Physiology: the microcirculation Flashcards
Small arteries branch into?
Arterioles
Arterioles branch into?
Capillaries
Little metarterioles that divert from?
Divert from capillaries direct to venules
Define ‘shunts’
Used when skeletal muscle at rest -> closure of capillary beds and shunting of blood into venous system)
Pre-capillary sphincters are?
Small vessels lined with smooth muscle. Can contract and occlude the capillaries and halt blood flow into the capillaries
Pre-capillary sphincters constrict at?
Low levels of metabolic activity and at higher levels, the muscle relaxes and allows blood to flow through
Pre-capillary sphincters enable the body to?
Match the level of blood flow to metabolic activity.
Relaxation increases the ______ of the capillary bed.
Cross-sectional area
Relaxing pre-capillary sphincters means that the rate of flow _____ so that the average time for exchange increases whilst also ____ the distance of diffusion.
decreases; reducing
Factors that make cells use more oxygen and produce more metabolites (CO2 etc)
Exercising muscle, increase in metabolic activity
These metabolites (CO2 etc) have local effects on the arterioles which cause?
Arteriolar vasodilation which reduces resistance to flow and increase capillary blood flow.
Describe simple diffusion in moving blood into cells
- Lipid soluble small molecules (O2, CO2, Cortisol) pass through the membrane based on concentration gradients. - Epithelial cell is not barrier.
Describe carrier mediated diffusion
non-lipid soluble small molecules: i.e. ions, glucose, amino acids need a channel to diffuse, so pores and intercellular clefts allow movement of these things
Describe pinocytosis regarding blood moving into cell
- Exchangeable proteins are moved across by vesicular transport. - It is encapsulated by part of the membrane and released into the interstitial fluid where it then moves into the cell. - e.g. insulin and fatty acids
Describe plasma proteins in moving blood into cell
Plasma proteins generally will not cross the capillary wall as they are too big.
Define Fick’s law
The rate of transfer of water and solutes across the capillary wall is primarily by diffusion.
Describe Fick’s Law in this picture
P = the capillary permeability to the molecule, permeabiliy is inversed related to molecular weight.
S = the surface area available for exchange, so greater surface area will increase diffusion (i.e. more capillaries).
Co = concentration of the substance outside the capillary.
Ci = concentration of the substance inside the capillary.
Rate of diffusion becomes progressively less, until at a molecular weight of ~60,000 the diffusion is minimal.
Permeability of the capillary endothelial wall is not the same in all tissues, so it depends on the tissue type e.g. very high in liver and kidney capillaries, but very low in brain capillaries.
The blood plasma and dissolved solutes move across the capillary membrane via the process of _____.
bulk flow
The fluid moves as a unit in contrast to _____ based on individual concentration gradients.
Diffusion
The driving force for reabsorption and filtration is not concentration, rather it is ____.
Pressure
When the pressure inside the capillary exceeds pressure outside, fluid is ?
Fluid is pushed out -> filtration
when the pressure outside is greater than the pressure inside, fluid moves?
Moves in -> reabsorption
Colloid osmotic pressure is due to?
Due to presence of blood plasma proteins
When separated by a semipermeable membrane, colloid osmotic pressure allows for?
Allows for movement of water, but not solute.
Osmosis means?
Means water will move into the area of high concentration in order to equalize the solute concentration.
Hydrostatic pressure moves fluid in?
Moves fluid in the other direction. You can get a measure of the osmotic pressure in this case.
Define the Starlings Hypothesis in terms of the formula
Drive for fluid flow outwards is = K x (sum of outward forces - sum of inward forces)
What does starlings hypothesis give you?
Gives you the net force that would drive filtration or absorption.
Capillary hydrostatic pressure
this drops from 35 mm Hg to 17 mm Hg over the course of the capillary.
The pressure due to presence of water inside the capillary i.e. BP an outward force.
Interstitial fluid hydrostatic pressure
This is typically very low but it can increase with swelling etc (in blood vessel).
This is the pressure due to water inside the interstitial fluid, normally zero, but an inward force.
Plasma osmotic pressure
Pressure due to proteins in the blood, which is typically around 26 mm Hg.
The proteins inside the capillary will try to draw water into the capillar, an inward force.
Interstitial fluid osmotic pressure
Due to proteins in the interstitial fluid, generates about 1 mm Hg, an outwards force.
when pressure falls as you move from arteriole to the venule: the only factor that has changed here is?
Capillary hydrostatic pressure, so at the venous end we have a negative value and hence movement of fluid into the capillary will occur so reabsorption.
