22- Digestion & Absorption Flashcards
This is a failure in ability to digest dairy carbohydrates.
Lactose Intolerance
In lactose intolerance, the brush border ________ enzyme activity is deficient or absent resulting in undigested and unabsorbed lactose.
Lactase
In low lactase activity, the lactose will not be absorbed in the small intestine. This causes it to be converted to ________ and ________, producing acetate, butyrate, and propionate in the lumen. This causes water to hold in the lumen and ________ _______ results. Ferments into methane and H+ gas.
SCFAs
Hydrogen
Osmotic Diarrhea
What are the major primary sugars in the human diet?
Sucrose
Lactose
Starch
What are the major secondary sugars in the human diet/
Amylose Glycogen EtOH/Alcohol Lactic Acid Pyruvic Acid Pectins Dextrins
This major sugar in the human diet has no digestive enzymes.
Cellulose
In the mouth, this is where we begin breaking down starch by the use of the enzyme _______ _______. This breaks it down into Maltose and 3-9 polymers of Glucose.
Salivary Amylase
In the small intestine, most of the starch breaks down here by the use of the enzyme ________ ________. This breaks it down into Maltose and 3-9 polymers of Glucose. Many disaccharides reach the small intestine intact.
Pancreatic Amylase
Brush border enterocytes has specific hydrolases that complete the process of breaking down carbohydrates. What are Maltose, Trehalose, Lactose, and Sucrose broken down into and by what enzymes?
Maltose (via Maltase) — Glucose + Glucose
Trehalose (via Trehalase) — Glucose + Glucose
Lactose (via Lactase) — Glucose + Galactose
Sucrose (via Sucrase) — Glucose + Fructose
Absorption of carbohydrates occurs via co-transport mechanisms and facilitated diffusion. What are these forms of transport and what are their transporter names?
– Na/K ATPase creates concentration gradient for secondary active transport for Glucose and Galactose (co-transporter SGLT1)
– Facilitated diffusion for Fructose (GLUT5)
– Facilitated diffusion into blood (GLUT2)
Which carbohydrates utilize SGLT1, GLUT5, and GLUT2?
SGLT1 = Glucose and Galactose
GLUT5 = Fructose
GLUT2 = Glucose, Galactose, and Fructose
Explain how we can test for CHO assimilation problems.
After overnight fasting, patient ingests 25g D-xylose and their urine is collected for the next 5 hours. Absorption is normal if less than 4 g is excreted in the 5 hours.
***D-xylose absorbed by both Na+ cotransport and passive diffusion
This occurs due to a deficiency of pancreatic enzymes, specifically a lack of proteases (i.e., trypsinogen).
Chronic Pancreatitis
This occurs due to the absence of trypsin. All pancreatic enzymes are gone.
Congenital Trypsin Absence
This occurs due to defects in transport (SLC3A1) or absence of di-basic AA transporter (SLC7A9). Thus, cysteine, lysine, arginine, and ornithine are not reabsorbed at the proximal tubule. This occurs in 1:7,000 live births and is due to an intestinal deficiency. The AAs are secreted in the feces.
Cystinuria
***Cysteine builds up and forms stones in kidney, bladder, and ureter. High levels of it in the urine.
This occurs when a person cannot absorb neutral AAs. Symptoms resemble pellagra (niacin deficiency). It is an autosomal recessive genetic disorder. Symptoms include diarrhea, mood changes, neurological problems, red scaly skin, photosensitivity, short stature, and high levels of neutral AAs in urine.
Hartnup Disease
***i.e., Tryptophan in the urine
This occurs due to mutations in the CFTR gene, which is a regulated Cl- channel on apical membrane of duct cells. It’s important in sweat, digestive fluid, and mucous production. Without it, fluids that should be thin become thick. Loss of HCO3- secretion. Pancreas problems persist and present early.
Cystic Fibrosis
In the stomach, ________ is secreted as ________ which is activated at low pH (2-3). It is responsible for 10-20% of protein breakdown but is not essential for protein digestion.
Pepsin
Pepsinogen
The pancreas mostly breaks proteins down into di- and tripeptides and some amino acids. What are the enzymes in the pancreas?
Trypsin
Chymotrypsin
Carboxypeptidase
Elastase
What does Trypsin and Chymotrypsin break down ________ ________.
Small Polypeptides
What does Carboxypeptidase cleave AAs into?
Carboxyl ends
What enzymes are present in the small intestines for protein digestion?
Aminopolypeptidase
Dipeptidases
In the small intestines, di- and try-peptides are absorbed into _________.
