Anatomy and Physiology: Body Organization, Homeostasis and Feedback

1. Anatomy and Physiology
Anatomy: The study of body structure. It asks: What parts does the body have, and what do they look like?

Physiology: The study of body function. It asks: How do body parts work?

Complementarity: Structure and function are related. The way a body part is built helps it do its job.

Example: Anatomy studies the heart's structure. Physiology studies how the heart pumps blood.

2. Levels of Organization

Memorize the order: subatomic particles > atoms > molecules > macromolecules > organelles > cells > tissues > organs > organ systems > organism

• Subatomic particles: Protons, neutrons, and electrons.
• Atoms: The smallest units of an element.
• Molecules: Two or more atoms joined together.
• Macromolecules: Large molecules, such as proteins, carbohydrates, and lipids.
• Organelles: Small structures inside cells that perform specific functions.
• Cells: The basic units of structure and function in living things.
• Tissues: Groups of similar cells, together with some extracellular material, arranged to perform a function.
• Organs: Structures made of two or more tissues that perform a specialized function.
• Organ systems: Groups of organs that work together to perform a specialized function.
• Organism: One individual living thing.

Organ Systems

4. Directional Terms

Superior / Inferior: Superior means toward the head or above. Inferior means away from the head or below.

Example: The head is superior to the abdomen. The navel is inferior to the chin.

Anterior / Posterior: Anterior means toward the front of the body. Posterior means toward the back. In humans, anterior is also called ventral, and posterior is also called dorsal.

Example: The breastbone is anterior to the spine.

Medial / Lateral: Medial means toward the body’s midline. Lateral means away from the midline. Intermediate means between a medial and a lateral structure.

Example: The heart is medial to the arms. The arms are lateral to the chest. The clavicle is intermediate between the breastbone and the shoulder.

Proximal / Distal: Proximal means closer to where a limb attaches to the body. Distal means farther from that point.

Example: The elbow is proximal to the wrist. The fingers are distal to the elbow.

Superficial / Deep: Superficial means at or near the body surface. Deep means farther inside the body.

Example: The skin is superficial to the muscles. The lungs are deep to the skin.

5. Body Planes

Sagittal plane: Divides the body into right and left parts.

Midsagittal, or median, plane: A sagittal plane through the midline; divides the body into equal right and left halves.

Frontal, or coronal, plane: Divides the body into anterior and posterior parts, front and back.

Transverse, or horizontal, plane: Divides the body into superior and inferior parts, upper and lower.

Oblique section: A cut made diagonally.

Quick cue: sagittal = right/left; frontal = front/back; transverse = upper/lower; oblique = diagonal.

6. Characteristics of Life

• Movement: Change in position; motion.
• Responsiveness: Reaction to change.
• Growth: Increase in body size; no change in shape.
• Reproduction: Production of new organisms and new cells.
• Respiration: Obtaining oxygen; removing carbon dioxide; releasing energy from foods.
• Digestion: Breakdown of food substances into simpler forms.
• Absorption: Passage of substances through membranes and into the body.
• Circulation: Movement of substances in body fluids.
• Assimilation: Changing of absorbed substances into chemically different forms.
• Excretion: Removal of wastes produced by metabolic reactions.

7. Body Cavities and Membranes

Dorsal body cavity: The posterior cavity that protects the nervous system.

• Cranial cavity: Inside the skull; contains the brain.
• Vertebral, or spinal, cavity: Inside the vertebral column; contains the spinal cord.

Ventral body cavity: The anterior cavity that contains many internal organs.

• Thoracic cavity: The chest cavity; contains the heart and lungs.
• Pleural cavities: The cavities surrounding the lungs, one around each lung.
• Mediastinum: The region between the lungs.
• Pericardial cavity: The cavity around the heart, within the mediastinum.
• Abdominopelvic cavity: The cavity below the diaphragm. It has abdominal and pelvic subdivisions.
• Abdominal cavity: Contains the stomach, intestines, liver, spleen, gallbladder, and other organs.
• Pelvic cavity: Contains the bladder, reproductive organs, and rectum.
• Diaphragm: The dome-shaped muscle separating the thoracic cavity from the abdominopelvic cavity.

Thoracic cavity layout: Two pleural cavities + mediastinum. The mediastinum contains the pericardial cavity.

Serous membranes: Thin membranes that secrete serous fluid, reducing friction between organs and cavity walls.

• Parietal serosa: Lines the internal body wall.
• Visceral serosa: Covers an internal organ.
• Serous fluid: Separates the serous membrane layers and reduces friction.

Membrane names: Pleura = lungs; pericardium = heart; peritoneum = abdominopelvic organs. The peritoneal cavity is the space between the parietal and visceral peritoneum.

Other cavities: Oral = mouth; nasal = inside the nose; orbital = eyes; middle ear = sound-transmitting bones; synovial = joint cavities.

8. Homeostasis

Homeostasis: Maintaining a stable internal environment. The body keeps its internal conditions within certain limits, even when changes occur inside or outside the body. Normal body temperature is approximately 37 °C (98.6 °F). The set point is usually a range, not an exact number.

REMEMBER: Negative feedback corrects a change and brings the body toward normal. Positive feedback increases a change until an event is complete.

Stimulus → Receptor → Control center → Effector → Response

VOCABULARY

• Set point: The normal value or range for a body condition.
• Variable: A body condition that can change, such as body temperature.
• Stimulus: A change in the internal environment.
• Receptor: Detects a change and sends information to the control center.
• Integrating center: Processes the information and sends a message to the effector.
• Control center: Receives and processes information from the receptor. It compares the change with the set point and directs the effectors.
• Effector: A muscle, gland, cell, or organ that carries out the control center’s instructions.
• Response: The action that corrects or changes the variable.
• Afferent pathway: Carries information from the receptor to the control center.
• Efferent pathway: Carries instructions from the control center to the effector.

How the Homeostatic Loop Works

A stimulus causes a change. A receptor detects it and sends information to the control center through the afferent pathway. The control center compares the information with the set point and sends instructions to an effector through the efferent pathway. The effector produces a response.

• Nervous system: Uses electrical signals called action potentials. It acts rapidly.
• Endocrine system: Uses hormones. It usually acts more slowly.

Negative Feedback

Negative feedback opposes the original change and moves the body back toward the set point. It is the most common feedback mechanism and helps prevent large changes in the body. Examples include regulation of body temperature, blood pressure, and blood glucose.

When body temperature is too high, blood vessels in the skin dilate and sweat glands secrete sweat. The body loses heat, and the temperature moves toward normal.

When body temperature is too low, blood vessels in the skin constrict, sweat glands become inactive, and muscles shiver to produce heat. The body conserves or produces heat, and the temperature moves toward normal.

Positive Feedback

Positive feedback increases or accelerates the original change. It is less common and usually controls events that end after a short time, such as blood clotting and childbirth.

During childbirth, the baby presses against the cervix. The cervix stretches and sends nerve signals to the brain. The brain signals the pituitary gland to release oxytocin. Oxytocin causes stronger uterine contractions, which push the baby further against the cervix. This cycle continues until delivery.