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 Mechanism: Myosin heads bind to actin, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

• Function of Sarcomere: Facilitates muscle contraction by shortening during activation.

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

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

Electrical Impulses and Muscle Contraction

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: Motor neuron releases neurotransmitter (acetylcholine), causing depolarization of muscle cell membrane, leading to calcium release and contraction.

• Release of Molecules: Calcium ions are released from the sarcoplasmic reticulum, enabling actin-myosin interaction.

Types of Muscle Contractions

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

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

Heat Generation

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

Example

• During running, isotonic contractions of leg muscles propel the body forward, while isometric contractions stabilize joints.

Human Respiratory System

Significance of Breathing

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

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart and then to the body.

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

Structures of the Respiratory System

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions: filtering, warming, and humidifying air.

• Lower Respiratory System: Includes trachea, bronchi, lungs, and alveoli. Functions: conducting air and facilitating gas exchange.

Mechanics of Breathing

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

• 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 during breathing.

Blood Flow Through the Heart

• Oxygen-rich blood flows from the lungs to the left atrium, then left ventricle, and out to the body.

Example

• During exercise, breathing rate increases to supply more oxygen and remove excess carbon dioxide.

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.

Enzymes and Digestion

• Function of Enzymes: Catalyze breakdown of macromolecules (e.g., amylase for starch, protease for proteins).

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

Surface Area and Digestion

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

Metabolic Rates

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

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

My Plate

• Purpose: Dietary guideline for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Mechanics

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

Example

• After eating, peristalsis moves food from the esophagus to the stomach for further digestion.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: Segment of DNA coding for a specific trait.

• Chromosome: Structure containing DNA and genes; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

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

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

Genotype and Phenotype

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

• Phenotype: Observable traits resulting from genotype and environment.

Punnett Square and Alleles

• Punnett Square: Tool to predict genetic outcomes of crosses.

• Dominant Allele: Expressed trait 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

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

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

Inheritance Patterns

• 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 located close together on a chromosome tend to be inherited together.

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

Meiosis and Genetic Variation

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

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

Example

• Using a Punnett Square, crossing Aa x Aa yields a 3:1 ratio of dominant to recessive phenotypes.

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype
Dominant/Recessive	AA, Aa, aa	Dominant trait (AA, Aa), Recessive trait (aa)
Incomplete Dominance	RR, RW, WW	Red (RR), Pink (RW), White (WW)
Codominance	IAIB	Both traits expressed (e.g., AB blood type)
Polygenic	Multiple genes	Continuous variation (e.g., height, skin color)

Additional info: Table entries inferred for clarity and completeness.