Phisio Cv3 Regional Circulation

Front 1

Control of CV requires

Back 1

A. Insure that perfusion-sensitive organs such as the brain and heart always receive the flow they require to maintain their normal function
B. Match the perfusion of every tissue and organ to its respective metabolism
C. Regulate (maintain) blood pressure so that the cardiac output (flow) can be apportioned among the organs by varying their resistance
D. All of the above require control of cardiac output, blood vessel size (resistance) and the regulation of blood volume

Front 2

flow to different regional circulations is
controlled

Back 2

1. central (exogenous)
- Autonomic innervation
- other material

2. local (endogenous).
- Basal tone
- Local tissue chemical (metabolic) modifiers
- Autoregulation of blood flow

Front 3

characteristics of the pulmonary and
regional circulations of the body

Back 3

-The pulmonary circulation: in series with the right heart and receives the entire cardiac output.

The regional circulations are in parallel between the left heart and the right heart and each of the regional circulations receives some fraction of the left
ventricular cardiac output.

Front 4

counter-current flow is and why it is a
useful paradigm in the some regional circulations

Back 4

Vessels running in counter directions are close together in order to exchange substances and take them different directions.

Skin:
Exchange of heat to preserve or lose heat in venous return.

Intestines: SA maximize surface area for absorption of food, but may lose O2. O2 from arterial vessels diffuse to venous vessel minimizes this loss.

Kidney's vasa recta: Na flows into tube in medulla to reabsorb water then Na+ flow out as tube goes to cortex.

Front 5

usefulness of ateriovenous anastomoses

Back 5

Resistance vessels
shunt blood from arterioles to venules and bypass capillary bed

Skin: Decrease resistance and increase flow to maximimal heat loss (b/c resistance is also high in capillary, so flow is slower).

Front 6

portal circulation is

Back 6

Two capillary bed in series
- intestine to liver via heptaic protal veins
- kidney glomerulus to vasa recta.

Front 7

muscle pump and why it is important

Back 7

Increase venous return during exercise. Muscle increases hydrostatic pressure between two valves, opening upper valve and force blood up and closeing lower valve.

Front 8

O2/100g/min: how metabolically active

Back 8

- The heart and the kidneys have very active cells with a many energy consuming processes such as ion transport and active contraction.

skin has a relatively low rate

Front 9

ml O2/min: how metabolically active, rate of oxygen consumed by entire organ

Back 9

splanchnic bed actually uses more O2 at rest because it weighs more.

Front 10

Over-perfused organs

Back 10

Skin & Kidneys

Receive much higher percentages of the cardiac output than the percentage of the total oxygen they consume.

Related to function of organ and not metabolism of the organ's tissues. E.g. kidneys filter's blood, thats why so much blood goes there.

Front 11

Under-perfused organs

Back 11

High metabolic rates relative to their blood.

Get enough flow b/c well regulated in order to supply their metabolism in times of need.

Front 12

volume % O2 difference = difference in O2 content between the arterial blood going in to the tissue and the venous blood coming out of the tissue.

Back 12

Under-perfused tissues
- high O2 difference because they have
extracted more O2 from the blood that they were supplied with.

Over-perfused
- low O2 difference b/t
tissues are being supplied with more blood and they extract only the O2 that they need.

Front 13

Pulmonary Circulation

Back 13

In series with the right heart and receives the entire cardiac output.

Low pressure (reduce filtration), low resistance, high compliance

Large, thin dry exchange surface

Must accommodate entire cardiac output (and its 4-5X increase during
exercise)

When erect, at base, vessel diameter increase, resistance decrease and more flow.

Highly parallel circulatory bed, with many channels closed at rest, open when CO increase and allow for pressure to remain low.

Hypoxic vasoconstriction

Front 14

Coronary circulation

Back 14

VO2/gm always high

Anaerobic capacity small, high extraction, low O2 reserve

Flow/gm must always be high

Diffusion distances must be short and uniform

Cardiac VO2 may increase 4-5X, so flow and diffusion distance must be closely coupled to VO2

Contraction compresses vessels and increases resistance during systole -> left coronary flow occurs mainly in diastole

Metabolic controls compensate for systolic compression

Metabolic controls are more powerful than neural controls

Capillary reserve is large (collateral vessel just in case of obstruction)

Front 15

normal cutaneous circulation

Back 15

Basal VO2 is relatively low

Perfusion: vasoconstrict when cold, vasodialte when hot

A-V shunts, decrease resistance increase flow to maximize heat loss (only under neural control)

COUNTER-CURRENT:
When cold: heat from A to V to warm venous return
When hot: heat from V to A to cool venous return

Participates in reflexes maintaining blood pressure

Front 16

Splanchnic circulation Liver

Back 16

GI/Splanchnic:
- Blood reservoir and control by Sym directly, and para indirectly
- counter current to preserve O2 due to increased SA
- Baroreflex (blood pressure)

Liver:
- VO2/gm high and increases with metabolic work (active hyperemia)

Portal system
- hepatic vein to intestines, then hepatic portal + hepatic artery to liver (moderate O2 content).

Capillary
- low hydrostatic pressure but even lower oncotic pressure (high permeability to protein) = filtration is still greater than reaborption.
- raise venous pressure a little, will increase filtration in capillary a lot --> fluid retention in stomach (cap hypertension and ascite)

Front 17

Renal

Back 17

Overperfused: filtration function.

high basal VO2, receive large CO%

Counter Current Exahcnge (retain Na)
- Vasa recta: dip into medulla (pick up sodium), up to cortex, lose sodium.

Need, stablized glomerular filtration rate (only occurs here) and high reabsorptive capacity at peritubular cap.

Thus,
Portal system with small pressure drop along first glomeruli (cap bed connect glomerulus, and vasa recta, which wraps around renal tubules to allow for reasorption

Powerful myogenic autoregulation

Reflex regulation of blood pressure

Front 18

Skeletal MM

Back 18

Characteristics
- Circulation Enormous tissue mass
- VO2 low at rest but can increase almost instantly and can increase more than 50X
- Large anaerobic capacity

Problems
- Flow and capillary density must be limited at rest
- Flow and capillary density must increase promptly in exercise (“recruitment” of capillaries)
- O2 debt must be avoided or repaid

Adaptations:
- Well developed basal tone and autoregulation
- Large flow and capillary reserve
- Large extraction reserve
- Active sympathetic vasodilatation may anticipate exercise
- Prompt vasodilatation during contraction via intrinsic mechanisms
- Prompt capillary recruitment

Front 19

Cerebral

Back 19

Characteristics
1. VO2/gm high in certain critical locations
2. No O2 storage; glycolysis can not meet metabolic demand so flow/gm must be high, and diffusion distances must be short and uniform.
3. Local VO2 can increase several fold, so total flow, flow distribution, and diffusion distance must be closely coupled to VO2
4. Rigid cranium, needs constant intracranial volume extracellular fluid volume must be small and constant.

Problems:
- CSF pressure rises if intracranial vascular volume increases
- High CSF pressure compresses cranial vessels and increases their resistance
- In erect human, cerebral perfusion pressure is about 20% less than aortic pressure

Adaptations:
- Low vasomotor tone (walls not too contracted at rest)
- Well-developed autoregulation of blood flow
- Powerful metabolic (intrinsic) controls
- Increase in CSF pressure reflexly increases arterial perfusion pressure