Homeostasis is the process by which an organism maintains the composition of the extracellular fluid (ECF) and intracellular fluid (ICF) in a steady-state condition.
ECF consists of the blood plasma and interstitial fluid. The composition of the ECF is maintained by the cardiovascular, pulmonary, renal, gastrointestinal, endocrine, and nervous systems acting in coordinated fashion.
ICF’s composition is maintained by the cell membrane, which mediates the transport of material between between the ICF and ECF by diffusion, osmosis, and active transport.
Blood levels of calcium are held constant at set point by hormones.
Normal value of calcium: 9-11 mg%
Parathyroid hormone or parathormone is one hormone that helps raise the blood calcium concentration.
Thyrocalcitonin – acts to reduce the blood level of calcium and to inhibit bone resorption. It also promotes the excretion of phosphate, sodium and calcium by decreasing their reabsorption in kidney tubules.
In homeostasis, the critical concept describing the body’s response to any deviation from some particular setpoint (such as temperature rising when exercising), which results the activation of mechanisms to oppose that deviation (return temperature toward normal), is known as negative feedback.
In this kind of homeostasis, the setpoint is analogous to the house thermostat setting that operates to regulate the temperature in the house.
The sequence that best reflects how the body maintains homeostasis (example, during a fever):
Audiometer an electric device used to test the sensitivity of the sense of hearing.
Tuning fork – a small metal instrument consisting of a stem and two prongs that produces a constant pitch when either prong is struck. It is used in auditory tests of nerve function and of air and bone conduction.
Rubber hammer or mallet – used in patelllar reflex or in ankle jerk reflex
The cell is the basic unit of structure and function in the body. Many of the functions of cells are performed by particular subcellular structures called organelles.
The human body contains about 100 trillion cells, each of which is a living structure. Several hundred basic types of cells exist in the body, Yet despite the difference between cells, they will have some functions in common, like their ability to live, grow and reproduce.
Some show characteristics of metabolism, irritability and even movement or locomotion .
Each is specially adapted to perform one particular function
rER – consists of flattened sacks of cisternae studded with ribosomes for the synthesis of proteins destined for secretion
sER - consists of an anastomosing network of interconnected citernae and tubules. It functions in glycogen breakdown, synthesis of cholesterol and phospholipids and serves to detoxify drugs and poisons
Lysosomes are membrane- bounded organelles containing hydrolytic enzymes.
They have several functions in cell physiology. They degrade phagocytized foreign materials, lipid aggregates and glycogen granules, responsible also in tissue degradation during regression, and are abundant in macrophages and in leukocytes.
Microfilaments This is a flourescence digital image of a fibroblast showing actin cytoskeletal network .
2 layers of globular proteins with phospholipid inside to make a layer and then join 2 layers together to make a channel for molecules to pass
Unit Membrane Model
Outer layer of protein with phospholipid bilayer inside, believed all cells same composition, does not explain how some molecules pass through or the use of proteins with nonpolar parts, used transmission electron microscopy
Fluid Mosaic Model
(Singer + Nicolson)
Phospholipid bilayer with proteins partially or fully imbedded, electron micrographs of freeze-fractured membrane
Fluid – the plasma membrane is the consistency of olive oil at body temperature, due to unsaturated phospholipids. (cells differ in the amount of unsaturated to saturated fatty acid tails)
Most of the lipids and some proteins drift laterally on either side. Phospholipids do not switch from one layer to the next.
Cholesterol affects fluidity: at body temperature it lessens fluidity by restraining the movement of phospholipids, at colder temperatures it adds fluidity by not allowing phospholipids to pack close together.
Mosaic – membrane proteins form a collage that differs on either side of the membrane and from cell to cell (greater than 50 types of proteins), proteins span the membrane with hydrophilic portions facing out and hydrophobic portions facing in. Provides the functions of the membrane
Osmosis is the diffusion of water through a semipermeable membrane. Water molecules bound to solutes cannot pass due to size, only unbound molecules. Free water molecules collide, bump into the membrane, and pass through.
SURFACE TENSION IS THE TENDENCY FOR A LIQUID TO CONTRACT AS A CONSEQUENCE OF ITS POSSESION OF FREE ENERGY, SINCE APPROACH TO EQUILIBRIUM IS ALWAYS ACCOMPANIED BY A DIMINUTION OF FREE ENERGY . We’ve all played with it- water drops being added one at a time, until that one drop breaks the surface and the water spills out.
IT IS HARD TO BELIEVE THAT H-BONDS AND SURFACE TENSION ARE ENOUGH TO KEEP THE VOLUME OF WATER THAT IS IN THESE BEADS STUCK TO THE PLANT
What are biologic activities which can be best explained in terms of surface tension?
- the spherical form of a falling dro of water
- a soap bubble floating in the air
- a globule of mercury resting on flat surface
Applications in the Body :
- phagocytosis or ameboid motion
- absorption of metabolites/nutrients
- transport of blood
DIALYSIS is the separation of the more diffusible from the less diffusible