Where is the thymus gland found?
In the thorax in the anterior mediastinum
Where does the thymus gland lie?
Posterior to the sternum, and anterior to the pericardium
What happens to the thymus gland as we age?
It gradually enlarges during childhood, but after puberty undergoes a process of involution
What is the result of the process of involution on the thymus gland?
Reduciton in the functioning mass of the gland
When does the thymus gland cease to function?
It doesn't- it continues to function throughout life
Label this diagram
- A - Fourth thoracic vertebra
- B - Right pulmonary artery
- C - Tracheobronchial lymph nodes
- D - Transverse pericardial sinus
- E - Left atrium
- F - Oblique pericardial sinus
- G - Thoracic duct
- H - Spinal cord
- I - Oesophagus
- J - Inferior vena cava
- K - Descending aorta
- L - Diaphragm
- M - Pericardial cavity
- N - Right atrium
- O - Right ventricle
- P - Ascending aorta
- Q - Sterum
- R - Thymus
- S - Transverse thoracic plane
- T - Arch of aorta
- U - Left brachiocephalic vein
- V - Branchiocephalic trunk
- W - Trachea
What is the thymus gland arranged into?
Outer cortex and inner cortex
How does the outer cortex differ from the inner medulla?
It is more cellular
What does the inner medulla of the thymus gland havw?
What are Hassall's corpuscles?
Aggregated thymic epithelial cells
What is the cellular composition of the thymus gland?
- Lymphoid cells
- Other supporting cells
- Epithelial cells
Describe the epithelial cells in the thymus gland
Have different appearances in different loations within the gland
What do the epithelial cells of the thymus gland form?
A continuous sub-capsular layer and network in the cortex and medulla
What happens to the thymus epithelial cells deep in the medulla?
They are aggregated into Hassall's corpuscles
Describe the passage of cells through the thymus gland during the process of T cell maturation
Immature T cells enter the cortex and proliferate, mature and pass on to the medulla. From the medulla, mature T lymphocytes enter the circulation
What is the lymphoid system?
An 'overflow system'
What does the lymphoid system provide?
Drainage of surplus tissue fluid and leaked plasma proteins to the bloodstream, and removal of debris from cellular decomposition and infection
What are lymphatic plexuses?
Networks of lymphatic capillaries that originate blinding in the extracellular spaces of most tissues
What are the lymphatic vessels?
A nearly body-wide network of vessels
Describe the structure of lymphatic vessels
Thin walled, abundant lymphatic valves
Where do lymphatic capillaries and vessels occur?
Almost everywhere blood capillaries are found
Where are lymphatic capillaries are vessels not found?
- Bone marrow
What are lymph nodes?
Small masses of lymphatic tissue
Where are lymph nodes located?
Along the course of lymphatic vessels
What happens at lymph nodes?
Lymph is filtered on it's way to the venous system
What are lymphoid organs?
Parts of the body that produce lymphocytes
Give 5 lymphoid organs
- Red bone marrow
What is lymph?
The tissue fluid that enters lymph capillaries and is conveyed by lymphatic vessels
Describe the appearance of lymph
Usually clear, watery, and slightly yellow
What do superficial lymph nodes drain into?
Deep lymph nodes
What do deep lymph nodes do?
Join to form lymphatic trunks
What do lymphatic trunks do?
Unite to form either the right lymphatic duct or the thoracic duct
What does the right lymphatic duct drain into?
The junction of the right subclavian and right internal jugular veins (right venous angle)
Where does the thoracic duct drain?
Into the junction of the left subclavian and left internal jugular veins (left venous angle)
Label this diagram
- A - Area draining to right lymphatic duct (pink)
- B - Right and left venous angles
- C - Deep cervical nodes
- D - Right lymphatic duct
- E - Right subclavian vein
- F - Central and posterior axillay nodes
- G - Deep lymphatic vessels
- H - Cubital nodes
- I - Deep inguinal nodes
- J - Superficial inguinal nodes
- K - Iliac nodes
- L - Lumbar (caval/aortic) nodes
- M - Lymphatic trunks
- N - Cisterna chyli
- O - Superficial lymphatic vessels
- P - Thoracic duct
- Q - Posterior mediastinal nodes
- R - Anterior axillary nodes
- S - Left subclavian vein
- T - Thoracic duct
- U - Superficial cervical nodes
- V - Left internal jugular vein
- W - Area draining to thoracic duct (grey)
- X - Blood blow
- Y - Venule
- Z - Lymphatic capillaries
- Ai - Blood flow
- Bi - Arteriole
- Ci - Tissue cells
- Di - Capillary bed
- Ei - Lymph flow
- Fi - Lymphatic valve
- Gi - Lymph node
- Hi - Vein
- Ii - Efferent lymphatic vessel to vein or to secondary node
- Ji - To thoracic duct
- Ki - Artery
- Li - Lymphatic valve
- Mi - Traveculae
- Ni - Follicle
- Oi - Afferent lymphatic vessel to node
- Pi - Interstitial fluid
- Light - Superficial
- Dark - Deep
What are the main functions of lymph nodes?
