Haemophilia
How factors VIII and IX amplify thrombin to build a stable clot, why their lack lets a platelet plug form but fail, why bleeding goes into joints and muscles, and how the X-linked inheritance shapes who is affected.
By the end, you can
- Describe primary and secondary haemostasis and the role of factors VIII and IX.
- Explain why haemophilia causes delayed, prolonged bleeding rather than immediate bleeding from small cuts.
- Relate severity to the factor level and explain the X-linked inheritance.
- Explain how repeated joint bleeding damages the joint.
- Interpret the pattern of a prolonged APTT with a normal PT and platelet count.
- Recognise the joint pathology, severity bands and tests of haemophilia, and explain how factor replacement, non-factor therapies and supporting medicines act on its mechanism.
What it is
Haemophilia is an inherited bleeding disorder caused by deficiency of a clotting factor: factor VIII in haemophilia A and factor IX in haemophilia B. Both genes are on the X chromosome, so the condition mainly affects males. Severity depends on how much factor activity remains.
3 types to tell apart
- Haemophilia A
- Factor VIII deficiency, about four in five cases.
- Haemophilia B
- Factor IX deficiency; clinically indistinguishable without measuring the factor.
- Severity
- Severe below 1% of normal activity (bleeding into joints without injury), moderate 1–5%, mild above 5% (bleeding mainly after injury or surgery).
US spelling: haemophilia → hemophilia, haemostasis → hemostasis.
Normal function
How a clot forms and holds
When a vessel is injured, it constricts and platelets stick to exposed collagen, change shape and clump together into a plug. This primary haemostasis stops bleeding from small cuts within minutes, but the plug is fragile.
Secondary haemostasis builds a mesh of fibrin through the plug. Tissue factor from the damaged vessel wall starts the process with factor VII, producing a small amount of thrombin. That first thrombin activates platelets and factors V, VIII and XI.
On the platelet surface, activated factor IX with its cofactor factor VIII converts factor X to its active form far faster than tissue factor alone. This amplification produces the large burst of thrombin that turns fibrinogen into enough fibrin to hold the clot together.
Underlying change · Step 1 of 4
A missing factor on the X chromosome
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
The plug forms, but the clot does not hold
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 3 of 4
Bleeding into joints and muscles
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Serious bleeds and treatment complications
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .