Body Logistics:

Define the term homeostasis with respect to water, temperature and pH

Homeostasis is the process by which the body maintains a stable internal environment despire external or internal changes.

Homeostasis means ‘steady state‘ while body is never static and continually adjusts to maintain dynamic equilibrium especially key variables like temperature, fluid levels and pH.

Explain the concepts behind positive and negative feedback loops:

• Negative feedback loops, restore balance

• Positive feedback: Amplify a response

Basic system:

Stimulus → receptor → sensory neuron → CNS → Motor neuron → Effector

State the ‘normal range‘ for core body temperature, and what happens when body is not in normal temperature range:

36.5 - 37.5

When body not in normal temperature range:

Hypothermia: Core body temperature below 35 degrees

• Passive rewarming: removing patient from cold environment, remove wet clothes, cover with dry blankets (head to toe)

• Active external rewarming: Heat packs and lamps, warm blankets, bair hugger system

• Active core rewarming: warmed intravenous fluids, warm humidified oxygen

Hyperthermia: Core body temperature above 37.5 degrees

• Body’s reaction to infection (more than 38 degrees = pyrexia), extra heat can be helpful for immune system to deal with pathogens

State the mechanisms in broad terms that regulate core body temperatures:

Sensors in the skin and hypothalamus detect temperature. The hypothalamus triggers responses such as:

• When cold: Shivering, piloerection (hairs standing), vasoconstriction

• When hot: Sweating, pilorelaxation (hairs lying flat), vasodilation

State the ‘normal range‘ for pH in tissues including blood:

Normal blood pH is 7.35 -7.45

Explain the importance of acid-base balance for normal human physiology:

Below pH 7.35 is acidosis

Above pH 7.45 is alkalosis

The kidney maintains pH in safe range:

• Metabolic = the kidneys (remove the HCO3) => base

• Respiratory = The lungs (remove CO2) => acidic

The conditions:

Metabolic acidosis = Build up of acidic metabolites such as lactic acid in severe infection or ketoacids in untreated diabetes

Metabolic alkalosis = Loss of H+ ions the acid through vomitting // Excess HCO3- lost through urine

Respiratory acidosis = Inability to breath out enough carbon dioxide // builds up as carbonic acid

Respiratory alkalosis = Breathing out too much carbon dioxide // hyperventillation during panic attack

Recall the percentage of water in a standard 70kg male:

60% of body weight

of which 40% is intracellular (2/3) fluid and 20% is extracellular (1/3)

State the body compartments where fluid accumulate:

Intra = inside // This is water inside the cell // contain 2/3 of total body water

Extra = outside // This is water outside cells (blood plasma, interstitial fluid - fluid between cells, small amounts of other body fluids such as lympth) // 1/3 of total body water

• Interstitial fluid 75% of the extracellular fluid

• Plasma fluid is 25% of the extracellular fluid => the plasma part of the blood

Compare and contrast the water balance in males, females, in early life and in older populations:

Factors effecting body water:

• Age (main factor): water content decreases with age as body fat increases

• Gender: Men have higher water percentage than women due to less body fat

• Body composition: Higher body fat means, less water percentage (since fat is store anhydrously)

• Fitness level: Athletes may have slightly higher water percentage due to increased lean muscle mass

Definitions:

• Osmotic pressure

• Osmole

• Osmolarity

• Osmolality

Definitions:

• Osmotic pressure = the force of pulling where there is low solute concentration to high solute concentration

• Osmole = Number of moles that a solute contributes to the osmotic pressure of a solution

• Osmolarity = is the number of particles per L

• Osmolality = is the number of particles per kg (double ll = heavyyy )

Overall, osmolarity and osmolality is a form of osmotic direction, high osmolarity/ osmolality to low osmolarity/osmolality

Outline the physiological differences between dehydration and water toxicity and their effect on osmolality:

Dehydration: Water pressure outside the cell is lower than inside the cell, so water moves out by osmosis, increased blood viscosity since same number of RBC in less water which increases chance of muscle clots, because thicker blood moves more slowly increases heart pressure to pump and this causes the clotting factors to take place, fast heart rate, muscle cramp. An increase in plasma osmolality triggering thirst.

