Body Systems - Circulatory System

Non-AP Bio 20 content

Circulatory System

Closed system to cycle blood throughout body. 6 main functions

1. Deliver nutrients (O2) to cells

2. Takes waste away from cells

3. Distributes heat throughout body

4. Regulates body fluid levels

5. Sends out chemical messengers (hormones)

6. Defend against foreign agents

Blood Vessels

Channels to carry blood throughout body

1. Arteries

2. Arterioles

3. Capillaries

4. Venules

5. Veins

Arteries

Carry oxygenated blood away from the heart, exception of the pulmonary artery. 3 layers: inner and outer walls of connective tissue, middle layer of elastic connective tissue and muscle fibers

Arteriosclerosis

Group of disorders characterized by thickened, hardened, and less elastic blood vessels. Happens because of thicker vessel walls which become more brittle over time.

Atherosclerosis

Disorder that causes blood vessels to thicken and harden (lose elasticity) because of accumulation of plaque inside vessels. Leads to high blood pressure and increased chances for a heart attack

Plaque

Build-up of lipids, calcium, and other minerals in blood vessels. Can cause increased blood pressure through embolisms

Embolism

Blockage in a blood vessel. Can cause organ to be starved of oxygen which can cause increased blood pressure, blood clots, aneurysms, heart attacks, and strokes

Aneurysm

Bulge in the weakened wall of a blood vessel (typically arteries). Often due to atherosclerosis. If ruptures, depletes oxygen and nutrients arriving in a tissue which results in cell death.

Stroke

Aneurysm in the brain

Arterioles

Smaller arteries that connect to capillaries. Lower pressure than in arteries (further from the heart). Diameter controlled by autonomic nervous system (ANS). Can constrict and contract through messages from the ANS

Vasoconstriction

Narrowing of blood vessels after signal from ANS. Decreased blood flow

Vasodilation

Widening of blood vessels after signal from ANS. Increased blood flow

Precapillary Sphincters

Regulate blood flow to prevent certain arterioles from opening, prevents having too low of a blood pressure because there isn’t enough blood for the whole body at once. Closes access to capillary beds. Used for blood pressure control

Capillaries

Composed of single layer cells, small in diameter to slow flow of red blood cells and prevents large molecules from exiting (eg polypeptides). Thin walls for fluid/gas (oxygen and CO2) exchange but are easily ruptured or destroyed. As blood travels across bed, pressure decreases and osmotic pressure increases

Venules

Small veins that connect to capillaries. Lined with smooth muscle but thinner than in arteries/arterioles. Not enough pressure to return blood to heart

Veins

Blood vessels that transport blood back to the heart. Typically carry deoxygenated blood (exception pulmonary vein). Blood pressure is much lower, lined with valves to prevent backflow of blood and squeezed by skeletal muscles as blood moves through.

Varicose Veins

Caused by blood pooling in veins. Valves begin to bulge and discolour skin.

Heart

Made of cardiac/myogenic muscle, surrounded by the pericardium. 4 chambers, 4 valves. Right and left separated by septum

Pericardium

Fluid-filled sack that reduces friction in the heart. Keeps heart cool to continue beating

4 chambers of the heart

1. Right atrium

2. Right ventricle

3. Left atrium

4. Left ventricle

Right atrium

Where deoxygenated blood is received by the heart from the vena cavas. Pumps blood into right ventricle but separated by tricuspid (atrioventricular) valve.

Right ventricle

Receives deoxygenated blood from right atrium. Pumps blood into pulmonary vein through the pulmonary semi-lunar valve

Left Atrium

Where oxygenated blood is received from the pulmonary artery. Pumps blood into left ventricle through the bicuspid (atrioventricular) valve

Left ventricle

Most muscular of the four chambers, receives blood from left atrium. Pumps blood through the aortic semi-lunar valve to the aorta where it is then distributed throughout the body.

Atrioventricular valves

Valves to separate atriums and ventricles and prevent backflow of blood. Right = tricuspid, left = bicuspid. Supported by chordae tendinea, attached to papillary muscle

Semi-Lunar Valves

Valves to separate ventricles from arteries. Right = pulmonary semi-lunar valve, left = aortic semi-lunar valve.

Aorta

Largest artery in the body. Carries oxygenated blood away from heart

Coronary arteries

Smaller arteries that branch off from aorta to supply muscle cells of the heart with oxygen and nutrients. If blocked can cause a heart attack.

Blood Flow Right Side

1. Blood enters heart through vena cava (superior/inferior) into right atrium

2. High pressure opens tricuspid AV valve and blood empties into right ventricle. High pressure behind AV valve prevents backflow of blood

3. Right ventricle contracts to push open pulmonary semi-lunar valve. Blood flows into pulmonary artery and goes to lungs to get oxygenated.

