Unit 3 all notes

Digestive System: Structure and Function

  • Mouth

    • Structure & Function: Responsible for both mechanical and chemical digestion of food. Saliva mixes with food to form a food ball known as a bolus.

  • Tongue

    • Structure & Function: Functions in taste, as well as in moving, mixing, and positioning food for chewing and swallowing.

  • Teeth

    • Structure & Function: Cuts and crushes food, increasing its surface area and mixing it thoroughly with saliva.

  • Salivary Glands

    • Structure & Function: Produces approximately 1 L1\,\text{L} of saliva per day. Includes the parotid, submandibular, and sublingual salivary glands. Saliva contains salivary amylase, an enzyme that initiates the hydrolysis of starch into maltose.

  • Pharynx (Throat)

    • Structure & Function: Serves as a common passageway for both the food bolus moving to the esophagus and air entering the trachea. The swallowing reflex takes place here.

  • Epiglottis

    • Structure & Function: A flap of tissue that meets with the glottis during swallowing. It covers the opening to the trachea to ensure food moves into the esophagus rather than the respiratory tract.

  • Esophagus

    • Structure & Function: A muscular tube approximately 25 cm25\,\text{cm} in length. Smooth muscle contractions, termed peristalsis, propel the food bolus toward the stomach.

  • Cardiac Sphincter

    • Structure & Function: A ring of muscle located at the entrance to the stomach. It retains digested food (acid chyme) within the stomach, preventing acid reflux during gastric digestion.

  • Stomach

    • Structure & Function: A muscular organ that performs mechanical churning and chemical digestion. Produces hydrochloric acid (HCl\text{HCl}) that lowers stomach pH, activating pepsinogen into pepsin to digest proteins into peptides.

  • Pyloric Sphincter

    • Structure & Function: A muscular ring that controls the volume of acid chyme entering the duodenum by releasing small quantities at regular intervals.

  • Duodenum

    • Structure & Function: The initial section of the small intestine, critical for digestion and nutrient absorption. Produces enzymes such as maltase and peptidases. Receives pancreatic secretions (enzymes and sodium bicarbonate) and bile from the liver/gallbladder. Sodium bicarbonate neutralizes stomach acid, and bile emulsifies fats. Nutrient absorption is enhanced by internal villi.

  • Gallbladder

    • Structure & Function: Stores bile synthesized by the liver for the physical emulsification of fats and lipids.

  • Pancreas

    • Structure & Function: Synthesizes pancreatic juice containing multiple digestive enzymes and sodium bicarbonate, which neutralizes acid chyme entering the small intestine.

  • Small Intestine

    • Structure & Function: The major site essential for final chemical digestion and absorption of nutrients into the circulation.

  • Appendix

    • Structure & Function: A projection extending from the cecum at the entrance to the large intestine. Plays a supportive role in human immune functions.

  • Large Intestine (Colon)

    • Structure & Function: Key organ for the absorption of water and electrolytes, as well as the production of specific vitamins by resident bacteria.

  • Rectum

    • Structure & Function: Functions in the temporary storage of feces prior to elimination during defecation.

  • Anus

    • Structure & Function: Terminal sphincter mechanism involved in the execution of the defecation reflex.

Digestion from Mouth to Stomach

  • Mechanical Digestion versus Chemical Digestion

    • Mechanical Digestion: Physical breakdown of food into smaller particles. Teeth cut and crush food, while the tongue moves, mixes, and positions food for chewing and swallowing.

    • Chemical Digestion: Cleavage of chemical bonds using enzymes to convert polymers into absorbable monomers. In the mouth, salivary amylase breaks down starch molecules into maltose disaccharides.

  • Sequential Events from Mouth to Esophagus

    • Mouth: Teeth mechanically crush food while the tongue positions it and mixes it with saliva. Salivary amylase begins digesting starch to maltose.

    • Pharynx: Acts as a shared passageway for food and air. During swallowing, the soft palate pushes downward while the trachea moves upward, bringing the glottis and epiglottis together to seal off the airway.

    • Esophagus: A 25 cm25\,\text{cm} muscular tube that accepts the bolus and moves it down to the stomach in approximately 4 s4\,\text{s} to 8 s8\,\text{s} via peristalsis.

  • Swallowing Reflex, Bolus, and Peristalsis

    • Bolus: A rounded mass of chewed food mixed with saliva formed by mechanical and chemical actions in the oral cavity.

    • Swallowing Reflex: An automatic action that forces the bolus into the esophagus. The soft palate depresses, and the trachea elevates, bringing the epiglottis over the glottis to block entry into the lungs.

    • Peristalsis: Rhythmic, continuous waves of smooth muscle contractions that push contents through the gastrointestinal tract, analogous to squeezing toothpaste from a tube.

  • Components and Functions of Gastric Juices

    • Water: Acts as a solvent, aiding in chyme formation and participating directly in hydrolysis reactions.

    • Pepsinogen: Inactive zymogen secreted by gastric glands. Activated by low pH into the active enzyme pepsin, which hydrolyzes proteins into shorter peptide chains.

