FunMed Week 5: Infection

Question 1

1. What is the von Willebrand Factor and what is its role in haemostasis? (2 marks)

Answer 1

Von Willebrand Factor (vWF) is a glycoprotein found in blood plasma and endothelia of cells (1 mark)

and its function in haemostasis is to bind other clotting factors, particularly F VIII and help initiate a series of reactions that lead to platelet activation and aggregation and eventually blood clotting. (1 mark)

Question 2

1. What is the difference between primary and secondary intention healing? (2 marks)

Answer 2

Primary intention healing occurs in wounds with dermal edges that are close together (e.g. a scalpel OR surgical incision) OR wound that is stitched. (1 mark)

Secondary intention healing occurs when the sides of the wound are not opposed – and so healing must occur from the bottom of the wound upwards OR a wound that is left open and allowed to heal by itself. (1 mark)

Question 3

1. What are the main FOUR stages of wound healing AND what processes occur in each stage (4 marks)

Answer 3

Haemostasis – first response to stop bleeding through the activity of platelets and cytokines to form a clot and cause vasoconstriction. (1 mark)

Inflammation – specialized cells of the immune system remove dead cells and provide protection from infection, also cause local swelling and inflammation. (1 mark)

Proliferation - proliferation of new cells that make the extracellular matrix of the tissue (fibroblasts in the case of the dermis and keratinocytes for the epidermis) to rebuild new tissue.(1 mark)

Remodelling – remodelling of collagen fibres in the extracellular matrix rebuilds the durability and characteristics of the original tissue and creates the scaffolding for the rigid sealing of the wound. (1 mark)

Question 4

1. What is sepsis AND how can it lead to multiple organ failure? (2 marks)

Answer 4

• Sepsis is a rare life-threatening condition that can develop rapidly from an infection (1/2 mark).
• When the immune system overacts to an infection this initiates a series of reactions including widespread inflammation (1/2 mark).
• This can cause a significant decrease in blood pressure (1/2 mark) reducing the blood supply to vital organs and starving them of oxygen (1/2) which can lead to multiple organ failure.

Question 5

which type of infection is sepsis caused / triggered by?

Answer 5

Mostly endotoxin*-releasing gram -ve bacteria

*Endotoxins: complex lipopolysaccharides (LPS) which form a part of the outer cell wall of all gram –ve bacteria and are responsible for the organization and stability of the cell wall.

Question 6

what is the major complication of sepsis?

what is septic shock? [1]

Answer 6

•Multisystemic organ failure: Failure of 2 or more vital organ systems

•Septic shock: systemic hypotension and disturbed microcirculation perfusion, and direct tissue toxicity caused by the inflammatory immune response

Question 7

what are risk factors for sepsis? [5]

Answer 7

Extremes of age
frailty
immunocompromised and immunosuppression
recent trauma or surgery
breached skin integrity

Question 8

define gangrene [1]

where does it usually occur [1]

what are the two main types? [2]

Answer 8

• Definition: A clinical condition of ischaemic and necrotic tissue.
• Location: Often circumferential around a digit/extremity.

Types:
•Dry gangrene: Inadequate blood supply resulting in green/purplish/black discolouration, dryness and shrinkage.
E.g. Diabetes mellitus, arteriosclerosis / peripheral artery disease, tobacco smoking, traumatic injury (e.g. burns, penetrating injury), frostbite

•Wet gangrene: Bacterial infection à blistering, discharge, erythematous, foul odour

Question 9

what is initial response to getting cut? [2]

Answer 9

Inflammatory response

•Mast cells release histamine –> Inflammation, Vasodilation and increased capillary permeability to recruit phagocytes (macrophages and neutrophils)–> Redness and swelling

Question 10

what is the innate immunity response after inital response to infection?

Answer 10

1. Phagocytosis by Antigen-Presenting Cells (APCs)
Dendritic cells and macrophages non-specifically phagocytose pathogen, using Pattern Recognition Receptors (PRRs) to recognise Pathogen-Associated Molecular Patterns (PAMPs)

•E.g. PRRs: TLR-4 (Lipopolysaccharides (LPS) i.e. endotoxins), TLR-5 (Flagellin)

2. Activated APCs go to Lymph node to bind to active T-cells with MHC peptide and co-stimulatory molecules

Question 11

which TLRs are for LPS [1] & flagellin? [1]

Answer 11

•TLR-4 (Lipopolysaccharides (LPS) i.e. endotoxins), TLR-5 (Flagellin)

Question 12

what is adaptive immunity response to infection?

Answer 12

Adaptive immunity (specific)

•B-cells: Use BCR Ig to bind to foreign antigen –> Activation of B-cell –> Differentiate into plasma cells: secrete Ig with specificity of BCR e.g. IgM, G, E, A

•IgM is always the 1st antibody to be made before conversion to IgG!

