A Comprehensive Guide to Human Tissues: Bone, Cartilage, Blood, and Skin
Bone, Cartilage, and Blood
Bone
A bone is a rigid organ that constitutes part of the vertebrate skeleton. Bones have several vital functions:
- Support and protect various organs
- Produce red and white blood cells
- Store minerals
- Provide structure and support for the body
- Enable mobility
Cartilage
Cartilage is a firm, whitish, flexible connective tissue found in various forms in the:
- Larynx and respiratory tract
- Structures such as the external ear
- Articulating surfaces of joints
Blood
Blood is the red liquid that circulates in the arteries and veins of humans and other vertebrate animals. It carries oxygen to and carbon dioxide from the tissues of the body.
Cells of Cartilage and Bone
- Cartilage: chondrocytes
- Bones: osteocytes in lacunae
Types of Cartilage
Hyaline Cartilage
- Most common type of cartilage
- Found in the ribs, nose, larynx, trachea
- Precursor to bone
- Glassy appearance, slightly basophilic in H&E sections
- Widely dispersed fine collagen fibers (type II) for strength
- Has a perichondrium
- Weakest of the three cartilage types
Fibrocartilage
- Found in intervertebral discs, joint capsules, ligaments
- Strongest type of cartilage
- Alternating layers of hyaline cartilage matrix and thick layers of dense collagen fibers
- Collagen fibers oriented in the direction of functional stresses
- Does not have a perichondrium
- Transitional layer between hyaline cartilage and tendon or ligament
Elastic Cartilage
- Found in the external ear, epiglottis, and larynx
- Chondrocytes in a threadlike network of elastic fibers within the matrix
- Provides strength, elasticity, and maintains shape
- Has a perichondrium
Components of Blood
Erythrocytes (Red Blood Cells)
- Typically a biconcave disc without a nucleus
- Contain hemoglobin, which imparts the red color to blood
- Transport oxygen and carbon dioxide to and from the tissues
Leukocytes (White Blood Cells)
- Colorless cells that circulate in blood and body fluids
- Involved in counteracting foreign substances and disease
- Several types, all amoeboid cells with a nucleus
- Examples: lymphocytes, granulocytes, monocytes, macrophages
Platelets
- Small, colorless, disk-shaped cell fragments without a nucleus
- Found in large numbers in blood
- Involved in clotting
Connective Tissue Cells
- Fibroblast: Produces collagen and other fibers
- Mast cells: Filled with basophil granules, release histamine and other substances during inflammatory and allergic reactions
Organs and the Integumentary System
Organ
A part of an organism that is typically self-contained and has a specific vital function, such as the heart or liver in humans.
Skin Pigmentation
The relative coloration of the skin depends on the amount of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes.
Types of Muscle Tissue
Skeletal Muscle
- Attaches to and moves bones
- Contracts and relaxes in response to voluntary messages from the nervous system
- Composed of long cells called muscle fibers with a striated appearance
- Muscle fibers organized into bundles supplied by blood vessels and innervated by motor neurons
Cardiac Muscle
- Found only in the myocardium (middle layer of the heart wall)
- Responsible for the heart’s pumping action
- Contracts in response to signals from the cardiac conduction system
- Made from cells called cardiocytes, which have a striated appearance
- Cardiocytes are branched, forming a network for coordinated contraction
Smooth Muscle
- Found in the walls of hollow organs throughout the body
- Contractions are involuntary, triggered by impulses from the autonomic nervous system
- Arrangement of cells allows for contraction and relaxation with great elasticity
- Examples: urinary bladder, uterus, alimentary canal, eye, artery walls
Nail Bed Anatomy
The nail bed extends from the lunula to the hyponychium. Ridges on the underside of the nail plate extend to the lunula, with blood vessels oriented on the same axis. The epidermis of the nail bed is thick, becoming thicker at the nail folds. The dermis is sparse with little fat. Sweat ducts are present at the end of the nail bed.
Sweat Glands
Sweat glands, also known as sudoriferous or sudoriparous glands, are small tubular structures in the skin that produce sweat. They are a type of exocrine gland, secreting substances onto an epithelial surface through a duct.
Thermoregulation
During strenuous physical activities, dermal blood vessels dilate, and sweat secretion increases to prevent overheating. In cold temperatures, dermal blood vessels constrict to minimize heat loss.
Layers of the Skin and Burn Classification
The skin comprises the dermis, epidermis, and hypodermis. Burns are classified into three degrees based on the depth of damage:
- First-degree: Superficial, partial-thickness
- Second-degree: Deep, partial-thickness
- Third-degree: Full-thickness
Cellular Secretion (Exocytosis)
Cellular secretion is a process by which a cell directs secretory vesicles out of the cell membrane.
The Integumentary System
: consists of the skin, hair, nails, glands, and nerves. Its main function is to act as a barrier to protect the body from the outside world. It also functions to retain body fluids, protect against disease, eliminate waste products, and regulate body temperature.