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: 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, pull, and slide the filaments past each other, shortening the sarcomere.

• Order of Events in Muscle Contraction: 1. Nerve impulse triggers action potential in motor neuron. 2. Release of neurotransmitter (acetylcholine) at neuromuscular junction. 3. Action potential spreads across muscle cell membrane. 4. Calcium ions released from sarcoplasmic reticulum. 5. Calcium binds to troponin, exposing actin binding sites. 6. Myosin binds to actin, ATP is hydrolyzed, and contraction occurs.

• Electrical Impulses: Action potentials in motor neurons initiate muscle contraction by causing 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, gluteals, and others.

• Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities; intercostal muscles are between ribs.

• Isotonic vs. Isometric Contractions: Isotonic contractions produce movement (muscle changes length), while isometric contractions produce tension without movement (muscle length remains the same).

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

Sarcomere Substructures and Functions

• Z-line: Defines the boundaries of a sarcomere.

• A-band: Contains the length of the myosin filaments.

• I-band: Contains only actin filaments.

• H-zone: Area with only myosin, disappears during contraction.

Function: The sarcomere shortens during contraction, producing force and movement.

Muscle Contraction Mechanisms

• Action Potential: Electrical signal in motor neuron triggers muscle contraction.

• Release of Molecules: Calcium ions released from sarcoplasmic reticulum initiate contraction.

Formula:

$\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

Additional info: ATP hydrolysis provides energy for myosin head movement.

Human Respiratory System

Significance of Breathing

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

• Oxygen Transport: Oxygen is carried by hemoglobin in red blood cells.

• Carbon Dioxide Removal: CO2 is expelled during exhalation.

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, alveoli. Functions: conduct air, gas exchange.

Mechanics of Breathing

• Inhalation: Diaphragm contracts and moves downward, intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, causing air to flow in.

• Exhalation: Diaphragm relaxes, intercostal muscles relax, thoracic volume decreases, lung pressure increases, air flows out.

• Pressure Changes: $\text{Pressure}_{\text{lungs}} \downarrow$ during inhalation, $\uparrow$ during exhalation.

Intercostal Muscles

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

Blood Flow Through the Heart

• Oxygen-rich blood: Flows from lungs to left atrium, left ventricle, then to body.

• Oxygen-poor blood: Returns to right atrium, right ventricle, then to lungs.

Respiratory Diseases and Disorders

• Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

Additional info: Gas exchange occurs in alveoli, where oxygen diffuses into blood and CO2 diffuses out.

Human Digestive System

Major Structures and Functions

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

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes, churns food.

• Small Intestine: Main site of nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes in Digestion

• Function: Catalyze breakdown of macromolecules.

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

Surface Area in Digestion

• Importance: Increased surface area (villi, microvilli) enhances nutrient absorption.

Metabolic Rates

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

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

"My Plate" Purpose

• Function: Guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion of Molecules

• Carbohydrates: Digested by amylase, absorbed as glucose.

• Proteins: Digested by pepsin, trypsin, absorbed as amino acids.

• Fats: Digested by lipase, absorbed as fatty acids and glycerol.

Peristalsis

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

Formula:

$\text{Enzyme} + \text{Substrate} \rightarrow \text{Product}$

Additional info: Enzymes lower activation energy for digestion reactions.

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 trait.

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

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

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square

• Function: Predicts genetic outcomes of crosses.

Dominant and Recessive Alleles

• Dominant Allele: Expressed when present.

• Recessive Allele: Expressed only when homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can affect phenotypic expression.

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.

Sex-linked Genes

• Definition: Genes located on sex chromosomes (X or Y).

Nondisjunction

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

Comparison Table: Dominant vs. Recessive Alleles

Type	Expression	Example
Dominant	Expressed in heterozygous and homozygous	Widow's peak
Recessive	Expressed only in homozygous	Attached earlobes

Formula:

$\text{Phenotype} = \text{Genotype} + \text{Environment}$

Additional info: Nondisjunction can cause disorders such as Down syndrome (trisomy 21).