Exam 1 Review:  Chapter 19:  Blood Flow

blood flow = blood circulation - The movements and pathways of blood within the blood vessels of the body or any subregion of interest, e.g., the pulmonary, systemic, coronary, hepatic portal and fetal circulations.

blood reservoirs - A chamber for the storage of an extra source or supply of blood, a volume of blood held in reserve for use in emergencies, e.g., the spleen, the larger systemic veins, and the capillary beds of the dermis.

vascular tone = vasomotion - The change in muscular tension in, or composition of, the vessel wall and, therefore, in the diameter of a blood vessel; such changes may be regulated by the nervous and endocrine systems and by local hormones or they may be a response to a disease process; changes in vascular tone/vasomotion may cause changes in blood flow/circulation.

vascular anastomoses - Any vascular channels which permit intercommunication between two or more blood vessels, e.g., the cross communications between two arteries or two veins; such connections permit blood flow in either direction and serve to provide additional blood supply or drainage to a particular structure, tissue, or capillary bed; such connections lessen the risk of tissue damage or death if one of the connecting vessels becomes obstructed. 

circulation time - The time it takes for blood to flow from one part of the body to another; this time is usually measured by injecting a dye or radioisotope into a vein and timing how long it takes to return to the same point in the body.

venous return - A physiological term used in analysis of the regulation of cardiac output; it is the amount of blood being returned to either or both of the atria of the heart per unit time; changes in cardiac output itself, as well as blood volume, blood distribution, and venous blood pressure may influence venous return.

skeletal muscle pump - The contraction of skeletal muscles in the legs assists with venous return from the legs because veins in the legs are guarded by valves to prevent back flow of blood; as a result, skeletal muscle contraction provides an extravascular compression on these blood vessels which moves the blood forward (and against gravity) back toward the heart.

respiratory pump - The contraction of the diaphragm and intercostal muscles in the thoracic cavity assists with venous return to the right side of the heart because each time a person inhales, there is a slight but significant drop in internal thoracic pressure which creates a pressure gradient which assists in the flow of venous blood moving forward (and against gravity) back toward the heart.

fetal circulation - The pathways of blood within the embryo and fetus which differ in several routes from the post-partum and adult circulation:  (1) the umbilical arteries carry deoxygenated blood to the placenta where oxygen and nutrients are transferred from the maternal circulation by diffusion, (2) umbilical vein returns oxygenated nutrient-laden blood to the liver and to the inferior vena cava, (3) the ductus venosus in the liver shunts some of the oxygenated blood directly to the inferior vena cava without passing through the hepatic capillary beds, and (4) three shunts exist to permit much of the blood returning to the right side of the heart to continue directly into the systemic circulation, by passing the pulmonary circulation; these shunts are (a) the foramen ovale in the atrial septum, (b) the interventricular shunt, and (c) the ductus arteriosus.

The ductus venosus in the liver shunts some of the oxygenated blood directly to the inferior vena cava without passing through the hepatic capillary beds. Three shunts exist to permit much of the blood returning to the right side of the heart to continue directly into the systemic circulation, by passing the pulmonary circulation; these shunts are (a) the foramen ovale in the atrial septum, (b) the interventricular shunt, and (c) the ductus arteriosus.

hepatic portal* circulation - The separate pathway for a portion of the blood returned to the heart from certain the abdominal organs; the vessels involved are the hepatic portal vein and its branches (splenic vein, superior and inferior mesenteric veins and gastric vein and their smaller branches); venous blood from the capillary beds of the spleen, pancreas, stomach and intestines (large and small) is routed to the capillary beds of the liver where various compounds in the blood are processed or stored by the liver; after leaving the liver this blood is returned to the general venous return of the inferior vena cava.  [*Note:  A portal system is a vascular arrangement in which blood from the capillaries of one organ is transported to the capillaries of another organ by a connecting vein or veins without returning to the heart.]

portal system - A special type of venous drainage system in which blood from one tissue capillary bed or organ is delivered to the capillary beds of another tissue or organ without first being routed to the heart; such systems evolve when materials (e.g., nutrients, wastes, signal compounds) from the first structure should be delivered to the second structure without being diluted by returning them to the heart and then to the general circulation; examples in humans include the drainage system between the hypothalamus and the pituitary gland and the drainage system between certain abdominal organs (stomach, small and large intestines, pancreas and spleen) and the liver.

List:

6.  the five organs drained by the hepatic portal system, and for each organ, list a type of molecule which is routed to the liver from that organ and the type of processing the liver will do to that type of molecule.

Describe:

4. the relationship between velocity of blood flow and total cross-sectional area of blood vessels.

 

The relationship between velocity of blood flow and total cross-sectional area of blood vessels is inverse.  The greater the cross-sectional area, the slower the blood flows, and vice versa.  See diagrams below:

6. the factors regulating venous return.

Venous return, the amount of blood being returned to either or both of the atria of the heart per unit time, is regulated by changes in: (1) cardiac output, (2) blood volume, (3) blood distribution within the various regions of the circulatory system, and (4) venous blood pressure itself.

14. the differences between fetal and postpartum circulation, naming the specific structures involved.

The pathways of blood within the embryo and fetus which differ in several routes from the post-partum and adult circulation:  (1) the umbilical arteries carry deoxygenated blood to the placenta where oxygen and nutrients are transferred from the maternal circulation by diffusion, (2) umbilical vein returns oxygenated nutrient-laden blood to the liver and to the inferior vena cava, (3) the ductus venosus in the liver shunts some of the oxygenated blood directly to the inferior vena cava without passing through the hepatic capillary beds, and (4) three shunts exist to permit much of the blood returning to the right side of the heart to continue directly into the systemic circulation, by passing the pulmonary circulation; these shunts are (a) the foramen ovale in the atrial septum, (b) the interventricular shunt, and (c) the ductus arteriosus.

15. the hepatic portal circulation. What is the importance of this circulation?