The Human Body: An Orientation

The Human Body: An Orientation

Chapter 1: Human Anatomy and Physiology

Course: BIOL 243
Instructor: Dr. Elizabeth Easley

Overview of Anatomy and Physiology

Anatomy:

  • The study of the structure of body parts and their relationships to one another.

    • Gross or macroscopic anatomy: Involves examining structures visible to the naked eye.

    • Microscopic anatomy: Deals with structures that require magnification to be seen.

    • Developmental anatomy: Studies structural changes throughout the life span.

Physiology:

  • The study of the function of the body’s structural machinery.

Gross Anatomy

  • Regional anatomy: Examines all structures in a specific area of the body.

  • Systemic anatomy: Studies the anatomy of body systems.

  • Surface anatomy: Assesses internal structures as they relate to the skin's surface.

    • Example: Taking a pulse to assess the cardiovascular system.

Microscopic Anatomy

  • Cytology: The study of individual cells.

  • Histology: The study of tissues and their organization.

Developmental Anatomy

  • Examines structural changes throughout the organism's life.

  • Embryology: The study of developmental changes of the body before birth.

Topics of Physiology

  1. Integumentary system

  2. Nervous system

  3. Skeletal system

  4. Endocrine system

  5. Muscular system

  6. Cardiovascular system

  7. Lymphatic system

  8. Urinary system

  9. Respiratory system

  10. Digestive system

  11. Reproductive system

Levels of Structural Organization

  1. Chemical level: Atoms combine to form molecules.

  2. Cellular level: Cells are the smallest units of life and vary in shape and size.

  3. Tissue level: Groups of similar cells that share a common function.

  4. Organ level: More complex functions emerge from the organization of tissues.

  5. Organ system level: Organs work together to perform common purposes.

  6. Organismal level: The total of all structures working together constitutes the organism.

Survival Needs

  • Nutrients: Such as vitamins, carbohydrates, fats, proteins, and minerals.

  • Oxygen: Critical for cellular respiration and energy production.

  • Water: Essential for biochemical reactions and overall homeostasis.

  • Normal body temperature: Approximately 98.6°F (37°C) is required for optimal enzymatic and metabolic reactions.

  • Appropriate atmospheric pressure: Influences the body's processes (e.g., respiration).

Necessary Life Functions

  1. Maintaining boundaries: Keeping internal and external environments separate (e.g., skin).

  2. Movement: Activities involving locomotion or movement of internal substances.

  3. Responsiveness: The ability to sense and respond to stimuli.

  4. Digestion: The process of breaking down food for nutrient absorption.

  5. Metabolism: The chemical reactions that break down food and process energy.

  6. Excretion: The removal of waste products from the body.

  7. Reproduction: The ability to produce offspring.

Homeostasis

  • Homeostasis: The ability to maintain stable internal conditions despite external changes.

    • Components of homeostatic control:

    • Receptor: Senses changes in the environment.

    • Control center: Processes information and determines the response.

    • Effector: Carries out the response to restore balance. Using **body temperature regulation** as an example of how the human body maintains balance: 1. **The Receptor (The Sensor):** Temperature-sensitive nerve endings in your skin and brain detect that your internal temperature is rising above 98.6^{\circ}F. 2. **The Control Center (The Decider):** Your brain (specifically the **hypothalamus**) receives the 'too hot' signal. It compares your current temperature to your healthy 'set point' and decides the body needs to cool down. 3. **The Effector (The Doer):** Your brain sends commands to your **sweat glands** to produce sweat and to your **blood vessels** to widen. These actions release heat from the body, bringing your temperature back to normal.

Homeostatic Control Process

  1. A stimulus produces a change in the variable being monitored.

  2. The change is detected by the receptor.

  3. Information is transmitted from the receptor to the control center.

  4. The control center analyzes the information and generates a response sent to the effector.

  5. The effector instigates a change to correct the imbalance.

Definitions

  • Afferent: Refers to input to the control center; it approaches the center.

  • Efferent: Refers to output from the control center, exiting toward the periphery and controlling actions like muscle movements. An easy way to remember the difference is to use the first letter of each word as a mnemonic: 1. **A**fferent: Think of **A**rriving or **A**pproaching. These are signals that move toward the control center (the brain or spinal cord). 2. **E**fferent: Think of **E**xiting. These are signals that move away from the control center to cause an **E**ffect in the body, such as a muscle contraction or gland secretion. A common acronym used in anatomy is **SAME**: **S**ensory = **A**fferent, **M**otor = **E**fferent.

Negative Feedback

  • Negative feedback control: The output reduces the original effect of the stimulus.

  • Most homeostatic control systems operate through negative feedback.

    • Example: HVAC systems maintain room temperature.

