Circulation and Gas Exchange - Flashcards

Components of Blood

• Blood is a connective tissue with a fluid matrix called plasma, containing cells and formed elements.

• Functions of blood:

  1. Transportation of materials.

  2. Regulation of body functions.

  3. Protection from injury and invasion.

Blood Components

1. Red blood cells (erythrocytes):

   • Contain hemoglobin for oxygen transport.

   • Mature mammalian erythrocytes lack nuclei.

2. White blood cells (leukocytes):

   • Larger than erythrocytes and have nuclei.

   • Can migrate out of capillaries. a. Granular leukocytes:

     • Neutrophils, eosinophils, and basophils (named by staining properties).
       b. Agranular leukocytes:

     • Monocytes and lymphocytes.

3. Platelets:

   • Function in blood clot formation.

Blood Composition

• Blood = Plasma + RBCs + WBCs + platelets

• Plasma: Blood without cells.

• Serum: Plasma without clotting factors.

Hematopoiesis

• All formed elements develop from pluripotent stem cells.

• Hematopoiesis: Blood cell production in bone marrow.

Mammalian Blood Composition

• Plasma: 55% (water, ions, proteins like albumin and immunoglobulins, transported substances).

• Cellular elements: 45% (leukocytes, platelets, erythrocytes).

Leukocytes

• Number per microliter: 5,000-10,000.

• Functions: Defense and immunity.

• Types: Lymphocytes, basophils, neutrophils, eosinophils, monocytes.

Platelets

• Number per microliter: 250,000-400,000.

• Function: Blood clotting.

Erythrocytes

• Number per microliter: 5,000,000-6,000,000.

• Function: Transport of O2 and some CO2.

Hematopoiesis Details

• Lymphoid stem cell -> Lymphocytes.

• Myeloid stem cell -> All other blood cells.

• Erythropoiesis: Red blood cell production.

  • Kidney produces erythropoietin, stimulating erythrocyte production.

  • Old cells/fragments are digested in the spleen; iron and amino acids are recycled.

Cell Division and Differentiation

• Blastomeres: Nondifferentiated cells.

Stem Cells

• Tissue-specific: Give rise to one tissue.

• Pluripotent: Give rise to multiple cell types.

• Totipotent: Give rise to any cell type.

Cell Fate

• Determination: Cell commitment to a specific fate.

• Differentiation: Resulting specialization in structure and function.

Mitotic Cell Division

• Cleavage divisions: Rapid mitotic divisions increasing cell number but not size.

• Stem cell divisions: Replenish needed cells like blood cells.

• Patterning divisions: Daughter cells take on different fates.

Circulatory Systems

• Link exchange surfaces with cells throughout the body.

• Simple body plans: Cells in direct contact with the environment.

• Most animals: Circulatory system linked to gas exchange and body cells.

Direct Exchange

• Some animals exchange directly with the environment.

Invertebrate Circulatory Systems

• Sponges, cnidarians, and nematodes lack a separate circulatory system.

  • Sponges: Water circulation via ostia (incurrent pores) and osculum (excurrent pore).

  • Hydra/Cnidarians: Water circulation via gastrovascular cavity (also for digestion).

  • Nematodes: Use digestive tract as circulatory system.

Larger Animals

• Require separate circulatory system for nutrient/waste transport due to thick tissues.

Types of Circulatory Systems

• Open circulatory system: No distinction between circulating and extracellular fluid (hemolymph).

• Closed circulatory system: Distinct circulatory fluid enclosed in blood vessels.

Components of Circulatory System

• Circulatory fluid.

• Interconnecting vessels.

• Muscular pump (heart).

Open vs. Closed

• Open: Hemolymph bathes organs directly (insects, arthropods, some molluscs).

• Closed: Blood confined to vessels (annelids, cephalopods, vertebrates).

Open Circulation in Insects

• Hemolymph pumped from tubular heart into body cavities, then returns to vessels.

Closed Circulation in Earthworms

• Blood pumped from hearts remains within vessels.

• All vertebrates have closed circulatory systems.

Vertebrate Circulatory Systems

Single Circulation

• Sharks, rays, bony fishes have single circulation with a two-chambered heart.

• Blood passes through two capillary beds before returning to the heart.

Fish Heart

• Evolved a true chamber-pump heart.

• Four structures form two pumping chambers: Sinus venosus, atrium, ventricle, conus arteriosus.

• Contraction sequence: sinus venosus -> atrium -> ventricle -> conus arteriosus.

• Blood flows through gills, then to the body.

• Electrical impulse initiates in the sinus venosus (SA node in other vertebrates).

Double Circulation

• Amphibians: Pulmonary circulation (heart and lungs) and systemic circulation (heart and body).

• Pulmonocutaneous circuit in amphibians sends blood to lungs and skin.

Frog Heart

• Three-chambered heart (two atria, one ventricle).

• Oxygenated and deoxygenated blood mix very little.

Reptile Heart

• Septum partially subdivides the ventricle.

Mammalian, Bird, and Crocodilian Heart

• Four-chambered heart (two atria, two ventricles).

• Right atrium: Receives deoxygenated blood and delivers it to the right ventricle -> lungs.

• Left atrium: Receives oxygenated blood and delivers it to the left ventricle -> rest of the body.

Evolutionary Variation

• Four-chambered heart in mammals and birds separates oxygen-rich and oxygen-poor blood.

• Endotherms require more energy than ectotherms.

Cardiovascular System of Vertebrates

• Humans have a closed cardiovascular system with a heart and blood vessels.

• Three types of blood vessels: arteries, veins, capillaries.

