Final Review: Second Semester 25-26

Cardiovascular System Architecture and Blood Circulation

The cardiovascular system is a complex network centered around the heart, which acts as a pump for the systemic and pulmonary circuits. The Aorta is the largest artery in the body, responsible for carrying oxygen-rich blood from the left ventricle to the systemic circuit. The Systemic Circuit encompasses the pathway through which oxygenated blood is delivered to all body tissues and organs, returning deoxygenated blood to the heart. Conversely, the Pulmonary Circuit refers to the loop from the heart to the lungs, where deoxygenated blood releases carbon dioxide and picks up oxygen. The Vena Cava, divided into superior and inferior sections, serves as the primary gateway for deoxygenated blood entering the right atrium. The Pulmonary Arteries carry deoxygenated blood from the heart to the lungs, while the Pulmonary Veins return oxygenated blood from the lungs to the left atrium.

Internal regulation of blood flow is maintained by a series of valves. The Bicuspid valve (also known as the mitral valve) is located between the left atrium and left ventricle, while the Tricuspid valve is situated between the right atrium and right ventricle. These are supported by the Chordae tendineae, often called "heart strings," which are strong, fibrous strings that anchor the valves to the papillary muscles to prevent them from everting into the atria during ventricular contraction. The Aortic Semilunar valve and Pulmonary Semilunar valve are positioned at the bases of the aorta and pulmonary trunk, respectively, preventing the backflow of blood into the ventricles after it has been ejected.

Blood flow follows a specific sequence: deoxygenated blood enters the Right Atrium via the Vena Cava, passes through the Tricuspid valve into the Right Ventricle, and is then pumped through the Pulmonary Semilunar valve into the Pulmonary Arteries leading to the lungs. Once oxygenated, blood returns via the Pulmonary Veins to the Left Atrium, moves through the Bicuspid valve into the Left Ventricle, and is finally propelled through the Aortic Semilunar valve into the Aorta to be distributed throughout the body.

Respiratory System Structure and Respiration Phases

The respiratory system facilitates the exchange of gases through several distinct processes. External respiration involves the exchange of gases between the air in the alveoli and the blood within the pulmonary capillaries. Internal respiration describes the gas exchange occurring between the blood in systemic capillaries and the body's tissue cells. Cellular respiration refers to the metabolic process occurring within the mitochondria where cells utilize oxygen to generate energy in the form of ATP. The primary functions of this system include gas exchange, regulation of blood pH, and providing for vocalization.

Air enters through the Nasal cavity, which filters, warms, and moistens the air before it enters the Pharynx. The pharynx is divided into three regions: the Nasopharynx (superior), Oropharynx (middle), and Laryngopharynx (inferior). The Larynx, or voice box, contains the Thyroid cartilage and the vocal cords, which produce sound as air passes through the glottis. Below the larynx is the Trachea, a reinforced tube that leads into the lungs. The bronchial tree consists of Primary bronchi, which branch into Secondary (lobar) bronchi and then Tertiary (segmental) bronchi, eventually leading to Alveoli. Alveoli are the microscopic air sacs where the actual exchange of oxygen and carbon dioxide happens. The lungs are situated in the thoracic cavity; the right lung contains $3$ lobes, while the left lung contains $2$ lobes to accommodate the heart.

The mechanics of breathing involve Inspiration (inhaling), where the diaphragm contracts and lung volume increases, and Expiration (exhaling), where muscles relax and air is pushed out. Oxygen follows a path from the nasal cavity, through the pharynx, larynx, trachea, primary/secondary/tertiary bronchi, and into the alveoli, where it enters the blood and is transported to muscle cells. Carbon dioxide follows the reverse path: it moves from the body cell into the blood, then into the alveoli, and travels through the bronchioles, bronchi, trachea, larynx, pharynx, and finally out through the nasal cavity.

Lymphatic System and Mechanisms of Immunity

The lymphatic system is essential for maintaining fluid balance and mounting immune responses. Immunity is the body's ability to resist or eliminate potentially harmful foreign agents. Pathogens are disease-causing organisms such as bacteria, viruses, and fungi, while Antigens are specific protein markers on the surface of pathogens that the immune system recognizes as "non-self." The fastest "line of defense" is the innate or non-specific immune system (including physical barriers and immediate chemical responses), whereas the slowest "line of defense" is the adaptive or specific immune system, which builds a targeted response over time.

In response to infection, the body may develop a fever. During this state, the Liver and Spleen sequester nutrients like iron and zinc, which bacteria and fungi require for rapid multiplication as the temperature rises. Inflammation is a localized response characterized by redness, heat, swelling, and pain, caused by increased blood flow and the arrival of white blood cells (WBCs) to an injured or infected site. Antibodies, which are proteins designed to neutralize specific antigens, are produced by specialized B-cells known as Plasma cells. An active humoral response that is "Artificially acquired" is typically achieved through vaccination, where a person is exposed to a weakened or dead version of a pathogen to stimulate memory cell production without causing disease.

The immune response follows a specific chronological order: $1$. Pathogens enter the body and multiply in body tissues. $2$. Macrophages engulf the pathogens and release cytokines. $3$. Cytokines initiate the inflammation process, attracting more WBCs to the area, which in turn release more cytokines. $4$. Dendritic cells capture antigens and migrate to the lymph nodes to present them to T-cells. $5$. T-cells release cytokines to activate B-cells, prompting them to differentiate into Plasma cells. $6$. Plasma cells release antibodies into the bloodstream, while a subset of B-cells and T-cells transform into Memory T and B cells for long-term protection.

