Lymphatic, Immune, Respiratory, & Digestive Systems

• Study notes for the lymphatic, immune, respiratory, and digestive systems, including key terms, structures, functions, and processes.

Lymphatic System

• The lymphatic system consists of lymph, lymphatic vessels, primary lymphatic structures, and secondary lymphatic structures.
• Lymph composition includes leukocytes, with their percentages varying based on location and immune status.
• Lymphatic system functions include fluid recovery, immunity, and lipid absorption.
• B and T cells originate in the bone marrow.

Primary & Secondary Lymphatic Structures

• Primary lymphatic structures (red bone marrow and thymus) are where lymphocytes are produced and mature and secondary lymphatic structures (lymph nodes, spleen, tonsils) are where lymphocytes are activated.
• Functions of lymphatic structures include immune cell development, filtration of lymph, and initiation of immune responses.
• Locations of lymphatic structures: thymus in the mediastinum, lymph nodes throughout the body, spleen near the stomach, tonsils in the pharynx.
• Lymph flows through vessels, aided by skeletal muscle contractions and valves, draining into the venous system.
• Lymphatic vessels' structure includes valves to prevent backflow.
• Thymus histology shows a cortex and medulla; it functions in T-cell maturation and development.
• Lymph node histology reveals a capsule, cortex, and medulla; it functions to filter lymph and activate immune cells.
• Spleen histology shows red and white pulp; its function is to filter blood and remove old or damaged blood cells.
• Tonsils' histology indicates lymphoid nodules; their function is to protect against ingested or inhaled pathogens.

Immune System Divisions

• The immune system is divided into innate and adaptive branches.

Innate Immune System

• Innate immunity includes defenses that are present at birth, such as physical barriers, cellular defenses, chemical defenses, and physiological defenses.
• Physical barriers include skin and mucous membranes.
• Cellular defenses involve phagocytes (neutrophils, macrophages) and natural killer (NK) cells.
• Phagocytes engulf and destroy pathogens.
• NK cells induce apoptosis in infected or cancerous cells, secreting chemicals such as perforins and granzymes.
• Chemical defenses include interferons and complement.
• Interferons inhibit viral replication.
• Complement enhances phagocytosis, inflammation, and cell lysis by forming membrane attack complexes (MACs).
• Complement has 4 functions: opsonization, inflammation, cytolysis, and elimination of immune complexes.
• Physiological defenses include the inflammatory response and fever.

Adaptive Immune System

• Adaptive immunity involves specific responses to antigens.
• An antigen is a substance that triggers an immune response.
• An antibody is a protein that binds to a specific antigen.
• T cells include helper T cells, cytotoxic T cells, regulatory T cells, and memory T cells.
• Helper T cells (CD4+) enhance immune responses by releasing cytokines.
• Cytotoxic T cells (CD8+) kill infected or cancerous cells.
• Regulatory T cells suppress immune responses.
• Memory T cells provide long-lasting immunity.
• T cell receptors (TCRs) recognize antigens presented on MHC proteins.
• MHC proteins are Class I and Class II.
• Class I MHC proteins are found on all nucleated cells and present antigens to cytotoxic T cells.
• Class II MHC proteins are found on antigen-presenting cells and present antigens to helper T cells.
• B cells proliferate and differentiate into plasma cells and memory B cells.
• Activation steps involve antigen binding and T cell help.
• Plasma cells produce antibodies.
• Memory B cells provide long-lasting immunity.
• An antibody's structure includes heavy chains, light chains, constant regions, and variable regions.
• The function of antibodies is to bind antigens, neutralize pathogens, and activate complement.
• Antibodies have two binding sites for antigens.
• Antibody Classes:
  • IgG: most abundant, crosses placenta.
  • IgM: first antibody produced during an immune response.
  • IgA: found in mucous, saliva, tears, and breast milk.
  • IgD: activates B cells.
• IgE: involved in allergic reactions and parasitic infections.
• Primary immune response involves IgM first, then IgG.
• Secondary immune response involves a faster and greater IgG response.

Types of Immunity

• Active immunity is acquired through exposure or vaccination.
• Passive immunity is acquired through transfer of antibodies (e.g., from mother to fetus).
• Naturally acquired immunity is gained through natural exposure.
• Artificially acquired immunity is gained through medical intervention (vaccination).

