Human Body Vital Organs & Digestive System

• There are five vital organs: heart, brain, two kidneys, liver, and two lungs. Failure of any one leads to death without medical intervention.

Vital Organs Explained

• Heart: Located in the chest's center, circulates blood for nutrient and waste transport.
• Brain: Found in the head, the body's control center for thoughts, memories, feelings, and perceptions.
• Kidneys: Located in the back of the abdomen, filter blood and produce urine.
• Liver: Found on the right side of the abdomen, filters blood, produces digestive bile, and creates blood-clotting proteins.
• Lungs: In the upper chest, facilitate oxygen and carbon dioxide exchange with the blood.

Digestive System

• Breaks down food mechanically and chemically into monomers for cellular respiration.
• Digestion: Mechanical (teeth) and chemical (enzymes, low pH) breakdown for monomer availability.
• Absorption: Uptake of monomers by small intestine epithelial cells for cellular respiration.
• Small intestine villi and microvilli increase surface area, helping nutrient absorption, mucus secretion, and efficient digestion.

Circulatory System

• A closed system of blood vessels, a heart pump, and valves ensuring unidirectional blood flow.

Vessels

• Veins: Low-pressure vessels carry blood from tissues to the heart's atria
• Thin walls due to low internal pressure.
• Transports deoxygenated blood.
• Arteries: High-pressure vessels carry blood from the heart to tissues.
• Thick, elastic walls handle pressure changes.
• Carries oxygenated blood.
• Capillaries: Narrow, single-cell-thick vessels
• Highly permeable.
• Maximize surface area to volume ratio for efficient CO2/O2 diffusion.

Respiratory System

• Involves ventilation, gas exchange, and cellular respiration.

Ventilation

• Act of inhaling/exhaling air.
• Lungs lack muscle tissue and rely on antagonistic muscle pairs for air movement.
• Antagonistic Pairs: Muscles work oppositely; one contracts as the other relaxes.

Antagonistic Pairs Actions

• Inhale:

• Exterior costal muscles contract.

• Interior costal muscles relax.

• Abdominal muscles relax.

• Diaphragm contracts.

• Exhale:

• Exterior costal muscles relax.

• Interior costal muscles contract.

• Abdominal muscles contract.

• Diaphragm relaxes.

• Ventilation: Physical act of inhaling/exhaling air (O2/CO2)

• Gas exchange: The transfer of O2/CO2 between capillaries & alveoli by diffusion

• Cell respiration: The mitochondria take O2 (and glucose) to produce energy, having CO2 as a waste product.

• Breathing occurs when the diaphragm and chest muscles contract, creating space for the lungs to expand. The expansion lowers the air pressure inside your lungs, causing air to rush in through your nose or mouth, down your windpipe, and into your lungs

• Breathing out occurs when the diaphragm and chest muscles relax, reducing the space in your chest cavity and causing your lungs to deflate. This increases the air pressure inside your lungs, forcing air out of your lungs and back out through your nose or mouth.

• Gas exchange occurs as oxygen from inhaled air diffuses across the thin walls of the alveoli into the bloodstream while carbon dioxide diffuses from the bloodstream into the alveoli

Nervous System

• Reflex: Involuntary response to a stimulus.
• Reflex arc: Neural pathway controlling reflex actions, involving the spinal cord, not the brain.
• Reflex arc steps: Stimulus detection, message via sensory neurons, relay to motor neurons in the spinal cord, effector contraction.
• Affector: Nerve cell activating muscles via the reflex arc.
• Effector: Organ/muscle reacting to a stimulus.
• Sensory neuron: Transmits impulses from receptors to the central nervous system.
• Motor neuron: Transmits impulses from the central nervous system to an effector.

Sensory Neurons and Function

• Thermoreceptor: Detects temperature changes.
• Photoreceptor: Detects light changes.
• Chemoreceptor: Detects chemical changes.
• Mechanoreceptor: Detects pressure/touch changes.
• Sonar receptor: Detects sound changes.

Endocrine System (ES)

• Works with the nervous system to maintain homeostasis, interacting with all body cells.
• Hormones are proteins that only act on targetted cells to allow for a specific action or reaction from cells/tissues via the lock and key theory
• The ES has a slower, longer response, using chemical messages transported to all targeted cells.
• The NS has a faster, shorter response using nerve impulses transported to only muscle cells.

Secreting Glands

• Hypothalamus: Controls basic needs like temperature, sleep, eating, and blood pressure.
• Pineal gland: Regulates sleep/wake cycles via melatonin.
• Thyroid: Controls mineral intake/output, especially Ca2+ for muscle contraction.
• Adrenal gland: Manages metabolism (fight, flight, freeze) via adrenaline.
• Pancreas: Controls appetite and blood sugar levels (insulin/glucagon).
• Ovaries & Testes: Control primary and secondary reproductive characteristics.

Hormones

• Insulin: Secreted by the pancreas in response to high blood glucose levels.
• Promotes glucose uptake by cells.
• Glucagon: Secreted by the pancreas in response to low blood glucose levels.
• Stops glucose uptake, raising blood sugar.
• Insulin and glucagon utilize a negative feedback loop.

Tropism

• Plants respond to stimuli by adjusting their growth direction.

Stimulus

• Change detected by sense organs.
• Positive growth is growth towards the stimulus.
• Negative = away from the stimulus.
• Tropism: Plant growth response affected by stimulus direction.
• Phototropism: Response to light (shoots grow towards it).
• Gravitropism: Response to gravity (shoots grow against, roots grow towards).
• Shoots and roots have receptors that release auxin (a hormone) when stimulated.
• Auxin: Plant hormone for cell elongation.

Immune System

• Recognizes and eliminates invaders (non-host DNA).
• Pathogen: Living disease-causing agent.
• Allergen: Living/non-living allergy-causing agent.
• The immune system has two lines of defense – Innate and Adaptive.

Innate Immune System

• Non-specific, acts as the first line of defense.
• Natural Barriers: Physical (skin, hair) and chemical (wax, mucus) barriers to entry.
• Macrophages: White blood cells that detect "Self vs. Non-Self". Engulf and digest invaders.

Adaptive Immune System

• Specific, active response as a second line of defense.
• Activated when macrophages fail, sending an SOS.
• T-Cells: Detect SOS and kill infected cells, activating B-cells.
• B-Cells: Produce plasma cells (antibodies to destroy invaders) and memory cells (for future recognition).
• Antigen: Membrane protein on pathogens for immune system recognition.
• Antibodies: Y-shaped proteins with "antigen specificity" that attach to pathogens.
• Cluster and isolate pathogens

Overview of the human body's vital organs—heart, brain, kidneys, liver, and lungs—essential for survival. Explanation of their roles and locations. Also an explanation of the digestive system, including digestion and asborption.