    • Hydrochloric Acid (HCl\text{HCl}): Drops gastric pH to approximately 33, liquefies food into acid chyme, kills harmful bacteria, and converts pepsinogen into pepsin.

    • Mucus: Forms a viscous protective barrier over the gastric mucosa, shielding the stomach lining from self-digestion by acid and pepsin.

The Pancreas: Exocrine and Endocrine Functions

  • Exocrine Functions of the Pancreas

    • Produces pancreatic juice delivered directly to the duodenum via the pancreatic duct.

    • Contains sodium bicarbonate (NaHCO3\text{NaHCO}_3), which neutralizes acidic chyme, maintaining duodenal pH between 7.57.5 and 8.58.5.

  • Pancreatic Digestive Enzymes Chart

    • Pancreatic Amylase: Source: Pancreas; Site of Action: Small Intestine (pH 7.5–8.07.5\text{--}8.0); Substrate: Starch; Product: Maltose.

    • Trypsin: Source: Pancreas; Site of Action: Small Intestine (pH 7.5–8.07.5\text{--}8.0); Substrate: Protein; Product: Peptides.

    • Lipase: Source: Pancreas; Site of Action: Small Intestine (pH 7.5–8.07.5\text{--}8.0); Substrate: Fat droplets; Product: Glycerol and fatty acids.

    • Nuclease: Source: Pancreas & Small Intestine; Site of Action: Small Intestine (pH 7.5–8.07.5\text{--}8.0); Substrate: Nucleic acids (DNA\text{DNA} and RNA\text{RNA}); Product: Nucleotides.

  • Endocrine Functions of the Pancreas

    • Production Site: Specialized endocrine cell clusters called the Islets of Langerhans produce protein hormones directly into the bloodstream.

    • Insulin:

      • Release Condition: Secreted in response to elevated blood glucose levels (e.g., following meals).

      • Mechanism: Binds to cell membranes to recruit carrier proteins, accelerating facilitated diffusion of glucose into body cells.

      • Effects: Lowers blood sugar to normal levels. Promotes glycogen synthesis in liver and muscle tissue and glycerol formation for lipid storage in adipose tissue.

    • Glucagon:

      • Release Condition: Secreted in response to low blood glucose levels (e.g., between meals or fasting).

      • Mechanism & Effects: Stimulates liver cells to hydrolyze glycogen into free glucose. Triggers gluconeogenesis (conversion of proteins and fats into glucose), raising blood sugar to normal physiological thresholds.

The Liver and Gallbladder

  • Primary Functions of the Liver

    • Detoxification of Blood: Receives nutrient-rich and potentially toxic blood directly from the small intestine via the hepatic portal vein. Removes and breaks down harmful compounds, alcohol, and toxins before they reach systemic circulation.

    • Maintenance of Blood Glucose: Maintains constant blood glucose at approximately 0.1%0.1\%. Converts post-prandial excess glucose into stored glycogen under insulin control; hydrolyzes glycogen back to glucose under glucagon control between meals.

    • Urea Waste Production: Converts excess amino acids into energy via gluconeogenesis when glycogen stores are low. Deamination removes amine groups, generating toxic ammonia (NH3\text{NH}_3). The liver combines ammonia with carbon dioxide (CO2\text{CO}_2) to form non-toxic urea, which is excreted by the kidneys in urine.

    • Synthesis of Essential Plasma Proteins: Uses amino acids to synthesize vital plasma proteins:

      • Albumin: Transports large molecules and maintains blood osmotic pressure.

      • Fibrinogen: Critical blood clotting factor.

      • Immune Complement Proteins: Aid antibodies in destroying blood-borne pathogens (including bacteria, fungi, and viruses like SARS-CoV-2).

    • Production of Bile: Synthesizes approximately 700 mL700\,\text{mL} of bile daily. Clears bilirubin (a hemoglobin degradation byproduct) from broken-down red blood cells and excretes it into bile.

    • Storage of Essential Nutrients: Reserves key minerals and vitamins including iron, Vitamin A, Vitamin D, Vitamin K, and Vitamin B12.

  • Role of Bile in Fat Digestion

    • Bile salts, synthesized from cholesterol, are stored in the gallbladder and released through the bile duct into the duodenum.

    • Bile physically emulsifies large lipid globules into microscopic droplets, dramatically increasing total surface area exposed to enzymatic action.

    • Bile does not chemically cleave bonds; chemical hydrolysis is subsequently performed by pancreatic lipase, producing glycerol and fatty acids.

  • Accessory Organs Classification

    • The liver, gallbladder, and pancreas are designated as accessory organs because food does not pass directly through them. Instead, they lie outside the gastrointestinal tract and synthesize or store essential secretions required for chemical and physical digestion.

  • Gallbladder and Hepatic Portal Vein

    • Gallbladder Function: Stores and concentrates bile synthesized by the liver, releasing it into the small intestine upon arrival of food.

    • Hepatic Portal Vein: Directly connects the capillary beds of the small intestine to the liver, routing absorbed nutrients and metabolic substances to liver cells for processing and filtration.

The Small Intestine

  • Structural Adaptations of the Small Intestine

    • Chemical Digestion: Receives pancreatic juice, bile, and secretes local intestinal mucosal enzymes.

