1. Unit 6.3: Circulation and Gas Exchange

2. Diffusion
Through diffusion, nonpolar molecules are able to move between cells and their other immediate surroundings. O2 and CO2 are examples of these molecules. However, diffusion is only efficient over small distances.
To find the diffusion time, find the square of the distance travelled.

3. Gastrovascular Cavity
A gastrovascular cavity functions in both digestion and distribution of substances throughout the body.
The body wall that encloses the gastrovascular cavity is only two cells thick.
Flatworms have a gastrovascular cavity and they have a flat body shape to optimize diffusional exchange with the environment.

4. Circulatory System
The circulatory system moves blood throughout the body, transporting nutrients and oxygen to the body’s cells, while removing waste such as CO2.
The circulatory system is made up of four parts: circulatory fluid, interconnecting vessels, interstitial fluid, and the heart.
There are two types of circuits in the circulatory system.
The Pulmonary circuit which carries blood without oxygen from the heart to the lungs and back.
The Systemic circuit carries oxygenated blood from the heart to the other organs and back to the heart.

5. Open Circulatory Systems
Common in insects, arthropods, and molluscs.
Rather than having a directed flow the hemolymph (similar to blood) bathes the organs keeping direct contact.
Hemocytes replace hemoglobin in hemolymph.
The hemolymph re-enters the heart through ostia pores.
Ostia pores allow for a passive flow back into the heart.

7. Closed Circulatory System
In closed circulatory systems, blood acts as the circulatory fluid. Unlike open systems, blood does not mix with interstitial fluid in closed systems.
The heart acts as the muscular pump, pushing blood throughout the body.
Closed systems are found in annelids, most cephalopods, and all vertebrates.

9. Cardiovascular System
The human closed circulatory system
The three main blood vessels are: arteries, veins and capillaries
Arteries branch into arterioles and carry blood away from the heart
Venules converge into veins and bring blood back to the heart
Arteries and veins are distinguished by blood flow and not O2 concentration
Blood enters through an atrium and leaves through a ventricle
Vertebrate heart contain 2 or more chambers

11. Single Circulation Found in bony fish, rays and sharks
Two chamber heart
Blood leaving the heart goes through two capillary beds before returning to the heart

13. Double Circulation Found in amphibians, reptiles, and mammals
Oxygen rich and oxygen poor blood are pumped to separate parts of the heart, left and right respectively
Both pump, creating a coordinated pumping cycle
Results in higher blood pressure in the animal
Oxygen rich blood delivers its oxygen through the systemic system

15. Mammals Four chambered heart
The left side deals with oxygen rich blood and the right deals with oxygen poor blood.
Blood loads O2 and unloads CO2 into the capillary beds of the lungs
The aorta provides blood to the heart through the coronary arteries
How the blood returns to the heart is through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs)
Both the superior vena cava and inferior vena cava flow into the right atrium.

16. Mammalian Heart: A Closer Look
A closer look at the heart will provide a better understanding of the double circulation.
When the heart contracts, it pumps blood; when the heart relaxes, its chambers fill with blood
One complete sequence of pumping and filling is called the cardiac cycle
Atria have thin walls and serve as a collective chambers for blood returning to the heart
The lower two chambers of the heart are called ventricles they pump blood from the heart to the body. The volume of blood each ventricle pumps per minute is called the cardiac output.

18. Cardiac Cycle

19. Heart Valves Four heart valves prevent backflow of blood in the heart
Backflow of blood through a defective valve causes a heart murmur
The atrioventricular (AV) valves separate each atrium and ventricle
The semilunar valves control blood flow to the aorta and the pulmonary artery

21. Maintaining the Heart’s Rhythmic Beat
Some of the cardiac cells are autorhythmic, meaning they contract without any signal from the nervous system.
The sinoatrial (SA) node, sets the rate or timing at which all other cardiac muscle cells contract
The SA node produces electrical impulses that spread rapidly through the heart and can be recorded as an electrocardiogram (ECG or EKG)

23. Blood Vessel Structure and Function
A vessel’s cavity is called the central lumen
Endothelium is the epithelial layer that lines blood vessel’s. The endothelium is smooth and minimizes resistance to blood flow.
Capillaries have thin walls, the endothelium and its basal lamina, to facilitate the exchange of substances
Arteries and veins have an endothelium, smooth muscle, and connective tissue
Arteries have thicker walls than veins to make it possible for the high pressure of blood pumped from the heart

25. Changes in Blood Pressure During the Cardiac Cycle
Systole is the contraction phase of the cardiac cycle
Pressure at the time of ventricle contraction is called the systolic pressure
Diastole is the relaxation phase of the cardiac cycle; diastole pressure is lower than the systolic pressure

26. Blood Pressure
Blood pressure is determined by cardiac output and peripheral resistance due to the constriction of arterioles
Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure
Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall
Vasoconstriction and vasodilation help maintain adequate blood flow as the body demands change. Nitric oxide is a major inducer of vasodilation. The peptide endothelin is an important inducer of vasoconstriction.

27. Capillary Function Two mechanisms alter blood flow in capillary beds
Vasoconstriction and vasodilation of the arteriole that supplies a capillary bed
Precapillary sphincters, rings of smooth muscle at the capillary bed entrance, open and close to regulate passage of blood
Critical exchange of substances take place across the thin walls of the capillaries. Blood pressure tends to draw fluid out of the capillaries.

28. Lymphatic System
The lymphatic system returns fluid, called lymph, that leaks out from the capillary beds
The lymphatic system drains into veins in the neck
Valves in lymph vessels prevent backflow of fluid
Lymph nodes are organs that filter lymph and play an important role in the body’s defense

30. Plasma Blood plasma is about 90 percent water
Plasma proteins influence blood pH, osmotic pressure, and viscosity
Particular plasma proteins function in lipid transport, immunity, and blood clotting.