Blood Flow Left Side

1. Blood enters left atrium through pulmonary vein

2. Atrium contracts and creates high pressure that opens the bicuspid AV valve, allowing blood flow into left ventricle. High pressure behind AV prevents backflow of blood into atrium

3. Left ventricle contracts and forces blood through aortic semi-lunar valve and into the aorta

Sinoatrial Node (SAN)

Generates an electric signal that causes the atria to contract. Regulated by the medulla oblongata. Acts as a pacemaker

Atrioventricular Node

Acts as a conductor to pass nerve impulses through the septum towards the ventricles. Signal goes through purkinje fibers

Purkinje Fibers

Two large nerve fibers that passes nerve impulses from the AV node through the septum towards the ventricles

Heart Rate

Frequency of a heartbeat. Measured in contractions per minute. Increases with stressors, influenced by the autonomic nervous system. Increases with higher CO2 levels (lower pH) because more CO2 needs to be diffused/more oxygen cycled. Beats/minute

Autonomic Nervous System

System that controls actions without the brain. Conduct impulses from the brain to the sinoatrial node

• Sympathetic

• Parasympathetic

Sympathetic Nervous System

System that prepares the body for stress (fight or flight). Increases heart rate, dilates pupils etc

Parasympathetic Nervous System

System that returns body to normal resting levels following stress (slows heart rate, un-dilates pupils)

Cardiac Cycle

One complete cycle of heart contracting and relaxing. Two stages

1. Systole

2. Diastole

Lub-Dub

Sound of heart valves closing. “Lub” caused by AV valves closing, “dub” caused by semilunar valves closing

Systole

Contracting of the heart where blood is pushed out of atria

Diastole

Relaxation of the heart where blood re-enters atria

Heart murmur

Condition where heart valves don’t close completely and blood leaks past closed valve (decreases pressure). Causes the heart to beat faster and eventually enlarge to compensate for decreased oxygen delivery

Cardiac output

Amount of blood pumped from the heart each minute. Calculated by stroke volume over heart rate. Increased cardiac output will increase blood pressure

Stroke volume

Quantity of blood pumped with each beat of the heart (contraction). Fitter people can have increased stroke volumes and lower heart rates

Blood pressure

Measure of the force on the walls of arteries. Measured with a sphygmomanometer in mmHg. Reads systolic (pressure when ventricles contract) and diastolic (pressure when ventricles relax). Depends on cardiac output and arteriolar resistance

Arteriolar Resistance

Resistance to blood flow in arteries. Construction of artery muscle reduces blood flow and increases pressure. Build-up of CO2/lactic acid causes muscles to relax/dilate and provides more oxygen to tissues, CO2 to lungs

Hypertension

High blood pressure. Caused by increased resistance of blood flow. If pressure remains too high, vessels weaken and may rupture. Body compensates by increasing connective tissue which hardens arteries. Known as the silent killer because symptoms aren’t obvious

Blood Pressure Regulation

Regulated by the medulla oblongata. When pressure is low, medulla oblongata stimulates sympathetic nervous system to increase heart rate and blood pressure. When pressure is high, medulla oblongata stimulates parasympathetic nervous system to dilate arterioles

Baroreceptors

Pressure receptors that are sensitive to pressure. Located on the walls of the aorta and cartoid arteries

ECG/EKG

Electrocardiogram. Reading of heart’s electrical activity.

1. p-wave

2. QRS complex

3. t-wave

p-wave

First bump of an ECG that shows wave of depolarization, contracting atria

QRS complex

Largest spike that shows ventricular systole. Followed by a delay to allow repolarization

T-wave

Re-establishment of voltage, recreates polarization in the heart

Heart during stress

Sympathetic nerves stimulate adrenal glands to release epinephrine (adrenaline). Increases oxygen transport, breathing and heart rates, vasodilation of arterioles near heart and muscles, vasoconstriction of digestive organs and kidneys

Thermoregulation

Maintenance of body temperature to allow efficient cell function. Typically 37C in humans

Regulating temperature in high temperatures

Hypothalamus in brain detects rise in body temperature. Sends signal to sweat gland to initiate sweating for evaporative cooling. Blood vessels dilate for more blood flow and increased blood near the surface (increase heat lost through radiation)

Regulating temperature in low temperatures

Thermoreceptors in skin send message to hypothalamus which causes arterioles to constrict (reduces heat loss). Message sent to hair follicles to stand up to trap air and reduce heat loss, skeletal muscles to contract (shiver). Prolonged exposure elevates metabolism of brown fat and possible hypothermia

Hypothermia

Condition where body temperature is lowered extremely. Can cause comas/death

Heatstroke

Condition where body temperature is too high

Capillary fluid exchange

Extracellular fluid outside cells/blood vessels allows for diffusion of materials (oxygen, glucose, CO2, amino acids) between blood and cells. Regulated by fluid and osmotic pressure

Movement out of capillaries

Done by ultrafiltration due to blood pressure pushing materials out towards cells (arteriole end). Selectively permeable nature of capillaries keep blood cells and proteins in blood

Movement into capillaries

Occurs because of osmotic pressure (venule end)

Hemorrhage

Excessive bleeding. Causes decreased blood volume, lowered blood pressure. Osmotic pressure remains the same, fluids drawn into capillaries (attempting to keep some pressure through flooding with other fluids (water)

Starvation

Causes swelling (edema). Plasma proteins in blood used as a last source of energy which reduces osmotic pressure. Reduces reabsorption of fluids into the capillaries which causes tissues to swell

Allergies/Inflammation

Histamine released by cells who believe they are under attack. Increases capillary permeability, proteins enter extracellular fluid and lower osmotic pressure in capillaries. Resolves with white blood cells

Lymphatic System

Process by which proteins drained from extracellular fluid and returned to the circulatory system

Lymph

Fluid found in lymph vessels which contain proteins that have leaked through capillary walls. Returned to venous system through left and right subclavian veins

Lymph Nodes

Masses of tissue that store lymphocytes (B-cells) and red bone marrow

Lymphocytes

White blood cells that produce antibodies. Removes bacteria/foreign particles through phagocytosis

Red Bone Marrow

Produces blood cells and stem cells

Spleen

Lymphoid organ that acts as a reservoir for blood and filtering site for lymph. Releases red blood cells in low blood pressure/low oxygen levels

Thymus Gland

Located at front of trachea and gets smaller with age. Where T-lymphocytes mature