Circulation and Fluid Balance Flashcards
Amoeba
- In direct contact with their environment to:
- Obtain nutrients
- Excrete wastes
- Conntractile vacuoles pump water in and out of the amoeba for these exchanges to occur
Circulatory System
- Essential in multicellular organisms for cell survival
- provide nutrients
- Remove wastes
- Maintain homeostasis
- Coordinate function of diverse tissues
Microcirculation
Blood vessels
Lymphatics vessels
Extracellular Matrix
Microcirculation:
Blood vessels
- Terminal Arterioles
- endothelium, basement membrane, muscle
- Capillaries
- endothelium, basement membrane
- Postcapillary venules
- endothelium, basement membrane, muscle
Microcirculation:
Terminal Arterioles
- Major resistance vessel of the arterial system
- Regulate the flow of blood into a capillary bed
- Pressure falls dramatically as blood flows through the arterioles into the capillary
Microcirculation:
Capillaries
- The most numerous of all vessels, but generally contain only 5-10% of blood volume
- Blood is directed into a capillary based on tissue needs
- Interendothelial pores at the junctions between endothelial cells provide capillaries with a semipermeable nature
- important to facilitiate diffusion of materials between the intravascular and extravascular spaces
Microcirculation:
Postcapillary Venule
Collect blood from a capillary bed to begin the venous retrum to the heart
Important site of cellular events associated with inflammation
Microcirculation:
Lymphatics
Blind-ended lymphatic vessels originate in association iwht the microcirculation
Important participants in fluid balance at the microcirculatory level
Microcirculation:
Interstitium
The space between cells and the microcirculation
COmposed of the extracellular matrix
Fluid Homeostasis
- Fliud is in a constant flux between compartments of the microcirculatory environment
- Interactions occur between
- Cells and interstitium
- Interstitium and blood vessels
- Interstitium and lymphatic vessels
Normal water distribution
- Total body water (60% body weight)
- Extracellular water (20% body weight)
- Plasma (4-5% body weight)
- Interstitium (15-16% of body weight)
- Intracellular water (40% body weight)
- relatively stable compartment
Interactions:
Interstitium - Blood vessel
- Blood vessel wall is the barrier that separates intravascular and interstitial compartment
- Capillary wall is a semi-permeable membrane that allows selective movement of fluid and molecules
- lipid soluble substances can move through the endothelial cells
- Water and water soluble substances move through inter-endothelial pores
Interactions:
Interstitium - Lymphatic Vessels
- Lymph vessel wall separeates the lymphatic and interstitial compartments
- The wall functions similar to the capillary wall, but is much more permeable
- Water moves freely between lymphatic vessel lumens and interstitium based on pressure gradients
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Control of intravascular/interstitial Fluid distribution
- Anatomic integrity of the circulation
- Osmostic pressure
- plasma
- Interstitium
- Hydrostatic pressure
- plasma
- Interstitium
Intravascular/interstitial water distribution
- Water flow across the endothelium is described by the following formula (See pic)
- Differences in hydrostatic pressure are determined mainly by the volume of water in a compartment and any driving force acting on that volume
Intravascular/interstitial water distribution:
Osmotic Pressure
- Determined mainly by large proteins or protein-disaccharides
- small proteins and electrolytes account for most osmolality, but are equally distributed between fluid compartments
- 84% of plasma osmolality is due to sodium and chloride
- less than 1% of plasma osmolality is due to plasma protiens
- Protein-disaccharides contribute to interstital osmolality
- small proteins and electrolytes account for most osmolality, but are equally distributed between fluid compartments
Intravascular/interstitial water distribution:
Differences in Hydrostatic/osmotic pressure
- Intravascular and interstital osmotic, and interstital hydrostatic pressures are relatively constant in the normal microcirculation
- Differences in intravascular hydrostatic pressure between arteriolar and venular ends of the microcirculation are the major factor in driving water exchange between the plasma and interstitium
Control of Fluid Distribution:
Net Filtration Pressure
Plasma/interstitium pressure differential at the arteriole
Net flow (nutrients) into the interstitium
Control of Fluid distrobution:
Net absorption Pressure
Plasma/interstitium pressure differential at the venule
Net flow (wastes) into the plasma
Control of Fluid Distrobution:
Lymph
Lymphatic vessels pick up excess fluid
Changes in intravascular/interstitial water distrobution:
Edema
the increased accumulation of fluid in interstitial spaces or body cavities
Changes in water distribution:
Edema
- Mechanisms:
- decreased plasma osmotic pressure
- Increased plasma hydrostatic pressure
- Decreased lymphatic drainage
- Increased vascular permeability.
