MedicoPlexus
Human Anatomy & Histology
1. Osteology – Common study of bones. Shape and internal structure. The bone as an organ.
Skeletal system: The framework of the body, consisting of bones and other connective tissues such as cartilage, which protects and supports the body tissues and internal organs.
The adult human skeletal system consists of 206 bones, as well as a network of tendons, ligaments and cartilage that connects them. The skeletal system performs vital functions — support (bones hold the entire weight of the body) , movement (skeletal muscles use the bones as levers), protection (e.g., the ribs protect the lungs and heart), blood cell production, calcium and phosphorus storage and endocrine regulation — that enable us to survive.
Two types of bone:
-Axial skeleton: skeleton that consists of the bones of the head and trunk of a vertebrate. In the human skeleton, it consists of 80 bones and is composed of six parts: the skull bones, the ossicles of the middle ear, the hyoid bone, the rib cage, sternum and the vertebral column.
-The axial skeleton is formed by the vertebral column, the rib cage (12 pairs of ribs and the sternum), and the skull. The appendicular skeleton is formed by the pectoral girdles, the upper limbs, the pelvic girdle, and the lower limbs.
four types of bone:
-Long bones have a tubular shaft and articular surface at each end. The major bones of the arms (humerus, radius, and ulna) and the legs (the femur, tibia, and fibula) are all long bones.
-Short bones also have a tubular shaft and articular surfaces at each end but are much smaller. The short bones include all of the metacarpals and phalanges in the hands, the metatarsals and phalanges in the feet, and the clavicle (collarbone).
-Flat bones are thin and have broad surfaces. The flat bones include the scapula (wing bone), the ribs, and the sternum (breastbone).
-Irregular bones are irregular in size and shape and are usually quite compact. They include the bones in the vertebral column, the carpal bones in the hands, tarsal bones in the feet, and the patella
Normally bones are composed of osseous tissue, fibrous connective tissue, cartilage, vascular, lymphatic, adipose and nervous tissue. They normally have dense compact bone on the outside and spongy bone on the inside. bones are made from:
Osteoblasts:
Osteoblasts are bone-forming cells that descend from osteoprogenitor cells. They form a protein mixture known as osteoid, which mineralizes to become bone. Osteoid is primarily composed of Type I collagen. Osteoblasts also manufacture hormones, such as prostaglandins, to act on the bone itself. They robustly produce alkaline phosphatase, an enzyme that has a role in the mineralization of bone, as well as many matrix proteins. Osteoblasts are the immature bone cells, and eventually become entrapped in the bone matrix to become osteocytes, which are the mature bone cells. All bone lining cells are osteoblasts.
Osteocytes:
Osteocytes are mature bone cells that originate from osteoblasts, which have migrated into and become trapped and surrounded by bone matrix, produced by themselves. The spaces they occupy are known as lacunae. Osteocytes have many processes that reach out to meet osteoblasts and other osteocytes probably for the purposes of communication. Their functions include formation of bone, maintenance of matrix and homeostasis of Calcium.
Osteoclasts:
Osteoclasts are the cells responsible for bone resorption and remodeling. They are large, multinucleated cells located on bone surfaces in what are called Howship’s lacunae or resorption pits. These lacunae, or resorption pits, are left behind after the breakdown of the bone surface. Because the osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with phagocytic-like mechanisms similar to circulating macrophages.
Bone matrix: The intercellular substance of bone tissue consisting of collagen fibers, ground substance, and inorganic bone salts.
2. bone development and growth.
Osteogenesis: formation of bone.
Occurs via:
- embryonic laying down of bony skeleton in 8th week
- bone growth continuing to adulthood.
- remodeling and repair in adulthood via ossification (Ossification is the process in which cartilage is transformed into bone.)
calcification: Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue, causing it to harden. type of ossification:
Intramembranous ossification: Occurs along a template of membrane, as the name implies, primarily in compact flat bones of the skull that do not have Haversian systems. The skull and mandible (lower jaw) of the fetus are first laid down as a membrane. Osteoblasts attach to the membrane, ossifying from the center of the bone outward. The edges of the skull’s bones do not completely ossify to allow for molding of the head during birth. Instead, six soft spots, or fontanels, are formed: one frontal, two sphenoidal, two mastoidal, and one occipital.
Endochondral or intracartilaginous ossification: Occurs when mineral salts calcify along the scaffolding of cartilage formed in the developing fetus beginning about the fifth week after conception. This process, known as calcification, takes place in the presence of vitamin D and a hormone from the parathyroid gland. The absence of any one of these substances causes a child to have soft bone, resulting in a disorder called rickets.
A primary ossification center is the first area of a bone to start ossifying. It usually appears during prenatal development in the central part of each developing bone. In long bones the primary centers occur in the diaphysis/shaft and in irregular bones the primary centers occur usually in the body of the bone. The site where bone formation continues after beginning in the long shaft or body of the bone, usually in an epiphysis, secondary ossification center.
Blood supply to bones:
Nutrient artery:
This artery enters the shaft through the nutrient foramen and runs obliquely through the cortex. In the medullary cavity this artery divides into ascending and descending branches. Each one of these two branches divides into parallel channels that head towards the respective end of the bone. At the place of metaphysis in case of adult bones these branches anastomose with epiphyseal, metaphyseal and periosteal arteries. The nutrient artery in this way nourishes the whole medullary cavity and inner 2/3 of the cortex as well as metaphysis.
