Cell Membrane Transport and Hormonal Regulation

Cell Membrane Transport

Diffusion

Some substances move through diffusion inside and outside cells. Diffusion is a physical process based on random movement. The kinetic energy associated with the random motion causes diffusion, the net movement of particles (atoms, ions, and molecules) from a region of high concentration to a region of low concentration, resulting in a uniform distribution.

Conveyor-Mediated Transport

For the transport of ions and nutrients, conveyor systems (permease proteins) evolved early in the origin of cells. This transfer of solutes by membrane proteins is called carrier-mediated transport. There are two variants: facilitated diffusion (along the concentration gradient or electrochemical-chemical-concentration difference, independent of metabolic energy) and active transport (against the electrochemical and concentration gradient, energy-dependent).

Endocytosis and Exocytosis

Both simple and facilitated diffusion, as well as active transport mediated by carrier molecules, move molecules and ions across the plasma membrane. Sometimes, cells need to take in or expel larger quantities of materials, such as food particles or even whole cells. These transport processes involve vacuoles formed from or merged with the cell membrane, known as exocytosis and endocytosis.

Hormonal Regulation

Endocrine System

The endocrine system consists of glands and tissues that secrete hormones, chemical messengers responsible for regulating many body processes.

The endocrine system is essential for:

• Maintenance of homeostasis: For example, blood glucose levels remain stable due to hormones like insulin and glucagon.
• Response to external circumstances: Adrenaline provides immediate energy availability.
• Implementation of developmental and cyclical physiological programs: Sexual differentiation and maturation, menstruation, and pregnancy, controlled by sex hormones.

Hormone Concept

A hormone is an organic molecule secreted by a part of the body in response to internal or external signals, including those from the nervous system. Hormones are transported by the bloodstream to their receptors located in another part of the body, where they exert an effect on a specific organ or tissue. They are active in very small quantities.

Hormone Chemical Groups

1. Steroids (synthesized from cholesterol): Sex hormones (progesterone, testosterone, estradiol), adrenal cortex steroid hormones.
2. Amino acid derivatives: Epinephrine and norepinephrine.
3. Peptides or proteins: ADH and oxytocin (short peptides), glucagon, adrenocorticotropic hormone, and calcitonin (longer peptides), insulin, growth hormone, and gonadotropic hormones.
4. Fatty acid derivatives: Prostaglandins.

Mechanism of Hormone Action

Hormones exert their effects through two mechanisms, both involving receptor molecules. One involves intracellular receptor molecules (found in the nucleus or cytoplasm), and the other involves receptors found in the host cell membrane. Steroid and thyroid hormones act through intracellular receptors; amine, peptide, and protein hormones act through cytoplasmic membrane receptors.