Blood and Lymph Physiology Flashcards
functions of blood?
transport, hemostasis, defence from infection, homeostasis (pH and temperature)
effect of relaxation of blood vessel smooth muscle?
vasodilation, increased blood flow
effect of contraction of blood vessel smooth muscle?
vasoconstriction which decreases blood flow
what are the 2 routes of transport through capillary walls?
paracellular and transcellular
what is paracellular transport through capillary walls? what is transported this way?
molecules diffuse between endothelial cells. water and small solutes (radius < 3nm)- limited by tight junctions and gap junctions
what is transcellular transport through capillary walls? what is transported this way?
molecules actively transported through endothelial cells. transport of larger solutes
how are large solutes transported transcellularly across capillary walls?
receptor mediated endocytosis, transcytosis, transendothelial channels such as VVOs
what are VVOs?
vesicular vacuolar organelles
what are vesicular vacuolar organelles?
interconnected vesicles forming channels across the cell
what is transcytosis?
cells take up extracellular medium through caveolae mediated micropinocytosis and transfer to the opposite side of the cell
where are capillaries with fenestrated endothelium found?
in GI tract, glomerulus and endocrine glands
structure of fenestrated endothelium?
spaced cells form fenestrae (windows) connected through a porous diaphragm which acts as ‘sieve’ allowing only water and small molecules to pass
where are capillaries with discontinuous endothelium found?
in the liver
structure of discontinuous endothelium?
spaced cells with fenestrae without diaphragms and poorly organised basement membrane. high level of clathrin-mediated receptor endocytosis activity
how does water and small solutes pass in continuous non-fenestrated endothelium?
pass between the ECs
how do larger solutes pass in continuous non-fenestrated endothelium?
pass through ECs via transcytosis or transendothelial channels
why is the permeability of ECs particularly restricted in the brain?
to minimise risk of infection
what forms the blood brain barrier?
tight endothelial junctions, thick basement membrane, supporting layer of astrocytes
how do substances pass the blood brain barrier?
water, gases, lipid-soluble hormones pass by passive diffusion, selective transport of nutrients such as amino acids and glucose. antibodies too large to pass
how does the blood brain barrier prevent entry of lipophilic neurotoxins?
active transport mechanism mediated by P-glycoprotein
what is the key hallmark of inflammation?
flow of plasma and WBCs into site of injury or infection- important to protect tissue from infection- endothelial cells increase permeability to allow this
functions of RBCs?
responsible for carrying oxygen
adaptations of RBCs?
biconcave disc shape facilitates movement through capillaries, enucleated so increased capacity for Hb and ability to go through small capillaries
what species have nucleated RBCs?
fish and reptiles
how does a pulse oximeter measure blood oxygenation?
using absorption- Hb has different absorption spectra when bound with O2 versus in free form
where does erythropoiesis take place in adults?
bone marrow
where does erythropoiesis take place in the developing fetus?
liver and spleen
what happens to erythrocyte progenitor cells to become erythrocytes?
lose nucleus, ribosomes and organelles
what happens to erythrocytes at the end of their lifespan?
digested by macrophages in liver or spleen
importance of regulation of erythropoiesis?
important to adjust to environments with different O2 levels
where is erythropoietin produced?
kidney
when is erythropoietin released?
when O2 levels are low
role of erythropoietin?
stimulates erythrocyte release
negative feedback loop of erythropoietin?
release stimulated by low O2 levels, erythropoietin stimulates erythrocyte release, resulting high O2 levels suppress erythropoietin production
what regulates the erythropoietin response to hypoxia?
transcription factor Hif-a (hypoxia inducible factor)
role of Hif-a?
in normal conditions is hydroxylated leading to its degradation, in hypoxia activity of hydroxylase is reduced, Hif1-a can activate erythropoietin transcription
why is RBC elimination important?
damaged RBCs can release Hb and free iron which are then sequestered in the kidney and can cause local inflammation and damage
effect of deregulation of RBCs?
anaemia (low hematocrit), polycthemia (high hematocrit)
blood group if no antigens present?
O
what does being group O blood type mean?
both anti-B and anti-A antibodies in plasma so no antigens on RBCs
blood group if A and B antigens present?
AB
what does being in group AB blood type mean?
no antibodies in plasma for A or B so both A and B antigens present on RBCs
what does being in group A blood type mean?
anti-B antibodies in plasma so only A antigens present on RBCs
what does being in group B blood type mean?
anti-A antibodies in plasma so only B antibodies present on RBCs
what does it mean to be Rh positive?
having Rh antigen on surface of RBCs
role of WBCs?
fighting infection
how do WBCs move through tissues to eliminate microbes?
use active ‘amoeboid’ movement
what are the granulocytes?
neutrophils, eosinophils, basophils
what dyes make neutrophils visible?
neutral dyes
what are the most abundant cells in the blood?
neutrophils
what dyes make eosinophils visible?
acidic dyes (eosin)
role of neutrophils?
crucial for bacterial infections
role of eosinophils?
role in some parasitic infections. granules contain peroxides and enzymes toxic to parasites
what dye allows basophils to be visualised?
basic dyes (methylene blue)
role of basophils?
produce histamine and heparin. play role in allergy
what are the agranulocytes?
