what does the skeletal system consist of
- bones
- cartilage
- joints
how many bones are there in a human adult
around 206
what are the categorisation of skeletons in the human body
- AXIAL skeleton (80 bones)
- skull (29)
- vertebral column (26)
- thorax [ribs & sternum] (25) - APPENDICULAR skeleton (126)
- Pectoral girdle & upper limbs (64)
- Pelvic girdle & lower limbs (62)
Types of bones
- Long
- Short
- Flat
- Irregular
Functions of bones
- Support
- Movement
- Protection
- Blood formation (bone marrow)
- Electrolyte balance (in blood)
- Acid-base balance
- Storage of energy
Composition of bones
- BONE TISSUE
- PERIOSTEUM: fibrous outer & osteogenic underneath layer (not on articular cartilage)
- ENDOSTEUM: covering the yellow bone marrow
*lines MARROW CAVITY (holding red/yellow bone marrow) - Articular cartilage: covers ends of bones
- Blood vessels
- Nerves
*BONE MARROW (in centre of bone):
- Yellow: fat tissue (MAY redifferentiate to RED marrow at stress)
- Red [in FLAT, IRREGULAR bones and ENDS of adult femur/humerus: Hematopoietic
Segments of a (long) bone (end -> middle): EPIphysis -> METAphysis -> DIAphysis (shaft)
*growth place for children
Composition of Bone tissue
*bone tissue: MAIN component of bones
HARD connective tissue composition:
1. Cells
- Osteocytes (trapped in lacunae/space within BONE MATRIX): bone maintenance, remodeling, mechano-sensing
- Osteoclasts: bone resorption & remodeling, dissolves bone matrix (related to WBCs)
- Osteoblasts: generate NEW bone matrix & osteocytes
- Mineralised matrix
- ORGANIC: protein fibers (primarily collagen) & other materials
- Inorganic: hydroxypatite (specialised crystals) Ca2+ salts, Mg2+, Na+, K+, F-, SO42-, CO32-, OH-) - Compact bone tissue *osteon (structural unit)
> found at OUTER layer of bones (+ shafts/diaphysis of long bones) - Spongy bone tissue
> found in INTERIOR of skull bones, vertebrae, sternum, pelvis (+ ends of long bones)
*resembles sponge due to cavities between trabeculae (beams/plates of bone); cavities contain BONE MARROW
*OSTEOPOROSIS (porous bone): bone has too much RESORPTION and/or too little bone formation -> Ca2+/ PO43-/ Vit D/ diet/ Hormones/ exercise/ therapeutics
important bones of the body
Cranium -> skull
Mandible -> jaw
clavicle -> collarbone
scapula -> shoulder blade
sternum -> central chest bone
rib
vertebrae -> lower back (spinal cord)
humerus -> upper arm
ulna -> lower/ INNER arm (smaller)
radius -> lower/OUTER arm (bigger)
hip bone
femur -> upper thigh
patella -> knee cap
tibia -> calf/ INNER (bigger)
fibula -> calf/ OUTER (thinner)
Cartilage composition, location, features, types
Composition: made of TOUGH cartilaginous connective tissue
Location: in articulating ENDS of bones, thorax, nose, trachea, outer ear, larynx *structures not related to bone directly
Cells involved: chondrocytes (in lacunae, arise from perichondrium) - secrete cartilage matrix
- in lacunae, extracellular matrix
*EXTRACELLULAR MATRIX
> collagen/elastic fibers
> ground substances: H2O, glycosaminoglycans (chondoitin sulfates, keratan sulfate, hyaluronic acid etc), proteoglycans
*almost always covered by PERICHONDRIUM
** NO BLEED VESSELS/ NERVE (except in perichondrium)
Types:
1. Elastic cartilage (elastic fibers in matrix)
2. FIBROcartilage (COLLAGEN fibers in ground substance)
3. HYALINE cartilage (associated with perichondrium)
Muscle tissue features, types
Mainly composed of SPECIALISED cells -> MUSCLE FIBERS
- Contracts/ shortens with force
- Moves human body, organs, pumps blood
Types:
1. SKELETAL muscle tissue: Striated, Voluntary
2. CARDIAC muscle tissue: Striated, INVOLUNTARY
3. Smooth muscle tissue: non-striated, INVOLUNTARY
function: regulates all movements of human body (muscle contraction)
*except: cilia, flagellum, ameboid movement (some WBCs)
Skeletal muscle tissue features
- Elongated
- Cylindrical
- UNBRANCHED
- Striated muscle fibers
- Plasma membrane -> sarcolemma
- Cytoplasm -> Sarcoplasm (contents: myofibrils/ myofilaments, mitochondria, Golgi complex, ER/ sarcoplasmic reticulum)
- MULTI-NUCLEI: FLATTENED (near periphery beanth sarcolemma)
How muscles are formed (->: bundling): myofilaments -> myofibrils -> muscle fibers (cells) -> fasicles -> muscle fibers
Sacromere components/ feature
SARCOMERE: contractile unit of myofibril
I band (light) -> Z line(disc)
A band (dark) -> M line, H zone
made of thin & thick myofilaments