- Phagocytic cells act as filters for particulate matter and microorganisms
- Antigen presentation to the immune system
Describe the structure of a lymph node
- Fibrous capsule from which trabecular extend towards the centre
- Node itself made of three components
What is the result of the trabecular extending from the fibrous capsule of the lymph nodes?
Forms a framework
What components is the node made of?
- Lymphatic sinuses
- Blood vessels
What does the parenchyma of the lymph nodes consist of?
Label this diagram
- A - Medulla
- B - Paracortex
- C - Cortex
- D - Afferent lymphatic vessels
- E - Lymphoid follice
- F - Postcapillary high endothelial venule
- G - Marginal sinus
- H - Medually sinus
- I - Efferent lymphatic vessel
- J - Artery
- K - Vein
What does the cortex of the lymph nodes consist of?
Mainly B cells
What does the paracortex of the lymph nodes consist of?
Mainly T cells
How to B cells enter the lymph nodes?
Via post-capillary venules that have high endothelium, High Endothelial Venules (HEV)
What happens once B cells have entered the lymph nodes?
They pass to follicles
What happens to unstimulated B cells in the lymph nodes?
They pas out rapidly from the node to return to circulation with the lymph
What happens to B cells activated by antigenic stimulation?
They proliferate and remain in the node
What are activated B cells within the lymphoid follicles known as?
Follicle centre cells
What kind of nucleus do follicle centre cells have?
Either cleaved nuclei or more open/several nuclei
What are follicle centre cells called when they have cleaved nuclei?
What are follicle centre cells called when they have more open/several nuclei?
What is the pale staining central area of a secondary follicle known as?
A geminal centre
What is a germinal centre surrounded by?
A mantle zone of small, naive B cells and a few T cells
What happens to stimulated B cells in the cortex?
They proliferate and undergo somatic hypermutation and are selected for high affinity antibodies to the antigen displaced by follicular dendritic cells
What happens once stimulated B cells have been selected for high affinity antibodies?
They take up the antigen, process it, and present it to T cells
What happens once antigens have been presented to T cells?
T cells then further promote the development of B celsl by releasing cytokines
What cytokines to T cells release on presentation of an antigen by B cells?
What do B cells become when T cells have released IL-4
Centrocytes, then centroblasts
What happens to centroblasts once they have been produced?
They leave the follicle and pass to the paracortex and medullary sinuses
What do centroblasts become when they have passed to the paracortex and medullary sinuses?
What do immunoblasts give rise to?
Plasma cells or memory B cells
What does the paracortex of the lymph node contain?
- Accessory cells
- Supporting cells
What is the paracortex of the lymph node the predominant site for?
T-Lymphocytes in the lymph node
What is the medulla of the lymph node rich in?
What does the medulla of the lypmh nodes comprise?
- Large blood vessels
- Medullary cords
- Medullary sinuses
What are the medullary cords rich in?
What happens to the antibodies produced in the medullary cords?
They pass out of the node via the efferent lymphatics
What is the cellular composition of the lymphoid follicles?
What is the cellular composition of the paracortex?
What is the cellular composition of the medulla?
What do HEVs allow?
Lymphocytes (B cells) to pass into lymph nodes from the circulation
What % of lymphocytes enter the node in the lymph?
How do the majority of lymphocytes the lymph node?
From the blood via HEVs
Describe the passage of lympho through lymph nodes
Afferent lymphatics -> Marginal sinus -> Cortical sinus -> Medually sinus -> Efferent lymphatics
How is the particulate matter in the lymph removed?
