REvision

Question 1

About the nucleus and its associated structures:

Answer 1

a nuclear pore is made of many subunits namely the annular, luminal, ring and column

Question 2

About the Golgi Apparatus:

Answer 2

GA is a smooth structure. Vesicles budding from it usually contain macromolecules and are 50nm or larger. Vesicles originating from the GA carry material to for extracellular secretion and also towards other organelles.

Question 3

tIGHT JUNCTIOS

Answer 3

Tight junctions are also known as zonula occludens
Tight junction are present in endothelia
Tight junctions with more elaborate cell-cell interactions give tighter seals
X Tight junctions act as a barrier to the free diffusion of plasma membrane components between membrane domains.

Question 4

Which of the following is NOT a property of absorptive epithelia?

Answer 4

mitotic divisions do not occur.

Within absorptive epithelia the absorptive cells e.g. enterocytes, undergo constant renewal. The relevant stem cells are found in the intestinal crypts.

Question 5

Which best describes secretory cells and their actions?

Answer 5

exocrine secretion is usually from the luminal plasma membrane

Question 6

Which statement concerning the epithelium of the skin is FALSE?

Answer 6

the epidermis is directly external to the hypodermis.

The epidermis is directly external to the dermis, which in turn is external to the hypodermis.

Question 7

Covalent cross-links are found between elastin molecules (proteins). The core of an elastin molecule is made up of elastin, fibrillin and microfibrils. The extent of stretch is limited by the ‘interwoven-ness’ of the elastin molecules.
Source: Extracellular matrix lecture.

Answer 7

in elastin, the α-helical regions are rich in alanine and lysine

Question 8

Action potentials

Answer 8

are non-decremental.

Non-decremental means that the size of an action potential is maintained throughout transmission.

Question 9

Regarding force generation by motor units.

Answer 9

increasing recruitment results in more force.

The 1st statement is wrong because recruitment means increasing the number of ‘active’ motor units i.e. a motor unit being a single motor neurone and all its muscle fibres. The 2nd statement is wrong because increased speed of filament sliding decreases number of cross-bridges able to be formed since there is less chance of attachment. The 3rd statement is wrong because increased cross-bridges means increased force produced. The last statement is wrong it defines motor unit incorrectly.

Question 10

Cardiac and smooth muscles.

Answer 10

in cardiac cells, the shape of the action potential is almost independent of heart rate.

Cardiac cells are larger than smooth muscle cells. Smooth muscles are only innervated by autonomic nerves. Cardiac a.p.s are much brieer at high heart rates. Both cardiac and many smooth muscle cells are electrically coupled and spontaneously active (with myogenic contractions not requiring innervation).

Question 11

what is salbutamol?

Answer 11

Salbutamol is an agonist.

Question 12

The actions of second messengers. Which statement is FALSE?

Answer 12

IP3 is an extracellular receptor. THIS Is FALSE

Question 13

Ca2+ as a second messenger.

Answer 13

changes in Ca2+ concentration can be detected by proteins e.g. calmodulin

Another example of Ca2+ sensitive proteins are Ca2+-dependent protein kinases.

Question 14

Which of the following mechanism is NOT used to switch off the intracellular signal?

Answer 14

increased activity of the Golgi Apparatus

Question 15

Which protein the major component of the mitotic spindle?

Answer 15

Microtubules form the mitotic spindle. But “microtubule” is a structure, not a protein. Microtubules are made of the protein tubulin, thus tubulin is the answer instead of microtubules.

Question 16

Which protein is the major component of microfilaments?

Answer 16

Actins can be further subdivided into F (filamentous) and G (globular)

Question 17

This intermediate filament connects desmosomes.

Answer 17

Cytokeratins (polymers of filamentous rope-like proteins) are associated with epithelia. Different intermediate filament types are expressed by different cell types.

Question 18

This intermediate filament type forms a network in the nucleus.

Answer 18

Nuclear lamins form a network on the internal surface of the nuclear envelope. It helps to stabilise the envelope.

Question 19

Which substance consists of three chains, one each of an α, β and γ chain, forming a cross-shaped molecule?

