Bone marrow has two types: red marrow (myeloid tissue) and yellow marrow. Red marrow produces red blood cells, platelets, and most white blood cells. Yellow marrow, rich in fat, produces some white cells.

From birth, most marrow is red. With age, red marrow converts to yellow marrow in the long and flat bones.

Bone marrow contains hemopoietic stem cells (for blood cells) and mesenchymal stem cells (for bone, cartilage, and muscle).

Bone marrow transplantation involves destroying malignant marrow with chemotherapy/radiation and infusing healthy harvested cells.

Fractures occur due to abnormal load/stress on normal bone or normal stress on weakened bone (e.g., osteoporosis).

In children, fractures can occur across the growth plate or shaft. Shaft fractures often involve partial cortical disruption, resembling a broken young tree branch.

Healing involves blood clot formation, new vessel growth, matrix formation, collagen migration, osteoblast activity producing calcium hydroxyapatite, and bone matrix deposition, forming a callus.

Treatment requires fracture reduction, maintained by a cast or internal/external fixation with screws and rods.

Avascular necrosis is cellular death of bone due to a loss of blood supply, often occurring in the femoral head after a fracture.

Fractures of the femoral neck in elderly patients can disrupt blood flow to the femoral head, leading to necrosis and collapse, often requiring prosthesis replacement.

Growth spurts increase cellular activity around growth plates, making them vulnerable to injury, including dislocation or fracture.

Compression injuries to the growth plate can destroy it, leading to asymmetrical growth. All growth plate fractures require prompt and careful treatment.

Joints are sites where two skeletal elements meet. They are categorized as synovial (with a cavity) or solid (without a cavity).

Synovial joints have an articular cavity, are lined with cartilage (usually hyaline), and possess a joint capsule with an inner synovial membrane (producing lubricating fluid) and an outer fibrous membrane.

Additional structures like articular discs (absorb compression), fat pads (cushioning), and bursae (reduce friction) can be found in synovial joints.

Synovial joints are classified by shape as plane, hinge, pivot, bicondylar, condylar (ellipsoid), saddle, and ball and socket.

Based on movement, synovial joints are uniaxial (one plane), biaxial (two planes), or multiaxial (three planes).

Solid joints include fibrous joints (sutures, gomphoses, syndesmoses) and cartilaginous joints (synchondroses, symphyses).

Osteoarthritis involves cartilage breakdown, leading to bone changes, cyst formation, and osteophytes (bony spurs), causing joint deformation and pain.

Arthroscopy is a minimally invasive technique using a small telescope to visualize the inside of a joint, allowing for diagnosis and treatment, especially in the knee.

Joint replacement surgery is performed for severe degenerative joint disease or joint destruction, commonly on the hip, knee, and shoulder, to relieve pain and restore function.

The skin, the body's largest organ, consists of the avascular epidermis and the vascular dermis. It functions as a barrier, sensory organ, and thermoregulator.

Superficial fascia, located beneath the dermis, is loose connective tissue with fat. It allows skin movement, conduits for vessels/nerves, and stores energy.

Deep fascia is dense connective tissue that compartmentalizes muscles, surrounds structures, and forms retinacula to hold tendons in place near joints.

Fascias limit the spread of infection and malignant disease. Crossing a fascial plane can necessitate more extensive surgical dissection.

Surgical incisions are ideally placed along Langer's lines (skin tension lines) to promote better healing with less scarring.

The body has three muscle types: skeletal (voluntary, striated), cardiac (involuntary, striated, heart), and smooth (involuntary, non-striated, organs/vessels).

Skeletal muscle is multinucleated, striated, capable of powerful contractions, and used for movement, support, and body form. It's innervated by somatic nerves.

Cardiac muscle is found in the heart and large vessels. It's striated, forms a branching network, contracts less powerfully than skeletal muscle, and is resistant to fatigue. It's innervated by visceral nerves.

Smooth muscle is non-striated, spindle-shaped, and capable of slow, sustained contractions. It's found in blood vessels, skin, eyes, and various organ systems. It's innervated by visceral nerves.

Muscle paralysis is the inability to move a muscle or group of muscles, caused by issues in the brain, spinal cord, or nerves. Long-term paralysis leads to muscle wasting.

Testosterone promotes muscle hypertrophy, while feminizing hormones can lead to muscle atrophy and decreased bulk.

