Diversity of cells and their function

Question 1

How are tissue samples preserved in as life-like a state as possible?

Answer 1

Tissue is ‘fixed’. Usually a chemical that cross-links proteins such as formalin is used.

Question 2

How do you prepare tissue for light/electron microscopy?

Answer 2

Tissue has to be thinly sliced (1-15µm) to allow light to penetrate the tissue.
Must impregnate tissue with a support material, usually wax (not necessary for cell smears).
To do this tissue is: dehydrated, put into organic solvent and placed in hot wax until it has fully penetrated the tissue.
Thin sections are cut on a microtome and put onto microscope slides, the wax is washed out and the tissue rehydrated.
Produces distortions/changes from the original tissue and we term these artifacts (e.g shrinkage). Then a dye is added.

Question 3

Name two common dyes

Answer 3

Haematoxylin: a basic dye that has an affinity for acidic molecules and stains them purplish blue – for example the nucleus (remember what the A stands for in DNA) or ribosomes. Eosin: an acidic dye that has an affinity for basic molecules and stains them pinkish red. Most proteins in the cytoplasm are basic and so the cytoplasm of a cell is usually stained pink or red. You will see this abbreviated: ‘H&E’

Question 4

Name the four basic tissue types.

Answer 4

There are 4 basic tissue types. • Epithelium • Connective tissue • Muscle • Nervous tissue  Nearly all tissues and organs are made up of combinations of these 4 types.

Question 5

What are the common features of epithelial cells?

Answer 5

• Adhesion between epithelial cells is strong, thus forming sheets of cells, with a minimum of intercellular space. They are therefore perfect to cover surfaces and line body cavities.
• All have, at their basal surface, a layer of extracellular matrix components, called a basal lamina (basement membrane), to which the cells are attached.
• All are non-vascular. Nutrients from capillaries in underlying tissue must diffuse across the basal lamina.
• The cells are usually polarized, that is the apical and basal ends of the cell differ.

Question 6

List the functions of epithelial cells.

Answer 6

 Mechanical barrier (e.g. skin)
 Chemical barrier (e.g. lining of stomach)
 Absorption (e.g. lining of intestine)
 Secretion (e.g. salivary gland)
 Containment (e.g. lining of urinary bladder)
 Locomotion (by cilia) (e.g. oviduct)
 Minor functions include: sensation (neuroepithelium, e.g. taste buds) and contractility (myoepithelial cells)

Question 7

What are the three shapes of epithelial cells?

Answer 7

 Squamous (flattened, like a fish scale)
 Cuboidal (cube shaped)
 Columnar (like a column, relatively tall and thin)

Question 8

Describe epithelial cells according to the number of layers present.

Answer 8

 ‘Simple’ = one layer
 ‘Stratified’ = two or more layers
 ‘Pseudostratified’ = tissue appears to have multiple layers, but in fact all cells are in contact with the basal lamina

Question 9

List some different cell surface specialisations of epithelial cells.

Answer 9

 Prominent microvilli (termed a ‘brush border’)
 Cilia
 Presence of layers of keratin proteins on the tissue surface (termed keratinized).
Goblet cells may also be present in between other epithelial cells.

Question 10

List some secretions produced by glandular epithelial cells.

Answer 10

sweat, milk, oil, hormones, mucous, enzymes and others.

Question 11

Whats the difference between endocrine and exocrine glands?

Answer 11

Endocrine glands: product secreted toward the basal end of the cell (end sitting on basal lamina), then distributed by the vascular system throughout the body. Termed ‘ductless’ glands.
Exocrine glands: product secreted toward the apical end of the cell either into the lumen of an internal space, into a duct, or onto the body surface. Termed ‘ducted’ glands.

Question 12

what are the three types of connective tissue?

Answer 12

1. Soft connective tissue: Tendons, ligaments, mesentery, stroma of organs, dermis of the skin, etc
2. Hard connective tissue: Bone and cartilage
3. Blood and lymph: many authors consider blood and lymph as a specialized form of connective tissue

Question 13

What does the extracellular matrix of connective tissue consist of?

Answer 13

• Fibres: collagen, reticular and elastic fibers
• Ground substance: an amorphous, space occupying material made of huge unbranched polysaccharide molecules called glycosaminoglycans (GAGs), most of which are bound to protein cores to form glycoproteins
• Tissue fluid

Question 14

Name some of the cells that make up connective tissue.

