Circulatory System - Hemodynamics And blood vessels

Question 1

What is hemodynamics

Answer 1

Hemodynamics is the study of blood flow and the forces involved in circulation.

Are the basic parameters associated with cardiovascular function which facilitate blood flow during each cardiac cycle.

Question 2

Blood pressure

Answer 2

Blood flow : volume of blood flowing through the vessels of the body ( given period; mL/min)
- circulation time ( Rt atrium to Rt atrium) =~ 1 min
- velocity : speed a volume of blood flows through a tissue ( slow at branching, eg capillary networks, fast in large vessels eg aorta)

Responsible for blood movement via flow from high to low pressure
- 2 measures: systolic pressure and diastolic pressure
-120/75 ( difference = pulse pressure:45)

Mean Arterial pressure (MAP) - average blood pressure between systolic and diastolic pressure in the aorta
- Map = cardiac output (Q) x peripheral resistance (PR)
- BP of 120/75. MAP = 75+45/3 which 90mm Hg

Question 3

Atherosclerosis

Answer 3

Ageing = less distensible (arteriosclerosis)
Atherosclerosis is the growth of lipid deposits in the arterial walls

Question 4

Cardiac output

Answer 4

Volume of blood pumped from the heart per minute
Q= HR x SV
Heart Rate (HR) - number of times the heart beats per minute (bpm)
Stroke Volume (S) - volume of blood pumped per heartbeat (cardiac cycle)

Eg. Q = 75 bpm x 70 ml per beat
Q = 5,250 ml min-1 / 5.25 L min-1

Cardiac output varies with levels of activity - vigorous exercise increases Q to as much as 35 L/min (maximum Q) (elite athletes)

Cardiac reserve = maximum Q - resting Q ( measures heart output in response to exercise)

Question 5

Determining cardiac output- fick equation

Answer 5

Q=
O2 consumption (ml min-1)
Over
a-VO, difference (mI per 100ml blood) X100
Oxygen consumption is measured via expired gases
a-VO, difference is the difference between oxygen content of arterial and mixed venous blood and oxygen uptake in 1 minute

Question 6

Stroke volume- preload

Answer 6

EDV = end diastolic volume
ESV = end systolic volume
SV= EDV - ESV

Governed by
Preload -Preload
- Volume coming Into ventricles (end diastolic pressure)
- Increased in: Hypervolemia
Regurgitation of cardiac values
-Preload- the amount of tension in ventricular myocardium immediately before it begins to contract
• exercise increases venous return and stretches myocardium
• cardiomyocytes generates more tension during contraction

Question 7

Contractility

Answer 7

How hard the myocardium contracts for a given preload
1. Positive inotropic agents increase contractility:
• Hypercalcemia: cause strong, prolonged contractions and even cardiac arrest in systole
• Catecholamines: (adrenaline)increase calcium levels
• Glucagon: stimulates cAMP production
•Digitalis: raises intracellular calcium levels and contraction strength

2. Negative inotropic decrease contractility:
   Hyperkalemia: has a negative inotrophic effect, reduce force of heart contraction
   Hypokalemia: has little effect on contractility

Question 8

After load

Answer 8

The blood pressure in the aorta and pulmonary trunk immediately distal to the semilunar valves
• Opposes the opening of these valves
• Limits stroke volume

Hypertension increases afterload and opposes ventricular ejection ( high blood pressure heart has to work harder)

Anything that impedes arterial circulation can also increase afterload (scar tissue e.g emphysema)

Ventricular hypertrophy and heart failure

Question 9

Stroke volume

Answer 9

Governed by -
• Preload
• Contractility.
• Afterload

Question 10

Heart rate

Answer 10

Heart Rate
Pulse: surge of pressure produced by each heartbeat that can be felt by palpating a superficial artery with the fingertips
• Infants have HR of 120 bpm or more
• Young adult females average 72 to 80 bpm
• Young adult males average 64 to 72 bpm
• Heart rate rises again in the elderly

1. Tachycardia-resting adult heart rate above 100 bpm( high heart rate)
2. Bradycardia-resting adult heart rate of less than 60 bpm ( lower heart)
3. Positive chronotropic agents- factors that raise the heart rate
4. Negative chronotropic agents- factors that lower heart rate

