Anatomy and Physiology II: Lymphatic, Immune, Respiratory, and Digestive Systems Study Notes

Lymphatic System and Immunity

Overview and Functions

The lymphatic system is a network of vessels, tissues, and organs that helps maintain fluid balance, absorbs dietary fats, and provides immune defense.

• Drains interstitial fluid and leaked plasma proteins back to the blood.

• Transports dietary fats from the digestive tract.

• Protects the body from disease through immune responses.

Lymphatic Vessels and Circulation

• More fluid leaves blood capillaries than returns, risking edema or shock if not drained.

• Five principal lymphatic trunks unite into two main channels:

  • Right lymphatic duct: drains right side of head, neck, chest, and arm.

  • Thoracic duct: drains all remaining regions.

• Both ducts empty into the subclavian veins.

• Lymphatic capillaries are blind-ended and drain into larger vessels, returning lymph to cardiovascular circulation.

Comparison with Venous System

• Both return fluid to the heart and use movement (muscle contraction, respiratory pump) to assist flow against gravity.

• Veins return blood; lymphatic vessels return lymph.

Lymphatic Organs and Tissues

• Primary lymphatic organs: thymus and red bone marrow (site of lymphocyte maturation).

• Secondary lymphatic organs: lymph nodes, lymph nodules, spleen (site of immune responses).

Lymph Nodes and Nodules

• Lymph nodes: encapsulated, filter lymph, destroy foreign substances via T cells and macrophages.

• Lymph nodules: non-encapsulated, found in mucous membranes (MALT).

Spleen

• Largest mass of lymphoid tissue, located inferior to the stomach in the left upper quadrant.

• Two regions:

  • White pulp: lymphatic tissue, filters pathogens, contains T & B cells, macrophages, dendritic cells.

  • Red pulp: contains macrophages that destroy old RBCs.

Lines of Defense

• 1st line: Surface barriers (skin, mucous membranes) – non-specific.

• 2nd line: Innate immunity (cells and proteins) – non-specific.

• 3rd line: Adaptive immunity (cells and proteins) – specific, with memory.

Innate Immunity

• Physical barriers: skin, mucous membranes.

• Chemical barriers: secretions (tears, saliva, sebum, sweat, gastric juices) create antimicrobial environments.

• Mechanical removal: urination, defecation, vomiting, vaginal excretions.

• Antimicrobial substances: interferons (inhibit viral replication), complement proteins (enhance immune function).

• Natural killer (NK) cells: destroy infected cells by releasing perforins and granzymes.

• Fever: increases body temperature, inhibits microbial growth, enhances tissue repair.

• Phagocytosis: neutrophils and macrophages ingest and digest invaders (chemotaxis, adherence, ingestion).

• Inflammation: redness, swelling, pain, heat; stages include vasodilation, phagocyte migration, tissue repair.

Adaptive Immunity

• Specific defense against particular antigens; involves memory.

• Antibody-mediated immunity: B lymphocytes produce antibodies.

• Cell-mediated immunity: T lymphocytes destroy infected cells.

Maturation and Clonal Selection

• B cells mature in bone marrow; T cells mature in thymus.

• Clonal selection: proliferation and differentiation of immune cells after antigen exposure.

• Produces effector cells (active response) and memory cells (faster secondary response).

Antigens and Antigen Processing

• Antigens: foreign substances (whole microbes or macromolecules) that provoke immune responses.

• Antigenic determinants (epitopes): specific regions that trigger responses.

• Self-antigens: major histocompatibility proteins (MHC) mark cells as "self".

• Endogenous antigens: originate within the body (e.g., viral proteins, cancer proteins), presented by MHC I.

• Exogenous antigens: originate outside the body, processed by antigen-presenting cells (APCs), presented by MHC II.

T Cells

• Helper T cells (Th, CD4): recognize antigens with MHC II, secrete cytokines to stimulate other immune cells.

• Cytotoxic T cells (Tc, CD8): recognize antigens with MHC I, destroy infected cells via perforin (cytolysis) and granzymes (apoptosis).

B Cells and Antibodies

• B cell activation: antigen binds to B cell receptor, with costimulation from Th cells.

• Plasma cells secrete antibodies.

• Antibody structure: Y-shaped, 2 heavy and 2 light chains, variable region (antigen-binding), constant region.

Classes of Immunoglobulins

Class	Structure	Function
IgG	Monomer	Main antibody in blood, crosses placenta
IgA	Dimer	Localized protection in secretions
IgM	Pentamer	First antibody produced, anti-A & anti-B blood antibodies
IgE	Monomer	Involved in allergies and hypersensitivity

Immunological Memory

• Memory cells enable a faster, stronger response upon second exposure (secondary response).

