Bio Human Systems Unit Review

Digestive System

The group of organs that work together to break down food physically and chemically so nutrients can be absorbed into the blood and wastes eliminated.

Main Functions of Digestive System

1) Ingestion – taking food in. 2) Digestion – mechanical & chemical breakdown of food. 3) Absorption – moving nutrients into the bloodstream. 4) Elimination – removing indigestible material.

Mechanical Digestion

Physical breakdown of food into smaller pieces by chewing, churning, and segmentation; increases surface area for enzymes.

Chemical Digestion

Enzymatic hydrolysis of macromolecules (carbohydrates, lipids, proteins, nucleic acids) into smaller subunits that can be absorbed.

Mouth

Entry point for food; performs mechanical digestion by chewing (mastication) and chemical digestion of starch via salivary amylase.

Salivary Glands

Secrete saliva containing the enzyme amylase that begins the hydrolysis of starch into maltose; also lubricates food for swallowing.

Pharynx

Common passage for food and air; connects mouth to esophagus and triggers swallowing reflex.

Epiglottis

Flap of cartilage that covers the trachea during swallowing to prevent food from entering the airway.

Esophagus

Muscular tube that transports food from pharynx to stomach via peristaltic contractions.

Esophageal Sphincter

Circular muscle at the top of the stomach that controls entry of food and prevents acid reflux.

Stomach

Muscular, J-shaped organ that churns food (mechanical digestion) and secretes gastric juice (HCl + enzymes) for protein digestion.

Gastric Juice

Acidic mixture of hydrochloric acid, mucus, and the enzyme pepsin secreted by the stomach lining.

Hydrochloric Acid (HCl)

Lowers stomach pH (~2) to kill bacteria, denature proteins, and activate pepsinogen into pepsin.

Pepsin

A protein-digesting enzyme that breaks long polypeptide chains into shorter chains called peptides.

Mucus in Stomach

Protects stomach wall from self-digestion by acid and enzymes.

Pyloric Sphincter

Muscular valve controlling the release of chyme from the stomach into the duodenum.

Chyme

Semi-liquid mixture of partially digested food and gastric secretions leaving the stomach.

Small Intestine

Long muscular tube (≈6 m) where most digestion and nutrient absorption occurs; divided into duodenum, jejunum, and ileum.

Duodenum

First 25 cm of small intestine; site where chyme mixes with secretions from pancreas, liver, and gall bladder for chemical digestion.

Jejunum

Middle region (~2.5 m) with many folds and villi to maximize absorption.

Ileum

Last portion (~3 m) that absorbs remaining nutrients and passes undigested material to the large intestine.

Pancreas

Produces digestive enzymes (amylase, lipase, trypsin, nuclease) and bicarbonate to neutralize acidic chyme entering the small intestine.

Liver

Largest internal organ; produces bile, detoxifies chemicals, stores glycogen, and metabolizes nutrients.

Gall Bladder

Stores and releases bile into the duodenum through the bile duct when fat is present.

Bile

A greenish fluid containing bile salts that emulsify large fat globules into smaller droplets, increasing surface area for lipase action.

Emulsification

The physical breakup of fat globules into smaller droplets by bile salts; not chemical digestion but essential for efficient lipid breakdown.

Bicarbonate Ion (HCO₃⁻)

Secreted by pancreas; neutralizes acidic chyme to protect intestinal walls and provide optimal pH for enzymes.

Enzyme

Protein catalyst that lowers activation energy to speed up chemical reactions without being consumed.

Carbohydrase (Amylase)

Enzyme that catalyzes hydrolysis of carbohydrates; converts starch to simple sugars.

Lipase

Enzyme that catalyzes breakdown of triglycerides into glycerol and fatty acids.

Protease (Trypsin/Pepsin)

Enzyme that catalyzes breakdown of proteins into peptides and amino acids.

Nuclease

Enzyme that catalyzes breakdown of nucleic acids (DNA, RNA) into nucleotides.

