Human Anatomy: Kidney and Cartilage Structure

Cartilage

• Definition: A specialized supportive connective tissue with a firm, non-vascular matrix.
• Histological Structure: Composed of cells and extracellular matrix.
• Extracellular Matrix Components: Fibers (type II collagen fibrils) and ground substance (75% tissue fluid) for nutrient diffusion.
• Cells: Chondroblasts and chondrocytes.
• General Histological Characteristics: Cells are widely separated by abundant extracellular matrix, avascular, poor healing and repairing capacities.
• The cartilage is covered from outside by perichondrium for nutrition and repair.
• The perichondrium is absent in articular cartilage of joints and its nutrition depends from synovial fluid.
• The perichondrium is essential for repair and regeneration, especially in young age.
• Types of Cartilage cells: Chondroblasts and Chondrocytes
  • Chondroblasts: Located on inner layer of perichondrium, actively dividing cells, flat, oval, and actively synthesize cartilage matrix, secreting collagen type II. Eventually, chondroblasts change into chondrocytes when trapped inside lacunae.
  • Chondrocytes: Old, mature cells, located deeper in the cartilage matrix, rounded cells in lacunae, maintain cartilage matrix.

Types of Cartilage

• Hyaline Cartilage (Most common):
  • Covered by perichondrium
  • Homogenous and basophilic matrix containing type II collagen fibrils.
  • Found in ends of long bones, ends of ribs, trachea, and bronchi.
• Elastic Cartilage:
  • Covered by perichondrium.
  • Heterogenous and basophilic matrix containing type II collagen fibrils + abundant elastic fibers.
  • Flexible
  • Found in ear pinna, external ear, and Eustachian tube.
• Fibrocartilage:
  • No perichondrium.
  • Scanty matrix containing parallel bundles of collagen fibers (type I).
  • Chondrocytes within lacunae in between.
  • Found in intervertebral discs.

Bone

• Definition: A specialized supportive connective tissue with a hard (solid) matrix.
• Covered externally by periosteum and lined internally by endosteum.
• Formed of Bone cells and solid ECM (calcified calcium & phosphate) with less tissue fluid (25%) and collagen type I.
• Highly vascular.
• Functions: Protects and supports vital organs (brain and spinal cord), storage site for calcium and phosphate, and contains bone marrow which acts as a hematopoietic organ.
• Major Types of Bone Cells: Osteogenic cells, Osteoblasts, Osteocytes, and Osteoclasts.
  • Osteogenic Cells: Stem cells within inner layer of periosteum and endosteum.
  • Osteoblasts: Present side by side on bone surfaces (periosteum and endosteum), synthesize bone matrix
  • Osteocytes: Located within the bone matrix in lacunae, maintain bone tissue.
  • Osteoclasts: Present on bone surface (endosteum), in cavities (Howship's lacunae), resorb bone.

Types of Bone Tissue

• Compact Bone: Bone lamellae are regularly arranged, formed of concentric bone lamellae around haversian canals, haversian systems (osteons), contain osteocytes in lacunae in-between lamellae, and has one bone marrow cavity. Found in shafts of long bones.
• Spongy Bone (Cancellous Bone): Branching and anastomosing bone trabeculae with multiple bone marrow cavities, bone lamellae are irregularly arranged, contains osteocytes in-between, and lack haversian systems. Found in ends of long bones, vertebrae, ribs, and skull.

Neuron

• Structure: Cell body (perikaryon), dendrites, and axon.
  • Cell Body (perikaryon): Trophic center, receives impulses from other neurons (dendrites), conducts nerve impulse via axon to other neurons.
  • Dendrites: Branching extensions on cell bodies, numerous, short, receive impulses from other neurons, become thinner when branching, impulse towards cell body and contains Nissl granules, mitochondria, neurofilaments and microtubules.
  • Axon: Single long extension, not branching except at terminal axon terminals, has a constant diameter, impulse away from cell body and contains mitochondria, neurofilaments and microtubules, but no Nissl granules.
• Key Components: Nissl bodies/granules, Golgi complex, mitochondria, neurofilaments, microtubules and cytoplasmic organelles.