    • Physical Digestion: Emulsification of fats by bile occurs within its lumen.

    • Absorption: Epithelium features circular folds, finger-like villi, and columnar epithelial cells with microvilli (brush border). Columnar cells utilize ATP-driven active transport to move nutrients into circulation.

  • Intestinal Juice Enzymes

    • Maltase: Hydrolyzes maltose disaccharides into single glucose molecules.

    • Peptidases: Hydrolyze small peptide fragments into individual amino acids.

    • Nucleosidases: Hydrolyze nucleotides into constituent nitrogenous bases, pentose sugars, and phosphate groups.

  • Villus Anatomy and Nutrient Absorption Pathways

    • Villus Components: Covered by tightly packed columnar epithelial cells with microvilli. Contains an internal capillary network and a central lymphatic vessel called a lacteal.

    • Capillary Pathway (Bloodstream): Water-soluble nutrients (glucose, amino acids, nucleic acid components) cross columnar cells and enter blood capillaries, traveling via the hepatic portal vein to the liver.

    • Lacteal Pathway (Lymphatic System): Lipid components (fatty acids and glycerol) are reassembled and packaged within epithelial cells, then exocytosed into lacteals. These lymphatic vessels route lipids through the lymphatic system before emptying into the venous blood system.

The Large Intestine

  • Functions and Homeostasis

    • Reabsorbs water and dissolved salts from indigestible fluid chyme, converting it into solid feces.

    • Eliminates indigestible waste, maintaining body fluid balance and internal homeostasis.

    • Triggers the defecation reflex when feces fill the rectal vault.

  • Composition of Human Feces

    • Water Content: Feces consist of approximately 40%40\% water.

    • Solid Components: Composed of bacterial masses, dietary fiber, and undigested cellular debris.

    • Coloration: Derived from oxidized iron compounds and metabolic degradation products of bilirubin.

    • Odor: Produced by volatile bacterial metabolites generated during anaerobic breakdown of dietary residue.

  • Role of Anaerobic Intestinal Bacteria

    • Up to 99%99\% of gut flora are obligate anaerobes that cannot survive in oxygenated tissues, preventing systemic infections outside the gut.

    • Ferment indigestible fiber and produce metabolic byproducts useful to human health, specifically Vitamin K and various B vitamins.

    • Outcompete and inhibit colonization by pathogenic foreign bacteria.

  • Complete Digestive Pathway: Mouth to Anus

    • Mouth: Ingestion, mechanical breakdown via mastication, chemical starch breakdown via salivary amylase.

    • Pharynx: Swallowing reflex moves bolus while epiglottis blocks the trachea.

    • Esophagus: Peristaltic waves propel bolus past the cardiac sphincter.

    • Stomach: Churning, acid denaturation, and pepsin digestion convert food to liquid chyme.

    • Small Intestine (Duodenum, Jejunum, Ileum): Neutralization by sodium bicarbonate, lipid emulsification by bile, chemical cleavage by pancreatic and intestinal enzymes, followed by nutrient absorption through villi.

    • Large Intestine (Colon): Water reabsorption, bacterial vitamin synthesis, and compaction of indigestible matter.

    • Rectum: Temporary storage of fecal material.

    • Anus: Reflexive muscular elimination of fecal waste.

Enzyme Catalysis and Digestive Secretions

  • Master Enzyme Summary Table

    • Salivary Amylase: Secreted by Salivary Glands; Site of Action: Mouth (pH 7.07.0); Reaction: Starch+H2O→Maltose\text{Starch} + \text{H}_2\text{O} \rightarrow \text{Maltose}

    • Pepsin: Secreted by Gastric Glands; Site of Action: Stomach (pH 3.03.0); Reaction: Protein+H2O→Peptides\text{Protein} + \text{H}_2\text{O} \rightarrow \text{Peptides}

    • Pancreatic Amylase: Secreted by Pancreas; Site of Action: Small Intestine (pH 8.08.0); Reaction: Starch+H2O→Maltose\text{Starch} + \text{H}_2\text{O} \rightarrow \text{Maltose}

    • Trypsin: Secreted by Pancreas; Site of Action: Small Intestine (pH 8.08.0); Reaction: Protein+H2O→Peptides\text{Protein} + \text{H}_2\text{O} \rightarrow \text{Peptides}

    • Lipase: Secreted by Pancreas; Site of Action: Small Intestine (pH 8.08.0); Reaction: Fat droplets+H2O→Glycerol+Fatty Acids\text{Fat droplets} + \text{H}_2\text{O} \rightarrow \text{Glycerol} + \text{Fatty Acids}

    • Nuclease: Secreted by Pancreas & Small Intestine; Site of Action: Small Intestine (pH 8.08.0); Reaction: Nucleic Acids+H2O→Nucleotides\text{Nucleic Acids} + \text{H}_2\text{O} \rightarrow \text{Nucleotides}

    • Peptidase: Secreted by Small Intestine; Site of Action: Small Intestine (pH 8.08.0); Reaction: Peptides+H2O→Amino Acids\text{Peptides} + \text{H}_2\text{O} \rightarrow \text{Amino Acids}