•T-cells: Use TCR to bind to antigen on MHC of an APC

•Clonal expansion

Question 13

what causes lymph node swelling? [1]

Answer 13

1.T and B cell expansion causes LN swelling

Question 14

when can primary intention of healing only occur? [2]

Answer 14

when the wound is precise and there is minimal disruption to the local tissue and the epithelial basement membrane, e.g. surgical incisions.

Question 15

what are the key processes of haemostasis? [3]

Answer 15

1. Vasoconstriction to restrict blood flow to wound site
2. Formation of blood clot: Platelets adhere to sub-endothelium of injured site + coagulation cascade to reinforce platelet plug with fibrin mesh.
3. Platelets release growth factors to start healing process.

Question 16

what are the 3 key processes of inflammation? [3]

which leukocytes are involved? (eartly / late)?

Answer 16

Inflammation (4-6days):

1.Pro-inflammatory cytokines released: Histamine, prostaglandin, prostacyclins, thromboxane, bradykinin, serotonin à Swelling, heat, redness, pain, leaky blood vessels (capillary leakiness) à allows WBC migration

2. Early: Neutrophils release proteases (MMPs) to remove damaged tissue
3. Late: Macrophages phagocytose damaged/dead cells, pathogens and debris

Question 17

what are the 4 key processes of proliferation? [3]

which cells are involved?

Answer 17

proliferation: laying down collagen and ECM; formation of granulation tissue

1.Angiogenesis: Vascular endothelial cells form new blood vessels

2.Deposition of type III collagen (disorganised) and fibronectin by fibroblasts to form ECM —> granulation tissue

3.Epithelialisation: Epithelial cells migrate from wound margins

4.Wound edge contraction (myofibroblasts - modified smooth muscle cells)

Question 18

what are the key stages of remodelling wound?

Answer 18

remodelling: collagen remodeling to increase tensile strength of wound

1.Collagen type III –> I

2. Re-alignment of collagen along tension lines
3. Reabsorption of water to allow denser and cross-linked collagen

Question 19

when would you choose not to use primary intention to conduct wound healing? [3]

what is risk of doing primary intention when should be doing secondary? [1]

Answer 19

• considerable tissue damage or loss and we cannot approximate the wound edges.
• deep foreign bodies, there’s a significant risk of bacterial infection in the wound that can’t be easily debrided (cleaned)
• if there are areas of necrosis within the wound.

Particularly with infection, if we were to close up the wound using primary intention, we’re also trapping the infection in that tissue, worse so if these are anaerobic bacteria which can flourish in such circumstances. This could lead to chronic inflammation, abscess and pus formation which will either extend to cause a more widespread skin infection like cellulitis, or even burrow down to infect the bone, osteomyelitis. We end up with a much nastier and complicated wound than we began with.

Question 20

what are local factors [4] and systemic factors [4] that can affect wound healing?

Answer 20

local:
•Type, size, location of wound
•Local blood supply
•Infection
•Foreign material or contamination
•Radiation damage

Systemic factors:
•Advanced age
•Co-morbidities, esp. CVD or diabetes mellitus
•Nutritional deficiencies (esp. Vit C)
•Obesity

Question 21

what is defintiion of antibiotic resistance?

Answer 21

•Def.: When a microbe evolves mechanisms to evade the effects of antibiotics to which they were once sensitive, allowing them to survive and grow.

Question 22

what is antibiotic stewardship?

Answer 22

Aim of antibiotic stewardship: To reduce Abx prescription and also promote rational use by prescribing Abx only to patients who are expected to benefit from it.

Question 23

how can we undertake antiobiotic stewardship?

Answer 23

•Microbial samples help us to prescribe more targeted & narrow-spectrum Abx, and stop Abx that are ineffective or unnecessary

•Discussion with patient + family/carers about likely nature of condition, why Abx may not be the best option, alternatives, their views on Abx and what they expect from it, risks and benefits of prescribing Abx immediately etc.

