digestion and absorption SDL Flashcards
Describe the active biological mechanisms involved in ions exchange across the membrane of smooth muscle cells.
- Ca ion entry via voltage gated calcium channels/ligand gated Ca channels essential for contraction
- sodium/potassium pump maintining resting membrane potential
- chloride ions help maintain the electrochemical gradient necessary for contraction
Describe how smooth muscle cells contraction occurs and what are the key molecular elements involved.
contraction initiated by increase in intracellular Ca levels
synchronization by gap junctions (allow transfer of ions and small molecules) and pacemaker cells
Explain how a population of smooth muscle cells can synchronize contraction mechanisms in a tissue.
- gap junctions
- pacemaker cells
Describe the main difference between skeletal and smooth muscle cells with regard to the notion of neuromuscular junctions.
Skeletal muscle cells have well-defined neuromuscular junctions where motor neurons directly stimulate muscle fibers. In contrast, smooth muscle cells are often influenced by diffuse release of neurotransmitters in their environment, without specialized neuromuscular junctions.
What is the intestinal surface microenvironment – which three components make up this layer?
- mucus layer = secreted by goblet cells, protects and lubricates epithelium
- microbiot = commensal bacteria that aid in digestion and protect against pathogens
- immune cells = cells that provide immune surveillance and protection
What is the difference between the luminal phase of digestion and the membranous phase digestion?
- Luminal Phase Digestion: Enzymes secreted into the lumen of the gut break down food particles.
- Membranous Phase Digestion: Enzymes attached to the brush border membrane of enterocytes further digest nutrients for absorption.
list the pathophysiological mechanisms which can result in the development of diarrhea
- secretory
- osmotic
- motility related
- inflammatory
explain secretory diarrhea
Secretory diarrhoea means that there is an increase in the active secretion, or there is an inhibition of absorption. There is little to no structural damage.
explain osmotic diarrhea
Osmotic diarrhoea occurs when too much water is drawn into the bowels.
explain motility related diarrhea
Motility-related diarrhoea is caused by the rapid movement of food through the intestines (hypermotility).
explain inflammatory diarrhea
Inflammatory diarrhoea occurs when there is damage to the mucosal lining or brush border, which leads to a loss of protein-rich fluids and a decreased ability to absorb these lost fluids.
What is the zinc sulphate turbidity test?
diagnostic test to assess passive transfer of immunoglobulins from mother to neonate
measures ability of serum to form turbid solution when mixed with zinc sulphate - turbidity indicates presence of immunoglobulins
Describe the permeability of the GIT in neonates
permeable to large molecules, including proteins and immunoglobulins
crucial for absorption of maternal antibodies present in colostrum
How can medication cause diarrhoea?
Medication can alter gut microbiota, motility or absorptive capacity
How can neurological disorders cause diarrhoea?
dysregulation of intestinal motility and secreted can result in accelerated transit of contents through intestine => less time for absorption => diarrhoea
How can increased permeability cause diarrhoea?
allows leakage of water and electrolytes from bloodstream into intestinal lumen => diarrhoea
How can altered ion transport cause dairrhoea?
dysregulation of ion transport, including increased secretion of Cl ions impaires water absorption => diarrhoea
How does disruption of brush border enzymes cause diarrhoea?
indigested carbs reaching colon can serve as substrates for bacterial fermentation => production of osmotically active substances => diarrhoea
How do malabsorption disorders e.g. coeliac, lead to diarrhoea?
reduces absorption of nutrient => osmotic imbalance in lumen
unabsorbed nutrients and water increase osmotic pressure => draws more water into intestine
How can infection and inflammation lead to diarrhoea?
infection can directly effect GIT lining
inflammation disrupts normal absorption => impaired nutrient absorption and influx of water into lumen
discuss the ultrastructure of the intestinal epithelium
Microvilli: These are tiny hair-like projections on the apical surface of enterocytes, collectively forming the brush border. They greatly increase the surface area for absorption.
Tight Junctions: These structures seal adjacent enterocytes together at their apical surfaces, preventing paracellular leakage of substances.
Enterocytes: The main absorptive cells of the intestine, packed with transporters and enzymes necessary for nutrient absorption.
Basolateral Membrane: Contains transport proteins that facilitate the movement of nutrients from enterocytes into the blood or lymphatic system.
Goblet Cells: Secrete mucus, which lubricates the intestinal contents and protects the epithelium.
Paneth Cells: Located at the base of the crypts of Lieberkühn, they secrete antimicrobial molecules to maintain gut flora balance.
list the carrier mechanisms of nutrient absorption
- secondry active transport
- facilitated diffusion
- symport mechanisms
- simple diffusion
- trnasport proteins
Discuss the various mechanisms used to transport molecules across the neonatal intestinal membrane and describe how the components of colostrum are absorbed
Neonatal Intestine:
- Increased Permeability: The neonatal gut has higher permeability to macromolecules, facilitating the absorption of immunoglobulins and other large molecules from colostrum.
- Fc Receptors: Present on neonatal enterocytes, facilitating the endocytosis and transcytosis of maternal antibodies (e.g., IgG) into the bloodstream.
- Pinocytosis and Phagocytosis: Enhanced in neonates for the uptake of macromolecules from colostrum.
- Low Proteolytic Activity: Ensures that immunoglobulins and other proteins are not degraded before absorption.
Colostrum Absorption:
- Immunoglobulins: Absorbed intact via Fc receptors on enterocytes.
- Growth Factors and Hormones: Support gut maturation and immune development.
- Nutrients: Such as lactose and lipids, are digested and absorbed similarly to those in mature milk but in higher concentrations.
