Circulatory System

Open vs. Closed Circulatory Systems

The circulatory system is responsible for transporting nutrients, gases, and wastes throughout the body. Animals may have either open or closed circulatory systems, each with distinct features and evolutionary advantages.

• Closed Circulatory System: Blood is confined to vessels and pumped by a heart. Found in vertebrates (e.g., humans, fish, birds) and some invertebrates (e.g., earthworms).

• Open Circulatory System: Blood-like fluid (hemolymph) bathes organs directly in a body cavity called the hemocoel. Found in arthropods (e.g., insects) and most mollusks.

• Example: In grasshoppers, all tissues are bathed in hemolymph, and gas exchange occurs via tracheal tubes, not the circulatory system.

Vertebrate Circulation

Vertebrates have a closed circulatory system that efficiently transports oxygen and carbon dioxide between the lungs/gills and body tissues.

• Left Ventricle: Pumps oxygenated blood to the body (systemic circuit).

• Right Atrium & Ventricle: Receive deoxygenated blood and pump it to the lungs (pulmonary circuit).

• Aorta: The major artery leaving the left ventricle, distributing oxygenated blood.

Heart Chambers by Animal Group

The number and arrangement of heart chambers vary among vertebrate groups, affecting the separation of oxygenated and deoxygenated blood.

Blood Pressure & Valves

• Blood Pressure: Expressed as systolic/diastolic (e.g., 120/70 mmHg). Diastolic (70 mmHg) is the pressure during heart relaxation.

• Semilunar Valve: Located between the right ventricle and pulmonary artery, prevents backflow.

• Cardiac Cycle: Alternating contraction (systole) and relaxation (diastole) of heart chambers.

• SA Node: The pacemaker of the heart; initiates the heartbeat by stimulating the atria.

Blood Cells and Components

• Erythrocytes (Red Blood Cells): Most abundant; transport O2 via hemoglobin (each binds 4 O2 molecules). Lifespan ≈ 120 days.

• Plasma: ~90% water; carries dissolved gases, hormones, proteins, nutrients.

• Leukocytes (White Blood Cells): Defend against pathogens.

• Platelets: Cell fragments involved in blood clotting.

• Thrombin: Enzyme that converts fibrinogen to fibrin during clot formation.

Blood & Health

• Iron: Essential for hemoglobin; females need more due to menstruation.

• Blood Doping: Increases RBC count to enhance O2 delivery (used by some athletes).

• High Altitude: Stimulates erythropoietin (EPO) production, increasing RBCs.

• HDL: High-density lipoprotein, considered "good cholesterol."

• Atherosclerosis: Plaque buildup narrows arteries, increasing risk of heart disease.

• Hypertension: High blood pressure; risk factor for atherosclerosis.

Lymphatic System

• Function: Returns interstitial fluid to the circulatory system; fluid is called lymph inside lymph vessels.

• Immunity: Lymphatic organs (spleen, thymus) play roles in immune defense.

• Fat Absorption: Absorbs fats from the small intestine via lacteals.

• Not a Function: Does not transport oxygen to the lungs.

Respiratory System

General Gas Exchange

Respiration involves the exchange of O2 and CO2 across specialized, moist surfaces. Efficient gas exchange requires thin, moist membranes with a large surface area, often associated with capillaries.

• Diffusion: Gases move across membranes from high to low concentration.

• Bulk Flow: Movement of air or blood in large volumes (e.g., breathing, circulation).

Respiratory Structures by Organism

• Operculum: Bony flap protecting fish gills.

• Epiglottis: Prevents food from entering the airway during swallowing.

Breathing & Control

• Mechanism: Air moves into lungs by bulk flow due to pressure differences.

• Trachea: Supported by C-shaped cartilage rings to prevent collapse.

• Respiratory Center: Located in the medulla oblongata; responds primarily to increased CO2 levels.

• Surfactant: Reduces surface tension, preventing alveolar collapse.

• Control: Breathing is involuntary but can be consciously overridden for short periods.

Human Gas Transport

• Oxygen: Transported mainly bound to hemoglobin in RBCs.

• Carbon Dioxide: Transported primarily as bicarbonate ions () in plasma.

• Equation for CO2 Transport:

Smoking Effects

• Smoker’s Cough: Caused by mucus accumulation due to damaged cilia.

• Secondhand Smoke: Increases risk of respiratory and cardiovascular diseases.

• Quitting: Health improvements begin almost immediately after cessation.

Nutrition & Digestion

Nutrition Basics

Animals require nutrients for energy, growth, and maintenance. Macronutrients include carbohydrates, fats, and proteins, while micronutrients include vitamins and minerals.

• Carbohydrates & Fats: Primary energy sources.

• Proteins: Used for structure and as a backup energy source.

• Glycogen: Stored form of glucose in liver and muscle.

• Minerals: Calcium and phosphorus are important for bone health.

• Vitamins: Vitamin C (ascorbic acid) cannot be synthesized by humans; vitamin K is produced by gut bacteria.

• Cellulose: Most abundant carbohydrate; structural component in plants.

Digestive Systems by Organism

Human Digestion Highlights

• Mouth: Salivary amylase begins starch digestion.

• Stomach: Highly acidic (pH ≈ 2); initiates protein digestion.

• Small Intestine: Main site for digestion and nutrient absorption.

• Large Intestine: Absorbs water, produces vitamin K, compacts feces.

• Pancreas: Secretes bicarbonate to neutralize stomach acid.

• Hormones:

  • Gastrin: Stimulates gastric glands.

  • Cholecystokinin (CCK): Triggers bile and pancreatic juice release.

  • Secretin: Stimulates bicarbonate release from pancreas.

• Fat Absorption: Fats are absorbed as chylomicrons into lacteals (lymphatic vessels).

Excretion & Osmoregulation

Nitrogenous Wastes

Animals excrete nitrogenous wastes produced from protein and nucleic acid metabolism. The form of waste depends on the animal's habitat and evolutionary adaptations.

• Liver: Converts toxic ammonia to less toxic urea in mammals.

• Birds/Insects: Excrete uric acid, a water-conserving, paste-like substance.

Excretory Structures by Organism

Human Urinary System

• Urine Pathway: Renal pelvis → ureter → bladder → urethra.

• Nephron Flow: Glomerular capsule → proximal tubule → loop of Henle → distal tubule → collecting duct.

• Glomerular Filtration: Driven by blood pressure; filters plasma into nephron.

• Reabsorption: Nutrients and ions are reabsorbed into peritubular capillaries.

• Normal Filtrate: Should not contain proteins or blood cells.

Hormonal Regulation

• Distal Tubule: Main site of hormonal regulation of water and salt balance.

• ADH (Antidiuretic Hormone): Promotes water reabsorption; inhibited by alcohol.

• Aldosterone: Increases sodium reabsorption.

• Renin & Angiotensin: Increase blood pressure.

• Erythropoietin (EPO): Produced by kidneys; stimulates RBC production.

Adaptations

• Desert Mammals: Have long loops of Henle to maximize water reabsorption.

• Average Urine Output: Approximately 1.5 liters per day in humans.