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 and generate heat. 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 in motor neuron → Release of neurotransmitter (acetylcholine) → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.

• Electrical Impulses: Action potentials trigger calcium release from the sarcoplasmic reticulum, enabling contraction.

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and others.

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

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

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

Function of Sarcomere: To facilitate contraction and force generation.

Actin and Myosin Functions: Actin provides sites for myosin attachment; myosin uses ATP to pull actin filaments.

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.

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

• 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.

• Oxygen-rich Blood Flow: Oxygenated blood returns from lungs to left atrium → left ventricle → aorta → body.

• Pressure Changes: During inhalation, lung pressure decreases; during exhalation, pressure increases.

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

• Mechanics of Inspiration: Diaphragm contracts, chest expands, air enters lungs.

• Mechanics of Expiration: Diaphragm relaxes, chest contracts, air exits lungs.

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

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

Blood Flow Through the Heart

• Deoxygenated blood enters right atrium → right ventricle → lungs (via pulmonary artery).

• Oxygenated blood returns to left atrium → left ventricle → body (via aorta).

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: Salivary glands, liver, gallbladder, pancreas.

• Enzymes: Catalyze breakdown of food; 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": Dietary guideline for balanced nutrition.

• Digestion of Molecules: Carbohydrates, proteins, fats digested by specific enzymes in different organs.

• Peristalsis: Wave-like muscle contractions moving food through digestive tract.

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

Human Genetics and Inheritance

Genetic Concepts and Mechanisms

Genetics studies heredity and variation. Genes, chromosomes, and inheritance patterns determine traits.

• Genes: DNA segments coding for proteins; located on chromosomes.

• Chromosomes: Structures carrying genetic information; humans have 23 pairs.

• Genome: Complete set of genes in an organism.

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

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

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

• Punnett Square: Tool to predict genetic crosses.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes on different chromosomes assort independently.

• Dominant/Recessive Disorders: Dominant disorders can be lethal; recessive disorders persist due to carriers.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles expressed equally.

• 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.

• Meiosis: New allele combinations arise via crossing over.

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

• Nondisjunction: Failure of chromosomes to separate; leads to abnormal chromosome numbers (e.g., Down syndrome).

Example: Sickle cell anemia is a recessive disorder; color blindness is sex-linked.

Genetics Table: Key Terms and Concepts

Term	Definition	Example
Gene	DNA segment coding for a protein	Hemoglobin gene
Allele	Variant form of a gene	A, a
Genotype	Genetic makeup	AA, Aa, aa
Phenotype	Physical expression	Brown eyes
Homozygous	Same alleles	AA or aa
Heterozygous	Different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked allele	a
Codominance	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink flowers
Polygenic	Multiple genes affect trait	Skin color
Sex-linked	On X or Y chromosome	Color blindness
Nondisjunction	Chromosome separation error	Trisomy 21

Key Genetics Formulas

• Probability of genotype (Punnett Square):

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

• Law of Segregation:

$\text{Each parent contributes one allele to offspring}$

• Law of Independent Assortment:

$\text{Alleles of different genes assort independently during gamete formation}$

Additional info: Academic context and examples were added to clarify brief points and ensure completeness for exam preparation.