Chapter 18: Organ Donation – Tissues and Organs Study Guide

Introduction to Organ Donation and Tissues

• Conceptual Inquiry: The chapter begins by posing ethical considerations regarding organ donation, specifically when an individual is determined to be brain dead following an accident.     * Questions for consideration include: Should families donate the organs of loved ones? What would an individual want their own family to do in that situation?
• Definition of Tissue: Tissues are defined as groups of similar cell types that perform a common function.
• Tissue Transplants: These medical procedures are utilized to restore bodily functions that have been compromised or prevented due to tissue damage.
• Four Basic Types of Tissue: The human body consists of four primary tissue categories:     * Epithelial.     * Connective.     * Muscle.     * Nervous.

Epithelial Tissue (Epithelium)

• Structure and Morphology: Epithelial tissue is composed of tightly packed sheets of cells.     * Polarity: These sheets are anchored on one face to underlying structures but remain free on the other face.     * Free Side: The exposed side faces either body fluids or the external environment.     * Layering: Epithelium can exist as a single layer of cells or can be many layers thick.
• Functions: The primary functions include protection, secretion, and absorption.
• Regeneration: This tissue is constantly sloughing off and is replaced through active cell division.
• Locations and Examples:     * Outer Surfaces: Covers organs and the outer surface of the body (epidermis).     * Linings: Lines hollow organs, vessels, and body cavities.     * Common Sites: Heart and blood vessels, respiratory tract, digestive tract, and urogenital tract.     * Epidermis: This is the epithelium forming the outer layer of skin. Cells are frequently rubbed off by clothing and are totally replaced every $4$ to $6$ weeks.     * Small Intestine: Specifically noted for having a specialized epithelial lining.

Connective Tissue

• General Characteristics: Connective tissue is loosely organized and consists of cells embedded in a matrix.     * Matrix Composition: Composed of protein fibers and an amorphous, gel-like ground substance.     * General Function: Usually serves to bind organs or tissues to one another.
• Types of Connective Tissue:     1. Loose Connective Tissue:         * The most widespread connective tissue in animals.         * Made of loosely woven fibers.         * Fibroblasts: The specific connective tissue cells that secrete matrix proteins.         * Matrix Proteins: Includes collagen fibers (for strength) and elastin fibers (for stretching/elasticity).         * Functions: Connects epithelia to underlying tissues, holds organs in place, and provides padding under the skin.     2. Adipose Tissue (Fat Tissue):         * Consists mostly of cells (containing fat droplets and a nucleus) surrounded by a small amount of matrix.         * Functions: Connects skin to underlying structures, insulates the body, protects organs, and stores energy-rich fat reserves.     3. Blood:         * Composed of various blood cells and a liquid matrix called plasma.         * Cellular Components: Red blood cells (oxygen transport), white blood cells (infection fighting), and platelets (clotting).         * Matrix (Plasma): A liquid- and protein-rich matrix.         * Movement: Circulates through the body via blood vessels: arteries, veins, and capillaries.     4. Fibrous Connective Tissue:         * Composed of fibroblasts and a matrix of densely packed collagen fibers arranged in parallel.         * Tendons: Connect muscles to bones.         * Ligaments: Connect bones together at joints.     5. Cartilage:         * Composed of cells called chondrocytes.         * Matrix is dense and rich in collagen and structural proteins secreted by chondrocytes.         * Functions: Connects muscles with bones, provides flexible support (e.g., ears and nose), acts as a shock absorber, and permits smooth gliding at joint surfaces.         * Healing: Cartilage contains no blood vessels, which leads to slow healing processes.     6. Bone:         * A rigid connective tissue made of branched cells called osteocytes.         * The matrix consists of collagen and minerals.         * Function: Supports/protects other tissues and organs; serves as a reservoir for calcium and minerals.         * Marrow: Found inside bone; produces blood cells.         * Central Canal: Houses nerves and blood vessels within the bone structure.
• Transplantation: Many connective tissues can be transplanted from deceased donors. Certain types, specifically blood and bone marrow, can be donated by living donors.