Urinary System and Renal Function

The urinary system is tasked with filtering the blood and removing waste in the form of urine. The kidney is divided into an outer region called the Cortex and an inner region called the Medulla. The functional unit of the kidney is the nephron. Urine formation occurs via three distinct processes: Filtration (movement of fluid from blood into the nephron), Reabsorption (recovery of useful substances from the nephron back into the blood), and Secretion (active transport of waste from the blood into the nephron).

The journey of urine begins after it is produced in the nephrons. From the nephrons, urine flows into the collecting ducts, then into the renal pelvis. It travels down the Ureters to be stored in the Urinary Bladder. Finally, it is expelled from the body through the Urethra. The primary organs of the urinary system include the two kidneys, two ureters, one bladder, and one urethra.

Digestive Tract and Nutrient Processing

Digestive processes are split into Mechanical digestion, which involves physical breakdown (chewing or churning), and Chemical digestion, where enzymes like Amylase (found in saliva) break down complex molecules into simpler ones. Peristalsis is the wave-like muscular contraction that moves food through the tract. Food starts as a Bolus in the mouth, and once it reaches the stomach and mixes with gastric juices, it becomes a semi-liquid substance called Chyme. The stomach lining features folds called Rugae that allow it to expand. The Epiglottis is a flap of tissue that prevents food from entering the trachea during swallowing. Bile, produced by the liver and stored in the gallbladder, emulsifies fats. The Appendix is a small pouch located at the junction of the small and large intestines.

The salivary glands include the Parotid glands (near the ears), Submandibular glands (under the jaw), and Sublingual glands (under the tongue). The movement of nutrients through the wall of the digestive tract is called absorption, which primarily occurs in the small intestine, from which nutrients enter the bloodstream or lymphatic system. Digestive accessory organs—the Liver, Gallbladder, and Pancreas—never come into physical contact with ingested food but contribute essential enzymes and fluids. The large intestine is comprised of the Cecum, Colon (ascending, transverse, descending, and sigmoid), and Rectum; its primary function is the absorption of water and the formation of feces. Pathological conditions include Mumps (viral infection of the parotid glands), Diabetes (disruption of blood sugar regulation), Ulcers (erosions in the digestive lining), and Diarrhea (rapid passage of waste preventing water absorption).

Endocrine and Reproductive Systems

The endocrine system regulates bodily functions through hormones. Melatonin, produced by the Pineal gland, regulates sleep-wake cycles and is stimulated by light levels. Estrogen is produced by the Ovaries and is responsible for female secondary sexual characteristics and the uterine lining. Insulin is secreted by the Pancreas to lower high blood glucose levels by signaling the liver to take in glucose. Testosterone is produced in the Testes and is responsible for muscle growth, deep voice, and facial hair. Antidiuretic hormone (ADH) is released by the Pituitary gland to reduce water loss in urine during dehydration. Oxytocin, also from the pituitary, is involved in childbirth and social bonding.

Identifying specific glands based on function:

• The Thymus is the "vanishing gland" that is largest in childhood and shrinks after puberty; it belongs to both the endocrine and lymphatic systems and stimulates T-cell production.
• The Pancreas controls blood sugar using insulin and glucagon and aids in digestion.
• The Testes are responsible for male characteristics and sperm production.
• The Pituitary gland is the "tiny package" connected to the hypothalamus that performs a vast array of regulatory jobs.
• The Thyroid is shaped like a butterfly and regulates metabolism, mental/physical activity, and calcium storage in bones.
• The Adrenal glands come in pairs and have two parts (cortex and medulla); they regulate electrolytes (sodium and potassium), assist in pain control, and trigger the "fight or flight" response through the sympathetic nervous system.
• The Pineal gland is shaped like a pine cone and produces melatonin, which helps drop body temperature and may prevent early puberty.
• The Ovaries produce eggs (ova), stimulate female sexual development, and prepare the uterine lining.

Reproductive processes involve the formation of an egg cell (oogenesis) and a sperm cell (spermatogenesis). Fertilization typically occurs in the fallopian tubes (oviducts), and implantation occurs in the wall of the uterus.

Nervous System Control and Sensory Integration

The nervous system monitors the environment, processes information, and initiates responses. The Central Nervous System (CNS) consists of the brain and spinal cord, while the Peripheral Nervous System (PNS) consists of all nerves and supporting cells outside the CNS. Neurons are the cells that transmit impulses: Sensory neurons carry impulses from sense organs to the brain, Interneurons process that information, and Motor neurons carry impulses from the brain/spinal cord to muscles and glands. A bundle of neurons is called a nerve. The PNS is divided into the Sensory division (organs to CNS) and the Motor division (CNS to muscles/glands).

The Cerebrum's lobes have distinct roles:

• Frontal Lobe: Intellectual processes, voluntary skeletal muscle control, translation of thought into speech, personality, and olfaction.
• Occipital Lobe: Organized for vision and conscious seeing.
• Temporal Lobe: Interpretation of auditory sensations, olfactory cues, language, and emotional behavior.
• Parietal Lobe: Interpretation of cutaneous (skin) and muscular sensations, use of symbols, verbal articulation, and interpretation of textures and shapes.

The Autonomic nervous system is subdivided into two sections: The Sympathetic nervous system prepares the body for stress or intense activity, creating a "fight or flight" response (e.g., during a car accident or being chased by a predator). The Parasympathetic nervous system relaxes the body, creating a "rest and digest" response (e.g., while sitting on a couch after a meal or sleeping). Neurotransmitters are the chemicals that bridge the gap between neurons to transmit impulses.

Sensory receptors are categorized by the stimuli they respond to:

• Chemoreceptors: Respond to chemicals.
• Mechanoreceptors: Respond to touch, pressure, and stretch.
• Photoreceptors: Respond to light.
• Thermoreceptors: Respond to temperature.
• Pain receptors: Respond to tissue injury.