- More than one mechanism is often involved in clinical edema
Edema:
Decreased Plasma osmotic Pressure
- Hypoalbuminemia is a common underlying factor in decreased plasma osmotic pressure
- albumin is the major plasma protein that contributes to intravascular osmotic pressure
- Due to the systemic nature of hypoalbuminemia, edema tends to be generalized
Hypoalbuminemia
- Conditions resulting in this include:
- starvation
- inadequate protein intake
- Liver disease
- decreased protein produciton
- Renal Disease
- Glomerular loss of albumin
- Gastrointestinal Disease:
- Malabsorption
- Parasitism
- Severe Burns
- starvation
Edema:
Increased Plasma Hydrostatic Pressure
- Increased plasma Hydrostatic pressure creates a net outflow of fluid form the vessel to the interstitium
- normal absorptive pressure at the venule becomes a filtration pressure
- High venular hydrostatic pressure prevents reentry of fluid form the interstitium
- normal absorptive pressure at the venule becomes a filtration pressure
- Conditions resulting in this include:
- increased blood flow
- acute inflammation
- Passive blood accumulation
- venous obstruction
- thrombi
- masses; inflammatory or neoplastic
- Organ torsions
- Heart failure
- Flow backs up at the heart
- venous obstruction
- increased blood flow
Heart Failure:
Right Heart Failure
- Fluid maldistribution can vary depending on the nature of the failure
- right heart failure: Blood backs up in the protal circulation
- fluid accumulates in the abdominal cavity
- right heart failure: Blood backs up in the protal circulation
Heart Failure:
Left Heart Failure
- Fluid Maldistribution can vary depending on the nature of the failure
- Left Heart Failure:
- Blood backs up in pulmonary circulation.
- Fluid accumlates in the alveloli of the lung (Pulmonary edema)
- Blood backs up in pulmonary circulation.
- Left Heart Failure:
Heart Failure
- Generalized edema associated with generalized heart failure can result in reduced circulating blood volume
- ADH and aldosterone stimulate water and sodium retention to contribute to hypervolemia and increased plasma hydrostatic pressure
Edema:
Decreased Lymphatic Drainage
- Any decrease in lymphatic flow prevents removal of the slight excess of fluid taht normally persists in the interstitium furing intravascular/intertitial fluid exchange
- Conditions resulting in this include:
- Lymphatic Obstruction:
- Compression from inflammatory or neoplastic masses
- Intralumenal obstruction by thrombi or emboli
- Lymphatic Obstruction:
- Lymphatic Anomalies
- Congenital anasarca/lymphedema
Edema:
Increased Vascular Permeability
- Decreased structural integrity allows water to move out of a vessel intot he interstitium more freely
- Conditions resulting:
- Inflammation:
- Edothelial contraction and cytoskeletal rearrangement results in expansion of inter-endothelial junctions and fluid movement to the interstitium
- Caused by histamine, bradykinin, leukotrienes, platelet activating factor, substance P
- Immunologic Stimuli
- many of hte same events that accompany imlammations
- Direct endothelial injury
- Toxins, Chemicals or infectious agents
- Inflammation:
Edema is usually localized
Edema:
Morphology:
Gross:
- Clear, gel-like fluid within tissue
- tends to gravitate to ventral areas
- Can occur in body cavities
- ascites - abdomen
- Hydrothorax - thoracic cavity
- Hydropericardium - pericardial sac
Edema:
Morphology:
Histologic
Eosinophilic amorphous material within a tissue
Edema:
Significance
- Edema can be insignificant to fatal
- Subcutaneous edema has little functional significance
- Cerebral or pulmonary edema are life-threatening
- Clinical Classification:
- Nutritional
- Renal
- Cardiac
- Parasitic