THIN: mainly made of ACTIN (attached to Z line), TROPOMYOSIN, TROPONIN [ATT]
THICK: mainly made of MYOSIN (attached to M line)
- as muscle contrcts -> filaments on thick & thin (within A band) interact with one another
*Myofibril: formed by a bundle of thick & thin filaments
Terminology (skeletal muscle): Origin, Insertion, Action, Agonist, Synergist, Antagonist
Origin: muscle attachment that remains STATIONARY while the muscle contracts
Insertion: Muscle attachment that MOVES while the muscle contracts
Action: specific MOVEMENT (eg. flexion, extension) produced by a muscle contraction
Agonist: muscle(s) responsible for producing a particular movement
Synergist: muscle(s) ASSISTING agonist in performing the particular movement
Antagonist: muscle(s) OPPOSING the action of agonist - to control (eg. speed/ smoothness of movement)
impt muscles in human body
Face
Buccinator (around cheek) - for blowing/ smiling
Masseter (jaw) - for chewing
Neck
Sternocleidomastoid (from skull to chest, diagonal) - for bending/ tilting neck
[Chest] Pectoralis major
[Stomach] Rectus abdominus
Arm
deltoid* -> shoulder
biceps brachii
Triceps brachii
Leg
Gluteus maximus*
Adductor longus -> hip/thigh
Biceps femoris -> back of upper thigh
Quadriceps femoris -> above knee cap, front
Tibialis anterior -> front of calf
Gastrocnemius -> calf
*deltoid/ gluteus maximus - used for IM injection
> Gluteus: at upper outer corner - AVOID sciatic nerve (biggest nerve of body)
Functions of skeletal muscles
- Produce movements (skeletal muscles act on joints & bones)
eg. walking, pinching, respiration, facial expression (subtle) - Maintain posture, position & stability
eg. sitting, standing steady - Support & protect
- Abdominal wall - protects internal organs
- Pelvic diaphragm - protects pelvic organs (from prolapse) - Guards entrances/ exits
- Sphincters - enable voluntary control of swallowing, micturition (urination), defecation & parturition - Maintain body temperature
- Chemical energy converted to heat during muscle contraction & shivering
Joint definition, types
joint: SPECIALISED site of contact/ reunion between 2 or more bones
- actively moved by CONTRACTION/ shortening of skeletal muscles that stretch across
Types
1. Fibrous (eg. suture between skull bones)
2. Cartilaginous (eg. symphysis pubis - plate btw hip bones anteriorly)
3. Synovial *with synovial cavity (eg. shoulder, knee joints) ** MOST MOBILE
> Major components:
- Joint capsule (surrounds 2 knee bones, connective tissue)
- Synovial membrane (just beneath joint capsule)
- Joint cavity
- Articular cartilage *HYALINE (between bones)
> Major TYPES
1) Ball-and-socket joint (eg. shoulder, hip)
2) Hinge joint (eg. elbow, knee)
3) Pivot joint (eg. radioulnar joint - neck, wrist)
4) Planar joint *flat (eg. intercarpal joint)
*shoulder joint - movements of bone: Adduction // Abduction // Extension // Flexion // Medial rotation // Lateral rotation // Circumduction
*Knee joint (2 types)
1. Hinge: between femur & tibia
2. Gliding: between femur & patella (behind knee cap)
> Major components:
- Bones: Femur, tibia, patella
- Articular catilage
- Synovial membrane
- Joint capsule
- Joint cavity
*- Menisci & ligaments (increases fitting between bones)
> Movements: Flexion // Extension (quadriceps femoris contracts) // (possibility of) slight rotation & gliding *while flexed
~ Osteoarthritis: joint space narrowing // sclerosis of subchondral bone // osteophyte formation // eventual cystic changes in adjacent bone
^joint pain
^ use of chondroitin sulfates/ hyaluronic acid/ glucosamine as dietary supplements -> increase cartilage
blood components, characteristics
with anticoagulant + centrifuged (bottom -> top):
- RBCs (42- 47%)
- Buffy coat: leukocytes + platelets (1%)
- Plasma: water [~92%], proteins [~7%] (albumins, globulins, fibrinogen, regulatory proteins), other solutes [~1%] (electrolytes, organic nutrients, organic wastes)
*no anticoagulant -> coagulation (bottom -> top)
- Blood clot: fibrin-containing network trapping blood cells
- Serum: protein-rich fluid (albumin, immunoglobulins, other components) WITHOUT fibrinogen (converted to fibrin/ used for clotting)
Characteristics:
- Volume in adult: 5-6L (M) // 4-5L (F)
- pH: 7.35 - 7.45 (slightly alkaline)
- Color: scarlet/ bright red (oxygenated) -> deep/ dark red (deoxygenated)
Types of blood cells, features, functions
- Erythrocytes (RBCs): transport oxygen + part of CO2
