What are the 2 types of transporter proteins?
Carrier proteins and channel proteins (much faster)
What are the 2 types of ion channels?
Gated or non gated, pics
3 Types of carrier mediated transport
Uniport, symport, antiport NB: if both molecules are oppositely charged they are moved via symporters
Where does water absorption take place?
Most is reabsorbed - mainly in Jejunum, some in colon Needs power of ion absorption (mostly by diffusion)
Where does the water that you excrete come from?
Ingest (2L), saliva (1.2L), gastric secretions (2L), bile (0.7L), pancreas (1.2L), intestinal (2.4L) Small intestine absorbs (8L), colon (1.5L)
What is the standing gradient of osmosis driven by?
Driven by Na, and transport of Na from lumen into Enterocytes are complex and varies between species
How is sodium transported to keep the standing gradient of osmosis?
Counter-transport i exchange for H+ (proximal bowel), co-transport with a.a., monosaccharides (jejunum). co-transport with Cl- (ileum), restricted movement through ion channels (colon)
How do molecules cross the epithelium to enter the bloodstream?
Paracellular transport, transcellular transport
What type of gated can channel proteins be?
Voltage gated, ligand gated - extra/intracellular, mechanically gated
What is a uniport carrier?
Carries just on type of molecule across
What is an antiport/symport carrier?
Carries 2 molecules either in the same/opposite across the membrane
What are some examples for primary active transport?
Na/K ATPase, H/K ATPase
What are some examples for secondary active transport?
SGLT-1 co-transport, HCO3-/Cl- counter transport, Na/H counter transport
What are some examples for facillitated transport?
How is calcium absorbed in the intestines?
Cl- is co-transported with Na+ (ileum), exchanged with HCO3- (colon) into enterocytes - both secondary active transport
How is potassium absorbed in the intestines?
K+ diffuses in via paracellular pathways in small intestine, leaks out between cells in colon - passive transport
What happens to the intracellular sodium from the standing gradient osmosis?
Active transport of Na+ into lateral intercellular spaces by Na/K ATPase transport in the lateral plasma membrane
What happens when sodium is transported into the intercellular spaces?
Cl- and HCO3- are transported into the intercellular spaces as well and the high concentration of ions in the intercellular space causes the fluid to become hypertonic
What happens due to the fluid in the intercellular space becoming hypertonic?
Water distends in the intercellular channels and causes increased hydrostatic pressure, so ions and water move across the basement membrane of epithelium and are carried away by the capillaries
How is the standing gradient of osmosis maintained? (image)
Where calcium absorbed in the gut?
In the duodenum and ileum - if diet low in Ca, then gut's absorptive ability inceases
What stimulates calcium absorption?
Vitamin D and parathyroid hormone stimulate absorption
How much calcium is absorbed in a day?
Diet 1-6g/day, secretions 0.6g, absorb 0.7g
What are the intra/extracellular [Ca2+]?
Low intra, but can increase in during various cellular functions High extracellular fluid, (plasma around 2.2mM and luminal varying)
How does Ca2+ get carried across the apical membrane?
Intestinal Ca-binding protein (IMcal) - facilitated diffusion OR ion channel
What is the function of Ca2+?
Acts as an intracellular signalling molecule - so this proses a problem when needed to be transported across the membrane
How is calcium transported into the cytosol?
Binds to calbindin, which prevents the action of Ca as an intracellular signal
How do we get Ca out of the cell and into the blood stream?
Ca2+ is pumped out by PMCA against conc gradient OR Ca2+ pumped across basolateral membrane via Na/Ca exchanger
What is an advantage of PMCA?
It helps maintain basal levels of Ca inside the cell
What does PMCA stand for?
Plasma membrane Ca2+ ATPase