Physiology
#منشور_رقم_1
#cell_physiology
#cell_membrane
Introduction
I. Cell Membranes
■ are composed primarily of phospholipids and proteins.
A. Lipid bilayer
1. Phospholipids have a glycerol backbone, which is the hydrophilic (water soluble) head,
and two fatty acid tails, which are hydrophobic (water insoluble). The hydrophobic tails
face each other and form a bilayer.
2. Lipid-soluble substances (e.g., O2
, CO2
, steroid hormones) cross cell membranes because
they can dissolve in the hydrophobic lipid bilayer.
3. Water-soluble substances (e.g., Na+
, Cl−
, glucose, H2
O) cannot dissolve in the lipid of the
membrane, but may cross through water-filled channels, or pores, or may be trans-
ported by carriers.
B. Proteins
1. Integral proteins
■ are anchored to, and imbedded in, the cell membrane through hydrophobic interactions.
■ may span the cell membrane.
■ include ion channels, transport proteins, receptors, and guanosine 5′-triphosphate
(GTP)–binding proteins (G proteins).
2. Peripheral proteins
■ are not imbedded in the cell membrane.
■ are not covalently bound to membrane components.
■ are loosely attached to the cell membrane by electrostatic interactions.
C. Intercellular connections
1. Tight junctions (zonula occludens)
■ are the attachments between cells (often epithelial cells).
■ may be an intercellular pathway for solutes, depending on the size, charge, and charac-
teristics of the tight junction.
■ may be “tight” (impermeable), as in the renal distal tubule, or “leaky” (permeable), as in
the renal proximal tubule and gallbladder.
2. Gap junctions
■ are the attachments between cells that permit intercellular communication.
■ for example, permit current flow and electrical coupling between myocardial cells
https://t.me/physiology_yaqob
#منشور_رقم_1
#cell_physiology
#cell_membrane
Introduction
I. Cell Membranes
■ are composed primarily of phospholipids and proteins.
A. Lipid bilayer
1. Phospholipids have a glycerol backbone, which is the hydrophilic (water soluble) head,
and two fatty acid tails, which are hydrophobic (water insoluble). The hydrophobic tails
face each other and form a bilayer.
2. Lipid-soluble substances (e.g., O2
, CO2
, steroid hormones) cross cell membranes because
they can dissolve in the hydrophobic lipid bilayer.
3. Water-soluble substances (e.g., Na+
, Cl−
, glucose, H2
O) cannot dissolve in the lipid of the
membrane, but may cross through water-filled channels, or pores, or may be trans-
ported by carriers.
B. Proteins
1. Integral proteins
■ are anchored to, and imbedded in, the cell membrane through hydrophobic interactions.
■ may span the cell membrane.
■ include ion channels, transport proteins, receptors, and guanosine 5′-triphosphate
(GTP)–binding proteins (G proteins).
2. Peripheral proteins
■ are not imbedded in the cell membrane.
■ are not covalently bound to membrane components.
■ are loosely attached to the cell membrane by electrostatic interactions.
C. Intercellular connections
1. Tight junctions (zonula occludens)
■ are the attachments between cells (often epithelial cells).
■ may be an intercellular pathway for solutes, depending on the size, charge, and charac-
teristics of the tight junction.
■ may be “tight” (impermeable), as in the renal distal tubule, or “leaky” (permeable), as in
the renal proximal tubule and gallbladder.
2. Gap junctions
■ are the attachments between cells that permit intercellular communication.
■ for example, permit current flow and electrical coupling between myocardial cells
https://t.me/physiology_yaqob