Water toxicity: Excess water dilutes sodium → oedema, especially dangerous in brain (since high water intake can effect brain immediately) = causes seizures, coma and eventually death

Describe the process of odema:

1. When there is right hand heart failure, there is not effective pumping of the right heart to the lungs, so there is a build up of blood in the capillaries, this causes high hydrostatic pressure, so more fluid leaves capillaries

2. Large DVT = deep vein thrombosis, the pathway [Leg tissue → Leg vein → larger veins → heart], if there is a clot in the vein, the blood can’t go to the heart, and more blood travels to the vein via arteries. So, build up of blood, high hydrostatic pressure, so more fluid moves out of capillaries

3. Decreased levels of albumin in blood, less pull of water at venous end, so more fluid reabsorbed via lymph

Define histology:

• ‘histos‘ = tissue

• Logy = study

• The study of tissues under the microscope to understand how cells are organised

Describe common biopsy techniques, giving examples of tissues which can be sampled by each method

Tissue samples (biopsies) can be taken in several ways:
• Scraping: e.g., curettage for the endometrium.
• Needles: e.g., fine needle aspiration (thyroid), pipelle (uterus), trephine
(bone marrow), venepuncture (blood).
• Surgical excision: larger samples for solid organ tumours.
• Transvascular: access via blood vessels, e.g., heart or kidney.
• Patient collection: samples like sputum, semen, urine or stool. These are
not ‘true’ biopsies but are still samples which can be assessed and
visualised microscopically

Outline the steps involved in tissue processing from a biopsy sample to a slide which can be examined microscopically, and state why each step is necessary

Fixation: Preserves tissue structure (usually use formalin which contains
formaldehyde).
Dehydration: Removes water and prepares tissue for embedding (using alcohol
and solvents like xylene/toluene).
Embedding: Often in paraffin wax, infiltrates and surrounds tissue in a block.
Sectioning: Very thin slices cut using a microtome.
Mounting: Sections placed on glass slides.
Staining: Adds contrast for microscopic viewing.
These steps prevent decay, preserve fine detail, and allow light to pass through the
sample for microscope viewing.

Describe how tissue processing can lead to the formation of shrinkage and other artefacts

Processing may shrink tissue or create distortions (artefacts/artifacts). There are
many different types of artefacts in histology – the main artefact to be aware of is tissue folding, which can cause layers of cells to overlap or shift out of focus.

Outline the advantages and disadvantages of using frozen sections and formalin-fixed paraffin-embedded (FFPE) sections for microscopic examination:

Frozen vs FFPE Sections
FFPE (Formalin-Fixed, Paraffin-Embedded) sections are not always the best choice
for processing a biopsy sample. Frozen sectioning provides an alternative method.
Frozen: quicker process but lower quality; used during surgery while patient is
under anaesthetic. Will not remove fats or sugars from sample so related structures
can still be viewed. More prone to artefacts such as ice crystal damage.
FFPE: higher detail achieved but takes longer. Fats and sugars removed by
solvents. Stains better and can be stored indefinitely at room temperature.

Discuss the value of histological staining and state the components of tissue stained by routine stains and specalist methods

• Haematoxylin: a basic dye that binds to acidic (basophilic, base-loving)
  structures. Blue/purple colour. Highlights nuclei (due to DNA/RNA).

• Eosin: an acidic dye that binds to basic (eosinophilic, acid-loving)
  structures. Red/pink colour. Highlights cytoplasm, muscle fibres, connective
  tissue (due to mainly basic proteins).
  
