Comprehensive Study Notes: Blood, Respiratory, Digestive, and Renal Systems

Blood (Chapter 15)

Components and Separation of Blood

Blood is a specialized connective tissue with several components, each with distinct functions and physical properties. Centrifugation separates blood into three layers based on density:

• Plasma (55%): Least dense, mostly water, proteins, and electrolytes.

• Buffy coat (<1%): Contains leukocytes (white blood cells) and platelets.

• Erythrocytes (45%): Red blood cells, most dense; this layer is called the hematocrit.

The buffy coat and erythrocytes are collectively known as the formed elements of blood.

Plasma Characteristics

• Composed of ~90% water, 6-8% proteins (albumin, globulins, fibrinogen), and electrolytes.

• High concentrations of Na+ and Cl-; low concentrations of H+, HCO3-, K+, and Ca2+.

• Useful in research for studying dissolved substances and proteins.

Red Blood Cells (Erythrocytes)

• ~5 billion RBCs/mL of blood; lack nucleus and organelles.

• Flexible, biconcave disk shape (due to spectrin protein) increases surface area for gas exchange.

• Main function: Transport of O2 and CO2.

Hemoglobin Structure and Function

• Each RBC contains ~250 million hemoglobin molecules.

• Hemoglobin consists of 4 globin chains and 4 heme groups (each with an iron atom).

• 98.5% of O2 is transported bound to hemoglobin; 1.5% dissolved in plasma.

• High O2 affinity due to iron binding and cooperative binding.

Life Cycle of Erythrocytes

1. Formation in red bone marrow (erythropoiesis).

2. Circulation for ~120 days.

3. Aging and destruction in spleen, liver, and bone marrow.

4. Recycling of globin and heme; excretion of waste as urine and feces.

Blood Cell Lineages

• Myeloid lineage: Platelets and red blood cells.

• Lymphoid lineage: White blood cells.

Requirements for RBC Production

• Iron: For heme synthesis.

• Folic acid and Vitamin B12: For DNA replication.

Catabolism and Recycling of RBCs and Hemoglobin

• Old RBCs are filtered by the spleen.

• Hemoglobin is broken down; heme is converted to bilirubin, which is further catabolized and excreted.

Anemia: Types and Causes

• Anemia: Insufficient healthy RBCs or hemoglobin.

• Types: Dietary (iron, B12), Hemolytic (malaria, sickle cell), Aplastic (bone marrow defect), Renal (kidney disease), Hemorrhagic (bleeding).

White Blood Cells (Leukocytes)

• Function: Immunity.

• Relative abundance: Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils (mnemonic: Never Let Monkeys Eat Bananas).

Platelets and Hemostasis

• Platelets are fragments from megakaryocytes.

• Hemostasis involves vascular spasm, platelet plug formation, and blood clotting.

• Healthy vessels release substances to prevent platelet aggregation.

• Positive feedback in platelet aggregation is mediated by Thromboxane A2 and ADP.

Respiratory System

Pathway of Air and Respiratory Anatomy

• Air pathway: Nose/Mouth → Nasal cavity → Pharynx → Larynx → Trachea → Primary bronchi → Secondary bronchi → Tertiary bronchi → Bronchioles → Alveoli.

• Upper respiratory tract: Nose, paranasal sinuses, pharynx.

• Lower respiratory tract: Larynx, trachea, bronchial tree, alveoli, lungs, pleurae.

Zones of the Respiratory System

• Conducting zone: Tubes that transport air (trachea to terminal bronchioles).

• Respiratory zone: Site of gas exchange (respiratory bronchioles, alveolar sacs).

Branching and Surface Area

• Branching increases surface area for gas exchange but also increases resistance (similar to capillaries).

• Diffusion rate equation: $Rate\ of\ diffusion = k \times A \times \frac{(P_2-P_1)}{D}$ where k = diffusion constant, A = area, P2-P1 = partial pressure difference, D = distance.

Lung Lobes and Bronchi Diameters

• Right lung: 3 lobes; Left lung: 2 lobes (cardiac notch).

• Bronchi diameters: Primary (10-12 mm), Secondary (5-10 mm), Tertiary (1-5 mm), Bronchioles (<1 mm).

Alveoli and Gas Exchange

• Gas exchange occurs by simple diffusion across the respiratory membrane.

• Alveolar cell types:

  • Type I pneumocytes: Gas exchange.

  • Type II pneumocytes: Secrete surfactant.

  • Alveolar macrophages: Immune defense.

• Surfactant reduces surface tension, preventing alveolar collapse and increasing lung compliance.

Respiratory Pressures and Boyle’s Law

• Four pressures: Atmospheric, Intrapulmonary, Intrapleural (always negative), Transpulmonary.

• Boyle’s Law: $P_1 \times V_1 = P_2 \times V_2$ (at constant temperature, pressure and volume are inversely related).

Lung Compliance and Airway Resistance

• Lung compliance: Ease of lung expansion.

• Airway resistance: Increases as airway diameter decreases.

Spirograph and Lung Volumes

• Spirograph: Graphical representation of lung volumes over time.

• Tidal volume (Vt): Air inspired/expired in a single unforced breath.

• Inspiratory reserve volume (IRV): Extra air inhaled after normal inspiration.

• Expiratory reserve volume (ERV): Extra air exhaled after normal expiration.

Obstructive vs. Restrictive Disorders

• Obstructive: Hard to exhale (e.g., asthma, COPD).