    • Maltase: Secreted by Small Intestine; Site of Action: Small Intestine (pH 8.08.0); Reaction: Maltose+H2O→Glucose\text{Maltose} + \text{H}_2\text{O} \rightarrow \text{Glucose}

    • Nucleosidases: Secreted by Small Intestine; Site of Action: Small Intestine (pH 8.08.0); Reaction: Nucleotides+H2O→Bases+Sugars+Phosphates\text{Nucleotides} + \text{H}_2\text{O} \rightarrow \text{Bases} + \text{Sugars} + \text{Phosphates}

  • Roles of Non-Enzymatic Digestive Secretions

    • Water: Primary solvent; acts as a reactant in enzymatic cleavage (hydrolysis) of polymers into monomers.

    • Sodium Bicarbonate (NaHCO3\text{NaHCO}_3): Secreted in pancreatic juice; elevates duodenal pH to basic range (7.5–8.57.5\text{--}8.5) to optimize enzymatic catalysis.

    • Hydrochloric Acid (HCl\text{HCl}): Secreted by stomach lining; lowers gastric pH to 3.03.0, denaturing proteins, killing microbes, and activating pepsinogen into pepsin.

    • Mucus: Secreted along the gastrointestinal tract; forms a physical protective barrier against acidic self-digestion and mechanically lubricates food transport.

Blood Vessels and Cardiovascular Dynamics

  • Types and Structures of Blood Vessels

    • Arteries: Transports blood away from the heart. Possesses thick, elastic, three-layered walls (tunica) designed to withstand high systolic pressures.

    • Arterioles: Small arterial branches supplying tissue capillary beds. Involuntary smooth muscle walls constrict or dilate to regulate regional blood flow and blood pressure.

    • Capillaries: Microscopic exchange vessels with narrow diameters (≈10 μm\approx 10\,\mu\text{m}) and single-cell-thick endothelial walls allowing efficient diffusion of gases, nutrients, and metabolic wastes.

    • Venules: Small vessels collecting blood draining from capillary beds, converging to form veins.

    • Veins: Returns blood to the heart. Features wider lumens and thinner walls than arteries, operating under low pressure. Contains internal one-way valves to prevent backflow.

  • Blood Pressure versus Blood Velocity Dynamics

    • Blood Pressure: The hydrostatic pressure exerted by blood against vessel walls. Drops continuously with distance from the heart, showing a sharp decay across arterioles due to vessel branching and friction.

    • Blood Velocity: The speed of blood flow through vessels. High in the aorta, slows to its lowest rate in capillaries due to an immense increase in total cumulative cross-sectional area, then accelerates slightly as venules converge into large veins.

Systemic and Pulmonary Circuits

  • Overview of Circulatory Circuits

    • Pulmonary System: Routes deoxygenated blood from the right ventricle through pulmonary arteries to alveolar capillaries for gas exchange (CO2\text{CO}_2 loss, O2\text{O}_2 uptake), returning oxygenated blood via pulmonary veins to the left atrium.

    • Systemic System: Pumps oxygenated blood from the left ventricle into the aorta to supply all bodily tissues, collecting deoxygenated blood through systemic veins and returning it to the right atrium via the venae cavae.

  • Anatomy of Major Blood Vessels

    • Aorta: Largest artery in the body; receives oxygenated blood under high pressure from the left ventricle for systemic distribution.

    • Superior Vena Cava: Large vein draining deoxygenated blood from the head, neck, and upper limbs into the right atrium.

    • Inferior Vena Cava: Large vein draining deoxygenated blood from the trunk, abdomen, and lower limbs into the right atrium.

    • Pulmonary Artery: Carries deoxygenated blood under pressure from the right ventricle to the pulmonary capillaries.

    • Pulmonary Vein: Returns oxygenated blood from the lungs into the left atrium.

    • Coronary Arteries: Branches off the aortic base supplying oxygenated blood directly to the myocardium (heart muscle).

    • Coronary Vein: Collects deoxygenated blood from the myocardium, returning it into the right atrium.

    • Carotid Arteries: Delivers oxygenated blood directly to the head and brain.

    • Jugular Vein: Drains deoxygenated blood from the head and brain into the superior vena cava.

    • Subclavian Arteries: Passes beneath the clavicles to deliver oxygenated blood to the upper extremities.

    • Subclavian Veins: Drains deoxygenated blood from the upper extremities into the superior vena cava.

    • Mesenteric Arteries: Delivers oxygenated blood to the intestines and gastrointestinal organs.

    • Hepatic Portal Vein: Transports nutrient-rich, non-oxygenated blood from intestinal capillaries to liver capillary beds.

    • Hepatic Vein: Drains filtered deoxygenated blood from the liver into the inferior vena cava.

    • Renal Arteries: Delivers oxygenated blood to the kidneys for metabolic filtration.

    • Renal Veins: Returns filtered deoxygenated blood from the kidneys into the inferior vena cava.

    • Iliac Arteries: Branches from the abdominal aorta delivering oxygenated blood to the pelvic region and legs.

