Case 1- Lymphatics and blood vessels Flashcards
Organisation of lymph vessels
Lymph travels along lymphatic vessels which connect to lymphoid organs. The afferent lymphatics take lymph to the lymph nodes and the efferent lymphatics take it away. The organ plexus (capillary system within organs) drains lymph into the lymphatic vessels. Most lymph drains via the thoracic duct. Lymph drains into the venous system at the left venous angle
Function of lymphatic system
1) Drains interstitial fluid- between cells, eventually returns to venous system
2) Transport of dietary lipids- transported as chyomicrons,
3) Immune response- act as a phagocytic filter, preventing unwanted particles entering blood circulation.
Function of lymph nodes
Provide a site for lymphocytes to come into contact with antigens, increasing immune response through lymphocyte proliferation
Structure of lymph vessels
Contain microvalves between the cells of the wall, tiny gaps which can be open or closed. Allow fluid to move between the lymphatics and the interstitium. Valves to prevent backflow at low pressure.
How is lymphatic fluid maintained
Maintained by hydrostatic pressure between the interstitial fluid and lymph. This is the pressure difference between the interstitial fluid and the lymph. Regulates expansion phase and compression phase.
Expansion phase
Pressure in the interstitium (extracellular space) is higher than in the lymphatic, primary microvalves open and secondary valves close. Fluid flows from the interstitium to the lymphatic.
Compression phase
Pressure in the lymphatic is higher than in the interstitium, the primary microvalves close and the secondary valves open. The lymph travels along the lymphatic.
Lymph node structure
Bean shaped. They are split into cortex’s which are then divided, from the outside in into the cortex follicle, the paracortex and the medulla. The Cortex is surrounded by the subcapsular sinus which is surrounded by the capsule. In the capillary bed there are postcapillary (high endothelial) venules, this is where the lymphocytes enter the lymph nodes into the cortex and paracortex, and where the blood supply comes from.
Passage of lymph through the lymph node
The afferent lymphatic enters the lymph node. The lymph will then drain through the subcapsular sinus and medullary sinus and into the efferent lymphatic, some will go through the cortex
Functional properties of the structures in the lymph nodes
1) The paracortex contains high endothelial venules which drain lymphocytes into the paracortex, they then move to the cortex to form follicles of tightly packed lymphocytes.
2) The follicles are where lymphocytes come into contact with antigens. When an antigen is recognised the lymphocytes proliferate to produce an immune response.
3) The lymphocytes then travel through the medullary cords into the medullary sinus and efferent lymphatics, where they will be transported out of the lymph node.
Lymph node cortex
The follicles consist of a germinal centre (maturing B cells) containing lymphocyte aggregation surrounded by the mantle zone (lymphocytes and T cells)
Types of lymphoid tissue
- Thymus- T-cell development and maturation
- Spleen- Filters and is the site of immune response, destroys erythrocytes (red blood cells)
- Tonsils, Adenoids, Appendix- Contain lymphoid follicles
- Bone marrow- produces B-cells, T-cells and macrophages
- Lymph node
- Peyer’s patches
How lymph travels through your lower limbs
From the inguinal nodes, through the iliac then aortic node and into the cisterna chyle. Now contains fatty chyle from the gut, then into the thoracic duct
How lymph travels through your left arm
Through the axillary nodes into the subclavian trunk and and into the left venous angle
How lymph travels from your head and neck
Through the jugular trunk
How does lymph drain from the right side of your body
Into the right lymphatic trunk
What drains into the left venous angle
Left side of your body, lower limbs and trunk (after it goes through the thoracic duct
Vasoconstriction
Reduces the diameter of blood vessels increasing blood pressure and resistance causing blood flow to decrease
Vasodilation
When the smooth muscle relaxes, it increases the diameter of the blood vessels. Resistance decreases and blood flow increases
Local factors that effect arteriole diameter
Metabolic: the production of CO2 will cause vasodilation which will increase blood flow, removing CO2 and bringing O2.
Myogenic factors refer to the blood vessel itself which means that when it stretches, due to an increase in blood pressure, it will try and constrict (vasoconstriction).
External factors that affect blood diameter
Autocrine system, when there is a sympathetic activation it will cause vasoconstriction in the GI tract and Kidneys reducing blood flow.
Endocrine system, when epinethrin, ADH, angeotensin 2 are released they can increase the blood pressure.
4 starting forces for tissue fluid formation
Capillary hydrostatic pressure
Capillary oncotic pressure
Interstitial fluid hydrostatic pressure
Interstitial fluid oncotic pressure
How is tissue fluid formed
Due to the leaky nature of the capillaries some of the fluid will leak out into the external space to become tissue fluid. The more blood pressure there is the more fluid that will leak out.
