Circulatory Systems By: Tim Nguyen Ezequiel Jauregui

What is the Circulatory System? The circulatory system is an organ system that passes nutrients (such as amino acids, electrolytes, and lymph), gases, hormones, blood cells, etc. to and form cells in the body to help fight diseases, stabilize body temperature and pH, and to maintain homeostasis.

Importance The timely delivery of oxygen to the body’s organs is critical. For example, brain cells die within a few minutes if their oxygen supply is interrupted. Thus, maintaining heart function is crucial for survival.

Circulatory systems All animals have: o circulatory fluid = “blood” o tubes = blood vessels o muscular pump = heart openclosed

Open circulatory system Taxonomy o invertebrates insects, arthropods, mollusks Structure o no separation between blood & interstitial fluid hemolymph

Closed circulatory system Taxonomy o invertebrates earthworms, squid, octopuses o vertebrates Structure o blood confined to vessels & separate from interstitial fluid 1 or more hearts large vessels to smaller vessels material diffuses between blood vessels & interstitial fluid closed system = higher pressures

The Mammalian Heart Figure 42.6 Aorta Pulmonary veins Semilunar valve Atrioventricular valve Left ventricle Right ventricle Anterior vena cava Pulmonary artery Semilunar valve Atrioventricular valve Posterior vena cava Pulmonary veins Right atrium Pulmonary artery Left atrium

Vertebrate cardiovascular system Chambered heart o atrium = receive blood o ventricle = pump blood out Blood vessels o arteries = carry blood away from heart arterioles o veins = return blood to heart venules o capillaries = thin wall, exchange / diffusion capillary beds = networks of capillaries

Mammalian Circulation pulmonary systemic

Mammalian Circulation: The Pathway 1.The Right ventricle pumps blood to the lungs Lungs 1

Mammalian Circulation: The Pathway 2 & 3. Leads to the pulmonary arteries as the blood flows through capillary beds in the left and right lungs. It loads O2 and unloads CO2.

Mammalian Circulation: The Pathway 4. Oxygen rich blood returns from the lungs via the pulmonary veins to the left atrium of the heart. Lungs 4

Mammalian Circulation: The Pathway 5. Next, the oxygen-rich blood flows into the left ventricle as the ventricle pumps the oxygen-rich blood out to body tissues through the systemic circuit. Lungs 5

Mammalian Circulation: The Pathway 6. Blood leaves the left ventricle via the aorta, which conveys blood to arteries leading throughout the body. The first branches from the aorta are the coronary arteries (not shown), which supply blood to the heart muscle itself. 6

Mammalian Circulation: The Pathway 7. Then come branches leading to the capillary beds in the head and arms (forelimbs).

Mammalian Circulation: The Pathway 8. The aorta continues in a posterior direction, supplying oxygen- rich blood to arteries leading to arterioles and capillary beds into the abdominal organ and legs.

Mammalian Circulation: The Pathway 9 & 10. Two other large veins called the anterior (or superior) vena cava and posterior (or inferior) vena cava drains blood back to the heart.

Mammalian Circulation: The Pathway 11. The two vena cava empty their blood into the right atrium, from which the oxygen-poor blood flows into the right ventricle

Blood vessels arteries arterioles capillaries venules veins artery arteriolesvenules veins

Arteries: Built for high pressure pump Arteries o thicker walls provide strength for high pressure pumping of blood o narrower diameter o elasticity elastic recoil helps maintain blood pressure even when heart relaxes

Veins: Built for low pressure flow Veins o thinner-walled o wider diameter blood travels back to heart at low velocity & pressure lower pressure o distant from heart o blood must flow by skeletal muscle contractions when it move squeeze blood through veins o valves in larger veins one-way valves allow blood to flow only toward heart Open valve Blood flows toward heart Closed valve

Capillaries: Built for exchange Capillaries o very thin walls lack 2 outer wall layers only endothelium o enhances exchange across capillary o diffusion exchange between blood & cells

Mammalian Circulation: The Pathway Heart valves o Dictate a one-way flow of blood through the heart

Cardiac cycle 1 complete sequence of pumping o heart contracts & pumps o heart relaxes & chambers fill o contraction phase systole ventricles pumps blood out o relaxation phase diastole atria refill with blood

