covering epithelia
- Protection - mechanical and bacterial damage
- Prevent water loss. Water uptake
- Absorption - e.g. intestine with microvilli
- Active transfer - e.g. endothelium of capillaries
- Removal of particles - e.g. cilia in trachea
Membrane specialisations of epithelia
- Intercellular surfaces - cell junctions
- Luminal surfaces - microvilli and cilia
- Basal surfaces - basement membrane
Types of cell junctions between epithelial cells
- composed of transmembrane proteins & link adjacent epithelial cells to form continuous cohesive layer. Operate as communication channels.
THREE FUNCTIONAL TYPES
1. Tight (occluding) junctions - located beneath luminal surface and forms a band around the cell. Fn: blockage of molecules between adjacent cells
- Adhering junctions - anchorage points linking cytoskeletons of adjacent cells. Fn: structural support for entire epithelium.
a) zona adherens: actin
b) desmosomes: intermediate filaments
c) hemidesmosomes: basement membrane - Gap junctions - composed of numerous transmembrane channels. Fn: allow passage of small molecules between cells.
Luminal surface specialisations of epithelial cells
- Microvilli: fingerlike, NB in absorptive cells. Fn: increase S.A.
- Cilia: Hairlike structures which move. Fn: transport (respiratory tract & uterine tube)
Basal surface specialisations of epithelial cells
BASEMENT MEMBRANE
- non-cellular structures
- selective barrier to material between epithelium and underlying tissue. Provide METABOLIC support
- structural support for epithelium (hemidesmosomes)
- consists of ECM proteins (collagen IV, fibronectin, laminin)
PATHOLOGY: associated w/ diabetes, cancer, congenital muscular dystrophy, autoimmunity
Epithelial glands: types and functions
- epithelial glands: organised collection of secretory epithelial cells. Most develops as epithelial outgrowths into underlying CT.
- Fn: secretion
TYPES
1) Exocrine glands: remain connected to surface of epithelium by exocrine duct
2) Endocrine glands: lack excretory duct, product is released into blood circulation
Structure and characteristics of exocrine glands
- secretions are released into ducts
Structure:
1) excretory duct: can be simple or compound
a) simple: duct unbranched
b) compound: branched
2) secretory units: may be simple tubes or clusters of units (acini)
e. g. tear glands, sebaceous glands, sweat glands, prostate gland
Intestinal gland: simple tubular
Sweat gland: simple acinar
Sebaceous gland: simple branched acinar
Mechanisms of secretion of exocrine glands
- Merocrine: exocytosis of contents (sweat)
- Apocrine: pinching off (mammary)
- Holocrine: destruction/destruction of whole cell (sebaceous gland)
Structure and characteristics of endocrine glands
- lack ducts
- secrete hormones into capillaries or lymphatic system
- may be discrete organs whose primary functions are the production and secretion of hormones
General properties of connective tissue
- comprises of cells, fibres and ground substance
- cells are widely spaced by ECM and have direct blood supply
- provides structural and metabolic support, binds other tissues and cushion, protect and fill spaces
- does not occur on surfaces of the body
- able to regenerate
- derived from MESODERM
Structure (tissue components) of connective tissue
1) Cells (fibroblasts, chondro-, osteo- blast/cytes, adipocytes, mast cells, plasma cells, leukocytes)
2) Extracellular matrix
a) Fibres: Collagenous, Elastic, Reticular
b) Ground substance: Glycosaminoglycans
Four major cell types of connective tissue & their functions
1) fibroblasts - most abundant, produce collage; elastin & ground substance
2) macrophages - phagocytic
3) mast cells - produce histamine and heparin. Inflammation & allergies
4) plasma cells - produce antibodies, involved in immune response
Fibers in the ECM of cognitive tissues & their functions
- Collagenous: parallel collagen fibrills, for tensile strength and support. (prevent distortion of tissue)
- Elastic: stretchable, resilient, recoil after stretch. for elasticity
- Reticular: thin fibrils, form a loose mesh for cells to sit on (liver) - scaffolding
Ground substance of connective tissue
- consists of glycosaminoglycans. CHO that have negative charges that bind salt and water to form a gel.
- bound water act as a transport medium for nutrients, gases and metabolites.
- prevents and retards the spread of micro-organisms and toxins from infected areas.
Classification of connective tissue
- consistency of ground substance in ECM
- fluid: loose CT, blood
- semisolid: cartilage
- solid: bone - arrangement of fivers in extracellular matrix
- loose/tight
2 major types of cognitive tissue
- connective tissue proper
a) loose CT
b) dense CT - Specialised CT
a) adipose
b) cartilage
c) bone
2 types of connective tissue proper & their functions and characteristics
- Loose CT
- more cells, less fibres
- elastic and collagen fibres give wavy appearance (skin) - Dense CT
- many collage fibres, less cells
- sub classified acceding to orientation of fibres:
a) regularly arranged: collage fibres in the same direction for tensile strength eg. ligaments and tendons
b) irregularly arranged: orientation random - resists force applied in many directions. for mechanical support. e.g. capsules and sheaths
Adipose tissue - classification, characteristics, functions
SPECIALISED CT
2 classes:
1) white fat - major reserve of long term energy
2) brown fat - dissipate energy instead of storing (in babies)
- adipocytes synthesise and store fat. Cytoplasm stretched around central globule of fat & nucleus pushed to an eccentric position.
Cartilage - classification, characteristics and functions
SPECIALISED CT - fibrous CT
- closely packed collagenous fibres
- avascular
- highly specialised matrix
- chondrocytes
- fn: support and protect tissue; elastic properties to tissues; precursor to many bones; articular surfaces on joints, nose and ears.