Histology of Cell Body

• Nucleus: Single, spherical, large, central, pale vesicular, euchromatin, prominent nucleolus.
• Cytoplasm: Nissl bodies/granules (large basophilic granules scattered in perikaryon and dendrites but not in axon; involved in neurotransmitter transport), free ribosomes & RER; nerve cell Nissl's granules disappear (chromatolysis) after injury.
• Golgi complex: Network around nucleus in cell body, well-developed in EM.
• Mitochondria: Scattered in cytoplasm, abundant in axon terminals.
• Neurofilaments & Microtubules: In cell body, axon and dendrites, supportive and maintain shape, neuro-tubules share in neurotransmitter transport.

Blood Vessel Wall

• Structure: Endothelium, Intima (inner layer), Media (middle layer), Adventitia (outer layer)
• Layers: Endothelium (innermost layer), Subendothelium (layer of connective tissue beneath endothelium), Intima (internal elastic lamina, and smooth muscle layer), Media (smooth muscle cells, connective tissue, and elastic fibers), Adventitia (outermost layer, composed of connective tissue and contains large blood vessels that supply the vessel wall (vasa vasorum)).

Connections Between Arteries & Veins

• Capillaries: Endothelial cell rests on basal lamina, surrounded by pericytes, forms a tube.
• Sinosoids: Specialized capillaries.
• Arteriovenous anastomosis: Direct connections between arterioles and venules.

Respiratory System

• Divided into conducting portion and respiratory portion.
• Conducting portion: Nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles.
• Respiratory portion: Bronchioles, alveolar ducts, alveolar sacs (alveoli)
  • Alveoli: Basic structural and functional unit for gas exchange, thin walls enable CO2 and O2 exchange between inspired air and blood, lined by alveolar epithelium.
• Type I pneumocytes: Majority of alveolar epithelium, simple squamous epithelium, abundant in alveolar space, and involved in gas exchange.
• Type II pneumocytes: Secretory cells, synthesize and secrete pulmonary surfactant, cuboidal-shaped, prevent alveolar collapse, allow for gas exchange between inspired air and blood.

Skin

• Largest organ in the body (about 16% of total body weight).
• Two layers: Epidermis (outer layer, epithelium) and dermis (deeper layer, connective tissue).
• Epidermis cell types: Keratinocytes (85%), Melanocytes, Langerhans cells, Merkel cells.
• Keratinocytes: Stratified squamous epithelium, keratin formation; linked by desmosomes; superficial layers continuously shed off; deep layers dividing, accumulating keratin filaments.
• Thick and Thin skin: Differences in epidermal thickness, presence of sweat glands, and hair follicles.

Liver

• Largest internal organ.
• Mixed exocrine and endocrine gland.
  • Endocrine: Synthesis of plasma proteins and coagulation factors.
  • Exocrine: Production of bile to aid fat digestion.
  • Hepatocytes: Liver cells arranged in anastomosing cords, with spaces (sinusoids) between cords, and bile canaliculi.
• LM & EM of Hepatocytes: Hepatocytes have large nuclei, prominent nucleolus, abundant cytoplasm, extensive SER, RER, Golgi, mitochondria, and glycogen.
• Histological Structure: An anastomosing cords of cells, blood sinusoids (dilated spaces) lined by fenestrated endothelium and permanent macrophages

Kidney

• 2 bean-shaped organs with a thin connective tissue capsule and surrounded by adipose tissue.
• Formed of outer cortex and inner medulla.
  • Outer Cortex: Reddish due to rich blood supply, granular (renal corpuscles), underneath the capsule.
  • Inner Medulla: Gray in color, consists of 6-12 medullary pyramids, each with an apex directed to the minor calyx, opening into major calyx, then to the renal pelvis.
  • Urinary passages lined by transitional epithelium.

Uriniferous Tubules

• Nephron and collecting ducts form uriniferous tubules.
  • Nephrons: Structural and functional units, form urine.
    • Renal corpuscle: Double-walled capsule, outer layer (parietal, lined by simple squamous epithelium), inner layer (visceral, modified simple squamous cells called podocytes), and glomerulus.
• Collecting ducts: Concentrate and carry urine to ureters.

This quiz covers essential topics in human anatomy, focusing on the structure and function of the kidney and different types of cartilage. Test your knowledge on nephron components, cartilage types, and bone formation. Perfect for students studying anatomy and physiology.