Lecture 21

Question 1

the cardiovascular system transports…..

Answer 1

• Substances entering the body (oxygen, nutrients, water)
• Substances leaving the body (metabolic waster, heat, CO2)
• substances moved around the body (wastes, hormones, immune cells, antibodies)

Question 2

pulmonary versus systemic circulations

Answer 2

pulmonary
- to the lungs
- low pressure
- low resistance

systemic
- to the body/tissues
- high pressure
- high resistance

Question 3

explain an overview of the cardiovascular system

Answer 3

• each side of the heart functions as an independent pump
• the elastic systemic arteries are a pressure reservoir that maintains blood flow during ventricular relaxation
• the arterioles shown with adjustable screws that alter their diameter are the site of variable resistance
• exchange between the blood and cells takes place at the capillaries
• Systemic veins serve as an expandable volume reservoir
• total blood volume = 5L

Question 4

explain how the cardiovascular system exhibits positive feedback

Answer 4

More blood leaves = more venous return= more CO
- some blood stays in the veins to decrease venous return

Question 5

what is the function and composition of arteries

Answer 5

• receive and propel high pressure blood flow
• muscular, highly elastic
• one layer of endothelium cells
• lots of smooth muscle

Question 6

what is the function and composition of arterioles

Answer 6

• vary resistance to blood flow
• muscular, well innervated
• not elastic
• more muscle tissue can clamp down to stop backward blood flow
• single layer of endothelium cells

Question 7

what is the function and composition of capillaries

Answer 7

• exchange of materials
• thin walled, highly permeable
  -single layer of endothelium cells

Question 8

what is the function and composition of the venules

Answer 8

• collect blood from capillaries
• thin walled, some fibrous tissue
• single layer of endothelium cells

Question 9

what is the function and composition of veins

Answer 9

• easily collapse or expand to maintain venous return
• Fairly muscular, Highly distensible
• single layer of endothelium cells
• can constrict

Question 10

what is the distribution of blood flow at rest

Answer 10

• blood flow = flow rate = volume/time
  = CO (L/min)
• variable distribution to tissues possible due to parallel arrangement of arterials

Question 11

explain the variability in distribution depending on organ needs

Answer 11

• at rest CO = 5.8 L/min
• during exercise CO = 25.6 L/min
• increase blood flow to skeletal muscles and directed away from GI tract

Question 12

what are the physical properties of circulation

Answer 12

• heart contracts-> creates a high pressure (driving pressure) ->blood flows out
  -> pressure decreases with distance due to friction
• resistance to blood flow increases as radius of a blood vessel decreases
  -> vasodilation = decreased resistance
  -> vasoconstriction = increased resistance
• blood flow rate
  -> volume of blood moved past a point per unit time (L/min)
• velocity of blood flow (cm/min)
  -> distance traveled by a fixed volume of blood per unit time
  -> increases as flow rate increases
  -> decreases as cross sectional area of blood vessels increases
  -> larger tubes = slower flow
• narrow vessel = faster velocity
• wider vessel = slower velocity

Question 13

explain how pressure drops with distance from the heart

Answer 13

• as blood flows through circulation it loses pressure which establishes a pressure gradient
• pressure lost due to friction
  -> friction within the blood
  -> friction between blood and vessel walls

Question 14

explain how blood obeys the laws of fluid flow

Answer 14

• flow is directly proportional to the pressure gradient
  -> more pressure equals more flow
• flow is inversely proportional to resistance
  -> more flow equals decreased resistance
  F=P/R

Question 15

explain the pressure difference across the different blood vessels

Answer 15

• different mean pressures in connected blood vessels create a pressure gradient through circulatory system
• blood flow around the circulatory system is driven by the pressure gradient which is generated by cardiac contractions
• thick elastic arteries are a pressure reservoir (high pressure)
• thin compliant expandable veins are a volume reservoir (low pressure)

Question 16

what is Venous return

Answer 16

• the flow of blood into the right atrium from the peripheral vessels
• the skeletal muscle pump helps maintain VR
• valves in the veins prevent backflow of blood
• when the skeletal muscle compresses the veins they force blood toward the heart

Question 17

why is blood flow velocity slowest through capillaries

Answer 17

• capillaries have the smallest individual diameter but the largest total cross sectional diameter
• it is the total cross sectional area of the vessels that determines the velocity of blood flow
• linear blood flow is slowest in capillaries
  -> good because exchange happens here so it ensures enough time for adequate exchange

Question 18

explain the varying blood flow through capillary beds

Answer 18

• precapillary sphincters open and close off capillaries in response to local metabolic conditions
• metarterioles divert blood flow if sphincters are closed
  -> allow larger materials (white blood cells) to bypass narrow capillaries and reach venous circulation

Question 19

explain the exchange of capillaries

Answer 19

• capillary density is related to metabolic activity of cells
• blood flow velocity is slowest through capillaries
  -> capillaries have greatest cross sectional area of all vessels
• single layer of flattened epithelial cells
  -> diffusion of gases
  -> osmosis
  -> protein transport
  -> movement of materials through larger pores, fenestrations, gaps
• Fick’s Law of diffusion

Question 20

What is Bulk Fluid Flow

Answer 20

• approximately three liters a day of fluid filtered out of capillaries
• excess tissue fluid is picked up by lymphatic vessels and returned to venous circulation