Coelom, Cardiovascular, and Lymphatic Systems Lecture

Coelom & Viscera

• Definitions

  • Coelom: A fluid-filled body cavity entirely lined by serous membrane (mesothelium) derived from embryonic mesoderm; houses and cushions internal organs.

  • Viscera (sing. viscus): The internal organs contained within the coelomic cavities (e.g., stomach, heart, intestines, lungs).

  • Peritoneum: Continuous serous membrane lining the abdominopelvic cavity and covering most abdominal organs.

  • Membrane (anatomical): A thin sheet of tissue acting as a boundary, lining, or partition (e.g., mucous, serous, synovial, cutaneous).

  • Pleura: Serous membrane of the lungs; parietal pleura lines thoracic wall, visceral pleura covers lung surface.

  • Pericardium: Double-walled serous sac surrounding the heart (fibrous + serous layers).

• Body Cavities

  • Ventral Body Cavity: Entire anterior coelom, subdivided into thoracic and abdominopelvic cavities, separated by the diaphragm.

  • Thoracic Cavity

    • Two pleural cavities (lungs)

    • Mediastinum (contains pericardial cavity, great vessels, esophagus, trachea, thymus)

  • Abdominopelvic Cavity

    • Abdominal cavity: stomach, liver, spleen, small intestine, most of large intestine.

    • Pelvic cavity: urinary bladder, reproductive organs, rectum.

    • Peritoneal cavity: potential space between parietal and visceral peritoneum containing serous fluid.

• Parietal vs. Visceral Peritoneum

  • Parietal: Lines internal surface of abdominal wall; sensitive to pain, temperature, touch.

  • Visceral: Covers abdominal organs; insensitive to touch and temperature, sensitive to stretch & chemical irritation.

• Peritoneal Specializations

  • Omenta

  • Greater omentum: Four-layer fatty apron from greater curvature of stomach to transverse colon; immune “policeman.”

  • Lesser omentum: Two-layer sheet from lesser curvature & duodenum to liver (hepatogastric + hepatoduodenal ligaments).

  • Mesentery Proper: Double fold suspending jejuno-ileum to posterior abdominal wall, conduit for superior mesenteric vessels.

  • Mesocolon: Mesentery of parts of large intestine (transverse & sigmoid mesocolons most prominent).

  • Ligaments (peritoneal sense): Double-layered peritoneum connecting organ to organ or wall (e.g., gastrosplenic, falciform, splenorenal).

• Retroperitoneal Organs (SAD PUCKER)

  • Suprarenal (adrenal) glands

  • Aorta & IVC

  • Duodenum (2nd–4th parts)

  • Pancreas (except tail)

  • Ureters

  • Colon (ascending, descending)

  • Kidneys

  • Esophagus (abdominal part)

  • Rectum (lower two-thirds)

  • Term “retroperitoneal” means organs lie posterior to parietal peritoneum, only anterior surface covered by peritoneum.

Serous vs. Mucous Membranes

• Serous Membranes

  • Structure: Simple squamous epithelium (mesothelium) + thin areolar connective tissue; secretes watery, protein-poor serous fluid.

  • Function: Reduces friction between moving organs; forms closed cavities (pleural, pericardial, peritoneal).

• Mucous Membranes

  • Structure: Epithelium (varies) + lamina propria + muscularis mucosae; goblet cells produce mucus (glycoprotein-rich).

  • Line body tracts that open to exterior (respiratory, digestive, urinary, reproductive) and provide protection, lubrication, absorption.

Diaphragm

• Three Muscular Parts (periphery to center)

  1. Sternal part (from xiphoid process)

  2. Costal part (from lower six ribs)

  3. Lumbar part (from L1–L3 vertebrae via right & left crura)

• Central Tendon: Strong aponeurotic insertion of all parts.

• Openings

  • Caval opening (T8): IVC, right phrenic nerve branches.

  • Esophageal hiatus (T10): Esophagus, vagal trunks, esophageal vessels.

  • Aortic hiatus (T12): Aorta, thoracic duct, azygos vein.

Embryonic Germ Layers & Their Derivatives

• Ectoderm: Epidermis, hair, nails, lens, inner ear, enamel, neural tissue, adrenal medulla.

• Mesoderm

  • Paraxial: Somites → skeletal muscle, vertebrae, dermis.

  • Intermediate: Urogenital system (kidneys, gonads, gonadal ducts).

  • Lateral plate: Serous membranes, cardiovascular system, limbs, spleen.

• Endoderm: Epithelia of GI tract, respiratory tract, urinary bladder, liver, pancreas, thyroid, parathyroids.

Inguinal vs. Femoral Canal

• Inguinal Canal

  • Oblique passage in lower anterior abdominal wall; contains spermatic cord (♂) or round ligament (♀).

  • Bounded by inguinal ligament (floor), transversalis fascia (posterior wall), etc.; site of inguinal hernias.

• Femoral Canal

  • Medial compartment of femoral sheath below inguinal ligament; contains lymphatic vessels & node of Cloquet; site of femoral hernias.

