Lecture 8 & 9: Intro To Histology

Question 1

Numerous cell types- selective activation of genes determines ultimate size shape and function.
Describe these different cells:
Erythrocytes 
Adipocytes
Myocytes
Neurones
Gametes

Answer 1

Erythrocytes: isolated, anucleated, flexible, abundant haemoglobin.
Adipocytes: large lipid vacuole, peripheral condensed nucleus
Myocytes: contractile filaments, respond to nerve input
Neurones: afferent axon, multiple efferent dentrites

Question 2

Tissues

Answer 2

Collections of cells performing related functions

-Group or layer of similarly specialised cells that together perform specialised functions

Question 3

Epithelia

Answer 3

Continuous sheet like layer of cells in combination with a thin, underlying, non-cellular, basement membrane (across which blood vessels don’t pass)

• forms barrier/active interface- separates body from external environment (surfaces, tube and cavity linings)
• lines hollow organs and forms glands and more solid structures such as the liver

Question 4

What are the 5 major functional types of epithelia?

Answer 4

Protective: outer surface of body and openings of cavities eg skin
Exchange: rapid exchange of gases eg lungs, blood vessels
Transporting: exchange of non gaseous materials; selective eg gut and kidney
Ciliated: moves fluid across the surface
Secretory:
A) exocrine: release secretory products to external environment eg sweat or mucous
B) endocrine: internal environment eg thyroid or islets of langerhans

Question 5

What are the different types of epithelia, describe each

Answer 5

Pseudostratified ciliated columnar: all cells rest on basement membrane but their nuclei lie on different levels.
Columnar (Ciliated epithelium): can be found in respiratory and female reproductive system.
Stratified squamous (protective epithelium): cells are flattened towards the surface. In some areas the cells have lots of keratin protein and very thick superficial layer that makes the partially tough eg on skin and footpads
Exchange epithelia (squamous): eg in alveoli in lungs, here the cells are flattened and form only a single layer, as it has to be thin enough to allow for rapid gas exchange but also good fluid exchange.
Transport epithelium: in small intestine

Question 6

Epithelia are characterised by being held together by various types of intercellular junctions. Why?
Tight junctions
Anchoring junctions
Gap junctions

Answer 6

Tight junctions prevents movement of material passing between epithelia cells. Hence material is forced to cross through the cell itself.
Anchoring junctions: responsible for joining one cell to its neighbour, and these are called desmosomes. Additionally some epithelia are anchored to their underlying basement membrane by a further type of anchoring junction called a hemidesmosome.

Gap junction: a channel between adjacent cells that allows electrical continuity by way of a cytoplasmic bridge and is important, for ex, in the heart by allowing synchronised contraction of the heart.

Question 7

Secretory epithelia (cuboidal)

Answer 7

These cells form small clusters or glands. They synthesis materials within the cell for secretion into the extracellular space. Sometimes they are individual cells that are able to secrete material or they form a gland.

Question 8

Gland development:

How do both exocrine and endocrine glands develop?

Answer 8

Exocrine: a hollow centre or lumen, forms in exocrine glands, creating a duct that provides a passageway for secretions to move to the surface of the epithelium.
Endocrine: endocrine glands lose the connecting bridges of cells that links them to the parent epithelium. Their secretions go directly into the bloodstream.

Question 9

Tissue: muscle-> generates contractile force when electrically stimulated. 
List some properties of:
Skeletal
Smooth 
Cardiac

Answer 9

Skeletal: striated, voluntary contraction often agonist and antagonist, (biceps/triceps) , also diaphragm, tongue, extrinsic eyes muscles etc
Smooth: involuntary contraction (autonomic) eg intestinal wall with agonist and antagonist (circular and longitudinal layers) also blood vessels, uterus etc
Cardiac: involuntary contraction (intrinsic modified autonomic)

Question 10

Connective tissue

Answer 10

In narrow sense: Connective tissue refers to any structure whose primary function is physical support for other structures (tendons anchor muscles to bones’ ligaments anchor bones together)
In broader sense: connective tissue encompasses fluids eg blood, lymph, which serve to connect various parts of the body by providing routes of communication

Question 11

What are the 6 different types of connective tissue? Give brief explanation of each

Answer 11

1. Loose- fibroelastic tissue that underlie epithelia- (support, biological packing)
2. Dense- tissue for strength, flexibility, bio mechanical action eg tendons, ligaments, muscle and nerve sheaths
3. Adipose tissue- adipoctyes (fat storage)
4. Cartilage- supporting tissue, eg ear, nose, knee menisci, joints
5. Bone- calcified supporting tissue- mechanical support/ leverage
6. Blood- watery, ions and dissolved, molecules, soluble proteins

Question 12

Nervous tissue:

Answer 12

Nerve cells (neurons): specialised cells that receive, integrate and transmit info in form of electrical signals 
Glial cells: astrocytes- for metabolic support, Schwann cells and oligodendrocytes for myelin)

Question 13

Organs

Answer 13

Anatomically discrete collection of 2 or more tissue types (often 4) together performing specific functions eg eye, liver, brain.
Using the liver as an example
It as hepatocytes (epithelial cells), supporting stromal tissues (connective tissue, blood vessels), and blood (round cells)