Chapter 3 - Bone Physiology Flashcards
What are two categories of skeleton?
Axial and Appendicular
Axial
skull, vertebral column, sternum, and ribs
Appendicular
bones of upper/lower limbs, the girdles that support them, hands and feet
What makes up bones?
osseous tissue and bone marrow
What is osseous tissue?
mineralized bone tissue, major structural and supportive connective tissue of the body
What is marrow?
soft, fatty tissue found in cavities of bones. Active red marrow can perform hemopoiesis (blood formation), and inactive yellow marrow is capable of converting back to active marrow and is for fat storage.
Bone is highly:
vascular
What are the 5 types of bones
Long, short, flat, sesamoid, and irregular
Long bones
- longer than they are wide
ex. toes, humerus, femur
Sesamoid bones
- sesame seed shape; specialized bones found within tendons; small, flat, and oval shaped; important to increase muscle leverage and increase longevity of tendons
ex. patella
Irregular bones
bones that do not easily fit into other classifications
ex. vertebrae
Periosteum
outermost layer of bone, formed from dense, irregular collagenous tissue
- vascularized connective tissue enveloping bones except at surfaces of joints
- richly supplied with blood vessels and axons
- anchored to the deeper regions of a bone by collagen fibers called perforating fibers
What is the layer underneath the periosteum?
Compact Bone (cortical bone)
Compact bone
- aka cortical bone
- provides strength and resistance to compression, twisting, and shear stress
What is the layer underneath compact bone?
Spongy bone (cancellous/trabecular)
Spongy bone
- aka cancellous/trabecular bone
- has a spongy/honeycomb appearance
- collagenous interior walls of honeycomb are called trabeculae and are covered by a thin layer of connective tissue called ENDOSTEUM
- wells of honeycomb, between the trabeculae, are cavities filled with bone marrow; wells are collectively called the MEDULLARY CAVITY
What are the ends of long bones covered in?
Hyaline cartilage
What is the significance of epiphyseal lines?
indicate what remains of epiphyseal plate (aka growth plate); made of hyaline cartilage
In flat bones, what is the spongy bone region called?
Diploe
Some ___________ bones have an inner region called __________ with and ____ filled cavity that is lined w/ ____________________.
irregular; the sinus; air; mucous membranes
Hematopoietic Stem Cells
stem cells derived from mesoderm that produce all other blood cells through hematopoiesis
Yellow marrow is mostly:
blood vessels and adipocytes
When do you have more red marrow than yellow marrow? Why?
infantry and young childhood; to support their rapid growth and increasing blood cell requirements.
Stem cell growth factors
- granulocyte-macrophage colony-stimulating factor (GM-CSF)
- granulocyte colony-stimulating factor
— both allow for isolation of hematopoietic stem cells from peripheral blood and not bone marrow
Osteoblast
- BUILD bone
- ossification (secretion of organic and inorganic components into extracellular matrix)
Osteocytes
- most common cell
- mature osteoblast
- maintain blood health
- entrapped in lacuna
- recruit osteoblasts to strengthen areas of bone with increased tension/compression
- resemble an octopus
Osteoclasts
- bone BREAKDOWN (resorption)
- secretion of acid-forming protons and specialized metallo-proteases
- large, multinucleated cells that originate from macrophages
- sit in shallow depressions on both internal and external bone surfaces
Osteoprogenitor cells
- only bone cells that undergo mitosis and therefore increase their number through cell division
- during development, these cells differentiate into osteoblasts (allows new bone to form in places where there was previously no bone tissue)
Bone Marrow Transplants
- Pioneered by E. Donnall Thomas
- Transplanted to produce new red blood cells
- Used to treat leukemia, lymphoma, neuroblastoma, and other cancers
- Risks: infections, severe liver injury, damage to mucosal membranes, graft-versus-host disease
HIGH plasma calcium levels
- triggers the release of CALCITONIN from the thyroid gland
- calcium salts deposited in the bone
LOW plasma calcium levels
- triggers the release of PTH from the parathyroid glands
- Calcium is released from the bones by osteoclast activity and resorbed by the kidneys and intestine
Wolff’s Law
bones adapt and are remodeled based on the compressive force or load placed on them
Inorganic matrix makes up _____ of bone’s total weight
65%
Ca+ and P- of inorganic matrix =
hydroxyapatite
Organic matrix makes up _______ of bone’s total weight
35%
Organic matrix
- supplies flexibility
- collagen, protein, fibers, proteoglycans, glycosaminoglycans, glycoproteins, etc.