Muscle Tissue

• Definition: A highly specialized tissue capable of contraction.
• Anatomy of Muscle: Most is composed of bundles of muscle fibers, which are long, thin, cylindrical cells.     * Proteins: Muscle contraction is driven by specialized proteins: actin and myosin.     * Striations: The arrangement of these proteins often forms a banded pattern or stripes known as striations.
• Classification by Control:     * Voluntary: Requires conscious thought (e.g., skeletal muscle for walking).     * Involuntary: Requires no conscious thought (e.g., cardiac muscle for heartbeats).
• Three Types of Muscle Tissue:     1. Skeletal Muscle:         * Striated.         * Usually attached to bone.         * Responsible for all voluntary movements.         * Exercise results in the increase of the size of skeletal cells.     2. Cardiac Muscle:         * Found exclusively in heart tissue.         * Striated and involuntary.         * Produces rhythmic contractions for the heartbeat.         * Cells are branched and interwoven to help propagate the contraction signal.         * Transplant Note: A donor heart must be undamaged and transplanted within $4$ hours of removal to prevent tissue breakdown.     3. Smooth Muscle:         * Composed of spindle-shaped cells.         * Not striated and involuntary.         * Located in the musculature of internal organs (e.g., intestines), blood vessels, and the digestive system.         * Contracts more slowly than skeletal muscle but can remain contracted for a longer duration.

Nervous Tissue

• Definition: Tissue composed of specialized cells called neurons that conduct and transmit electrical impulses.
• Location: Found in the brain, spinal cord, and nerves.
• Primary Functions:     * Sensing stimuli.     * Processing stimuli.     * Transmitting signals from the brain to the rest of the body.
• Healing Constraint: Most nerve cells do not undergo cell division, making it difficult or impossible to repair damage.
• Signal Pathway Example: An impending accident triggers the brain, which reacts and sends a signal through the spinal cord via motor neurons to move an arm. The signal is transmitted across specialized nerve cells.

Organ Donation and Death

• Brain Death: Defined as the permanent cessation of function in the cerebrum and brain stem.     * Causes: Head injuries preventing oxygen to the brain, motor vehicle/cycling accidents, ruptured blood vessels, or drowning.     * Prognosis: A brain-dead person will not recover. This is distinct from a coma or vegetative state, where some recovery of function is possible.
• Cardiac Death: Occurs when the heart stops functioning.
• Scope of Tissue Donation: One person’s tissue donation can improve the lives of up to $50$ people.     * Donatable Tissues: Bones, tendons, ligaments, cartilage, veins, skin, and corneas.     * Processing: Tissues are checked for pathogens, chemically treated to remove proteins that might cause immune rejection, frozen, and can be stored in tissue/eye banks for up to $5$ years.

Organs and Organ Systems

• Organ: A structure composed of two or more tissue types packaged together to produce a specific function (e.g., heart, lungs, kidney, brain).
• Organ System: A collection of organs that interact to perform a common function.
• Biological Hierarchy: Muscle cell $\rightarrow$ Muscle tissue $\rightarrow$ Heart organ $\rightarrow$ Circulatory system $\rightarrow$ Organism.
• Human Organ Systems:     * Digestive: Ingests and breaks down food (e.g., esophagus, stomach, liver, pancreas, intestines).     * Cardiovascular: Transports nutrients, gases, hormones, and wastes (e.g., heart, blood vessels).     * Excretory: Eliminates liquid wastes and regulates water balance (e.g., kidney, bladder).     * Endocrine: Secretes hormones to regulate body activities (e.g., pituitary, thyroid).     * Respiratory: Gas exchange (oxygen in, CO2 out) (e.g., trachea, lungs).     * Nervous: Senses environment and activates body parts (e.g., brain, spinal cord).     * Skeletal: Mechanical support, mineral storage, blood cell production (e.g., bones, cartilage).     * Lymphatic and Immune: Protects against infection (e.g., thymus, lymph nodes, spleen).     * Muscular: Movement, posture, and balance (skeletal muscles).     * Reproductive (Female): Produces eggs and supports offspring development (e.g., ovaries, uterus).     * Reproductive (Male): Produces and delivers sperm (e.g., testes, prostate).     * Integumentary: Protection from environment/infection and fat storage (e.g., skin, hair, nails).