Blood Pressure Blood pressure o Is the hydrostatic pressure that blood exerts against the wall of a vessel Blood pressure is determined partly by cardiac output o And partly by peripheral resistance due to variable constriction of the arterioles

Systolic pressure o Is the pressure in the arteries during ventricular systole o Is the highest pressure in the arteries Diastolic pressure o Is the pressure in the arteries during diastole o Is lower than systolic pressure

Blood pressure Figure Artery Rubber cuff inflated with air Artery closed 120 Pressure in cuff above 120 Pressure in cuff below 120 Pressure in cuff below 70 Sounds audible in stethoscope Sounds stop Blood pressure reading: 120/70 A typical blood pressure reading for a 20-year-old is 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high. 1 A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure in an artery. The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery. 2 A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure. 3 The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed systolic ________ diastolic pump (peak pressure) _________________ fill (minimum pressure) 110 ____ 70

The heart rate, also called the pulse o Is the number of beats per minute The cardiac output o Is the volume of blood pumped into the systemic circulation per minute

The cardiac cycle Semilunar valves closed AV valves open AV valves closed Semilunar valves open Atrial and ventricular diastole 1 Atrial systole; ventricular diastole 2 Ventricular systole; atrial diastole sec 0.3 sec 0.4 sec

Maintaining the Heart’s Rhythmic Beat Some cardiac muscle cells are self-excitable o Meaning they contract without any signal from the nervous system

A region of the heart called the sinoatrial (SA) node, or pacemaker o Sets the rate and timing at which all cardiac muscle cells contract Impulses from the SA node o Travel to the atrioventricular (AV) node At the AV node, the impulses are delayed o And then travel to the Purkinje fibers that make the ventricles contract

The pacemaker is influenced by o Nerves, hormones, body temperature, and exercise The impulses that travel during the cardiac cycle o Can be recorded as an electrocardiogram (ECG or EKG)

The control of heart rhythm Figure 42.8 SA node (pacemaker) AV node Bundle branches Heart apex Purkinje fibers 2 Signals are delayed at AV node. 1 Pacemaker generates wave of signals to contract. 3 Signals pass to heart apex. 4 Signals spread Throughout ventricles. ECG

Capillary Function Capillaries in major organs are usually filled to capacity o But in many other sites, the blood supply varies Two mechanisms o Regulate the distribution of blood in capillary beds In one mechanism o Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel In a second mechanism o Precapillary sphincters control the flow of blood between arterioles and venules

Figure a–c Precapillary sphincters Thoroughfare channel Arteriole Capillaries Venule (a) Sphincters relaxed (b) Sphincters contracted Venule Arteriole (c) Capillaries and larger vessels (SEM) 20  m

Platelets Platelets function in blood clotting When the endothelium of a blood vessel is damaged o The clotting mechanism begins

Blood Clotting blood contains self-sealing materials that plug up leaks when blood vessels are injured. Clotting response is vital to survival. Hemophiliacs = lack a key component of clotting response; susceptible to excessive bleeding during minor injuries.

sealants are always present in the blood: include: platelets: circulating cell fragments which form temporary plugs at site of injury. fibrinogen: when blood vessels are injured, a chain of reactions (cascade) leads to conversion of a soluble fibrinogen into fibrous, insoluble fibrinogen, which is deposited around injury site and traps platelets and white blood cells, forming a clot, until connective tissue forms a permanent patch.

A cascade of complex reactions Converts fibrinogen to fibrin, forming a clot Platelet plug Collagen fibers Platelet releases chemicals that make nearby platelets sticky Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Prothrombin Thrombin Fibrinogen Fibrin 5 µm Fibrin clot Red blood cell The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky. 1 The platelets form a plug that provides emergency protection against blood loss. 2 This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via a multistep process: Clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma, forming an activation cascade that converts a plasma protein called prothrombin to its active form, thrombin. Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM). 3 Figure 42.17

Cardiovascular Disease Cardiovascular diseases o Are disorders of the heart and the blood vessels o Account for more than half the deaths in the United States

One type of cardiovascular disease, atherosclerosis o Is caused by the buildup of cholesterol within arteries Figure 42.18a, b (a) Normal artery (b) Partly clogged artery 50 µm250 µm Smooth muscle Connective tissue Endothelium Plaque

Hypertension, or high blood pressure o Promotes atherosclerosis and increases the risk of heart attack and stroke A heart attack o Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries A stroke o Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head