The Cell The Cell RevisedRevised

The Cell Revised Histology

The study of the structure and form of cells and tissues

What is a cell? Bases of all life Smallest unit of matter that can live independently

and reproduce itself Exist in all shapes and sizes

Elongated Square Star-shaped Oval

The Cell Revised What is a cell composed of?

What is a cell look like?

Protoplasm Made up of 70% water and Compounds of

Organic and inorganic saltsCarbohydrates LipidsNitrogenous substances

Generalised picture The cell is a living structure, thus is only possible to show a

general picture. Remember – that cells constantly move and change

The Cell Revised

‘Protein factories’ of the cell

Structures within the cell

Cytoplasm

Mitochondria

Ribosomes

Protoplasm inside the cell but outside the nucleus

Organelles - referred to as the ‘power houses’

The Cell Revised

Organelles containing digestive enzymes

Structures Cont.

Endoplasmic reticulum

Golgi apparatus

Lysosomes

‘Circulatory system’ of a cell Two types:

Rough Smooth

Communication network from deep within the cells to its membrane Also used to make Lysosomes

The Cell Revised

Dense areas of cytoplasm containing the Centrioles

Structures Cont.

Vacuoles

Centrioles

Centrosomes

Used for storage or digestive purposes in different types of cell

Paired, rod-like organelles which play an important role in mitosis

The Cell Revised

The point where two chromatids join in the chromosome

Structures Cont.

Nucleus

Chromatids

Centromere

Largest organelle Controls the cells processes

Two strands of DNA held together by a centromere form a chromosome

The Cell Revised

Chromatin – A combination of DNA and proteins that makes up chromosomes.

Structures Cont.

Nucleolus

Chromosomes

Chromatin

Programmes the formation of ribosomes which then move into the cytoplasm of the cell and produce protein

Chromosome is an organized building of DNA and protein that is found in cells

The Cell Revised Structures Cont.

Nucleoplasm

Specialised protoplasm, in which the nucleoli and Chromatin/chromosomes are suspended along with Nutrients and other necessary chemicals

Structures finished

Cells MembraneThe Cell Revised

A thin semi-permeable membrane made of protein threads and lipids Two functions

To act as a regulator To exchange harmful products

Fluid inside is called – Intracellular fluidFluid outside is called – Extracellular fluid

Not all substances can cross through the cell membrane

TYPES OF MOVEMENT ACROSS THE CELL MEMBRANE

The Cell Revised

Passive Transport The movement of molecules across the cell membrane and does not require energy

There are four main kinds

Diffusion Osmosis Dissolution Filtration

TYPES OF MOVEMENT ACROSS THE CELL MEMBRANE

The Cell Revised

Diffusion

The movement of molecules from a region of higher concentration to a region of lower

concentration.

OsmosisProcess of transferring water across the

membrane is by

Equal pressure on both sides of the membrane

Isotonic pressure

Osmotic pressure

TYPES OF MOVEMENT ACROSS THE CELL MEMBRANE

The Cell Revised

Dissolution

Movement of water and soluble substances across a membrane.

Filtration

Hydro-static pressure

Substances can diffuse directly through the lipid bi-layer part of the membrane

TYPES OF MOVEMENT ACROSS THE CELL MEMBRANE

The Cell Revised

Active transport Energy is used When too large Not soluble on fat

The pumping of substances across a membrane by a trans-membrane protein

pump molecule

Cell ReproductionThe Cell Revised

Mitosis

The process at which cell reproduce Exact replicas of chromosomes in parent cells are duplicated to form daughter cells

Consists of four main stages

Anaphase Metaphase

Prophase

Telophase

Interphase Normal metabolic functions DNA is reproduced Nuclear protein is synthesised Cell increases in size

Cell ReproductionThe Cell Revised

Metaphase

ProphaseCentrosomes divide into two CentriolesThe chromatin in the cell’s nucleus shortens and thickens Two visible pairs of rods called chromosomes are formedThe nucleolus disappears

The chromosomes arrange themselves at the centre of the cellEach individual chromosome can be seen distantly as two chromatids

The nuclear membrane disappears

Cell ReproductionThe Cell Revised

Telophase

Anaphase Centromere stretches Pairs of chromatids divideSpindle threads of the Centrioles divide to form new centromeres Cell membrane begins to constrict

Spindle fibres disintegrate and Centrioles replicate Membrane continues to constrict