Answer 19

Laminins are basement membrane glycoproteins. They can interact with cell surface receptors and associate with other basement membrane proteins. They regulate tissue differentiation, cell migration etc.

Question 20

This substance is a major cartilage matrix component, it is a supramolecular complex comprising a core protein, link proteins, chondroitin sulfate, keratan sulfate, and hyaluronan.

Answer 20

Aggrecans are mainly negatively charged due to the GAGs and carboxyl groups. The negative charges attract Na+, which is osmotically active. Hence, large quantities of water associate with the aggrecan molecules and under compressive load, water is lost but regained under reduced loads.

Question 21

Which of the following correctly identifies the order (from superficial to deep) of layers in the skin?

Answer 21

Epidermis, dermis, hypodermis.
The epidermis is the stratified squamous epithelium, consisting of mainly keratinocytes but also melanocytes, Langerhans cells and Merkel cells.
The dermis forms the structural foundation of the skin and contains blood vessels, nerves and adnexal structures (e.g. hair follicles, sweat glands, sebaceous glands).
The hypodermis is a deep, subcutaneous adipose layer and acts as both a fat and heat store.

Question 22

Which of the following is the correct order of cell layers in the epidermis of the skin (from deep to superficial)?

Answer 22

Stratum basale, Stratum spinosum, Stratum granulosum, Stratum corneum

The layers of the epidermis describe cells that gradually keratinise to form the waterproofing layer of the skin.
The Stratum basale is the deepest layer and cells have large nuclei and dense cytoplasm.
The Stratum spinosum is next, and is characterised by intracellular spines seen upon microscopy.
The cells of the Stratum granulosum layer have granules containing the precursor of filaggrin (which help bind keratin filaments). The staining of these granules helps to identify this layer upon microscopy.
The most superficial layer is the Stratum corneum which contains dead, flattened cells filled with keratin.

Question 23

What is the function of hemidesmosomes?

Answer 23

Attach a single cell to the extracellular matrix

Question 24

Which of these options correctly matches a hair type and a description of it?

Answer 24

Lanugo hair is fine and long, formed in the fetus at 20 weeks and often lost before birth; it can also appear after birth as a consequence of malnutrition due to anorexia.
Vellus hairs are short, fine, light coloured and covers most of the body.
Terminal hair is longer, thicker and pigmented. It is found on the scalp, eyebrows, eyelashes and also in the pubic, axillary and beard areas

Question 25

How long does the Catagen phase last?

Answer 25

The anagen phase lasts 2-6 years,

catagen lasts 2-3 weeks and

telogen lasts 2-3 months.

Question 26

Which part of the nail can lead to permanent nail deformities when damaged?

Answer 26

Lunula
The distal end of the matrix is seen as the lunula (half-moon). This area is critical to the proper growth of the nail plate.

Question 27

Nail structuere

Answer 27

The nail matrix contains dividing cells which mature, keratinize and move forward to form the nail plate. The matrix can also contain melanocytes.

The nail root is where the nail growth begins. It is embedded underneath the skin at the base of the nail.

The cuticle/eponychium ensheathes the nail plate from both above and below. It acts as a barrier to the external environment.

Hyponchium

The nail bed produces a small amount of keratin and is adherent to the nail plate.

Question 28

Which of the following is the main component of hair, nails and the epidermis of the skin?

Answer 28

Keratin is one of a family of fibrous structural proteins that protects epithelial cells from damage or stress. It contains many cysteine residues allowing formation of disulfide bonds. In nails, the keratin is hardened and densely packed. Albumin is the most abundant plasma protein.

Question 29

Which of the following is the main component of hair, nails and the epidermis of the skin?

Answer 29

Keratin is one of a family of fibrous structural proteins that protects epithelial cells from damage or stress. It contains many cysteine residues allowing formation of disulfide bonds. In nails, the keratin is hardened and densely packed. Albumin is the most abundant plasma protein.

Question 30

This gel-like substance makes up proteoglycans and when hydrated, resists compression.

Answer 30

glycosaminoglycans (GAGs)