1. Circulation and Gas Exchange
AP Biology

2. Invertebrate Open Circulatory System
Arthropods and mollusks
Blood and interstitial fluid are the same (hemolymph)
Tubular heart pumps hemolymph through a dorsal vessel out into sinuses
Hemolymph bathes cells and allows for exchange of nutrients
When heart relaxes, hemolymph flows back into vessels through ostia
Body movements squeeze sinuses to aid circulation

3. Invertebrate Closed Circulatory System
Annelids (earthworms) have closed circulatory system
5 Aortic arches or ‘hearts’ force blood down to the ventral vessel, which carries blood to posterior and up to complete the circuit
Blood carries O2 and CO2 between cells and the skin where gas exchange takes place
Blood also circulates nutrients from digestive tract to the rest of the body

4. Vertebrate Circulatory System
Closed system with a chambered heart that pumps blood through arteries that lead away from the heart to capillaries.
Capillaries—small vessels in tissues where exchange of materials take place
Blood is carried back to heart through veins

5. Fish
2 chamber heart
One artrium
One ventricle
Blood from ventricle picks up O2 in gills, then is collected into a large artery to pass directly to the rest of the body before returning to the atrium

6. Amphibian 3 chamber heart
Two artria
One ventricle
Ventricle pumps blood to both the lungs and the rest of the body simultaneously through 2 different major arteries
Allows oxygenated blood from lungs and deoxygenated blood from the body to mix in the ventricle before it is delivered back to the body
Allows higher arterial pressure in blood pumped to vessels

7. Birds and Mammals 4 chamber heart
Two artria
Two ventricle
Higher metabolic need met by division of heart into 2 pumps
Right atrium and ventricle pumps deoxygenated blood to lungs through pulmonary circulation
Left atrium and ventricle pumps oxygenated blood to the rest of the body through systemic circulation
Avoids mixing of oxygenated and deoxygenated blood
Allows high arterial pressure required for quick delivery

8. Human Heart Located beneath the sternum About the size of your fist
Composed mostly of cardiac muscle tissue
2 atria have thin walls and function as collection chambers for returning blood
2 ventricles have thick, powerful walls that pump blood to the organs

10. Four valves function to prevent backflow of blood
Atrioventricular valves
Prevent backflow when ventricles contract
Semilunar valves
Prevent backflow when ventricles relax

11. Cardiac Cycle
Systole—heart muscles contract and the chambers pump blood
Diastole—heart muscles relax and fills with blood
Cardiac output—volume of blood per minute that the left ventricle pumps into the systemic circuit

12. Control of Heart Rhythm
Sinoatrial (SA) node—cells are self-excitable—generate electrical impulses
Cardiac muscle cells are electrically coupled by intercalated discs b/w cells

13. Control of Heart Rhythm
Atrioventricular (AV) node—receives signal from atria, delays 0.1 sec, and then sends signal throughout walls of ventricle via the bundle branches and Purkinje fibers

14. Blood Vessels Arteries—carry blood away from the heart to the tissues
Branch into smaller arterioles, which supply blood to tissues via capillaries
Thick-walled, muscular (smooth muscle), and elastic, transporting blood at high pressure
Blood is oxygenated, except the pulmonary artery that carries deoxygenated blood from tissues to lungs through the right atrium and ventricle

15. Veins—carry blood to the heart from the capillaries
Capillaries branch into larger venules, which supply blood to veins and back to the heart
Thin-walled, little smooth muscle, transporting blood at low pressure, and contain many valves to prevent backflow
Veins have no pulse and carry deoxygenated blood, except the pulmonary vein which carries oxygenated blood from the lungs
Skeletal muscle contraction aids in systemic circulation

17. Capillaries—thin-walled vessels (simple squamous)
Permit exchange of materials between blood and body cells
Controlled by precapillary sphincters

18. Capillaries
Fluid containing water with nutrients and hormones seep from capillaries into tissues, driven by pressure
Cells and proteins are retained in the capillaries and draw water back into the capillaries by osmosis
Excess fluid in tissue can enter lymphatic system to be filtered and cycled back to the circulatory system

20. Capillary Exchange

21. Regulation of Blood Flow
Regulated to match the metabolic needs
Smooth muscle in walls of arterioles constrict to reduce blood flow to capillaries
Smooth muscle relaxes when blood leaving capillaries is low in O2, allowing more blood to flow through capillary bed