The Liver

• Anatomy: A large, reddish-brown organ made of epithelial tissue covered with connective tissue. Located on the right side of the abdominal cavity below the diaphragm.     * Structure: Divided into four lobes, further subdivided into lobules.     * Lobules: Contain a central vein to allow blood to reach all parts of the liver.     * Hepatocytes: Liver cells that filter toxic materials (dead cells, pathogens, drugs, alcohol) from the blood.
• Functions:     * Circulatory: Synthesizes blood-clotting factors, detoxifies substances, regulates blood volume, and destroys old red blood cells.     * Digestive: Produces bile (to metabolize fat), metabolizes/stores nutrients, and stores/releases glycogen (stored glucose).
• Liver Failure and Transplantation:     * Causes: Hepatitis C virus infection and chronic alcohol abuse.     * Regeneration: The liver is unique because it can regenerate in both the donor and the recipient after a small portion is transplanted from a living donor.     * Statistics: Approximately $7000$ liver transplants occur annually in the United States.     * Impact: Liver failure affects both the circulatory and digestive systems and compromises homeostasis.

Homeostasis and Feedback Mechanisms

• Homeostasis: The ability to maintain a consistent internal environment under changing conditions (a "steady state").     * Regulated Conditions: Heart rate, blood pressure, water/mineral balance, temperature, and blood glucose.
• Feedback: Information sent to a control center that directs a response from a cell, tissue, or organ.
• Negative Feedback: The product of a process inhibits that same process; it negates change.     * Analogy: A thermostat turning off a heater when it gets too hot.     * Temperature Regulation:         * Too Hot: Brain sends signals, blood vessels dilate, sweat glands activate, and body cools.         * Too Cold: Blood vessels constrict, muscles shiver, and body temperature increases.     * Blood Glucose Regulation:         * High Glucose: Pancreas secretes insulin; Liver converts glucose to glycogen.         * Low Glucose: Pancreas secretes glucagon; Liver breaks glycogen back into glucose.
• Positive Feedback: The product of a process intensifies the process; it promotes change.     * Example: Labor and Childbirth:         1. Hormones cause uterine contractions.         2. Baby's head creates pressure, stimulating more hormone release.         3. Contractions increase in rate and duration.         4. Process continues until the baby is born and contractions end.

Questions & Discussion

• Question: Would you consider being an organ donor? (Options: Yes, No, Maybe).
• Question: What type of cells make up cartilage?     * Answer: A. chondrocytes.
• Question: The state of being brain dead is the same as being in a coma or vegetative state.     * Answer: B. False.
• Question: Which organ can regenerate after a small portion is received from a living donor?     * Answer: C. liver.
• Question: Three-dimensional printers can be used to produce any organ from a patient’s stem cells.     * Answer: B. False (Current context implies this is not yet a universal truth for all organs).
• Question: What percentage of people on waiting lists for replacement organs may die before one becomes available?     * Answer: C. $10\%$.

Organ Donation Statistics and Procedures

• Donor Selection: The best candidates are typically young, healthy individuals who died from brain injury.
• Cardiac Death Candidates: Can be tissue donors but are less suitable for organ transplants because organs deteriorate quickly without oxygen.
• Transplant Shortages: There remains a significant gap between patients waiting and transplants performed. The number of patients waiting has increased significantly from $2003$ to $2015$, surpassing $120,000$ while transplants remained relatively stable.
• Expressing Intentions: Intentions can be indicated on a driver's license/state ID, by carrying a signed organ donor card, using the Donate Life America app, and informing family members.