Skeletal System & Innate Immunity Lecture Review

Question-and-Answer flashcards covering key concepts from the lecture on skeletal physiology and innate immunity, including bone structure, cell types, calcium regulation, types of skeletons, biomechanics, innate immune defenses, white blood cells, Toll-like receptors, and lymphatic system functions.

What is the functional relationship between the muscular and skeletal systems?

Muscles generate force by pulling on skeletal elements, producing movement and supporting functions such as posture and heat generation.

What are the three major types of skeletons found in animals?

Hydrostatic skeletons, exoskeletons, and endoskeletons.

Describe a hydrostatic skeleton.

A fluid-filled cavity that provides structural support through internal pressure; common in soft-bodied invertebrates such as earthworms and jellyfish.

Give two examples of animals with hydrostatic skeletons.

Earthworms and jellyfish (or sea anemones).

Which skeletal components in vertebrates possess hydrostatic properties?

Intervertebral discs and synovial joint capsules, which are fluid-filled and cushion joints.

What is an exoskeleton and which major animal groups exhibit it?

A rigid outer covering that protects and supports the body, found in arthropods (chitin) and many mollusks (calcium carbonate shells).

What are the two main chemical compositions of exoskeletons?

Chitinous polysaccharide (arthropods) and calcium carbonate (mollusks).

Why must arthropods molt?

Their exoskeleton cannot grow with the body, so it must be shed (molting) and replaced to allow growth.

Which endocrine-controlled process allows growth in arthropods?

Molting, regulated by hormones (e.g., ecdysone pathways).

What is an endoskeleton in vertebrates primarily composed of?

Bone tissue made of collagen fibers mineralized with calcium phosphate (hydroxyapatite).

Name three general shapes of bones.

Long (rod), flat (plate), and irregular bones.

What protein fibers form the organic component of bone and what do they provide?

Collagen fibers; they give flexibility and a scaffold for mineral deposition.

Which inorganic crystal hardens the bone matrix?

Hydroxyapatite, a crystalline form of calcium phosphate.

Why is the collagen-hydroxyapatite ratio important?

Too much collagen makes bones overly flexible (rickets); too much mineral makes them brittle (osteogenesis imperfecta).

What is rickets?

A disorder of inadequate bone mineralization causing bowed, flexible weight-bearing bones, often from vitamin D or calcium deficiency.

Name the three major types of bone cells.

Osteoblasts, osteocytes, and osteoclasts.

What is the function of osteoblasts?

Build bone by secreting new matrix; they become osteocytes once surrounded by their matrix.

What is the function of osteocytes?

Mature bone cells embedded in lacunae that maintain bone matrix and sense mechanical stress.

What is the function of osteoclasts?

Multinucleated cells that resorb and dissolve bone, releasing calcium into the bloodstream.

Which hormone stimulates bone resorption when blood calcium is low?

Parathyroid hormone (PTH).

Which hormone lowers blood calcium by stimulating bone deposition?

Calcitonin (and the active form of vitamin D, calcitriol, acts similarly).

Why are bones considered a "calcium bank"?

They store large amounts of calcium that can be withdrawn or deposited to maintain blood calcium homeostasis.

What is the epiphysis of a long bone?

The end portion containing secondary ossification centers and spongy (trabecular) bone.

What is the diaphysis?

The shaft of a long bone housing the primary marrow cavity.

What is the metaphyseal (epiphyseal) plate?

A cartilage layer between epiphysis and diaphysis where longitudinal bone growth occurs; the growth plate.

Define endochondral ossification.

The developmental process in which a cartilage model is gradually replaced by bone to form long bones.

What are osteons and Haversian canals?

Osteons are cylindrical units of compact bone with concentric lamellae; Haversian canals run through their centers containing blood vessels and nerves.

What is spongy (trabecular) bone and where is it found?

Porous bone with a lattice of trabeculae, located mainly in epiphyses and internal bone regions; aligns along stress lines for support.

Define the basic lever components in musculoskeletal biomechanics.

Fulcrum (joint), effort arm where muscle force is applied, and load arm where the weight acts.

Give an example of an antagonistic muscle pair in the leg.

Quadriceps extend the knee; hamstrings flex the knee.

What are the three phases of an immune response?

Recognition, activation, and effector phases.

Distinguish innate from adaptive immunity in specificity and timing.

Innate immunity is non-specific and rapid (minutes–hours); adaptive immunity is highly specific, slower on first exposure, and forms memory.

Name two common first-line innate defenses.

Physical barriers (skin, mucous membranes) and chemical secretions (sweat’s low pH, lysozyme).

What are pattern-recognition receptors? Give an example.

Receptors that detect conserved pathogen motifs; Toll-like receptors (TLRs) are the classic example.

What do Toll-like receptors (TLRs) bind to?

PAMPs – pathogen-associated molecular patterns on microbes.

What happens after TLR activation?

A signaling cascade activates transcription factors that induce production of antimicrobial proteins.

What are the two main functional categories of white blood cells?

Phagocytes and lymphocytes.

Name two granulocytes involved in allergic responses.

Basophils and eosinophils.

Which leukocyte is specialized for destroying multicellular parasites?

Eosinophils, which release neurotoxic granules.

What is the primary function of mast cells?

Release histamine to initiate inflammation and recruit other immune cells.

Which phagocytic white blood cell is most abundant in blood?

Neutrophils; they engulf pathogens or release toxic chemical clouds.

Differentiate leukocyte and lymphocyte.

Leukocyte is any white blood cell; lymphocyte is a subset that includes B cells, T cells, and NK cells.

Which phagocytes also present antigen to the adaptive immune system?

Macrophages and dendritic cells.

Describe the monocyte–macrophage lineage.

Blood monocytes exit vessels to become tissue macrophages or dendritic cells for pathogen surveillance.

What is the role of natural killer (NK) cells?

Innate lymphocytes that kill virus-infected or abnormal cells and bridge innate and adaptive immunity.

What is lymph and how is it formed?

Excess interstitial plasma (~15%) that leaks from capillaries and is collected by lymphatic vessels.

Why are lymph nodes important?

They filter lymph and provide sites rich in immune cells to detect and respond to pathogens.

Name two lymphoid organs other than lymph nodes and their roles.

Thymus (T-cell maturation) and spleen (filters blood, initiates immune responses, recycles old RBCs).

How does the lymphatic system return fluid to the bloodstream?

Lymphatic vessels drain toward the heart, emptying lymph into large veins near the heart.

Roughly what percentage of fluid filtered from capillaries is reabsorbed directly, and what system handles the remainder?

About 85% reenters capillaries; the lymphatic system collects the remaining ~15%.