Human Anatomy and Physiology: Systems and Functions
Musculoskeletal System
Axial Skeleton
The axial skeleton consists of the skull, vertebrae, and thoracic cage, forming the main central framework of the body.
Pectoral Girdle
Made of the clavicle and scapula, this structure attaches the upper limbs to the axial skeleton at the joint between the sternum and clavicle.
Pelvic Girdle
The pelvis includes the hip bones, sacrum, and coccyx. The pelvic girdle attaches the lower limbs to the axial skeleton.
Sarcomere
The smallest unit of muscle contraction. These repeating contractile units in muscle fibers shorten to cause muscle contraction.
Muscle Types
- Skeletal muscle: Voluntary and striated; attached to bones to produce body movement.
- Cardiac muscle: Involuntary and striated; found only in the heart.
- Smooth muscle: Involuntary and non-striated. Most smooth muscle, called visceral muscle, forms layers in the walls of blood vessels and the digestive, respiratory, urinary, and reproductive tracts.
Circulatory and Respiratory Systems
The respiratory and cardiovascular systems work together to fuel cellular respiration. The respiratory system exchanges carbon dioxide for oxygen, while the circulatory system delivers oxygen to the body’s cells.
Steps of Respiration
- Ventilation
- Gas exchange between alveoli and blood
- Blood transport of gases
- Gas exchange between blood and tissue cells
Respiratory Pathway
Air enters through the nose and mouth, passes through the pharynx and larynx, travels down the trachea, and enters the bronchi, bronchioles, and finally the alveoli. Cilia help sweep dust and particles trapped in mucus.
Diaphragm
The primary skeletal, voluntary muscle for breathing. Breathing requires pressure changes: when it contracts, chest volume increases and air flows in; when it relaxes, chest volume decreases and air flows out.
Blood Vessels and Cells
- Arteries: Carry blood away from the heart.
- Veins: Carry blood to the heart.
- Red blood cells: Carry oxygen absorbed in the lungs to tissues and transport carbon dioxide from tissues to the lungs.
Gas exchange occurs at the alveoli by simple diffusion: oxygen moves from the air in the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli to be exhaled.
Digestive System
The digestive system maintains nutrient homeostasis through a four-step process: ingestion, digestion, absorption, and elimination.
Basic Structures and Locations
Key organs include the mouth, esophagus, stomach, small intestine, large intestine, and liver. The pharynx, salivary glands, pancreas, gallbladder, rectum, and anus serve as important parts or accessory organs.
Digestion and Absorption
- Mechanical digestion: Physically breaks food into smaller particles; occurs in the mouth and stomach.
- Chemical digestion: Uses enzymes to break food molecules into small subunits; occurs in the mouth, stomach, and small intestine.
- Absorption: Occurs mainly in the small intestine for food and water, and in the large intestine mainly for water. Elimination occurs at the anus.
Liver and Pancreas
- Liver: Produces bile, a fluid loaded with lipids and salts that breaks large fat droplets into smaller droplets for lipases. Bile is stored in the gallbladder and released into the small intestine.
- Pancreas: Produces digestive enzymes: amylase (digests carbohydrates), trypsin (digests proteins), and lipase (digests fats).
Nutrients
Nutrients are required for metabolism, growth, maintenance, and repair, providing potential energy and chemical building blocks.