Homeostasis and Histology

Question 1

What does the term homeostasis mean

Answer 1

Homeostasis is the physiological process by which the internal systems of the body are maintained at equilibrium, despite variations in factors, (internal or external), that act on the system.

Question 2

How does negative feedback work

Answer 2

Negative feedback tends to buffer/dampen changes in the system to bring it back to its equilibrium

Question 3

How does positive feedback work

Answer 3

Positive feedback enhances/amplifies changes which tends to move a system away from its equilibrium state and makes it more unstable, e.g., fruit ripening, blood clotting

Question 4

In a standard 70kg male, what is the percentage of water and volume of blood

Answer 4

60% of wight is water = 42kg
Volume of blood = 5 litres for a 70kg male

Question 5

What are the body compartments where fluid accumulate

Answer 5

2/3 of water is intracellular water
1/3 of water is extracellular water
3/4 of extracellular water is interstitual fluid
1/4 of intracellular water is blood plasma

Question 6

What are the differences in water balance in males and females, and infants

Answer 6

Normal adult male = 60% of body weight
Normal adult female = 50% of body weight
Normal infant = 70% of body weight
In general, the hight the percentage of body fat, the lower the percentage of total body water

Question 7

What happens when you are dehydrated

Answer 7

Cells and tissue will absorb water from the interstitial space, and then from each other.
This cause the cells and tissues to die as water is then absorbed by organs, and as they die, the water is absorbed by the brain liver, kidneys and heart.

Question 8

What happens when there is too much water, (water toxicity).

Answer 8

When there is too much water, the osmotic pressure is high. The cells will absorb water and swell.
This will cause enzyme and proteins to stop working and cells will keep swelling until they burst.

Question 9

Why is the acid-base balance important for normal human physiology

Answer 9

The human body must ne maintained in a very narrow range of acid-base balance, (between 7.35-7.45 PH).
Since normal cellular metabolism happens in this range. If the enzymes, fall outside of this range, the enzymes will denature.

Question 10

What is the normal range for PH in tissues and blood

Answer 10

7.35-7.45

Question 11

What is the normal range for core body temperature

Answer 11

36.5-37.5

Question 12

What mechanism regulate PH

Answer 12

The two major organs are
-The lungs for respiratory balance
-The kidneys for metabolic balance

Question 13

What mechanisms regulate temperature when you are cold

Answer 13

-Blood vessels constrict (vasoconstriction)
-Shivering
-Hairs on skin stand up (piloerection)
-Curling up to reduce surface area

Question 14

What mechanisms regulate temperature when you are hot

Answer 14

-Blood vessels dilate (vasodilation)
-Sweat glands start producing sweat
-Hairs on skin lie flat (pilorelaxation)
-Stretching out to increase surface area

Question 15

what is an oedema

Answer 15

Oedema is fluid retension. Swollen ankles is due to peripheral oedema and it occurs when hydrostatic pressure is greater than osmotic pressure.

Question 16

What is a tissue and examples of all 4 types

Answer 16

A tissue is a group of similar cells working together to perform a specific task.
Epithelial tissue
Connective tissue
Muscle tissue
Nerve tissue

Question 17

What is the relationship between milli micro and nano

Answer 17

Milli = 1x10^-3
Micro = 1x10^-6
Nano = 1x10^-9

Question 18

Why is histology important in diagnosis

Answer 18

Histology allows for the visualisation of tissue structures and the characteristic changes the tissue may have undergone.

Question 19

Why do tissues need to be fixed and what fixatives are most commonly used.

Answer 19

Tissues are fixed to preserve cell and tissue components, which allows for the preparation of thin, stained sections. It: inhibits cellular autolysis, preserves cellular components and morphology and presents cells with distinct microscopical appearance.
The most common type of fixation is:
- Formalin solution

Question 20

How does tissue processing lead to the formation of shrinkage and other artefacts

Answer 20

During fixation, tissues shrink due to dehydration and also cause fixation artifacts, which are unwanted effects of the process, (such as tissue hardening and brittleness from some fixatives).

Question 21

Discuss the value of histological staining

Answer 21

Histological stains are used to highlight important features of the tissue as well as enhance tissue contrast

Question 22

Explain how Haemotoxylin and Eosin work

Answer 22

Haemotoxylin is a basic dye that binds to acidic structures such as DNA and RNA. Eosin is an acidic dye that binds to basic structures such as intracellular and extracellular proteins such as: cytoplasm, collagen, elastic fibres etc. Haemotoxylin stains the nucleus blue, whilst Eosin stains the cytoplasm and extrcellular matrix pink. When combined, the nuclei are clearer and there is more detail in the cytoplasm

Question 23

Explain specialist methods such as immunohistochemistry and immunoflorescence.

Answer 23

These techniques utilise labelled antibodies specific cell and tissue targets, (antigens that are complementary to the shape of the antibodies).
Antibodies labelled with the flourescent dyes allow the structure to be visualised directely, with the incident light being from a UV light source such as confocal microscopy.
Indirect immunohistochemistry works by using an enzyme activated secondary complex that precipitates a coloured product at the site of interaction. This allows for as little as 100 anitgens to be detected per cell.

Question 24

Define the term ‘limit of resolution’

Answer 24

Limit of resolution is the minimum distance at which two objects can be distinguished.

Question 25

Why do electron microscopes have a finer resolution then light microscopes

Answer 25

Electron microscopes use electrons whilst light microscopes use visible light. The limit of resolution is proportional to the wavelength and since electrons have a much smaller wavelength then visible light, it has a smaller limit of resolution and therefore a finer resolution.

Question 26

How does Confocal microscopy work

Answer 26

1) Laser excites a fluorescent dye and electrons are raised to a higher energy level
2) As the electron relaxes back to its ground state, (lower energy level), a light with higher wavelength emitted
3) Emitted light is sent through mirrors and a pinhole screen to a CMOS detector
Because only one part of light reaches the detector, the images are very sharp
Motorisation allows full section scanning meaning the entire depth of the cell/tissue can be examined

Question 27

Explain the preparation of live cells and how phase contrast microscopy can be used

Answer 27

• Cutting and dicing
• Collagenase and DNAse
• Centrifugation steps on basis of cell density
• Put cells into appropriate growth medium
• Culture cells and view under phase contrast microscopy.

Question 28

Explain dark field

Answer 28

Dark field is a very specialised technique used with living cells. It works by illuminating the sample with light that will not be collected by the objective lens and thus will not form part of the image.
This produces the classic appearance of a dark, almost black background with bright objects on it.

Question 29

Compare paraffin wax formalin with frozen section

Answer 29

Specimens: Paraffin used fixed tissue whilst frozen uses fresh tissue
Making time: Paraffin is 24-48 hours whilst frozen is 10-20 minutes
Saving time: Paraffin is permanent whilst frozen is a few months
Morphology under microscope: Paraffin shows clarity whilst frozen is opaque
Application: Paraffin is a pathological diagnosis whilst frozen is intraoperative consultation