Histology

Question 1

What is a tissue?

Answer 1

Collection of one or more cell types working together for a common purpose.
Tissues are the building blocks of organs

Question 2

What are the 4 major types of tissues in the human body?

Answer 2

Epithelial
Connective
Muscle
Nervous

Question 3

What are the functions of epithelial tissues?

Answer 3

Secretion, protection and absorption

Question 4

What are the functions of connective tissues?

Answer 4

Support, binding, transport and protection

Question 5

What are the functions of muscle tissues?

Answer 5

Movement

Question 6

What are the functions of nervous tissues?

Answer 6

Coordination

Question 7

Where are epithelial tissues found?

Answer 7

Resting on the basement membrane (composed of peptidoglycan)

Question 8

Describe simple epithelial tissue

Answer 8

Single layer of cells resting on basement membrane

Question 9

Describe stratified epithelial tissue

Answer 9

Multiple layers of cells stacked on top of each other like bricks in a wall

Question 10

Summarise simple squamous epithelia

Answer 10

• Thin and flat
• Found where thin membranes are necessary
• Adapted for the diffusion of gases e.g. O2 and CO2
• Relatively elastic - this property is exploited in the alveolar air sacks in the lungs

Question 11

Link simple squamous epithelial tissue to diffusion in the lungs

Answer 11

• The alveolar walls of the lungs are
  composed predominantly of simple
  squamous epithelial cells
• Each alveolar air sac or alveolus is
  surrounded by a dense network of
  blood capillaries which themselves
  are also composed of simple
  squamous epithelial cells

Question 12

Link simple squamous epithelial tissue to arteries and veins

Answer 12

• Each artery and vein has an inner
  layer called the endothelium which is
  composed predominantly from a layer
  of simple squamous epithelial cells
• This endothelial layer is in direct
  contact with the blood and the
  smooth squamous epithelial cells
  ensure that resistance to blood flow
  is minimal
• The elastic nature of the squamous
  cells ensures that the blood vessel
  can dilate to increase blood flow
  (vasodilation) and constrict to reduce
  blood flow (vasoconstriction)
• These squamous cells also produce a
  variety of chemicals such as Nitric
  Oxide (NO) which help regulate blood
  flow

Question 13

Link simple squamous epithelial tissue to capillary structure and function

Answer 13

Each capillary is formed from a
rolled up tube of simple squamous epithelial cells

Question 14

Link simple squamous epithelium to serous membranes

Answer 14

Throughout the body are a variety of fluid-producing membranes which are lined by a layer of simple squamous epithelial cells
When a squamous layer is
examined the surface can have an appearance resembling “crazy
paving” for this reason many
textbooks also refer to squamousvepithelium as “pavement epithelium”
The squamous layer secretes a thinvwatery fluid called “serous fluid” this is found forming a natural slippery lubricant in many regions of the body.

Question 15

What is the outer layer of the gut?

Answer 15

Serous membrane = serosa
Prevent abrasion and damage

Question 16

What is the pericardium?

Answer 16

Compound membrane supporting the heart, protects the heart and anchors it in position within the thorax

Question 17

What are the pleural membranes?

Answer 17

Two serous membranes
The parietal pleural membrane is
attached to the inner surface of the
thoracic cavity (ribcage)
The visceral pleural membrane is
attached to the outer surface of the
lungs
Between the two membranes is a
cavity termed the pleural cavity
which is filled with a serous fluid
produced by the pleura
This fluid is known as pleural fluid
and helps to adhere the outer
surface of the lungs to the inner
chest wall
Pleural fluid often can become
infected leading to inflammation to
the pleural membranes which is
known as pleurisy

Question 18

Describe simple cuboidal epithelium

Answer 18

• Single layer of cube-shaped cells
• One example of location is forming the walls of the kidney tubules
• Much greater volume of cytoplasm compared to simple squamous epithelium, it is the cytoplasm of the cell which is primarily involved in biochemical processing.
• In the kidney tubules these cells are
  excellent at regulating the
  composition of renal filtrate (the
  precursor to urine) where they ensure
  that waste products remain within
  the tubules whilst simultaneously
  ensuring that useful chemicals such
  as glucose, amino acids and
  hormones are reabsorbed back into
  the blood
• Some simple cuboidal epithelial cells
  are ciliated; i.e. they have hair-like
  projections called cilia extending
  from their outer (apical) surfaces

Question 19

Describe Ciliated Cuboidal Epithelial Cells -
Ependymal Cells and the Choroid
Plexus

Answer 19

• The ventricles are hollow chambers
  within the brain which are lined by
  specialised cuboidal epithelial cells
  called ependymal cells
• Ependymal cells are found in greatest
  densities in areas known as the
  choroid plexus within the ventricles
  and produce the cerebrospinal fluid
  (CSF) which fills the ventricles and
  surrounds the brain and spinal cord

Question 20

Describe Simple Columnar epithelium

Answer 20

• Single-layer of column-shaped cells
• Found lining the gastrointestinal (GI)
  tract
• Large cytoplasmic volume ensures
  slow absorption of nutrients into the
  blood
• Many columnar epithelial cells have
  their surface area increased by small
  finger-like projections termed
  microvilli
• These enhance the absorption of
  nutrients and in the ileum have
  enzymes embedded into their
  surfaces which help complete the
  process of chemical digestion
• The layer of columnar epithelial cells
  lining the gut have associated mucus-
  producing goblet cells
• The mucus produced helps lubricate
  the passage of food through the GI
  tract and also coats the intestinal
  mucosa preventing chemical
  autodigestion

Question 21

What are goblet cells?

