Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells and structures to produce movement. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic contractile unit of muscle, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

• Sliding Filament Theory: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Substructures: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

Example: During contraction, the H-zone and I-band decrease in width, while the A-band remains constant.

Muscle Contraction Mechanism

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Calcium ions are released from the sarcoplasmic reticulum.

  4. Calcium binds to troponin, exposing binding sites on actin.

  5. Myosin binds to actin, ATP is hydrolyzed, and contraction occurs.

• Electrical Impulses: Cause release of calcium ions, which are essential for contraction.

Example: The release of acetylcholine is necessary for the muscle cell to respond to neural stimulation.

Types of Muscle Contractions

Muscle contractions can be classified based on whether the muscle changes length.

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle does not change length (no movement, but tension increases).

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Muscle Groups and Functions

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, etc.

• Body Heat Generation: Most body heat is generated by muscle activity, especially skeletal muscles.

• Muscles Sectioning Cavities: Diaphragm separates thoracic and abdominal cavities.

Example: The diaphragm is essential for breathing and separates the chest from the abdomen.

Human Respiratory System

Significance of Breathing

Breathing is vital for oxygen intake and carbon dioxide removal, supporting cellular respiration.

• Oxygen: Required for aerobic metabolism in cells.

• Carbon Dioxide: Waste product that must be expelled.

Example: Without oxygen, cells cannot produce ATP efficiently.

Respiratory System Structures

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

• Lower Respiratory System: Includes trachea, bronchi, lungs. Functions: gas exchange, air conduction.

Example: The nasal cavity filters dust and pathogens from inhaled air.

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

• Intercostal Muscles: Assist in expanding and contracting the rib cage.

Example: During inspiration, lung pressure drops below atmospheric pressure, drawing air in.

Blood Flow and Gas Exchange

• Oxygen-rich Blood: Flows from lungs to left atrium, then left ventricle, then systemic circulation.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body tissues.

Example: Oxygenated blood leaves the lungs via pulmonary veins.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema.

• Impact: Affect gas exchange and breathing efficiency.

Example: Asthma causes constriction of airways, making breathing difficult.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Liver, pancreas, gallbladder. Functions: produce enzymes, bile, and aid digestion.

Example: The pancreas produces digestive enzymes and insulin.

Enzymes and Digestion

• Function: Enzymes catalyze breakdown of macromolecules.

• Production Sites: Salivary glands, stomach, pancreas, small intestine.

Example: Amylase breaks down starch in the mouth.

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine increase absorption efficiency.

Example: Microvilli provide a vast surface for nutrient absorption.

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy used at rest.

• Standard Metabolic Rate (SMR): Energy used under specific conditions.

Example: BMR is measured after fasting and rest.

Nutrition and "My Plate"

• "My Plate": A guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Example: "My Plate" recommends half the plate be fruits and vegetables.

Digestion Process and Peristalsis

• Peristalsis: Wave-like muscle contractions that move food through the digestive tract.

• Molecule Digestion: Carbohydrates, proteins, and fats are digested in different regions.

Example: Peristalsis pushes food from the esophagus to the stomach.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

Genetics is the scientific study of heredity and variation in organisms.

• Gene: A segment of DNA coding for a specific protein.

• Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

• Genome: The complete set of genes in an organism.

Example: The human genome contains about 20,000-25,000 genes.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pairs with the same genes but possibly different alleles.

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Example: Down syndrome is identified by an extra chromosome 21 in a karyotype.

Genotype and Phenotype

• Genotype: Genetic makeup (e.g., AA, Aa, aa).

• Phenotype: Observable traits (e.g., brown eyes).

Example: Genotype Aa may produce a dominant phenotype.

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Example: Crossing Aa x Aa yields a 3:1 ratio of dominant to recessive phenotypes.

Mendelian Laws

• Law of Segregation: Each parent passes one allele to offspring.

• Law of Independent Assortment: Genes for different traits are inherited independently.

Example: Traits for eye color and hair color are inherited separately.

Dominant and Recessive Disorders

• Dominant Disorders: Expressed with one dominant allele; can be lethal.

• Recessive Disorders: Expressed only with two recessive alleles; can persist in populations.

Example: Huntington's disease is dominant; cystic fibrosis is recessive.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

• Codominance: Both alleles are fully expressed (e.g., AB blood type).

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

• Environmental Impact: Environment can affect phenotypic expression.

Example: Height is influenced by both genes and nutrition.

Linked Genes and Meiosis

• Linked Genes: Genes located close together on a chromosome; inherited together.

• New Allele Combinations: Crossing over during meiosis creates genetic diversity.

Example: Linked genes may not follow independent assortment.

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes; often affect males more.

• Nondisjunction: Failure of chromosomes to separate during meiosis, leading to abnormal chromosome numbers.

Example: Color blindness is a sex-linked trait; nondisjunction can cause Turner syndrome.

Term	Definition	Example
Genotype	Genetic makeup of an organism	AA, Aa, aa
Phenotype	Observable traits	Brown eyes
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Allele expressed in heterozygote	A
Recessive	Allele expressed only in homozygote	a
Incomplete Dominance	Intermediate phenotype	Pink flowers (red x white)
Codominance	Both alleles expressed	AB blood type
Polygenic	Trait controlled by multiple genes	Skin color

Additional info: Academic context and examples were added to clarify concepts and provide a self-contained study guide.