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 and generate heat. The sliding filament mechanism is central to muscle contraction.

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

• Actin and Myosin: Actin filaments provide sites for myosin heads to attach and pull, causing contraction. Myosin filaments have heads that bind to actin and use ATP to generate force.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

• Order of Events in Muscle Contraction:

  1. Action potential arrives at the motor neuron.

  2. Release of neurotransmitter (acetylcholine) at the neuromuscular junction.

  3. Depolarization of muscle cell membrane.

  4. Release of calcium ions from the sarcoplasmic reticulum.

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

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

• Electrical Impulses: Action potentials in motor neurons trigger muscle contraction by causing the release of calcium ions.

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

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle length remains the same (no movement, but tension increases).

Example: During lifting a weight, the biceps undergo isotonic contraction; holding a weight steady involves isometric contraction.

Human Respiratory System

Structure and Function 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 structures, each with specific functions.

• Significance of Breathing: Essential for cellular respiration and energy production.

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

• Lower Respiratory Structures: Includes trachea, bronchi, bronchioles, and lungs. Functions: conduct air to alveoli, site of gas exchange.

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

• Pressure Changes During Breathing:

  • Inhalation: Diaphragm contracts, thoracic cavity expands, pressure decreases, air enters lungs.

  • Exhalation: Diaphragm relaxes, thoracic cavity contracts, pressure increases, air exits lungs.

• Intercostal Muscles: Located between ribs; contract during inhalation to expand chest, relax during exhalation.

• Mechanics of Inspiration and Expiration: Inspiration is active (muscle contraction), expiration is usually passive (muscle relaxation).

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, emphysema.

Example: During exercise, breathing rate increases to meet oxygen demand.

Human Digestive System

Structure and Function of the Digestive System

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

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas. Functions: produce enzymes, bile, and aid digestion.

• Enzymes: Biological catalysts that speed up digestion; produced in salivary glands, stomach, pancreas, small intestine.

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

• Metabolic Rates:

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

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

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

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

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

Example: Amylase in saliva begins carbohydrate digestion in the mouth.

Human Genetics and Inheritance

Genetic Concepts and Mechanisms

Genetics is the study of heredity and variation in organisms. Human inheritance is governed by genes, chromosomes, and various genetic laws.

• Genes: Segments of DNA that code for proteins; basic units of heredity.

• Chromosomes: Structures made of DNA and proteins; humans have 23 pairs.

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

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

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

• Genotype: Genetic makeup of an individual.

• Phenotype: Observable traits resulting from genotype and environment.

• Punnett Square: Diagram used to predict genetic crosses and inheritance patterns.

• Dominant and Recessive Alleles:

  • Dominant: Expressed when present ($AA$ or $Aa$).

  • Recessive: Expressed only when homozygous ($aa$).

• Homozygous vs. Heterozygous:

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

  • Heterozygous: Two different alleles ($Aa$).

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

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

• Dominant/Recessive Disorders: Dominant disorders can be lethal if expressed; recessive disorders persist due to carriers.

• Incomplete Dominance: Heterozygotes show intermediate phenotype (e.g., pink flowers from red and white parents).

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

• Polygenic Inheritance: Traits controlled by multiple genes (e.g., skin color).

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

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

• Meiosis and New Allele Combinations: Crossing over during meiosis creates new allele combinations.

• Sex-linked Genes: Genes located on sex chromosomes (e.g., X-linked traits).

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

Example: Hemophilia is an X-linked recessive disorder.

Genetic Terms Comparison Table

Term	Definition	Example
Genotype	Genetic makeup	$AA$, $Aa$, $aa$
Phenotype	Physical expression	Brown eyes, blue eyes
Homozygous	Same alleles	$AA$ or $aa$
Heterozygous	Different alleles	$Aa$
Dominant	Expressed when present	$A$
Recessive	Expressed only when homozygous	$a$

Additional info: Table entries inferred for clarity and completeness.