Transcapillary Exchange physiology .pptx

Physiology concept of Capillary exchange in CVS

1. TRANSCAPILLARY EXCHANGE By Anuvarshini M K

2. CONTENTS MODES OF TRANSPORT ACROSS CAPILLARIES STARLING FORCES EDEMA

3. DIFFUSION Most common method Small, lipid-soluble substances (e.g., oxygen, carbon dioxide) diffuse directly through the capillary endothelial cell membranes. Water-soluble substances (e.g., glucose, ions) pass through pores or clefts between endothelial cells.

4. VESICULAR TRANSPORT Substances are engulfed by the endothelial cells in vesicles through endocytosis. These vesicles are transported across the cell and released via exocytosis on the opposite side. This process is important mainly for transport of large lipid-insoluble substances that cannot pass through the capillary wall by means of other mechanisms.

5. Capillary Filtration Bulk flow of fluid and small solutes out of the capillaries into the interstitial space due to pressure gradients. 2 major pressures : HYDROSTATIC PRESSURE OSMOTIC PRESSURE The balance between these pressures determines net filtration

6. hydrostatic pressure forces fluid out osmotic pressure draws fluid back in

7. STARLINGS FORCES The forces that control capillary filtration are named as Starling’s force The four Starling's forces are Capillary Hydrostatic Pressure (Pc): Interstitial Hydrostatic Pressure (Pif) Capillary Oncotic Pressure (πc) Interstitial Oncotic Pressure (πif)

8. HYDROSTATIC PRESSURE GRADIENT Capillary Hydrostatic Pressure (Pc): The pressure exerted by blood against the capillary wall Hydrostatic pressure is higher at the arterial end of the capillary than at the venous end. This is because the pressure of blood in the aorta is high. In skeletal muscle at the arteriolar end- 37 mm Hg at the venular end -17 mm Hg respectively, Interstitial Hydrostatic Pressure (Pif): The pressure exerted by fluid in the interstitial space .Its value is negligible .

9. OSMOTIC PRESSURE GRADIENT A region higher in solute concentration has higher osmotic pressure. Capillary Oncotic Pressure (πc): Osmotic pressure due to plasma proteins (primarily albumin) in the blood. Pulls fluid into the capillaries (reabsorption). the osmotic pressure of blood is 25 mm Hg , and the osmotic pressure in the interstitial tissue space, which is very negligible (almost zero).

10. NET FILTRATION PRESSURE Positive NFP: Filtration (fluid moves out of the capillary, occurs at the arterial end). Negative NFP: Reabsorption (fluid moves into the capillary, occurs at the venous end).

11. Net Filtration Pressure= (Capillary Hydrostatic Pressure-Tissue Hydrostatic Pressure) - (Capillary Osmotic Pressure-Tissue Osmotic Pressure) NFP= (Pc- Pi) - (πc - πi)

12. AT ARTERIOLAR END At the arteriolar end of the capillary: NFP= (Pc- Pi) - (πc - πi) NFP= (37 mm Hg-1)-(25-0) = 11mm Hg The net filtration pressure is 11 mm Hg [(37 – 1) – 25] in outward direction Thus, at the arteriolar end, fluid moves out of the capillaries

13. AT VENULAR END At the venular end of the capillary: NFP= (Pc- Pi) - (πc - πi) NFP = (17 -1)-(25-0) =-9 mm Hg • The net filtration pressure is 9 mm Hg [25 – (17 – 1)] in the inward direction. At the venular end, fluid moves into the capillaries.

14. ROLE OF LYMPHATICS About two units of fluid are left in the interstitial tissue space as the outward filtration at the arteriolar end is 2 mm Hg more than the inward filtration at the venular end. This amount of fluid is usually taken up by the lymphatics in the interstitial space, which is finally brought back to the circulation as lymphatics at last drain into the veins.

15. SUMMARY

16. EDEMA The accumulation of free fluid in excess in the interstitial tissues space is called edema. Edema can occur due two important mechanisms: Increased filtration of fluid into the interstitial tissues space Decreased removal of fluid from the interstitial tissues space

17. Decreased Removal of Fluid From interstitial space water is removed by lymphatics . Thus, decreased lymphatic drainage causes edema formation. This can occur either due to diseases of the lymphatics (lymphangitis) surgery (radical mastectomy that removes lymphatic ducts) infection (filariasis). The decreased lymph flow decreases the removal of excess fluid from the interstitial tissues space that results in edema formation. Edema due to lymphatic obstruction is usually non-pitting type

18. Increased Filtration of Fluid This can occur by three mechanisms: increased hydrostatic pressure of capillary blood decreased oncotic pressure increased capillary permeability.

19. Increased Hydrostatic Pressure Common causes: Heart failure: Right-sided heart failure → Peripheral edema Left-sided heart failure → Pulmonary edema. Venous obstruction: Deep vein thrombosis (DVT). External compression of veins (e.g., tumor). Fluid overload: Excessive IV fluids or kidney failure.

20. Decreased Oncotic Pressure The oncotic pressure decreases due to hypoproteinemia liver diseases (decreased production of plasma proteins) kidney diseases (increased excretion of plasma proteins) malnutrition (decreased intake of pro-teins), and burns (exudation of protein rich fluid from the burn surface).

21. Increased Capillary Permeability Damage or inflammation increases capillary wall permeability, allowing proteins and fluid to leak into the interstitial space. Common causes: Inflammatory conditions: Infection, sepsis, or allergic reactions (e.g., angioedema). Trauma: Burns, surgery, or physical injury. Toxins: Bacterial toxins or certain drugs (e.g., chemotherapeutic agents).

22. TREATMENT 1. Elevate Limbs: Raise the swollen area to reduce fluid accumulation. 2. Compression Therapy: Use stockings or bandages to improve circulation. 3. Diuretics : Medications like furosemide help eliminate excess fluid. 4 . Low-Sodium Diet: Reduce salt intake to prevent fluid retention. 5. Treat Underlying Cause: Manage conditions like heart failure, kidney disease, or liver cirrhosis effectively.

23. TEST YOURSELF! Small lipid-soluble substances cross the capillary membrane primarily by: a) Filtration b) Vesicular transport c) Simple diffusion d) Facilitated diffusion Which Starling force promotes fluid movement out of the capillaries? a) Plasma oncotic pressure b) Capillary hydrostatic pressure c) Interstitial hydrostatic pressure d) Lymphatic pressure

24. TEST YOURSELF! 1. At which end of the capillary is the hydrostatic pressure higher? A) Arteriolar end B) Venular end C) Mid-capillary D) Equal at both ends Non-pitting edema is commonly associated with: a) Hypoalbuminemia b) Venous insufficiency c) Lymphedema d) Heart failure

25. TEST YOURSELF! Filtration occurs primarily at which end of the capillary? a) Arterial end b) Venous end c) Both ends equally d) Neither end What is the effect of hypoproteinemia on oncotic pressure? A) Increases oncotic pressure B) Decreases oncotic pressure C) No effect on oncotic pressure D) Increases hydrostatic pressure