Grade 8 General Science: Human Body Systems and Health Study Guide
Overview of Human Body Systems and Health
Learning Outcomes:
Identification of major organs constituting human body systems.
Explanation of the main functions of major human body systems.
Listing of main diseases or disorders associated with each system.
Discussion on the effects of these diseases.
Main Contents of Unit Four:
4.1 Integumentary System
4.2 Muscular System
4.3 Skeletal System
4.4 Digestive System
4.5 Respiratory System
4.6 Circulatory System
4.7 Reproductive System
The Integumentary System
Definition: The integumentary system is the organ system that forms a physical barrier between the external environment and the internal body parts it serves to protect and maintain.
Major Components: Includes the skin, associated glands, hair, and nails.
Key Statistical Facts about Skin:
It is the body’s largest and heaviest organ.
It covers an area of to .
It composes approximately of total body weight.
Structural Layers of the Skin:
Upper Layer (Epidermis): The outermost layer made of dead cells. Functions include reducing excess water loss, protecting from ultraviolet (UV) light rays, and preventing the entry of disease-causing microorganisms.
Middle Layer (Dermis): Contains blood vessels (responsible for thermoregulation), lymph vessels, sweat glands, sensory receptors, and hair follicles.
Lower Layer (Hypodermis): Contains fatty tissue used to store energy and acts as an insulation layer to prevent the loss of excess heat.
Hair Structures and Layers:
Hair originates from follicles made of epithelial cells.
Shaft: The outer layer made of dead cells turned into keratin and binding materials.
Medulla: The deepest layer of the hair shaft, typically only visible in large, thick hairs.
Cortex: The middle layer providing strength, color, and texture.
Cuticle: The thin, colorless outer layer that protects the cortex.
Functions of Hair: Helps insulate the body by trapping warm air, protects the skin, regulates temperature, and assists in evaporation/perspiration.
Nail Components:
Nail Plate: The visible part of the nail.
Nail Bed: The skin lying beneath the nail plate.
Cuticle: Thin tissue at the base overlapping the nail plate.
Nail Folds: Skin folds on the sides of the nail plate.
Lunula: The white, half-moon-shaped area at the base.
Matrix: The non-visible part under the cuticle responsible for nail growth.
Exocrine Glands of the Integumentary System:
Sudoriferous Glands: Hollow, cylindrical sweat glands that excrete sweat to the skin surface.
Sebaceous Glands: Small tubular glands in the dermis that release oil into hair follicles to lubricate and protect the hair shaft.
Ceruminous Glands: Located in the ear canal; produce ear wax (cerumen) to prevent dust and pathogens from entering.
Mammary Glands: Found in females; function to produce breast milk after childbirth.
Major Functions Summary:
Enclosing barrier and environmental protection.
Thermoregulation (process of body temperature regulation).
Production of pigment and Vitamin D.
Sensory perception (touch, temperature, pressure, pain).
Homeostasis.
Major Skin Diseases and Disorders:
Acne: Caused by pores blocked with oil, dead skin, or bacteria; located on face, neck, and back.
Rosacea: Associated with redness; has four subtypes with varying symptoms.
Eczema: Persistent conditions including dryness, rashes, swelling, and itching.
Hives: Itchy raised welts caused by allergic reactions, stress, or tight clothes.
Warts: Caused by viral infections, specifically human papilloma virus (HPV).
Cold Sore: Red, fluid-filled blisters near the mouth caused by the herpes simplex virus.
Carbuncle: A red, irritated lump under the skin filled with pus; caused by Staphylococcus aureus bacteria.
Blister: A bubble of fluid (serum) under the skin; serum provides natural protection if the blister remains unopened.
Actinic Keratosis: Rough, scaly patches resulting from years of sun exposure.
Latex Allergy: Reaction to rubber tree proteins; can cause hives or life-threatening anaphylaxis.
Chickenpox: Itchy red rash caused by the varicella-zoster virus.
The Muscular System
Definition: Muscles are tissues composed of cells called muscle fibers. The system is a collection of muscles used for movement and stability.
Types of Muscle Tissue:
Skeletal Muscle: Striated muscles attached to bones. They are voluntary (consciously controlled). Examples: chewing, talking, facial expressions.
Smooth Muscle: Non-striated muscles lining internal organs (stomach, lungs, blood vessels). They are involuntary.
Cardiac Muscle: Located only in the heart. They are involuntary and auto-rhythmic (contract spontaneously without hormonal control).