Respiratory System

• The respiratory system has 4 main functions: gas exchange, air purification, sound production, and olfaction.
• Structural divisions include the upper and lower respiratory tracts.
• Functional divisions include the conducting zone and respiratory zone.
• The conducting zone filters, warms, and moistens air.
• The respiratory zone is where gas exchange occurs.
• Histology of normal human lung shows alveoli and capillaries.
• Emphysema shows enlarged alveoli with damaged walls.
• Viral pneumonia shows inflammation and fluid accumulation.
• Respiratory mucosa lines the respiratory tract.
• The general structure of the respiratory mucosa includes epithelial cells and a basement membrane.
• Epithelial tissue transitions from pseudostratified columnar in the upper respiratory tract to simple squamous in the alveoli.
• Mucus traps pathogens and debris.
• Cilia move mucus toward the pharynx.
• The upper respiratory tract includes the nose, nasal cavity, pharynx, and larynx.
• Upper respiratory tract structures function in filtering, warming, and humidifying air.
• The lower respiratory tract includes the trachea and lungs.
• Lower respiratory tract structures function in gas exchange.
• Vocal folds vibrate to produce sound.
• Bronchi divisions progress from the trachea to the alveoli.
• The path of bronchi divisions: trachea, main bronchi, lobar bronchi, segmental bronchi, bronchioles, terminal bronchioles.
• Bronchi function to conduct air.
• The five lobar bronchi are the superior, middle, and inferior on the right lung; superior and inferior on the left lung.
• Cartilage and epithelial layers become thinner from the trachea to the alveoli.
• Alveoli are the sites of gas exchange.
• Alveoli's structure includes thin walls and a large surface area.
• Alveolar type I cells are simple squamous cells for gas exchange.
• Alveolar type II cells secrete pulmonary surfactant.
• Pulmonary surfactant reduces surface tension in the alveoli.
• Alveolar macrophages engulf pathogens and debris.
• Lungs' structure includes lobes and fissures.
• Lungs function in gas exchange.
• Pleura, pleural cavity, and pleural membranes facilitate breathing.
• The diaphragm contracts, ribs elevate, pleural membranes connect lungs to the thoracic cavity.
• Respiratory volumes: tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume.
• Respiratory capacities: vital capacity, total lung capacity.
• Respiratory volume plot shows changes in lung volumes during breathing.

Digestive System

• The digestive system includes the GI tract and accessory digestive organs.
• The 6 digestive system functions include ingestion, propulsion, mechanical breakdown, chemical digestion, absorption, and defecation.
• A bolus is a mass of chewed food.
• Chyme is a semi-fluid mixture of partly digested food and gastric secretions.
• Salivary glands include parotid, submandibular, and sublingual glands.
• Saliva functions to moisten food, begin starch digestion, and cleanse the mouth.
• Cells that produce saliva include serous and mucous cells.
• The oral cavity is the site of mastication (chewing).
• Oral cavity structures include teeth, tongue, and salivary glands.
• Teeth names and functions: incisors (cutting), canines (tearing), premolars (grinding), molars (grinding).
• The pharynx is a passageway for food and air.
• The esophagus is a muscular tube that transports food to the stomach.
• The esophagus' structure includes smooth muscle layers.
• The esophagus' function is to transport food.
• Esophagus' histology shows mucosa, submucosa, muscularis externa, and adventitia.
• Superior and inferior esophageal sphincters regulate food passage.
• The 3 phases of swallowing are the voluntary, pharyngeal, and esophageal phases.
• The stomach's structure includes the fundus, body, and pylorus.
• The stomach's function is to store food, mix it with gastric secretions, and begin protein digestion.
• The bolus of food flows from the stomach to the small intestine.
• The 3 phases of digestion include the cephalic, gastric, and intestinal phases.
• Nerve signals, stomach contractions, and secretions such as HCl and pepsin are involved in the process of digestion.
• Gastrin, CCK, and secretin regulate stomach activity.
• Stomach wall histology shows gastric pits and glands.
• Stomach wall cells of the gastric pits & glands include mucous cells, parietal cells, chief cells, and enteroendocrine cells.

Hormones in Digestion

• CCK: secreted by the small intestine, stimulated by fats and proteins, and functions to stimulate gallbladder contraction and pancreatic enzyme secretion.
• Secretin: secreted by the small intestine, stimulated by acidic chyme, and functions to stimulate bicarbonate release from the pancreas.
• Gastrin: secreted by the stomach, stimulated by stomach distension, and functions to stimulate HCl secretion.
• VIP: secreted by the small intestine, stimulated by chyme, functions to inhibit gastric acid secretion and promote intestinal blood flow.
• GIP: secreted by the small intestine, stimulated by glucose and fats, functions to stimulate insulin release.
• The liver's structure includes lobes and lobules.
• The liver's function is to produce bile, metabolize nutrients, and detoxify substances.
• Liver's histology shows hepatocytes.
• The hepatic portal system transports blood from the digestive organs to the liver.
• Liver produces and moves bile to the gallbladder.
• Hepatic lobules are functional units of the liver.
• The gallbladder stores and concentrates bile.
• The bile ducts transport bile.
• The pancreas' structure includes a head, body, and tail.
• The pancreas' function is to produce digestive enzymes and hormones.
• Pancreas ducts transport pancreatic juice.
• Bile from the liver, gallbladder, and pancreas empties into the small intestine (duodenum).
• The small intestine includes the duodenum, jejunum, and ileum.
• The small intestine's structure includes villi and microvilli.
• The small intestine's function is to digest and absorb nutrients.
• The small intestine's histology shows mucosa, submucosa, muscularis externa, and serosa.
• The large intestine includes the cecum, colon, rectum, and anal canal.
• The large intestine's structure includes haustra.
• The large intestine's function is to absorb water and electrolytes and form feces.
• The large intestine's histology shows mucosa with goblet cells.
• The rectum and anus control defecation.
• The large intestine contains internal and external anal sphincters.
• Defecation process involves peristalsis and relaxation of sphincters.