“Brief Life Story” (Fertilization → Organogenesis)

1. Fertilization: Sperm + oocyte → zygote.

2. Cleavage: Rapid mitotic divisions forming morula.

3. Blastocyst formation: Inner cell mass + trophoblast; implantation in uterine wall.

4. Gastrulation (week 3): Formation of ectoderm, mesoderm, endoderm.

5. Neurulation (week 3-4): Neural tube formation.

6. Folding (week 4): Embryo transforms from flat disc to C-shape, forming body cavities.

7. Organogenesis (weeks 4-8): Differentiation of organ systems; by week 8, embryo has basic body plan.

Cardiovascular & Lymphatic Systems

• Terminology

  • Circulatory system = Cardiovascular + Lymphatic.

  • Cardiovascular system: Heart + blood vessels + blood.

  • Lymphatic system: Lymph, lymphatic vessels, lymphoid organs.

Functions of Cardiovascular System

• Transport O2, CO2, nutrients, wastes, hormones.

• Temperature regulation, pH balance, immunity, clotting.

Blood

• Components

  • Plasma (55 %): Water, proteins (albumin, globulins, fibrinogen), electrolytes.

  • Formed elements (45 %): RBCs, WBCs, platelets.

• RBCs (Erythrocytes)

  • Fxn: transport O_2 via hemoglobin , carry CO2 (protein, globin)

  • Small cells, no nucleus

  • Life span- live 120 days, removed by macrophages in spleen & liver

• WBCs (Leukocytes)

  • well defined nucleus & organelles

  • Granulocytes: Neutrophils (phagocytes), Eosinophils (parasites, allergy), Basophils (histamine).

  • Agranulocytes: Lymphocytes (B, T, NK cells), Monocytes → macrophages.

• Platelets (Thrombocytes): Cell fragments aiding hemostasis

  • formed by Megakaryocytes

  • No nucleus, not a cell

  • Helps plug small holes in blood vessels, granules contain chemicals upon release to help clot

  • Life span 5-9 days, removed by phagocytes in spleen, liver

• Fxn: of blood- transport: Oxygen, nutrients, waste, hormones, heat

Regulation: pH, temperature

Protection : prevents blood loss by clotting mechanism

Prevents/ limits infection via actions of WBC’s and plasma proteins: Antibodies, complement

• Formation of blood cells: Hemopoiesis

Heart Anatomy

• Pericardial Sac

  • Fibrous pericardium (outer) + serous pericardium (parietal + visceral/epicardium).

• Heart Wall: Epicardium, myocardium (cardiac muscle), endocardium.

• Chambers & Valves

  • Right atrium → Tricuspid → Right ventricle → Pulmonary valve → Pulmonary trunk.

  • Left atrium → Mitral (bicuspid) → Left ventricle → Aortic valve → Aorta.

• Coronary Circulation: Right & left coronary arteries (from aortic sinuses), cardiac veins → coronary sinus.

Circulatory Routes

• Pulmonary: RV → lungs → LA.

• Systemic: LV → body → RA.

• Hepatic Portal: GI tract & spleen → portal vein → liver → hepatic veins → IVC.

Vessels Structure & Function

• Arteries: Thick tunica media, elastic tissue; high pressure.

• Arterioles: Resistance vessels; regulate BP.

• Capillaries

  • Continuous (muscle, CNS), Fenestrated (kidney, endocrine), Sinusoidal (liver, spleen).

• Venules & Veins: Thin walls, valves, blood reservoir; aided by skeletal muscle pump, respiratory pump.

“Trace a Drop of Blood” (Example: Left index finger)

1. LV → Ascending aorta → Aortic arch → Left subclavian → Axillary → Brachial → Radial → Palmar arches → Digital arteries → Capillaries (finger) → Digital veins → Cephalic/Basilic → Axillary → Subclavian → Brachiocephalic → SVC → RA → RV → Pulmonary arteries → Lungs → Pulmonary veins → LA → LV.

Lymphatic System

• Components: Lymph, lymphatic capillaries, vessels, trunks, ducts, lymph nodes, spleen, thymus, tonsils, MALT.

• Primary Organs: Red bone marrow (B-cell maturation), Thymus (T-cell maturation).

• Secondary Organs: Lymph nodes, spleen, tonsils, Peyer’s patches, appendix.

• Functions

  • Return interstitial fluid to blood (~3\ L/day).

  • Absorb lipids via lacteals.

  • Immune surveillance: lymphocytes & macrophages destroy pathogens.

• Thymus: Bi-lobed, in mediastinum; involutes after puberty; educates T cells (positive/negative selection).

• Lymph Nodes: Filter lymph; cortex (B-cell follicles), paracortex (T cells), medulla (plasma cells, macrophages).

• Spleen: Largest lymphoid organ; white pulp (immune), red pulp (RBC recycling, blood reservoir).

Nervous System (Information Flow Overview)

• Receptors detect stimuli → Afferent (sensory) neurons → CNS integration → Efferent (motor) neurons → Effectors (muscles/glands).

  • Somatic vs. Visceral divisions; sympathetic vs. parasympathetic outputs.