Periosteal arteries:
Periosteal arteries are the arteries of periosteum being especially numerous beneath the muscular and ligamentous attachment. Beneath the periosteum they divide into branches and thereby entering the Volkmann’s canals to supply the outer one third (1/3) portion of the cortex. Remember that the inner 2/3 of the cortex was supplied by the nutrient artery discussed above.
Epiphyseal arteries:
These are the arteries of epiphyses and are derived from the peri-articular vascular arcades found on the nonarticular bony surfaces. This area also has numerous foramina out of which only few are the entrance points of these arteries while the remaining are the venous exits.
Metaphyseal arteries:
These arteries are derived from the neighboring systemic vessels. These arteries directly go into the metaphysis and reinforce the metaphyseal branches of the primary nutrient artery.
Hormones affecting growth: Growth hormone (GH)
Parathyroid hormone (PTH).
Estrogens.
Calcitonin and thyroid stimulating hormone (TSH), both of which inhibit the activity of osteoclasts.
Calcitriol (1,25[OH]2 vitamin D3.
Dietary regulations:
Ca, P, Mg, F, Fe, vit.d ,vit.c, vit.a, vit.k
3. Cranial Calvaria. (skull cap)
The calvaria (skullcap) is made up of the superior portions of the frontal bone, occipital bone, and parietal bones. In the human skull, the sutures between the bones normally remain flexible during the first few years of postnatal development, and fontanelles are palpable. Premature complete ossification of these sutures is called craniosynostosis.
Structure
Resistance structures of calvaria
The outer surface of the skull possesses a number of landmarks. The point at which the frontal bone and the two parietal bones meet is known as “Bregma”. The point at which the two parietal and occipital bones meet is known as “Lambda”. Not only do these landmarks indicate the fontanelle in newborns, but they also act as reference points in medicine and surgery.
The inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, together with numerous furrows for the lodgment of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several depressions for the arachnoid granulations, and at its back part, the openings of the parietal foramina when these are present.
It is crossed in front by the coronal suture and behind by the lambdoid suture, while the sagittal suture lies in the medial plane between the parietal bones.
Layers
The outer layer of the skull has been removed and shows the diploic veins and inner layer.
Most bones of the calvaria consist of internal and external tables or layers of compact bone, separated by diploë. The diploë is cancellous bone containing red bone marrow during life, through which run canals formed by
diploic veins. The diploë in a dried calvaria is not red because the protein was removed during preparation of the cranium. The internal table of bone is thinner than the external table, and in some areas, there is only a thin plate of compact bone with no diploë.
4. internal surface of cranial base.
Introduction to skull base anatomy:
The skull base forms the floor of the cranial cavity and separates the brain from other facial structures. This anatomic region is complex and poses surgical challenges for otolaryngologists and neurosurgeons alike. Working knowledge of the normal and variant anatomy of the skull base is essential for effective surgical treatment of disease in this area.
The 5 bones that make up the skull base are:
ethmoid bone
sphenoid bone
occipital bone
temporal bone petrous portion
paired frontal bones
paired parietal bones
Bones forming palate:
Palatine bone
Maxilla bone
The skull base can be subdivided into 3 regions: anterior cranial fossa accommodates the anterior lobe of brain (or frontal lobes, left and right)
Formed by:
orbital plate of the frontal bone cribriform plate of ethmoid bone lesser wings of the sphenoid bone
Boundaries:
Anteriorly: posterior wall of frontal sinus
Posteriorly: roof of sphenoid sinus
Laterally: frontal bone (paired, both sides)
Centrally: ethmoid bone
In the center of this region is the cribriform plate, through which the olfactory tracts pass
If cribriform plate is injured, then there will be loss of sensation of smell middle cranial fossa
The petro-occipital fissure subdivides the middle cranial fossa into 1 central component and 2 lateral components
contain the 2 temporal lobes of brain
Boundaries:
Anteriorly: Greater wing of sphenoid bone
Posteriorly: superior borders of petrous part of temporal
Laterally: squamous part of temporal and some part if parietal and greater wings of sphenoid Centrally: Sella turcica (or Sella turcica) of body of sphenoid posterior cranial fossa accommodates the occipital lobes of the brain
Boundaries:
Anteriorly: superior border of the petrous part of temporal bone
Posteriorly: lesser part of the occipital squama
Laterally: Temporal & parietal bone
Floor: Occipital bone
Centrally: Foramen magnum
The anterior cranial fossa is separated from the middle cranial fossa by the lesser wing of the sphenoid, and the middle cranial fossa is separated from the posterior cranial fossa by the petrous part of the temporal bone. vessels, nerves passing through skull structure:
Incisive canal: nasopalatine nerve and artery.
greater palatine foramen: greater palatine nerve and artery lesser palatine foramine: lesser palatine nerve and artery foramen ovale: mandibular nerve, venous plexus of foramen ovale.
foramen spinosum: meningeal branch of mandibular nerve and middle meningeal artery carotid canal: internal carotid artery, sympathetic carotid plexus, internal carotid venous plexus.
petrotympanic fissure: anterior tympanic artery, chorda tympani, jugular foramen: inf. petrosal sinus, glossopharyngeal nerve, post. meningeal artery, jug vein hypoglossal canal: hypoglossal nerve stylomastoid foramen: facial nerve, stylomastoid artery condylar canal: condylar emissary vein foramen magnum: medulla oblongata, spinal part of accessory nerve, 2 vertebral arteries, ant. spinal artery, post. spinal artery, spinal vein.
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