1 and 2 epithelial cells and tissues

Question 1

What are the 4 main cell types

Answer 1

“epithelial cells: cells forming continuous layers, these layers line surfaces and separate tissue compartments
mesenchymal cells: cells of the connective tissues, e.g. fibroblasts (many tissues), chondrocytes (cartilage), osteocytes (bone), muscle cells (skeletal, cardiac, smooth), the endothelial cells lining blood vessels.
haematopoietic cells: blood cells and the cells of the bone marrow from which they are derived.
neural cells: cells of the nervous system having two main types; neurones (carry electrical signals) and glial cells (support cells) ”

Question 2

What are the tumours that arise from different cell types

Answer 2

“epithelial cancers are carcinomas
mesenchymal cancers are sarcomas
haematopoietic cancers are leukaemias (from bone marrow cells) or lymphomas (from lymphocytes)
neural cell cancers are neuroblastomas (from neurone precursors) or gliomas (from glial cells)
”

Question 3

Describe microtubules

Answer 3

Microtubules are polymers of α tubulin and β tubulin. They are involved in the cell shape and act as tracks for the movement of other organelles and cytoplasmic components. Many accessory
proteins are involved in these functions
They are the major component of cilia and flagellae
They radiate from out of a point in the centre of the cell, called the centrosome (MTOC)
Microtubules also form the mitotic spindle

Question 4

Describe intermediate filaments

Answer 4

Intermediate filaments (IFs) are a grup of polymers of filamentous proteins which form rope like filaments
  The type of IF a cell has depends on the cell type e.g. epithelia have cytokeratins, mesenchymal cells have vimentin, neurones have neurofilament protein etc.
  They give mechanical strength to cells
  Desmosomes are connected by cytokeratins
  Nuclear lamins are IFs found forming a network on the internal surface of the nuclear envelope, and thus are involved in stabilising the envelope

Question 5

Describe microfilaments

Answer 5

Microfilaments are polymers of actin that associate with adhesion belts in epithelia and endothelia, and with other plasma membrane proteins
They are involved in the cell shape and cell movement (i.e. cells crawling, cell contractility e.g. in muscle)
They have accessory proteins such as myosin which act with the actin to control actin organisation and cell movement by giving even non muscle cells contractile properties

Question 6

What is a tissue

Answer 6

cells whose type, organisation and architecture are integral to its function
Made from cells and ECM and fluid

Question 7

Describe tight junctions

Answer 7

Called zonula occuldens (belt junction)
These are points on adjacent lateral membranes that form close contacts at apical lateral
membranes
They form a network of contacts, the more elaborate the network, the tighter the seal
They act to seal paracellular pathways i.e. between cells
They also segregate the apical and basolateral membranes, contributing to polarity

Question 8

Describe the adhesion belt

Answer 8

Called zonula adherens
Usually formed just basal to the apical tight junction
The transmembrane adhesion molecule is cadherin (family of Ca2+ ion dependent cell adhesion
molecules)
Cadherins associate with the microfilament (actin) cytoskeleton
This junction controls the stability of the other junctions (master junction)

Question 9

Describe the desmosome

Answer 9

Called macula adherens
These are found at multiple spots between adjacent cell membranes
It uses a transmembrane adhesion molecule that is like cadherin
It is linked to the intermediate filament cytoskeleton
It provides mechanical continuity between cells

Question 10

Describe gap junctions

Answer 10

Called macula communicans
It is made up of clusters of pores from six identical subunits in the membrane. These pores are
continuous with pores in the adjacent cell membrane
This allows the passage of ions and small moleculesb between cells
The pH, Ca2+ concentration, voltage and some signalling molecules can affect the passage i.e. can
open and close pores controlling intracellular communication

Question 11

Where are simple squamous epithelial cells found

Answer 11

lung alveolar, mesothelium and endothelium

Question 12

Where are simple cuboidal cells found

Answer 12

kidney collecting duct

Question 13

Where are simple columnar cells found

Answer 13

Entereocytes

Question 14

Where are stratified squamous cells found

Answer 14

Keratinisinge.g.epidermis,skin,nucleinotvisibleinsurfacelayercells
In the base, there are stem cells, which are there to replace any surface cells, as they are lost, so deep cells move up
o Non keratinisinge.g.liningsofthemouth,oesophagus,GItract,cervix,nucleiarevisiblein surface layer cells

Question 15

Where are pseudostratified cells found

Answer 15

Upper airway epithelium

Question 16

Why does epithelial function require polarity?

Answer 16

Polarised transport allows directional flow

Allows secretion from one surface only

Question 17

Why are TJs important

Answer 17

Seal the paracellular pathway
Prevent moisture of proteins and lipids between palms membrane compartments mixing, maintaining apical-basolateral polarity
Prevents gradients being lost by diffusion

Question 18

Describe the specialisation of epithelium such as in DCT

Answer 18

In the distal tubules, mitochondria are aligned with the basal membrane’s infoldings to allow energy for active transport to be used here:
The location of the mitochondria allow the ions to be pumped in the basal direction more efficiently, leading to a net flow of ions out this way

Question 19

How are absorptive epithelial cells specialised

Answer 19

Absorptive epithelia have carriers transporting nutrients that are found on the brush border membranes e.g. absorptive enterocytes, kidney proximal tubules

Question 20

How do exocrine and endocrine epithelial cellls differ?

Answer 20

Endocrine cells have their secretory vesicles in the basal cytoplasm and secrete contents into the basal aspect and exocrine cells secrete contents have their secretory vesicles in their apical cytoplasm and secrete into the apical aspect.

Question 21

What are the 3 main layers of skin?

Answer 21

Epidermis – keratinising stratified squamous epithelium, acts as a barrier to the
environment
o Dermis – cuboidal basal cell layer (stem cells) form the layer of cells that will renew the top
later. Callouses are responses to pressure. Continued pressure produces callouses as skin
responds to pressure with mitosis o Hypodermis

Question 22

Describe cell turnover in intestinal epithelium

Answer 22

Cell division, for the renewal of the surface epithelial cells is by stem cells in the intestinal crypts
There is a continuous production and loss of cells – cell turnover

Question 23

What is under the basal lamina?

Answer 23

The ECM and interstitial connective tissue

Question 24

What are the 3 surfaces on cells

Answer 24

Basal, apical, lateral

Question 25

Describe the nuclear envelope

Answer 25

The nuclear envelope consists of an inner membrane and an outer membrane, the space within is known as the perinuclear space. Since the nuclear envelope and the ER are continuous, their lumens are also continuous. The nucleolus within the nucleus produces ribosomal subunits, and it is not surrounded by peripheral heterochromatin. The peripheral heterochromatin lines the inner side of the nuclear envelope.