• IgG levels increase significantly during secondary response.

Respiratory System

Overview and Functions

The respiratory system facilitates gas exchange between the atmosphere, blood, and cells. It is divided into conducting and respiratory zones.

• Ventilation: movement of air in and out of lungs.

• External respiration: gas exchange between alveoli and blood.

• Internal respiration: gas exchange between blood and tissues.

Conducting Zone

• Nose: warms, moistens, filters air; lined with olfactory epithelium.

• Pharynx: common passage for respiratory and digestive tracts; regions include nasopharynx (respiratory), oropharynx, and laryngopharynx (both).

• Larynx: connects pharynx to trachea; contains epiglottis, thyroid cartilage, cricoid cartilage, and vocal cords.

• Trachea: connects larynx to bronchi; supported by C-shaped hyaline cartilage rings.

• Bronchial tree: trachea divides into primary, secondary, and tertiary bronchi; tissue transitions from cartilage to smooth muscle.

Respiratory Zone

• Includes respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli (main site of gas exchange).

• Alveoli contain:

  • Type I cells: gas exchange.

  • Type II cells: secrete surfactant to reduce surface tension.

  • Alveolar macrophages: immune defense.

Lungs and Pleura

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

• Pleural membrane: visceral (covers lungs), parietal (lines cavity), pleural space (fluid-filled).

Mechanics of Ventilation

• Boyle’s Law: At constant temperature, pressure and volume are inversely related.

• Inhalation: diaphragm and external intercostals contract, thoracic volume increases, pressure decreases.

• Exhalation: relaxation of muscles, thoracic volume decreases, pressure increases.

• Forced breathing involves additional muscles (e.g., sternocleidomastoid, abdominal muscles).

Equation (Boyle's Law):

$P_1 V_1 = P_2 V_2$

Lung Volumes and Capacities

• Tidal Volume (TV): air moved in normal breath.

• Minute Volume: TV × breaths per minute.

• Total Lung Capacity (TLC): sum of inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV).

Equation (Minute Volume):

$\text{Minute Volume} = \text{TV} \times \text{breaths per minute}$

Gas Laws

• Dalton’s Law: Each gas in a mixture exerts its own partial pressure.

• Henry’s Law: Amount of gas dissolved in a liquid is proportional to its partial pressure and solubility.

Equation (Dalton's Law):

$P_{\text{total}} = P_{N_2} + P_{O_2} + P_{CO_2}$

Equation (Henry's Law):

$C = k P$

where C = concentration of dissolved gas, k = solubility constant, P = partial pressure

Gas Exchange and Transport

• External respiration: O2 diffuses from alveoli to blood; CO2 diffuses from blood to alveoli.

• Internal respiration: O2 diffuses from blood to tissues; CO2 diffuses from tissues to blood.

• O2 transport: 1.5% dissolved in plasma, 98.5% bound to hemoglobin (Hb).

• CO2 transport: 7% dissolved, 23% bound to Hb (carbaminohemoglobin), 70% as bicarbonate ions.

Equation (CO2 transport):

$CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow H^+ + HCO_3^-$

Oxygen-Hemoglobin Dissociation Curve

• S-shaped curve; affinity affected by pH, CO2, temperature (Bohr effect).

• Low pH, high CO2, or high temperature promote O2 unloading.

Respiratory Control

• Medullary rhythmicity area (DRG: normal breathing, VRG: forceful breathing).

• Ventilation patterns: normal inhalation (2 sec), exhalation (3 sec).

• Chemoreceptors monitor CO2 and O2 levels; hypercapnia and hypoxia stimulate increased ventilation.

Digestive System

Overview and Functions

The digestive system processes food for nutrient absorption and waste elimination. It consists of the GI tract and accessory organs.

• Ingestion: taking in food.

• Secretion: release of digestive fluids.

• Propulsion: movement (peristalsis).

• Digestion: mechanical (chewing, churning) and chemical (enzymatic hydrolysis).

• Absorption: uptake of nutrients.

• Defecation: elimination of waste.

GI Tract Structure

• Mucosa: epithelium, lamina propria, muscularis mucosa.

• Submucosa: connective and nervous tissue.

• Muscularis: 2-3 layers of muscle.

• Serosa/adventitia: outermost layer, varies by location.

Peritoneum

• Largest serous membrane; parietal (lines cavity) and visceral (covers organs) layers.

