Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

• gm separates thoracic and abdominal cavities.

• Isotonic vs. Isometric Contractions: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 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.

  • Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Contraction.

  • Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

  • 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 Cavities: Diaphra

  • Isotonic: Muscle changes length (movement occurs).

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

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Sarcomere Substructures and Functions

• 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 with only myosin, disappears during contraction.

Action Potential and Muscle Contraction

• Action Potential: Electrical signal in motor neuron triggers muscle contraction.

• Calcium Release: Calcium ions released from sarcoplasmic reticulum enable myosin-actin binding.

Equation:

$\text{ATP} + \text{Myosin} \rightarrow \text{Myosin-ATP} \rightarrow \text{Myosin-Actin} \rightarrow \text{Contraction}$

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 to the body.

• Respiratory Structures:

  • Upper Respiratory: Nose, pharynx, larynx – filter, warm, and humidify air.

  • Lower Respiratory: Trachea, bronchi, lungs – conduct air and facilitate gas exchange.

• Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

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

• Mechanics of Breathing:

  • Inspiration: Diaphragm contracts, chest expands, air enters.

  • Expiration: Diaphragm relaxes, chest contracts, air exits.

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

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

Blood Flow Through the Heart

• Order: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body tissues.

Equation:

$\text{Pressure}_{\text{lungs}} < \text{Pressure}_{\text{atmosphere}} \rightarrow \text{Inhalation}$

$\text{Pressure}_{\text{lungs}} > \text{Pressure}_{\text{atmosphere}} \rightarrow \text{Exhalation}$

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.

• Accessory Organs: Liver, pancreas, gallbladder – produce enzymes and bile.

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

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

• Metabolic Rates:

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

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

• "My Plate": Dietary 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.

Digestion of Molecules

• Carbohydrates: Digested by amylase, maltase, sucrase.

• Proteins: Digested by pepsin, trypsin.

• Fats: Digested by lipase, bile emulsifies fats.

Equation:

$\text{Food} + \text{Enzyme} \rightarrow \text{Nutrients}$

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: Segment of DNA coding for a trait.

• Chromosome: Structure containing DNA; humans have 23 pairs.

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

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

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

Genotype, Phenotype, and Punnett Squares

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

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

• Punnett Square: Diagram to predict genetic crosses.

Example: Crossing Aa x Aa yields 1 AA, 2 Aa, 1 aa.

Dominant and Recessive Alleles

• Dominant Allele: Expressed if present (A).

• Recessive Allele: Expressed only if homozygous (aa).

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers).

• Codominance: Both alleles 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 on sex chromosomes (e.g., X-linked traits).

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

Table: Dominant vs. Recessive Alleles

Allele Type	Expression	Example
Dominant	Expressed in heterozygous and homozygous	Huntington's disease
Recessive	Expressed only in homozygous	Cystic fibrosis

Table: Types of Inheritance

Type	Description	Example
Complete Dominance	One allele masks the other	Widow's peak
Incomplete Dominance	Intermediate phenotype	Pink snapdragons
Codominance	Both alleles fully expressed	AB blood type
Polygenic	Multiple genes affect trait	Height

Equation:

$\text{Probability of trait} = \frac{\text{Number of favorable outcomes}}{\text{Total outcomes}}$

Example: Sex-linked traits like color blindness are more common in males due to X-linked inheritance.