Organ Systems I
Lesson focus - Describe the structure, functions, and clinical clues of the skin; the divisions, major bones, joints, and fractures of the skeletal system; the types of muscle tissue and the sliding filament mechanism; the organization and signal transmission of the nervous system; and the action of hormones and the stress response of the endocrine system.
The Skin (Integumentary System)
Structure of the Skin
| Layer | Description |
|---|
| Epidermis | Superficial, thinner portion composed of epithelial tissue; avascular; 90% keratinocytes |
| Dermis | Contains blood vessels, nerve endings, hair follicles, and oil-producing glands |
| Subcutaneous layer / hypodermis | Contains adipose tissue for insulation; large veins and arteries |
Functions of the Skin
- Thermoregulation
- Blood reservoir
- Protection
- Cutaneous sensations
- Excretion and absorption
- Synthesis of vitamin D
Skin as a Diagnostic Clue
| Sign | Cause | Appearance |
|---|
| Cyanosis | Blood is not carrying adequate O₂ (hypoxemia) | Blue coloration in nail beds, lips, and skin |
| Jaundice | Buildup of bilirubin; generally indicative of liver failure | Yellow skin and whites of the eyes |
| Erythema | Engorgement of capillaries due to skin injury, heat, infection, inflammation, or allergic reaction | Reddening of the skin |
| Pallor | Indicative of shock and anemia | Paleness of the skin |
The Skeletal System
Functions of Bone and the Skeletal System
- Support
- Protection
- Movement
- Mineral homeostasis (storage and release)
- Blood cell production (hemopoiesis - the process by which the formed elements of blood develop)
- Triglyceride storage
Divisions of the Skeletal System
| Division | Includes |
|---|
| Axial skeleton | Bones along the vertical axis: skull, rib cage, and vertebrae |
| Appendicular skeleton | The limbs and their supporting structures |
Major Bones
| Bone | Note |
|---|
| Hyoid bone | Supports the muscles in the tongue, neck, and pharynx |
| Ribs | — |
| Spine | — |
| Clavicle and scapula | — |
| Sternum | Manubrium (superior portion, above the suprasternal notch); body (flat surface used during CPR); xiphoid process (inferior portion) |
Joints
A joint is a point of contact between two bones.
| Joint | Description |
|---|
| Fibrous | Bones held together by fibrous connective tissue; allows little to no movement |
| Cartilaginous | No synovial cavity; articulating bones held together by cartilage; little to no movement |
| Synovial | A movable joint |
Ligaments
Ligaments hold bones together and are made of parallel dense bundles of connective tissue.
Fractures
A fracture is any break in a bone, typically named according to severity or the shape/position of the fracture line.
| Fracture | Description |
|---|
| Open (compound) | Broken ends of bone protrude through the skin |
| Comminuted | Bone is splintered, crushed, or broken in pieces |
| Greenstick | One side of the bone is broken and the other bends; occurs only in children whose bones have not fully ossified |
| Impacted | One end of the bone is forcefully driven into the interior of another |
Muscular Tissue
Types of Muscle Tissue
| Type | Description |
|---|
| Skeletal | Striated; primarily voluntary movement |
| Cardiac | Striated; involuntary; autorhythmic |
| Smooth | Nonstriated; generally involuntary |
Auto-rhythmicity is the ability to repeatedly generate spontaneous nerve impulses; it controls the heart rhythm (the pacemaker of the heart).
Functions of Muscular Tissue
| Function | Description |
|---|
| Movement | — |
| Stabilization | — |
| Thermogenesis | Heat generated as muscles contract; used to maintain normal body temperature |
| Electrical excitability | Ability to respond to electrical stimuli |
| Contractility | Ability for fibers to shorten |
| Extensibility | Ability for fibers to stretch |
| Elasticity | Ability of tissue to return to its original shape after contracting and extending |
Muscle Proteins
| Category | Proteins | Role |
|---|
| Contractile | Actin, myosin | Generate force during contraction |
| Regulatory | Tropomyosin, troponin | Turn contraction on and off |
| Structural | Titin, myomesin, nebulin, dystrophin | Keep proper structure, elasticity, and extensibility |
- Tropomyosin prevents myosin from binding to actin
- Troponin is regulated by Ca²⁺ and controls the attachment of tropomyosin
Sliding Filament Mechanism
Skeletal muscle shortens during contraction due to the thick (myosin) and thin (actin) filaments sliding past one another.
