Blood Composition & Vessels

• Heat dissipates through blood flow.

Bone Marrow & Blood Composition

• Stem cells originate in bone marrow.
• Red bone marrow produces blood cells.
• Yellow bone marrow is a fat deposit region for energy use.

Blood Components

• Blood components separate upon spinning.
• Plasma and formed elements (red and white blood cells, platelets) are the 2 main parts of blood.
• Plasma consists of water, proteins, and other solutes, and maintains hydration.
• Formed elements include leukocytes (white blood cells) and red blood cells.

Blood Vessels

• Arterioles facilitate gas exchange.
• Arteries withstand high pressure from the left ventricle pumping.
• Pulse, equivalent to heartbeat, can be felt in arteries.
• Pulse can be sensed on the skin's surface due to strong heartbeats.

Vessel Structure

• Blood vessels have a layered structure (tunica externa, tunica media, tunica interna) and a lumen.
• Arteries have smaller lumens and stronger structures than veins due to high blood pressure.
• Large arteries (elastic arteries) like the aorta accommodate pressure changes.
• Arteries branch into muscular arteries, then arterioles (regulate tissue perfusion), and finally capillaries.
• Veins closer to the surface of the body and have a much larger lumen.
• Pulse cannot be felt in veins.
• Inferior and superior vena cava are the largest veins.

Vein Valves

• Veins contain valves to prevent backflow and redirect blood upward from lower body parts against gravity.
• Lack of valves can cause blood pooling in feet and fainting.
• Veins aren't pressurized so they require valves.
• Calves and the thoracic cavity act as pumps to assist blood flow.
• Veins constrict via muscles (VASOCONSTRICTION) to move blood upward.

Blood Distribution

• The heart contains 7% of the body's blood.
• The lungs contain 9% of the blood.
• Systemic circulation holds 84% of the blood.
• Veins hold 64% of the body's blood, acting as a reservoir.
• Systemic oxygenated portion holds 85% of the total blood volume.
• 15% of blood is under high pressure.
• The venous system holds the majority of blood at low pressure.
• Heart chambers always contain 5% of blood to maintain heartbeat function.

Blood Flow

• Resistance to blood flow can be caused by plaque buildup, blood clots, or vasoconstriction.
• Blood flow (Q) is determined by the formula: Q = Delta P/R (change in pressure divided by resistance).
• Blood velocity increases with an increase in diameter.
• Blood velocity refers to the speed of blood moving through a vessel.
• Blood flow relates to the total amount of blood passing through.
• Blood flows faster through smaller arteries if the cross sectional area DECREASES and velocity doesn't slow down.
• Blood velocity slows down in a smaller vessel.
• Overall amount of blood is smaller in a small cross sectional area
• Cross section refers to one vessel or overall area of vessels combined.
• Arterial blood flow is mainly determined by resistance.
• Venous blood flow is mainly determined by pushing capacity from reducing volume.
• Vasoconstriction in arteries increases resistance and decreases blood flow.
• Vasoconstriction in veins increases pressure and flow velocity.
• The pressure reduces as blood gets into the capillaries.

Blood Flow Rate, Artery to Veins

• Initially, a single unbranched vessel has a smaller cross section meaning less blood but flows at a higher rate.
• As a vessel branches out, the cross-sectional area increases, increasing blood volume but decreasing velocity.
• Pressure reduces as blood flows into the capillaries.
• Vasodilation and vasoconstriction affect blood pressure.
• As blood flow increases due to increased cross-sectional area, velocity decreases due to decreased pressure.
• As blood flow decreases due to a smaller cross-sectional area, velocity increases due to the increased blood pressure, but the volume decreases.

Laminar and Turbulent Blood Flow

• Laminar blood flow is normal and hyperbolic-shaped.
• Turbulent blood flow can be caused by clots or vasoconstriction.
• Major pressure differences between vessels may lead to turbulent flow.

Blood Pressure Measurement

• Blood pressure is measured by completely blocking an artery and then slowly releasing pressure via cuff.
• The cuff is inflated above normal blood pressure (e.g., to 200 mmHg when normal is 120/80).
• Turbulent blood flow results in audible murmurs called bruits when the artery is unoccluded.
• Bruits are rushing sounds heard over large or medium-sized arteries due to turbulent flow.
• The first bruit heard indicates systolic pressure.
• The last bruit heard indicates diastolic blood pressure.

Exercise

• During exercise, blood flow to muscles increases while perfusion to other organs reduces.

Autonomic Control

• Autonomic sympathetic tone maintains blood vessel function and blood pressure.
• Global tissue perfusion is regulated by local and autonomic tone.
• Vessels need to be slightly constricted by the sympathetic tone to maintain blood pressure.
• During heat stress, sympathetic withdrawal allows vessels to dilate.
• Local factors, such as oxygen, CO2, and hormone levels, influence change in physiological process.