Capillary filtration
Filtering the fluid out of the capillary into the surrounding. Tends to happen at arteriole end of capillary. Effected by capillary hydrostatic pressure and interstitial fluid oncotic pressure
Capillary reabsorption
Reabsorb the fluid from the surroundings back into the capillary. Tends to happen at venuous end of capillary. Effected by capillary oncotic pressure and interstitial fluid hydrostatic pressure.
What is vascular resistance
The force that impedes blood flow through the circulation
What affects vascular resistance
Blood viscosity and vessel length. Vessel radius is the most important factor, when the radius decreases by half the resistance increases by 16 times
Blood flow through an organ
Arranged in series. If blood resistance increases in an arteriole or vein, blood resistance in the series will increase as a whole. The total blood resistance in the series will be the total blood resistance in all the blood vessels added together
Blood flow through different organs
Arranged in a parallel structure. The resistance in one organ will not affect the other organs, this is advantageous
Blood resistance in the different vessels
The arterioles are called the resistance vessel because it offers resistance to blood flow and can adjust this. The vein is the compliance vessel because it can accommodate a large volume of blood without changing blood pressure. The capillaries are also called the site of exchange, as substances are exchanged here between the tissue fluid and blood.
Volume of blood flow equation (Q)
Q= P/R P= pressure gradient R= resistance
Velocity of blood flow equation (V)
V= Q/A Q= blood flow A= cross sectional areas, this increases in branching and decreases in merging. Blood flow slowest as capillaries which have the biggest cross-sectional area
Distribution of blood flow at rest
GI- 20-25%
Kidneys- 20%
Brain- 15%
Skeletal muscle- 15-20%
Distribution of blood flow when exercising
Skeletal muscle- 80-85%
Blood to other organs is greatly reduced. Blood is distributed according to metabolic needs at rest this is digestion and excretion. When exercising skeletal muscles will have a higher metabolic need
Blood pressure
The pressure exerted by the blood on the inner wall of the blood vessels. Regulated by baroreceptors in the short term and RAAS in the long term.
Systolic blood pressure
Blood pressure when the heart contracts (SBP)
Diastolic blood pressure (DBP)
Blood pressure when the heart relaxes
Pulse pressure
Systolic minus diastolic blood pressure
Mean arterial pressure
(MAP)= DBP + 1/3 (SBP-DBP). This equation is not just an average of SBP and DBP because the blood vessels are in DBP for a longer time.
High pressure baroreceptors
Located in the wall of the aortic arch and in the carotid sinus, where blood pressure is high. They detect blood pressure from 60 to 180 mm Hg. When arterial blood pressure increases they stretch their walls more. The more the baroreceptor is stretched, the more action potentials are fired, this will then be sent to the CNS.
Low pressure baroreceptors
Found between pulmonary vein and atrium and near the vena cava. They respond to blood volume not pressure. When Increased blood volume in the vena cava is detected by the baroreceptors, they will stimulate an increase in heart rate which increases cardiac output. This will increase renal perfusion (blood flow to the kidneys) and increased Na+ and water excretion. In the atria when there high blood volume the low pressure barometers will stimulate the secretion of atrial natriuretic peptide (ANP). This causes vasodilation which decreases vascular resistance, this increases renal perfusion, meaning more water and Na+ is excreted
Cardiac output
The volume of blood pumped out the ventricle per minute. When cardiac output increases resistance decreases to maintain MAP. through vasodilation
What do the blood vessels do when resistance increases
Vasoconstriction will increase so that cardiac output decreases to maintain a constant MAP
Mean arterial pressure= cardiac output x total peripheral resistance
Compliance in blood vessels
Describes the ease of stretching a vessel wall. If a vessel is compliant it means it can accommodate a larger volume without changing the pressure much, veins are more compliant then arteries. Sympathetic stimulation, vasoconstrictors (e.g. epinethrine) and aging decrease the compliance of blood vessels.
The walls of the blood vessels
From inside out tunica intima, tunica media and tunica adventitia/ externa
Tunica intima
The inner layer of the blood vessels, its made of squamous epithelium cells as well as connective tissue. Very smooth to minimise friction
Tunica media
Contains lots of smooth muscle, collagen and elastic fibre. The thickest wall in the arteries
Tunica adventitia/externa
Contains elastic fibre and lots of collagen fibres. In veins its the thickest layer
External elastic lamina
A distinct layer of connective tissue in large blood vessels. The inner one separates the tunica media and the tunica intima, the outer one separates the tunica media and the tunica externa. Amount of elastin determine the structure.