Define this picture
Effects oc hanges in metabolic activity on capillary exchange
Describe this slide
hydrostatic pressure difference balances colloid osmotic pressure
Describe this slide
Capillary exchange and the starling principle
Lymphatic capillaries interconnect with?
Interconnect with blood capillaries
On average, slightly more lymph fluid leaves capillaries than re-enters, such that we get a net-filtration of?
3L a day
Fluid that leaves capillaries is replaced back into the circulation by the ______ and eventually re-enters venous circulation via ______.
Lymphatic system; subclavian veins.
Lymphatic fluid moves via contraction of skeletal muscle by means of _____ and aided by ___.
Compression; one-way valves.
Define oedema
Build up of lymphatic fluid within a tissue
List 4 main causes of oedema
- Reduced concentration of plasma protein
- Increased capillary permeability
- Increase in venous pressure
- Blocking of lymphatic vessels
Describe cause of reduced concentration of plasma protein leading to oedema
- Lack of dietary protein to make up plasma proteins.
- Children in developing countries often have a very low plasma protein in the blood, and as a result have a large amount of oedema in the abdomen (Kwashiorkor) because the plasma osmotic pressure will be lower.
A possible cause leading to increased capillary permeability leading to oedema.
Release of histamine -> Increases flow rates
Increase in venous pressure causes increased _______ which leads to oedema.
Increased capillary hydrostatic pressure
Causes of blocking of lymphatic vessels that lead to oedema
Breast cancer lumpectomy and lymph node removal -> common side effect is oedema in arm because you’ve damaged lymphatic drainage.
Superior mediastinum is above _______.
Sternal angle
Inferior mediastinum is below ________.
Sternal angle
Anterior mediastinum is located where?
In front of heart.
Middle mediastinum area covers?
Heart area, at heart
Posterior mediastinum is located where?
Behind heart
Pericardium is in close contact with?
Parietal pleura
Pericardial effusion can be possible with?
Pleural inflammation
How many pulmonary veins are there usually?
4 pulmonary veins
LV is about _____ thicker than RV.
1.5-2 times
If BP is 140/80, this means ____ pressure is 140 and the ____ needs to overcome this to get new blood into systemic circulation.
Aortic pressure is 140; LV needs to overcome this
When you have pulmonary hypertension, ____ doesn’t cope because it is a reduced pressure system, especially when you have an acute effusion as there is no chance of adapting to the increased pressure.
Right ventricle
The ____ is the only part of the LA you will see when looking anteriorly.
Auricle
The ____ braciocephalic vein has a longer course than ____.
Left; right
JVP is the?
Internal jugular vein
Why is right sided internal jugular vein more useful?
Because it is straight, it tells you about the filling pressures of the right side of heart and hence it is a sign of right ventricular hypertension.
The ascending aorta originates to the right and posterior to the origin of the ______. It swaps around after arch of aorta.
Pulmonary trunk
Name 3 branches of the ascending aorta
- Braciocephalic trunk
- Left common carotid artery
- Subclavian artery
Pericardium is adjacent to parietal pleura: list sides of the pleura
- Cervical
- Mediastinal
- Costal
- Diaphragmatic
Describe this slide
Parietal pericardium - outer
Visceral pericardium - inner
Space between them is called pericardial cavity and is filled with fluid which allows for friction free heart movement. If this increases from about 20 mls, the heart will go into tamponade. Same with outer layer of heart itself (epicardium).
Fibrous pericardium fuses with what?
Fuses with sternum, walls of great vessels and diaphragm to retain heart in position.
Functions of fibrous pericardium
Limits chamber overdistension and retains heart in position by fusing with nearby structures.
Space between parietal and visceral pericardium allows for?
Fluid filled space allows for friction free heart movement.
Describe the right atrium
Coronary sinus -> deoxygenated blood from all of the heart veins drains into RA to become oxygenated again.
Anterior wall of the right atrium and the right auricle have muscular ridges called ______.
Musculi pectinati
Musculi pectinati attach to a posterior ridge called the _______.
Crista terminalis
Crista terminalis forms a line between the?
Between the superior and inferior vena cava separating the smooth portion of the atrium from the rough part.
Smooth portion is the common area shared by the atria.
Right side of the inter-atrial septum shows the remnant of the foetal ______ as a thumb print like depression called the ______ (open-side) surrounded by the _____.
Foramen ovale; fossa ovalis; limbus
A patent foramen ovale is when this doesn’t?
Doesn’t seal up completely (up to 30% of people have this), usually not clinically significant.
Natural hole in heart in utero because we don’t need to use lungs as a foetus.
Right atrioventricular orifice is guarded by the ____ valve which consists of three valve leaflets.
