Microcirculation and Tissue Fluid Formation Flashcards
(24 cards)
What are the walls of capillaries made up of?
Single layer of endothelial cells
What does the arteriole turn into?
Metarteriole (terminal end)
Explain Continuous Capillary
🔒 Most selective / least leaky
📍Where:
* Brain (blood-brain barrier)
* Muscles
* Lungs
* Skin
🧱 Structure:
* Tight junctions between endothelial cells
* No gaps or pores — only small molecules like gases, glucose, or water can pass (sometimes through vesicles).
🧠 Key Function:
* Protects tissues like the brain from unwanted substances.
* Low permeability = very controlled exchange.
Explain Fenestrated Capillary
🕳️ “Windowed” capillaries — more leaky
📍Where:
* Kidneys
* Small intestine
* Endocrine glands
🧱 Structure:
* Fenestrations = small pores in the endothelial cells
* Still has a basement membrane that acts like a filter
🧠 Key Function:
* Allows rapid exchange of small molecules (e.g., hormones, nutrients, waste)
* Ideal for places that need fast absorption or secretion
Explain Discontinuous (Sinusoidal) Capillaries
🌊 Most leaky / big gaps
📍Where:
* Liver
* Spleen
* Bone marrow
🧱 Structure:
* Large gaps between cells
* Discontinuous basement membrane
* Big enough for cells (like red blood cells, white blood cells, and proteins) to pass through.
🧠 Key Function:
* Allows movement of large molecules and even cells.
* Great for filtering blood (like in liver and spleen) or letting blood cells enter/leave (like in bone marrow)
How do substances transport across the capillary wall?
- Simple Diffusion (lipid soluble solutes and gasses like oxygen and CO2
- substances like ions, glucose, and amino acids can readily diffuse through clefts between endothelial cells depending on the hydrostatic pressure. - Vesicular Transport
(proteins that are too big to diffuse through the cell junctions can be transported by transcytosis/exocytosis - Osmosis
(movement of water is mostly through the endothelial junctions and goes from low solute to high solute concentration)
Explain Vasomotion
- blood flows intermittently, turning on and off every few seconds or minutes
- this means that there is intermittent contraction of the metarterioles and precapillary sphincters
What is the most important factor affecting the degree of opening or closing the metarterioles and precapillary sphincrers?
Concentration of oxygen in the tissues
How is Tissue Fluid derived?
- from blood capillaries
- metabolism of tissues
What are the factors affecting the formation of tissue fluid?
- permeability of capillaries (more fluid leaking out)
- Diffusion (fluid diffusing out)
- Filtration and reabsorption
- Metabolic activity of tissues
How much is reabsorbed?
- 85% reabsorbed in venular end of capillaries
- 15% drained in lymph
Forces pushing fluid out?
- capillary pressure
- interstitial fluid pressure (IF NEGATIVE)
- interstitial fluid colloid osmotic pressure
Forces pushing fluid in?
- interstitial fluid pressure (IF POSITIVE)
- capillary plasma colloid osmotic pressure
What is edema commonly caused by?
- increased capillary permeability (due to inflammation, toxins, burns)
- increased capillary hydrostatic pressure
- increased interstitial fluid colloid pressure
4, decreased plasma fluid colloid pressure
- increased heart failure or venous obstruction
- lymphatic blockage
- decreased plasma proteins (such as albumin) due to liver disease, nephrotic disease, malnutrition
another way to write colloid and hydrostatic pressure?
Those 3 outward forces are:
1.Capillary hydrostatic pressure (Pc)
2.Interstitial oncotic pressure (πi)
3. (Sometimes) low interstitial hydrostatic pressure (Pi, if it’s negative)
And the 1 inward force is:
1. Capillary oncotic pressure (πc)
Describe Left Sided HF?
The left side of the heart can’t pump blood to the body properly.
- The left ventricle gets oxygen-rich blood from the lungs
- It pumps that blood out to the body
- The blood backs up into the lungs
- Lungs get congested with fluid = pulmonary edema
😮💨 Symptoms:
- Shortness of breath
- Cough or wheezing, especially when lying down
- Fatigue (not enough oxygen getting to muscles)
- Crackles in lungs (on exam)
– Left-sided failure is more common and can lead to right-sided failure over time.
Why? Because if the left side backs up into the lungs, the right side has to push against more pressure, which tires it out.
Describe Right Sided HF?
The right side of the heart can’t pump blood to the lungs properly.
- The right ventricle gets blood from the body
- It pumps that blood to the lungs to get oxygen
❌ In failure:
- The blood backs up into the body
- Fluid leaks into legs, belly, and neck veins
🦵 Symptoms:
- Swelling in legs/ankles (edema)
- Bloating or ascites (fluid in belly)
- Neck vein bulging (JVD – jugular vein distention)
- Weight gain from fluid buildup
🧠 Easy Analogy:
Left side = lungs problem (breathing)
Right side = body problem (swelling)
Describe deep vein thrombosis
What is Deep Vein Thrombosis (DVT)?
DVT is when a blood clot forms in a deep vein, usually in the leg.
A blood clot is a clump of blood that has become solid.
It’s useful when you get a cut — but dangerous when it forms inside your veins.
Why is DVT dangerous?
Because the clot can break off, travel through your blood, and get stuck in the lungs — this is called a pulmonary embolism (PE) and can be life-threatening.