• Restrictive: Hard to inhale (e.g., fibrosis).

Alveolar Ventilation Rate

• Amount of fresh air reaching alveoli per minute.

• Equation: $Alveolar\ ventilation = (V_t \times RR) - (DSV \times RR)$

• Affected by tidal volume, respiratory rate, and dead space volume.

Gas Laws and Atmospheric Gases

• Dalton’s Law: Total pressure is the sum of partial pressures of each gas.

• Partial pressure calculation: $P_{total} = P_1 + P_2 + P_3 + \ldots$

• Ideal Gas Law: $PV = nRT$

• Atmospheric composition: 78% N2, 21% O2, 1% other gases.

Henry’s Law and Gas Solubility

• Gas dissolves in liquid in proportion to its partial pressure.

• Solubility increases with pressure, decreases with temperature.

Hemoglobin Loading/Unloading and CO2 Transport

• Hemoglobin loads O2 in lungs, unloads in tissues.

• CO2 is more soluble in water than O2.

• CO is toxic because it binds hemoglobin, blocking O2 transport.

• Primary CO2 transport: As bicarbonate (HCO3-).

Digestive System

Main Functions of Digestion

• Digestion: Breakdown of food into absorbable units.

• Absorption: Movement of nutrients into blood/lymph.

• Elimination: Removal of indigestible substances.

Mechanical vs. Chemical Digestion

• Mechanical: Physical breakdown (chewing, churning, segmentation).

• Chemical: Enzymatic hydrolysis of macromolecules.

• Major biomolecules digested: Proteins, carbohydrates, lipids, nucleic acids.

Absorption Mechanisms

• Simple diffusion, facilitated diffusion, active transport, endocytosis.

• Most absorption occurs in the small intestine.

GI Tract Anatomy

• Alimentary canal: Mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus.

• Accessory organs: Teeth, tongue, gallbladder, salivary glands, liver, pancreas.

Muscle Types in the GI Tract

• Smooth muscle: No striations, involuntary, gap junctions, no troponin.

• Pacemaker cells: Interstitial cells of Cajal.

• Two layers: Circular (constricts lumen), longitudinal (shortens organ).

Smooth Muscle Contraction

• Ca2+ binds calmodulin → activates myosin light chain kinase → phosphorylates myosin → cross-bridge formation with actin.

• Dense bodies anchor actin; contraction causes corkscrew shape.

GI Motility

• Peristalsis: Wave-like motion propelling food forward.

• Segmentation: Mixing movements, bidirectional.

• Six essential activities: Ingestion, propulsion, mechanical breakdown, digestion, absorption, defecation.

GI Tract Layers

Layer	Main Components	Function
Mucosa	Epithelium, lamina propria, muscularis mucosae	Secretion, absorption, protection
Submucosa	Connective tissue, blood/lymph vessels, nerves	Support, elasticity, vascular supply
Muscularis externa	Inner circular, outer longitudinal muscle	Motility (peristalsis, segmentation)
Serosa/Adventitia	Connective tissue, epithelium	Protection, structural support

Enteric Nervous System and Regulation

• Myenteric plexus: Between muscle layers, controls motility.

• Submucosal plexus: In submucosa, controls secretion and blood flow.

• Enteric NS: Local control; ANS modulates (parasympathetic increases, sympathetic decreases activity).

Digestive Secretions and Phases

• Salivary enzymes: Amylase, lingual lipase (activated in stomach).

• Gastric phases: Cephalic (sight/smell), gastric (stretch/peptides), intestinal (chyme in duodenum).

• Stomach cell types: Mucous (protection), parietal (acid, B12 absorption), chief (protein digestion), enteroendocrine (stimulate acid).

Liver, Gallbladder, and Pancreas Functions

• Liver: Produces bile (emulsifies fats), exocrine function.

• Gallbladder: Stores/releases bile, exocrine function.

• Pancreas: Exocrine (enzymes, bicarbonate), endocrine (insulin, glucagon).

Renal System

Anatomy of the Renal System

• Organs: 2 kidneys, 2 ureters, urinary bladder, urethra.

• Kidney regions: Cortex (outer), medulla (inner, contains pyramids, collecting ducts, calyces, pelvis).

• Nephron structure: Renal corpuscle (Bowman’s capsule, glomerulus, afferent/efferent arterioles), renal tubule (proximal tubule, loop of Henle, distal convoluted tubule, connecting tubule).

Functions of the Renal System

• Regulate plasma ionic composition, volume, osmolarity, and pH.

• Remove metabolic wastes and foreign substances.

Types of Nephrons

• Cortical nephrons: 80-85% of total, primarily in cortex.

• Juxtamedullary nephrons: 15-20%, maintain medullary osmotic gradient for concentrated urine.

Renal Processes

• Filtration: Bulk flow of protein-free plasma from glomerulus to Bowman’s capsule.

• Reabsorption: Selective movement from tubule to interstitial fluid.

• Secretion: Selective movement from interstitial fluid to tubule.

Regulation of Glomerular Filtration Rate (GFR)

• Blood pressure (MAP) drives urine production via afferent arterioles.

• Intrinsic regulation (MAP 80-180 mmHg): Myogenic response, tubuloglomerular feedback, mesangial cell contraction.

• Extrinsic regulation (outside 80-180 mmHg): Sympathetic nervous system via baroreceptors.

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