• Functions: protection, suspension, blood/nerve supply.

• Major folds: mesenteries, greater and lesser omentum.

Oral Cavity and Teeth

• Formed by cheeks, lips, tongue, hard and soft palate.

• Teeth: crown, neck, root; two sets (deciduous and permanent); types include incisors, canines, premolars, molars.

• Mastication increases surface area for enzyme action.

Salivary Glands

• Three pairs: parotid, submandibular, sublingual.

• Saliva: 99.5% water, 0.5% solutes (enzymes, salts, organics, gases).

• Functions: lubricates, moistens food, begins chemical digestion.

Pharynx and Esophagus

• Pharynx connects oral cavity to esophagus; functions in propulsion only.

• Esophagus: upper (skeletal muscle), middle (mixed), lower (smooth muscle); contains upper and lower sphincters.

Deglutition (Swallowing)

• Three stages:

  1. Voluntary: tongue pushes food to oropharynx.

  2. Pharyngeal: epiglottis closes trachea, food moves to esophagus.

  3. Esophageal: peristalsis moves food to stomach.

Stomach

• J-shaped organ; regions: cardia, fundus, body, pylorus.

• Three layers of smooth muscle; mucosa folded into rugae when empty.

• Histology: simple columnar epithelium, gastric pits (mucous cells), gastric glands (parietal, chief, enteroendocrine cells).

• Mechanical digestion: churning; chemical digestion: pepsin (proteins), gastric lipase (lipids).

• Minimal absorption (alcohol, aspirin, some electrolytes).

Phases of Digestion

• Cephalic phase: initiated by sensory input, stimulates gastric secretion and motility.

• Gastric phase: triggered by food in stomach.

• Intestinal phase: digestion in small intestine; both gastric and intestinal phases are under neural and hormonal control.

Small Intestine

• Primary site for chemical digestion and nutrient absorption.

• Regions: duodenum, jejunum, ileum.

• Features: circular folds, villi (with lacteals and blood supply), microvilli (brush border enzymes).

• Secretory cells: absorptive cells (enterocytes), goblet cells, enteroendocrine cells.

• Motility: segmentation (churning), peristalsis (propulsion).

Large Intestine

• Functions: absorbs water, forms feces, produces vitamins.

• Regions: cecum, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.

• Histology: increased goblet cells, no villi, taeniae coli (longitudinal muscle bands), haustra (pouches).

Defecation Reflex

• Triggered by stretch receptors in sigmoid colon.

• Voluntary contraction of diaphragm and abdominal muscles, relaxation of external anal sphincter.

Accessory Organs

• Pancreas: posterior to stomach; 1% endocrine (islets), 99% exocrine (acini); secretes digestive enzymes (amylase, trypsin, lipase, nucleases).

• Liver: largest gland; produces bile (emulsifies fats), processes nutrients, detoxifies substances.

• Gall bladder: stores and releases bile.

Liver Histology and Blood Supply

• Hepatocytes arranged in lobules around a central vein.

• Bile flows through canaliculi to bile ducts; portal triads (bile duct, hepatic arteriole, hepatic portal venule) between lobules.

• Blood drains into hepatic sinusoids, then central vein.

Nutrient Digestion and Absorption

• Carbohydrates → monosaccharides (glucose, galactose).

• Proteins → amino acids.

• Lipids → fatty acids and monoglycerides.

• Absorbed into blood capillaries (except most lipids, which enter lymphatics as chylomicrons).

Lipid Digestion and Absorption

1. Lipids are emulsified by bile salts in the small intestine.

2. Pancreatic lipase digests lipids into free fatty acids and monoglycerides.

3. Bile salts form micelles with digested lipids for absorption.

4. Lipids are absorbed into lacteals as chylomicrons, bypassing the liver initially.

Absorption of Water, Electrolytes, and Vitamins

• Most water (about 8 L/day) is absorbed in the small intestine; remainder in large intestine.

• Electrolytes (Na+, K+, Ca2+) and vitamins are absorbed throughout the intestines.

• Fat-soluble vitamins (A, D, E, K) are absorbed with micelles; water-soluble vitamins (B, C) are absorbed in the small intestine.

• Vitamin B12 requires intrinsic factor (from parietal cells) for absorption in the ileum.

Example: The absorption of vitamin B12 is clinically important; deficiency can lead to pernicious anemia due to lack of intrinsic factor.

Additional info: The notes above expand on the original class notes with definitions, examples, and equations for clarity and completeness.