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, forming cross-bridges, and pull the actin filaments inward, 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 binding sites on actin. 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, and others.

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

• 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 a bicep curl, the biceps brachii undergoes isotonic contraction to lift the weight.

Muscle Contraction Types

• Isotonic Contraction: Muscle changes length, producing movement.

• Isometric Contraction: Muscle generates tension without changing length.

Sarcomere Substructures

• 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 within the A-band where only myosin is present.

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, then distributed throughout the body.

• Respiratory Structures: Upper respiratory system includes nose, pharynx, larynx; lower respiratory system includes trachea, bronchi, lungs.

• Function of Structures: Nose filters, warms, and moistens air; pharynx and larynx direct air; trachea and bronchi conduct air; lungs facilitate gas exchange.

• Pressure Changes: During inhalation, lung pressure decreases, drawing air in; during exhalation, pressure increases, expelling air.

• Intercostal Muscles: Contract during inhalation to expand the chest cavity; relax during exhalation.

• Mechanics of Inspiration: Diaphragm contracts and moves downward, chest cavity expands, air enters lungs.

• Mechanics of Expiration: Diaphragm relaxes, chest cavity decreases, air is expelled.

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

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

Blood Flow Through the Heart

• Oxygen-rich blood enters the left atrium from the lungs, passes to the left ventricle, and is pumped to the body.

• Deoxygenated blood returns to the right atrium, moves to the right ventricle, and is sent to the lungs for oxygenation.

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: Salivary glands, liver, gallbladder, pancreas.

• Enzymes: Proteins that catalyze digestion; produced in salivary glands, stomach, pancreas, small intestine.

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

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

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

Metabolic Rates

• Basal Metabolic Rate (BMR): The energy expended at rest to maintain basic bodily functions.

• Standard Metabolic Rate (SMR): The metabolic rate under standardized conditions, often used for comparison across species.

"My Plate" Purpose

• Guides healthy eating by dividing food groups into appropriate portions.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: A segment of DNA that codes for a specific protein.

• Chromosome: A structure composed of DNA and proteins; humans have 23 pairs.

• Genome: The complete set of genes or genetic material in an organism.

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

• Karyotype: The visual representation of all chromosomes in a cell.

Genotype and Phenotype

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

• Phenotype: The observable traits resulting from the genotype.

Punnett Square and Alleles

• Punnett Square: A diagram used to predict the outcome of genetic crosses.

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

• Dominant Allele: Expressed when present (e.g., AA or Aa).

• Recessive Allele: Expressed only when homozygous (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

Laws of Genetics

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

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

Inheritance Patterns

• Incomplete Dominance: Heterozygotes show 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).

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

Genetic Disorders

• Dominant Allele Disorders: Can be lethal if expressed in homozygous form.

• Recessive Disorders: Can persist in populations due to carriers.

Punnett Square Table Example

The Punnett Square is used to predict the probability of offspring genotypes from parental crosses.

Parent 1	Parent 2	Offspring Genotype	Offspring Phenotype
Aa	Aa	AA, Aa, aa	Dominant, Dominant, Recessive
AA	aa	Aa	Dominant
aa	aa	aa	Recessive

Key Equations

• Mendelian Probability:

$P = \frac{\text{Number of desired genotype}}{\text{Total number of possible genotypes}}$

• Metabolic Rate Equation:

$\text{BMR} = \text{Energy expended per unit time at rest}$

• Muscle Contraction Equation:

$\text{Force} = \text{Number of cross-bridges} \times \text{Force per cross-bridge}$

Additional info: Academic context and definitions were added to expand brief review points into comprehensive study notes.