  

Describe the main differences in preparing tissue for electron microscopy compared to light miscroscopy

D

Define the term ‘limit of resolution‘

Explain why electron microscopes are capable of finer resolution than light miscroscopes

Depending on the situation, light or electron microscopy can be used to view the
final sample/slide. Keep in mind, tissue preparation differs for electron microscopy.
• Fixed with glutaraldehyde instead of formaldehyde
• Embedded in epoxy resin instead of paraffin wax
• Stained with electron-dense chemicals e.g. osmium tetroxide
• TEM samples sliced on special microtome using diamond knife to 30-60nm
depth

Conversion between milli-, micro-, nanometres, pico

Define ‘tissue‘ and ‘organ‘ and ‘organ system‘:

• Tissue: A collection of cells adapted to perform a specific function

• Organ: A structural unit composing of two or more tissue types working together to perform a function

• Organ system: When several organs work together to form a system which performs complex functions

State the four types of tissue:

• Epithelia - lining cells, glands

• Connective tissue - Bone, blood, fat, cartilage

• Muscle tissue = Cardiac, skeletal, smooth

• Nervous tissue - Peripheral nerves, spinal cord, brain

Describe how cells are held together at the molecular level: HORIZONTALLY

Tight junctions (Zonula occludens):

• Structure: Belt-like seals between neighbouring cells, nearest to the apical surface

• Function: Prevent paracellular leakage (leakage between cells), control passage of ions, water and solutes from => so act as selective barriers, restricting diffusion of water-soluble molecules.

Adherens Junctions (Zonula adherens):

• Structure: Belt-like adhesion complexes just below tight junctions, about ½ way down from apical surface

• Function: Provide mechanical stability and additional transport barrier

Desmosomes (macula adherens):

• Structure: Spot-like junctions with cadherin molecules anchored to intermediate filaments, strongest cell-cell adhesion, found ½ way down lateral membranes

• Function: Provide strong adhesion, especially in tissues under mechanical stress (skin and heart)

Gap Junctions:

• Structure: Most widespread of cell-cell junction, made up of connexin proteins towards the base of the lateral membrane

• Function: Allow direct cell-cell communication via small molecules and ions, can be opened/closed by changes in pH and calcium concentration (important in muscle contraction)

Define epithelia and explain classification terminology:

Epithelia are layers of closely packed cells that line the surfaces and cavities of the body. They serve as protective barriers and are involved in absorption, secretion, filteration and sensation.

Classification:

Simple: One layer of cells above the basement membrane

Stratified: Multiple layers of cells above the basement

Pseudostratified: May appear to have multiple layers of cells (with nuclei at different heights), but actually only have one layer.

Shapes:

Squamous (flat):

Cuboidal:

Columnar:

Explain the position, structure and function of basement membrane

The basement membrane is beneath the epithelium and above the lamina propria, anchoring epithelial cells to underlying connective tissue.

Function:

• Anchors epithelial cells

• Supports epithelium

• Separates epithelium from connective tissue

Explain the reason for the different rates of renewal of each type of epithelium:

Epithelial Renewal Rates
• High renewal: oral mucosa, oesophagus, vagina, intestines
• Moderate: transitional (urothelium), pseudostratified respiratory, bile duct
lining (simple cuboidal/columnar), epidermis (skin)
• Low: renal tubules (simple cuboidal), blood vessel lining (simple squamous)

Why?

High renewal rate: Due to abrasion, friction and microbes

Low renewal rates: Relatively protected, renew slowly

Differentiate between simple and stratified (compound) epithelia from micrographs:

Recognise the different types of surface specialisation found on epithelial cells (keratin, microvilli, stereocilia and cilia) and descrive how their structure relates to function

Keratinisation (skin surface):

Location: Epidermis of the skin, especially thick on palms and soles

Structure: surface cells become filled with keratin (tough protein), where cells eventually die and form a protective outer layer

Function: Protection against abrasion, waterproofing, reduce water loss, barrier against pathogens

Microvilli (brush border in gut):

Location: Small intestines, kidney tubules

Structure: Tiny finger-like projections of cell membrane, contain actin filaments, form a brush border.