22. Regulation of Blood Flow
Secretion of epinephrine by adrenal glands  heart rate and constricts arteries to  arterial pressure
Angiotensin secreted from the kidney acts on smooth muscle in the arterioles and arteries to cause constriction and  arterial pressure
Vasopressin secreted by posterior pituitary in response to stretch sensors causes constriction in arterioles and arteries to  arterial pressure

24. Erythrocytes: Red Blood Cells
Primary function to carry oxygen
Production in red bone marrow of bones stimulated by erythropoietin (produced by kidneys)
Mature cells lack nuclei and circulate ~4mos.
Mature cells lack mitochondria—produce ATP without oxygen through glycolysis
Contain hemoglobin-pigment that binds oxygen

25. Erythrocytes: Red Blood Cells
Red blood cells (rbc) manufacture 2 antigens, antigen A (Blood Type A) and antigen B (Blood Type B)
Plasma carries antibodies for the antigens that are not present on the rbcs

26. Leukocytes: White Blood Cells
Involved in immune functions in the body
Phagocytes—engulf bacteria
Neutrophils—1st to arrive at site of inflammation
Macrophages and Monocytes
Lymphocytes (B and T cells)—immune response
B cells produce antibodies
Helper T cells kill infected cells

28. Leukocytes: White Blood Cells
Platelets—cell fragments produced in marrow
Involved in blood clotting mechanism
Activation of protease thrombin cleaves fibrinogen protein in the blood to make fibrin that polymerizes to for a net across the wound, trapping more cells and blocking the flow of blood

29. Cardiovascular Disease
Heart attack—death of cardiac muscle tissue resulting from artery blockage of one or more coronary arteries which supply oxygen to the heart
Stroke—death of nervous tissue in the brain resulting from artery blockage in the head

31. Cardiovascular Disease
Atherosclerosis—plaques develop on inner walls of arteries
Forms where smooth muscle thickens abnormally and is infiltrated by fibrous connective tissue
Arteriosclerosis—hardening of the arteries by calcium deposits
Hypertension—high blood pressure

33. Cardiovascular Disease
Hypertension and atherosclerosis have genetic component and environmental component (smoking, lack of exercise, high fat and cholesterol diet)
Low-density lipoproteins (LDLs)—add deposits of cholesterol in arterial plaques
High-density lipoproteins (HDLs)—may reduce cholesterol deposition
Exercise increases HDL concentration
Smoking increases LDL concentration

34. Gas Exchange
Involves both Respiratory system and Circulatory system

35. Invertebrate Gas Exchange
Water contains less oxygen than air
As an adaptation, most aquatic animals have gills
Total surface area of gills is often larger than that of the rest of the body

36. Invertebrate Gas Exchange
Arthropods respiratory system consists of a series of respiratory tubules, tracheae
Open to the outside in the form of pairs of orifices called spiracles
Tracheae subdivide into smaller and smaller branches, to make close contact with most cells
Direct diffusion through tracheae is one factor that limits body size in arthropods

37. Fish

38. Countercurrent Exchange
Maximizes exchange of gases between blood inside the gills and the water flowing over the gills
Blood flows through capillaries in direction opposite of water flowing across gills

39. Amphibians Simple air sac with little surface area
Must supplement gas exchange in lungs with exchange across the thin moist skin

40. Avian Respiration
Air sacs permit a unidirectional flow of air through the lungs
Unidirectional flow means that air moving through bird lungs is largely 'fresh' air & has a higher oxygen content

41. Air Flow through Avian System
On first inhalation, air flows through the trachea & bronchi & primarily into the posterior (rear) air sacs
On exhalation, air moves from the posterior air sacs & into the lungs
With the second inhalation, air moves from the lungs & into the anterior (front) air sacs
With the second exhalation, air moves from the anterior air sacs back into the trachea & out
Air flow is driven by changes in pressure within the respiratory system:
So, it takes two respiratory cycles to move one 'packet' of air completely through the avian respiratory system

