digestion and absorption SDL

Question 1

Describe the active biological mechanisms involved in ions exchange across the membrane of smooth muscle cells.

Answer 1

• 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

Question 2

Describe how smooth muscle cells contraction occurs and what are the key molecular elements involved.

Answer 2

contraction initiated by increase in intracellular Ca levels
synchronization by gap junctions (allow transfer of ions and small molecules) and pacemaker cells

Question 3

Explain how a population of smooth muscle cells can synchronize contraction mechanisms in a tissue.

Answer 3

• gap junctions
• pacemaker cells

Question 4

Describe the main difference between skeletal and smooth muscle cells with regard to the notion of neuromuscular junctions.

Answer 4

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.

Question 5

What is the intestinal surface microenvironment – which three components make up this layer?

Answer 5

• 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

Question 6

What is the difference between the luminal phase of digestion and the membranous phase digestion?

Answer 6

• 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.

Question 7

list the pathophysiological mechanisms which can result in the development of diarrhea

Answer 7

• secretory
• osmotic
• motility related
• inflammatory

Question 8

explain secretory diarrhea

Answer 8

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.

Question 9

explain osmotic diarrhea

Answer 9

Osmotic diarrhoea occurs when too much water is drawn into the bowels.

Question 10

explain motility related diarrhea

Answer 10

Motility-related diarrhoea is caused by the rapid movement of food through the intestines (hypermotility).

Question 11

explain inflammatory diarrhea

Answer 11

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.

Question 12

What is the zinc sulphate turbidity test?

Answer 12

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

Question 13

Describe the permeability of the GIT in neonates

Answer 13

permeable to large molecules, including proteins and immunoglobulins
crucial for absorption of maternal antibodies present in colostrum

Question 14

How can medication cause diarrhoea?

Answer 14

Medication can alter gut microbiota, motility or absorptive capacity

Question 15

How can neurological disorders cause diarrhoea?

Answer 15

dysregulation of intestinal motility and secreted can result in accelerated transit of contents through intestine => less time for absorption => diarrhoea

Question 16

How can increased permeability cause diarrhoea?

Answer 16

allows leakage of water and electrolytes from bloodstream into intestinal lumen => diarrhoea

Question 17

How can altered ion transport cause dairrhoea?

Answer 17

dysregulation of ion transport, including increased secretion of Cl ions impaires water absorption => diarrhoea

Question 18

How does disruption of brush border enzymes cause diarrhoea?

Answer 18

indigested carbs reaching colon can serve as substrates for bacterial fermentation => production of osmotically active substances => diarrhoea

Question 19

How do malabsorption disorders e.g. coeliac, lead to diarrhoea?

Answer 19

reduces absorption of nutrient => osmotic imbalance in lumen
unabsorbed nutrients and water increase osmotic pressure => draws more water into intestine

Question 20

How can infection and inflammation lead to diarrhoea?

Answer 20

infection can directly effect GIT lining
inflammation disrupts normal absorption => impaired nutrient absorption and influx of water into lumen

Question 21

discuss the ultrastructure of the intestinal epithelium

Answer 21

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.

Question 22

list the carrier mechanisms of nutrient absorption

Answer 22

• secondry active transport
• facilitated diffusion
• symport mechanisms
• simple diffusion
• trnasport proteins

Question 23

Discuss the various mechanisms used to transport molecules across the neonatal intestinal membrane and describe how the components of colostrum are absorbed

Answer 23

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.