Cellular Transport: Mechanisms and Quick Facts
Transport Mechanisms
Ca++ efflux from ventricular myocardial cells during diastole – secondary active (Na+ coupled)
Ca++ uptake by sarcoplasmic reticulum - primary active
Ca++ uptake by terminal varicosities of sympathetic nerve endings – restricted diffusion
Ca++ entry into heart muscle during plateau phase of the action potential - restricted diffusion
Glucose uptake by adipose cell – facilitated diffusion
Glucose entry into small intestinal mucosal membrane through apical villi - secondary active
Glucose transport across basolateral memb. of intestinal absorptive cell – facilitated diffusion
Glucose transport, insulin-dependent – facilitated diffusion
Glucose uptake by striated muscle cells – facilitated diffusion
Cl- transport across the basolateral membrane of secretory epithelial cells – secondary active
Cl- transport across the apical membrane of secretory epithelial cells – secondary active
H+ secretion by renal distal nephron – primary active (ATPase)
O2 passage across capillary endothelium – simple diffusion
CO2 movement across alveolar walls – simple diffusion
Vitamin A absorption by the small intestine - simple diffusion
Cholesterol movement across cell membranes – continuous (simple) diffusion
Bile salt absorption by the ileum – secondary active
Iodide uptake by the thyroid gland – secondary active
H2O movement across the apical memb. of leaky epithelial cells – restricted diffusion
Inulin movement across capillary walls – restricted diffusion
K+ accumulation by human red blood cells – primary active
Protein reabsorption for renal is endocytotic with Tm and RPT
Cl- transport across lumenal epithelium of tubule is Secondary Active (with Na)
Aldosterone-Binds to intracellular receptors ONLY, and causes increase in number of sodium channels in both medullary and collecting ducts. Also increases the Na/K-ATPase activity at basolateral membrane, and increases number of K channels (and activity as well). Excretion of K and reabsorption of Na. Also causes ADH release.
Renin-ONLY function is to convert Angiotensinogen to Angiotensin I. Also, put out due to less extra-cellular volume, less arterial pressure (or anything that leads to decreased RENAL PRESSURE and thus renal plasma flow). Also released by decrease in intracellular calcium and increased cAMP activity.
ADH-Causes cortical and medullary collecting ducts to have high water permeability (tubular fluid equilibrates with interstitium via water loss to interstitium; therefore urine is of high osmolarity). Also vasoconstrictor (want to up blood pressure by constricting and reabsorbing water!). AKA vasopressin.
Vasopressin-Vasoconstricter of all blood vessels, synonymous with AntiDiuretic Hormone.
ANP/ Atriopeptins-Caused by distention of the atria, wants to lower blood pressure by vasodilation and preventing aldosterone release. Also, as a vasodilator, wants to decrease mean circulatory filling pressure (or increase resting volume). Will reduce Na reabsorption in the collecting duct and proximal tubule (that whole water follows where solute goes thing). Reduced amounts of Aldosterone (due to reduced sensitivity of zona glomerulosa to Angiotensin II), ADH sensitivity to distal nephron, and reduced Renin release! Anything to rid of excess volume.
Angiotensin-From reaction of angiotensinogen in blood with Renin (makes Angiotensin I). AngioII is a powerful vasoconstrictor and causes release of aldosterone.
Prostaglandins-Inhibit Na reabsorption in the distal nephron.
Urea reabsorption (across basolateral renal membrane) is Passive Diffusion. However, urea and glycerol are other small, polar, non-electrolytic, water soluble molecules that enter other cells by restricted diffusion. The theory, in short, states that their permeation rates are too fast to be moving by simple diffusion through the lipid matrix, so there must be some size dependent pore that is invoked. Inorganic ions (e.g. Ca++) also travel down concentration gradients in this manner.
Tags: apical_membrane, bile_salt, capillary_endothelium, capillary_walls, glucose_transport, glucose_uptake, human_red_blood_cells, nerve_endings, red_blood_cells, secretory_epithelial_cells, simple_diffusion, small_intestine, sodium_channels, striated_muscle_cells, sympathetic_nerve, thyroid_gland, transport_mechanisms