Function: greatly increase surface area, increase absorption of nutrients

Cilia (respiratory tract):

Location: Trachea, Bronchi, Larger airways

Structure: Hair-like motile projections, beat in coordinated fashion

Function: Move mucus and trapped particles towards the throat, so lungs are clean

Stereocilia (epididymis):

Location: Epididymis (attached to the back of the testis), part of inner ear

Structure: Very long microvilli, not motile

Function: Increase surface area for absorption

Describe the functions of goblet cells, club cells and microfold (M cells)

Goblet cells: Found in the GI and Respiratory that secrete mucus rich in mucins. These form a protective barrier that traps pathogens and particles

Microfold (M) cells: They are located in the epithelium of Peyer’s patches (GALT) in the gut => located around the small intestine, they transport microorganisms from intestinal lumen to immune cells

Club cells: Bronchiolar secretion and detoxification => Non-ciliated found in bronchioles of lungs. They produce components that detoxify harmful substances via enzymes and contribute to epithelial repair after injury

Explain briefly the genetic cause of cystic fibrosis, how epithelial cells are affected by smoking and define different examples of common respiratory diseases.

Cystic Fibrosis:

A mutation in deltaF508, leads to the production of faulty CFTR proteins, so this protein can’t regulate the chloride and sodium ion transport across epithelial cells.

So, leads to thick, sticky mucus to accumulate in lungs, pancreas and other organs leading to chronic respiratory infections and digestion problems.

Smoking:

Smoking damages the respiratory epithelium: Destroying cilia, increase muscus prodiction and goblet cell hyperplasia, promoting inflammation and oxidative stress which causes permanent damage to airway lining

Distinguish between mucous and serous membranes

Mucous membranes (mucosae)

• Line body passages that communicate with the outside environment

• Examples: gastrointestinal, respiratory and urinary tracts

• Consist of:

  1. Epithelium

  2. Basement membrane

  3. Lamina propria: underlying connective tissue

  4. In some regions, a muscularis mucosae

• Often produce or are covered by mucus

• Functions include protection, secretion and absorption, depending on location.

Serous membranes (serosae)

• Line closed internal body cavities and cover organs within them

• Consist of:

  1. Mesothelium: simple squamous epithelium

  2. Thin layer of connective tissue

• Produce serous fluid, which lubricates surfaces and reduces friction as organs move.

• Examples:

  • Pleura: lungs

  • Pericardium: heart

  • Peritoneum: abdominal organs

Mucous membrane = lines passages connected to outside
Serous membrane = lines closed internal cavities and covers organs

For the gastrointestinal, urinary and respiratory mucosae:

• Describe the structural relationships between the epithelia and
  closely associated tissues (glands, underlying connective tissue,
  lamina propria and muscularis mucosae)

• Discuss how the structure of their constituent tissues relates to
  mucosal function

1. Epithelium

• Forms the surface facing the lumen

• Provides a barrier

• Its type varies depending on function.

2. Basement membrane

• Thin layer underneath the epithelium

• Anchors/supports the epithelium and separates it from underlying connective tissue.

3. Lamina propria

• Loose connective tissue underneath the epithelium

• Supports the epithelium

• Contains structures such as blood vessels and immune cells

• Glands may also be present depending on the location.

4. Muscularis mucosae

• Thin layer of smooth muscle

• Allows local movement of the mucosa

• Especially important as a distinct component of the GI mucosa

Describe how cells are joined together (2)

Integrins: Heterodimeric transmembrane receptors (alpha and beta subunits), function is to bind with ECM proteins (fibrinogen, collagen). Bidirectional signalling between inside and outside cells, regulating process like differentiation and cell death (Apoptosis).

Cadherins: Mediate cell-cell adhesion, through Adherens junctions and desmosomes, they link to cytoskeleton and maintain tissue architecture

Selections: Important for immune system

Proteoglycans: Core proteins with glycosaminoglycan (GAG) side chains. Function: Important in skin// hydration of extracellular matrix, mediating adhesion. Regulate growth factor availability which controls cell turnover and tissue repair.