Villi

Finger-like projections lining the small intestine that increase surface area for nutrient absorption; contain capillaries and lacteals.

Microvilli

Tiny membrane folds on epithelial cells of villi that further increase absorptive surface area.

Lacteal

A lymphatic vessel within each villus that absorbs fatty acids and glycerol for transport via the lymphatic system.

Capillaries in Villi

Absorb monosaccharides, amino acids, and water-soluble vitamins into bloodstream.

Large Intestine

Absorbs water and salts from undigested food, houses beneficial bacteria, and compacts waste into feces.

Rectum

Stores feces before elimination.

Anus

Opening through which feces leave the body; controlled by internal and external sphincters.

Accessory Organs

Liver, pancreas, and gall bladder; they aid digestion but food does not pass through them.

Enzyme Specificity

Each enzyme acts on a particular substrate due to its unique active-site shape.

Factors Affecting Enzyme Action

Temperature, pH, substrate concentration, enzyme concentration, presence of inhibitors.

Feedback Inhibition

Process where end product of a pathway inhibits an earlier enzyme, preventing excess product formation.

Competitive Inhibition

Occurs when a molecule similar to the substrate competes for the enzyme’s active site, reducing enzyme activity.

Dehydration Synthesis

Reaction joining subunits by removing water; builds macromolecules.

Hydrolysis

Reaction that uses water to split macromolecules into smaller subunits; basis of digestion.

Carbohydrates

Macromolecules containing C, H, O in 1:2:1 ratio; source of quick energy (glucose, starch, glycogen).

Lipids

Hydrophobic macromolecules (fats, oils, phospholipids, steroids) used for long-term energy storage and membrane structure.

Proteins

Macromolecules made of amino acids joined by peptide bonds; used for structure, enzymes, hormones, transport.

Nucleic Acids

DNA and RNA; store and transmit genetic information.

Digestive Enzymes Summary

Amylase – starch → maltose; Pepsin/Trypsin – proteins → peptides; Lipase – lipids → fatty acids + glycerol; Nuclease – nucleic acids → nucleotides.

Hormone Gastrin

Secreted by stomach; stimulates release of HCl and pepsinogen to promote digestion.

Hormone Secretin

Produced by duodenum; triggers pancreas to release bicarbonate and slows stomach activity.

Hormone CCK (Cholecystokinin)

Released by duodenum in response to fats; stimulates gall bladder to release bile and pancreas to release enzymes.

Hormone GIP (Gastric Inhibitory Peptide)

Released by duodenum; inhibits stomach activity to allow time for fat digestion.

Digestive System and Homeostasis

Provides cells with nutrients and water, removes wastes, and works with circulatory system to distribute absorbed materials, maintaining internal equilibrium.

Respiratory System

The body system responsible for gas exchange—bringing oxygen (O₂) into the body and removing carbon dioxide (CO₂); essential for cellular respiration and maintaining homeostasis.

Main Functions of the Respiratory System

1) Exchange gases between the external environment and the bloodstream. 2) Maintain pH by regulating CO₂ levels. 3) Filter, warm, and moisten incoming air. 4) Enable sound production.

External Respiration

Exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in pulmonary capillaries.

Internal Respiration

Exchange of oxygen and carbon dioxide between blood in systemic capillaries and the body’s tissue cells.

Cellular Respiration

Series of chemical reactions in mitochondria that use oxygen to release energy (ATP) from glucose, producing CO₂ and water as by-products.

Nasal Passages

Filter, warm, and humidify incoming air; lined with cilia and mucus-secreting cells to trap dust and pathogens.

Pharynx

Common passageway for air, food, and liquids; connects nasal and oral cavities to the larynx and esophagus.

Epiglottis

Flap of cartilage covering the trachea during swallowing to prevent food or liquid from entering the airway.

Glottis

The opening of the trachea through which air enters the larynx.

Larynx

Structure of cartilage housing the vocal cords; produces sound when air passes through.

Trachea

Tube carrying air from the pharynx to the lungs; supported by C-shaped rings of cartilage to prevent collapse and lined with cilia to trap particles.