•Decide if an antimicrobial is needed or not (Self-limiting conditions)
- Self-limiting conditions (e.g. colds, most coughs, sinusitis, earache, sore throats/URTIs): Share self-care, resources (verbal + written + online or community pharmacists) + safetynet to phone helplines like 111 in case of deterioration

Question 24

Q1) What is the most abundant cell in scar tissue?

a. Adipocytes
b. Endothelial cells
c. Fibroblasts
d. Macrophages
e. Neutrophils

Answer 24

Q1) What is the most abundant cell in scar tissue?

a. Adipocytes
b. Endothelial cells

c.Fibroblasts

d. Macrophages
e. Neutrophils

Question 25

Q2) There are two types of MHC proteins, which are important for T-cell activation. Class I and Class II. Class I proteins are expressed and displayed by all nucleated cells in the body. Class II are less widely distributed and are only found on the surfaces of cells that present antigens to CD4 cells. Which of the following cell types would not display MHC type I on its surface? A B-cells B Dendritic cell C Endothelia cell D Erythrocyte E Macrophages

Answer 25

Q2) There are two types of MHC proteins, which are important for T-cell activation. Class I and Class II. Class I proteins are expressed and displayed by all nucleated cells in the body. Class II are less widely distributed and are only found on the surfaces of cells that present antigens to CD4 cells. Which of the following cell types would not display MHC type I on its surface? A B-cells B Dendritic cell C Endothelia cell **D Erythrocyte** E Macrophages

Question 26

Q4) Briefly explain how antibodies help prevent bacterial infections? [4]

Answer 26

Antibodies are critical for defence against pathogens, especially extracellular bacteria: * Bind to them to increase their uptake by phagocytes (for example, macrophages or neutrophils), * or to induce their killing by complement activation * or by cellular components of the immune system (antibody dependent cellular cytotoxicity, ADCC). * Block infection by preventing the binding of pathogens to critical receptors on host cells and can neutralise the activity of toxins that cause disease.

Question 27

Q5) What is the difference between naïve and memory T-lymphocyte cells? [2]

Answer 27

* Memory T-cells do not require costimulatory signals from APCs to become activated in response to an infection and * respond more quickly to antigenic stimulation (proliferate faster and reach higher numbers than naïve T-cells following antigenic stimulation).

Question 28

which is the prinicpal clotting factor of blood? how does it work?

Answer 28

**Thrombin** clots blood by activating cells called **platelets** and chopping up a protein called **fibrinogen** to form **fibrin. Forms a fibrin mesh** which forms around the **platelet plug to reinforce it and hold it together.** However, stable clots can only form if thrombin also stimulates a factor called **prothrombin** to produce more **thrombin.**

Question 29

what are the intrinsic and extrinsic clotting pathways?

Question 30

what is the difference betwen primary and secondary hameostasis?

Answer 30

**Primary hemostasis** refers to the interaction between the **blood vessel, von Willebrand factor, and platelets in order to form the initial platelet plug** **secondary hemostasis** refers to the cascade of enzymatic reactions that ultimately results in the conversion o**f fibrinogen to fibrin monomers**

Question 31

how does secondary haemostasis work?

Answer 31

Both **extrinsic and instrisic pathways can become activated independentl**y and **ultimately culminate** in the activation of **factor X**, which then proceeds to activate the rest of the coagulation cascade via the common pathway. Let's start with the extrinsic pathway. It starts when t**rauma damages the blood vessel,** and exposes the cells under the endothelial layer, like smooth muscle cells, which have tissue factor or factor III in their membrane. Now, it turns out that there’s an enzyme called **factor VII floating around in the blood,** and some of it is active, meaning that it’s already set to proteolytically cleave other proteins. When it’s in that state, it’s called active **factor VII or VIIa.** “a '' for active. Factor VIIa binds to a tissue factor and a calcium ion -which get released by nearby activated platelets--and it forms a VIIa-TF complex on the surface of the smooth muscle cell. Both the calcium ions and tissue factors are co-factors, meaning that they need to bind to the enzyme factor VIIa to allow it to really get going. **This complex then cleaves clotting factor X yielding the active form called factor Xa.** Once **factor Xa** is generated **via the extrinsic pathway**, it cleaves **factor V into V**a and then it uses **factor Va and a calciu**m ion as the cofactors to form the prothrombinase complex which activates **prothrombin or factor II, into thrombin or factor IIa.** In fact, each prothrombinase complex can activate thousands of thrombin, so there’s enormous amplification that occurs at this step. Thrombin uses calcium ion as a cofactor and it has a number of pro-coagulative effects. First, thrombin binds to receptors on platelets causing them to activate. Activated platelets change their shape to form tentacle-like arms that allow them to stick to other platelets. Second, thrombin activates three cofactors; factor V, which is used in the common pathway; factor VIII; and fabin, which proteolytically cleaves fibrinogen or factor I, into factor Ia or fibrin. Third, the effect of **thrombin on fibrinogen plays a big role. Fibrinogen is soluble in blood, but fibrin isn’t, so fibrin precipitates out of the plasma and forms long protein chains that are like ropes.** The fibrin tether platelets to one another, holding the platelet plug together.

Question 32

treatment for sepsis? [3]

Answer 32

Oxygen to maintain oxygen saturations 94-98% (or 88-92% in COPD) Empirical broad spectrum antibiotics IV fluids

Question 33

whats the pathophysiology of sepsis?

Answer 33