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

Human Muscular System

Muscle Cell Structure and Sliding Filament Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is explained by the sliding filament theory, which involves the interaction of actin and myosin filaments within the sarcomere.

• Sarcomere: The basic contractile unit of muscle fiber, bordered by Z-lines. It contains overlapping actin (thin) and myosin (thick) filaments.

• Sliding Filament Mechanism: During contraction, myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere and thus the muscle.

• Actin: A protein forming thin filaments; provides sites for myosin attachment.

• Myosin: A motor protein forming thick filaments; its heads bind to actin and use ATP to generate force.

• Function of Sarcomere: To convert chemical energy (ATP) into mechanical work for muscle contraction.

Example: When you flex your arm, sarcomeres in your biceps shorten as actin and myosin filaments slide past each other.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials, which originate in motor neurons and are transmitted to muscle fibers.

• Action Potential: A rapid change in membrane potential that travels along neurons and muscle cells.

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitters (e.g., acetylcholine) to trigger an action potential in the muscle.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

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

  3. Action potential travels along the sarcolemma and into T-tubules.

  4. Calcium ions are released from the sarcoplasmic reticulum.

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

  6. Myosin heads bind to actin, initiating contraction.

• Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement (e.g., lifting a weight).

• Isometric Contraction: Muscle tension increases but length remains the same; no movement occurs (e.g., holding a weight steady).

Major Muscle Groups and Functions

• Major Muscle Groups: Include biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, gluteals, and more.

• Muscles Sectioning Body Cavities: The diaphragm separates the thoracic and abdominal cavities; intercostal muscles are located between ribs.

Human Respiratory System

Significance and Structure of the Respiratory System

The respiratory system enables gas exchange, supplying oxygen to the body and removing carbon dioxide. It consists of upper and lower respiratory tracts, each with specialized structures.

• Upper Respiratory System: Includes the nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air; provides resonance for speech.

• Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and lungs. Functions: conducts air to alveoli, where gas exchange occurs.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing lung pressure, pushing air out.

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure, and vice versa for exhalation.

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

Blood Flow and Gas Exchange

• Oxygen-Rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, passes to the left ventricle, and is pumped to the body.

• Gas Exchange: Occurs in alveoli; oxygen diffuses into blood, carbon dioxide diffuses out.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, emphysema, pneumonia, and lung cancer.

• Significance: These conditions impair gas exchange and can affect overall health.

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes the alimentary canal and accessory organs.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Function of Enzymes: Biological catalysts that speed up chemical digestion; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for efficient nutrient absorption.

Metabolic Rates and Nutrition

• Basal Metabolic Rate (BMR): The energy expended at rest to maintain vital functions.

• Standard Metabolic Rate (SMR): The metabolic rate under specific conditions (e.g., temperature, activity).

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

Digestive Processes

• Digestion of Molecules: Carbohydrates, proteins, and fats are broken down by specific enzymes in different parts of the digestive tract.

• Peristalsis: Rhythmic contractions of smooth muscle that propel food through the digestive tract.

Human Genetics and Inheritance

Basic Concepts and Molecular Structure

Genetics is the scientific study of heredity and variation. Genes, chromosomes, and genomes are central to inheritance.

• Gene: A segment of DNA that codes for a specific protein or trait.

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

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

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

• Karyotype: A visual representation of all chromosomes in a cell, used to detect chromosomal abnormalities.

Genotype, Phenotype, and Inheritance Patterns

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits resulting from the genotype and environment.

• Punnett Square: A diagram used to predict the outcome of genetic crosses.

• Dominant Allele: Expressed when present (e.g., A).

• Recessive Allele: Expressed only when homozygous (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws and Extensions

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white = pink flowers).

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

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

• Environmental Impact: Environment can affect phenotypic expression (e.g., nutrition, temperature).

Chromosomal and Genetic Variations

• Linked Genes: Genes located close together on the same chromosome; tend to be inherited together.

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

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y); often show different inheritance patterns in males and females.

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked by dominant	a

Example: A Punnett square can predict the probability of offspring inheriting certain traits based on parental genotypes.

Additional info: Some dominant allele disorders are lethal because a single copy can disrupt essential functions, while recessive disorders persist because carriers (heterozygotes) do not show symptoms and can pass the allele to offspring.