What do APCs facilitate?
The specific immune response
Where is the spleen located?
In the upper left quadrant, or hypochondrium, of the abdomen
Describe the appearance of the spleen
- Usually purplish
- Pulpy mass
- About the size and shape of a fist
What is the spleen considered to be?
The most vulnerable abdominal organ, as it is relatively delicate
What is the arterial supply of the spleen from?
The splenic artery
What is the splenic artery?
The largest branch of the coeliac trunk
What course does the splenic artery follow?
A tortuous course posterior to the omental bursa, anterior to the left kidney, and along the superior border of the pancreas
What does the coeliac trunk give rise to?
What happens between the layers of the splenorenal ligament?
The splenic artery divides into five or more branches that enter the hilum
What do the branches of the splenic artery between the layers of the splenorenal ligament do?
Supply different vascular semgments of the spleen
Label this diagram
- A - Aorta
- B - Celiac artery
- C - Common hepatic artery
- D - Dorsal pancreatic artery
- E - Greater pancreatic artery
- F - Splenic artery
What does the venous drainage of the spleen flow via?
The splenic vein
What is the splenic vein formed by?
Several tributaries that emerge from the hilum
What is the splenic vein joined by?
The inferior mesenteric vein
Where does the splenic vein run for most of its course?
Posterior to the body and tail of the pancreas
What does the splenic vein unite with?
The Superior Mesenteric Vein
Where does the splenic vein unite with the superior mesenteric vein?
Posterior to the neck of the pancreas
What is formed when the splenic vein units with the superior mesenteric vein?
It forms the hepatic portal vein
Label this diagram
- A - Superior pancreaticoduodenal vein
- B - Hepatic portal vein
- C - Short gastric vein
- D - Pancreatic veins
- E - Splenic vein
- F - Inferior mesenteric vein
- G - Inferior pancreatiocoduodenal vein
- H - Superior mesenteric vein
What is red pulp?
A 'sponge-like' blood filtration system
A complex system of blood vessels
What does red pulp do?
Removes old or damaged RBCs from the circulation
What does white pulp contain?
- T cells
- B cells
- Accessory cells
What does white pulp have many similarities with?
Lymph node structure
What is the purpose of white pulp?
To mount an immunological response to antigens within the blood
What may removal of the spleen lead to?
Enhanced susceptibility to infection, especially by polysaccharide encapsulated bacteria, in particular Streptococcus pneumoniae, Haemophillus influenzae, and meningococcus
Where is Gut Associated Lymphoid Tissue (GALT) found?
- Tonsils/adenoids (Waldeyer's ring)
- Peyer's patches
- Lymphoid aggregates in the appendix and large intestine
- Lymphoid tissue accumulating with age in the stomach
- Diffusely distributed lymphoid cells and plasma cells in the gut lamina propria
What do large aggregates of GALT have?
APCs, and distinct B cell follicles and T cell areas
What are Peyer's Patches?
Quite large aggregates of lymphoid tissue found in the small intestine
What do Peyer's Patches do?
Generate an immune response within the mucosa
What do some epithelial cells in the 'dome' overlying Peyer's Patches have?
Complex microfolds (M cells)
Are HEVs present in Peyer's Patches?
What happens in Peyer's Patches?
- B cell precursors and memory cells in Peyer's Patches are stimulated by antigens
- Cells pass to the mesenteric lymph nodes, where response is amplified
- Activated lymphocytes pass into the blood via the thoracic duct
- Activated cells home in to the gut to carry out final effector functions
What can happen to lymphocytes and some mononuclear phagocytes?
They can recirculate between lymphoid and non-lymphoid tissues
What does the recirculation between lymphoid and non-lymphoid tissues help in?
Allowing lymphocytes to be exposed to the antigens that they recognise
What is the advantage of allowing lymphocytes to be exposed to the antigens that they recognise?
It is valuable in the distribution of effector cells of the immune response to sites where they are needed
How may naive lymphocytes move?
From the primary to secondary lymphoid tissue via the blood
How may activated lymphocytes move?
From the spleen, lymph nodes, and MALT into the blood, and from there to other lymphoid and non-lymphoid tissues
How may APCs such as macrophages and dendritic cells move?
May carry antigen back to lymphoid tissues from the periphery
What do the complex patterns of recirculation depend on?