Introduction to Physiology

• Physiology is the study of how living organisms function

Levels of Organization

• Physiological study spans from molecular to organismal levels
• Molecular physiology examines the interactions of molecules in cells
• Cellular physiology focuses on the functions of individual cells
• Organ physiology studies the function of specific organs like the heart or kidney
• Systemic physiology looks at the interactions of organ systems, such as the cardiovascular system
• Organismal physiology studies the integrated functions of the entire organism

Homeostasis

• Homeostasis is the maintenance of a stable internal environment
• It is essential for cell survival
• Homeostasis is maintained via feedback control loops
• A feedback loop includes a sensor, control center, and effector
• Sensors detect changes in the internal environment
• The control center processes information and sends out commands
• Effectors implement changes to restore balance

Cell Physiology

• Cells are the basic functional units of the body
• Cell membranes regulate the movement of substances in and out of the cell
• Transport mechanisms across membranes include diffusion, osmosis, and active transport
• Diffusion is the movement of molecules from an area of high concentration to low concentration
• Osmosis is the movement of water across a semipermeable membrane from an area of low solute concentration to high solute concentration
• Active transport requires energy to move substances against their concentration gradients
• Cells communicate with each other through chemical signals and electrical signals
• Membrane potentials are differences in electrical charge across the cell membrane

Muscle Physiology

• There are three types of muscle tissue: skeletal, smooth, and cardiac
• Skeletal muscle is responsible for voluntary movements
• Smooth muscle is found in the walls of internal organs
• Cardiac muscle is found in the heart
• Muscle contraction involves the interaction of actin and myosin filaments
• In skeletal muscle, contraction is initiated by nerve impulses
• These impulses cause the release of calcium ions from the sarcoplasmic reticulum
• Calcium binds to troponin, exposing binding sites on actin
• Myosin then binds to actin, forming cross-bridges and initiating contraction
• Smooth muscle contraction is regulated by various factors
• These factors include hormones and neurotransmitters
• Cardiac muscle contraction is intrinsic and coordinated by specialized cells

Cardiovascular Physiology

• The cardiovascular system consists of the heart, blood vessels, and blood
• The heart pumps blood throughout the body
• Blood vessels include arteries, veins, and capillaries
• Arteries carry blood away from the heart
• Veins carry blood back to the heart
• Capillaries are the site of exchange between blood and tissues
• Blood transports oxygen, nutrients, hormones, and waste products
• Blood pressure is the force exerted by blood against blood vessel walls
• Regulation of blood pressure involves neural and hormonal mechanisms

Respiratory Physiology

• The respiratory system is responsible for gas exchange
• This includes the intake of oxygen and the elimination of carbon dioxide
• The lungs are the primary organs of respiration
• Ventilation is the movement of air into and out of the lungs
• Gas exchange occurs in the alveoli of the lungs
• Oxygen diffuses from the alveoli into the blood
• Carbon dioxide diffuses from the blood into the alveoli
• Respiration is regulated by the respiratory center in the brainstem

Renal Physiology

• The kidneys regulate fluid and electrolyte balance
• They also remove waste products from the blood
• The functional unit of the kidney is the nephron
• Nephrons filter blood and produce urine
• Urine formation involves filtration, reabsorption, and secretion
• Filtration occurs in the glomerulus
• Reabsorption occurs in the renal tubules
• Secretion also occurs in the renal tubules
• Kidney function is regulated by hormones

Neurophysiology

• The nervous system controls and coordinates bodily functions
• It consists of the brain, spinal cord, and nerves
• Neurons are the basic functional units of the nervous system
• Neurons communicate through electrical and chemical signals
• Action potentials are electrical signals that travel along axons
• Synapses are junctions between neurons
• Neurotransmitters are chemical messengers that transmit signals across synapses
• The brain is the control center of the nervous system
• Different brain regions are responsible for different functions

Endocrine Physiology

• The endocrine system regulates bodily functions through hormones
• Hormones are chemical messengers secreted by endocrine glands
• Hormones travel through the bloodstream to target cells
• Hormones bind to receptors on target cells, initiating a response
• The pituitary gland is the master endocrine gland
• It secretes hormones that regulate other endocrine glands
• The hypothalamus controls the pituitary gland
• Endocrine function is regulated by feedback mechanisms

Gastrointestinal Physiology

• The gastrointestinal system is responsible for digestion and absorption of nutrients
• It consists of the mouth, esophagus, stomach, small intestine, and large intestine
• Digestion begins in the mouth with mechanical and chemical breakdown of food
• The stomach stores food and mixes it with gastric juices
• The small intestine is the primary site of nutrient absorption
• The large intestine absorbs water and electrolytes
• Waste products are eliminated through the anus
• Gastrointestinal function is regulated by neural and hormonal mechanisms

Reproductive Physiology

• The reproductive system is responsible for sexual reproduction
• Male reproductive system includes the testes
• The testes produce sperm and testosterone
• Female reproductive system includes the ovaries, uterus, and vagina
• The ovaries produce eggs and estrogen
• Fertilization occurs when a sperm cell unites with an egg cell
• Pregnancy involves the development of a fetus in the uterus
• Reproductive function is regulated by hormones