31. Cellular Elements Blood contains two classes of cells
Red blood cells (erythrocytes) transport oxygen
White blood cells (leukocytes) function in defense
Platelets, a third cellular element, are fragments of cells that are involved in clotting

33. Erythrocytes
Red blood cells, or erythrocytes, you have more red blood cells in your body than any other blood cell.
They contain hemoglobin, the iron-containing protein that transports oxygen
Each molecule of hemoglobin binds up to four molecules of O2
In mammals, mature erythrocytes lack a nuclei
Sickle-cell disease is caused by an abnormal hemoglobin that polymerizes into aggregates. The aggregates can distort an erythrocyte into a sickle shape.

34. Leukocytes
There are five different types of white blood cells, or leukocytes
They function in defense by engulfing bacteria and waste or by mounting immune responses against foreign substances
They are found both inside and outside the circulatory system

35. Blood Clotting
Platelets are fragments of cells and function in blood clotting
Coagulation is the formation of a solid clot from liquid blood
A blood clot formed within a blood vessel is called a thrombus and can block blood flow

37. Cardiovascular Disease
Cardiovascular disease are disorders of the heart and the blood vessels
Low-density lipoprotein (LDL) delivers cholesterol to cells for membrane production
High-density lipoprotein (HDL) scavenges excess cholesterol for return to the liver
Risk for heart disease increases with a high LDL to HDL ratio
Inflammation is also a factor in cardiovascular disease

38. Atherosclerosis, Heart Attack, and Stroke
One type of cardiovascular disease, atherosclerosis, is caused by the buildup of fatty deposits within arteries
A fatty deposit is called a plaque; as it grows, the artery walls become thick and stiff and the obstruction of the artery increases

40. A heart attack, or myocardial infarction, is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
Coronary arteries supply oxygen-rich blood to the heart muscle
A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head
Angina pectoris is caused by partial blockage of the coronary arteries and may cause chest pain

41. Risk Factors
Having a high LDL to HDL ratio will increase risk of getting cardiovascular disease.
Smoking increases the ratio of LDL to HDL as well as consuming trans fat, while exercising decreases it.
Statins are drugs that reduce the levels of LDL
High blood pressure, called hypertension, can contribute to the risk of heart attack and stroke.

42. Gas Exchange
The uptake of O2 from the environment and the discharge of CO2 is known as gas exchange.
Partial pressure is the pressure exerted by a specific gas in a mixture of gases. Partial pressures also apply to gases dissolved in liquid, like water.
When water is exposed to air, an equilibrium is reached in which the partial pressure of each gas is the same in the water and the air.
A gas always undergoes net diffusion from a region of higher partial pressure to a region of lower partial pressure.

43. Respiratory Surface
Gas exchange across a respiratory surface takes place by diffusion
Respiratory surfaces are always moist tend to be large and thin
Varys by animal and can include the skin, gills, and lungs

44. Gills in Aquatic Animals
Gills create a large surface area for gas exchange
Ventilation is the movement of the respiratory medium over the respiratory surface. Aquatic animals move through water or move water over their gills for Ventilation
Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills

46. Lungs
Lungs are an infolding of the body surface, usually divided into many pockets
The circulatory system transports gases between the lungs and the rest of the body.
The uses of lungs for gas exchange varies among vertebrates that lack gills
Lungs have a vital capacity which is the maximum volume of air that can be expelled from your lungs after filling them completely.

47. Mammalians Respiratory System: A Closer Look
A system of branching ducts conveys air to the lungs
The pharynx directs food to the stomach and air to the lungs
Exhaled air passes over the vocal cords in the larynx to create sounds
“Mucus escalator” cleans the respiratory system that allows particles to be swallowed into the esophagus
Gas exchange takes place in the alveoli, air sacs at the tip of the bronchioles

49. Lung alveoli are at the ends of the the respiratory “tree”
Lung alveoli are at the ends of the the respiratory “tree”. They are a transfer zone for gas. The oxygen and carbon dioxide are transferred from blood by diffusion through alveolar blood vessels.
Looking at the bronchioles in specific...
Pulmonary surfactant is released into the alveolar space by epithelial cells.
Pulmonary surfactant lowers surface tension between air and liquid.

50. Breathing ventilates the lungs
Breathing ventilates the lungs. An amphibian as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea
Birds have eight or nine air sacs that function as bellows that keep air following through the lungs
In birds air passes through the lungs in only one direction
Passage of air through the lungs and air sacs require two cycles inhalation and exhalation.

51. How a Mammal Breathes
Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs
Lung volume increases as the ribs muscles and diaphragm contract
The tidal volume is the volume of air inhaled with each breath
After exhalation, residual volume of air remains in the lungs

53. Respiratory Pigments
Circulates in blood or hemolymph and greatly increase the amount of oxygen transported
The Respiratory pigment of almost all vertebrates and many invertebrates is hemoglobin
A single hemoglobin molecule can carry four molecules of O2, one molecule for each iron containing heme group
Hemoglobin binds oxygen reversibly, loading it in the gills or lungs and releasing it in other parts of the body.
CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2; this is called Bohr shift

54. Respiratory Adaptations of Dividing Mammals
These animals have a high blood to body volume ratio
Deep-diving air breathers can store large amount of O2
Oxygen can be stored in their muscles in myoglobin proteins
Diving mammals also conserve oxygen by: decreasing blood supply to muscles and deriving ATP in muscles from fermentation once oxygen is depleted.

55. THE END