1.5 Anatomy - Liver + Spleen Flashcards
- What do you understand by
the term t10?
- Vertebral level
Anatomical level of T10 vertebra - Dermatomal level
° Dermatome is the area of skin whose sensory innervation
is derived from a single spinal nerve (dorsal root)
° Not the same as vertebral body level but refers
to the cutaneous area at the level of umbilicus
- Myotomal level
° Muscle distribution of a single spinal nerve (ventral root)
° T10 myotome includes the abdominal muscles
° Useful in clinical and electromyographic localisation
of radicular lesion causing motor defect
What are the common causes
of pneumoperitoneum?
Spontaneous
* Perforated hollow viscus
* Secondary to bowel obstruction
* Secondary to peptic ulcer
Iatrogenic
* Endoscopic perforation
* Secondary to mechanical ventilation
* After laparotomy and laparoscopy
Miscellaneous
* In females, the fallopian tube acts as a
conduit between the vagina and the peritoneal cavity
Look at the third ct image in
Figure 1.7. comment on the
liver texture.
Diffuse fatty liver. The liver is of low density in keeping with fatty infiltration.
(Tip: Use the spleen for comparison. The liver density should be equal to or
higher than the spleen.)
What are the causes of liver lesions?
- Benign lesions
* Simple cysts
* Abscesses
* Hepatic adenoma
* Focal nodular hyperplasia - Malignant lesions
* Hepatocellular carcinoma
* Cholangiocarcinoma
* Angiosarcoma - Miscellaneous
* Fatty liver
* Cirrhosis
Tell me about the liver
The liver is the second largest organ (second to skin).
Weight is 1500 g, which accounts for 2.5% of body weight.
- Hepatocytes are
polyhedral epithelial cells
arranged in sheets separated
from each other by spaces
filled with hepatic sinusoids
- Hepatic sinusoids are vessels
that arise at the portal triad and run
between sheets of hepatocytes
receiving blood from the portal triad to
deliver to central vein
What is the significance of various
types of divisions of the liver?
- Anatomical division
- Divided into right and left lobes by the falciform ligament,
with the caudate and quadrate lobes arising from the right lobe - No clinical or surgical significance
- Surgical divisions (corinaud’s classification)
* Total of eight independent segments
* Each segment has its own blood supply and biliary drainage,
so they can be resected without damage
to the adjacent segments - Functional classification
Liver lobule is the structural unit of liver. See Figure 1.8.
Fig. 1.8
Functional classification
- Classic lobule
- Portal lobule
- Hepatic acinus
- Classic lobule
Based on direction of blood flow
° Hexagonal structure with the central vein in the middle
and portal triad (branches of portal vein, hepatic artery, and bile duct) in the six corners.
The hepatic arterial and portal venous blood flows from portal
triad to the central vein
- Portal lobule
° Based on direction of bile flow
° The portal triad is in the middle and the central veins form the corners
of the triangle
- Hepatic acinus
- Hepatic acinus
° Based on changes in oxygen and nutrient content
as blood flows from the portal triad to the central vein
° It is rhomboid tissue as shown in the image,
containing two triangles of adjacent classic lobule,
whose apices are the central veins
° Hepatocytes in the acinus are divided into three zones
° Zone 1 or periportal zone, where the blood supply is the highest.
This zone is susceptible to damage by
blood-borne toxins and infection
° Zone 2 or intermediate zone
° Zone 3 or centrilobular zone is closer to the central vein.
This area is higher in CYP 450 levels but gets the
least blood supply and is susceptible to ischaemia
What is special about the blood
supply of the liver?
Liver has a dual blood supply.
Total liver blood flow = 1200–1400 mls/min
= 25% of cardiac output
It contains 10%–15% of the total blood volume,
thereby acting as a powerful reservoir.
Hepatic artery
Portal vein
Deoxygenated, detoxified blood exits the liver via hepatic veins to join the
inferior vena cava.
Hepatic artery
- High-pressure/high-resistance system
- Branch of the coeliac trunk (branch of abdominal aorta)
- Carries oxygenated blood
- 20%–30% of total blood supply
- 40%–50% of total oxygen supply
Portal vein
- Low pressure/low resistance
- Formed by the union of superior mesenteric vein and splenic vein
- Carries oxygen-poor but nutrient-rich blood from the abdominal viscera
- 70%–80% of total blood supply
- 50%–60% of total oxygen supply
What are the factors that determine the hepatic blood flow?
Like any other ‘factors affecting blood flow’ question,
have a general classification of factors.
(I have listed here the factors in no order of importance.)
What are the factors that determine the hepatic blood flow?
Like any other ‘factors affecting blood flow’ question,
have a general classification of factors.
- Myogenic autoregulation
- Metabolic/chemical control
- neural control
- Humoral control
- Hepatic arterial buffer response (HABR)
Myogenic autoregulation
Metabolic/chemical control
Myogenic autoregulation
* Applicable only to the hepatic arterial system in metabolically active liver
Metabolic/chemical control
* CO2, o2, and pH changes can alter the hepatic blood flow
- Postprandial hyperosmolarity increases the
hepatic arterial and portal venous blood flow
Neural control
Humoral control
Neural control
- Autonomic nervous system via the vagus
and splanchnic nerves also
control the hepatic blood flow - An important example is the stimulation
of the sympathetic system in haemorrhage
resulting in constriction of arterioles and expulsion of blood
into the general circulation,
thus acting as a major reservoir of blood
Humoral control
- Adrenaline, angiotensin II, and vasopressin are the main constrictors of
the arterial and venous system
Hepatic arterial buffer response (HABR)
Hepatic arterial buffer response (HABR)
- Phenomenon where
decrease in portal venous blood flow
increases the hepatic arterial blood flow and
vice versa so that a constant oxygen
supply and total blood flow is maintained
- The mechanism of HABR is unknown,
but the local production of
adenosine is predicted to be
one of the causative factors
What are the functions of the
spleen?
What are the functions of the spleen?
- Immune responses: formation of plasma cells and lymphocytes
- Phagocytosis
- Haematopoiesis: in foetus
- Lymphopoiesis: throughout
- Storage of red cells: 8% of the circulating red cells are present in spleen
What are the causes of splenomegaly?
- Infection: malaria, infectious mononucleosis
- Malignancy: lymphomas, leukaemia
- Portal hypertension
- Sickle cell disease
- Collagen vascular diseases
- Polycythemia
Indications for splenectomy
- Trauma
° Commonest organ injured in blunt abdominal trauma
° Associated with lower rib fractures - Hypersplenism
° Hereditary spherocytosis
° Idiopathic thrombocytopenic purpura - Tumour
° Lymphoma or leukaemia - Surgical
° Along with gastrectomy, pancreatectomy, etc. - Others
° Splenic cysts and abscess
° Hydatid cysts
What do you understand by oPsi?
Overwhelming Post-Splenectomy infections (OPSI)
- Infection due to encapsulated bacteria:
50% mortality - Organisms
° Strep. Pneumoniae
° Haemophilus influenza
° Neisseria meningitides - Occurs post-splenectomy in 4% patients without prophylaxis
Prevention of OPSI
Prevention of OPSI
- Antibiotic prophylaxis
° Penicillin (amoxicillin)
° Lifelong
° Prophylaxis required in children up to 16 years
___________________________________________________
* Immunisation
° Pneumococcal, haemophilus, and meningococcal
° Perform 2 weeks prior to planned operation
° Immediately post-op for emergency cases
° Repeat every 5 to 10 years
