stpm: specialization of animal cells

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* Specializatio n of Animal Cells STPM BIOLOGY bY sHALENI kAVIRAJAN

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Page 1: STPM: Specialization of animal cells

*Specialization of Animal

CellsSTPM

BIOLOGYbY sHALENI kAVIRAJAN

Page 2: STPM: Specialization of animal cells
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Covering epitheliao Layers of cell that line the external/internal surfaces

of organso cells are arranged in:

a) single layer – simple epitheliumb) more than one layer – stratified epithelium

o Shape of the cells depends on the typesi. scale-like squamous epithelium

Epithelial Tissues

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o

ii. cube-like cuboidal epithelium

iii.column-like columnar epithelium

o the cells are attached to a thin layer of fine connective tissue (basement membrane) – helps in attaching with other tissues

o no capillaries in the cells because they are too thin to enter

o mitosis takes place to replace dead/worn out cells of the skin epidermis

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Functioning in:a) protecting tissues/organs below themb) help to absorb substances & allow substances to cross themc) some are modified to form special receptors for stimuli

Arrangement of cellssimple epithelium – arranged in one layerstratified epithelium – arranged in more than one layerpseudo-stratified epithelium – seemed to be arranged in layers but each of the cells are attached to the basement membrane

Cell shapessquamous epithelium – flattened cells like scales/tilescuboidal epithelium – shaped like cubescolumnar epithelium – cell s that look like pillars; height is longer than their base widthtransitional epithelium - changes shape when stretched

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EIGHT TYPES OF COVERING EPITHELIA1. Simple squamous epithelium

• single layer of cells attached to the basement membrane, thin & flattened with central nucleus

• found in the outer layer of Bowman capsule, endothelium of blood vessel & alveolar walls

• the thin wall permits diffusion ex: gases across the alveolus• protects underlying tissues & act as a barrier, regulating

movement of substances across it

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2. Simple cuboidal epithelium

• single layer of cuboidal shaped cells• forms lining of many ducts ex: salivary &

pancreatic ducts, proximal & distal convoluted tubules, salivary & thyroid glands

• secretion, absorption & protection

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3. Simple columnar epithelium

• apical surface may have cilia/microvilli• found lining the innermost layer of the intestines

and stomachs• for mechanical support & protection

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4. Stratified squamous epithelium

• consists of several layers of cells • new cells are cuboid in shape but become flattened

to form squamous epithelium at the surface & is attached to the basement membrane, divide mitotically to produce new cells

• found in the epidermis of skin, lining the innermost layer of the oseophagus

• act as protective layer in areas of higher friction

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5. Stratified cuboidal epithelium

• consist of 2/3 layers of cuboidal cells• found in the excretory ducts of sweat glands

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6. Stratified columnar epithelium

• consists of several layers of columnar cells

• found in the salivary gland ducts

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7. Pseudo – stratified epithelium

• consist of only one layer of cells with all the cells attached to the basement membrane

• apical surface may have cilia• found in the innermost layers of trachea, bronchi

and bronchioles

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8. Transitional epithelium

• consist of 3-4 layers of cells • able to modify their shape under different

conditions• found in walls of urinary bladders• allows stretching of the bladder• act as a barrier against urine flowing out into the

surrounding tissues

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Glandular epithelium

this epithelia contains secretory cellssecretes liquid containing mucus,

hormones or enzymestwo types of glandular epithelia

a) exocrine glandsb) endocrine glands

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Exocrine glands

certain surface epithelial cells become active and divide mitotically. A cord of ingrowing epithelial cells are formed which grow inward to form a duct/tubule

there are little capillaries in them the cells at the lower end of the duct become specialised as

secretory cells they produce liquid with proteins or enzymes

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exocrine glands remain connected to the surface epithelium by a duct. the duct transports the secretion to the surface

Ex: salivary glands, digestive glands, sweat glands & sebaceous glands

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Endocrine glands

a cord of cells are formed from surface epithelium and invaginate inward

the cord cells at the end divide to form a clump of cells which specialise to form secretory cells

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the cord connecting the epithelium dissolves during development the endocrine gland has no duct and is highly vascular Hormones are secreted into the surrounding capillaries and the

bloodstream carry them to the target cells Ex: pituitary gland, thyroid gland, adrenal gland, pancreas,

ovaries(in females) & testes(in males)

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Nervous Tissue is composed mainly densely packed

neurones which are specialised for trasmitting nerve impulses

neurones can be divided into 3 main types:a) Sensory neuronesb) Interneuronesc) Motor neurones

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Motor neurone

o a typical cell body consist of nucleus and cytoplasm(consist many organelles ex: mitochondria & Nissl’s granules/ribosomes)

o Nissl’s granules(ribosomes) consists of ER & polyribosomes(protein synthesis)

o has a number of processes called dendrons(conduct impulses towards the cell body) & finer branches called dendrites

o in some neurones, the axons have a fatty myelin sheath formed by Schwann cells which insulates the axon to enable the impulses to travel faster & as a protective layer

o Axon transmits impulses away from the cell body. Axon dendrites end with little knobs called synaptic knobs

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o the small uncovered part between the Schwann cells are called the nodes of Ranvier

o Motor neurone transmits impulses from the central nervous system (CNS) to the motor organs / effectors, usually muscles or glands

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Sensory neurone

o Transmits nerve impulses from receptors or sensory organs to the CNS

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Interneurones

o are found within the brain and spinal cordo connects one neurone to another neurone,

frequently connects a sensory neurone to a motor neurone

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Neurogliao are cells other than neurones found in the

CNSo Ex: astrocytes, oligodendrohydrcytes,

microglia and ependymal cellso supply nutrients to neurones, remove

wastes from neurones, guide axon migration, provide immune functions and structural support

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Muscle Tissue is a group of cells or multinucleated

syncytial tissue which can contract major function of muscles is to provide

motion there are 3 types of vertebrate muscle

a) Smooth muscleb) Cardiac musclec) Striated / skeletal muscle voluntary muscle because they are under conscious(voluntary) control

involuntary muscle

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SMOOTH MUSCLE

the cell is spindle-shaped consist of one centrally located nucleus, arranged in strands/layers and not branched

made up of individual cells, each having its own nucleus & plasma membrane, contract rhythmically like peristalsis & produces waves of contraction as in intestines

controlled by autonomic nervous system (involuntary muscle)

line the walls of hollow organs such as arteries & veins, urinary bladder, uterus, dermis, trachea and in the alimentary canal

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CARDIAC MUSCLE

are tissues that make up the heart, cardiac muscle cells have a single nucleus, many mitochondria(individual cells)

cardiac muscle fibre is branched & connected to the neighbouring fibres by bridges forming a net-like arrangement

each cells is separated by intercalated discs from its adjacent ones to enable excitation transmitted effectively

myogenic because it has its own pacemaker to generate excitation before they contract

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STRIATED(SKELETAL) MUSCLE

arranged in antagonistics pairs consist of a bundle of muscle fibres attached

to the bone by tendons at the both ends the contraction produces movement of the

skeleton and organs ex: the eyeballs & tongue

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each myofibril is made up of 2 types of filaments. Myosin( A band) & Actin( I band). The A band shows dark band that produces striations under light microscope & the I band shows light band that produces striations under light microscope.

The thick/dark myosin filaments are supported at the centre by M membrane. Thin/light actin filaments are supported at the centre by Z membrane

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The thick/dark myosin filaments are supported at the centre by M membrane. Thin/light actin filaments are supported at the centre by Z membrane

the whole myofibril containing many units are called sacromeres

the SER forms the sarcoplasmic reticulum. It consists of longitudinal interconnected tubules between the myofibrils & contains sacs filled with calcium ions for muscle contraction

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Connective Tissues is made up of a variety of cells embedded in

a large amount of intracellular substances called matrix & fibres which are non-living products of the cells

found between 2 different tissues protect & support the body & internal

organs, act as connecting systems, binding all other tissues together & also form surrounding sheath to separate the various organs

Ex: cartilage, bones, blood, adipose tissue, areolar tissue, white fibrous tissue & yellow elastic tissue

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BONE compact bone consists of living cells (abt.30%

collagen, glycoprotein fibres,70% inorganic substances)

the major mineral deposits are calcium hydroxyapatite crystals, a form of calcium phosphate & varying quantities of Mg, Na & hydrogencarbonate & Cl ions

compact bone is made up of numerous cylinders. Each cylinders is a Haversian system/osteon

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each osteon is made up of concentric circles called lamellae around a Haversian canal containing an artery,a vein, lymph vessels & nerve fibres

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the osteocytes are found in small spaces called lacunae with intricate tiny canaliculi/fine channels for distributing the matrix during bone formation

Haversian canal is supplied with blood vessels that bring raw materials for bone reconstruction

Volkmann’s canal connects the Haversian canals of adjacent osteons to each other for blood circulation

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Cartilage

consists of cells embedded in a matrix of chondrin

not hard, flexible but of high tensile strength

3 types of cartilage hyaline, yellow elastic & white fibrous cartilage

Yellow elastic cartilage located in the pinna(the projecting part of the external ear of mammals/the primary division of a leaf) & epiglottis

White fibrous cartilage found in the ligamentous capsules surrounding joints & the intervertebral discs

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Hyaline cartilage-the matrix is chondrin(mucopolysaccharides & chondroitin)secreted by chondroblasts(cells)

the fine fibres in the matrix are mainly collagen & elastic fibres

the chondroblasts later become chondrocytes enclosed in spaces called lacunae surrounded by capsule

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the hyaline cartilage is protected by an outer perichondrion layer. It produces the new chondroblasts which secrete the cartilage matrix

there are no blood vesels in hyaline cartilage. Exchange of materials occurs by diffusion with surrounding tissue

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Functions is elastic, compressible tissue located ex: hyaline

cartilage found in the rings of trachea. the u-shaped rings prevent the trachea from collapsing, thus allowing easy air-passage

covers the ends of bones and reduces friction between joints during movement

forms the skeleton of cartilaginous fish ex: sharks and rays

forms the embryonic skeleton in many bony vertebrates

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Blood Blood cells are formed through haemopoiesis.

The blood cells arise from pluripotent stem cells in the bone marrow

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Erythrocytes(RBC) formed in the bone marrow before it matures, erythrocyte which has nucleus

is later digested to enable more haemoglobin to be filled the carrying of oxygen

very thin – easy gaseous exchange biconcave so that its surface to volume ratio is

increased for gaseous exchange

contains haemoglobin that transport oxygen and carbon dioxide

act as buffer to maintain the pH of the blood

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Leucocytes ( WBC) contains nucleus & organelles pigment haemoglobin is absent generally larger than RBC, are spherical/irregular in

shape divided into granulocytes & agranulocytes Granulocytes have granular cytoplasm &lobed nuclei formed & mature in the bone marrow divided into 3 types:

i) Neutrophilsii) Eosinophilsiii) Basophils

Agranulocytes have relatively clear cytoplasm & the nuclei are not lobed

formed in the bone marrow but mature in the thymus gland divided into 2 types:

i) Lymphocytesii) Monocytes

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Monocytes come out the capillary into the tissue fluid becoming bigger to form macrophages – consumes bacteria & dead tissue cells

o Lymphocytes are divided into T lymphocyte(mature in the thymus gland) & B lymphocyte(mature in the bone marrow). B lymphocyte produces antibody