• Blood flows one way.

Blood Vessel Organization

• Arteries -> arterioles -> capillaries (chemical exchange between blood and interstitial fluid).

• Capillaries converge into venules -> veins.

Arteries vs Veins

• Distinguished by blood flow direction, not oxygen content.

• Hearts have atria (blood entry) and ventricles (blood exit).

Mammalian Circulation

• Right ventricle pumps blood to lungs via pulmonary arteries.

• Oxygen-rich blood returns to the left atrium via pulmonary veins.

• Left ventricle pumps blood to body tissues via the aorta.

• Coronary arteries supply the heart muscle.

• O2 diffuses from blood to tissues, CO2 diffuses from tissues to blood.

• Capillaries rejoin to form venules -> veins.

• Superior vena cava: Drains head, neck, and forelimbs.

• Inferior vena cava: Drains trunk and hind limbs.

• Venae cavae empty into the right atrium.

Cardiac Cycle

Two Contraction Cycles

1. Atrial contraction.

2. Ventricular contraction.

• Includes resting period.

Systole and Diastole

• Systole: Contraction or pumping phase.

• Diastole: Relaxation or filling phase.

Heart Valves

Atrioventricular (AV) Valves

• Between atria and ventricles.

  • Tricuspid (right).

  • Bicuspid or mitral (left).

Semilunar Valves

• Guard exits from ventricles.

  • Pulmonary (right).

  • Aortic (left).

Lub-Dub Sounds

• Lub: AV valves close during ventricular contraction.

• Dub: Semilunar valves close during ventricular relaxation.

Blood Flow

• Right and left pulmonary arteries deliver deoxygenated blood to the lungs.

• Pulmonary veins return oxygenated blood to the left atrium.

• Aorta and its branches (systemic arteries) carry oxygen-rich blood to the body.

• Superior vena cava drains upper body.

• Inferior vena cava drains lower body.

Blood Pressure Measurement

Sphygmomanometer

• Systolic pressure: Peak pressure during ventricular contraction.

• Diastolic pressure: Minimum pressure between heartbeats.

• Typical blood pressure: 120/75 mm Hg.

Heartbeat Initiation

• Autorhythmic cells initiate heart muscle contraction.

• Sinoatrial (SA) node: Pacemaker in right atrium wall.

SA Node

• Produces spontaneous action potentials.

• Depolarization travels to the atrioventricular (AV) node.

• Conducted over ventricles by atrioventricular bundle (bundle of His).

• Relayed to Purkinje fibers stimulating myocardial cells to contract.

Electrocardiogram (ECG or EKG)

• P wave: Atrial depolarization (atrial systole).

• QRS complex: Ventricular depolarization (ventricular systole).

• T wave: Ventricular repolarization (ventricular diastole).

Pacemaker Regulation

• Sympathetic division speeds up pacemaker.

• Parasympathetic division slows down pacemaker.

Blood Vessels

Types

Arteries

• Carry blood away from the heart.

Arterioles

• Microscopic branches of the arterial tree.

Capillaries

• Where blood from arterioles enters.

Venules

• Collect blood.

Veins

• Carry blood back to the heart.

Structure

All Vessels

• Endothelium-lined lumen (minimizes resistance).

Capillaries

• Thin walls (endothelium + basal lamina).

Arteries and Veins

• Endothelium, smooth muscle, connective tissue.

Arteries

• Thick, elastic walls (high pressure).

Veins

• Thinner walls, valves (unidirectional flow).

Tissue Layers

• Endothelium, elastic fibers, smooth muscle, and connective tissue.

Capillaries

• Single layer of endothelial cells.

Blood Pressure

Systolic Pressure

• Pressure in arteries during ventricular systole.

Diastolic Pressure

• Pressure in arteries during diastole.

Regulation

• Homeostatic mechanisms alter arteriole diameter.

Vasoconstriction

• Narrowing of arteriole walls increases blood pressure.

Vasodilation

• Increased diameter of arterioles causes blood pressure to fall.

Veins and Venules

Characteristics

• Thinner smooth muscle layer.

• Return blood via skeletal muscle contractions and venous valves.

Lymphatic System

Components

• Lymphatic capillaries, vessels, nodes, and organs.

• Excess fluid drains into lymph capillaries -> larger vessels (one-way valves) -> subclavian veins.

• Lymph nodes contain germinal centers (lymphocyte activation).

Cardiovascular Diseases

Heart Attacks (Myocardial Infarctions)

• Insufficient blood supply to the heart.

Angina Pectoris

• Chest pain (less severe than a heart attack).

Stroke

• Interference with blood supply to the brain.

Atherosclerosis

• Accumulation of fatty material within arteries.

Arteriosclerosis

• Arterial hardening due to calcium deposition.

Blood Flow and Blood Pressure Regulation

Autonomic Nervous System

• Norepinephrine (sympathetic) increases heart rate.

• Acetylcholine (parasympathetic) decreases heart rate.

Cardiac Output (CO)

• Volume of blood pumped per ventricle per minute.

• Increases during exertion.

• Arterial blood pressure (BP) = CO x Resistance (R).

• BP = CO
  eq R

Baroreceptor Reflex

• Negative feedback loop responding to BP changes.

• Baroreceptors detect changes in arterial BP.

• Decreased BP -> decreased impulses to cardiac center -> BP increase.

• Increased BP -> increased impulses to cardiac center -> BP decrease.

Blood Volume Regulation

Hormones

• Antidiuretic hormone (ADH).

• Aldosterone.

• Atrial natriuretic hormone.

• Nitric oxide (NO).