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 muscle fibers, composed of actin and myosin filaments.

• Actin Filaments: Thin filaments that interact with myosin during contraction.

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to shorten the sarcomere.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads attach to actin, forming cross-bridges and pulling actin filaments inward.

Function of the Sarcomere: To facilitate contraction by shortening its length through the sliding of actin and myosin filaments.

Order of Events in Muscle Contraction:

1. Action potential travels down 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 heads bind to actin, initiating contraction.

Isotonic vs. Isometric Contractions:

• Isotonic: Muscle changes length (movement occurs).

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

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

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

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

Electrical Impulses and Molecule Release: Electrical impulses trigger calcium release, which is essential for contraction.

Example: The biceps brachii contracts to flex the forearm.

Human Respiratory System

Structure and Function

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It consists of upper and lower respiratory tracts.

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

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

Significance of Breathing: Provides oxygen for cellular respiration and removes carbon dioxide, a metabolic waste.

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

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.

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

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

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.

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

Function of Enzymes: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, and 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.

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

Digestion of Molecules: Carbohydrates, proteins, and fats are digested by specific enzymes in different regions.

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

Human Genetics and Inheritance

Basic Concepts

Genetics is the scientific study of heredity and variation in organisms. Genes are segments of DNA that code for traits.

• Genes: Molecular units of heredity, composed of DNA.

• Chromosomes: Structures that organize and carry genes; humans have 23 pairs.

• Genome: The 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.

Genotype vs. Phenotype:

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

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

Punnett Square: Tool to predict genetic outcomes of crosses.

Dominant vs. Recessive Alleles:

• Dominant: Expressed when present (e.g., 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: Alleles separate during gamete formation.

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

Dominant/Recessive Disorders: Dominant disorders can be lethal; recessive disorders persist due to carrier status.

Incomplete Dominance: Heterozygotes show intermediate phenotype.

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

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

Environmental Impact: Environment can influence phenotype (e.g., nutrition affects height).

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

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

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

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

Punnett Square Table Example

Parent Genotype	Possible Gametes	Offspring Genotypes
AA x aa	A, a	Aa
Aa x Aa	A, a	AA, Aa, aa
Additional info: Table shows Mendelian inheritance patterns.

Example: A cross between two heterozygous parents (Aa x Aa) yields a 3:1 ratio of dominant to recessive phenotypes.