Histology

Question 1

Definition and Classification of tissues. General properties of tissues.

Answer 1

4 types of tissues:
Connective tissue - several types of wandering and fixed cells. has an abundant amount of ECM. Function is support and protection of tissues and organs.

Epithelial tissue - aggregated polyhedral cells - small amount of ECM produced by its cells. Function is lining the surface or body cavities.
Can be parynchema (responsible for organ function) or stroma (supporting tissue)

Nerve tissue - elongated cells with fine processes. Receive, generate and transmit nerve impulses.
Very small amount of ECM

Muscle tissue - Elongated contractile cells
moderate amount of ECM
Function - strong contractions and body movements

Question 2

Epithelial tissue. Definition and general characteristics

Answer 2

Epithelial tissue cover, line and protect surfaces as well as helping in absorption and secretion of hormones.

-Made up of aggregated polyhedral cells with little ECM to have strong adhesion to the surface.
-have an apical and a basal surface
–no blood supply so receive nutrients from connective tissue through basal membrane
- organised into clusters - exocrine or endocrine

Basement membrane
-Attach epithelia to underlying connective tissue and regulates what passes between them.
- Thin layer of proteins with a basal (type 3 collagen) and reticular (type 4 collagen) lamina

Intercellular junctions:
Tight/occluding junctions - surround apical ends with transmembrane proteins preventing passage between cells.
- Adherent / anchoring junctions - made from cadherin and holds cells together at epithelium
- Gap junctions - both membranes have transmembrane connexons which allow small molecules to pass between cells

Apical structures:
Microvilli - small membrane projections for absorption
Stereocilia - long microvilli with specialised absorptive function in male reproductive tract and inner ear
cilia - large projections with microtubules which move substances along the surface.

Question 3

Covering epithelia, simple epithelium types

Answer 3

simple epithelia are only one cell layer thick

Simple squamous epithelia - flat in shape. air sacs of lungs and lining of blood vessels for diffusion. flatter nucleus

Simple cuboidal epithelia - cube shaped. form glands to secrete and absorb. more spherical nucleus

simple columnar epithelia - tall column shaped. elongated nucleus. Form cilia to secrete and move mucus.

Pseudo-stratified epithelia - Appear layered under microscope but are not. Form cilia to secrete and move mucus

Question 4

Covering Epithelium. Stratified epithelia

Answer 4

• More than one layer thick
  -Generally have protective functions
• Stratified squamous epithelia - multi layer of flat cells which line oesophagus , mouth and vagina to protect against abrasion
  -Stratified cuboidal epithelia - Multi layers of cuboidal cells which protect salivary and sweat glands.
  -Stratified columnar epithelia - Multi layers of tall columnar cells which form the urethra and some gland ducts and protect them
  -Transitional epithelia - Multi layers of different types of epithelial cells which allows expansion and stretching in bladder, urethra and ureters.

Question 5

Glandular epithelium - exocrine type. Classification of glands

Answer 5

Retain connections with surface epithelium at development so have tubular ducts lined with epithelial cells through which secretions reach surface

proliferation of cells and their downgrowth into connective tissue

simple glands have simple unbranched ducts compound glands have branched ducts.

merocrine glands secrete substances by exocytosis with no loss of other cellular materials

Holocrine glands undergo cell differentiation, culminating in complete cell disruption whereby secretory product and cell debris are released e.g. sebaceous gland of skin

Apocrine gland secrete product in part of apical end with cytoplasm and plasma membrane e.g. lipid droplet secretion in mammary gland

produce mucous (mucus glands) or enzymes (serous glands)

Question 6

Glandular epithelium Endocrine type

Answer 6

Lose connection with surface epithelia at development so lack ducts.

Secretions are picked up in interstitial fluid and transported by blood vessels not duct system.

Specialised to secrete hormones which are transported by paracrine (receptors on separate cell to secreting cell) and autocrine (receptors present on same cell that produces hormone) signalling.