Positive Feedback

  • Positive feedback: The output enhances the initial stimulus, leading to an amplified response.

  • Physiological examples include childbirth and blood clotting processes. A classic human anatomy example of positive feedback is **childbirth**. As the baby's head pushes against the cervix, it causes stretching. This stretch is detected by receptors that send nerve impulses to the brain (the control center). The brain then triggers the pituitary gland to release the hormone **oxytocin**. Oxytocin acts as the effector, causing the uterus to contract more forcefully. These contractions push the baby further, increasing the stretch on the cervix and leading to more oxytocin release. This loop continues to amplify the response until the baby is delivered and the stimulus is removed.

Homeostatic Imbalance

  • Most diseases relate to homeostatic imbalances.

  • With aging, control systems may diminish in efficiency, increasing disease susceptibility.

  • Over time, feedback systems can become overwhelming, allowing potentially destructive positive feedback mechanisms to take precedence.

Anatomical Position

  • The standard body position used as a reference point:

    • Standing upright

    • Head facing forward

    • Feet in a normal stance

    • Palms facing anteriorly

    • Thumbs pointed outward.

Directional Terms

  • Superior (Cranial): Toward the head.

  • Inferior (Caudal): Away from the head, toward the feet.

  • Ventral (Anterior): Front of the body.

  • Dorsal (Posterior): Back of the body.

  • Medial: Closer to the midline of the body.

  • Lateral: Further from the midline.

  • Intermediate: Between medial and lateral.

  • Proximal: Closer to the point of attachment or origin.

  • Distal: Further from the point of attachment or origin.

  • Superficial: Towards the surface of the body.

  • Deep: Away from the surface of the body.

Refer to Table 1.1 for additional examples.

Axial Region

  • Regional Terms: Refers to the body’s main axis, including the head, neck, and trunk.

  • Appendicular Region: Pertains to the limbs of the body.

Body Planes

  • Sagittal plane: A vertical plane that divides the body into left and right sides.

  • Frontal plane: A vertical plane that divides the body into anterior and posterior parts.

  • Transverse plane: A horizontal plane that divides the body into superior and inferior parts.

Refer to Figure 1.9 for visual illustration.

Body Cavities

  • There are two main sets of internal body cavities:

    1. Dorsal body cavities

    2. Ventral body cavities

    • Both sets are closed to the outside and provide varying levels of protection to internal organs.

Refer to Figure 1.10 for comparison of protection levels.

Dorsal Body Cavity

  • Function: Protects the nervous system organs.

    • Cranial cavity: Located in the skull, protecting the brain.

    • Vertebral (spinal) cavity: Runs through the vertebral column and encloses the spinal cord.

    • Note: Cranial and vertebral cavities are continuous with one another.

Ventral Body Cavity

  • Thoracic cavity: Major subdivision surrounded by the ribs and chest muscles.

    • Divided into:

    • Lateral pleural cavities: Enclose each lung.

    • Medial mediastinum: Contains the pericardial cavity, enclosing the heart, along with surrounding thoracic structures.

  • Abdominopelvic cavity: Lower subdivision separated from the thoracic cavity by the diaphragm.

    • Abdominal cavity: Contains stomach, spleen, intestines, liver, and other organs.

    • Pelvic cavity: Encloses the bladder, reproductive organs, and rectum.

Refer to Figure 1.10 for visual representation.

Membranes in the Ventral Body Cavity

  • Serosa or serous membrane: A thin, double-layered lining of the walls of the ventral cavity and the exterior surfaces of internal organs.

    • Parietal serosa: The portion lining the walls of the cavity.

    • Visceral serosa: The portion that folds over to cover the organs.

    • Serous fluid: Lubricates the space between the membranes, reducing friction.

Refer to Figure 1.11 for more information.

Abdominopelvic Quadrants

  1. Right upper quadrant (RUQ)

  2. Left upper quadrant (LUQ)

  3. Right lower quadrant (RLQ)

  4. Left lower quadrant (LLQ)

Refer to Figure 1.12 for visual depiction.

Abdominopelvic Regions

  1. Umbilical region

  2. Epigastric region

  3. Hypogastric (pubic) region

  4. Right iliac or inguinal region

  5. Left iliac or inguinal region

  6. Right lumbar region

  7. Left lumbar region

  8. Right hypochondriac region

  9. Left hypochondriac region

Refer to Figure 1.13 for a detailed illustration.

Other Body Cavities

  • Oral and digestive cavities: Mouth and digestive tract.

  • Nasal cavity: Internal space of the nose.

  • Orbital cavities: House the eyes.

  • Middle ear cavities: Contain the structures for hearing.

  • Synovial cavities: Joint spaces that facilitate movement.