Properties of Muscle Cells:
Contractility: The ability to forcefully shorten/pull.
Extensibility: The ability to be stretched. This reduces with age (spasticity).
Excitability: The ability to respond to stimuli from motor neurons and hormones.
Elasticity: The ability to recover original size and shape after deformation.
Major Muscle Disorders:
Muscular Dystrophy: Inherited diseases characterized by the wasting away of muscle tissue.
Muscle Strains: Injuries to muscles or tendons (fibrous tissue connecting muscle to bone), often called "pulled muscles."
Statistical Note: Muscles account for approximately of a person’s weight. The largest muscle is the Gluteus Maximus.
The Skeletal System
Definition: Also called the musculoskeletal system, it consists of bones and connective tissues including cartilage, tendons, and ligaments.
Bone Composition: Mineralized connective tissue containing collagen, calcium phosphate, and mineral crystals. An adult human skeleton contains bones.
Classification of Bones by Shape:
Long Bones: Hard, compact, tubular, and filled with yellow bone marrow. Examples: Humerus, Femur, Finger bones.
Short Bones: Compact bones without marrow. Examples: Wrist (carpals), ankle (tarsals).
Flat Bones: Thin, flat, and typically curved with no cavity. Examples: Ribs, Sternum, Cranial bones, Scapula.
Irregular Bones: Thin membranes with nerves and blood vessels. Examples: Hip bones, facial bones, vertebrae.
Divisions of the Skeleton:
Axial Skeleton: Divides the body into equal right/left regions. Includes the Skull (cranium, face, auditory ossicles), Hyoid (U-shaped neck bone), Vertebral Column, and Thoracic Cage (ribs and sternum).
Appendicular Skeleton: Supports limbs. Includes the Pectoral Girdle (clavicle and scapula), Pelvic Girdle (hip bones), Upper Limbs (Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges), and Lower Limbs (Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges).
Connective Tissues and Joints:
Cartilage: Flexible support for the nose, trachea, and ears.
Tendon: Connects muscle to bone.
Ligament: Stretchy band connecting bone to bone at joints.
Joints: Sites where bones join. Types include Immovable (Skull) and Movable (Hinge joints like elbow/knee; Ball and socket joints like shoulder/hip).
Functions of the Skeletal System:
Movement and support of body weight.
Production of blood cells (WBC and RBC) in the bone marrow.
Protection of internal organs (e.g., ribs protect heart/lungs).
Storage of minerals like calcium, phosphate, and fats.
Major Skeletal Diseases:
Leukemia: Cancer of blood-forming tissues and bone marrow.
Osteoporosis: "Porous bone"; condition where bones lose density and become fragile.
Osteoarthritis: Degradation of joints causing pain and stiffness.
Fracture: A partial or complete break in bone continuity.
The Digestive System
Definition: The process of changing large, complex, insoluble food into smaller, simpler, soluble substances usable by body cells through the action of enzymes and organs.
The Alimentary Canal (Gut): The passage from mouth to anus, including the mouth, esophagus, stomach, small intestine, large intestine, and anus.
Human Teeth and Dentition:
Layers: Enamel (hardest, outer), Dentine (living layer), and Pulp Cavity (contains blood vessels/nerves).
Sets: Milk teeth ( teeth) and Permanent teeth ( to teeth including wisdom teeth).
Types: Incisors (cutting), Canines (tearing), Premolars (crushing), and Molars (grinding).
Adult Dental Formula:
Key Organs and Substances:
Stomach: Produces pepsin (protein digestion) and Hydrochloric Acid (HCl).
Small Intestine: Includes the duodenum; uses Villi for absorption. Digestion end products: amino acids (from protein), fatty acids, and glycerol (from fats).
Bile: Produced by the liver, stored in the gall bladder; neutralizes stomach acid and emulsifies fats.
Large Intestine: Absorbs water and forms faeces (defecation/egestion).
Digestive Diseases:
Constipation: Caused by lack of fiber (roughage) or water.
Diarrhea: Watery faeces caused by gut infection; can lead to dehydration.
Gastritis: Inflammation of the stomach lining.
Peptic Ulcer: Painful sores in the stomach or duodenum lining.
Hemorrhoids (Piles): Swollen veins in the anus/rectum.
The Respiratory System
Definition: The process of taking in oxygen (inhalation) and removing carbon dioxide (exhalation).
Anatomy of the Respiratory Tract:
Nose: Contains hair (filters dust), mucus (collects bacteria), and large surface area (moistens air).