3 types:
1) Hyaline cartilage - respiratory tract
2) Fibrocartilage - intervertebral discs, articular discs of knee
3) Elastic cartilage - external ear, epiglottis
Bone - classification, characteristics, functions
SPECIALISED CT - mineralised CT
- cells + intercellular material
- mineralised intercellular material (mineral = Ca in the form of hydroxyapatite crystals)
cells:
- osteoblasts: bone-forming cells
- osteoclasts: bone resorbing cells in bone remodelling. Multinucleated
- osteocytes: osteoblasts that are trapped in lacunae, less active
Canaliculi
processes of osteocytes lie in these little tunnels to get nourishment
Lamellae (in bone)
concentric layers of bone
Functions of connective tissue
- structural support - capsules of organs, ligaments, tendons, cartilage, bone, filling spaces
- metabolic support - storing fats and metabolites
- role in immune and inflammatory responses
- repair after injury
Function of muscle
- specialised for contraction
fn: movement, posture, heat production (due to metabolism w/in cells that increase w/ exercise)
Characteristics of muscle
- contractility - shorten to cause movement
- extensibility - stretch to original length and more
- elasticity - returns to original shape
- irritability - sensitive to nerve impulses
Characteristics of skeletal muscle
- voluntary & striated. (attached at bones at ends by tendons)
- multiple peripheral nuclei (cigar shaped)
- elongated, cylindrical, blunt ends
Formation and repair of skeletal muscles
- one muscle fibre can be up to 10cm long and is formed by the fusion of many (100s) of myoblasts. (thus multinucleated)
- after tissue damage, adult muscle precursor cells divide to form new muscle cells
Striations
in muscles, striations exist in skeletal and cardiac muscles and they are due to the uniform arrangement of myofibrils.
Arrange the following from the smallest unit to the largest:
myofibrils; fascicle; myofibre
myofibril -> myofibre -> fascicle
Sarcoplasm
cytoplasm of muscle cell
Sarcomere
contractile unit of a muscle cell
Dark band of the sarcomere
consists of actin and myosin
Light band of the sarcomere
consists only of actin filaments
Characteristics of cardiac muscles
- involuntary, found only in the heart
- striated, branched and single nuclei (round shape)
- elongated, cylindrical, fibres branch and fuse
- myocardial cells are interconnected to form a continuous unit
- intercalated discs couple cells to contract as a unit (function together mechanically and electrically) = syncytium
Characteristics of smooth muscles
- spindle-shaped, not striated (myofilaments not uniformly arranged)
- one central nucleus (cigar shaped)
- involuntary, stimulated by nerves, hormones or contract spontaneously
- found in GIT, blood vessels, bronchioles, ducts of urinary and reproductive systems. Walls of viscera
Connective tissue associated with skeletal muscle
- epimysium - around whole muscle
- endomysium - around myofibres
- perimysium - around each fascicle
Function and division of the nervous system
fn: communication between different parts of the body by conducting electrical impulses after receiving some stimulus
Division:
- CNS - brain and spinal cord
- PNS - outside of CNS
Cells of the nervous system - types and functions
- neurons - produce and conduct electrical impulses
a) sensory neuron: affarent, periphery to CNS
b) motor neuron: efferent, CNS to periphery
c) interneuron: connections - neuroglia - supporting cells. Assist function of neurons, provide mechanical and metabolic support to neurons, do not transmit impulses
Structure of a neuron
- Dendrites (cytoplasmic extensions) - receive input
- Cell body (containing nucleus) - metabolic centre, produces proteins, main concentration of organelles
- Axon (single extension) - conducts nerve impulses away from cell body
Types of neurons
- unipolar - sensory neurons. singly process divides into dendrite and axon. e.g. spinal nerves
- bipolar - rare, spindle-shaped, dendrite at one end and axon at the other. e.g. in the retina
- multipolar - most common, numerous cell processes. e.g. spinal cord, interneurons, spinal nerve motor neurons
Functions of neuroglia
supporting cells in the connective tissue of nervous system. Provide anatomical and functional support to neurons.
Neuroglia cells in the PNS
- schwann cells - forms myelin around axons
2. satellite cells - support neuron cell bodies
Neuroglia in the CNS
- oligodendrocytes - forms myelin around axons
- microglia - phagocytose foreign material or unwanted cellular wastes
- astrocytes - regulate external environment
Characteristics, functions and structure of myelin
- lipid rich covering that wraps around axons, serves as insulating covering
- fn: allows rapid conduction of action potentials (saltatory conduction)
- produced by oligodendrocyte/schwann cells
PATHOLOGY: destruction of myelin prohibit normal conduction of impulses resulting in neurological diseases such as multiple sclerosis
Synapse
specialised contacts between neurons, provide for transmission of information from one neuron t the next
White matter of the spinal cord
contains myelinated axons, has spinal tracts which ascend and descend the spinal cord
Grey matter of the spinal cord
area of cell bodies, dendrites and unmyelinated axons of motor and inter-neurone. sensory - motor neuron connections can occur
Position of sensory neuron cell body
dorsal root ganglion
Nerve
collection of axons linked together by connective tissue
Components of a peripheral nerve
- axons (myelinated and non-myelinated)
- Schwann cells
- Fibroblasts (spindle shaped)
- Blood vessels
Connective tissue associated w/ peripheral nerve
- endoneurium: surrounds individual axons and their schwann cells
- perineurium: surrounds groups of axons to form fascicles
- epineurium: outer sheath that binds individual fascicles into a nerve