Answer 14

• Fibroblasts: widely distributed cells that produce and maintain the extracellular matrix.
• Adipose cells: fat cells, found scattered in many connective tissues, but predominant cell in adipose tissue (fat)
• Osteocytes: cells of bone
• Chondrocytes: cells of cartilage

Question 15

Describe some of the different types of soft connective tissue.

Answer 15

Loose: Loosely packed fibres separated by abundant ground substance. Cells are relatively plentiful

Dense regular: Densely packed bundles of collagen fibres. Can be dense regular CT if the fibres are aligned (e.g. tendon).

Dense irregular: if the fibre bundles run in many directions (e.g. dermis of the skin).

Question 16

Describe the features of cartilage.

Answer 16

 Strong, flexible, compressible, semi-rigid tissue.  The semi-rigid nature of the matrix comes from the highly hydrated nature of the ground substance (GAGs and proteoglycans).

 Cartilage is avascular and receives nutrients from adjacent tissues by diffusion through its matrix.

 Three types: hyaline (found at Articular surfaces Tracheal rings, Costal cartilage, Epiphyseal growth plates), elastic and fibrocartilage. The type is defined by the extracellular matrix.

Question 17

What are the two types of bone?

Answer 17

 An outer shell of dense cortical bone makes up the shaft (diaphysis).

 Cancellous or trabecular bone occupies the ends of the bone (the epiphyses). Cancellous bone is a fine meshwork of bone that looks a bit like the inside of an Aero bar.

Question 18

Name the small canals that penetrate bone and describe their function.

Answer 18

Haversian canals and for blood vessels and nerves to enter bone, and living cells called osteocytes.

Question 19

Name the three types of muscle tissue.

Answer 19

Smooth, skeletal and cardiac.

Question 20

Describe smooth muscle.

Answer 20

 Also called involuntary or visceral, is structurally the simplest of the muscle types.
 It is called smooth because it has no visible striations  Involuntary because it is not under conscious control, and
 Visceral because it is predominantly found in organs.

 The individual fibres are elongated, spindleshaped cells with great range in length (20 - 200 µm).
 A cigar-shaped nucleus lies near the centre of each fibre.
 Note: the muscle cells have been sectioned along their long axis (termed longitudinally) on the left and across their long axis (termed transversely) on the right.

Question 21

Describe skeletal muscle.

Answer 21

 Skeletal muscle is also called voluntary or striated muscle,
 Constitutes the muscles of the body that respond to conscious control.
 Note: neither skeletal, voluntary, nor striated are entirely accurate terms. Some skeletal muscles are not always under the control of will, and all striated muscles are not skeletal, eg cardiac.

 The typical skeletal muscle fibre is a giant multinucleated, cylindrical cell. The fibres may attain considerable lengths (1 to 40 mm), with a diameter ranging from 10 to 100 µm.
 Each fibre has many nuclei that are elongated and located at the periphery of the cell, just internal to the cell membrane, which in muscle cells is called the sarcolemma.

Question 22

Describe cardiac muscle.

Answer 22

 Forms the major part of the walls of the heart chambers and origins of the great vessels.
 Like skeletal muscle, cardiac muscle has striations, however they are less prominent.
 The fibres are much shorter than striated muscle (50100µm) and branch to form a complex network.
 Cardiac muscle cells have a single nucleus located near the centre of the fibre.
 Intercalated discs, can be seen passing across the fibres at irregular intervals. These are the sites of end-to-end attachments between adjacent cells. Not surprisingly these contain multiple intercellular junctions to maintain mechanical integrity.

Question 23

Describe nervous tissue.

Answer 23

 Consists of neurons and support cells (glia).
 Glia outnumber neurons by about 10:1 in the central nervous system.
 Surrounded by connective tissue ‘coat’ Meninges for central nervous system (CNS) Epineurium for peripheral nervous system (PNS)

Question 24

List some of the types of neurons.

Answer 24

Multipolar: most common, many dendrites (D) one axon (A)

Bipolar: one dendrite one axon (found in the cochlea of the ear)

Pseudounipolar: short process gives rise to axon in both directions (no dendrites)

Question 25

Name some of the glia cells found in the CNS.

Answer 25

 Astrocytes: support, ion transport, induce blood brain barrier

 Oligodenrocytes: produce myelin in the brain and spinal cord

 Microglia: provide immune surveillance

Question 26

Name the glia cell found in the PNS.

Answer 26

 Schwann cells: produce myelin and support axons. There are no cell bodies of neurons in the PNS btw.