Tissues (5)

Question 1

What is a tissue?

Answer 1

Groups of cells similar in structure and perform a common/related function

Question 2

What are the 4 types of tissue?

Answer 2

Epithelial- lining of digestive tract organs, glands and skin surface

Connective- Bones, tendons and fat

Muscular- Muscles attached to bones and muscles of heart

Nervous- brain, spinal cord and nerves

Question 3

Characteristics of epithelium- polarity

Answer 3

> All have an apical surface (upper free surface exposed to the body exterior or the cavity of an internal organ).
Many apical surfaces are smooth and slick but most have microvilli (extensions on the plasma membrane) which massively increase the SA.
All have a basal surface which consist of a thin supporting sheet called the basal lamina which acts as a selective barrier and selectively allows molecules to enter the epithelium
Basal layer also acts as scaffolding along which epithelial cells can migrate to repair a wound
Some epithelial, such as that lining the trachea have cilia that propel substances along their free surface

Question 4

Characteristics of epithelium- specialised contacts

Answer 4

> Cells fit tightly together to form continuous sheets
Sides of adjacent cells are tied together by tight junctions (prevent substances from leaking through spaces between cells) and desmosomes (keep cells from pulling apart).

Question 5

Characteristics of epithelium- avascular but innervated

Answer 5

> Contains no blood vessels but is supplied by nerve fibres

> Nutrients are provided to cells from the underlying connective tissue

Question 6

Characteristics of epithelium- regeneration

Answer 6

> Has high regenerative capacity
Some cells rub off through friction
Some damaged by harmful substances in the external environment e.g. smoke and bacteria
As long as they receive adequate nutrition, they can replace lost cells by cell division.

Question 7

What is epithelial tissue/epithelium?

Answer 7

A sheet of cells that cover a body surface or lines a body cavity
> Epithelia form boundaries between different environments
> Nearly all substances have received/given off by the body must pass through epithelial tissue

Question 8

What are the two types of epithelium?

Answer 8

1) Covering and lining epithelium- forms the outer layer of the skin; dips into and lines the open cavities of the Genito-urinary, digestive and respiratory systems and covers the walls of the abdominal cavity
2) Glandular epithelium- forms the glands of the body

Question 9

Characteristics of epithelium- supported by connective tissue

Answer 9

> Forms the basement membrane which reinforces the epithelium
Helps it to resist stretching and tearing
Defines the epithelium boundary

Question 10

What are the functions of epithelium?

Answer 10

1) Protection
2) Absorption
3) Filtration
4) Excretion
5) Sensory reception

Question 11

How is epithelium classified?

Answer 11

> Each has 2 names- the first indicates the number of cells present and the second describes the shape of the cells

Question 12

What is simple epithelium?

Answer 12

> Consists of a single cell layer

> Usually found where absorption, secretion and filtration occur

Question 13

What is stratified epithelium?

Answer 13

> Composed of 2 or more layers stacked on top of each other

> Common in high abrasion areas where protection is important such as skin surface, lining of mouth and vagina

Question 14

What are the three shapes of epithelial cells?

Answer 14

1) Squamous- flattened and scale like
2) Cuboidal- as tall as they are wide
3) Columnar- tall and column shape
In each, the nucleus forms the same shape as the cell

Question 15

What is simple squamous epithelium?

Answer 15

> Single cell layer
Very thin
Protection is not one of their specialities
Flattened cells with disc-shaped nuclei and little cytoplasm

Question 16

What are the functions of simple squamous epithelium?

Answer 16

> Found where filtration/exchange of substances by rapid diffusion is a priority
In the kidney it forms part of filtration membrane
In lungs it forms the walls of the air sacs across which gaseous exchange occurs
In the CVS it provides a slick, friction-reducing lining, where its thinness encourages efficient exchange of nutrients and wastes between bloodstream and surrounding tissue cells (endothelium)

Question 17

What is simple cuboidal epithelium?

Answer 17

> A single layer of cells, as tall as they are wide, with large, spherical and central nuclei
Functions are secretion and absorption
Found in kidney tubules, ovary surface and ducts of small glands

Question 18

What is simple columnar epithelium?

Answer 18

> Single layer of tall, closely packed cells with round/oval nuclei
Many have microvilli and some have cilia
Mostly associated with absorption and secretion- cilia type propels mucus
Non-ciliated type lines most of digestive tract (stomach to rectum), gallbladder and ducts of some glands
Ciliated type lines small bronchi, uterine tubes and some parts of uterus

Question 19

What is stratified squamous epithelium?

Answer 19

> Most widespread of stratified epithelium
Thick and well suited for a protective role in the body
It’s free surface are squamous while cells of deeper layers are cuboidal or columnar
Found in areas subject to wear and tear where surface cells are constantly being rubbed away and replaced by dividing cells from the basal layer
Epidermis of skin, lining of oesophagus, mouth and vagina.

Question 20

What is stratified cuboidal epithelium?

Answer 20

> Rare
Mostly found in large glands (e.g.sweat glands and mammary glands)
Typically 2 layers thick

Question 21

What is stratified columnar epithelium?

Answer 21

> Rare

> Small amounts found in pharynx, male urethra and lining of some glandular ducts

Question 22

What is transitional epithelium?

Answer 22

> Forms lining of hollow urinary bladder which stretches as it fills with urine
Cells of basal layer are cuboidal/columnar
Apical cells vary depending on degree of distension (stretching) of organ
When distended, thins from 6 layers to 3 and apical cells flatten and become squamous like
This ability allows a greater volume of urine to be stored.

Question 23

What is pseudostratified columnar epithelium?

Answer 23

> Single layer of cells with different heights, some not reaching the free surface
Nuclei seen at different levels
May contain mucus-secreting cells and have cilia
Function is to secrete substances, mostly mucus and to propel it by ciliary action
Ciliated type line trachea and most of upper respiratory tract
Non-Ciliated type in male sperm-carrying ducts and ducts of large glands