Nuclear membrane appears

Two daughter cells are formed

Tissue types

Four types of tissue:

Epithelial Connective Nervous Muscular

Tissue types

Epithelial tissue (or Epithelium)

Simple epithelium - usually functions as a covering or lining for organs and vessels

Compound epithelium - provides external protection and internal elasticity

Tissue typesSimple Epithelium

Consists of a single layer of cells attached to a basement membrane Goblet cells often found in simple epithelium Four types of simple epithelium: Squamous Cuboidal Columnar Ciliated

Squamous Flattened cells Forms thin, often permeable lining Allows diffusion and filtration

Tissue typesCuboidal

Cube-shaped cells Forms lining of kidney tubules as well as some glands

Columnar Tall, rectangular cells Forms lining in very active parts of the body such as the stomach intestines and urethra; some cells secrete mucus and some absorb mucus

Ciliated Mostly columnar cells Tiny hair-like projections, or cilia, stick out from the cell membrane The cilia work in waves Help to remove mucus, foreign matter and debris

Tissue types

Compound epithelium

Many layers of cells and no basement membrane Formed from a combination of deep layers of columnar cells plus flatter cells towards the surface Protects and delicate parts of the body Two types of compound epithelium:

StratifiedKeratinised (dry) – surface layer

Non-keratinised (wet)

Transitional

Tissue typesStratified

Keratinised (dry)o Surface layer has dried out into keratin,o Compound epithelium with dry surface cells o Forms a dead layero The skino keratinisation

Non-keratinised (wet)o Compound epithelium with wet surface cellso Provides lubrication

Transitional o Similar to stratified epitheliumo Surface cellso Deeper cellso Found in organs that need waterproof and expandable lining

Tissue typesNervous tissueo Arranged in bundles of fibreso Composed of nerve cells and neurogliao Have long fibrous processes – called dendrites and axonso Capable of transmitting signals to and from the brain – protective

Muscular tissue Three types:

Skeletal – striated and voluntary – support and movement

Smooth - non-striated and involuntary – carry out involuntary movements

Cardiac – striated and involuntary – heart muscle to pump blood

Tissue typesConnective tissue Supporting tissue of the body Mostly mechanical functions and connect more active tissues Can be semi-solid, solid or liquid – can have fibres present or not Mainly mechanical connecting other more active tissues

There are eight types:

Areolar Adipose White Fibrous

Lymphoid Yellow Elastic

Blood Bone

Cartilage

Tissue types AreolarLoose connective tissueMost general connective tissueSemi-solid and permeable Contains yellow elastic and white fibres, fibrocytes and mast cellsFound all over the body

Adipose Known as fatty tissue Made up of fat cells containing fat globules Found between muscle fibres and under the skin Also found in the kidneys and the back of the eyes Protective and insulator properties

Tissue types

White Fibrous Strongly connective Closely packed bundles of collagen fibres Few cells in rows that run in the same direction Function is connection and protection of parts of the body

Lymphoid Semi-solid tissue Majority of cells are lymphocytes and reticular cells which have a disease control function Forms lymphatic system cells and blood cells Protects against disease

Tissue types

Yellow elastic Composed of elastic fibres Enables stretch and capable of considerable extension and recoil Forms lung tissue, bronchi and trachea, arteries, stomach and bladder

Bone Hardest structure in the body; Two types – compact and cancellous Compact is dense bone for strength Cancellous for structure bearing and cellular development Composition – 25% water, 30% organic material, 45% inorganic salts Supports and protects the body and all organs, also produces cells in bone marrow

Tissue types

Blood Fluid connective tissue Contains 45% cells and 55% plasma Cell content is erythrocytes, leucocytes and thrombocytes Transports food , oxygen and waste to and from the body

Cartilage Firm, though tissue; solid Contains cells called chondrocytes

Three types Hyaline Yellow elastic cartilage White fibro-cartilage

Tissue types

Hyaline

Bluish – white, smooth; Chondrocytes cells are grouped together in nests in a solid matrix Particularly resilient Connects and protects Found on articular surfaces of joint Bone which forms joints

Yellow elastic cartilage:

Runs through a solid matrix Contains fibrocytes and chondrocytes cells which Lie between multidirectional fibres Flexible in areas of need

Tissue types

White fibro-cartilage While fibres Contains chondrocytes cells Extremely tough and slightly flexible Absorbs shock Example – forms intervertebral discs as well as the semi-lunar cartilages (menisci)