Bronchi

Two main branches of the trachea that carry air into each lung; also contain cartilage rings.

Bronchioles

Smaller branches of the bronchi within the lungs; have smooth muscle and control airflow to alveoli.

Alveoli

Tiny, thin-walled air sacs at the ends of bronchioles; site of gas exchange between air and blood. Surrounded by capillary networks.

Pleural Membrane

Double-layered membrane surrounding each lung and lining the thoracic cavity; secretes fluid to reduce friction during breathing.

Diaphragm

Dome-shaped sheet of muscle separating thoracic and abdominal cavities; contraction causes inspiration, relaxation causes expiration.

Intercostal (Rib) Muscles

Muscles between ribs that contract and expand the chest cavity during breathing, assisting the diaphragm.

Thoracic Cavity

The chest cavity enclosed by ribs, diaphragm, and spine that houses the lungs and heart; expands and contracts during breathing.

Inhalation (Inspiration)

Active process: diaphragm and external intercostal muscles contract → thoracic volume increases → air pressure in lungs decreases → air moves in.

Exhalation (Expiration)

Passive process: diaphragm and intercostal muscles relax → thoracic volume decreases → air pressure in lungs increases → air moves out.

Air Pressure and Volume Relationship

Based on Boyle’s Law: when volume increases, pressure decreases (and vice versa), driving airflow in and out of the lungs.

Spirograph

Graph showing volumes of air that move into and out of the lungs during various breathing activities.

Tidal Volume

Volume of air inhaled or exhaled in a normal breath at rest.

Inspiratory Reserve Volume

Additional air that can be forcibly inhaled beyond a normal inhalation.

Expiratory Reserve Volume

Additional air that can be forcibly exhaled beyond a normal exhalation.

Residual Volume

Air remaining in the lungs after a maximal exhalation; prevents lung collapse and allows continuous gas exchange.

Vital Capacity

Maximum volume of air that can be moved into and out of the lungs (tidal + inspiratory + expiratory reserve volumes).

Total Lung Capacity

Sum of vital capacity and residual volume; total amount of air the lungs can hold.

Mechanism of Gas Exchange

Occurs by diffusion across the alveolar and capillary walls due to concentration gradients: O₂ diffuses from alveoli to blood; CO₂ diffuses from blood to alveoli.

Partial Pressure

Pressure exerted by a single gas in a mixture; determines direction of gas diffusion during respiration.

Hemoglobin

Oxygen-carrying protein in red blood cells that binds O₂ in lungs (forming oxyhemoglobin) and releases it in tissues.

Transport of Carbon Dioxide

70% as bicarbonate ions in plasma, 23% bound to hemoglobin, 7% dissolved in plasma; important for blood pH regulation.

Carbonic Anhydrase

Enzyme in red blood cells that catalyzes CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻; helps control blood acidity.

pH Regulation by Respiratory System

Increased CO₂ lowers pH (more acidic); respiratory rate adjusts to maintain acid-base balance and homeostasis.

Medulla Oblongata

Part of brainstem that monitors CO₂ and H⁺ levels in blood; increases breathing rate when levels rise.

Chemoreceptors

Specialized sensors in the carotid and aortic arteries that detect changes in O₂ and CO₂ concentrations and signal the medulla to adjust breathing.

Hyperventilation

Breathing rate above normal; reduces CO₂ and increases blood pH.

Hypoventilation

Reduced breathing rate; increases CO₂ and lowers blood pH.

Coughing Reflex

Protective mechanism to remove irritants or blockages from lower respiratory tract.

Cilia Function

In trachea and bronchi, cilia move mucus and trapped particles upward toward the pharynx for removal (“mucociliary escalator”).

Smoking Effects on Respiratory System

Paralyzes cilia, increases mucus, decreases gas exchange efficiency, can lead to chronic bronchitis, emphysema, or lung cancer.

Bronchitis

Inflammation of the bronchi causing excessive mucus and narrowed airways.