Circulation and Gas Exchange AP Biology

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Capillary Exchange

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

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

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

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

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

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

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

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

                                                                                             

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

Gas Exchange Involves both Respiratory system and Circulatory system

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

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

Fish

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

Amphibians Simple air sac with little surface area Must supplement gas exchange in lungs with exchange across the thin moist skin http://www.answersingenesis.org/home/area/magazines/images/v22frogR.jpg

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 http://numbat.murdoch.edu.au/Anatomy/avian/fig3.2.GIF http://people.eku.edu/ritchisong/RITCHISO/birdrespiration.html

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 http://people.eku.edu/ritchisong/RITCHISO/birdrespiration.html

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.

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.

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).

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.

Ventilating Lungs: Breathing

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

Loading and Unloading of Respiratory Gases

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.

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

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

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