    • Iliac Veins: Returns deoxygenated blood from the pelvic region and legs into the inferior vena cava.

  • Path of Blood Through the Pulmonary Circuit

    • Right Atrium →\rightarrow Right Ventricle →\rightarrow Pulmonary Trunk / Pulmonary Arteries →\rightarrow Lung Capillaries (Alveoli gas exchange) →\rightarrow Pulmonary Veins →\rightarrow Left Atrium.

Capillary-Tissue Fluid Exchange

  • Hemodynamic Profiles Across Vessel Beds

    • Arteries to Arterioles: High pressure and high velocity. Branching into arterioles causes high frictional resistance, inducing a sharp drop in both parameters.

    • Capillaries: Total cross-sectional area reaches its maximum peak. Blood velocity drops to its absolute lowest point, allowing extended residence time for substance exchange.

    • Venules to Veins: Cumulative cross-sectional area decreases as vessels converge, causing velocity to increase again. Pressure remains very low due to continuous energy loss to vessel wall friction.

  • Mechanisms of Capillary-Tissue Fluid Exchange

    • Arterial End Dynamics: Blood Pressure (30 mmHg30\,\text{mmHg}) exceeds Blood Osmotic Pressure (21 mmHg21\,\text{mmHg}). The net filtration pressure forces plasma fluid, oxygen, and nutrients out through capillary wall pores into interstitial space.

    • Mid-Capillary Dynamics: Blood Pressure (21 mmHg21\,\text{mmHg}) equals Osmotic Pressure (21 mmHg21\,\text{mmHg}). Hydrostatic equilibrium results in zero net bulk fluid movement; movement of dissolved oxygen, carbon dioxide, and nutrients occurs purely via concentration gradients.

    • Venule End Dynamics: Blood Pressure drops to 15 mmHg15\,\text{mmHg} while Osmotic Pressure remains constant at 21 mmHg21\,\text{mmHg}. Net reabsorption pressure pulls fluid containing metabolic wastes and carbon dioxide from tissue space back into the capillary blood.

    • Osmotic Pressure Maintenance: Generated by hypertonic concentrations of plasma proteins (e.g., albumin) and dissolved salts in the blood, maintaining a persistent inward suction force of 21 mmHg21\,\text{mmHg}.

    • Excess Fluid Recovery: Net fluid outward filtration slightly exceeds inward reabsorption. Unabsorbed interstitial fluid is collected by blind-ended lymph capillaries and returned to the venous circulation.

The Lymphatic System

  • Lymphatic System Structures

    • Lymph Capillaries: Blind-ended microvessels originating in tissue spaces. Collect unabsorbed interstitial fluid to prevent tissue edema.

    • Lymph Veins: Vessels equipped with internal one-way valves that collect fluid from lymph capillaries, routing it toward the thoracic cavity to join jugular and subclavian blood veins.

    • Lymph Nodes: Encapsulated organs positioned along lymph vessels. The outer cortex contains lymphocytes for antibody production; the inner medulla contains macrophages that filter and phagocytize cellular debris and pathogens.

    • Lacteals: Specialized lymphatic capillaries located within intestinal villi designed specifically for the absorption of digested dietary fats.

    • Valves: Flaps within lymph veins ensuring unidirectional fluid flow toward the chest cavity.

  • Three Main Functions of the Lymphatic System

    • Fluid Balance Maintenance: Collects excess tissue fluid and returns it to the cardiovascular system, preventing tissue swelling.

    • Immune Defense: Distributes lymphocytes and antibodies to neutralize foreign pathogens.

    • Metabolic Cleansing: Filters metabolic wastes and misfolded protein debris from tissue spaces (including cerebral tissue clearance during sleep).

  • Composition, Origin, and Movement of Lymph

    • Origin: Formed from interstitial tissue fluid derived from filtered blood plasma that fails to reenter venous capillary ends.

    • Composition: Contains water, ions, dissolved nutrients, and white blood cells (lymphocytes and macrophages); lacks large plasma proteins and erythrocytes.

    • Movement: Moves without a central pump. Skeletal muscle contractions compress adjacent lymph vessels, driving fluid through one-way valves toward the subclavian veins.

Fetal Circulation

  • Specialized Fetal Structures

    • Umbilical Cord: Connects fetal circulation to the placenta. Contains one umbilical vein delivering oxygenated, nutrient-rich maternal blood to the fetus, and two umbilical arteries returning deoxygenated blood and metabolic waste to the placenta.

    • Venous Duct (Ductus Venosus): A vascular shunt bypassing the non-functional fetal liver. Connects the umbilical vein directly to the inferior vena cava.

    • Oval Opening (Foramen Ovale): An interatrial opening covered by a tissue flap, allowing blood to flow directly from the right atrium to the left atrium, bypassing the non-functional fetal lungs.

    • Arterial Duct (Ductus Arteriosus): A short vascular vessel connecting the pulmonary trunk directly to the aorta, shunting blood away from pulmonary circulation into systemic circulation. Closes shortly after birth.

Composition and Components of Blood

  • Blood Fractionation

    • Composed of 55%55\% liquid plasma and 45%45\% formed cellular elements.