- [M] 4.5-6.3 x 10^6 per uL // [F] 4.2-5.5 x 10^6 per uL
- Generated in RED bone marrow, lifespan ~3-4months -> worn-out RBCs removed by macrophages/ destroyed in liver & spleen
- Appearance: Biconcave disc (diameter 6-8um, ~2um thick at rim) -> LARGE surface area for O2 entry/exit + allow RBC to bend, flex in small capillaries; [Mature] NO nucleus & organelles
- Hemoglobin-containing (red, [M] 14-18g/dl, [F] 12-16g/dl, [infant] 14-20g/dl] -> binds to O2 & part of CO2
**Sickle cell anemia: point mutation of Hb beta chain -> HbS
- HbS polymerise & aggregates when de-oxygenated ‘sickled erythrocytes’
- Increased blood viscosity & shortened RBC lifespan -> anemia, anoxia
- HbS carrier: resistant to malaria
- Leucocytes (WBCs): defense & immune systems -> remove pathogens + toxins, abnormal/damaged cells
- contains nuclei + various organelles (vs RBCs)
- 6000-9000/uL blood
- Migrates to other tissues - Body WBCs mostly found in connective & lymphoid tissues
- Originates from BONE MARROW STEM CELLS, lifespan mostly a few days
- Granulocytes vs Agranulocytes: visible granules (neutrophils, basophils, eosinophils) vs NO visible granules under LM (lymphocytes, monocytes) - Thrombocytes (platelets): Blood clotting
Neutrophils characteristics
Neutrophil - Polymorphonuclear leukocyte
- 50-70% of circulating WBCs (stay in bloodstream ~10h)
- 12-15um (diameter)
- Nucleus: segmented (3-5 lobes connected by fine strands)
- Cytoplasm: packed with pale (“neutral colored”) granules containing bactericidal compounds
- HIGHLY MOBILE & generally the 1st WBC to arrive @ site of acute inflammation/ phagocytosis; specialised in attacking & digesting bacteria that have been ‘marked’ for destruction
Eosinophil characteristics (size/color/features, lifespan, function)
- 2-4% of circulating WBCs
- Size similar to neutrophils
- Reddish-orange
- Usually bilobed nucleus
- Survive for minutes to days, move to tissues after a few hours
- Function: phagocytise antibody-coated bacteria, protozoa, cellular debris
*main method of attack: exocytosis of toxic compounds onto surfaces of target - IMPORTANT defenders against LARGE, MULTICELLUALR parasites (number increases dramatically in parasitic infeciton)
Basophil characteristics (feature, appearance, location)
- <1% of circulating WBCs
- contain deep purple/ blue basophilic granules
- Usually bilobed nucleus (often obscured by granules)
- Migrate to injury sites & discharge contents of granules (eg. histamine, heparin) -> enhance local inflammation initiated by mast cells + attract other WBCs
*involved in INFLAMMATORY reactions during immune response + in acute & chronic ALLERGIC reactions (anaphylaxis, asthma)
Monocyte characteristics (appearance, lifespan, function)
- 2-8% of circulating WBCs
- 13-25um in diameter (almost 2x RBC)
- Nucleus: LARGE, eccentrically placed, tends to be oval/ kidney-shaped
- Lifespan: stays in circulation for ~24h before entering other tissues to become macrophages (aggressive phagocyte)
FUNCTIONS
- Generate TISSUE MACROPHAGES
- Phagocytise & digest protozoa, virus & aged cells (might not be effectively dealt with by neutrophils)
- Antigen presentation
Lymphocyte characteristics (appearance, location)
- 20-30% of circulating leukocytes
*T & B lymphocytes CANNOT be differentiated on blood smear (typical lymphocytes: thin halo of cytoplasm around a relatively large nucleus)
- Slightly larger than RBCs
- Continuously migrate from blood to other tissues & back to blood
- Lymphocytes in blood stream only a fraction of body’s total lymphocytes; most lymphocytes found in other connective tissue + in lymphatic organs
platelets (thrombocytes) characteristics (appearance, lifespan, levels/range, LM features, functions)
- Appearance: flattened disk-like cell fragments (~1-4um) [produced from shedding of megakaryocytes]
- Part of blood clotting system to stop hemorrhage
- Lifespan: circulate for ~9-12d before being removed by splenic phagocytes (continuously being replaced)
LM features:
- Non-nucleated cell fragments
- Varying in size (1-4um)
- Purple stained & granular appearance on blood smear
Functions
1) Adhere to collagenous tissue @ margin of vascular damage to form temporary patch (platelet plug)
2) Release chemicals/factors inducing platelet aggregation
3) Promote blood clot (thrombus) formation, retraction, or removal (at a later stage)
4) Secrete factors involved in vascular repair
