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 called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

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

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

• Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force and movement.

• Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Muscle contraction.

• Electrical Impulses: Action potentials in motor neurons trigger the release of neurotransmitters (e.g., acetylcholine), leading to muscle fiber activation.

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

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

Muscle Groups and Functions

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

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

Types of Muscle Contractions

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

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

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

Human Respiratory System

Significance and Mechanics of Breathing

Breathing is essential for gas exchange, supplying oxygen and removing carbon dioxide.

• Upper Respiratory Structures: Nose, pharynx, larynx – filter, warm, and humidify air.

• Lower Respiratory Structures: Trachea, bronchi, lungs – conduct air and facilitate gas exchange.

• Intercostal Muscles: Located between ribs; contract during inhalation to expand the chest cavity.

• Diaphragm: Contracts and flattens during inspiration, increasing thoracic volume.

• Pressure Changes: Inhalation decreases lung pressure, drawing air in; exhalation increases pressure, expelling air.

Example: During inspiration, the diaphragm contracts, chest volume increases, and air flows into the lungs.

Blood Flow and Gas Exchange

• Oxygen-rich Blood: Flows from lungs to left atrium, then left ventricle, and out to the body.

• Respiratory Diseases: Include asthma, bronchitis, pneumonia, and emphysema.

Human Digestive System

Structures and Functions

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

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

• Accessory Organs: Liver, pancreas, gallbladder – produce enzymes and bile for digestion.

• Enzymes: Catalyze breakdown of carbohydrates, proteins, and fats; produced in salivary glands, stomach, pancreas, and small intestine.

• Surface Area: Increased by villi and microvilli in the small intestine, enhancing nutrient absorption.

• Peristalsis: Rhythmic contractions that move food through the digestive tract.

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

Metabolic Rates and Nutrition

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

• Standard Metabolic Rate: Energy used under specific conditions.

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

Human Genetics and Inheritance

Basic Concepts

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

• Genes: Segments of DNA encoding traits; located on chromosomes. (houses on street)

• Chromosomes: Structures carrying genetic information; humans have 23 pairs. (street)

• Genome: Complete set of genes in an organism.

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

• Karyotype: Visual representation of chromosome number and structure. (addresses of neighbors)

Genotype, Phenotype, and Inheritance Patterns

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

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

• Punnett Square: Diagram predicting genetic crosses.

• Dominant Allele: Expressed if present; Recessive Allele: Expressed only if homozygous.

• Homozygous: Two identical alleles dominant or recessive; Heterozygous: Two different alleles.

Mendelian Laws and Exceptions

• Law of Segregation: Alleles separate during gamete formation.

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

• Incomplete Dominance: Heterozygote shows 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.

• Linked Genes: Genes close together on a chromosome tend to be inherited together.

• Sex-linked Genes: Located on sex chromosomes; often affect males more (e.g., color blindness).

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

Sample Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant/Recessive	AA, Aa, aa	Dominant or recessive trait	Widow's peak
Incomplete Dominance	RR, RW, WW	Intermediate trait	Pink snapdragon flowers
Codominance	IAIB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Human height

Key Equations

• Mendelian Probability:

• $P = \frac{\text{Number of desired outcomes}}{\text{Total number of outcomes}}$

• Hardy-Weinberg Equation:

• $p^2 + 2pq + q^2 = 1$

Example: A Punnett Square can predict the probability of offspring inheriting a recessive disorder.

Additional info: Academic context was added to clarify mechanisms, structures, and inheritance patterns, and to provide examples and equations for exam preparation.

Cas 9cuts the DNA