  • Plasma Composition

    • Water: Primary biological solvent (≈90%\approx 90\% of plasma volume).

    • Plasma Proteins: Albumin (maintains blood volume and osmotic pressure), Immunoglobulins (antibodies for defense), Fibrinogen (clotting enzyme precursor).

    • Salts/Electrolytes: Na+\text{Na}^+, K+\text{K}^+, Cl−\text{Cl}^-, Ca2+\text{Ca}^{2+}.

    • Nutrients: Glucose, amino acids, fatty acids, vitamins.

    • Gases: CO2\text{CO}_2 (primarily dissolved as bicarbonate ions) and O2\text{O}_2.

    • Wastes: Nitrogenous compounds such as urea.

    • Hormones: Circulating chemical signals including thyroxine, insulin, adrenaline, and estrogen.

  • Formed Elements (Blood Cells)

    • Red Blood Cells (Erythrocytes): Biconcave, enucleate cells making up 45%45\% of blood volume. Produced in red bone marrow; function up to 120 days120\text{ days} (4 months) before breakdown by the liver and spleen. Packed with hemoglobin, an iron-containing quaternary protein specialized for O2\text{O}_2 and CO2\text{CO}_2 transport.

    • White Blood Cells (Leukocytes): Nucleated defensive cells involved in cellular immunity and foreign particle phagocytosis. Subtypes include:

      • Neutrophils: Multi-lobed phagocytic cells that engulf bacterial invaders.

      • Lymphocytes: B lymphocytes produce targeted antibodies; T lymphocytes directly destroy infected or foreign cells.

      • Monocytes: Large circulating cells that differentiate into tissue macrophages to phagocytize debris and microbes.

      • Eosinophils: Participate in allergic reactions and anti-parasitic responses.

      • Basophils: Release histamine to initiate inflammatory responses and increase localized vascular permeability.

    • Platelets (Thrombocytes): Anucleate cell fragments shed from megakaryocytes in red bone marrow. Initiate primary hemostasis by forming a platelet plug at vessel lesions and triggering the coagulation cascade (involving prothrombin, fibrinogen, Ca2+\text{Ca}^{2+}, and Vitamin K).

Heart Structure and Cardiac Mechanics

  • Anatomical Structures of the Heart

    • Right Atrium: Upper right chamber; receives deoxygenated blood from systemic circulation via the venae cavae.

    • Left Atrium: Upper left chamber; receives oxygenated blood from pulmonary circulation via pulmonary veins.

    • Right Ventricle: Muscular lower right chamber; pumps deoxygenated blood through the pulmonary valve into the pulmonary artery.

    • Left Ventricle: Thick-walled lower left chamber; pumps oxygenated blood through the aortic valve into the aorta.

    • Coronary Arteries: Vessel network branching off the aortic base to nourish the myocardium with oxygenated blood.

    • Coronary Veins: Drains deoxygenated myocardial blood into the right atrium via the coronary sinus.

    • Vena Cava (Superior and Inferior): Primary systemic veins returning deoxygenated blood to the right atrium.

    • Pulmonary Vein: Returns oxygenated blood from lungs to the left atrium.

    • Pulmonary Artery: Transports deoxygenated blood from right ventricle to the lungs.

    • Aorta: Primary systemic artery distributing oxygenated blood to the entire body.

    • Atrioventricular (AV) Valves: Tricuspid (right) and Bicuspid/Mitral (left) valves preventing backflow from ventricles into atria during systole.

    • Chordae Tendineae: Fibrous tendinous cords tethering AV valve cusps to papillary muscles, preventing valve eversion under high ventricular pressures.

    • Semilunar Valves: Pulmonary and Aortic valves preventing blood backflow from major arteries into ventricles during diastole.

    • Septum: Muscular central wall separating left and right cardiac chambers, preventing mixing of oxygenated and deoxygenated blood.

  • Sequential Pathway of Cardiac Blood Flow

    • Superior/Inferior Vena Cava →\rightarrow Right Atrium →\rightarrow Tricuspid AV Valve →\rightarrow Right Ventricle →\rightarrow Pulmonary Semilunar Valve →\rightarrow Pulmonary Trunk/Arteries →\rightarrow Lungs (Gas Exchange) →\rightarrow Pulmonary Veins →\rightarrow Left Atrium →\rightarrow Bicuspid/Mitral AV Valve →\rightarrow Left Ventricle →\rightarrow Aortic Semilunar Valve →\rightarrow Aorta →\rightarrow Systemic Circulation.

Cardiac Conduction and Regulation

  • Intrinsic Nerve Regions

    • Sinoatrial (SA) Node: Located in the upper posterior wall of the right atrium. Functions as the primary cardiac pacemaker, spontaneously generating an intrinsic depolarization signal every 0.85 s0.85\,\text{s}.

    • Atrioventricular (AV) Node: Positioned in the inferior wall of the right atrium. Receives the SA node signal and enforces a brief delay, allowing atria to fully empty before propagating impulses down the bundle of His/AV bundles.

