Immune System

Lymph System

The lymphatic system is a network of vessels and organs that help maintain fluid balance and play a key role in immune defense.

• Components: Lymph nodes, lymphatic vessels, and lymphoid organs.

• Functions: Contrast lymph vessels with blood vessels; lymph nodes are sites of immune cell activation.

Physical Barriers

Physical barriers are the body's first line of defense against pathogens.

• Epidermis: Outermost skin layer, provides a tough barrier.

• Mucous Membranes: Line body cavities, trap pathogens.

Internal Non-Specific Strategies (Innate Immunity)

Innate immunity provides immediate, non-specific defense against pathogens.

• Inflammation:

  • Characterized by redness, heat, swelling, and pain ("color et dolor et tumor et rubor").

  • Caused by vasodilation, increases fluid delivery and immune cell delivery to site of infection.

  • Fever increases effectiveness of immune cells.

• Complement System:

  • Increases rate of phagocytosis and formation of membrane attack complex (MAC).

  • MAC forms pores in pathogen membranes, leading to cell lysis.

  • Activation can be classical (antibody-mediated) or alternative (pathogen surface-mediated).

Specific (Adaptive) Immunity

Adaptive immunity targets specific pathogens and provides memory for future protection.

• Antibody Formation: B cells produce antibodies that bind to antigens.

• B Cells:

  • Differentiate into plasma cells (produce antibodies) and memory B cells.

  • Antibodies neutralize toxins, opsonize pathogens, activate complement.

• T Cells:

  • Helper T cells: Activate B cells and other T cells.

  • Killer (cytotoxic) T cells: Destroy infected or abnormal cells.

  • Involved in autoimmunity and tissue graft rejection.

Integumentary System (Skin)

Layers of the Skin: Epidermis, Dermis, Hypodermis

The skin is composed of three main layers, each with distinct functions.

• Epidermis: Outermost layer, provides barrier and produces vitamin D3 from 7-dehydrocholesterol upon UV exposure.

• Stratum Corneum: Outermost epidermal layer, dead cells filled with keratin.

• Stratum Lucidum: Present in thick skin (palms, soles), clear layer.

• Stratum Granulosum: Keratinization begins, cells lose nuclei.

• Stratum Spinosum: Provides strength and flexibility.

• Stratum Basale: Deepest layer, site of cell division.

• Dermis: Connective tissue, contains blood vessels, nerves, and glands.

• Hypodermis: Subcutaneous fat, insulates and cushions.

Melanin and Skin Color

Melanin is the pigment responsible for skin color, produced by melanocytes in the epidermis.

• Skin color determined by the ratio of eumelanin (brown-black) to pheomelanin (red-yellow).

• Tyrosinase enzyme is required for melanin synthesis.

Hair Follicle Development

Hair follicles are complex structures that produce hair through coordinated growth cycles.

• Layers:

  • Dermal sheath: Connects with papillary layer of dermis.

  • Hair bulb: Base of follicle, site of cell division.

  • External root sheath: Continuous with stratum basale.

  • Internal root sheath: Contains soft keratin.

  • Hair cortex: Many layers of hard keratin.

  • Hair medulla: Few layers of soft keratin.

Exocrine Glands

Exocrine glands in the skin secrete substances to the surface.

• Types: Eccrine (sweat), apocrine (scent), holocrine (sebaceous/oil).

Bone and Cartilage

Hyaline Cartilage Formation

Hyaline cartilage is a flexible connective tissue found in joints, respiratory tract, and fetal skeleton.

• Chondrocytes: Cartilage cells embedded in a matrix of fibers and ground substance.

• Ground Substance: Contains carbohydrates and proteins (mainly hyaluronic acid and chondroitin sulfate).

• Chondroblasts produce matrix; chondrocytes maintain it.

Endochondral Ossification

Endochondral ossification is the process by which bone tissue replaces cartilage during fetal development and growth.

1. Chondrocytes proliferate and hypertrophy, causing matrix to calcify.

2. Chondrocytes die, leaving cavities.

3. Blood vessels invade, bringing osteoblasts.

4. Osteoblasts lay down bone matrix on cartilage scaffold.

5. Bone remodeling occurs as osteoclasts resorb old bone and osteoblasts form new bone.

Calcium Regulation

Calcium homeostasis is regulated by hormones and is essential for bone health.

• Parathyroid hormone (PTH): Increases blood calcium by stimulating bone resorption.

• Calcitonin: Lowers blood calcium by inhibiting bone resorption.

• Vitamin D: Increases calcium absorption from the gut.

Respiratory System

Ventilation

Ventilation is the process of moving air in and out of the lungs, driven by pressure changes.

• Pleural Pressure: Inversely correlated with lung volume.

• Boyle's Law: Pressure and volume are inversely related:

• During inspiration, lung volume increases and pressure decreases, drawing air in.

Diffusion

Gas exchange in the lungs occurs by diffusion across the respiratory membrane.

• Fick's Law of Diffusion:

• Diffusion is directly proportional to pressure gradient, surface area, and solubility; inversely proportional to membrane thickness.

Gas Transport in the Blood

Oxygen and carbon dioxide are transported in the blood by different mechanisms.

• Oxygen: Mostly carried by hemoglobin; small amounts dissolved in plasma.

• Hemoglobin Regulation: Oxygen saturation is affected by pH, CO2, and 2,3-BPG (Bohr effect).

• Carbon Dioxide: Highly soluble; carried as bicarbonate ion (HCO3-), dissolved CO2, and bound to hemoglobin.

• Carbonic Anhydrase: Enzyme that catalyzes the conversion of CO2 and H2O to H2CO3 (carbonic acid):

Respiratory Control

Breathing is regulated by centers in the brainstem that respond to chemical and neural signals.

• Pontine Respiratory Group: Modulates rhythm.

• Dorsal Respiratory Group: Controls inspiration.

• Ventral Respiratory Group: Controls expiration.

• Chemoreceptors: Sense CO2, O2, and pH to adjust breathing rate.

Additional info:

• These notes expand on brief points to provide a comprehensive overview suitable for exam preparation.