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Capillary Exchange and Lymphatics – outline notes

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II. Capillary Exchange
A. Filtration — 24 L of plasma move out capillary into interstitial fluid / day

B. Reabsorption — 85% is returned from interstitial fluid to capillary
1. Remaining 3.6 L is returned to blood via the lymphatic vessels

C. Net Filtration Pressure (NFP) – difference between hydrostatic pressure and osmotic
1. Determines direction of fluid movement (into or out of capillary)

D. 2 net forces
1. Net hydrostatic pressure – pushes fluid out of capillary
2. Net colloid (oncotic) osmotic pressure – pulls fluid into capillary

E. Net Hydrostatic Pressure
1. difference between capillary hydrostatic pressure (CHP) and interstitial
hydrostatic pressure (IHP)
2. capillary blood pressure drops from arterial to venous end — 35-18 mmHg

F. Net Colloid Osmotic Pressure
1. difference between blood colloid osmotic pressure (BCOP) and interstitial fluid
colloid osmotic pressure (ICOP)
2. BCOP is ~25 mmHg ——– stays constant over length of capillary

G. BCOP and CHP are driving forces
1. if BCOP > CHP —— fluid is reabsorbed
2. if BCOP < CHP —– fluid is filtered out
3. if BCOP = CHP —– no net fluid movement

H. Fluid loss at arterial end and fluid gain (reabsorption) at venous end
1. more fluid lost than reabsorbed
2. lost fluid is returned by lymphatics

I. Fluid shifts in tissue
1. anything that affects hydrostatic or osmotic pressures
2. Hemorrhaging
a. reduction in CHP
b. increases reabsorption —- recall of fluids
3. Dehydration
a. water loss — increase BCOP —–recall of fluids
4. Edema – accumulation of fluid in interstitium

a. increased filtration pressure
b. decreased BCOP
c. increased capillary permeability
d. inadequate lymph flow

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III. Lymphatic System
A. Lymphatic vessels (lymphatics)
a. Lymph – plasma-like fluid; less plasma proteins
B. Lymphoid tissue
C. Lymphoid organs

D. Lymphatic vessels
1. Lymphatic capillaries
a. blind-ended tubes
b. endothelium
c. one-way valves
1) allows interstitial fluid to enter, but not exit
2) also, proteins, toxins, bacteria, viruses
d. return of lost fluid back to blood
e. lacteal – lipid absorption in the small intestine

2. Lymph collection vessels
a. one-way valves ——– like veins
1) muscle contraction, body movement — moves lymph
b. valves give a beaded appearance
c. superficial (skin/mucosae) and deep (skeletal muscle/viscera)
3. Lymphatic trunks
4. 2 lymphatic ducts
a. Thoracic duct
1) cisterna chyli – expanded sac at base
2) drains into the left subclavian vein
b. Right lymphatic duct
1) drains into the right subclavian vein

E. Lymphoid tissue
1. connective tissue dominated by lymphocytes
2. Lymphoid nodule – dense aggregation of organized lymphocytes
a. scattered throughout mucosae
3. Tonsils
a. large nodules in the pharynx
b. 2. palatine, 2 lingual, 1 adenoid (pharyngeal)

F. Lymphoid Organs
1. Lymph nodes
a. kidney bean shape
b. located along lymph vessels
c. large clusters
d. structure
1) afferent and efferent vessels
2) cortex and medulla
3) lymphocytes and macrophages
4) nodules – B-cells
5) subcapsular space – macrophages
e. function
1) filters lymph before it is returned to the blood
2) cleansed – macrophages
3) immunological response – lymphocytes
4) lymphocytes circulate —- blood to lymph to blood
5) infection — lymphocytes proliferate — swollen glands

2. Spleen
a. largest – fist size
b. cleanses blood; immune response
c. macrophages and lymphocytes
d.  macrophages remove old RBCs
e. fetal RBC production
f. splenectomy
1) Liver and Red bone marrow — remove old RBCs
2) decrease immune function — greater chance of infections
3. Thymus
a. posterior to the sternum
b. largest size at puberty
c. involution — atrophies and becomes fibrous
d. by 50-60 years old ——– immune function decreased
e. Thymosins — hormones for T lymphocyte differentiation


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