Enterocytes
Pancreatic enzymes are secreted as _________ activated by either Enterokinase (Trypsinogen) or Trypsin itself.
Zymogens
***These are inactive substance activated by another enzyme (Trypsinogen or Trypsin in this case)
For protein absorption, there are separate ________ and separate ________ ________ mechanisms for each amino acid type (neutral, acidic, basic, imino). The amino acids can’t just go through by themselves!
Co-transporters Facilitated Diffusion (of dipeptides and tripeptides)
For protein absorption, ________ establishes a Na+ gradient for co-transport. There can also be _____-dipeptide or ______-tripeptide cotransporters.
Na/K ATPase
H+
H+
Antibodies can develop against a gluten component, called ________. This leads to destruction of small intestine villi (atrophy), and hyperplasia of the intestinal crypts. This leads to malabsorption related to deficiencies in folate, iron, calcium, and Vitamins A, B12, and D.
Gliadin
How can we manage problems with the antibodies against gliadin?
Maintain a gluten-free diet
If there is a loss or decreased number of intestinal epithelial cells, that means there is a reduced microvilli surface area. Fat absorption is impaired due to the loss, and there is excess fat in feces (steatorrhea). Nutritional deficiencies in _______ and _______ also occur.
Folate
Vitamin B12
***Remember, this is greasy poops!
How can we treat poor fat absorption due to decreased intestinal epithelial cells?
Treatment with tetracycline (antibiotic) and folate for 6 months
The structure of the intestinal mucosa is ideal for absorption of large amounts of nutrients. The lumen surface of small intestine is arranged in longitudinal folds called _______ _______ _______ and the villi and microvilli increase surface area for absorption. Villi are longest in the ________.
Folds of Kerckring
Duodenum
The microvillar surface contains the _______ _______, which is the site of activity of a number of digestive enzymes. This barrier also must be traversed by nutrients, water, and electrolytes.
Brush Border
These intestinal cells are epithelial cells and are used for digestion, absorption, and secretion. They turnover every 3-6 days and are susceptible to irradiation and chemotherapy.
Enterocytes
These intestinal cells are mucus-secreting cells. This mucus provides physical, chemical, and immunological protection.
Goblet Cells
These intestinal cells are part of mucosal defenses against infection. They secrete agents that destroy bacteria or produce inflammatory responses.
Paneth Cells
This occurs at the base of microvilli and is a major mechanism for uptake of protein.
Pinocytosis
This type of passage in enterocytes is through pores in the cell membrane and occurs between cells.
Passive Diffusion
For fat digestion, _______ _______ and _______ emulsify fat products into micelles.
Bile Salts
Lecithin
In the stomach, _______ _______ and _______ _______ act on TAGs. Dietary proteins perform emulsification here, 10% of TAG digestion.
Lingual Lipase
Gastric Lipase
In the stomach, time is required so ________ inhibits gastric emptying for more mixing along with activating gallbladder emptying.
CCK
Most digestion of lipids occur in small intestine. _______ _______ emulsify lipids and pancreatic enzymes secreted into the small intestine complete the digestion.
Bile Salts
_______ _______ is secreted as an active enzyme. It is inactivated by Bile Salts without Colipase.
Pancreatic Lipase
________ is activated by Trypsin. Once activated, it displaces Bile Salts by binding to Pancreatic Lipase.
Colipase
This is secreted as an active enzyme and catalyzes production of free cholesterol. It hydrolyzes triglycerides to glycerol.
Cholesterol Ester Hydrolase
This is secreted as a proenzyme activated by Trypsin.
Phospholipase A2
Describe the steps of fat absorption.
1) Solubilization by micelles (via bile salts)
2) Diffusion of micellar content across apical membrane
3) Re-esterification
4) Chylomicron formation
5) Exocytosis of chylomicrons into lymphatics
______ is important in the formation of Chylomicrons, and a lack of it leads to abetalipoproteinemia (no lipid absorption).
ApoB
This is the failure to secrete proper amounts of pancreatic enzymes.
Pancreatic Insufficiency
This syndrome is due to a gastrin-secreting tumor of the pancreas. It causes increased H+ secretion by gastric parietal cells and leads to an overload of acid into the duodenum.
Zollinger-Ellison Syndrome
This occurs when pancreatic enzymes (trypsin) become activated and self-digest the pancreas. There is impaired HCO3 and enzyme secretions.