- most abundant protein fibers are collagen fibers = tropocollagen
Cells in parathyroid glands detect changes in plasma calcium concentration and respond by releasing either _____ or ______________ into blood stream
PTH; Calcitonin
Processes induced by PTH
- stimulation of osteoclast activity leads to breakdown of bone matrix which leads to release of stored calcium into the blood
- retention of calcium by the kidneys so less is excreted in urine
- reabsorption of calcium by the intestines so that less is excreted in feces
If plasma calcium levels > 9-11 mg/100 mL of blood:
- reduction of PTH secretion
- release of calcitonin hormone from cells in thyroid gland (opp. effect of PTH)
- reduction of osteoclast activity and stimulation of osteoblast activity and stimulation of osteoblast activity leads to promoting uptake and storage of calcium in bone matrix
Stages of Bone Repair
- clotting of blood to form hematoma and death of bone cells being deprived of nutrients
- a soft CALLUS is formed via fibroblasts (secretes ECM proteins) and holds pieces of bone together temporarily stabilizing fracture.
- spongy bone formation begins
- bone remodeling occurs over next several months, compact bone is added, etc.
Osteoporosis
- weakens bone to a point where they cannot adequately support weight or resist breakage
- stooped posture and loss of vertical height
Causes of Osteoporosis
- bone mass decreases as we age by osteoclast activity outpaces osteoblast activity
- common in menopausal women
Osteoporosis Diagnosis
- bone density measured with dual-energy X-ray absorptiometry
- compares bone density to healthy young adult female’s and T-score is done
Contributors to Osteoporosis
- chronic alcoholism
- dietary imbalances
- removal of ovaries
- endocrine disorders (hyperthyroidism and cortisol imbalances)
- kidney disorders
Trabeculae
loosely gathered mesh-work of extensively branched bone tissue; lack OSTEONS and central/perforating canals; cells can obtain oxygen and nutrients from blood vessels supplying marrow.
2 types of Bone growth
- intramembranous
- endochondral
Most bone growth is completed by age
7 years old
First immature bones are called
Primary bones (irregularly arranged collagen bundles, osteocytes, some inorganic matrix)
Mature secondary bone
resorbed primary bones by osteoclast activity; fully formed lamellae, regularly arranged bundles, more inorganic matrix therefore its MUCH stronger.
Intramembranous ossification
- occurs within membrane made of embryonic mesenchyme
1. mesenchyme thickens and develops a rich supply of blood capillaries; differentiation into osteoblasts; osteoid will calcify to form islands of new bone
2. some osteoblasts become completely surrounded by bone; osteoblasts become osteocytes; spicules of new bone extend from ossification centers
3. bone needs O2 and nutrients to grow; small blood vessels branch in mesenchyme
4. layer of spongy bone is formed; marrow forming
5. bone is remodeled over time; layer of compact bone forms on both external and internal surfaces with a layer of spongy bone sandwiched between them.
Endochondral Ossification
- occurs in hyaline cartilage
1. fetal hyaline cartilage model develops
2. cartilage calcifies, and a periosteal collar forms around diaphysis
3. primary ossification center forms in the diaphysis
4. secondary ossification centers form in epiphysis
5. bone replaces cartilage, except at articular cartilage and epiphyseal plates
6. epiphyseal plates solidify and form epiphyseal lines
2 peptide hormones that influence bone lengthening process
Growth Hormone (GH) and Insulin-like growth factor (IGF)
Growth Hormone (GH)
- peptide released from somatotroph cells of anterior pituitary gland
- regulated by hypothalamus w/ 2 separate peptide hormones: growth hormone releasing hormone (GHRH) and somatostatin (SST)
- DOES NOT DIRECTLY PROMOTE GROWTH
Growth Hormone Releasing Hormone (GHRH)
promotes release of GH from anterior pituitary
Somatostatin (SST)
reduces GH release
Insulin like growth factor (IGF)
- as GH circulates around body, it induces the release of a second peptide hormone (IGF)
- several forms of IGF; IGF-1 is most relevant
- IGF-1 (aka somatomedin C) is primarily produced in liver and skeletal muscles (DIRECTLY MEDIATES GROWTH OF BONES BY STIMULATING THE PROCESSES AND CELLULAR CHANGES IN EPIPHYSEAL PLATE)
GIGANTISM
abnormal excess of GH secretion during childhood before the epiphyseal plates close
- can be cause by hypersecreting benign tumor
Short Stature/Dwarfism
- 4’10” or less
- common causes: radiation treatments affecting GH secretion from anterior pituitary, deficiency of GH secretion w/ poorly developed pituitary gland, genetic mutations of GH receptors in the cells that secrete IGF-1 OR genetic mutations in GH receptors in the cells that RESPOND to IGF-1, or genetic mutations that impair the secretion of IGF-1
Appositional Bown Growth
- bones growing thick/wide
- increase in diameter of bones by addition of bony tissue at outer surface
Acromegaly
- bones of hands, feet, and face abnormally thicken while tissues in the extremities abnormally soften
- abnormal enlargement of internal organs
- all caused by increased secretion of GH (hypersecreting tumors in anterior pituitary)
- AFTER epiphyseal plate closure
Bone breakage is determined by 3 things:
- total mass or density of bone
- geometric distribution/orientation of the force on bone
- material properties of bone
Viscoelasticity
a bone will react differently to applied loads based on weight, angle, and speed of load’s application
Load-deformation curve
measure strength of a bone by comparing external force and internal reaction
Stress-strain curve
stress vs. strain
