Human Digestive & Circulatory System Anatomy
Classified in Biology
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Digestive System Components
Salivary Glands
These glands help moisten the food bolus. Saliva moistens food to aid swallowing and begins the process of food degradation. The main salivary glands are:
- Parotid
- Submandibular (formerly Submaxillary)
- Sublingual
Pharynx
Located just after the mouth, the pharynx serves as a junction for both the respiratory and digestive systems.
Esophagus
The esophagus is a long, muscular tube connecting the pharynx to the stomach. It ends at the cardia, regulated by the lower esophageal sphincter.
Stomach
A thick-walled muscular sac located on the left side of the upper abdomen, below the ribs. It churns food and mixes it with digestive juices.
Small Intestine
A long, coiled tube (approximately 6-7 meters) where most nutrient absorption occurs. It consists of three parts:
- Duodenum: The first, C-shaped section connected to the stomach via the pylorus.
- Jejunum: The middle section.
- Ileum: The final section, connecting to the large intestine.
Pylorus
The valve controlling the passage of partially digested food (chyme) from the stomach into the duodenum (small intestine).
Cardia
The area where the esophagus connects to the upper part of the stomach.
Liver
The largest gland in the human body, located in the upper right abdomen, next to the stomach. It produces bile, detoxifies blood, and performs many metabolic functions.
Pancreas
An elongated gland located behind the stomach. It produces digestive enzymes and hormones like insulin.
Digestion Process Terms
Mechanical Digestion
Refers to the physical breakdown of food through actions like chewing, churning in the stomach, and segmentation in the small intestine.
Chemical Digestion
Encompasses the chemical reactions, primarily involving enzymes, that break down complex food molecules into simpler ones that can be absorbed.
Chyme
The semi-fluid mass of partially digested food expelled by the stomach into the duodenum.
Chyle
A milky fluid consisting of lymph and emulsified fats, formed in the small intestine during the digestion and absorption of fats.
Circulatory System Components & Functions
Functions of the Circulatory System
The circulatory system performs several vital functions:
- Carries oxygen from the lungs to body tissues.
- Transports metabolic waste products (like carbon dioxide and urea) from tissues to organs of excretion (lungs, kidneys).
- Distributes hormones from endocrine glands to target organs.
- Helps maintain the body's fluid and electrolyte balance.
- Defends the body against infections via immune cells and antibodies in the blood.
- Helps regulate body temperature by distributing heat.
Blood Composition
Blood is a fluid connective tissue. An average adult has about 5 liters, roughly 8% of body weight. It consists of plasma and formed elements.
Plasma
The liquid matrix of blood (about 55% of volume), composed of:
- Water (approximately 92%)
- Proteins (approximately 7%, e.g., albumin, globulins, fibrinogen)
- Other solutes (approximately 1%, e.g., salts, gases, nutrients, hormones, waste)
Formed Elements
- Red Blood Cells (Erythrocytes): Biconcave, disc-shaped cells lacking a nucleus when mature. They contain hemoglobin and are responsible for oxygen transport.
- White Blood Cells (Leukocytes): Diverse group of cells crucial for the immune system, defending against pathogens and foreign materials.
- Platelets (Thrombocytes): Small cell fragments essential for blood clotting (hemostasis). They form a plug at injury sites.
Blood Vessels and Heart Structure
Veins
Blood vessels that generally carry deoxygenated blood from the body tissues back towards the heart (exceptions include pulmonary and umbilical veins).
Heart Layers
- Pericardium: The protective double-walled sac surrounding the heart.
- Myocardium: The thick middle layer composed of cardiac muscle tissue, responsible for pumping action.
- Endocardium: The thin inner layer lining the heart chambers and valves.
Heart Chambers
- Atria (singular: Atrium): The two upper chambers (right and left) that receive blood returning to the heart. The right atrium receives deoxygenated blood from the body; the left atrium receives oxygenated blood from the lungs.
- Ventricles: The two lower, muscular chambers (right and left) that pump blood out of the heart. The right ventricle pumps blood to the lungs; the left ventricle pumps blood to the rest of the body.
Atrioventricular valves (tricuspid on the right, mitral/bicuspid on the left) separate the atria from the ventricles.
Pulse
The rhythmic expansion and recoil of arteries felt externally, caused by the surge of blood pumped by the heart during systole (contraction).