Week 5 Flashcards
What are the three components of the lymphatic system?
Lymphatic vessels
Lymph
Lymphoid tissues & organs
What are the key functions of the lymphatic system?
Circulatory function
Returns fluid that has leaked from the vascular system to the blood
Transport of nutrients, hormones, wastes
Immunity
Lymphocytes housed within lymphoid organs are activated by immune responses
Some lymphoid organs also contain macrophages, which engulf foreign material
What are the lymphatic vessels?
An elaborate network of drainage vessels that transport protein-rich interstitial fluid back to the bloodstream
Lymphatic capillaries drain the interstitial spaces of most tissues
When the interstitial fluid enters these vessels, it is called lymph
What is the flow of lymph?
Lymphatic capillaries –>lymphatic collecting vessels –>lymphatic trunks –>lymphatic ducts
What are lymphatic collecting vessels?
Thin-walled vessels that drain lymphatic capillaries
Possess numerous valves (beaded appearance)
In general, superficial lymphatic vessels (those in the skin and subcutaneous tissues) follow veins and eventually drain into deep lymphatic vessels
Deep lymphatic vessels follow arteries
What are lymphatic trunks?
Are formed by large collecting vessels
Named for the regions that they drain
Which lymphatic ducts drain into the thoracic duct or Rt lymphatic duct near the junction of subclavian and int. jugular veins?
Jugular trunks (x2) Subclavian trunks (x2) Bronchomediastinal trunks (x2)
Which lymphatic trunks drain into the cisterna chyli?
Lumbar trunks (x2) Intestinal trunk (x1)
What is the thoracic duct?
Major vessel of the lymphatic system
38 - 45 cm long, 3-5 mm in diameter
What is the pathway of the thoracic duct?
Formed by the convergence of the lumbar & intestinal trunks (anterior to L1/2 vertebrae)
In 50% of people, it begins as an enlarged sac, the cisterna chyli
Cisterna (L. ‘box’), chyli (Gr. ‘juice’)
Ascends through the aortic hiatus into the posterior mediastinum
Enters the venous system at the junction of the Lt internal jugular and Lt subclavian veins
Receives lymph from the Lt jugular, subclavian & bronchomediastinal trunk before entering junction
What is the right lymphatic duct?
~ 1.25 cm long
Drains Rt upper limb, Rt side of head and thorax
What is the pathway of the right lymphatic duct?
Formed by lymphatic trunks draining the right upper quadrant of the body:
Rt jugular, subclavian & bronchomediastinal trunks
Enters the venous system at the junction of the Rt internal jugular and Rt subclavian veins
What does the lymphatic system rely on to prevent back flow?
Lymphatic system lacks a pump
Relies on valves to prevent backflow
What are the factors affecting lymphatic flow?
Rhythmic contraction of lymphatic vessels (smooth m.) & pulsations of nearby arteries
Intermittent pressure on lymphatic vessels
e.g. skeletal m. contraction, movement of viscera
Pressure changes in the thorax during respiration
Flow is almost negligible in an immobile limb
e.g. swelling of feet after a long plane trip
What are the 3 lymphoid cells?
Consist of lymphocytes, auxiliary immune cells and supporting cells
What are lymphocytes?
T cells: cellular adaptive immunity
~75% circulating lymphocytes
Subtypes: cytotoxic, helper, regulatory T cells
B cells: humoral adaptive immunity
Subtypes: plasma, memory cells
Natural Killer cells: innate (nonspecific) immunity
Induce apoptosis of virus- or cancer-infected cells
What are auxiliary immune cells?
MACROPHAGES
Widely distributed throughout lymphoid organs
Functions include:
Phagocytosis
Enhancement of inflammatory response
Presentation of antigens to T cells
DENDRITIC CELLS
Mobile, antigen-presenting cells
Possess wispy cellular extensions for antigen capture & phagocytosis
Migrate to lymph nodes and present antigens to naïve lymphocytes (initiates adaptive immune response
What are supporting cells?
Reticular cells: fibroblast-like cells that produce a connective tissue stroma (L. ‘bed covering’) for lymphoid tissues and organs
What is the function of lymphoid tissue? (2)
Proliferation site for lymphocytes
Surveillance point for lymphocytes & macrophages
What are the types of lymphoid tissue? (2)
Diffuse lymphoid tissue
Loose arrangement of lymphoid cells & reticular fibres
Occur in most organs of the body
e.g. lamina propria of the GIT
Lymphoid follicles
Solid, spherical bodies consisting of tightly packed lymphoid cells & reticular fibres
Have germinal centres of proliferating B lymphocytes
Form part of lymphoid organs
What are primary lymphoid organs?
Sites of B & T cell maturation
Red bone marrow, thymus
What are secondary lymphoid organs?
Where mature lymphocytes first encounter their antigens and become activated
Lymph nodes*, spleen, tonsils, appendix, intestinal follicles (Peyer’s patches)
*Only lymph nodes filter the lymph, other lymphoid organs possess drainage but lack afferent lymphatics
What are lymph nodes?
Widely distributed secondary lymphoid organs, clustered along lymphatic vessels
Vary in size from a pin-head to an olive (and bigger during pathology)
What is the gross structure of lymph nodes?
Dense fibrous capsule
Compartmentalised by trabeculae
Stroma of reticular connective tissue
What are the functions of lymph nodes?