Trachea: Reinforced by -shaped incomplete rings of cartilage to keep it open while allowing swallowing.
Pharynx: Cavity behind nose/mouth.
Larynx: Vocal cords/air passage.
Bronchi and Bronchioles: Diverging air passages.
Alveoli: Tiny air sacs where gas exchange between oxygen and carbon dioxide occurs.
Two Parts of Respiration:
Breathing: Physical inhalation and exhalation.
Cellular Respiration: Chemical reaction inside the body where food and oxygen create energy.
Mechanics: Lung shape is controlled by the diaphragm and intercostal muscles.
Respiratory Diseases:
Asthma: Chronic airway obstruction and wheezing.
Sinusitis: Swelling of tissue inside the sinus.
COPD: Includes emphysema and chronic bronchitis, often caused by smoking.
Influenza (Flu): Viral infection of the respiratory system.
COVID-19: Severe acute respiratory syndrome.
The Circulatory System
Definition: The transport system for air, food, minerals, vitamins, and waste materials between cells.
Double Circulation:
Pulmonary Circulation: Blood flow between heart and lungs.
Systematic Circulation: Blood flow between heart and rest of body.
The Heart: Muscular pump made of cardiac muscle with four chambers:
Right Atrium: Receives deoxygenated blood from body.
Right Ventricle: Lower chamber pumping deoxygenated blood to lungs.
Left Atrium: Receives oxygenated blood from lungs via pulmonary vein.
Left Ventricle: Thicker muscular walls; pumps oxygenated blood to the body via the aorta.
Valves: Prevent the backflow of blood.
Blood Vessels:
Arteries: Carry blood away from the heart. Thick, elastic walls. Mostly oxygenated (except pulmonary artery).
Veins: Return blood to the heart. Mostly deoxygenated (except pulmonary vein).
Capillaries: Thin-walled; connect arteries and veins; site of tissue exchange.
Blood Components:
Plasma (): Liquid portion composed of water.
Solid Parts ():
Red Blood Cells (Erythrocytes): Disc-shaped, no nucleus; contain hemoglobin to carry oxygen (–).
White Blood Cells (Leucocytes): Irregular shape, nucleated; defend against pathogens (–).
Platelets (Thrombocytes): Biconvex, no nucleus; initiate blood clotting (–).
Circulatory Diseases: Hypertension (high blood pressure), Heart attack, Stroke, Heart failure.
The Reproductive System
Reproductive Cells (Gametes): Sperm cells (male) and egg cells/ova (female).
Male Organs and Functions:
Testes: Produce sperm and testosterone.
Penis: Cylindrical organ for intercourse; ejaculates semen.
Scrotum: Sac holding testes.
Vas Deferens: Tube transporting sperm to the urethra.
Female Organs and Functions:
Ovaries: Produce ova (eggs) and hormones (estrogen and progesterone).
Fallopian Tube: Site of fertilization; moves egg to uterus.
Uterus (Womb): Site of pregnancy and implantation.
Vagina: Birth canal and intercourse organ.
Sexual Characteristics:
Primary: Present at birth (the reproductive organs themselves).
Secondary: Appear during puberty triggered by FSH and sex hormones (Testosterone in males; Estrogen in females).
Menstruation and Menopause:
Menstrual Cycle: Roughly every four weeks. Involves ovulation (release of egg) and thickening of the uterus wall.
Menstruation: Monthly discharge of blood if pregnancy does not occur.
Menopause: The stopping of ovulation and menstruation, typically around age .
Reproductive Health and STDs:
STDs: Diseases transmitted via sexual contact, including HIV/AIDS (attacks T-cells), Gonorrhea (Neisseria gonorrhea), Chancroids (Hemophilus ducreyi), and Syphilis (Treponema palladium).
Prevention (ABC Rules): A = Abstain, B = Be faithful, C = Condomise.
Questions & Discussion
Activity 4.1: Observation of integumentary system charts and presenting results.
Activity 4.2: Group discussion on skin layers and their specific functions.
Activity 4.3: Brainstorming skin diseases from personal experience.
Activity 4.7: Identify the role of the skeletal system and labeling bone parts.
Activity 4.11: Explain primary vs. secondary sexual characteristics and list bodily changes in males/females.
Review Exercise Question: Why is breathing through the nose better than the mouth? (Answer: The nose filters, warms, and moistens the air via hair, mucus, and blood supply).