Pancreatitis
One overlying theme of problems with pancreatic enzyme secretion is the improper acidity of duodenum contents. The lumen here must be neutralized by _______-containing pancreatic secretions.
HCO3
Interference with formation of micelles in the small intestine are caused by factors that cause deficits in _______ _______.
Bile Salts
An _______ _______ can cause the total bile salt pool to be reduced. This is because there is a loss of enterohepatic circulation of the bile salts.
Ileal Resection
This interferes with formation of micelles because bacteria deconjugate bile salts. Severe bacterial overgrowth damages the intestinal mucosa. The two main causes are too little gastric secretion and small intestine dysmotility.
SIBO (Small Intestinal Bacterial Overgrowth)
SIBO is due to inappropriate growth of bacteria in the SI, causing pain, bloating, gas, and diarrhea/constipation. It can result in malabsorption issues, steatorrhea, and vitamin/mineral deficiency. Changes in ______ result in improper activity of lipase enzymes in small intestine.
pH
How can we detect for SIBO?
Breath test – detect methane and hydrogen
Vitamins must be acquired often from the diet and absorbed along the GI tract. What are the fat-soluble and water-soluble vitamins?
Fat-soluble = A, D, E, K Water-soluble = B vitamins, C
Fat-soluble vitamins have the same absorption mechanisms as lipids, while water-soluble vitamins are absorbed via…
Na+ dependent cotransport
***Except Vitamin B12 (forms complexes with other proteins to be absorbed)
Water-soluble vitamins are mostly absorbed via Na+-dependent cotransport, except for _________ which forms complexes with other proteins to be absorbed.
Vitamin B12 (Cobalamin)
This vitamin performs several metabolic functions. It is a hydrogen acceptor coenzyme, acts as a coenzyme for reducing ribonucleotides to deoxyribonucleotides (gene replication), and is a cofactor in folate coenzyme recycling and nerve myelination.
Vitamin B12
Vitamin B12 deficiency causes __________ of the large nerve fibers of the spinal cord.
Demyelination
Vitamin B12 and ________ are important in DNA synthesis in RBCs.
Folate
This is caused by the failure of RBC maturation when Vitamin B12 is deficient.
Pernicious Anemia
What are some other hematological disorder due to Vitamin B12 deficiency?
Macrocytic Anemia
Megaloblastic Anemia
If the stomach does not produce enough IF, it can lead to chronic inflammation of the stomach mucosa that leads to loss of parietal cells. This is called…
Atrophic Gastritis
If the stomach does not produce enough IF, the immune system could attack IF protein or gastric parietal cells. This is called…
Autoimmune Metaplastic Atrophic Gastritis
This type of surgical procedure can cause a loss of parietal cells, which are the source of IF. Lead to decreased Vitamin B12 absorption.
Gastrectomy
In this surgical procedure, exclusion of the stomach, duodenum, and proximal jejunum alters absorption of Vitamin B12.
Gastric Bypass
Calcium absorption depends on the presence of ________. It is absorbed across enterocytes, but also reabsorbed in the ________.
Vitamin D
Kidney
In small intestine, there is Vitamin D-dependent Calcium binding protein called ___________. Calcitriol and PTH also govern.
Calbindin D-28K
Vitamin D deficiency results in inadequate calcium absorption. This can lead to ________ in children, and ________ in adults.
Rickets
Osteomalacia
The liver secretes __________ into bile, which enters the duodenum. This then binds with free iron and with hemoglobin, forming _________.
Apotransferrin
Transferrin
Transferrin binds to receptors on membranes of ________ epithelial cells, absorbed into cells via pinocytosis and later released.
Intestinal
The small intestine and colon not only absorb large quantities of _________ and ________, but the epithelial cells lining the crypts of the small intestine also secrete them.
Electrolytes (Na+, Cl-, HCO3-, K+)
Water
The first step in electrolyte absorption is the absorption of solute, followed by the absorption of water. Absorbate is always _________, meaning that solute and water absorption occur in proportion to each other.
Isosmotic
In the jejunum, lots of ________ is absorbed.
Sodium
In the ileum, ________ absorbed and ________ is secreted.
Sodium
HCO3
In the colon, there is _________ absorption and ________ secretion.
Sodium
Potassium
This occurs due to increased Cl- secretion. It increases cAMP, resulting in increased Cl- secretion. The increased Cl- is accompanied by secretion of Na+ and H2O. The volume of fluid secreted into the intestinal lumen overwhelms the absorptive mechanisms of the SI and colon, leading to massive secretory diarrhea.
Cholera
