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: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.

• Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin and pull, shortening the sarcomere.

• Structure Identification: Key structures include the sarcolemma, sarcoplasmic reticulum, T-tubules, and mitochondria.

• Substructures of Sarcomere: Z-line, M-line, A-band, I-band, H-zone; each plays a role in contraction.

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

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

Order of Muscle Contraction Events:

1. Motor neuron releases neurotransmitter (acetylcholine).

2. Action potential travels along sarcolemma.

3. Sarcoplasmic reticulum releases calcium ions.

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

5. Myosin binds to actin, ATP is hydrolyzed, contraction occurs.

Isotonic vs. Isometric Contractions:

• Isotonic: Muscle changes length (movement occurs).

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

Muscles and Body Cavities: Diaphragm separates thoracic and abdominal cavities; intercostal muscles assist in breathing.

Example: During running, quadriceps contract isotonically to extend the knee.

Human Respiratory System

Structure and Function

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It consists of upper and lower structures, each with specific functions.

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

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

Significance of Breathing: Essential for cellular respiration and energy production.

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 contracts, intercostal muscles expand rib cage, lung volume increases, pressure decreases, air enters.

• Exhalation: Diaphragm relaxes, intercostal muscles contract, lung volume decreases, pressure increases, air exits.

Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

Intercostal Muscles: Assist in expanding and contracting the thoracic cavity during breathing.

Respiratory Diseases: Examples include asthma, bronchitis, pneumonia, and emphysema.

Example: During exercise, breathing rate increases to supply more oxygen.

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes primary and accessory organs.

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

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

Enzymes in Digestion: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, small intestine.

Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency.

Metabolic Rates:

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

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

"My Plate": USDA guideline for balanced nutrition.

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

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

Human Genetics and Inheritance

Genetic Concepts and Mechanisms

Genetics is the scientific study of heredity and variation. Genes, chromosomes, and inheritance patterns determine traits.

• Genes: Segments of DNA coding for proteins.

• Chromosomes: Structures containing DNA; humans have 23 pairs.

• Genome: Complete set of genetic material.

• Homologous Chromosomes: Pairs with same genes, may have different alleles.

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

• Genotype: Genetic makeup.

• Phenotype: Observable traits.

Punnett Square: Tool to predict genetic crosses.

Alleles: Variants of a gene; can be dominant or recessive.

• Dominant: Expressed in homozygous or heterozygous state.

• Recessive: Expressed only in homozygous state.

Law of Segregation: Alleles separate during gamete formation.

Law of Independent Assortment: Genes on different chromosomes 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 modify phenotypic expression.

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

• Sex-linked Genes: Located on sex chromosomes; often show unique inheritance patterns.

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

Example: Sickle cell anemia is caused by a recessive allele; color blindness is often sex-linked.

Term	Definition
Genotype	Genetic makeup of an organism
Phenotype	Observable characteristics
Homozygous	Two identical alleles for a gene
Heterozygous	Two different alleles for a gene
Dominant	Allele that masks the effect of another
Recessive	Allele whose effect is masked
Incomplete Dominance	Intermediate phenotype in heterozygotes
Codominance	Both alleles fully expressed
Polygenic	Trait controlled by multiple genes
Sex-linked	Gene located on sex chromosome

Additional info: The notes above expand on brief review points, providing definitions, examples, and context for exam preparation.