T and B lymphocytes, natural killer cells, monocytes, megakaryocytes
role of T lymphocytes?
kill infected cells or produce signals that assist function of other immune cells
role of B lymphocytes?
produce antibodies
role of natural killer cells?
important for antitumour responses
role of monocytes?
differentiate into macrophages and dendritic cells that can mediate phagocytosis and activation of T cells upon infection
role of megakaryotes?
large multinucleated cells, segmentation gives rise to platelets- important in haemostasis
what is haemostasis?
response of vessels to local injury/disruption which aims to seal the wound and prevent haemorrhage
what happens in haemostasis?
endothelium rupture followed by vascular spasm, decrease in vessel diameter by muscle contraction, platelets aggregate at the site forming plug that temporarily seals the wound. general inflammatory response recruiting WBCs to site to prevent infection
what triggers the ‘coagulation’ reaction in haemostasis?
release of factors from platelets- ADP, serotonin, prostaglandin
what seals the wound in haemostasis?
fibrinogen converted into fibrin by thrombin to form gelatinous mesh that provides long-lived stable seal
once the tissue has healed in haemostasis what follows?
fibrinolysis, plasminogen converted into plasmin which breaks down fibrin. bradykinin (vasodilator) relaxes muscles and restores blood flow
functions of the lymphatic system?
returns interstitial fluid + plasma proteins into blood, filters blood by removing harmful agents like toxins or microbes, structural basis for immune system, transports dietary lipids from GI tract to blood
what is the pathway of lymphatic system?
one-way circulation from interstitial tissue of peripheral organs to the blood
which are more permeable blood vessels or lymphatic vessels?
lymphatic vessels- allow passage of proteins and even cells
structure of lymphatic vessels?
blind ends with openings in form of overlaid flaps that allow passage of interstitial fluid carrying small proteins and cells
what facilitates lymph flow?
muscle movements during breathing, exercise, good posture
where does lymph drain to?
thoracic duct which feeds into the subclavian vein and thus returns filtered blood into circulation
what is elephantiasis?
infection of the lymphatic system with parasitic worms that causes oedema and tissue swelling as result of lymphatic obstruction
cells present in lymph?
B cells, T cells, macrophages, dendritic cells
where are B cells produced?
bone marrow
where are T cells produced?
thymus
role of macrophages?
clearing dead cells
role of dendritic cells?
activating T cells
what are the primary lymphoid organs?
bone marrow and thymus
what are the secondary lymphoid organs/tissues?
lymph nodes, spleen, mucosa associated lymphoid tissue (MALT)
role of primary lymphoid organs?
produce blood cells
role of secondary lymphoid organs?
enable immune responses, sites of immunosurveillance
what cells produce blood cells?
hematopoietic stem cells
how does hematopoiesis decline with age?
replacement of hematopoietic tissue by fat
colour and location of active bone marrow?
red, spongey part of bone
colour of fat/adipose tissue relating to bone marrow?
yellow
where does age-related decrease in hematopoietic count begin?
lower limbs
where is the thymus located?
behind sternum, above heart
where are T cell precursors from?
migrate from bone marrow to thymus
selective function of thymus?
selecting lymphocytes that react with foreign and not ‘self’ components
what is thymic involution?
size of thymus decreasing dramatically with age
name of lymph nodes in neck?
cervical lymph nodes
name of lymph nodes near groin?
inguinal lymph nodes
name of lymph nodes under arm?
axillary lymph nodes
what does lymph enter and exit lymph nodes from?
enters through afferent lymphatic vessels, exits through efferent lymphatic vessels
what are lymph nodes surrounded by?
capsule
regions in lymph node?
subcapsular sinus receives lymph, contains macrophages that capture toxins and microorganisms. below sinus cortex and medulla are dense cellular areas of lymphocyte residence
location of the spleen?
attached to the lateral border of the stomach
function of the spleen?
to remove old RBCs from the circulation and filter blood-borne antigens, serves as location for initiation of immune responses to blood pathogens
structure of spleen?
surrounded by weak capsule, below capsule in RBC rich area called red pulp where blood antigens filtered and RBCs removed, WBC rich area called white pulp where lymphocytes initiate immune responses to blood pathogens
what is the mucosa associated lymphoid tissue?
lymphoid tissues attached to mucosal surfaces of the GI tract (Peyer patches and lymphoid tissue of appendix) and respiratory tract (tonsils)
purpose of MALT?
provide additional pathogen filtering in exposed tissues (GI tract and respiratory tract)
why is constant recirculation of lymphocytes through the lymphatic system needed?
only a few lymphocyte clones that can react with a specific antigen from an invading pathogen and they have to detect an invading pathogen anywhere in the body
what are naive lymphocytes?
ones that haven’t seen an antigen
what do lymphocytes enter lymph nodes via?
High Endothelial Venules- specialised venules
what do B cells home to in lymph nodes?
follicles in the cortex
what do T cells home to in lymph nodes?
the paracortex beneath the cortex
pathway taken by antigens/microbes in the body?
travel in soluble form to the closest draining lymph node via the lymph, entire microbes and larger molecules engulfed and broken down by antigen presenting cells present in every tissue- then actively migrate to nearest lymph node to present antigen to clones of relevance
