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 the filaments together, and shorten the sarcomere.

• Electrical Impulses: Action potentials in motor neurons trigger the release of calcium ions in muscle cells, initiating contraction.

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

Example: During exercise, muscle contractions increase body temperature due to ATP hydrolysis.

Muscle Contraction Mechanism

Muscle contraction is initiated by nerve impulses and involves a series of events:

1. Motor neuron releases neurotransmitter (acetylcholine) at the neuromuscular junction.

2. Action potential travels along the muscle cell membrane.

3. Calcium ions are released from the sarcoplasmic reticulum.

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

5. Myosin heads attach to actin and perform a power stroke.

6. ATP is required for myosin head detachment and re-cocking.

Isotonic vs. Isometric Contractions:

• Isotonic: Muscle changes length (movement occurs).

• Isometric: Muscle tension increases, but length does not change (no movement).

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

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

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 Structures: Upper (nose, pharynx, larynx) and lower (trachea, bronchi, lungs) respiratory tracts have distinct functions.

Structure and Function of the Respiratory System

• Upper Respiratory System: Filters, warms, and moistens air; includes nasal cavity, pharynx, larynx.

• Lower Respiratory System: Conducts air to lungs; includes trachea, bronchi, bronchioles, alveoli.

• Alveoli: Site of gas exchange; oxygen diffuses into blood, carbon dioxide out.

Example: The trachea is lined with cilia to trap particles and prevent infection.

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.

Human Digestive System

Structure and Function

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; produce enzymes and bile for digestion.

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

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

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

Metabolic Rates and Digestion

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

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

• "My Plate": Dietary guideline for balanced nutrition.

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

Human Genetics and Inheritance

Basic Concepts

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

• Genes: Segments of DNA that code for proteins.

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

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

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

• Karyotype: Visual representation of chromosome number and structure.

Genotype, Phenotype, and Inheritance Patterns

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

• Phenotype: Observable traits.

• Punnett Square: Tool to predict genetic crosses.

• Dominant Allele: Expressed when present.

• Recessive Allele: Expressed only when homozygous.

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws and Variations

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

• Meiosis: New allele combinations arise from crossing over.

• 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.

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant	AA, Aa	Trait expressed	Widow's peak
Recessive	aa	Trait expressed	Attached earlobe
Incomplete Dominance	Aa	Intermediate	Pink snapdragon
Codominance	AB	Both traits	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color

Example: Sickle cell disease is caused by a recessive allele; color blindness is X-linked.

Additional info: The notes above expand on brief review points to provide academic context and explanations for exam preparation.