Capillaries

• Fenestrations (small openings/pores) in capillaries facilitate nutrient and waste exchange.
• Bulk flow is important for waste removal and nutrient absorption.
• Transcytosis involves endocytosis and exocytosis.
• Higher hydrostatic pressure results in net filtration out into tissues.
• Small hydrostatic and osmotic pressures result in net filtration into the capillary.
• Fluid movement (JV) is determined by these forces.

Fluid Exchange

• Extracellular fluid (ECF) dynamics:
  • Arteriole end: higher blood pressure than osmotic pressure leads to net fluid out (filtration).
  • Venule end: higher osmotic pressure than blood pressure leads to net fluid in (absorption).
• The lymphatic system captures remaining plasma proteins that are not reabsorbed.
• 15% of fluids are taken up by capillaries in lymph, filtered for waste, and returned to the blood.
• 85% of fluid in absorbed initially, with the rest absorbed eventually.

Tissue Needs

• Tissue requirements are driven by metabolic demand.
• High metabolic demand requires more blood in capillaries.
• Sphincters automatically open and close to sustain metabolic demand.
• Local factors such as oxygen levels and hormones influence vasomotion (opening and closing of sphincters).

Hyperemia

• Hyperemia is an increase in blood flow to vessels and HYPEREMIA happens when their is a lot of metabolic demand for skeletal muscle in exercise, occluding blood flow to muscle.
• Active hyperemia involves increased muscle blood flow during exercise.
• Reactive hyperemia involves increased blood flow after occlusion.
• The longer a vessel is occluded, the greater the blood flow upon release.

Kidney Autoregulation

• Kidneys use autoregulation to maintain constant blood flow irrespective of systemic blood flow.
• Optimal blood flow comes into the kidneys at 80mmHg of systolic blood pressure
• Smooth muscle in arterioles in kidney is relaxed, meaning blood flow is normal
• Two mechanisms:
  1. Tubuloglomerular Feedback
  2. Arteriole Myogenic Mechanism

Tubuloglomerular Feedback

• Response to changes in blood flow rate at the distal convoluted tubule (DCT).
• An increase in blood flow increases glomerular filtration rate (GFR) and glomerular pressure.
• Macula densa cells sense fluids and ions from DCT and GF, release adenosine, increase arterial resistance, and decrease filtration rate.
• Solute and fluid sensing impacts constriction or dilation.

Arteriole Myogenic Mechanism

• Arterioles in the kidney contract and relax in response to changes in blood flow to maintain optimal renal blood pressure.
• In response to stretch variations blood pressures smooth muscle will change the amount of pressure based on the stretch that it is seeing. trying to maintain flow based on pressure using ability to respond to stretch occurring

Kidney Regulation

• The kidneys rely on sympathetic tone and local factors

Sympathetic Effects

• Sympathetic increase causes vasoconstriction, less blood flow, less filtration, and less demand for O2, this occurs during exercise to redirect blood flow to skeletal muscle.
• Sympathetic decrease causes vasodilation, increased flow, and increased filtration.

Abdominal Circulation

• In the abdomen, the aorta branches off to supply blood to organs.

Celiac Artery

• The celiac artery first branches into the liver via the hepatic artery, then supplies blood to the stomach, spleen, and pancreas.

Superior Mesenteric Artery

• The superior mesenteric artery supplies blood to the pancreas, small intestines, and colon.

Inferior Mesenteric Artery

• The inferior mesenteric artery supplies blood to the colon.

Blood Flow to Liver

• Veins from each organ join into the portal vein, which brings deoxygenated blood into the liver.
• The liver receives 1000-1300mL/min of blood.
• Blood from the veins have a lot of nutrients and are rich, while oxygen poor, get filtered in the liver to remove waste ect
• Pressure on hepatic is low
• This is a high-volume, low-pressure system in the venous system.
• Blood then goes to the hepatic veins into the inferior vena cava.

Liver Lobule

• Each lobule has a portal triad, consisting of a hepatic arteriole, portal venule, and bile duct.
• Hepatic sinusoid filters components of this triad.
• When alcohol is consumed a lot, the sinusoid can build up, meaning blood can not get filtered out properly leading to blood build up in the portal vein . This causes portal vein hypertension.
• Sinusoids drain back into the vena cava.

Lymphatic System

• Lymph is the colourless fluid that floats in the vessels
• Lymph - colorless fluid in vessels.
• Lymphatic tissues have capillaries which run in parallel with blood capillaries.
• This allows lympocytes (white blood cell) to get to specific parts of the body.

Major Functions:

• Fluid balance
• Drain interstiual fluid into capillaries
• Innate immune response transport
• Transport dietary lipids absorbed in the GI into the blood

Tissue Fluid

• Lymph capillaries intertwine with circulatory capillaries.
• Tissue fluid transport depends on valve pumps and interstitial fluid pressure.