Pathology 3500 Lecture 6: Week 5
WEEK 5: Disturbed Blood Flow and Hemodynamics
Vascular Hemodynamics
• There are several disorders of hemodynamics:
o Abnormalities in blood flow/maintaining normal fluid homeostasis
▪ Edema
▪ Hyperemia
▪ Hemorrhage
o Abnormalities in maintenance of blood as a liquid
▪ Thrombosis
o Embolism
o Infarct
o Shock
EDEMA
• Edema – accumulation of the fluids in the interstitial tissue or swelling the subcutaneous tissues
o Due to disturbance in hydrostatic and/or oncotic pressure between intra-capillary and
interstitial component
INTRODUCTION
• Distribution of blood fluid:
o 60% of person’s body weight is water
▪ Intracellular – 40%
▪ Extracellular
• Plasma – 5%
• Interstitial – 15%
• Survival of cells and tissue is dependent on:
o Oxygen provided in the blood supply
o Normal fluid balance
▪ Depends on:
• Starling’s law
• Systemic factors:
o Intact circulation
▪ Ex there is no hemorrhage, etc
o Overall fluid balance
▪ Ex no diarrhea, vomiting, etc
o Salt retention
▪ Results in more retention of water in the body
• Physiologic ranges of:
o Intravascular pressure
o Osmolarity
HOMEOSTASIS
• Process of maintaining a constant internal environment despite changing external conditions
• Several factors must be regulated including:
o Temperature
o Heart rate
o Respiratory rate
o Blood pressure
o Water balance
o Blood sugar levels
• Altered vascular homeostasis results change in net movement of water across the vascular wall
o Ex more water leaving the vasculature and going into the interstitium → edema
• Circulatory and lymphatic system quick review:
o There is an arterial side and a venous side of the circulatory system, and they are
connected by the capillaries
▪ Present in the lungs and in the tissues
o The circulatory system is closely related to the lymphatic
system
▪ The lymphatic system drains into the venous side
o Each day, about 50% of the total blood proteins leak out of
the capillaries into the interstitial component, and return to
the blood via the lymphatic vessels
▪ Thus, the lymphatic system plays and important role
in maintaining the osmolarity and fluid balance
• Under normal circumstances only a small amount of fluid leaks from
vessels to form interstitial fluid which is removed by lymphatic
vessels
• Starling’s Law – the movement of fluid between vascular and interstitial spaces (at level of
capillaries) is controlled by 4 forces:
o Hydrostatic pressure (HP) (aka filtration pressure)
o Plasma oncotic pressure (OP)
o Tissue/interstitial pressure (tissue tension)
o Interstitial/tissue fluid osmotic pressure
o ***movement is mainly controlled by the opposing effect between HP and OP
• Hydrostatic pressure (HP)
o Force exerted by a fluid against the capillary wall (pushing force)
o Forces fluid out of the capillaries
▪ Fluid contains oxygen and nutrients that move into the surrounding tissue
where they are less concentrated
▪ Similarly, the tissue contains carbon dioxide and waste products that move into
the capillaries where they are less concentrated
▪ **this process of substances moving from areas of higher concentration to
areas of lower concentration is diffusion
o The HP in the capillaries varies:
▪ 32mmHG at arteriolar end
• Fluid goes outside with the nutrients and the oxygen
▪ 12mmHG at the venous end
• Wastes and CO2 go into the circulation
▪ 25mmHG mean
• Plasma oncotic pressure (OP)
o Created by the presence of large molecules/particles that can’t diffuse and are
prevented from moving through the capillary membrane
▪ These large molecules are plasma proteins such as albumin
▪ They encourage osmosis and draw water towards them (from the interstitial
fluid into the capillaries)
o Because capillary blood has a high content of plasma proteins, the capillary has a high
oncotic pressure of 26mmHg
o The oncotic pressure doesn’t vary from one end of the capillary bed to another
• How do we know which direction the fluid is moving and whether there is a net gain or net loss
of fluid in a particular compartment?
o Net filtration pressure (NFP) must be calculated
▪ Difference between the two pressures, the hydrostatic and the oncotic pressure
o Fluids will leave the capillary if hydrostatic > oncotic pressure
o Fluids will enter the capillary if hydrostatic < oncotic pressure
Normal Physiological Conditions
• At the arterial end:
o Hydrostatic pressure → 32mmHg
o Oncotic pressure → 25mmHg
o NFP: +6mmHg
▪ Hydrostatic pressure dominates
o Thus, the fluid moves out with the oxygen and the nutrients
• At the venous end:
o Hydrostatic pressure → 12mmHg
o Oncotic pressure → 12mmHg
o NFP: -14mmHg
Document Summary
Week 5: disturbed blood flow and hemodynamics: there are several disorders of hemodynamics: Vascular hemodynamics: abnormalities in blood flow/maintaining normal fluid homeostasis, edema, hyperemia, hemorrhage, abnormalities in maintenance of blood as a liquid, thrombosis, embolism. Infarct: shock, edema accumulation of the fluids in the interstitial tissue or swelling the subcutaneous tissues, due to disturbance in hydrostatic and/or oncotic pressure between intra-capillary and. Edema interstitial component: distribution of blood fluid, 60% of person"s body weight is water. Intracellular 40: extracellular, plasma 5% Interstitial 15: survival of cells and tissue is dependent on, oxygen provided in the blood supply, normal fluid balance, depends on, starling"s law, systemic factors: Intact circulation: ex there is no hemorrhage, etc, overall fluid balance, ex no diarrhea, vomiting, etc, salt retention, results in more retention of water in the body, physiologic ranges of: Intravascular pressure: osmolarity, process of maintaining a constant internal environment despite changing external conditions, several factors must be regulated including:
