Circulatory Physiology

Question 1

Distribution of cardiac output at rest

Answer 1

Blood flow is adjusted depending on metabolic need

Question 2

Blood flow

Answer 2

From higher to lower pressure
Directly proportional to pressure gradient
Inversely proportional to vascular resistance
F=🔺P/R
F = flow rate of blood through a vessel
P = pressure gradient
R = resistance of blood vessels

Question 3

Pressure change

Answer 3

Driving pressure for systemic flow is created by LV

If blood vessels construct = BP increases

Question 4

Resistance

Answer 4

Measure of opposition to blood flow
Depends on = blood viscosity (p), vessel length (1), vessel radius(r) (biggest effect)
R = 1xp/r^4

Question 5

Effect of vessel radius

Answer 5

If vessel radius decreases by a factor of 2, flow would decrease by a factor of 16
Decrease radius (vasoconstrict) = increased resistance, decreased flow 
Increase radius (vasodilate) = decreases resistance, increased flow 
Thus vessel vasoconstriction and dilation controls flow

Question 6

Vascular tree

Answer 6

Consists of = arteries, arterioles, capillaries, venules, veins, lymph vessels

Question 7

Vasculature

Answer 7

Layers = connective tissue, smooth muscle, endothelium

Question 8

Arteries

Answer 8

High flow rate/high pressure
Large radius (low resistance)
Pressure reservoir when heart is relaxing
Collagen fibres (tensile strength), elastin fibres (stretch/recoil of walls)
Pulsatile flow
Systolic pressure ~120, Diastolic pressure ~80

Question 9

Atherosclerosis

Answer 9

Cardiovascular disease

Caused by cholesterol buildup within arteries

Question 10

Arterioles

Answer 10

Major resistance vessels
Acts to smooth out pulsatile flow
Radius can be adjusted to: distribute cardiac output among organs depending on bodies need, help regulate arterial blood pressure

Question 11

Only blood supply to _______ remains constant

Answer 11

Brain

Blood supply to other organs alter via arteriole radius

Question 12

Vasoconstriction

Answer 12

Narrowing of vessel (increased resistance)

Contraction of smooth muscle

Question 13

Vasodilation

Answer 13

Enlargement of vessel
Relaxation of smooth muscle
Decreased resistance
Increased flow

Question 14

Factors affecting vascular tone

Answer 14

Local influences = local metabolic changes, histamine release, endothelial factors (nitric oxide, EDRF, endothelin)
Local physical influences = heat or cold, myogenic response to stretch

Question 15

Arterioles (vasodilation occurs with:)

Answer 15

Decreased oxygen 
Increased carbon dioxide 
Increased acid 
Increased potassium 
Increased osmolarity
Adenosine release 
Prostaglandin release

Question 16

Extrinsic control

Answer 16

Sympathetic input
Hormones
Alpha 1 receptors = norepinephrine (vasoconstriction)
Alpha 2 receptors = epinephrine, heart/skeletal muscles (vasodilation)

Question 17

Capillaries

Answer 17

Thin walled (decrease diffusion distance)
Small radius (velocity of blood flow is slow, gas exchange time increases)
Extensively branched (increased surface area)
Site of gas exchange

Question 18

Pre-capillary sphincters

Answer 18

Constrict sphincter = closes capillary bed (many capillaries are not open at rest)
Relax sphincter = opens capillary bed
Met arterioles = runs between an arteriole and a venule

Question 19

Capillary types

Answer 19

Continuous = most common, least permeable, (muscle, lungs, brain, CT)
Fenestrated = have pores, (kidneys, small intestine)
Sinusoids = large clefts for RBCs, proteins, (liver, bone marrow, spleen)

Question 20

Capillary bulk flow

Answer 20

Sterling forces that determine fluid flow between tissue and capillary
Capillary blood pressure
Interstitial fluid hydrostatic pressure (Pif)
Plasma colloid osmotic pressure (pi cap)
Interstitial fluid colloid osmotic pressure (pi if)

Question 21

Capillary blood pressure

Answer 21

Hydrostatic pressure

Encourages fluid flow into tissue

Question 22

Interstitial fluid hydrostatic pressure

Answer 22

Opposes hydrostatic pressure

Question 23

Plasma colloid osmotic pressure

Answer 23

Encourages movement of fluid into capillary

Question 24

Interstitial fluid colloid osmotic pressure

Answer 24

Opposes plasma colloid osmotic pressure

Question 25

Hydrostatic pressure and osmotic pressure regulate...