Question 11

Chronotopic effect on heart rate

Answer 11

Nervous System
• Cardiac centers in the medulla oblongata initiate autonomic output to the heart

1. Cardiostimulatory effect: some neurons of the cardiac center transmit signals to the heart by way of sympathetic pathways
2. Cardioinhibitory effect- others transmit parasympathetic signals by way of the vagus nerve

• Feedback from receptors to medulla oblongata provides information regarding a need for change in heart rate
- Proprioceptors
- Baroreceptors
- Chemoreceptors: looking for changes in oxygen ph etc

Question 12

Chronotopic Effects on Heart Rate

Answer 12

Chemicals
• Affect heart rate as well as NTs from cardiac nerves

Drugs that stimulate heart
• Nicotine
• Thyroid hormone
• Caffeine

Electrolytes
• K+ has greatest chronotropic effect high levels slows down heart rate
• Ca2+ increase heart rate of levels are high

Question 13

Blood vessels

Answer 13

General Anatomy of Blood Vessels

Arteries carry blood away from heart
Veins carry blood back to heart
Capillaries connect smallest arteries to veins

Question 14

General Anatomy of Blood Vessels

Answer 14

1. Tunica interna (intama)
   • lines inside of the vessel exposed to blood,
   • Simple squamous epithelium (endothelium)
   • continuous with endocardium of the heart
2. Tunica media
   • Middle layer typically thickest
   • Smooth muscle, collagen and elastic tissue at places
   • Strengthen and regulates vessels diameter because of smooth muscle that is able to contract
3. Tunica externa (adventitia)
   • Outermost layer of loose connective tissue
   • Providing an anchor for the vessel to connect to surrounding tissue

Question 15

Arteries

Answer 15

‘Arteries
. ‘Resistance vessels’ due to relatively strong, resilient tissue structure that resists
high blood pressure

1. Large elastic or conducting arteries eg aorta or carotid
2. Medium muscular or distributing artieries.
   Distribute blood to specific organs. Eg branc

Question 16

Capillaries

Answer 16

Site where nutrients, wastes, hormones pass between the blood and tissue fluid through the walls of the vessels (exchange vessels)
• Composed of endothelium and basal lamina

Three capillary types distinguished by ease with which substances pass through their walls/ greater or lesser permeability
1. Continuous;
2. Fenestrated; present of pores
3. Sinusoids. Wider winding capillaries large wholes that allow things to pass through

Question 17

Capillary beds

Answer 17

• Capillary beds - Capillaries are organized into networks
- Usually supplied by a single metarteriole

• Thoroughfare channel-metarteriole that continues through capillary bed to venule

• Precapillary sphincters control which beds are well perfused

When sphincters open -
- Capillaries are well perfused with blood and engage in exchanges with the tissue fluid

2. When sphincters closed
   - Blood bypasses the capillaries
   Flows through thoroughfare channel to venule

Question 18

Veins

Answer 18

• Greater capacity for blood containment than arteries
• Thinner walls, flaccid, less muscular and elastic tissue
• Collapse when empty, expand easily
• Have steady blood flow
• Merge to form larger veins ( allow for steady blood flow back to the heart )
• Subjected to relatively low blood pressure
- Remains 10 mm Hg with little fluctuation
• the have valves that aid the flow of blood back to the heat

Question 19

Veins

Answer 19

1. Postcapillary venules: smallest veins
   • more porous than capillaries (leukocytes)
2. Muscular venules: up to 1 mm in diameter
   - Even more porous than capillaries so also exchange fluid with surrounding tissues
3. Medium veins: up to 10 mm in diameter
   - Skeletal muscle pump propels venous blood back toward the heart
4. Venous sinuses:
   - Especially thin walls, large lumen, no smooth muscle no vasoconstriction ( can’t contract)
5. Large Veins (>10mm)
   -Some smooth muscle in all three tunics
   - Venae cavae, pulmonary veins, internal jugular veins, and renal
   veins

Question 20

Circulatory route

Answer 20

• Simplest and most common route
- Heart - › arteries -› arterioles -› capillaries -› venules -> veins

• Passes through only one network of capillaries from the time it leaves the heart until the time it returns

• Exceptions: portal system (kidneys, hypothalamus and pituitary, intestines and liver)

• Anastomosis: Bypass areas exposed to cold (e.g. palms, fingers, toes)