House lymphocytes AND macrophages
Site of immune system activation
Filtering of lymph (microorganisms, debris)
What is the histology of lymph nodes? (3)
CORTEX
Germinal centres of proliferating B cells
T cells in transit (circulating in lymph & blood)
Numerous dendritic cells
MEDULLA
Medullary cords – thin inward extensions from the cortex, contain numerous B & T cells
LYMPH SINUSES
Lymphatic channels crossed by a network of reticular fibres (macrophages reside on these fibres)
Subcapsular sinus, medullary sinus
What is nodal circulation?
Lymph flows into the node through numerous afferent lymph vessels (convex side)
Lymph moves through the subcapsular sinus towards the medulla
Flow occurs through medullary sinuses
Exits via efferent lymph vessels
Located at hilum (indented region on concave side)
What is the gross structure of the spleen?
Largest lymphoid organ, roughly the size of a clenched fist
Dark red, highly vascular, ovoid organ
Enclosed by a thin (easily ruptured) capsule of fibroelastic connective tissue + smooth m. cells
Trabeculae extend inward to the interior to form a supporting framework
Intraperitoneal: surrounded by visceral peritoneum except the hilum (entry of splenic artery & exit of splenic vein)
What are the surfaces of the spleen?
Diaphragmatic surface: outer, convex
Visceral surface: inner, concave
Impressions from stomach, kidney, colon, pancreas
What are the peritoneal ligaments of the spleen?
The gastrosplenic & splenorenal ligaments attach to the hilum of the spleen
These ligaments contain the splenic vessels
What is the location of the spleen?
Lt Hypochrondriac region, LUQ behind stomach
Roughly deep to Ribs 9 - 11 ribs (separated by diaphragm)
Rests on the Lt colic flexure
What is the function of the spleen? (5)
Immunity: site for lymphocyte proliferation, surveillance & response
Blood filter: macrophages remove debris, foreign matter
Reservoir: blood, platelets, monocytes
When needed, spleen contracts and releases these substances into the circulation
Recycles: by-products of RBC breakdown e.g. iron
Erythropoiesis (foetus)
What is the histology of the spleen? (2 main components)
Two main components: islands of white pulp in a sea of red pulp (L. ‘flesh’) Friable texture (easily crumbled)
White pulp: site of immune functions
Mostly lymphocytes suspended on reticular fibres
Red pulp: where senescent RBC and bloodborne pathogens are destroyed
Huge numbers of erythrocytes and the macrophages that engulf them
What is the arterial supply to the spleen?
Splenic a.: largest branch of the celiac trunk
Splenic a. runs a tortuous course along the superior border of the pancreas
At the splenic hilum, it divides into a number of branches (~5) before entering
What is the venous drainage of the spleen?
Splenic v., formed by several tributaries emerging from the hilum (and joined by IMV)
Runs posteriorly to the tail and body of the pancreas for most of its course
Unites with SMV posterior to the neck of the pancreas to form the portal v.
What is the lymphatic drainage of the spleen?
Lymph nodes in the splenic hilum
Drain to the pancreaticosplenic lymph nodes –>celiac nodes –>intestinal trunk
What is the nerve supply of the spleen?
Sympathetic: abdominopelvic splanchnic nerves via the celiac ganglion (T6-T10)
*Stimulate contraction of the spleen.
Parasympathetic – CNX Vagus
Discuss a splenectomy
(Why is it performed?)
(What replaces the function of the spleen?)
The spleen is one of the most easily and frequently injured abdominal organs
Rupture can lead to extensive haemorrhaging (highly vascular organ)
Splenectomy (full or partial) may be performed to prevent haemorrhagic shock
Liver & red bone marrow can replace the functions of the spleen
In children <12 years, the spleen can regenerate if partially removed
What is a microbiome?
a collection of microbial genomes
What is a microbiota?
a collection of microbes
What is the human microbiome?
Is an integral part of the human body
Varies according to body site: GIT, vagina, urethra, skin
Is plastic and influenced by environmental exposures
90% of the cells in and on the body are microbial
Define these key terms:
Commensal
Probiotic
Pathogen
Dysbiosis
Commensal: a colonising organism that is neither beneficial nor detrimental
Probiotic: an organism that elicits health benefits to the host
Pathogen: an organism that is detrimental to the host or causes disease
Dysbiosis: loss of balance within a microbial community
What can dysbiosis cause?
Can shift a healthy microbiome to a disease-associated state
Disease can arise when:
Microbiome diversity increases at sites that normally have restricted diversity
Or when there is reduced diversity at body sites that usually have great diversity
BACTERIAL SIGNALS & COMPOUNDS
Can modulate signalling pathways (e.g. metabolism), immune cell responses and change host gene expression
Dysbiosis and disease (GIT microbiome & vaginal and urethral microbiome)
Can be local or systemic in nature
GIT microbiome
Dental caries
Peptic ulceration, oesophageal & gastric carcinoma
Obesity
Ulcerative colitis, Crohn’s disease*
Irritable bowel syndrome
Sleep, mood, stress disorders**
Vaginal & urethral microbiome
Bacterial vaginosis
Recurrent UTIs
Susceptibility to infection during pregnancy
Pre-term birth
Implications for vaginal vs. C-section delivery
What is disease management for the human microbe?
Microbial manipulation strategies
Human nutrition
Antibiotics
Microbial supplementation (probiotics)