    • Purkinje Fibers: Specialized conduction fibers spreading through the ventricular myocardium. Delivers depolarization signals to drive coordinated upward ventricular contraction.

  • Five Steps of the Cardiac Cycle

    • Step 1: SA Node Initiation: The SA node fires automatically every 0.85 s0.85\,\text{s}.

    • Step 2: Atrial Systole: Impulse spreads rapidly across both atria, causing atrial contraction and topping off ventricular volumes.

    • Step 3: AV Node Delay: The AV node receives the wave and briefly delays impulse propagation.

    • Step 4: Ventricular Conduction: Impulse travels down septum via AV bundles into branching Purkinje fibers.

    • Step 5: Ventricular Systole: Ventricles contract forcefully from apex upward, forcing blood through semilunar valves into systemic and pulmonary trunks, followed by ventricular diastole (relaxation).

  • Autonomic Neural and Hormonal Control

    • The cardiac control center in the medulla oblongata regulates intrinsic heart rate.

    • Sympathetic Stimulation: Triggers release of epinephrine and norepinephrine during stress, exercise, or fight-or-flight scenarios, increasing heart rate and contractile force.

    • Parasympathetic Stimulation: Mediated by the vagus nerve during restful states, slowing pacemaker firing rates.

Blood Pressure Regulation and Pathologies

  • Systolic and Diastolic Blood Pressure

    • Systolic Pressure: Peak arterial pressure generated during active ventricular contraction (systole).

    • Diastolic Pressure: Resting arterial pressure measured during ventricular relaxation and refilling (diastole).

  • Cardiovascular Pathologies

    • Hypertension: Chronically elevated blood pressure where systolic pressure exceeds 140 mmHg140\,\text{mmHg} or diastolic pressure exceeds 90 mmHg90\,\text{mmHg}. Pathological causes include excessive dietary sodium, renal fluid retention, elevated sympathetic drive, and atherosclerosis (fatty plaque deposition narrowing vessel lumens and increasing peripheral resistance).

    • Hypotension: Abnormally low systemic blood pressure resulting from autonomic dysfunction or severe fluid loss/hemorrhage. Triggers fainting reflexes to lower the head relative to the heart, preserving cerebral perfusion.

  • Sphygmomanometer Measurement Protocol

    • Wrap inflatable cuff over the brachial artery of the upper arm.

    • Inflate cuff above 170–180 mmHg170\text{--}180\,\text{mmHg} to occlude arterial flow.

    • Slowly deflating cuff: blood pressure at which turbulent flow first forces past the cuff during ventricular contraction yields the systolic reading.

    • Continued deflation: pressure at which blood flow sounds vanish and flow becomes smooth yields the diastolic reading.

Anatomy and Physiology of the Respiratory System

  • Respiratory System Structures and Functions

    • Nasal Cavity: Warms, moistens, and filters incoming air. Lined with ciliated olfactory receptor cells for odor detection.

    • Pharynx: Muscular passageway connecting nasal and oral cavities to the larynx and esophagus.

    • Epiglottis: Flap covering the glottal opening during swallowing to protect the lower respiratory tract from aspiration.

    • Larynx: Cartilaginous vocal box containing vocal cords that vibrate under air tension to generate vocalization pitch.

    • Trachea: Main windpipe reinforced with C-shaped cartilaginous rings to maintain airway patency. Lined with ciliated pseudostratified columnar epithelium and mucus glands to trap debris.

    • Bronchi: Left and right primary branches entering the lungs, supported by decreasing amounts of cartilage.

    • Bronchioles: Microscopic smooth-muscle-walled branches lacking cartilage; constrict or dilate to control pulmonary airflow.

    • Alveoli: Microscopic terminal air sacs surrounded by pulmonary capillaries; primary site of respiratory gas exchange.

    • Diaphragm & Ribs: Diaphragm is a muscular sheet separating thoracic and abdominal cavities. External intercostal muscles elevate ribs to expand thoracic cavity volume.

    • Pleural Membrane: Double-layered serous membrane enclosing lungs. Produces lubricating fluid to reduce friction and creates surface tension binding lungs to the thoracic wall.

    • Thoracic Cavity: Enclosed upper body cavity bounded by the rib cage and diaphragm, housing heart and lungs.

  • Path of Air Flow

    • Nostrils →\rightarrow Nasal Cavity →\rightarrow Pharynx →\rightarrow Glottis / Larynx →\rightarrow Trachea →\rightarrow Primary Bronchi →\rightarrow Bronchioles →\rightarrow Alveoli.

  • Alveolar Structural Features and Functional Benefits

    • Grape-like Clusters: Microscopic arrangement massively expands total functional surface area for diffusion.

    • Single-Cell Wall Thickness: Extremely short diffusion distance maximizes rapid exchange of O2\text{O}_2 and CO2\text{CO}_2.

    • Dense Capillary Network: Ensures continuous blood flow to maintain steep concentration gradients.

    • Pulmonary Surfactant Coating: Lipoprotein lining lowers internal surface tension, preventing alveolar collapse during exhalation.

    • Moist Inner Surfaces: Facilitates gas solution necessary for efficient diffusion across membranes.

