Body Fluids and Membrane Dynamics

• The notes provided delve into body fluids, transport mechanisms, and membrane dynamics, useful for general physiology. This details functional compartments, membrane transport, and the concept of homeostasis.

Three Major Body Cavities

• The body comprises of various cavities that aren't completely enclosed by walls.
• The three major body cavities; The cranial cavity (skull), the thoracic cavity (thorax), and the abdominopelvic cavity.
• Bones and tissues separate the cavities, which are also lined with tissue membranes.

Functional Compartments of the Body

• The cranial cavity houses the brain.
• The thoracic cavity is defined by the spine, ribs, and diaphragm
• The heart is enclosed by the pericardial sac.
• Two lungs are enclosed in separate pleural sacs.
• The abdomen and pelvis form a continuous cavity
• An abdominopelvic cavity has a lining of tissue called the peritoneum, which covers the stomach, intestines, liver, gallbladder, and spleen.
• The kidneys are positioned outside the abdominal cavity, between the peritoneum, muscles, and bones of the back.
• The pelvis contains bladder, reproductive organs, and the end of the large intestine.
• Hollow organs like the heart, lungs, blood vessels, and intestines, create compartments within the body.
• The interior of a hollow organ is its lumen, filled wholly or partially with air or fluid

Lumens of Hollow Organs

• These organs feature spaces filled with substances other than the organ's tissue, such as blood in vessels and food in the intestines.
• Examples are the Heart, lungs, blood vessels and intestines
• The fluid-filled interior lumen, which is not part of the internal environment, especially in the GI tract.

Fluid Compartments

• The body contains two main fluid compartments separated by the cell membrane:
• Intracellular fluid (ICF) is found inside cells.
• Extracellular fluid (ECF) is is located outside cells.
• The fluid portion of blood is the plasma.
• Between blood vessels and tissue cells is the interstitial fluid.
• Inside tissue cells is the intracellular fluid.

Relationships Between an Organism’s Internal and External Environments

• The organization includes cells, intracellular fluid, extracellular fluid, the organism, and the external environment.
• The extracellular fluid provides a watery internal environment for multicellular animals.
• Protective and exchange cells are part of an organism.

Homeostasis and Mass Balance

• Body fluids are vital for homeostasis; proper intake and output must be balanced.
• An example of total intake includes
  • 1900ml/day of Water intake
  • 200ml/day of food intake
  • 200ml/day of metabolism oxidation of lipids and carbohydrates.
• An example of total output includes:
  • 1400ml/day of Urine output
  • 100ml/day of solid faeces output
  • 100ml/day of sweat output
  • 500ml/day of invisible fluid loss.
• The total intake and total output are generally around 2300ml/day.
• The body is an open system, exchanging heat and materials.
• Mass balance must be maintained for homeostasis. If a substance remains constant the body needs to offset the loss and gain.
• Blood fluids, which are Plasma and ICF of blood cells, contain <0.1 % total body fluids.
• Total body fluids is about 42L at 60% of body weight.
• Intracellular fluids at held at 28L or 40 %.
• Extracellular fluids are held at 14L or 20 %.
• Interstitial fluids contribute an 11L, 15.7 % concentration.
• Plasma fluids contribute 3L at a 4.3% concentration
• Examples of clearance organs can also include the Kidneys, saliva, sweat, breast milk, lungs, and hair

Functional Compartments of the Body

• Hollow organs create another set of compartments within the body.
• The interior of any hollow organ is its lumen.
• A lumen may be partially filled with air or fluids depending on the organ.

Membrane Proteins

• Membrane receptors bind specific ligands, demonstrated by hormones and recognition molecules

Passive Transport

• Passive transport, including facilitated diffusion, does not need energy to get across.

Channel and Carrier Proteins

• Transport involves membrane proteins, classified as channel or carrier proteins.
• Channel proteins form a pore that allows ions to pass using passive transport.
• Carrier Proteins transport molecules using facilitated diffusion or active transport.
• Channel Proteins are also selective to allow specific ions in.
• Voltage-gated and ion-gated channels allow signals across neurons

Vesicular Transport

• Two types of Processes involved are Active transport (Protein Mediated), and Vesicular transport.
• Vesicular transport requires the help of ATP.
• Both transport require energy and a transmembrane process.
• Endocytosis transports materials into the cells in the form of Phagocytosis, Pinocytosis, and Receptor-mediated endocytosis
• Transport moves outside of cells using exocytosis for proteins synthesized in the cell.

Phagocytosis

• Phagocytosis is an actin-mediated process where bacteria is engulfed into a phagosome.
• White blood cells can eat bacteria.

Endocytosis

• Vessicles form and indent rather than protrude during the process.

Pinocytosis

• Absorbs extracellular fluids and solutes into a cell for a sampling of the environment through a membrane.

Coated-Pits

• Cell membranes have regions known as coated-pits, that contain a common protein known as clathrin

Exocytosis

• Exocytosis transports molecules too large, and fuses them with the cell to transport.
• The reverse direction of endocytosis.

Osmosis

• Osmosis is an important part of maintaining the body fluid contents
• It occurs through the cell membranes or through particular channels and active transport.
• If there is the same the concentration in a solution it is known as isosmotic.
• If something has a higher concentration it is known as hyperosmotic.
• If something has a lower concentration it is known as hyposmotic.
• Osmotic concentration is regulated by the particles that displace it in litre of volume.