The swelling and inflammation happens below the blockage site
Edema due to Liver Failure (cirrhosis)
What goes wrong:
- The liver can’t make enough albumin leading to hypoproteinemia due to decreased protein synthesis, which leads to decreased oncotic pressure in capillaries that decreases the reabsorptive force
- Less albumin = less “pull” to keep fluid inside vessels
- Fluid leaks out into tissues → edema (and sometimes ascites, which is belly fluid)
Also:
- Blood backs up in liver → ↑ pressure in belly veins (portal hypertension) → even more fluid leaks out.
- What does it mean when blood backs up in the liver?
In liver failure or cirrhosis, the liver becomes stiff and scarred.
That means blood can’t flow through it easily.
So instead of smoothly passing through, blood builds up before the liver — like a traffic jam.
What is Portal Hypertension?
The portal vein brings blood from the intestines and stomach to the liver.
If the liver is blocked or stiff (due to cirrhosis), then:
- Blood can’t pass through easily
- So pressure in the portal vein goes up
→ This is called portal hypertension
How does this cause fluid to leak out?
When pressure in the portal system increases:
- Tiny veins in the belly and intestines get overwhelmed
- Fluid leaks out of these blood vessels into the surrounding space
- This causes ascites (fluid buildup in the belly)
And because the liver also makes albumin (a protein that helps keep fluid in vessels), a damaged liver:
- Produces less albumin
- So fluid leaks out even more easily
Summary:
🔻 Albumin ↓ + 🔺 pressure in veins = swelling in belly and legs
Edema due to Renal Failure
- hypoproteinemia due to proteinuria
What goes wrong:
- Kidneys can’t remove salt and water properly → body holds onto fluid
- Some kidney diseases cause loss of protein in urine (like nephrotic syndrome)
- Less protein in blood = less oncotic pressure → fluid leaks out
Summary:
💧 Too much fluid + 🔻 blood protein = swelling, especially in legs and face
Define Anascara
- Generalized Edema due to abnormal amount of fluid in extracellular spaces of body either due to fluid overload or hypoproteinaemia
Explain the Lymphatic system
- 10-15% of fluid enters the lymphatic system through lymph capillaries
- When muscles contract and relax, lymphatic vessels perform a pumping function creating a negative interstitial fluid hydrostatic pressure (sucks fluid inwards).
- Flow of lymph is slow and depends on the movement of muscles, valves in vessels, and the negative pressure in chest when we breathe in.
- most of the lymph re-enters the blood stream at the subclavian vein under the collar bone
- long chain fatty acids are absorbed into the lymph through the lacteals in the villi of the small intestine
What happens to long-chain fatty acids after you eat them?
Where does it happen?
In the small intestine, specifically in the villi — finger-like projections that absorb nutrients.
Each villus contains:
- Blood capillaries → absorb most nutrients (sugars, amino acids)
- Lacteals → tiny lymphatic vessels that absorb fats
Step-by-step: How long-chain fatty acids are absorbed
1. Fats are digested in the small intestine into fatty acids + monoglycerides
- These get packed into tiny droplets called micelles (with the help of bile)
- Micelles bring the fatty acids into the cells lining the intestine (called enterocytes)
- Inside these cells:
- Long-chain fatty acids are repackaged into triglycerides
- Then they’re packed into chylomicrons (fat transport particles) - Chylomicrons enter the lacteals, not blood vessels
- From the lacteals, they travel through the lymphatic system
- Eventually, they drain into the bloodstream near the neck (thoracic duct)
Why lymph, not blood?
- Chylomicrons are too big to enter blood capillaries directly
- But they fit into lacteals, which are more “leaky”
- That’s why fats take a detour through the lymphatic system
Where does Lymph drain?
What is lymph?
Lymph is a clear fluid that comes from tissue and contains waste, immune cells, and some nutrients. It gets collected by the lymphatic system, kind of like the body’s drainage pipes.
Eventually, all that lymph fluid needs to get back into your blood — and it does that by draining into veins near your collarbones.
Where does the lymph drain?
There are two main ducts that collect lymph from the body:
- 🟢 Thoracic Duct (left side – BIGGER)
- Drains lymph from:
- Left side of head & neck
- Left arm
- Entire lower body (both sides!)
- It empties into the left subclavian vein (just under the left collarbone) - 🔵 Right Lymphatic Duct (right side – SMALLER)
- Drains lymph from:
- Right side of head & neck
- Right arm
- Right upper chest
- it empties into the right subclavian vein (under the right collarbone)
Final Step: Lymph Enters the Bloodstream
- Both subclavian veins feed into the heart (through the superior vena cava), so the lymph rejoins the blood and goes back into circulation.
The subclavian vein (under the collarbone) carries blood from the arm
- The internal jugular vein (in the neck) carries blood from the head and brain
- These two veins join together to form a larger vein called the:
Brachiocephalic vein (also called the innominate vein)
There are two brachiocephalic veins — one on the right, one on the left.
📍So on the right side:
1. The right subclavian vein
(from the right arm)
2. Joins the right internal jugular vein (from the right side of the head)
3. Together they form the right brachiocephalic vein
✅ This is also where the right lymphatic duct drains its lymph — into the corner where those two veins meet.
Both the left and right brachiocephalic veins come together to form the: Superior vena cava → which goes directly into the heart
Yess, on the left side, the same thing happens:
- The left subclavian vein (from the left arm)
joins with
- The left internal jugular vein (from the left side of the head & neck)
👇
Together, they form the left brachiocephalic vein
