PLTW HUMAN BODY SYSTEMS FINAL

What is the Endocrine System?

A network of glands and organs that produce and release hormones to regulate various body functions such as metabolism, growth, and reproduction.

Pituitary Gland

Known as the 'master gland,' it regulates other glands. Key hormones include:

• Growth Hormone (GH): Stimulates physical growth in bones and tissues.
• Antidiuretic Hormone (ADH): Regulates water balance by controlling kidney output.

Thyroid Gland

Located in the neck, it produces:

• Thyroxine (T4) and Triiodothyronine (T3): Regulate the body's metabolic rate, heart function, and digestive health.
• Calcitonin: Helps regulate calcium levels in the blood.

Adrenal Glands

Located on top of the kidneys, they produce:

• Cortisol: A stress hormone that manages metabolism and blood sugar.
• Adrenaline (Epinephrine): Triggers the 'fight or flight' response, increasing heart rate and energy.

Pancreas

Regulates blood sugar levels through:

• Insulin: Decreases blood glucose levels by helping cells absorb sugar.
• Glucagon: Increases blood glucose levels by signaling the liver to release stored glucose.

Pineal Gland

A small gland in the brain that secretes Melatonin, which regulates sleep-wake cycles and the body's internal circadian rhythm.

Parathyroid Glands

Four tiny glands behind the thyroid that produce Parathyroid Hormone (PTH), which maintains proper calcium levels in the blood and bones.

Gonads (Ovaries and Testes)

Responsible for reproductive hormones:

• Ovaries (Female): Produce Estrogen and Progesterone for the menstrual cycle and secondary sex characteristics.
• Testes (Male): Produce Testosterone for sperm production and secondary sex characteristics.

Hypothalamus

The link between the nervous and endocrine systems. It produces releasing hormones that tell the Pituitary Gland which hormones to secrete or suppress.

How do hormones provide regulation within the body?

Hormones maintain homeostasis through feedback loops:

1. Negative Feedback: The most common mechanism where a change in a physiological peak triggers a response that counteracts the initial change (e.g., insulin lowering high blood sugar).
2. Positive Feedback: A process where the set point is moved further away from the norm to complete a specific process (e.g., oxytocin during childbirth).
3. Target Cells: Hormones only affect specific cells that have receptors for that hormone, ensuring precise control.

Anatomical Directional Terms

Terms used to describe the location of body parts relative to one another:

• Superior / Inferior: Above / Below.
• Anterior (Ventral) / Posterior (Dorsal): Front / Back.
• Medial / Lateral: Toward the midline / Away from the midline.
• Proximal / Distal: Closer to the point of attachment / Farther from the point of attachment (used for limbs).
• Superficial / Deep: Near the surface / Internal.

Anatomical Regional Terms

The body is divided into two main regions:

• Axial: Relating to the head, neck, and trunk (the axis of the body).
• Appendicular: Relating to the limbs and their attachments (girdles) to the axis.

Levels of Biological Organization

The hierarchy of complexity in a living organism:

Chemical (Atoms/Molecules) $\rightarrow$ Cells $\rightarrow$ Tissues $\rightarrow$ Organs $\rightarrow$ Organ Systems $\rightarrow$ Organism.

Four Primary Tissue Types

1. Epithelial: Covers surfaces and lines cavities (protection/absorption).
2. Connective: Supports, protects, and binds tissues together (e.g., bone, blood).
3. Muscle: Specialized for contraction and movement.
4. Nervous: Responsbile for internal communication via electrical impulses.

Specific Facial Muscles: Location and Function

• Orbicularis Oculi: Circular muscle around the eye; closes the eyelid (blinking/squinting).
• Orbicularis Oris: Circular muscle around the mouth; closes and protrudes the lips (kissing muscle).
• Temporalis: Fan-shaped muscle over the temporal bone; elevates the mandible to close the jaw.

Classification of Bones by Shape

• Long Bone: Longer than they are wide (e.g., Femur, Humerus).
• Short Bone: Cube-shaped (e.g., Carpals in the wrist, Tarsals in the ankle).
• Flat Bone: Thin, flattened, and usually curved (e.g., Sternum, Skull bones, Ribs).
• Irregular Bone: Complex shapes that don't fit other categories (e.g., Vertebrae, Hip bones).

Anatomy of a Long Bone

Key structures include:

• Diaphysis (Shaft): The long main body of the bone.
• Epiphysis: The expanded ends of the bone.
• Metaphysis: The region where the diaphysis joins the epiphysis (contains the epiphyseal plate/line).
• Articular Cartilage: Covers the epiphysis to reduce friction at joints.
• Periosteum: Fibrous outer covering of the bone.
• Compact Bone: Dense outer layer providing strength.
• Spongy Bone (Cancellous): Internal honeycombed network found in epiphyses.
• Medullary Cavity: Central hollow in the diaphysis containing Yellow Bone Marrow (fat).
• Blood Vessels: Supply nutrients via the nutrient foramen.

Axial vs. Appendicular Skeleton

• Axial Skeleton (80 bones): Includes the skull, vertebral column, and thoracic cage (ribs and sternum).
• Appendicular Skeleton (126 bones): Includes the pectoral (shoulder) girdle, pelvic (hip) girdle, and upper and lower limbs.

The Human Skull

Composed of two sets of bones:

1. Cranium: Protects the brain (e.g., Frontal, Parietal, Temporal, Occipital).
2. Facial Bones: Form the face and provide cavities for eyes/nose/mouth (e.g., Maxilla, Mandible).

• Sutures: Immovable joints that connect skull bones.

Types of Bone Fractures (Breaks)

• Comminuted: Bone fragments into three or more pieces.
• Compression: Bone is crushed (common in porous bones).
• Depressed: Broken bone portion is pressed inward (skull).
• Spiral: Ragged break occurs when excessive twisting forces are applied.
• Greenstick: Incomplete break; one side of the shaft breaks, the other bends (common in children).

Four Stages of Bone Repair (Healing)

1. Hematoma Formation: A mass of clotted blood forms at the fracture site.
2. Fibrocartilaginous Callus Formation: Splinting of the break by a network of cartilage and collagen fibers.
3. Bony Callus Formation: Osteoblasts replace soft callus with spongy bone.
4. Bone Remodeling: Excess material is removed; compact bone is laid down to reconstruct the shaft walls.

Bone Cells: Osteoblasts vs. Osteoclasts

• Osteoblasts: Bone-building cells; they secrete the matrix (osteoid) to form new bone.
• Osteoclasts: Bone-destroying cells; they use enzymes/acids to break down (resorb) bone matrix and release minerals into the blood.

Diagnostic Imaging Techniques

• X-ray: Best for viewing hard structures like bones and teeth.
• CT (Computed Tomography): Specialized X-ray that provides detailed cross-sectional 3D views.
• MRI (Magnetic Resonance Imaging): Uses magnets to provide high-contrast images of soft tissues (ligaments, brain, etc.).
• Ultrasound: Uses high-frequency sound waves to view soft tissues in real-time (often used in pregnancy).