    • Stretch Receptors: Neural sensory units that detect over-inflation and signal the medulla oblongata to cease inhalation.

  • Mucociliary Clearance Mechanism

    • Goblet cells produce sticky mucus that traps inhaled particulate matter, dust, and pathogens.

    • Cilia arranged in a 9+29+2 microtubule pattern beat in a coordinated upward rhythm, propelling trapped debris out of the respiratory tree into the pharynx to be swallowed or expectorated.

    • Cigarette smoke paralyzes, damages, and destroys ciliated cells, impairing pulmonary clearance.

Mechanics of Breathing

  • Mechanics of Inhalation

    • Elevated blood CO2\text{CO}_2 and H+\text{H}^+ levels are detected by the respiratory center in the medulla oblongata.

    • Nerve signals travel to the diaphragm (causing it to contract, shorten, and flatten) and external intercostal muscles (causing them to contract and pull ribs up and out).

    • Thoracic cavity volume increases, dropping intrapleural and intrapulmonary air pressure below atmospheric pressure.

    • Environmental air rushes down the pressure gradient into the lungs.

  • Mechanics of Exhalation

    • Alveolar stretch receptors fire signals back to the medulla oblongata via negative feedback, shutting off inspiratory signals.

    • Diaphragm relaxes, returning to its dome shape; intercostal muscles relax, allowing the ribcage to drop downward and inward.

    • Thoracic cavity volume decreases, raising intrapulmonary air pressure above atmospheric pressure.

    • Air containing excess CO2\text{CO}_2 and water vapor is forced out into the environment.

Internal and External Respiration

  • Internal Respiration Dynamics

    • Location: Occurs in systemic tissue capillary beds between systemic blood and interstitial fluid.

    • Exchange: Oxygen diffuses out of blood into metabolizing cells; carbon dioxide diffuses out of cells into blood.

    • Local Conditions: Characterized by higher metabolic temperatures (≈37∘C\approx 37^\circ\text{C}) and slightly lower pH (≈7.2\approx 7.2), conditions that weaken hemoglobin's affinity for oxygen and promote O2\text{O}_2 unloading.

  • External Respiration Dynamics

    • Location: Occurs in pulmonary capillaries surrounding lung alveoli.

    • Exchange: Carbon dioxide diffuses out of pulmonary blood into alveoli; oxygen diffuses from alveoli into blood.

    • Local Conditions: Characterized by lower temperatures (≈3Markov/3fresh∘C\approx 3 Markov/3 fresh^\circ\text{C} or cooler) and slightly higher pH (≈7.6\approx 7.6), conditions that enhance hemoglobin binding affinity for oxygen.

  • Gas Transport Molecules and Enzymes

    • Oxyhemoglobin (HbO2\text{HbO}_2): Hemoglobin bound to oxygen; primary transport mode of O2\text{O}_2 from lungs to tissues.

    • Carbaminohemoglobin (HbCO2\text{HbCO}_2): Hemoglobin bound to carbon dioxide; transports a minority fraction of blood CO2\text{CO}_2

    • Reduced Hemoglobin (HHb\text{HHb}): Hemoglobin bound to excess hydrogen ions (H+\text{H}^+); functions as an essential blood buffer to maintain physiological pH.

    • Bicarbonate Ion (HCO3−\text{HCO}_3^-): The predominant form in which CO2\text{CO}_2 is transported within plasma.

    • Carbonic Anhydrase: Erythrocytic enzyme catalyzing the reversible conversion of CO2\text{CO}_2 and H2O\text{H}_2\text{O} into carbonic acid (H2CO3\text{H}_2\text{CO}_3).

  • Chemical Equations for Respiration

    • Internal Respiration Equations:

      • Oxygen Unloading: HbO2→Hb+O2\text{HbO}_2 \rightarrow \text{Hb} + \text{O}_2

      • Carbon Dioxide Hydration: CO2+H2O→carbonic anhydraseH2CO3→H++HCO3−\text{CO}_2 + \text{H}_2\text{O} \xrightarrow{\text{carbonic anhydrase}} \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-

      • Hydrogen Ion Buffering: H++Hb→HHb\text{H}^+ + \text{Hb} \rightarrow \text{HHb}

      • Carbamino Formation: CO2+Hb→HbCO2\text{CO}_2 + \text{Hb} \rightarrow \text{HbCO}_2

    • External Respiration Equations:

      • Oxygen Binding: Hb+O2→HbO2\text{Hb} + \text{O}_2 \rightarrow \text{HbO}_2

      • Proton Release: HHb→H++Hb\text{HHb} \rightarrow \text{H}^+ + \text{Hb}

      • Bicarbonate Conversion: H++HCO3−→H2CO3→carbonic anhydraseH2O+CO2\text{H}^+ + \text{HCO}_3^- \rightarrow \text{H}_2\text{CO}_3 \xrightarrow{\text{carbonic anhydrase}} \text{H}_2\text{O} + \text{CO}_2

      • Carbamino Breakdown: HbCO2→Hb+CO2\text{HbCO}_2 \rightarrow \text{Hb} + \text{CO}_2