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 functional unit of muscle fibers, 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. Action potential travels down motor neuron.

  2. Release of neurotransmitter (acetylcholine) at neuromuscular junction.

  3. Depolarization of muscle cell membrane.

  4. Release of calcium ions 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: Initiated by action potentials in motor neurons, leading to muscle contraction.

• 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: Muscle changes length (movement occurs).

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

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

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 include filtering, warming, and humidifying air.

• Lower Respiratory Structures: Trachea, bronchi, lungs, alveoli. Functions include conducting air and facilitating 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.

• Pressure Changes in Lungs: Inhalation decreases pressure (air enters), exhalation increases pressure (air exits).

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

• Mechanics of Inspiration: Diaphragm contracts, chest cavity expands, air flows in.

• Mechanics of Expiration: Diaphragm relaxes, chest cavity contracts, air flows out.

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

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

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.

• Accessory Organs: Liver, pancreas, gallbladder. These produce enzymes and bile to aid digestion.

• Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, and small intestine; speed up digestion.

• 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 standard 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.

Example: The pancreas releases digestive enzymes into the small intestine to break down carbohydrates, proteins, and fats.

Human Genetics and Inheritance

Genetic Concepts and Mechanisms

Genetics is the scientific study of heredity and variation in organisms. Human inheritance is governed by genes, chromosomes, and various genetic laws.

• Genes: Segments of DNA that code for proteins; basic units of heredity.

• Chromosomes: Structures made of DNA and proteins; humans have 23 pairs.

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

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

• Karyotype: Visual representation of chromosome number and structure.

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits resulting from genotype and environment.

• Punnett Square: Diagram used to predict genetic crosses.

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

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

• 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 carriers.

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Traits controlled by multiple genes.

• Environmental Impact: Environment can influence phenotypic expression.

• Linked Genes: Genes located close together on a chromosome; inherited together.

• Meiosis: New allele combinations arise from crossing over.

• Sex-linked Genes: Genes located on sex chromosomes; often affect males more.

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

Example: Color blindness is a sex-linked trait, more common in males due to inheritance of X-linked genes.

Genetic Crosses Table

The following table summarizes the outcomes of genetic crosses using Punnett Squares:

Parent Genotypes	Possible Offspring Genotypes	Phenotype
AA x aa	All Aa	Dominant trait expressed
Aa x Aa	AA, Aa, aa	3:1 ratio (dominant:recessive)
Aa x aa	Aa, aa	1:1 ratio
Additional info: X-linked cross (XAXa x XaY)	XAXa, XaXa, XAY, XaY	Varies by sex and allele

Key Equations

• Mendelian Probability:

$P = \frac{\text{Number of desired outcomes}}{\text{Total number of outcomes}}$

• Metabolic Rate:

$\text{BMR} = \text{Energy expenditure at rest}$

• Muscle Contraction:

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

Additional info: Academic context was added to clarify mechanisms, structures, and genetic principles for exam preparation.