The Contraction Cycle
| Step | Description |
|---|
| 1. ATP hydrolysis | The phosphate bond on ATP is broken by water and energy is released; products are ADP + a phosphate group; the energy is stored in the myosin head |
| 2. Attachment of myosin to actin | The energized myosin head attaches to the myosin binding site; the phosphate group is released |
| 3. Power stroke | The myosin head pivots; the thin filament is pulled past the thick filament; ADP is released from the myosin head |
| 4. Detachment of myosin from actin | Regulatory proteins turn contraction "off"; ATP binds to the myosin head; myosin releases from actin |
The Nervous System
Organization of the Nervous System
| Division | Description |
|---|
| Central nervous system (CNS) | Brain and spinal cord |
| Peripheral nervous system (PNS) | All nervous tissue outside the CNS |
The PNS is further divided:
| PNS division | Function |
|---|
| Somatic | Conveys output to skeletal muscles for voluntary muscle function (e.g., walking, talking, writing) |
| Autonomic | Sympathetic and parasympathetic control of involuntary functions (e.g., heart rate) |
Functions of the Nervous System
- Sensory - detects internal stimuli (such as an increase in blood pressure) and external stimuli (such as touching a hot surface)
- Integrative - processes sensory information by analyzing it and making decisions for appropriate responses
- Motor - effectors are activated; stimulation of effectors causes muscles to contract and glands to secrete
Communication and Signal Transmission
A synapse is a region where communication occurs between two neurons or between a neuron and an effector cell (such as a muscle cell).
| Synapse type | Description |
|---|
| Electrical | Communication occurs through gap junctions - tube-like structures that act like tunnels or "electrical cords" connecting two cells directly; allows rapid communication and synchronization; occurs in the heart and smooth muscle |
| Chemical | Communication occurs between presynaptic and postsynaptic neurons through the synaptic cleft; the presynaptic neuron releases neurotransmitters that diffuse through the cleft and bind to receptors on the postsynaptic neuron; communication takes longer; chemical synapses never close and are usually filled with interstitial fluid |
ANS Neurotransmitters and Receptors
- Neurotransmitter - the body's chemical messenger / stimulus
- Receptor - the receiver of the stimulus
| Pathway (division) | Receptors | Neurotransmitters |
|---|
| Cholinergic (parasympathetic) | Muscarinic | Acetylcholine |
| Adrenergic (sympathetic) | Alpha, Beta | Epinephrine, norepinephrine |
The Endocrine System
Comparison of Control: Nervous vs. Endocrine
Hormones are molecules (mediators) released in one part of the body that regulate the activity of cells in other parts.
- Slower action than nerve impulses, but the effects last longer
- Released by endocrine glands
Mechanisms of Hormone Action
Responsiveness depends on:
- Concentration of the hormone
- Abundance of receptors
- Influences of other hormones
| Effect | Description |
|---|
| Permissive | A hormone cannot exert its full effects without the presence of another hormone |
| Synergistic | The effects of two or more hormones acting together is greater than the effect of each hormone acting alone |
| Antagonistic | The effect of one hormone on a target cell is opposed by another hormone |
Control of Hormone Secretion
Hormone secretion is regulated by:
- Signals from the nervous system
- Chemical changes in the blood
- Other hormones
Stress Response
A stressor is any disturbance of the human body (e.g., heat/cold, toxins, emotional reactions). The stress response is controlled mostly by the hypothalamus.
| Stage | Description |
|---|
| 1. Fight or flight | Mobilizes the body's resources for immediate physical activity; increases glucose and O₂ to organs; increases blood to the brain and muscles; nonessential body functions are inhibited; effects are short term |
| 2. Resistance reaction | Hormones are released for a longer-lasting response; the body begins to return to homeostasis |
| 3. Exhaustion | Prolonged exposure to high levels of cortisol; weakened immune system; deterioration of muscles and organs; development of chronic diseases |
Review
- The skin (integumentary system): structure, functions, and diagnostic clues
- The skeletal system: functions, divisions, major bones, joints, ligaments, and fractures
- Muscular tissue: types, functions, proteins, and the sliding filament mechanism
- The nervous system: organization, functions, signal transmission, and neurotransmitters/receptors
- The endocrine system: hormone action, control of secretion, and the stress response