Answer 25

Bulk flow

Question 26

Lymphatic system

Answer 26

Network of open-ended vessels (helps drain fluid from tissues) Lymph vessels = similar in structure to veins, low pressure, have valves Functions = return of excess filtered fluid, defence against disease, (lymph nodes = phagocytes), transport of absorbed fat, return of filtered proteins

Question 27

Edema

Answer 27

Swelling of tissues Occurs when too much interstitial fluid accumulates Causes = reduced concentration of plasma proteins, increased permeability of capillary wall, increased venous pressure, blockage of lymph vessels

Question 28

Venules

Answer 28

Formed when capillary beds unite Very porous (allows fluids and WBCs into tissues) Larger venules have one or two layers of smooth muscles

Question 29

Veins

Answer 29

``` Return to heart Low pressure Low resistance Larger radius Slow flow Serves as a blood reservoir Capillaries drain into venules (smaller venules merge to form larger vessels) ```

Question 30

Venous return

Answer 30

Decreased by = venous compliance Increased by = driving pressure from cardiac contraction, sympathetically induced venoconstriction, skeletal muscle activity, effect of venous valves, respiratory activity, effect of cardiac suction Venous valves = prevent backflow Skeletal pump = pushes blood upward

Question 31

Varicose veins

Answer 31

Weak valve = allows backflow | Blood stagnates and clots

Question 32

Blood pressure is determined by

Answer 32

Cardiac output and total peripheral resistance | Mean arteriole pressure = cardiac output x total peripheral resistance

Question 33

Blood pressure control

Answer 33

Short term = within seconds, baroreceptors, cardiovascular system Long term = minutes to hours, kidneys

Question 34

Short term control - baroreceptors

Answer 34

Fast control = cardiovascular | Pressure receptors = send input to cardiovascular centre, output to heart and blood vessels

Question 35

Response to low blood pressure

Answer 35

Decrease firing of baroreceptors to cardiovascular centre Triggers = increase in vasoconstriction and venoconstriction, increase contractility so stroke volume increases and heart rate increases These things increase cardiac output = increases blood pressure

Question 36

Long term mechanisms: renal regulation

Answer 36

Control blood pressure by altering blood volume | Kidneys = direct renal mechanism, indirect renal (renin-angiotensin) mechanism

Question 37

Direct renal mechanism

Answer 37

Alters blood volume independently of hormones Increased blood pressure or blood volume (increased filtration, causes kidneys to eliminate more urine thus reducing blood pressure) Decreased blood pressure or blood volume causes the kidneys to conserve water and blood pressure rises

Question 38

Indirect (renin-angiotensin) mechanism

Answer 38

Decreased arteriole blood pressure = release of renin Renin triggers production of angiotensin ll (potent vasoconstrictor) Angiotensin ll = aldosterone and ADH secretion (conservation of fluid)

Question 39

Blood pressure abnormalities

Answer 39

Hypertension and hypotension

Question 40

Hypertension

Answer 40

Blood pressure above 140/90 mm Hg | Two broad classes = primary hyper tension and secondary hypertension

Question 41

Primary hypertension

Answer 41

``` Potential causes = poor kidney function Excessive salt intake or hormones Na+ K+ or Ca++ imbalance (eg- defective Na+/K+ pumps) Abnormalities in arterioles Stress Smoking ```

Question 42

Secondary hypertension

Answer 42

Accounts for 10% of hypertension cases Occurs secondary to another known primary problem Examples - renal hypertension, endocrine hypertension, neurogenic hypertension

Question 43

Complication of hypertension

Answer 43

``` Congestive heart failure Stroke Heart attack Spontaneous hemorrhage Renal failure Retinal damage ```

Question 44

Hypotension

Answer 44

Blood pressure below 100/60 mm Hg Low blood pressure Occurs when = there is too little blood to fill the vessels, heart is too weak to drive the blood

Question 45

Orthostatic (postural) hypotension

Answer 45

Transient hypotension condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position

Question 46

Hypotension (circulatory shock)

Answer 46

``` Occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained Four main types = Hypovolemic (low volume) shock Cardiogenic (heart produced) shock Vasogenic (vessel produced) shock Neurogenic (nerve produced) shock ```