Muscle atrophy is muscle wasting due to causes like nerve damage or disuse. It requires extensive rehabilitation after long periods of rest.

These often occur during sudden exertion, involving muscle tears from small interstitial injuries to complete disruption. Identifying the affected muscle and tear extent is crucial for treatment.

The cardiovascular system includes the heart (pump) and blood vessels (arteries, veins, capillaries) that transport blood throughout the body.

Arteries carry blood away from the heart, veins carry blood toward the heart, and capillaries are the smallest vessels where exchange occurs.

Blood vessel walls typically have three layers: tunica externa (outer connective tissue), tunica media (middle smooth muscle), and tunica intima (inner endothelial lining).

Arteries are classified as large elastic arteries (aorta), medium muscular arteries (regulate flow), and small arteries/arterioles (control capillary filling).

Veins are classified as large veins (superior/inferior vena cava), small and medium veins, and venules (drain capillaries). Veins have thinner walls and larger lumens than arteries.

Veins have thinner walls, larger luminal diameters, often have multiple venae comitantes alongside arteries, and frequently possess valves to facilitate unidirectional blood flow.

Atherosclerosis is an arterial disease involving inflammation and deposition of cholesterol, leading to vessel narrowing, calcification, and potential plaque rupture, causing clots and occlusions.

Varicose veins are tortuous, dilated superficial veins, typically in the legs, caused by damaged valves in perforating veins allowing blood to flow backward, increasing pressure.

Anastomoses are multiple pathways for blood supply/drainage. Collateral circulation involves smaller vessels maintaining perfusion if a main vessel is blocked, though some organs (like the brain) have poor collateral circulation.

Lymphatic vessels collect excess fluid (lymph) from tissues and return it to the venous system. They also transport absorbed fats (chyle) from the small intestine.

Lymph is the clear fluid in most lymphatic vessels. Chyle is the opaque, milky fluid from the small intestine containing chylomicrons.

Lymph nodes are filters that trap particulate matter and foreign antigens. They contain lymphocytes and macrophages and are crucial for immune surveillance.

Enlarged lymph nodes can indicate infection or malignancy. Metastatic cancer cells often lodge and grow in lymph nodes.

Lymphatic vessels converge into larger trunks and ducts that drain into the subclavian veins in the neck, returning lymph to the bloodstream.

Structurally, the nervous system is divided into the Central Nervous System (CNS - brain and spinal cord) and the Peripheral Nervous System (PNS - nerves outside the CNS).

Functionally, the nervous system is divided into somatic (voluntary control, external environment) and visceral (involuntary control, internal environment) parts.

The CNS comprises the brain (cerebral hemispheres, cerebellum, brainstem) and the spinal cord.

The meninges are three protective connective tissue coverings of the brain and spinal cord: dura mater (outer), arachnoid mater (middle), and pia mater (inner).

The space between the arachnoid mater and pia mater contains cerebrospinal fluid (CSF).

The somatic part innervates skin and skeletal muscles, involved in conscious sensation and voluntary movement.

The visceral part innervates organs, smooth muscle, and glands, controlling the internal environment. It includes the autonomic division (sympathetic and parasympathetic).

A dermatome is the area of skin supplied by a single spinal cord level or spinal nerve. Testing dermatomes helps localize neurological lesions.

A myotome is the portion of skeletal muscle innervated by a single spinal cord level or spinal nerve. Testing muscle movements helps localize lesions.

The autonomic nervous system is divided into the sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) systems.

Sympathetic fibers originate from the thoracolumbar regions of the spinal cord (T1 to L2) and form the sympathetic trunk.

Parasympathetic fibers originate from cranial nerves (III, VII, IX, X) and sacral spinal cord levels (S2 to S4).

Referred pain occurs when pain from one area (often visceral) is perceived as originating from another area innervated by the same spinal cord level (often somatic).

Early appendicitis pain is often referred to the umbilical region (T10 dermatome) due to visceral nerve stimulation. Later, as it irritates the parietal peritoneum, pain localizes to the right iliac fossa.

Nerve plexuses are networks of nerve fibers that combine fibers from different sources to form new nerves with specific targets, including somatic plexuses (cervical, brachial, lumbar, sacral) and visceral plexuses (cardiac, pulmonary, prevertebral).

The enteric nervous system, within the gastrointestinal tract walls, controls reflex activity like peristalsis and secretion, operating independently but modifiable by the autonomic nervous system.