42. The conducting components of the respiratory system include: Nasal cavity and paranasal sinuses, pharynx, larynx, trachea, bronchi, distributing bronchioles. The conducting components function to conduct air to the lungs, as well as to clean, humidify and adjust its temperature before it reaches the lungs.   The respiratory components include: Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli. The respiratory components function in the exchange of gas. Air enters the respiratory system through the nose and mouth and passes down the throat (pharynx) and through the voice box (larynx). The entrance to the larynx is covered by a small flap of muscular tissue (epiglottis) that closes when swallowing, thus preventing food from entering the airway. The largest airway is the windpipe (trachea), which branches into two smaller airways (bronchi) to supply the two lungs. The bronchi themselves divide many times before evolving into smaller airways (bronchioles). These are the narrowest airways—one fiftieth of an inch across. At the end of each bronchiole are dozens of bubble-shaped, air-filled cavities (alveoli) that resemble bunches of grapes. Each lung contains millions of alveoli, and each alveolus is surrounded by a dense network of capillaries. The extremely thin walls of the alveoli allow oxygen to move from the alveoli into the blood in the capillaries and allow carbon dioxide to move from the blood in the capillaries into the alveoli.

43. Here can be seen the progressive transition from terminal bronchiole (T) to respiratory bronchiole (R) to alveolar duct (AD) to alveolar sac (AS) to alveolus (A). Respiratory bronchioles are similar in structure to terminal bronchioles, except that their wall is interrupted by alveoli. Alveolar ducts do not have walls of their own. They are simply linear arrangements of alveoli. Each one ends as a blind out-pouching of two or more small clusters of alveoli, where each cluster is known as an alveolar sac. Alveoli are the terminal air spaces of the respiratory system and are the site of gas exchange. Emphysema is shortness of breath due to destruction of alveoli, caused by chronic inhalation of foreign particulate matter, most commonly from smoking.

44. After the trachea, inspired air passes to the bronchi, distributing bronchioles, respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli. (Gas exchange occurs in alveoli, which first appear on the respiratory bronchioles).

45. The alveolar wall consists of epithelial cells, supporting tissue and capillaries. The epithelium consists of two cell types, type I and type II pneumocytes. Type I pneumocytes (PI) are thin, squamous cells that represent 95% of the alveolar lining. Gas exchange occurs across their membrane. Type II pneumocytes (P2), interspersed among the Type I cells, secrete surfactant that reduces surface tension within the alveoli, preventing alveolar collapse during expiration. Left: Two alveoli and their cellular components. PI: nucleus of type I pneumocyte; P2: type II pneumocyte; E: nucleus of capillary endothelial cell; C: capillary; M: alveolar macrophage. Upper right: Vascular cast, showing the capillaries surrounding an alveolus. Lower right: Close up view of an alveolar wall, showing red blood cells passing by a type II pneumocyte. To get into the capillary, gas must cross the air-blood barrier, which consists of the type I pneumocyte (cytoplasm indicated by asterisks), the basal lamina (BL) and the endothelial cell (En) lining the capillary.

46. Ventilating Lungs: Breathing

47. Automatic Control of Breathing
Breathing control center in brain = medulla oblongata and pons
Monitors CO2 levels in blood by changes in pH
CO2 + H2O  Carbonic acid
 pH =  depth and rate of breathing
altitude =  O2 levels
Sensors in aorta and carotid arteries detect and signal control center to  breathing rate

48. Loading and Unloading of Respiratory Gases

49. The site of gas exchange is shown at high magnification in the lower figure from a different preparation. PI: Cytoplasm of a type I pneumocyte; BM: Basement membrane; E: Cytoplasm of a capillary endothelial cell; Er: Erythrocyte in capillary lumen.

50. Oxygen Transport Oxygen carried by respiratory pigments
Invertebrates utilize hemocyanin—Cu is the oxygen-binding component
Vertebrates utilize hemoglobin—four heme groups surrounding an Fe atom
Can carry four oxygen atoms

51. Oxygen Dissociation Curves for Hemoglobin
Bohr Shift:
Active tissue releases CO2
CO2 reacts with H2O to form carbonic acid
This ↓ pH which induces hemoglobin to release more O2

52. Carbon Dioxide Transport
Hemoglobin transports CO2 and assists with buffering the blood—prevents dramatic changes in pH
7% CO2 released by cells transported as dissolved CO2
23% binds to amino group of hemoglobin
70% transported in form of bicarbonate ions in red blood cells