Tricuspid valve
Tricuspid valve’s 3 valve leaflets attach to ______
Papillary muscles
Chorda tendinae function
Attach tricuspid valve leaflets to papillary muscles
If chorda tendinae fails, what happens?
Mitral or tricuspid regurgitation
The muscular interventricular septum in right ventricle has a small membranous portion where?
Small membranous portion superiorly
Right ventricle wall has muscular ridges called?
Trabeculae carinae
Right ventricle’s smooth part of pulmonary trunk is called?
Infundibulum.
Conus arteriorus refers to?
RV’s trabeculae carinae and infundibulum
Pulmonary trunk leaves the right ventricle and contains ________ that make up the pulmonary semilunar (SL) valve.
3 semilunar cusps
Which valve is closer to the apex of the heart? RV tricuspid valve or LV’s mitral valve
RV tricuspid valve
RV or LV has more trabeculations?
RV has more trabeculations.
Right ventricle’s moderator band function?
Moderator band connects the interventricular septum to the base of the anterior papillary muscle.
Left atrium is smooth-walled throughout except for?
Except for the finger-like atrial auricle/appendage, containing pectinate muscles.
Clotting in left atrium causes?
Atrial fibrillation
Left atrium shares septum with the?
Right atrium. Notable landmark is the valve of foramen ovale.
Afrer birth, remnant of the _______ is a small flap of tissue covering the foramen ovale on the left side.
Septum primum.
Compare left atrium to right atrium
Smaller than RA but thicker
Left atrium receives _____ via _______.
oxygenated blood via 4 pulmonary veins.
Right pulmonary artery overlies the ______.
Left atrium.
Left pulmonary artery overlies the ____.
Auricle
Location of trabeculations?
Trabeculations on the inferior part but no smooth infundibulum (only muscular part).
When trabeculations are absent in the aortic outflow area, they are called?
Aortic vestibule
Left atrioventricular orifice is guarded by the _______ valve.
Mitral/bicuspid valve
Aortic root function?
It’s a dilatation which accommodates the 3 cusps so when the valve opens, there is room to fit.
Coronary arteries location? Where do they receive blood from?
Coronary arteries just distal to the aortic valve and get their blood during diastole.
Ascending aorta leaves the left ventricle and contains?
3 semilunar cusps
LV adapts to pressure load by _____ and volume load by _______.
Hypertension; volume load
Describe the travel path of the right coronary artery
Travels in anterior atrioventricular groove (coronary sulcus) -> continues as right posterior interventricular (descending) artery in posterior interventricular groove and right marginal artery on inferior border of heart.
Describe passage of left coronary artery
L coronary from trunk and splits into two:
- Left anterior descending artery travelling to apex
- Circumflex supplying the lateral part of the LV
Posterior descending artery is equivalent to _____ but for the back.
Left anterior descending artery
Right and left coronary arteries branch from ascending aorta and fill from the _____ above aortic semilunar valve.
Aortic sinus
Left coronary artery supplies the?
Supplies the left atrium and most of the left ventricle.
Left circumflex branch supplies the?
Supplies the lateral wall
Left anterior descending artery supplies?
Supplies the anterior wall (the largest territory)
Right coronary artery supplies the?
Right atrium, most of the right ventricle and the inferior part of the left ventricle.
Also supplies the SA node 60% of the time and the AV node 80% of the time.
Which coronary veins are not seen unless the heart is turned around?
Great, middle and small vein and coronary sinus
Cardiac veins accompany the?
Accompany the coronary arteries
What is the coronary sinus?
Dilated collection point for venous return from the heart itself
Coronary sinus is positioned where?
Posterior aspect of the heart
Coronary sinus drains into?
Right atrium and lies in the posterior atrioventricular groove (coronary sulcus) under the left atrium.
Describe coronary sinus
Largest vein draining the heart (posterior structure).
Coronary sinus receives blood from?
From the great, middle and small cardiac veins before draining into the right atrium.
Anterior cardiac veins drain directly into?
Right atrium
Cardiac plexuses (superficial and deep) are positioned where?
Positioned around the aortic arch (anterior to the trachea)
Cardiac plexuses (superficial and deep) contain?
Contain motor (autonomic) and sensory nerves that innervate the heart
Phrenic nerve C3, C4, C5 function and structure supply?
Sensation to fibrous and parietal pericardium
T1-5 nerve function and supply?
Sympathetic to visceral pericardium which can increase heart rate.
Sensation: pain travels across the precordium.
Vagus nerve function and structure supply
Parasympathetic: descend in neck with carotid arteries; decreases heart rate if there is a strong vagal tone.
Sensory: cardiac reflexes