Answer 21

• Produce mucin granules
• On release mucin granules expand on
  contact with water
• Freshly produced mucus is usually
  transparent and very sticky ensuring
  it coats the mucosal surfaces
• When mucus traps particulate
  material it becomes darker in colour
• Mucus also contains a variety of
  antimicrobial compounds such as
  lysozyme which can kill some forms
  of bacteria by attacking their cell walls
  initiating lysis (bursting)

Question 22

Describe ciliated columnar epithelium

Answer 22

• Some forms of columnar epithelium
  have mobile hair-like projections
  called cilia extending from their apical
  surface
• This ciliated form of columnar
  epithelium is found lining the
  fallopian tubes
• Here the cilia beat in co-ordinated
  waves where they function to
  transport the ova released during
  ovulation along the fallopian tubes
  into the uterus

Question 23

Explain the effects of chlamydia trachomatis

Answer 23

• In some women it can migrate into the
  fallopian tubes damaging the ciliated
  columnar epithelium thereby
  preventing it from acting as an
  effective transport mechanism for ova
• Loss of the ability to transport ova
  into uterus is a leading cause of
  infertility in females
• If an ovum is fertilised there is a risk
  that it can become stuck within the
  fallopian tube potentially leading to
  an ectopic pregnancy
• Ectopic pregnancy is a medical
  emergency since there is a risk that
  the tube can rupture

Question 24

Describe stratified squamous epithelium

Answer 24

• Composed predominantly of multiple
  layers of thin flat (squamous) cells
• The first layer of cells resting on the
  basement membrane are cube-
  shaped and continually dividing by
  mitosis
• A good example of a stratified
  squamous epithelium is the epidermis
  of the skin
• In the epidermis newly produced
  layers of cells gradually get pushed to
  the surface and become flattened as
  they are compressed by the overlaying
  layers
• These epidermal cells gradually
  accumulate the protein keratin as
  they move to the surface; this protein
  renders the cells impermeable to
  oxygen and so they gradually die
• The outer layers of epidermal cells
  are entirely dead and gradually
  slough off at the surface to make way
  for the newer cells beneath

Question 25

Describe Stratified cuboidal epithelium

Answer 25

- A relatively rare tissue composed of multiple layers of cube-shaped cells - Found surrounding developing follicles within the ovaries - A strong epithelium which allows a build-up of pressure within the follicle as it enlarges - Eventually the pressure causes the stratified cuboidal layer to rupture expelling the ovum into the fallopian tube during ovulation

Question 26

Describe Stratified columnar epithelium

Answer 26

- Composed of multiple layers of column-shaped cells - A rare tissue found lining the male urethra and the conjunctiva of the eyes - Also found in portions of the pharynx (throat) and vas deferens (sperm ducts) - A relatively thick and robust tissue with its major role being protection

Question 27

Describe Pseudostratified epithelium

Answer 27

- The term pseudostratified means "falsely stratified" this is because on superficial inspection this tissue appears to be composed of multiple layers of cells but in reality this is a single layer of cells with each cell in contact with the basement membrane - The falsely stratified appearance is due to the fact that some cells in the layer extend all the way to the surface while other smaller cells remain compressed below. The larger cells extending to the surface are ciliated with their hair-like cilia beating in sweeping, co-ordinated waves - This tissue is found lining the respiratory tract where it forms the mucociliary escalator - Goblet cells in the pseudostratified layer produce mucus which traps particles inhaled into the airway. - The beating cilia then move this contaminated mucus upwards toward the pharynx (throat) where it is swallowed before being sterilised in the acidic gastric juice of the stomach

Question 28

What is whooping cough?

Answer 28

- The bacterium Bordetella pertussis causes whooping cough. - This bacterium infects the respiratory tract damaging the mucociliary escalator. - Since the contaminated mucus cannot be cleared effectively it sinks down into the respiratory tract triggering a vigorous coughing reflex - Recently, because of a drop-off in the uptake of the whooping cough vaccine, this disease has become more prevalent in the UK - Whooping cough is a potentially deadly infection, particularly in young children

Question 29

Describe Transitional epithelium

Answer 29

- An elastic stratified epithelium lining certain hollow organs such as the bladder; Called transitional because the cells change shape according to the current volume of fluid in the organ. - When the bladder is full the cells are compressed and flat (squamous), as the bladder progressively empties the cells transition from flat to cube- shaped and eventually column- shaped when fully empty - The outer cells of the tissue slough off and collect in the urine where they may contribute to sediment found in urine samples